Research

Metal Fabrication

Cold spray, melt pool, friction stir welding, multifunctional coatings for biomedical Mg alloys, visual monitoring of metal powder

Corrosion and Inhibition

Corrosion inhibitors, corrosion of steel pipes in a soil environment, photocatalysts for CO2 hydrogenation, nano-sensing, optical sensing

Materials Modelling

Computational fluid dynamics (CFD), fluid-structure interaction (FSI), 3D printing (stereolithography, PolyJet), selective laser melting, modelling process, direct laser metal deposition, fused deposition modelling, object printing

Nanostructures

Functional strontium phosphate-coated magnesium alloys for orthopaedic use

Dr Rou Jun Toh

Abstract: Optimising of Surface Properties of Additive Components by using an Additive/Subtractive Machine

The Australian Research Council (ARC) Industrial Transformation Training Centre in Surface Engineering for Advanced Materials (SEAM) and their industrial partner, Romar Engineering Pty. Ltd. is investigating how the combination of both additive and subtractive manufacturing in a hybrid machine can be used to reduce the need for post-processing of additive components.

Factors such as quality of surface (i.e. roughness) and residual stress are key considerations.

The initial stages of the project will use the melt pool imaging available on the LASERTEC 65 3D machine and interpret this data with vision algorithms to provide input into machine learning. The machine learning will be used to assess if weld pool parameters can predict final project parameters.

Rou Jun Toh operating the LASERTEC 65 3D machine at Romar Engineering Pty. Ltd. Operating the LASERTEC 65 3D machine at Romar Engineering Pty. Ltd.

The project was conducted in conjunction with Surface Engineering for Advanced Materials ARC Training Centre (SEAM).

Dr Paul White

Abstract: Electrochemical Additive Manufacturing (ecAM) Prototype Development

Electrochemical AM is a complementary tool in the additive manufacturing toolbox that prints metals directly from aqueous solution. Any metal or alloy that can be electroplated can be printed allowing ecAM to fill in the gaps for metals not easily accessed by other AM methods (e.g. precious metals). Using an ecAM “pen” and an XYZ-controllable stage, 3D structures can be built under standard laboratory conditions.

Elias Salloum

PhD abstract: Optimising Friction Stir Welding & Alloy Design to Ensure the Durability of Lightweight Carriages in the Rail Fleet

The friction stir welding (FSW) is a solid-state welding process which utilises a rotating tool with a pin and shoulder design to create a sound defect free weld by plastic deforming and mixing of the abutting surfaces (fig. 1). Limitation exist when FSW aluminium and its alloys due to thermal cycle activity and shearing resulting in, recrystallisation, grain grow, recovery, and precipitate dissolution, which leads to adversely effects mechanical property in and around the weld that can be seen in a hardness vs. distance from weld centre graph (fig. 2). Addition of grain refinement, recrystallisation retardant, and thermodynamically stable micro-alloying elements, such as scandium and zirconium, has shown to increase hardness and improve joint efficiency but altering the microstructure.

However, their effects is limited materials in the annealed state, hardened aluminium alloys still suffer a loss of mechanical property upon FSW (Fig. 2c). This study will investigate alternative micro-alloying element for possible alternatives for improved mechanical properties of post friction stir welded aluminium alloys. Other means of weld improvement include optimizing of welding parameters to control heat generation and coupling this with micro-alloy optimisation. Cold-working of aluminium and its alloys has shown to increase microhardness by increase dislocation density within the subgrain structure. Micro-alloying coupled with FSW optimization is the focus of this research.

Image a
Image b
Image c

The project was conducted in conjunction with Rail CRC and CSIRO.

Magdi Morks

PhD abstract: Properties of Titanium Cold Spray Additive Components with Consideration of Post-Fabrication Treatment

The cold spray process is currently used as a metal spray technique in which solid powder particles (1-100 μm diameter) are accelerated to speeds above supersonic velocities (~1500 m/s) by a supersonic gas jet. The powder particles undergo significant deformation on impact with the substrate, thereby forming a coating. The quality of the coating depends on the powder and substrate types, as well as the processing parameters, such as the gas pressure and type, gas temperature, standoff distance, and particle velocity. In this project cold spray will be employed as additive manufacturing technique to fabricate complex components from CP titanium and titanium alloy feedstock. This fundamental study will investigate the relationship between the deposit’s microstructure & mechanical properties. Different microscopic and analytical techniques such as SEM, TEM, OM, XRD, EDS, and BSED will be used to analyse the microstructure & grain structure. Mechanical tests will characterise properties including tensile strength, fatigue, fracture toughness, and hardness. A selection of the sprayed components will be heat treated to improve properties including residual stress, as well as their microstructure and porosity. Treatments will range from low-temperature tempers through to high-temperature anneals and hot isostatic pressing. The changes in properties (both local and general) after these treatments will be studied. Mechanical strength at the joins of components will also be studied.

3D titanium components manufactured using the cold spray process 3D titanium components manufactured by Lab 22 (CSIRO) using the cold spray process.

This project was conducted in conjunction with IMCRC, Titomic Ltd and CSIRO.

Jiayu Ye

PhD abstract: In-situ Monitoring of Laser Metal Deposition for Additive Manufacturing

Additive manufacturing (AM) has been widely used in the aerospace, medical implant, and other industry sectors in recent years due to its extraordinary capability of net-shape building of parts with complex geometries. As a member of the AM category, laser metal deposition (LMD) is a superior technology for repair, coating, and refurbishment. Following its name, the mechanism of LMD is that metal powders are heated by a laser beam and become molten, after which they are blown from a nozzle. The molten metal drops are then directly deposited and solidified onto the surface of the substrate along the laser scanning path, which builds the part layer by layer. However, this technology still faces many challenges despite its inherent advantages. System inputs such as heat input rate and scanning speed are usually set empirically. If they are set inappropriately, defects (e.g. porosity & cracking) will occur and cause the failure of the part and material wastage. 

In recent years, many researchers have focused on in-situ monitoring of the process signatures (e.g. melt pool temperature & size) to characterise the impacts of the chosen values for these system inputs. But after measuring these signatures, what do they mean for final product qualities? Are there enough signatures to be monitored? This unclear relationship between process signatures & final product qualities is currently the most challenging problem in AM. Therefore, the aims of this research are to (i) determine if there is other process information that relates to product quality, and (ii) build the bridge between the family of process signatures and the family of final product qualities using a data-driven method (machine learning). 

Figure 1: Workflow schematic for this study. The training set for the ML algorithms contains three dataset; predefined process parameters, process signatures extracted from in-situ image data, and target features. Input features were selected based on Spearman's correlation with target features. Six ML algorithms were compared for predictive performance [1]. Figure 1: Workflow schematic for this study. The training set for the ML algorithms contains three dataset; predefined process parameters, process signatures extracted from in-situ image data, and target features. Input features were selected based on Spearman's correlation with target features. Six ML algorithms were compared for predictive performance [1].
Figure 2: Experimental setup of laser metal deposition system used throughout this study
Figure 3: An example of the cross-section of stainless steel 316L multi-track cladding. The lack-of-fusion defects occur at the bottom between neighbouring tracks.

The project was conducted in conjunction with CSIRO.

Aaqil Sameem

MRes abstract: ‘Cutting Tool Development using a Novel Non-Traditional Manufacturing Process’

ALUMNUS – Current LinkedIn profile including contact details.

Conventional cutting tools are made from high-carbon steel, high-speed steel, cemented carbides and diamonds. These tools must be able to withstand high temperatures and mechanical loads caused by friction against the workpiece. However, common metallurgical knowledge is that very hard materials are brittle and thus have low toughness and break more easily, particularly at high temperatures. One of the commonest materials used for cutting tools is cemented carbides due to their excellent mechanical properties. These are metal-matrix composites (MMC) in which the carbide particles are a solid aggregate within the metallic binder/matrix. During the life of a cutting tool, the cutting edge wears out more quickly than the tool base. Once worn out, they are either discarded or recycled. Recycling of cemented carbides is difficult due to their superior hardness and very high melting temperature. 

My research aims to rebuild the cutting edge on an existing tool base by using additive manufacturing methods such as DED. I will use of pre-alloyed powders with finely dispersed carbides as the AM feedstock to deliver a homogenous microstructure in the rebuilt tool edge. I will also vary AM process parameters (laser power, scan speed, powder flow rate) to obtain suitable microstructures, hardness values over 1100 HV0.5, and good wear performance. The results will then be compared to the characteristics of conventionally sintered carbides.

This project was conducted in conjunction with ANCA Pty Ltd and CSIRO. 

This project has a patent pending.

 

ABB robot at CSIRO Clayton connected to laser optics Figure 1: ABB robot at CSIRO Clayton connected to laser optics
Laser-cladded cutting tools on a steel shank Figure 2: Laser-cladded cutting tools on a steel shank
Finished cutting tools after grinding to the desired geometry Figure 3: Finished cutting tools after grinding to the desired geometry

Vijay Sisarwal

PhD abstract: Antibacterial Coatings with Ingredients from Natural Sources

Implantable medical devices, such as orthopaedic devices, trauma devices, cardiac valves, pacemakers, dental implants, cardiac implants, and coronary stents may all suffer from implant-related infections, leading to failure and high associated economic & social costs. The literature defines the most critical pathogenic event during infection is biofilm formation, which starts immediately after bacterial adhesion on an implant and effectively protects the microorganisms from the immune system and systemic antibiotics. A sound rationale for the prevention of biomaterial-associated infections should thus focus specifically on the inhibition of both bacterial adhesion & biofilm formation. However, prevalent antibacterial strategies consisting of organic & inorganic biocides incur significant concerns with respect to the safety of the patient’s healthy cells & organs.

This PhD project aims to develop a natural biocide-based coating (with low toxicity to bone cells) for countering bacterial strain adhesion and the subsequent formation of biofilms upon the implant surfaces. Strontium, which is a key player in facilitating bone formation, will be combined into the coating system to provide the additional benefit of accelerated bone formation. Several coating techniques will be explored to identify optimal ways to produce a composite coating system upon the surface of implant materials, which may be made from metal, polymer, or ceramic.

Figure 1: Implantable devices are made of biomaterials that are broadly classified into metals, polymers, ceramics, and composites Figure 1: Implantable devices are made of biomaterials that are broadly classified into metals, polymers, ceramics, and composites
Figure 2: The complex sizes, shapes, and surface features characterizing microorganisms. (A) The spherical shape of Staphylococcus epidermidis. (B) The rod-like structure of E. coli. (C) The spiral shape of leptospires. (D) The polysaccharide capsule of S. pneumoniae avoids bacterial clearance performed by host cells, since the bacterial antigens are hidden to both immunoglobulin proteins & phagocytic cell lines, e.g. macrophages. (E) The adhesive organelles’ type 1 fimbriae allow bacteria to adhere to both host tissues & abiotic surfaces, thus starting the colonization processes, followed by biofilm formation & development. Figure 2: The complex sizes, shapes, and surface features characterizing microorganisms. (A) The spherical shape of Staphylococcus epidermidis. (B) The rod-like structure of E. coli. (C) The spiral shape of leptospires. (D) The polysaccharide capsule of S. pneumoniae avoids bacterial clearance performed by host cells, since the bacterial antigens are hidden to both immunoglobulin proteins & phagocytic cell lines, e.g. macrophages. (E) The adhesive organelles’ type 1 fimbriae allow bacteria to adhere to both host tissues & abiotic surfaces, thus starting the colonization processes, followed by biofilm formation & development.
Figure 3: Correlation between flagella orientation & surface geometries. (A & B) Contact atomic force microscope images of Pseudomonas fluorescens attached to patterned gold substrates. The black arrows indicate flagella surrounding microorganisms or towards neighbouring bacteria, the white arrows show bacterial division, the dashed white arrows indicate the presence of pili connecting cells, and the dotted black arrow indicates an elongated bacterium. (C) Atomic force and (D) scanning electron microscope images of P. fluorescens growing on unpatterned gold substrates. Arrows display groups of flagella oriented towards other cells. Inset numbers indicate the different stages of formation of a raft-like structure. Figure 3: Correlation between flagella orientation & surface geometries. (A & B) Contact atomic force microscope images of Pseudomonas fluorescens attached to patterned gold substrates. The black arrows indicate flagella surrounding microorganisms or towards neighbouring bacteria, the white arrows show bacterial division, the dashed white arrows indicate the presence of pili connecting cells, and the dotted black arrow indicates an elongated bacterium. (C) Atomic force and (D) scanning electron microscope images of P. fluorescens growing on unpatterned gold substrates. Arrows display groups of flagella oriented towards other cells. Inset numbers indicate the different stages of formation of a raft-like structure.

Vijay Sisarwal is supported by a Government of India scholarship.

Project Publications

Sisarwal, V., Dong, S., Toh, R.J., Gamaleldin, K., Kulkarni, S., Li, H., Cole, I.S., Dong, J., and Chen, X. (2022). ‘Plasma electrolytic oxidation upon Mg alloys: fundamentals, state-of-the-art progress and challenges’, pp 445-464 in: Saji, V.S., Sankara Narayanan, T.S.N., Chen, X. (eds) ‘Conversion Coatings for Magnesium and its Alloys’, Springer, Cham. DOI: 10.1007/978-3-030-89976-9_20.

Sun Yeang Chew

MRes abstract: Exploratory Analysis of the Use of Simultaneous Localisation & Mapping (SLAM) during Cold Spray Additive Manufacturing

Cold spray additive manufacturing (CSAM) technology exhibits a high potential for producing large-scale complex objects. However, ensuring product quality & process consistency is still a challenge due to the associated high-rate deposition and the lack of a real-time monitoring system. We believe that today's computer vision technology is capable of solving this problem, despite the limited scholarly literature in this area, i.e. no such literature has thus far reported a detailed analysis of the performance of 3D visually based sensors in a cold spray environment.

This research project will implement and analyse the existing 3D reconstruction algorithms and 3D vision-based sensors to discover their limitations within cold spray environments. Hence, we will deepen our understanding of the problem and develop improved solutions. This project will develop a heuristic approach to choosing sensors based on 3D reconstruction methods, modelling, simulation, and testing datasets.

Photos of resulting square brackets with same toolpath plan but with different ratios of contour speed to infill speed Figure 1: Toolpath planning case study of a square bracket [1]. Three samples were additively manufactured in copper using the same toolpath plan but with different ratios of contour speed to infill speed. The desired shape is barely (or not) achieved if this ratio of build parameter is incorrectly selected.
Illustration showing the 3D visualisation system used for cold spray robotic additive manufacturing. Figure 2: Block diagram of the 3D visualisation system used here for cold spray robotic additive manufacturing. A 3D visual sensor will be used to collect the geometric shape of printed object during the spraying process, after which a 3D reconstruction algorithm (e.g. SLAM) will reconstruct a 3D model from the raw sensor data.

This project is conducted in conjunction with CSIRO.

References

[1] A. Vargas-Uscategui and P.C. King. ‘Cold spray additive manufacturing of 3D objects using a continuous toolpath planning strategy’, Materials Innovations in Surface Engineering Conference (MISE2020), Melbourne (Australia), 11-12 February 2020.

Subash Gautam

PhD abstract: Vision-Based Process Control in Robotic Metal Additive Manufacturing

Cold spray technology offers many possibilities for manufacturing complex and freeform metallic parts with a high deposition rate, and it stands out as a potential candidate in rapid manufacturing. However, the current process lacks control over the geometrical shape, which tends to present defects that can be amplificated/propagated during the process. This fundamental problem necessitates a control system with real-time monitoring for consistent geometrical accuracy. So, the research will focus on detecting, measuring, validating, and representing the defects in real-time. Furthermore, the research will explore how to use the information to implement a control strategy by optimising parameters and toolpath planning to amend those defects and obtain the desired shape. (For the images behind the above-described work, see my abstract included with the Metal Fabrication subteam’s research.)

This project is conducted in conjunction with CSIRO.

Flow chart of materials that are typically deposited using cold spray, currently used open loop process workflow and proposed closed loop control strategy Figure 1: Materials that are typically deposited using cold spray, currently used open loop process workflow and proposed closed loop control strategy

Muhammad Azhar Shahzad

MRes abstract: Topic: 3D Transient Thermal Finite Element Modelling of AlSi10Mg Alloy to Develop Correlations Between Process Parameters & Microstructural Evolution

Most cutting-edge additive manufacturing processes involve complex thermal phenomena and a large number of controlling process parameters that collectively dictate the final product quality, i.e. its microstructure & mechanical properties. However, it is time consuming and expensive to investigate the correlations between these process parameters and quality metrics through experimentation. Therefore, the aim of this research is to develop a thermal finite element model for the additive manufacture of aluminium alloy AlSi10Mg during multilayer deposition via the laser powder bed fusion process. This will be used to predict the temperature history for developing the above correlations.

A schematic representation of solution domain Figure 1. A schematic representation of solution domain [1].

In this research, a transient thermal finite element model will be developed using the commercial package Abaqus. Elements will be activated/‘born’ as the heat source moves along the part, and the temperature field will be tracked over the addition of multiple layers to build a complete thermal history prediction for the part. These results will include the heat-affected zone (HAZ), i.e. regions of the part that experience rapid heating and cooling followed by reheating and recooling as the layers above them are deposited & fused. It will also investigate the impact of heat flux on the microstructure of the HAZ. In the final analysis, the temperature field of the solidifying part will correlate microstructure evolution with localised thermal history, leading to a predictive model for the local part properties given the local thermal history (process parameter values) recorded during the part’s build. The results of the transient thermal simulations will furthermore be validated against experimental work.

This project is conducted in conjunction with CSIRO.

Temperature distribution during multilayer laser powder bed fusion process. Different colours show temperature distribution Figure 2. Temperature distribution during multilayer laser powder bed fusion process. Different colours show temperature distribution [1].

References

[1] Hu, H., Ding, X. & Wang, L. (2016). ‘Numerical analysis of heat transfer during multi-layer selective laser melting of AlSi10Mg’. Optik, 127(20), 8883-8891, https://doi.org/10.1016/j.ijleo.2016.06.115.

Felix Nugraha Lomo

MRes abstract: Towards Fabrication of Aerospace Components via Cold Spray Additive Manufacturing

Cold spray (CS) is a solid-state, high-rate material deposition process that results in metallic 3D structures built at the order of kg/hour [1]. This high deposition rate, combined with the kinematics of the cold spray gun, controls how powder is deposited onto the part, which may play a critical role in the part’s microstructure and mechanical properties. Postprocessing of a CSAM component also significantly affects its mechanical properties by restoring ductility and toughness to the material, which are typically low in the as-sprayed part thus reducing its tensile strength.

Cold spray additive manufacturing (CSAM) of complex, structural aerospace components has received little attention in the open literature. This project will develop & demonstrate CSAM of a titanium jet engine bracket. Specifically, as the tool path strategy affects as-sprayed part geometry, mechanical anisotropy, porosity distribution, and residual stress, the strategy must be robustly developed before manufacturing commences to ensure the part’s manufacturability and (critically) its in-service performance. (For the images behind the above-described work, see my abstract included with the Metal Fabrication subteam’s research.)

This project is conducted in conjunction with CSIRO.

Schematic of a typical cold spray additive manufacturing system. A 6-axis industrial robot arm is used to either hold the spray gun or the workpiece [2] Figure 1: Schematic of a typical cold spray additive manufacturing system. A 6-axis industrial robot arm is used to either hold the spray gun or the workpiece [2]
A potential tool path plan developed using the Continuous3D software (CSIRO, Clayton, Australia) for the jet engine bracket being manufactured for this project. Figure 2: A potential tool path plan developed using the Continuous3D software (CSIRO, Clayton, Australia) for the jet engine bracket being manufactured for this project. The jet engine bracket challenge is taken from the GrabCAD challenge (https://grabcad.com/challenges/ge-jet-engine-bracket-challenge).

S T Tanushi De Silva

MRes abstract: Measurement of Powder Spreadability in Electron Beam Melting (EBM) Powder Bed Fusion (PBF) Systems

Current powder bed fusion (PBF) systems rely on spherical powders, which are known to have excellent flowability & spreadability. These result in uniform powder bed layers that to build parts with both excellent & spatially consistent mechanical properties, e.g. high tensile & yield strengths. However, the production of spherical powders relies on expensive processes such as gas atomisation (GA), plasma rotating electrode processing (PREP), and plasma spheroidization. The cost of additively manufactured parts can be greatly reduced if cheaper non-spherical powders can be employed without loss of mechanical properties.

Traditional methods such as the Hall flowmeter are used to characterise the flowability of powders. However, these are performed external to the PBF systems and are not always adequate to determine whether powders can flow and spread sufficiently well for use with a PBF system. This issue drove CSIRO to develop the universal powder bed (UPB), which can more accurately analyse the powder behaviour within the manufacturing system in which they are to be used.

The objective of this research is to produce economically manufactured parts with predictable properties while using irregularly shaped powders as feedstock and electron beam melting (EBM) as the additive manufacturing process. This objective be achieved in two stages, namely (i) quantitatively analysing the spreadability using the UPB system, and (ii) assessing the quality of built parts built. The material selection is titanium-tantalum (Ti-Ta), which reflects their highly promising properties when used to construct implants for the biomedical industry, i.e. their excellent biochemical compatibility & biomechanical compatibility (Young modulus close to human bone). Two TiTa blends at 20wt% & 30wt% will be used (Ti-20Ta and Ti-30Ta). Test specimens will be built using both spherical & non-spherical powders, and the microstructure, defects, and hardness of the built parts will be examined in detail.

This project is conducted in conjunction with CSIRO.

Universal Powder Bed (UPB) system developed at CSIRO (Clayton, Australia), which is comprised of the internals of an electron beam melting (EBM) machine. Figure 1: Universal Powder Bed (UPB) system developed at CSIRO (Clayton, Australia), which is comprised of the internals of an electron beam melting (EBM) machine. This setup will be used to analyse the behaviour of powders during the powder spreading process.

Sana Awan

PhD abstract: Non-Destructive Defect Detection & Analysis for Additive Manufacturing (AM) of Metals

Approach

Additive manufacturing is mainly used in industrial sectors where achieving zero part defects is crucial. Therefore to guarantee certification & industrial acceptance of 3D-printed parts, it is essential to characterise their structure & defects. In particular, defect detection & classification during the manufacturing process are highly relevant to improving part quality, as this would allow corrective actions to be performed before component fabrication is completed. However, despite continuous technological advances in additive manufacturing, there is still a lack of non-destructive inspection techniques for use during manufacturing. As a preliminary, this project will investigate X-ray micro-CT & data constrained modelling (DCM) as non-destructive method for this purpose of online defect detection & classification. The AM processes chosen for testing are cold spray (CS) and electron beam melting (EBM), while the materials chosen for testing are titanium and titanium-ceramic composites.

Method

The existing DCM software takes quantitative multi-energy X-ray CT data as its input and applies the DCM technique to generate microscopic partial volume distributions of material phases and pores at the original resolution of the 3D micro-CT dataset. Critically, unlike general CT image segmentation which treats each voxel as having a single phase, DCM can approximate more than one phase per voxel, including porosity (Xavier et al., 2020; Ren et al., 2017).

Materials

Titanium & its alloys are widely used for metal AM. Mixing commercially pure titanium (CPTi) with ceramics can further enhance its capability and reduce defect severity, thus improving finished part quality. DCM will be used here with titanium & its alloys to characterize their microstructure and classify the different type of defects.

This project is conducted in conjunction with CSIRO.

Screenshot demonstrates the basic features of the DCM software using a pre-existing CIPS sandstone sample dataset Figure 1: The above screenshot demonstrates the basic features of the DCM software using a pre-existing CIPS sandstone sample dataset. The microscopic distributions of pores, quartz, and calcite are derived from the CT data in the Sandstone-CT-35keV and Sandstone-CT-45keV dataset directories. Upper left/Panel 1 - void distribution, upper right/Panel 2 - real electric current, lower left/Panel 3 - induced real electric potential, lower right/Panel 4 - real electric potential.

References

Ren, Y. Q. et al. (2017) ‘Characterization of heat treatment-induced pore structure changes in cold-sprayed titanium’, Materials Characterization, 132, pp. 69–75. DOI: 10.1016/j.matchar.2017.08.006.

Xavier, M. S. et al. (2020) ‘Nondestructive quantitative characterisation of material phases in metal additive manufacturing using multi-energy synchrotron X-rays microtomography’, International Journal of Advanced Manufacturing Technology, 106 (5–6), pp. 1601–1615. DOI: 10.1007/s00170-019-04597-y.

Guang Zeng - ALUMNUS

PhD abstract: Novel Fast Manufacturing Approaches for Biocompatible Ti-Ta Structures

Current LinkedIn profile including contact details.

Titanium (Ti) and its alloys are widely used as load-bearing implants, however, slow but continuing release of toxic metal irons and wear debris may incur undesirable side effects.

Tantalum (Ta), an emerging metallic biomaterial, exhibits high corrosion and wear resistance in vivo, but the extremely high melting temperature of Ta (3017 ºC) is a critical technical challenge for manufacturing fully dense structures through conventional processing approaches. As such, new and feasible manufacturing techniques for Ta-based implant materials are highly desired. Cold spray, a new additive manufacturing technology, provides a promising solution to depositing metallic coatings on Ti implants with a variety of benefits, including low-temperature and solid-state process with no phase transitions in Ti/Ta mixture. These unique microstructures of cold sprayed coatings with discrete Ta particles enable large contacting surface area for cell attachment, which is quite distinct compared with bulk Ti-Ta alloys. In this study, uniform and dense Ti-Ta composite coatings (pure Ta and Ti-30 wt. %Ta) were developed on Ti-based substrates (Ti-6Al-4V) using cold spray. The unique microstructures of cold sprayed coatings were led to better cellular biocompatibility than bare Ti-6Al-4V substrate.

Figure 1. A commercial impact system by Impact Innovations Figure 1. A commercial impact system by Impact Innovations
Figure 2. Microstructure of Cold Sprayed Ti-30%Ta coating Figure 2. Microstructure of Cold Sprayed Ti-30%Ta coating

This project was conducted in conjunction with CSIRO.

Ming-Shi Song - ALUMNUS

PhD abstract: Multifunctional Coatings for Biomedical Mg Alloys

Current LinkedIn profile including contact details.

Magnesium (Mg) and its alloys are emerging materials for biomedical applications owing to their desirable mechanical and biological features. However, their clinical applications are significantly restricted by the rapid and uncontrollable degradation progress, which gives rise to hydrogen gas evolution, deterioration of mechanical strength and dramatic changes in local pH in chloride-rich physiological environments. Furthermore, a comprehensive understanding of biocompatibility is essential for design and employment of biomedical Mg implants. In particular, it is of great significance to prevent the implant-related infections caused by dwelling of pathogen colonies and degradation products after implantation. Existing research focuses either on the corrosion or pathogenic issues of Mg-based implants. It is a pressing requirement to discover a feasible solution to such two key issues at the same time.

This project aims to develop a series of gallium (Ga) based multifunctional coatings, which not only suppress the initial degradation kinetics, but also reduce the risk of implants associated infections through sustainable release of antibacterial agents from coatings during the degradation process to surrounding tissues simultaneously.

Though Ga is a recognised broad-spectrum antibacterial element, its use as coating materials for Mg alloys is yet to be assessed. In this study, protective coatings containing Ga ions as germ-killer will be prepared through a cost-effective technique.

Physical, chemical, electrochemical and antibacterial features will be characterised by SEM-EDX, FIB-TEM, XRD, XPS, potentiodynamic polarisation curves, EIS, and in vitro cell and bacteria cultures. It is anticipated that such a new series of coatings will open up new possibilities for clinical applications of degradable Mg alloys.

Multifunctional Ga based coatings with MAO and RF sputtering process Figure 1. Multifunctional Ga based coatings with MAO and RF sputtering process
The illustration of conversion coating process Figure 2. The illustration of conversion coating process

Ming-Shi Song and the project were supported by ARC Linkage project LP150100343 'Functional Strontium Phosphate Coated Magnesium Alloys For Orthopaedic Use'. Visit the project's grant page on the ARC website for more information.

Dr Xiao-Bo Chen

Abstract: Functional Strontium Phosphate Coated Magnesium Alloys for Orthopaedic Use

This project aims to develop a functional strontium (Sr)-release surface upon magnesium-based orthopaedic implants to suppress the rapid degradation rate of Mg, facilitate new bone formation and ultimately shorten healing process. The project will establish theunderstanding of the formation mechanisms of Sr-releasing coatings, and determine the critical release rate of Sr to activate bone cell responses. The project is significant for the development of practical, bone-favourable and degradation-inhibiting surfaces for magnesium implants, which are in demand and can bring significant patient benefits. The project will forge new and important collaborations and provide an output for biomedical technology locally and internationally.

Figure 1. Bioactivity evaluation of Mg implants (Sham: no implant; SrPO₄@Mg: pure Mg with strontium phosphate coating, Pure Mg: bare Mg implant) in mice model for 7 weeks - (top row) Bone tissue response to the implanted rods - µCT analysis.  (bottom row) quantitative results of new bone formation at the implant sites of mice femur after 7 weeks’ implantation. Figure 1. Bioactivity evaluation of Mg implants (Sham: no implant; SrPO₄@Mg: pure Mg with strontium phosphate coating, Pure Mg: bare Mg implant) in mice model for 7 weeks - (top row) Bone tissue response to the implanted rods - µCT analysis. (bottom row) quantitative results of new bone formation at the implant sites of mice femur after 7 weeks’ implantation.

The project is supported by ARC Linkage project LP150100343 'Functional Strontium Phosphate Coated Magnesium Alloys For Orthopaedic Use'. Visit the project's grant page on the ARC website for more information.

Dr Paul White

Abstract #1: High-Throughput Discovery of New Corrosion Inhibitors

The generation of new corrosion inhibitor leads requires the experimental testing of many hundreds of chemicals under varying conditions (concentration, pH, etc) on multiple different metal samples with perhaps thousands of synergistic inhibitor combinations, a virtual impossibility by standard corrosion techniques. I developed a high-throughput method that allows for 88 simultaneous corrosion inhibitor tests in 24 hours on a single metal plate (Corrosion Science, 2012, 58, 327). Leads generated by this technique are then analysed further by electrochemistry and also incorporated as a pigment in a coating for further electrochemical & salt spray testing (New Journal of Chemistry, 2020, 44, 7647-7658). Successful inhibitors or inhibitor combinations, discovered by these methods, have been patented.

Fig 1. Wells rig designed to perform 88 simultaneous corrosion inhibitor experiments
Fig 2. Aluminium substrate after 24-hour wells experiment with 88 different inhibitors. Note that droplets with no corrosion show the desired result.

Publication highlights

  • White, P. A., Collis, G. E., Skidmore, M., Breedon, M., Ganther, W. D., Venkatesan, K., Towards materials discovery: assays for screening and study of chemical interactions of novel corrosion inhibitors in solution and coatings. New Journal of Chemistry, 2020, 44, 7647-7658.
  • Taheri, P., Milosev, I., Meeusen, M., Kapun, B., White, P., Kokalj, A., Mol, J. M. C., On the importance of time-resolved electrochemical evaluation in corrosion inhibitor screening studies. NPJ Materials Degradation, 2020, 4, 12.
  • White, P. A.; Smith, G. B.; Harvey, T. G.; Corrigan, P. A.; Glenn, M. A.; Lau, D.; Hardin, S. G.; Mardel, J.; Markley, T. A.; Muster, T. H.; Sherman, N.; Garcia, S. J.; Mol, J. M. C.; Hughes, A. E. A new high-throughput method for corrosion testing. Corrosion Science, 2012, 58, 327.
  • Harvey, T. G.; Hardin, S. G.; Hughes, A. E.; Muster, T. H.; White, P. A.; Markley, T. A.; Corrigan, P. A.; Mardel, J.; Garcia, S. J.; Mol, J. M. C.; Glenn, A. M., The effect of inhibitor structure on the corrosion of AA2024 and AA7075.  Corrosion Science 2011, 53 (6), 2184.
  • White, P. A.; Hughes, A. E.; Furman, S. A.; Sherman, N.; Corrigan, P. A.; Glenn, M. A.; Lau, D.; Hardin, S. G.; Harvey, T. G.; Mardel, J.; Muster, T. H.; Garcia, S. J.; Kwakernaak, C.; Mol, J. M. C, High-throughput channel arrays for inhibitor testing: Proof of concept for AA2024-T3. Corrosion Science, 2009, 51 (10), 2279.

Patents

  • Methods for Inhibiting Corrosion. US Patent 2020/0040465A1
  • Soluble Corrosion Resistant Sol-Gel. US Patent 2019/0241752A1
  • Polymeric Agents and Compositions for Inhibiting Corrosion. International Patent WO 2017/152240 A1
  • Compositions for Inhibiting Corrosion. International Patent WO 2016/154680 A1
  • Recovery of Precious Metals. US Patent 2003/0154822 A1

 

Abstract #2: Australian War Graves project

Project duration: 03/2022 - 03/2023

RMIT’s RDF Team is working with the Department of Veterans’ Affairs’ Office of Australian War Graves (OAWG) to help ensure that commemorative bronze plaques and lettering on marble & granite headstones remain in good condition and are legible for the maximum time. OAWG is responsible for the care & maintenance of these commemorations in perpetuity. RMIT will work with OAWG to examine both fabrication & exposure conditions to provide guidance to enhance the life of these important memorials.

Dr Steffen Jeschke

Abstract: Next Generation Corrosion Inhibitors for Protection of Galvanised Steel and Cold Rolled Steel

Corrosion has a significant economic impact with losses in the magnitude of billions of USD annually in transportation, manufacturing and infrastructure. In this project, new corrosion inhibitors for galvanised and cold rolled steel are being screened experimentally and quantum chemically described using density functional theory and classical methods. A database is generated for computational model building to identify lead structures for the development of new highly effective inhibitors.

The project was conducted in conjunction with BASF Coatings.

Dr Rou Jun Toh

Abstract: Developing Functional Coating Systems for Bio-metal for Orthopaedic Implants

The desirable mechanical properties and superior biocompatibility of magnesium (Mg) and its alloys has placed them in the research frontier in materials for biomedical applications. However, their clinical applications are significantly restricted by the high degradation rate in physiological environment. In order to tackle such a limitation, functional polymeric coating systems will be developed to address rapid degradation as well as to reduce other clinical issues such as wear resistance, infection and low bone-inductivity.

The project was conducted in conjunction with Surface Engineering for Advanced Materials ARC Training Centre (SEAM).

Abstract: Development of a Robotic Electrochemical Testing Facility

Corrosion poses significant challenges to the transportation, manufacturing and infrastructure sectors. For this reason, it is imperative to prevent and control corrosion using corrosion inhibitors. A corrosion inhibitor protects a metal by restricting cathodic or anodic activity on the metal surface. Its exact performance depends on its exact molecular chemistry. Due to this dependence on molecular structure, there are literally tens of thousands of possible inhibitors so high throughput screening methods are required to select the best. In this work, a fully electrochemical robotic system will be developed for the purpose to select and design the best performing corrosion inhibitors. The robotic facility will carry out more than 100 electrochemical tests per day.  

The project was conducted in conjunction with BASF Coatings.

Simulation of final assembly Simulation of final assembly

Dr Ernane de Freitas Martins

Abstract: Multi-scale QM/MM + NEGF Formalism to Address Electrified Metal/Water/Corrosion Inhibitor Interfaces

The use of molecular modelling to investigate the performance of corrosion inhibitors can provide significant gain to the proposal of new and more efficient inhibitors. Although its use has increased over the last few years, the most commonly used models still do not consider some important aspects, such as solvent effects and the stability of the proposed inhibitors when a potential is applied. To address these gaps, we propose using a new approach that combines density functional theory (DFT), non-equilibrium Green's functions (NEGFs), and a quantum mechanics/molecular mechanics (QM/MM) method to include a realistic number of solvent molecules. Our project’s end goal is the best characterisation thus far of the metal/solvent/corrosion inhibitor interface.

Sketch of an electronic transport setup as implemented in the NEGF formalism Figure 1: Sketch of an electronic transport setup as implemented in the NEGF formalism. Left (source) and right (drain) electrodes (the three dots illustrates each electrode’s semi-infinite character) with an intermediate aqueous solution containing positive and negative ions. A potential difference, VDS, is illustrated between the source and drain electrodes.

The project was conducted in conjunction with the Catalan Institute of Nanoscience and Nanotechnology (ICN2, Spain).

Kai Rui Wang

PhD abstract: Developing an Agar System for Studying Microbiologically Influenced Corrosion of Ferrous Pipes in Soil

Risks of leakage and contamination are incurred by the corrosion of buried steel water pipelines, which cause health and safety hazards to the communities that potable water is delivered to. As much of the corrosion originates from the outer pipe surface, monitoring soil-to-steel interactions is crucial to understanding the physical and chemical mechanisms that cause corrosion. It was found that semi-solid agar could be a good analogue for simulating clay-based soil conditions for corrosion testing; however, a more systematic study needs to be carried out to investigate the metal-bacteria-environment interactions present in microbiologically influenced corrosion situations. Detailed studies are currently being performed to analyse such interactions in the novel semi-solid agar system. The system as an analogue of soil, if validated, would allow significant advancements to laboratory-based research of corrosion in a soil environment, thus allowing the scientific community to better combat MIC for pipelines buried underground.

Figure 1: SEM micrograph of HA1 steel after 5.5 h exposure in a semi-solid agar medium Figure 1: SEM micrograph of HA1 steel after 5.5 h exposure in a semi-solid agar medium
Figure 2: (a) Three-electrode corrosion cell and potentiostat for electrochemical corrosion studies, and (b) close-up view of cell chamber Figure 2: (a) Three-electrode corrosion cell and potentiostat for electrochemical corrosion studies, and (b) close-up view of cell chamber
Figure 3: Potentiodynamic polarisation curves of steel coupons in contact with 4 g/L semi-solid agar and nutrients Figure 3: Potentiodynamic polarisation curves of steel coupons in contact with 4 g/L semi-solid agar and nutrients

Project Publications

  • K. Wang, A. Spark, I. Cole, and L. Ward (2019). ‘Effects of electrochemical techniques on carbon steel in agar’, Corrosion & Prevention; 23-27 November 2019, Melbourne, Australia. Paper ID 45. p 1-11.
  • A Spark, K. Wang, I. Cole, D. Law, and L. Ward (2020). ‘Microbiologically influenced corrosion: a review of the studies conducted on buried pipelines’, Corrosion Reviews, 38(3), 231-262. DOI: 10.1515/corrrev-2019-0108.

Jakeria Mohd. Rafiuddin

PhD abstract: Corrosion Inhibition Studies of Aluminium Alloys 6XXX Series and Mechanisms of Film Formation

Corrosion protection of high-strength AA6xxxx alloys by film-forming small molecules such as 2mercaptobenzimidazole (2MBI) in a corrosive environment are potentially a useful contribution to the corrosion literature. 2MBI has been reported to interact with metal surfaces by S & N moieties from its five-membered ring structure, and promptly forms an inhibitor film. The produced film could hinder the diffusion of ions and reduce water adsorption on metal surfaces. However, time-dependent-dependent studies of 2MBI film growth in saline solution over AA6xxxx alloys, changes to barrier properties of inhibitor-induced film against ionic diffusion, alteration of bonding environments from the metal-coating interface to the coating-electrolyte interface, and consequent changes in coating structure aligned with mechanical properties have been minimally reported in the available literature. The aim of this PhD project is to highlight these critical issues and develop a methodology to systematically answer the relevant research questions on film-forming mechanisms. Results of electrochemical & complementary surface analysis techniques have indicated that 2MBI could adsorb over AA6xxxx in saline solution in the form of a film from as early as 30 mins, then become stabilised after 90 mins with a continuous but inhomogeneous structure. The adsorbed film maintains a higher inhibition efficiency (97%) by reducing current density, which drops gradually with time (Fig 1). The 2MBI-induced film appears to be complex with the coexistence of aluminum oxide & inhibitor constituents (Fig 2). During longer periods, the complex film becomes porous & defective with a gradual drop in inhibition efficiency & barrier properties (Fig 3). High-resolution AFM imaging coupled with nano-indentation has revealed changes to inhibitor film stiffness over time (Fig 4). The film stiffens both in the early stages of growth and again after 90 mins. Distribution of oxide inside the film structure is thought to play a key role in this regard. Chemical analysis of inhibited treated saline solution in the presence of AA6xxxx has revealed time-dependent inter- & intramolecular changes to 2MBI.

Fig 1. Potentiodynamic polarization results of inhibitor treated AA6xxxx in saline solution
Fig 2. FIB-SEM cross sections of inhibitor treated AA6xxxx at 90 mins and 3 h
Fig 3. In-situ surface topography of AA6xxxx flooded with inhibitor treated saline solution at 90 mins & 3 h
Fig 4. Changes of Young's modulus by AFM nano indentation with time

Project Publications

  • Jakeria, M.R., R.J. Toh, X.-B. Chen, and I.S. Cole (2022). ‘Evolution and stability of 2-mercaptobenzimidazole inhibitor film upon Al alloy 6061’, Journal of Applied Electrochemistry, p. 1-24, DOI: 10.1007/s10800-022-01687-w.
  • Jakeria, M., L. Ward, and I. Cole (2021). ‘Long term durability studies on the corrosion inhibition effect of 2-mercaptobenzimidazole (C3H4N2S) on AA6022: Mechanism of film formation and influence of IMPs’, Surfaces & Interfaces, 25: p. 101164. DOI: 10.1016/j.surfin.2021.101164.
  • I.S. Cole, L. Ward, and M.R. Jakeria (2019). ‘Influence of azole derivatives on corrosion inhibition of AA6022’, Corrosion & Prevention 2019, 25-28 November 2019, Melbourne, Australia.

Asma Lamin

PhD abstract: Study of Quorum Sensing (QS)-Driven Inhibitors for Mitigating Microbially Influenced Corrosion of Carbon Steel

Microbiologically influenced corrosion (MIC) is a process by which microorganisms initiate, facilitate, or accelerate the electrochemical corrosion reactions of metallic components. Several studies report that MIC accounts for 20-40% of the total cost of corrosion. For example, MIC in oil & gas pipelines can result in significant production loss & serious environmental effects. Biofilm formation caused by surface microorganisms upon metal components is known to play a vital role in MIC. The QS system plays a significant role in controlling the expression of some bacterial enzymes, e.g. catalase regulates biofilm formation and thus the MIC rate for metal. As such, avoiding biofilm formation via inhibiting QS is a sound potential strategy for mitigating MIC of metal. This PhD aims to elucidate the mechanistic role of QS both in biofilm formation & corrosion of carbon steel, a prevalent engineering material for construction of pipelines, with Pseudomonas aeruginosa as a model organism.

LuxI/LuxR QS in Gram-negative bacteria. LuxI is an autoinducer synthase and LuxR is an AHL receptor protein. At high cell density, AHL autoinducer binds to LuxR and activates the transcription of its target genes. Figure 1. LuxI/LuxR QS in Gram-negative bacteria. LuxI is an autoinducer synthase and LuxR is an AHL receptor protein. At high cell density, AHL autoinducer binds to LuxR and activates the transcription of its target genes.

Qiushi Deng

PhD abstract: Rapid Discovery of Next-Generation Inhibitors for Galvanised Steel

Great momentum has been gained in the development of corrosion inhibitor technologies to mitigate corrosion of metallic materials, in particular for zinc & galvanised steel. Corrosion inhibitors are crucial to ensuring the integrity, durability, and safety of many metallic structures. The use of metallic salts as corrosion inhibitors has been broadly explored since the early stages of corrosion science owing to their ability to passivate the metal surface and generate protective films. However, increasing environmental concerns and the pursuit of more cost-efficient techniques has shifted the focus toward organic alternatives due to their many advantages, including i) cost effectiveness, ii) pronounced inhibiting effect, and iii) flexibility to different applications with non-toxic nature. Unfortunately, candidate molecules acting as effective corrosion inhibitors are rich in diversity of chemistry and structural complexity, and their inhibition behaviour also depends on the existing form of molecules (i.e. de/protonation) and the metal’s surface condition (i.e. surface charge & presence of oxides). Given these challenges, this project aims to design a sound strategy to explore high-efficiency organic inhibitors from a large variety of candidate molecules in an attempt to reveal their inhibition mechanism from the viewpoint of inhibitor structural change, molecular evolution, and interfacial metal charge. The expected finding of this project is an improved understanding of the protection mechanism of organic inhibitors from a molecular viewpoint, which will form a concrete basis for the design & preparation of new inhibitor molecules of engineering relevance.

 

This project is conducted in conjunction with BASF Coatings.

High-throughput design for rapid screen of inhibitor candidates in this project Figure 1. High-throughput design for rapid screen of inhibitor candidates in this project

Project Publications

  1. Q. Deng, S. Jeschke, B.J. Murdoch, S. Hirth, P. Eiden, J.N. Gorges, P. Keil, X.B. Chen, I. Cole (2022). ‘In-depth insights of inhibitory behaviour of 2-amino-4-methylthiazole towards galvanised steel in neutral NaCl solution’, Corrosion Science, vol. 199, 110206. 10.1016/j.corsci.2022.110206.
  2. M.S. Song, Q. Deng, R.J. Toh, I. Cole, X.B. Chen (2022). ‘Permanganate, molybdate and vanadate conversion coatings’ in ‘Conversion coatings for magnesium and its alloys’, Springer, Cham, 2022. DOI: 10.1007/978-3-030-89976-9_5.

Karim Gamaleldin

MRes abstract: Rapid Evaluation Assessment of Corrosion Inhibitors

My MRes concerns the development of rapid screening techniques for evaluating a wide range of potential inhibitors for 5xxx aluminium alloy systems. The use of corrosion inhibitors for the protection of these alloys is well established. While various inhibitors have been developed and assessed for the protection of marine-grade Al alloys, the most common practice for many decades has been the addition of chromate-based pigments to paint films. Chromates are recognised as extremely robust and effective inhibitors, however, there is increasing awareness of their toxicity and associated environmental hazards. This has led to the search for alternative inhibitors that are less toxic, more affordable, and effective at low concentrations.

Traditionally, the development of an inhibitor system for a particular application can be extremely time consuming, particularly if a systematic study using various analysis techniques is applied to a large, diverse range of potential inhibitors. Testing times can range from hours (electrochemical testing) to weeks (weight loss experiments, pitting studies), and even years (outdoor exposure field trials). This project aims to use the droplet corrosion test method for the first time with 44 structurally related chemical compounds as corrosion inhibitors to rapidly evaluate their performance.

Figure 1: Corrosion events on the droplet site (2 microlitre) size Figure 1: Corrosion events on the droplet site (2 microlitre) size
Figure 2: Secondary spreading phenomena happened on the droplet edge Figure 2: Secondary spreading phenomena happened on the droplet edge

Shrinivas Kulkarni

PhD abstract: Optimising the Surface Condition of Additively Manufactured Implants

I started my PhD in August 2020. This is focused on environmentally assisted corrosion (EAC), specifically the stress corrosion cracking (SCC) of additively manufactured (AM) passive metals in a physiological environment. The performance of an implant in the human body is mainly controlled by two characteristics: mechanical environmental functionality and bio-compatibility. The most widely used alloys in such implants are stainless steel 316L (SS316L) and titanium-aluminium 6wt%-vanadium 4% (Ti6Al4V). Samples of SS316L and Ti64 will be produced using Selective Laser Melting (SLM) and Electron Beam Melting (EBM) AM processes. Surface characteristics including roughness and AM process-related defects including porosity, cracks, and segregation will be explored. The aim is to establish the relationship between surface/microstructure and the total life of commercial implant materials when subject to environmental assisted cracking and fatigue. The implants will be subjected to corrosion testing in both NaCl solution and simulated body fluid. Furthermore, these samples will be subjected to stress corrosion cracking and fatigue testing, and the results will be analysed for the stress concentration factor at pits and the lifetime of the implant.

Figure 1: Factors with influence on environmentally assisted corrosion Figure 1: Factors with influence on environmentally assisted corrosion
Figure 2: Parameters affecting metal implants in the human body Figure 2: Parameters affecting metal implants in the human body
Figure 3: AM lattice structures fabricated from Ti64 alloy using SLM for orthopaedic applications, reproduced from ref. [3] Figure 3: AM lattice structures fabricated from Ti64 alloy using SLM for orthopaedic applications, reproduced from ref. [3]
Figure 4: Typical defects and surface roughness observed in lattice structures, reproduced from ref. [3] Figure 4: Typical defects and surface roughness observed in lattice structures, reproduced from ref. [3]

References

[1] M. Talha, Y. Ma, P. Kumar, Y. Lin, and A. Singh, “Role of protein adsorption in the bio corrosion of metallic implants – A review,” Colloids and Surfaces B: Biointerfaces, vol. 176. Elsevier B.V., pp. 494–506, Apr. 01, 2019, doi: 10.1016/j.colsurfb.2019.01.038.

[2] A. Bandyopadhyay, B. V. Krishna, W. Xue, and S. Bose, “Application of Laser Engineered Net Shaping (LENS) to manufacture porous and functionally graded structures for load bearing implants,” J. Mater. Sci. Mater. Med., vol. 20, no. S1, pp. 29–34, Dec. 2009, doi: 10.1007/s10856-008-3478-2.

[3] X. Z. Zhang, M. Leary, H. P. Tang, T. Song, and M. Qian, “Selective electron beam manufactured Ti-6Al-4V lattice structures for orthopedic implant applications: Current status and outstanding challenges,” Current Opinion in Solid State and Materials Science, vol. 22, no. 3. Elsevier Ltd, pp. 75–99, Jun. 01, 2018, doi: 10.1016/j.cossms.2018.05.002.

José María Castillo Robles

PhD abstract: A Multiscale Approach to Bias-Dependent Electrochemical Processes at Metallic-Aqueous Interfaces: Corrosion Inhibitors

Corrosion is a pre-eminent problem in industry, causing compounding financial losses and environmental problems. To prevent the corrosion process, toxic inorganic compounds such as chromates are often used as pigment additives or conversion coatings. Over the last few years, these are increasingly being replaced by more environmentally friendly inorganic and organic compounds. These organic compounds (corrosion inhibitors) have lone pair electrons and are thus good donors of charge, preventing cathodic and anodic reactions. While many chemicals are being studied for this purpose, the fundamental mechanisms determining corrosion inhibitor performance are still far from understood. We use a multiscale approach to address this problem, specifically investigating the interactions of a database of 28 compounds with aluminium surfaces in the presence of an aqueous electrolyte. We are using first-principles methods to obtain insight into the corrosion processes taking place at the molecular level, which will aid us in designing more efficient and sustainable corrosion inhibitors.

An innovative approach for modelling electrochemistry processes from first principles is through a setup consisting of two electrodes acting as charge reservoirs, which are kept at different potentials and are separated by an aqueous electrolyte. This setup is widely used to simulate electronic transport in nano-devices, where electrodes held at different potentials are connected to a nano-device through which an electric current is established. The method, first described in the context of density functional theory (DFT) in [1] and now implemented in the TranSIESTA code [1,2] (part of the open-source SIESTA software [3,4]), is now a standard for simulation of electronic transport in electronic nano-devices.  To enable the use of realistic electrolyte solutions, we will apply the hybrid quantum mechanics/molecular mechanics (QM/MM) approach [5], in which the system is split into quantum and classical regions according to the chemical processes of interest. This domain decomposition allows us to include in the QM region a reduced number of atoms (the metallic surface + the adsorbed molecules) with the remaining atoms (aqueous solution) modelled in the MM region.

Figure 1: A sketch of a solvated Cu (111) device with an absorbed monolayer of mercaptobenzimidazole (MBI) under a bias. The ochre-, yellow-, blue-, cyan-, red-, and white-coloured atoms represent Cu, S, N, C, O, and H atoms, respectively. Figure 1: A sketch of a solvated Cu (111) device with an absorbed monolayer of mercaptobenzimidazole (MBI) under a bias. The ochre-, yellow-, blue-, cyan-, red-, and white-coloured atoms represent Cu, S, N, C, O, and H atoms, respectively.

José María Castillo Robles is cotutelle with the Autonomous University of Barcelona (UAB) & the Catalan Institute of Nanoscience and Nanotechnology (ICN2, Spain).

Palaniappan Nagarajan - ALUMNUS

Current Google Scholar profile including contact details.

PhD abstract: Functionalized Carbon Materials for Corrosion Inhibitors & Energy Storage Applications

Broadly, the research work concerns functionalized carbon materials for corrosion resistance coatings on metal alloys. Newly design organic molecules were synthesised and functionalized with graphene oxide for improved inhibition efficiency and stable corrosion resistance in aggressive environments. The long-term stability of organic inhibitor molecules is useful as conventional inorganic alternatives can fail in aggressive environments. However, some organic inhibitor molecules cause damage to the environment if they are made from non-biodegradable organic molecules. Heterocyclic compound-functionalized graphene oxide and imidazole-functionalized graphene oxides act as ‘green’ inhibition coating materials for Mg alloys, mild steel, and titanium as they are biodegradable.

 

Functionalized carbon materials for coatings on metal alloy surface – physisorption & chemisorption Figure 1: Functionalized carbon materials for coatings on metal alloy surface – physisorption & chemisorption

This project was conducted in conjunction with RMIT University (Melbourne) & Central University of Gujarat (India)

Chathumini Samarawickrama - ALUMNUS

Current LinkedIn profile including contact details.

MRes abstract: Study of Mechanisms of Film-Forming Behaviour of Corrosion Inhibitors for Commercial Grade Aluminium Alloys

In today's society, corrosion protection of structural aluminium alloys in the aerospace, marine, automotive, and construction industries is of paramount importance. This is commonly achieved via corrosion-inhibiting compounds. However, constraints such as potential health issues associated with exposure to conventional chromate-based corrosion inhibitors has led to the development of low-toxicity corrosion inhibitors for a wide range of industries. Since then, much work has been carried out to evaluate inhibitor performance and their mechanisms of action, but only a few studies have elucidated the precise film-forming characteristics of particular inhibitors. Therefore, this study presents key aspects of the film-forming behaviour of the selected inhibitors and the test methods used to evaluate the inhibitor-induced films in chloride solution. This study also aims to provide significant insights into film tenacity, influence of the molecular structure, and film stability in the absence of inhibitors to provide a deeper understanding of film-forming and film-breakdown mechanisms. This study focusses on two inhibitors known for their high corrosion inhibition efficiency for protection of aluminium AA2024-T3 alloy, namely 2-mercaptobenzothiazole and Na-mercaptopropionic acid. During this work, a wide range of electrochemical methods were utilised in conjunction with various surface analysis methods to understand inhibitor-induced film formation. (For the citations & images behind the above-described work, see my abstract included with the Corrosion and Inhibition subteam’s research.)

 

SEM image of the interface of a submersed AA2024‑T3 in a 2‑MBT solution for 30 days SEM image of the interface of a submersed AA2024‑T3 in a 2‑MBT solution for 30 days
Schematic of inhibitor-induced film formation over AA2024‑T3 Schematic of inhibitor-induced film formation over AA2024‑T3

This project was conducted in conjunction with BASF Coatings.

Dr Milan Patel

Abstract: Multiscale Modelling of Selective Laser Melting

RMIT is participating in a CSIRO-NTU Singapore-led project to develop cutting-edge simulation models of additive manufacturing – specifically the Selective Laser Melting process. This project will combine high-definition continuum fluid dynamics at the part scale, which models powder melting & melt pool tracking, with phase-field modelling at the grain scale that predicts solidification rate and finished-part microstructure. ‘Live’, bidirectional data exchange between these two sub-models permits the most accurate predictions of both the behaviour of the SLM process & the microstructure of the finished part to be obtained from one simulation platform.

All coding is performed using open source platforms, allowing for rapid technology transfer to industry partners. Enquiries should be addressed to dayalan.gunasegaram@csiro.au.

Figure 1: Computational fluid dynamics simulation of melt pool linked to phase field model of alloy microstructure Figure 1: Computational fluid dynamics simulation of melt pool linked to phase field model of alloy microstructure

Dr Xiangdong Li

Abstract: A Spatiotemporally Solved Predictive Model for COVID-19 Transmission in Indoor Spaces

Since the outbreak of the COVID-19 pandemic, indoor spaces have been the major venue for the disease to spread from person to person.

Spatiotemporally solved predictive models that can comprehensively account for various engineering and clinical/epidemiological factors (e.g. building design, HVAC layout, occupant movement, SARS-CoV-2 variants and stage of infection, the extent of personal protective equipment (PPE), and immunisation) are highly demanded in the global fight against COVID-19.

Supported by the Victorian Higher Education State Investment Fund (VHESIF) and in collaboration with partners from the healthcare, commerce, and manufacturing sectors, RMIT University is developing such a comprehensive predictive platform that holistically integrates the above factors into a single model. By combining the latest computational fluid dynamics (CFD) techniques, epidemiological models, and clinical/virological data for COVID-19 variants, the platform can generate high-resolution, quantitative ‘risk maps’ for COVID-19 infection in indoor spaces (Figure 1).

This capability is critical to the development of effective prevention & protection strategies. The predictive platform also provides a universal theoretical framework to develop fit-for-purpose predictive models for other airborne diseases such as influenza, measles, tuberculosis, etc.

A chart showing predicted infections risk from COVID-19 in a hospital room Figure 1 - Predicted infection risk of COVID-19 in a hospital room

The project was conducted in conjunction with the Victorian Higher Education State Investment Fund.

Neil Wilson

PhD abstract: Conformal Tooling via Hybrid Manufacturing

Conformal tooling is an advanced technology used to construct moulds for the mass manufacture of parts with complex shape. Its development continues across the industrialised world due to its promise in producing moulded parts at lower cost. It achieves this by significantly reducing manufacturing cycle time, i.e. the time required to complete a single moulding cycle from material injection to extraction of the part from the tool, and also by improved quality of the moulded parts due to closer control of mould cavity temperature throughout the moulding process.

Numerous materials may be used in the creation of moulded parts, resulting in a potentially vast array of relevant client industries & products. The fundamental factors limiting the growth in scale and market penetration of conformal tooling are country specific, i.e. the presence of advanced manufacturing infrastructure, the availability of skilled multi-disciplinary toolmakers capable of incorporating the high-level additive manufacturing (AM) skillset, and simulation capability specific to the design of conformal tools. In Australia, the latter is only now becoming established in the form of specific design software components for use with conformal tooling, i.e. heat flux simulation, part deformation, heating/cooling fluid dynamics together with mould-filling fluid dynamics. These components alone do not deliver a generic methodology for the design of conformal tooling – for this purpose, generative design linkage modules are required that connect the modelling components. Such linkage modules promise conformal tooling design capability for use by non-expert users and are the focus of this thesis.

Well-designed conformal tooling demonstrates an optimal (i.e. uniform) temperature distribution (‘heat map’) along the inner surface of the tooling cavity. This is achieved by using additive manufacturing to include channels for heating/cooling fluid near both the mould’s cavity and core surfaces. Predictions of the required number, cross-sectional shape/size, pitch (inter channel distance & pattern), and distance between the channels & the cavity and tool surfaces must be reliably generated to achieve this homogenous heat map in a cost-effective manner, i.e. with the minimum of built prototypes. These typically multi-objective design calculations are conducted to a varying extent of accuracy by the current stable of process simulation software packages. However, none yet consider the varying heat map at the cavity face during the final material-filling stage of the injection process. This is now the subject of development within several software houses including Moldex, Altair, Siemens and nTopology. The research described in this thesis aims to achieve a manufacturer-independent (generic) software linkage module of this type, which is furthermore validated against experiments for both single-alloy and bi-metal combinations. We will also examine the effect of the air gap in cavity due to thermal shrinkage within the mould.

Figure 1: (a) Benchmark channel configuration. Figure 1: (a) Benchmark channel configuration. This design is common in pre-AM-built tooling; the channel cross section is usually round & the channels are straight due to the drilling construction method. (b) The spiral conformal channel design is a based on potential AM manufacturing methods with no reference to cavity surface heat map. The cycle times for (a-b) are predicted to be 19.3 s & 16.7 s, respectively, clearly demonstrating the utility of the spiral design.

This project was conducted in conjunction with Romar Engineering Pty Ltd and CSIRO.

Ayush Ranjan

MRes abstract: Digitization of Workplaces to Ensure Safety from Airborne Pathogens

The COVID-19 pandemic has highlighted the importance of estimating & managing risk from airborne pathogens in indoor environments. The building services (HVAC) system, as well as the environmental disturbances generated by human movement & large electrical/electronic systems all influence transmission of contaminants inside a building. Therefore, it is imperative & timely to understand the impacts of these factors on contaminant transport to mitigate the risk of infection by airborne biological pathogenic contaminants. 

Four RMIT project teams are working on different aspects of this project:

  1. Sensing team: Designing a digital model of a four different industry client buildings & installing multiple types of environmental sensors therein
  2. Aerosol team: Building large-scale Computational Fluid Dynamics (CFD) simulations of the four buildings to compute infection risk maps based on their floorplans & HVAC details
  3. Human Movement team: Tracking human-building interactions
  4. System Integration team: Combining insights from other teams and simplifying them into generalised rules/guidance for facility managers to implement to reduce infection risk

As a part of the ‘System Integration team’ of this project, I will be (i) analysing combined datasets from different sensor types to generate insights into human-building interactions of relevance to reducing infection risk, and (ii) developing micro-scale CFD simulations (‘micro-cases’) from common building floorplans. These micro-cases will provide low-order infection risk maps that we will eventually ‘stitch together’ to produce low-order infection risk maps for an a priori unknown, real floorplan that predict how to reduce its inherent infection risk. Running & analysing infection risk maps from a large set of micro-cases CFD results will then help us develop a simple set of general rules that can be transmitted to building/facilities managers to reduce infection risk for a priori unknown, real floorplans.

Figure 1: CFD results using floorplan layout of a COVID19 ward in an Australian hospital. The results show uneven distribution of COVID19 infection risk in the ward. (a) Airflow field at an ‘average’ human breathing height of 1.65 m, (b) particle concentration field throughout the space, and (c) spatial distribution of infection risk [1].

This project is conducted in conjunction with the Victorian Higher Education State Investment Fund.

Omid Bafkar - ALUMNUS

Current LinkedIn profile including contact details.

Phd abstract: Study of Airflow Phenomena in the Human Respiratory System

Obstructive Sleep Apnoea (OSA) is a common disorder, and continuous positive airway pressure (CPAP) is usually the therapy of choice. CPAP is known to have problems with adherence with many patients eventually abandoning the device. However, the development of an optimal OSA treatment for a specific patient requires a thorough understanding of the responses of the patient to the tailored OSA treatments which in turn need numerously costly clinical trials and measurements.

Therefore, accurate predictions of the responses of the patient to the tailored OSA treatments are highly desired. We implement numerical modelling methods and techniques to understand airflow behaviour in various sleeping positions and conditions.

This aims to provide a technique that can help specialists provide better treatment solutions to their patients. 

Ethical approval was obtained for all human trials.

National Computational Infrastructure (NCI) facilities were used for some of this research.

Figure 1. Airflow behaviour on the nasal cavities during the short inhalation Figure 1. Airflow behaviour on the nasal cavities during the short inhalation

This project was conducted in conjunction with Oventus Manufacturing Pty Ltd and CSIRO.

Dr Hong Yin

Abstract: Functional Nanoparticles for Sensing, Adsorption & Antimicrobial Applications

Heavy metal ions in water have posed severe environmental and health risks due to their high toxicity, high aqueous solubility, and difficulty participating in biological transformations to non-toxic end products.  Traditional water-monitoring equipment is heavy, costly, and normally only one or a few elements are detected at any one time. A cheap and multiplexed measurement using a portable device is urgently required to monitor water quality in rural and remote areas. This project will apply surface-functionalised fluorescent nanoparticles, such as quantum dots (QDs) and carbon dots (CDs), in a home-made portable device for detecting multiple heavy metal ions in a semi-quantitative way. 

Other applied research in the nanostructures area includes tailored synthesis and surface modification of activated carbon adsorption materials and antimicrobial particles such as zinc oxide, silver, and magnesium hydroxide nanosheets for water purification and biomedical applications.

(a) Semiconductor quantum dot solution with increasing Cu²⁺ concentration under UV light (a) Semiconductor quantum dot solution with increasing Cu²⁺ concentration under UV light
(b) Linear relationship between fluorescence intensity and Cu²⁺ concentration (b) Linear relationship between fluorescence intensity and Cu²⁺ concentration
(c) Various quantum dots for heavy metal detection (c) Various quantum dots for heavy metal detection
(d) ZnO nanostructures with different morphologies for antimicrobial applications (d) ZnO nanostructures with different morphologies for antimicrobial applications

The project was conducted in conjunction with E-Micromaterial Technology Pty Ltd.

Dr Haiyan Li - AFFILIATE

Abstract: Bioactive Hydrogels for Tissue Regeneration

Tissue engineering provides a promising technology to address the critical gap between the growing number of patients on waiting lists for organ transplantation due to end-stage failure and the limited number of donated organs available for such procedures. One of the important factors in this technology – the tissue engineering scaffold – provides a means for the delivery of cells and/or growth factors to the site of damage and an appropriate template for new tissue formation throughout the construct. Among the different types of scaffold, injectable hydrogels have emerged as leading candidates for engineered tissue scaffolds due to their remarkable characteristics, including flexibility and versatility in fabrication, variety in composition, high moldability in shape, excellent biocompatibility, and similarity to the extracellular matrix.

The aim of our research is to fabricate injectable hydrogels with different features to meet various clinical applications, including injectable hydrogels with multilayer structures or macroporous structures, sequential delivery ability, bifunctional function, or a combination of the above. 

Figure 1 Injectible hydrogels with sequential delivery ability Figure 1 Injectible hydrogels with sequential delivery ability
Figure 2 Injectable hydrogel with macroporous structure Figure 2 Injectable hydrogel with macroporous structure

This project is funded as part of Haiyan Li's RMIT Vice Chancellor's Senior Research Fellowship.

Dr Shadi Houshyar - AFFILIATE

Abstract: Electrically Active Scaffold

Peripheral nerve injuries are the most common types of injuries affecting the nervous system. In the US alone, 20 million people suffer from peripheral nerve injuries costing ~$150 billion annually. A potential issue with current nerve guides is that they do not transmit electrical nerve impulses between the distal and proximal ends of an injured nerve, i.e. a synapse. Conductivity is a desirable property for a nerve guide being considered for peripheral nerve regeneration. Unfortunately, most conductive polymers reported for the fabrication of tissue engineering scaffolds are non-biodegradable and possess weak mechanical properties, and thus cannot be fabricated into 3D structures. This study will design a new nanocomposite material for the fabrication of nerve conduits, facilitating the growth and migration of neurons towards the targeted end of an injured nerve. This support and navigation of the scaffold lead to better sensory and motor function, which are highly in demand.

The second phase of the project is innovatively integrating an electrically conductive scaffold with a tailored wireless power transfer (WPT) receiver. This project will realise a WPT-stimulated electroconductive permeable nerve conduit that promotes nerve growth factors and aligned nerve regeneration for the recovery of sensory functions. These outcomes are essential for improving the quality of life for numerous patients suffering from peripheral nerve injuries.

Figure 1: (a) Illustration of nerve conduit, (b) illustration of proposed electroconductive nerve conduit with WPT, and (c) resulting patterns & images of nerve cell growth. Figure 1: (a) Illustration of nerve conduit, (b) illustration of proposed electroconductive nerve conduit with WPT, and (c) resulting patterns & images of nerve cell growth.

This project is funded as part of Shadi Houshyar's RMIT Vice Chancellor's Research Fellowship.

Sabrina Beker - AFFILIATE

PhD abstract: Green Synthesis of Carbon Dots from Natural Resources as Potential Candidates for Nanobioremediation of Emerging Pollutants

A wide range of new & emerging pollutants (EPs) have been released into water bodies, mainly by human activities. Many of these EPs have been shown to be deleterious to the environment with some threatening the aquatic ecosystem.

Significant research & development is underway to develop new remediation technologies aimed at alleviating the environmental issues associated with EPs; however, the complete removal and efficient treatment of aquatic contaminants remains a huge challenge for water resource management. Advanced nanotechnology provides a promising alternative for increasing water treatment efficiency, especially carbon dots (CDs). CDs, which are fluorescent nanostructures in the size range of 2–10 nm, have attracted significant attention for their excellent physicochemical properties, low toxicity, chemical inertness, tunable fluorescence, good water solubility and potential applications in several fields of science and technology - particularly with respect to the environment. Recently, the conversion of natural resources into carbon-based dots has attracted major attention due to the environmental sustainability of the associated simple, economical and green synthesis.

Therefore, this research aims to synthesise CDs from green material and test them for their degradation of EPs in water. In particular, their ability to degrade industrial dyes and per- and poly-fluoroalkyl substances (PFAS) will be tested using the nanobioremediation technique developed in this study. In order to conduct a proper evaluation of the proposed nanobioremediation, an assessment of the impact of the CQDs on freshwater microbial community structure and the ecotoxicity of the CQDs will be conducted to minimise any adverse environmental impacts.

Figure 1. Green synthesis of fluorescent carbon dots (CDs) made of Prickly Pear extract Figure 1. Green synthesis of fluorescent carbon dots (CDs) made of Prickly Pear extract
Figure 2. Studies on dye degradation using CDs made of Prickly Pear extract Figure 2. Studies on dye degradation using CDs made of Prickly Pear extract

Sabrina Beker was supported by a Brazilian National Council for Scientific & Technological Development (CNPq) scholarship.

Jiajia Zhao

PhD abstract: Catalyst Development for CO₂ Hydrogenation & Mechanism Study

Concerns about record high (and still rising) atmospheric CO₂ concentrations is hastening the shift to the use of renewable fuels. One approach to mitigate this is CO₂ hydrogenation, i.e. the reaction of CO₂ & H₂ over a solid catalyst to produce carbon-neutral fuels including methane & methanol. Thermal- and photo-catalytic CO₂ conversion into hydrocarbons have been widely investigated as two promising CO₂ hydrogenation strategies. However, their cost-effective industrial applications will depend significantly on the design of efficient catalysts that are stable at relatively intense thermal-catalytic conditions or relatively mild photocatalytic conditions, whilst providing high conversion rate & selectivity. Supported plasmonic metals (e.g. Ru, Pt, Co, Ga, etc.) have demonstrated enhanced hydrocarbon formation by promoting H₂ dissociation and metal-support interaction. In addition, these metals can provide active sites by assisting with electron transfer during temperature- or light-driven reactions. The support material also plays an important role in stabilising metal particles and fine-tuning their electronic environment to improve reaction rate & selectivity, e.g. oxide supports such as ZrO₂ can provide adsorption sites for reactants or intermediates. The synergy amongst all the catalyst’s components is highly related to the reaction mechanism, and disclosing this mechanism via regulating the catalyst system is key to the rational design & optimisation of catalysts.

This project will design Ru/ZrO₂-based catalysts for CO₂ hydrogenation and investigate their reaction mechanism. A library of Ru/ZrO₂-based catalysts has been synthesised & characterised. Using a multi-reactor catalyst testing rig, catalysts have been screened in parallel for their performance at CO₂ hydrogenation. The results of this systematic investigation have been analysed together with insights obtained from in-operando PXRD characterisation and in-situ DRIFT. This synergistic approach is crucial to assembling credible reaction mechanisms for optimal CO₂ reduction using these catalysts, and will lead to further opportunities for carbon-neutral fuel production.

Figure 1: The carbon-neutral cycle Figure 1: The carbon-neutral cycle
Figure 2: Different approaches to synthesising useful products from gas-phase CO₂ hydrogenation Figure 2: Different approaches to synthesising useful products from gas-phase CO₂ hydrogenation
Figure 3: Graphical reaction mechanism for CO₂ methanation over Ru/ZrO₂ Figure 3: Graphical reaction mechanism for CO₂ methanation over Ru/ZrO₂
This project was conducted in conjunction with CSIRO and AINSE.

Dr Adam Truskewycz - ALUMNUS

Abstract: Nanoparticle Platforms for Environmental Remediation & Sensing

Release of heavy metals into the environment from industrial processes results in severe adverse social, environmental and human health problems. Many terrestrial and aquatic ecosystems contain persistent and undetected heavy metal concentrations which are unidentified due to the extensive cost associated with site sampling and expensive analytical measurements requiring trained scientific staff. On site detection of heavy metal contamination which is user friendly, cheap and rapid is therefore sought after to map out areas of concern and provide communities with information relating to the toxicity and suitability of their land and water resources for agricultural, potable and recreational use.

Nano-sensing of environmental pollutants is an emerging field of research possessing outstanding capacity for detecting low concentrations of pollutants (including heavy metals). This approach for pollution detection relies on a nanomaterial support which has fluorescent chemical functional groups attached to it which selectively bind the pollutant of interest. Upon binding, the fluorescence profile of the composite changes and can be measured. The concentration of heavy metal can be accurately associated with the amount of fluorescence output and heavy metal concentrations can be quantitatively determined.

Find out more about Adam:
Google Scholar
New team website

 

Figure 1: Zinc oxide hydrogel impregnated with fluorescent carbon dots as a 3D platform for heavy metal sensing Figure 1: Zinc oxide hydrogel impregnated with fluorescent carbon dots as a 3D platform for heavy metal sensing
Transmission electron microscope image of carbon dots capable of sensing hexavalent chromium. Figure 2: Transmission electron microscope image of carbon dots capable of sensing hexavalent chromium. Top inset shows their fluorescence under UV light and bottom graphical inset shows their selectivity to hexavalent chromium over other potentially interfering ionic species.

Bin Qian - ALUMNUS

Current LinkedIn profile including contact details.

Phd abstract: Development of Coumarins & Coumarin Composites as Optical Sensors for Cu2+ as Contaminants in Water & Soil

Copper contamination in soil and water is a major concern due to its direct impact on human health when present in excessive/inadequate amounts[1,2] and form complexes with ligand, such as protein, molecules, enzymes, which possess electron rich centres to donate electrons, such as N, O, P, and S. Thus, the development of rapid and reliable sensing methods that are selective and sensitive to metals ions of interest, and that can be utilized in aqueous media is essential in allowing for rapid and readily available management of both nutrient- and contaminant-levels. By inviting molecular design and materials engineering, a series of fluorescent coumarin derivatives were designed, synthesized, and evaluated for their Cu2+ sensing performance in aqueous media to gain fundamental understanding of the structural requirements towards such molecular probes (Figure 1) using NMR, IR and MS, single crystal X-ray study of the probes and their Cu2+ complexes resulted in the insight understanding of the essential heteroatom ratio and configuration, and the optimum relative distances among the molecular moieties, rigidity of the structure and electron density with selective sensing[1].

 

Figure 1: Single-crystal structure of one of the coumarin-Cu²⁺ complexes tested here Figure 1: Single-crystal structure of one of the coumarin-Cu²⁺ complexes tested here
Figure 2. Schematic illustration of design of fluorescent coumarin derivatives for Cu²⁺ sensing Figure 2. Schematic illustration of design of fluorescent coumarin derivatives for Cu²⁺ sensing

Meanwhile, aimed at the improvement of sensitivity and water solubility of previously developed Cu²⁺ - selective coumarin probes, SiO2-coumarin nanohybrid was formulated via electrostatic attraction with negatively charged SiO2 nanoparticles (SiO2 NPs) and the selected coumarin in aqueous media at certain pH value. This material possessed the identical Cu2+ selectivity of the coumarin with lowered limit of detection and an extended linear detection range. The coumarin nanohybrids were also applied to determine Cu2+ concentration in aqueous soil extracts with >94% recovery rates when compared to standard soil analysis method - inductively coupled plasma-mass spectrometry (ICP-MS).

Figure 3. Illustration of the formation of SiO₂-3 nanohybrid and its extended sensing range Figure 3. Illustration of the formation of SiO₂-3 nanohybrid and its extended sensing range

This project was conducted in conjunction with CSIRO.

References:

[1] Clemens, S.; Ma, J. F., Annual review of plant biology 2016, 67, 489-512.

[2] Giripunje, M. D.;  Fulke, A. B.; Meshram, P. U. Clean-Soil, Air, Water 2015, 43 (9), 1350-1354.

[3] Qian, B.; Váradi, L.; Trinchi, A.; Reichman, S.; Bao, L.; Lan, M.; Wei, G.; Cole, I. S.. Molecules 2019, 24 (19), 3569.

aboriginal flag
torres strait flag

Acknowledgement of country

RMIT University acknowledges the people of the Woi wurrung and Boon wurrung language groups of the eastern Kulin Nation on whose unceded lands we conduct the business of the University. RMIT University respectfully acknowledges their Ancestors and Elders, past and present. RMIT also acknowledges the Traditional Custodians and their Ancestors of the lands and waters across Australia where we conduct our business - Artwork 'Luwaytini' by Mark Cleaver, Palawa.

aboriginal flag
torres strait flag

Acknowledgement of country

RMIT University acknowledges the people of the Woi wurrung and Boon wurrung language groups of the eastern Kulin Nation on whose unceded lands we conduct the business of the University. RMIT University respectfully acknowledges their Ancestors and Elders, past and present. RMIT also acknowledges the Traditional Custodians and their Ancestors of the lands and waters across Australia where we conduct our business.