Johnson Matthey Technology Review - Current Issue

The pursuit of sustainable energy sources on a worldwide scale is a crucial and pressing matter, with the United Nations Sustainable Development Goals (UNSDGs) offering a comprehensive framework for properly addressing this challenge. This two-part paper provides an overview of the various technologies now available for the process of biomass gasification. Compared to other renewable energy sources, which have undergone significant technological advancements in recent years, the field of biomass conversion is still relatively new. Keeping up with the newest breakthroughs becomes increasingly crucial as new conversion techniques are rapidly being created. In the thermochemical conversion process called ‘biomass gasification’, biomass solid source materials are degraded or incompletely burned in an oxygen-free or oxygen-deficient high-temperature atmosphere, resulting in the production of biomass gas. Part I delves into different biomass gasification techniques, including upstream, gasification and downstream processes, highlighting their importance in transforming biomass into clean and combustible gases.

Part II of this review focuses on methodologies and protocols employed in biomass gasification, recognising its pivotal role in sustainable energy generation. Additionally, the article discusses the challenges associated with gasification technology, such as tar formation, biomass heterogeneity and uneven biomass supply in different seasons. It emphasises the need for further research and infrastructure development to overcome these barriers and facilitate the efficient distribution and commercialisation of biomass gasification technology. Overall, the scope of the article extends to providing insights into the status, challenges and future prospects of biomass gasification for achieving sustainable energy goals.

The paper presents a mathematical model to describe thermogravimetric curves of the growth of scale with its simultaneous sublimation during oxidation of the surface of a metal or alloy. For alloys iron-chromium and iron-chromium-aluminium, a decrease in the effective reaction area as a result of the formation of the oxide of the alloying element lanthanum or yttrium (together with the formation of the main oxide: chromia or alumina) is considered. For metals, the case of increasing this area is also considered. During the oxidation of the chromia-forming alloy, another secondary process is added: the evaporation of chromia. Therefore, the equations describing the kinetics of changes in mass of these alloys are different. Equations are also considered that make it possible to describe the kinetics of the oxidation process taking into account the initial non-isothermal heating. The formal equations of the oxidation process with an increase in the reaction surface as a result of crushing metal powder are also considered. The resulting equations are used to describe the kinetic curves of changes in the mass of the samples under study. The given equations can be considered as a more accurate approximation to describe the experimental data than the formulas known so far.

This two-part paper investigates the bioactivity and mechanical properties of coatings applied to Ti6Al4V, a common titanium alloy used in endoprosthetic implants. Coatings made from hydroxyapatite (HA) powder and commercially pure titanium (CP-Ti) wires were applied using microplasma spraying. The study focuses on the responses of rat mesenchymal stem cells (MSCs), which are essential for bone healing, to these coatings. Part I shows how adjusting the microplasma spraying process allows coatings with varying porosity and surface roughness to be achieved.

Part II presents the results which show that HA coatings significantly enhance MSC proliferation by 13% compared to the titanium alloy base, while titanium coatings also exhibit an 11% increase. Porosity inversely affects CP-Ti’s elasticity. Coatings with lower porosity demonstrate better corrosion resistance. HA coatings promote osteogenic activity and angiogenesis, which is crucial for implant integration.

This two-part study evaluates the antimicrobial efficacy of tantalum-copper and niobium-copper coatings, applied via magnetron sputtering (MS) on three dimensional (3D) printed porous Ti6Al4V (Ti-64) alloy scaffolds and gas-abrasive treated Ti-64 alloy, against Staphylococcus aureus and Candida albicans. Scanning electron microscopy (SEM) with energy-dispersive X-ray (EDX) analysis verified the application of coatings with 25 wt% copper, at thicknesses of 2 μm and 10 μm, to scaffolds (72% porosity) and roughened Ti-64 alloy (mean areal roughness of 4.6 ± 1 μm). The findings support the potential of these coatings in developing endoprosthesis implants with enhanced antimicrobial properties. Part I introduces the background research and describes the materials, methods and rationale for the present work.

This is Part II of a study on the antimicrobial efficacy of tantalum-copper and niobium-copper coatings, applied via magnetron sputtering (MS) on three dimensional (3D) printed porous Ti6Al4V alloy scaffolds and gas-abrasive treated Ti6Al4V alloy, against Staphylococcus aureus and Candida albicans. Thicker coatings were found to show superior antimicrobial activity; however, thin niobium-copper coatings and uncoated alloy did not exhibit inhibitory effects. The release dynamics of copper ions from tantalum-copper coatings into physiological solution, analysed over ten days via inductively coupled plasma mass spectrometry, matched the inhibition zone growth. These findings support the potential of these coatings in developing endoprosthesis implants with enhanced antimicrobial properties.

The present work adopts friction stir processing to process stainless steel (SS304) with cobalt-chromium-iron-copper-titanium and aluminium-silicon-beryllium-titanium-vanadium high entropy alloy and analyse its erosion performance. The processed samples with cobalt-chromium-iron-copper-titanium and aluminium-silicon-beryllium-titanium-vanadium display refined grain structure with uniform distribution of the reinforced high entropy alloys. The microhardness for the sample with cobalt-chromium-iron-copper-titanium is 22.1% better than the aluminium-silicon-beryllium-titanium-vanadium. The slurry jet erosion test conducted through different process parameters revealed 90° impingement angle and 10 m s⁻¹ impact velocity with 10 wt% slurry concentration on the processed sample with cobalt-chromium-iron-copper-titanium offered better erosion resistance. Oblique angle endured high erosion rate due to the ploughing effect of abrasive erodent than normal angle deforming the surface. Increasing velocity increased the erosion rate by increased material removal. Slurry concentration forms a cloud-like layer at higher concentrations lowering the erosion rate. The subsequent microstructural evaluation showed the failure mode through the formation of platelets, micro-cuts, ploughing and plastic deformation.

The data analysis workflow for in situ electron microscopy experiments can require a significant amount of human-intensive and repetitive effort. The generation of Python-based scripts that incorporate simple machine learning algorithms are quite well established in biological sciences but not often utilised in the study of catalytic systems. Such scripted analysis is not only more efficient, but readily reproducible and allows a wide range of quantitative results to be reported, including but not limited to average and total particle size, particle counting and particle size distributions. In this work we utilise these tools to examine the effect of cycling reducing and oxidising atmospheres on copper oxide nanoparticles.

This study aims to coat Ti6Al4V alloy with Ti-xHA (x = 2.5⁻¹0 wt%) mixture to improve its surface properties. A new approach using a powder metallurgical pressure-assisted sintering method was applied to the coating process. The in situ sintering and coating process was performed at 950°C for 45 min in a vacuum atmosphere of 10–4 mbar. A pressure of 50 MPa was applied during the sintering process. Staphylococcus aureus (ATCC^® 29213^TM) and Escherichia coli (ATCC^® 25922^TM) cultures were used to determine the antibacterial activity of the sintered and coated samples. The electrochemical properties of the samples were studied by Tafel extrapolation and potentiodynamic polarisation tests. The results showed that the coating layer containing 7.5 wt% of hydroxyapatite (HA) increased the antibacterial property against gram-positive and gram-negative bacterial cultures. Furthermore, it was determined that the icorr value of the material decreased and the corrosion resistance improved with an increasing HA ratio. In addition, no active-passive oxidation zone formation was observed up to 2000 mV in the HA-added samples.

The influence of hafnium content on the recrystallisation and aging behaviour of hot-rolled Pt-15Ir-xHf-0.5Y alloy was investigated by scanning electron microscope (SEM), electron backscatter diffraction (EBSD) and hardness tests. The results show that the alloy texture evolves from a multi-peak one biased towards rolling direction-transverse direction (RD-TD) in the hot rolling state to a multi-peak one symmetrical along the normal direction (ND) after recrystallisation annealing. The fibrous grains become equiaxial after recrystallisation annealing, increase of hafnium content refines the grains. Pt-15Ir-xHf-0.5Y alloy exhibits age-hardening behavior at the temperature range of 600~900°C, which is due to the precipitation of (Pt,Ir)5Y phase. Increasing hafnium addition effectively improves the hardness through promoting the precipitated amount of (Pt,Ir)5Y phase. However, the internal oxidation within grain boundaries is deteriorated with the high-content hafnium addition. The results of this study provide an insight into tailoring the microstructures and mechanical properties of the platinum-iridium high-temperature alloys.

Raman spectroscopy is a useful analytical tool for characterising the carbon chemistry of proton exchange membrane fuel cell (PEMFC) catalyst coated membranes (CCMs) and understanding changes in the carbon matrix due to corrosion and degradation processes. However, interpretation of the data is highly sensitive to the sampling and spectral analysis methods employed. Here we critically assess the use of Raman spectroscopy for diagnostic analysis of uncycled PEMFC CCMs and equivalent CCMs subjected to dynamic load cycling (DLC). We first consider different approaches to quantitative analysis of Raman spectra and show that a two peak spectral fitting model which only considers the characteristic D1 and G peaks in the Raman spectrum provides an inferior fit compared to a four peak fitting model that includes the minority D3 and D4 peaks associated with amorphous carbon and disordered graphitic domains. We furthermore demonstrate that in specific cases these two models can generate opposing trends. We then compare quantitative Raman metrics generated from spectral maps at different locations of CCMs subjected to different durations of cycling. A large degree of scatter in the data precluded conclusive correlation between Raman data and duration of cycling, highlighting the importance of sufficiently large sample sizes when performing quantitative analysis. However, a difference in behaviour between cathode and anode was observed, characterised most prominently by a higher degree of scatter in the Raman metrics associated with disordered and amorphous carbon, potentially pointing to contrasting ageing phenomena resulting from the different conditions at the cathode and anode. We also demonstrate that spectral differences across the cycled anode appear to be highly spatially heterogeneous, indicating that the associated chemical changes are localised on the <100 μm scale.