jcst
Abstract : Investigation of the Integrity of aC:H Coatings on Stainless Steel Micro-Moulds during Thermal Cycling
|
|
|
Abstract: Micro-injection moulding (µIM) is a key technology for scaling down larger geometry components and can include functional features at the micrometre scale and as far as the sub-micrometre length scale. Thermal cycling of amorphous hydrogenated carbon (aC:H) coated Stainless Steel (SS) has been investigated to simulate long-term micro-injection moulding (µIM) wearing and damage. Micro indentations and cracks were made into the mould and predictions of the crack behaviour were made using thermal expansion models. Validation of the results was performed with multiple heating and cooling cycles along with hardness measurements of the damage to the coating. The undamaged surfaces showed no major deformation but the cracks were shown to propagate and change in behaviour. The first two heat cycles of the testing had the most significant effect on the substrate with varying thermal expansions of materials being the main cause. The aC:H is shown to have excellent properties for mould tool applications but delamination could occur in areas susceptible to damaged and periodic surface inspection will be required preserve tool life. Keywords: Micro-injection moulding, aC:H, Microfabrication, Micro-indentation. |
Abstract : Diamond Deposition on Graphite in Hydrogen Microwave Plasma
|
|
|
Abstract: Hydrogen plasma etching of graphite generates radicals that can be used for diamond synthesis by chemical vapor deposition (CVD). We studied the etching of polycrystalline graphite by a hydrogen microwave plasma, growth of diamond particles of the non-seeded graphite substrates, and characterized the diamond morphology, grain size distribution, growth rate, and phase purity. The graphite substrates served simultaneously as a carbon source, this being the specific feature of the process. A disorder of the graphite surface structure reduces as the result of the etching as revealed with Raman spectroscopy. The diamond growth rate of 3 – 5 µm/h was achieved, the quality of the produced diamond grains improving with growth time due to inherently nonstationary graphite etching process. Keywords: Microwave plasma, diamond deposition, hydrogen plasma, graphite, etching. |
Abstract : The Adhesive Strength of Epoxy/Sol-Gel Materials Modified by Various Ratio ofγ-Al2O3 Nanoparticles
|
|
|
Abstract: In this study, the use of sol-gel/epoxy adhesive based on the combination of organic and inorganic components within the adhesive matrix have been studied. The combination of different amounts of ᵞ-Al2O3 nano-particles to the adhesive matrix was evaluated. Mild steel specimens were prepared for lap joints, which were cured in an oven at 200°C for 16 hours. The bond strength of the sol-gel/epoxy matrix was investigated using a universal tensile test machine. The presence of Al-OH and/or Si-OH bonds increases causing an increase in the strength of the bulk material. This process is seen through the appearance of an absorption peak shoulder which appears in the range of ~ 1088 to1100cm-1 which corresponds to Al-O-Si or Si-O-Si. The maximum adhesive strength of composite sol-gel/epoxy adhesive recorded was 23±0.4MPa. This was obtained when small amounts of γ-Al2O3 nano-particles (4.0 wt%), were incorporated within the matrix. However, as the level of these inorganic materials in the adhesive matrix increased further, the adhesive shear strength gradually decreased. At a high ratio of γ-Al2O3 particles, poor interfacial bonding or adhesion between the filler and the adhesive matrix is recorded. Scanning Electron Microscopy (SEM) is used to investigate the fracture surface with 4.0 wt% γ-Al2O3, the scanning shows a very small distance of cracks, suggesting the material may act as a barrier to crack propagation and thus increases the energy required for fracture. Keywords: γ-Al2O3 Nano-Particles, Sol-Gel/Epoxy, Adhesive Strength. |
Abstract : Solvent Vapor Induced Film Formation of PS/AgNPs Composites Using Spectroscopic Techniques
|
|
|
Abstract: In this work, pyrene labeled polystyrene (PS) latex dispersions and silver nanoparticles (AgNPs) were mixed at different weight ratios of AgNPS in the range of 0-50 wt%. Powder (PS/AgNPs) films were prepared on glass substrates from these mixtures by the drop-casting method at room temperature. The fast transient fluorescence (FTRF) technique was used to monitor the film formation process of PS/AgNPs composites by measuring the fluorescence lifetimes of pyrene during vapor exposure. It was observed that pyrene lifetimes decreased as vapor exposure time, t increased obeying Stern–Volmer kinetic. The optical transmission (UVV) experiments showed that the transparency of the films decreased with increasing AgNPs content. Transparent films were produced for the composites with 0 to 20 wt % of AgNPs content. The Prager–Tirrel model was employed to FTRF and UVV data to obtain back-and-forth frequencies, ν, of the reptating PS chains during vapor induced film formation process and polymer interdiffusion was found to obey a t1/2 law. Despite the conductivity increased by 3 orders of magnitude with increasing AgNPs content, the composites behaved like an insulator. The morphology of composite films also progressively changed during vapor exposure and affected by AgNPs content. Keywords: Polystyrene, Silver Nanoparticles, Films, Coatings, Solvent Vapor, Latex. |
