Growth of Carbon Nanofibers and Carbon Nanotubes by Chemical Vapour Deposition on Half-Heusler Alloys: A Computationally Driven Experimental Investigation.

The possibility of directly growing carbon nanofibers (CNFs) and carbon nanotubes (CNTs) on half-Heusler alloys by Chemical Vapour Deposition (CVD) is investigated for the first time, without using additional catalysts, since the half-Heusler alloys per se may function as catalytic substrates, according to the findings of the current study. As a carbon source, acetylene is used in the temperature range of 700-750 °C. The n-type half-Heusler compound Zr0.4Ti0.60.33Ni0.33Sn0.98Sb0.020.33 is utilized as the catalytic substrate. At first, a computational model is developed for the CVD reactor, aiming to optimize the experimental process design and setup. The experimental process conditions are simulated to investigate the reactive species concentrations within the reactor chamber and the activation of certain reactions. SEM analysis confirms the growth of CNFs with diameters ranging from 450 nm to 1 µm. Raman spectroscopy implies that the formed carbon structures resemble CNFs rather than CNTs, and that amorphous carbon also co-exists in the deposited samples. From the characterization results, it may be concluded that a short reaction time and a low acetylene flow rate lead to the formation of a uniform CNF coating on the surface of half-Heusler alloys. The purpose of depositing carbon nanostructures onto half-Heusler alloys is to improve the current transfer, generated from these thermoelectric compounds, by forming a conductive coating on their surface.

Low-Cost Magnesium-Based Thermoelectric Materials: Progress, Challenges, and Enhancements.

Magnesium-based thermoelectric (TE) materials have attracted considerable interest due to their high ZT values, coupled with their low cost, widespread availability, nontoxicity, and low density. In this review, we provide a succinct overview of the advances and strategies pertaining to the development of Mg-based materials aimed at enhancing their performance. Following this, we delve into the major challenges posed by the severe working conditions, such as high temperature and thermal cycling, which adversely impact the behavior and long-term stability of the TE modules. Challenges include issues like the lack of mechanical strength, chemical instability, and unreliable contact. Subsequently, we focus on the key methodologies aimed at addressing these challenges to facilitate the broader application of the TE modules. These include boosting the mechanical strength, especially the toughness, through grain refining and additions of second phases. Furthermore, strategies targeted at enhancing the chemical stability through coatings and modifying the microstructure, as well as improving the contact design and materials, are discussed. In the end, we highlight the perspectives for boosting the practical applications of Mg-based TE materials in the future.

Ceramic conversion treated titanium implant abutments with gold for enhanced antimicrobial activity.

INTRODUCTION: Peri-implantitis is an inflammatory process around dental implants that is characterised by bone loss that may jeopardize the long-term survival of osseo integrated dental implants. The aim of this study was to create a surface coating on titanium abutments that possesses cellular adhesion and anti-microbial properties as a post-implant placement strategy for patients at risk of peri-implantitis. MATERIALS AND METHODSMETHODS: Titanium alloy Grade V stubs were coated with gold particles and then subjected to ceramic conversion treatment (CCT) at 620 °C for 3, 8 and 80 h. The surface characteristics and chemistry were assessed using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD) analysis. The leaching profile was investigated by inductively coupled plasma mass spectroscopy (ICP-MS) for all groups after 7, 14 and 28 days in contact with distilled water. A scratch test was conducted to assess the adhesion of the gold coating to the underlying titanium discs. Two bacterial species (Staphylococcus aureus (SA) & Fusobacterium nucleatum (FN)) were used to assess the antibacterial behaviour of the coated discs using a direct attachment assay test. The potential changes in surface chemistry by the bacterial species were investigated by grazing angle XRD. RESULTS: The gold pre-coated titanium discs exhibited good stability of the coating especially after immersion in distilled water and after bacterial colonisation as evident by XRD analysis. Good surface adhesion of the coating was demonstrated for gold treated discs after scratch test analysis, especially titanium, following a 3-hour (3 H) ceramic conversion treatment. All coated discs exhibited significantly improved antimicrobial properties against both tested bacterial species compared to untreated titanium discs. CONCLUSIONS: Ceramic conversion treated titanium with a pre-deposited gold layer showed improved antimicrobial properties against both SA and FN species than untreated Ti-C discs. Scratch test analysis showed good adherence properties of the coated discs the oxide layer formed is firmly adherent to the underlying titanium substrate, suggesting that this approach may have clinical efficacy for coating implant abutments.

Silver-promoted ceramic conversion treatment of Ti6Al4V alloy and its mechanical performance.

In this paper, the Ti6Al4V alloy surface was modified via ceramic conversion treatment (CCT) with or without a pre-deposited silver layer. After characterizing the surface morphologies, microstructure and phase constituents of the ceramic oxide layer formed at 620 °C, we investigated the surface hardness and the cross-sectional nano-hardness profile under the oxide layer. The static load-bearing capacity of the oxide layers was examined by applying discrete loads via a Vickers indenter and observing the indentations. A scratch test was used to evaluate the load-bearing capacity and the adhesion/cohesion of the oxide layers. The wettability of the surface changed due to the incorporation of silver and the change of surface morphology. Reciprocating friction and wear test was used to assess the tribological properties. Small and dispersed silver nanoparticles and clusters were found in the oxide layer of the Ag pre-deposited Ti6Al4V samples, and they had much better tribological properties in terms of reduced coefficient of friction and wear volume. With the assistance of silver, the efficiency of the CCT was significantly improved.

The Development of Novel Cu/GO Nano-Composite Coatings by Brush Plating with High Wear Resistance for Potential Brass Sliding Bearing Application.

Low friction and high wear resistance are critical properties for sliding bearings. In this research, advanced Cu/GO nanocomposite coatings have been developed by a brush plating method to improve the tribological performance of brass-based sliding bearings. A series of brush plating studies under voltages from 2 to 6 V with different GO concentrations (0.2-0.8 g/L) was conducted, and the coating microstructures were characterised by SEM, EDX, GDOES and XRD and the tribological behaviour of the Cu/GO composite coatings were evaluated using dry ball-on-plane tribological tests The experimental results have demonstrated that GO can be successfully introduced into the whole composite coating layer; the Cu/GO composite coatings can reduce the friction of brass and increase its wear resistance by two orders of magnitude, mainly due to the self-lubricating GO added into the coatings.

The Ageing of µPlasma-Modified Polymers: The Role of Hydrophilicity.

Thermoplastic polymers exhibit relatively limited surface energies and this results in poor adhesion when bonded to other materials. Plasma surface modification offers the potential to overcome this challenge through the functionalisation of the polymer surfaces. In this study, three polymers of differing hydrophobicity (HDPE, PA12, and PA6) were subjected to a novel, atmospheric, µPlasma surface treatment technique, and its effectiveness at increasing the surface energies was evaluated via measurement of the contact angle. To characterise the physical and chemical changes following µPlasma surface modification, the surface morphology was observed using atomic force microscopy (AFM), and the functionalisation of the surface was evaluated using infrared spectroscopy. Immediately after treatment, the contact angle decreased by 47.3° (HDPE), 42.6° (PA12), and 50.1° (PA6), but the effect was not permanent in that there was a pronounced relaxation or ageing phenomenon in operation. The ageing process over five hours was modelled using a modified stretched exponential function Kohlrausch-Williams-Watts (KWW) model, and it was found that the ageing rate was dependent on the hydrophilicity of polymers, with polyamides ageing more rapidly than polyethylene.

High-Temperature Oxidation Behaviour of CrSi Coatings on 316 Austenitic Stainless Steel.

In this study, a closed-field unbalanced magnetron sputtering system, which is environmentally friendly and has high deposition efficiency, was used to deposit CrSi coatings on 316 austenitic stainless steel. This system utilised separate Cr and Si targets, and the appropriate content of Cr and Si of the coatings was adjusted by changing the currents applied to the targets. A series of CrSi coatings with different Si/Cr ratios were produced, and their oxidation behaviour at elevated temperatures was investigated. By analysing the weight gain, surface morphology and microstructure, composition and phase constituents, the oxidation behaviour at 600 °C, 700 °C and 800 °C was investigated and the optimized coating to protect the stainless steel has been identified. The outcome of the research indicated that a small amount of Si (between 4-7 at.%) in Cr coatings is effective in protecting the austenitic stainless steel against oxidation at high temperatures, while a high Si content (around 10 at.% or more) makes the coating more brittle and prone to cracking or delamination during oxidation at 800 °C.

A Novel Catalytic Ceramic Conversion Treatment of Zr702 to Combat Wear.

Zr and its alloys are widely used in multiple areas, including the nuclear and medical fields. Previous studies indicate that a ceramic conversion treatment (C2T) of Zr-based alloys can address the issues of low hardness, high friction, and poor wear resistance of Zr based alloys. This paper introduced a novel catalytic ceramic conversion treatment (C3T) to Zr702 by pre-depositing a catalytic film (such as silver, gold, platinum, etc.) before the ceramic conversion treatment, which efficiently promoted the C2T process, in terms of reduced treatment times, with a thick, good quality, surface ceramic layer. The formed ceramic layer significantly improved the surface hardness and tribological properties of Zr702 alloy. Compared with conventional C2T, the C3T technique provided two orders of magnitude reduction of wear factor and reduced the coefficient of friction from 0.65 to <0.25. Among the C3T samples, the C3TAg and the C3TAu samples have the highest wear resistance and lowest CoF, mainly due to the self-lubricant formation during the wear processes.

Characterization of Magnetron Sputtered BiTe-Based Thermoelectric Thin Films.

Thermoelectric (TE) technology attracts much attention due to the fact it can convert thermal energy into electricity and vice versa. Thin-film TE materials can be synthesized on different kinds of substrates, which offer the possibility of the control of microstructure and composition to higher TE power, as well as the development of novel TE devices meeting flexible and miniature requirements. In this work, we use magnetron sputtering to deposit N-type and P-type BiTe-based thin films on silicon, glass, and Kapton HN polyimide foil. Their morphology, microstructure, and phase constituents are studied by SEM/EDX, XRD, and TEM. The electrical conductivity, thermal conductivity, and Seebeck coefficient of the thin film are measured by a special in-plane advanced test system. The output of electrical power (open-circuit voltage and electric current) of the thin film is measured by an in-house apparatus at different temperature gradient. The impact of deposition parameters and the thickness, width, and length of the thin film on the power output are also investigated for optimizing the thin-film flexible TE device to harvest thermal energy.

A new approach to simultaneously reducing, nitrogen doping and noble metal coating of graphene oxide via active-screen plasma.

Graphene is widely used for various applications, especially after nitrogen doping and incorporation with metal nanoparticles. Herein, a simultaneous approach to reducing, nitrogen doping and noble metals coating of graphene oxide (GO) is reported using an advanced active-screen plasma (ASP) technique. With a noble metal plate added as an extra lid of active screen cage, the corresponding noble metal, mainly or fully in pure metal state, depending on the noble metal type, as well as a minority of Fe and Cr, is deposited on GO with simultaneous reduction and nitrogen doping. The ASP treated GO exhibits varying levels of improvement in electrical property depending on the type of noble metal nanoparticles hybridized with. Specifically, ASP treated GO incorporated with Pt or Au revealed 2-4 orders of magnitude of improvement in electrical property.

Nanoindentation of Multifunctional Smart Composites.

Three multifunctional smart composites for next-generation applications have been studied differently through versatile nanoindentation investigation techniques. They are used in order to determine peculiarities and specific properties for the different composites and to study the charge/matrix, charge/surface, or smart functions interactions. At first, a mapping indentation test was used to check the distribution of hardness and modulus across a large region to examine any non-uniformity due to structural anomalies or changes in properties for a carbon nanotubes (CNTs)-reinforced polypropylene (PP V-2) nanocomposite. This smart composite is suitable to be used in axial impeller fans and the results can be used to improve the process of the composite produced by injection moulding. Secondly, the interfacial properties of the carbon fibre (CF) and the resin were evaluated by a push-out method utilizing the smaller indentation tip to target the individual CF and apply load to measure its displacement under loads. This is useful to evaluate the effectiveness of the surface modification on the CFs, such as sizing. Finally, nanoindentation at different temperatures was used for the probing of the in situ response of smart shape memory polymer composite (SMPC) usable in grabbing devices for aerospace applications. Furthermore, the triggering temperature of the shape memory polymer response can be determined by observing the change of indentations after the heating and cooling cycles.

Enhancement and Evaluation of Interfacial Adhesion between Active Screen Plasma Surface-Functionalised Carbon Fibres and the Epoxy Substrate.

This paper investigated the modification of the advanced active screen plasma (ASP) technology on PAN-derived carbon fibres (CFs) with gas mixtures of N2-H2 and N2-H2-Ar, separately. A more-than-30% improvement was found in the interfacial shear strength (IFSS) between the modified CFs and the epoxy substrate in the resulting composites, as disclosed by single fibre push-out tests. Based on the study of surface morphology, surface chemistry and water-sorption behaviour, the interfacial adhesion enhancement mechanisms were attributed to (1) the increased chemical bonding between the introduced functional groups on the fibre surface and the matrix; (2) the improved surface hydrophilicity of CFs; and (3) the enhanced van der Waals bonding due to the removal of surface contaminations.

3D Printing Processability of a Thermally Conductive Compound Based on Carbon Nanofiller-Modified Thermoplastic Polyamide 12.

A polyamide (PA) 12-based thermoplastic composite was modified with carbon nanotubes (CNTs), CNTs grafted onto chopped carbon fibers (CFs), and graphene nanoplatelets (GNPs) with CNTs to improve its thermal conductivity for application as a heat sink in electronic components. The carbon-based nanofillers were examined by SEM and Raman. The laser flash method was used to measure the thermal diffusivity in order to calculate the thermal conductivity. Electrical conductivity measurements were made using a Keithley 6517B electrometer in the 2-point mode. The composite structure was examined by SEM and micro-CT. PA12 with 15 wt% of GNPs and 1 wt% CNTs demonstrated the highest thermal conductivity, and its processability was investigated, utilizing sequential interdependence tests to evaluate the composite material behavior during fused filament fabrication (FFF) 3D printing processing. Through this assessment, selected printing parameters were investigated to determine the optimum parametric combination and processability window for the composite material, revealing that the selected composition meets the necessary criteria to be processable with FFF.

Processing and interpretation of core-electron XPS spectra of complex plasma-treated polyethylene-based surfaces using a theoretical peak model.

Interpretation of X-ray photoelectron spectroscopy (XPS) spectra of complex material surfaces, such as those obtained after surface plasma treatment of polymers, is confined by the available references. The limited understanding of the chemical surface composition may impact the ability to determine suitable coupling chemistries used for surface decoration or assess surface-related properties like biocompatibility. In this work, XPS is used to investigate the chemical composition of various ultra-high-molecular-weight polyethylene (UHMWPE) surfaces. UHMWPE doped with α-tocopherol or functionalised by active screen plasma nitriding (ASPN) was investigated as a model system. Subsequently, a more complex combined system obtained by ASPN treatment of α-tocopherol doped UHMWPE was investigated. Through ab initio orbital calculations and by employing Koopmans' theorem, the core-electron binding energies (CEBEs) were evaluated for a substantial number of possible chemical functionalities positioned on PE-based model structures. The calculated ΔCEBEs showed to be in reasonable agreement with experimental reference data. The calculated ΔCEBEs were used to develop a material-specific peak model suitable for the interpretation of merged high-resolution C 1 s, N 1 s and O 1 s XPS spectra of PE-based materials. In contrast to conventional peak fitting, the presented approach allowed the distinction of functionality positioning (i.e. centred or end-chain) and evaluation of the long-range effects of the chemical functionalities on the PE carbon backbone. Altogether, a more detailed interpretation of the modified UHMWPE surfaces was achieved whilst reducing the need for manual input and personal bias introduced by the spectral analyst.

Effect of µPlasma Modification on the Wettability and the Ageing Behaviour of Glass Fibre Reinforced Polyamide 6 (GFPA6).

Glass fibre reinforced polyamide 6 (GFPA6) thermoplastic composites (TPCs) are promising materials with excellent properties, but due to their low surface free energy they are usually difficult to wet, and therefore, possesses poor adhesion properties. µPlasma modification offers potential solutions to this problem through functionalisation of the GFPA6 surface. In this study, the effect of µPlasma on the wetting behaviour of GFPA6 surfaces was investigated. Following single µPlasma treatment scans of GFPA6 samples, a substantial enhancement in wettability was observed. However, the effect of the µPlasma modification was subject to an ageing (hydrophobic recovery) phenomenon, although the enhancement was still partially maintained after 4 weeks. The ageing process was slower when the GFPA6 material was pre-dried and stored in low humidity conditions, thereby demonstrating the importance of the storage environment to the rate of ageing. Orientation of the fibres to the observed contact angle was found to be crucial for obtaining reproducible measurements with lower deviation. The influence of testing liquid, droplet volume and surface texture on the repeatability of the measured contact angle were also investigated.

Novel Catalytic Ceramic Conversion Treatment of Ti6Al4V for Improved Tribological and Antibacterial Properties for Biomedical Applications.

Titanium oxide layers were produced via a novel catalytic ceramic conversion treatment (CCCT, C3T) on Ti-6Al-4V. This CCCT process is carried out by applying thin catalytic films of silver and palladium onto the substrate before an already established traditional ceramic conversion treatment (CCT, C2T) is carried out. The layers were characterised using scanning electron microscopy, X-ray diffraction, transmission electron microscopy; surface micro-hardness and reciprocating tribological performance was assessed; antibacterial performance was also assessed with S. aureus. This CCCT has been shown to increase the oxide thickness from ~5 to ~100 µm, with the production of an aluminium rich layer and agglomerates of silver and palladium oxide surrounded by vanadium oxide at the surface. The wear factor was significantly reduced from ~393 to ~5 m3/N·m, and a significant reduction in the number of colony-forming units per ml of Staphylococcus aureus on the CCCT surfaces was observed. The potential of the novel C3T treatment has been demonstrated by comparing the performance of C3T treated and untreated Ti6Al4V fixation pins through inserting into simulated bone materials.

The Impact of Carbon Nanofibres on the Interfacial Properties of CFRPs Produced with Sized Carbon Fibres.

In this work, different amounts of CNFs were added into a complex formulation to coat the CFs surfaces via sizing in order to enhance the bonding between the fibre and the resin in the CF-reinforced polymer composites. The sized CFs bundles were characterised by SEM and Raman. The nanomechanical properties of the composite materials produced were assessed by the nanoindentation test. The interfacial properties of the fibre and resin were evaluated by a push-out method developed on nanoindentation. The average interfacial shear strength of the fibre/matrix interface could be calculated by the critical load, sheet thickness and fibre diameter. The contact angle measurements and resin spreadability were performed prior to nanoindentation to investigate the wetting properties of the fibre. After the push-out tests, the characterisation via optical microscopy/SEM was carried out to ratify the results. It was found the CFs sizing with CNFs (1 to 10 wt%) could generally increase the interfacial shear strength but it was more cost-effective with a small amount of evenly distributed CNFs on CFs.

α-Helical peptides on plasma-treated polymers promote ciliation of airway epithelial cells.

Airway respiratory epithelium forms a physical barrier through intercellular tight junctions, which prevents debris from passing through to the internal environment while ciliated epithelial cells expel particulate-trapping mucus up the airway. Polymeric solutions to loss of airway structure and integrity have been unable to fully restore functional epithelium. We hypothesised that plasma treatment of polymers would permit adsorption of α-helical peptides and that this would promote functional differentiation of airway epithelial cells. Five candidate plasma compositions are compared; Air, N2, H2, H2:N2 and Air:N2. X-ray photoelectron spectroscopy shows changes in at% N and C 1s peaks after plasma treatment while electron microscopy indicates successful adsorption of hydrogelating self-assembling fibres (hSAF) on all samples. Subsequently, adsorbed hSAFs support human nasal epithelial cell attachment and proliferation and induce differentiation at an air-liquid interface. Transepithelial measurements show that the cells form tight junctions and produce cilia beating at the normal expected frequency of 10-11 Hz after 28 days in culture. The synthetic peptide system described in this study offers potential superiority as an epithelial regeneration substrate over present "gold-standard" materials, such as collagen, as they are controllable and can be chemically functionalised to support a variety of in vivo environments. Using the hSAF peptides described here in combination with plasma-treated polymeric surfaces could offer a way of improving the functionality and integration of implantable polymers for aerodigestive tract reconstruction and regeneration.

Comparative Physical-Mechanical Properties Assessment of Tailored Surface-Treated Carbon Fibres.

Carbon Fibres (CFs) are widely used in textile-reinforced composites for the construction of lightweight, durable structures. Since their inert surface does not allow effective bonding with the matrix material, the surface treatment of fibres is suggested to improve the adhesion between the two. In the present study, different surface modifications are compared in terms of the mechanical enhancement that they can offer to the fibres. Two main advanced technologies have been investigated; namely, plasma treatment and electrochemical treatment. Specifically, active screen plasma and low-pressure plasma were compared. Regarding the electrochemical modification, electrochemical oxidation and electropolymerisation of monomer solutions of acrylic and methacrylic acids, acrylonitrile and N-vinyl pyrrolidine were tested for HTA-40 CFs. In order to assess the effects of the surface treatments, the morphology, the physicochemical properties, as well as the mechanical integrity of the fibres were investigated. The CF surface and polymeric matrix interphase adhesion in composites were also analysed. The improvement of the carbon fibre's physical-mechanical properties was evident for the case of the active screen plasma treatment and the electrochemical oxidation.

Improving the Tribological Properties and Biocompatibility of Zr-Based Bulk Metallic Glass for Potential Biomedical Applications.

Zr-based bulk metallic glasses (Zr-BMGs) are potentially the next generation of metallic biomaterials for orthopaedic fixation devices and joint implants owing to their attractive bulk material properties. However, their poor tribological properties and long-term biocompatibility present major concerns for orthopaedic applications. To this end, a novel surface modification technology, based on ceramic conversion treatment (CCT) in an oxidising medium between the glass transition temperature and the crystallisation temperature, has been developed to convert the surface of commercially available Zr44Ti11Cu10Ni11Be25 (Vitreloy 1b) BMG into ceramic layers. The engineered surfaces were fully characterised by in-situ X-ray diffraction, glow-discharge optical emission spectroscopy, scanning electron microscopy, transmission electron microscopy, and scanning transmission electron microscopy. The mechanical, chemical, and tribological properties were evaluated respectively by nano-indentation, electrochemical corrosion testing, tribological testing and the potential biocompatibility assessed by a cell proliferation assay. The results have demonstrated that after CCT at 350 °C for 40 h and at 380 °C for 4.5 h the original surfaces were converted into to a uniform 35-55-nm-thick oxide layer (with significantly reduced Ni and Cu concentration) followed by a 200-400-nm-thick oxygen-diffusion hardened case. The surface nano hardness was increased from 7.75 ± 0.36 to 18.32 ± 0.21 GPa, the coefficient of friction reduced from 0.5-0.6 to 0.1-0.2 and the wear resistance improved by more than 60 times. After 24 h of contact, SAOS-2 human osteoblast-like cells had increased surface coverage from 18% for the untreated surface to 46% and 54% for the 350 °C/40 h and 380 °C/4.5 h treated surfaces, respectively. The significantly improved tribological properties and biocompatibility have shown the potential of the ceramic conversion treated Zr-BMG for orthopaedic applications.