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Abstract: Growth aspects of pure and Calcium doped Zinc hydrogen phosphate single crystals from silica gel by the process of single diffusion technique are discussed. Crystals with different morphologies and effect on various parameters like gel pH, and gel ageing, gel density and concentration of reactants on the growth of pure and Calcium doped ZnHPO4 crystals were studied. Laser Raman spectra of the pure and Calcium doped ZnHPO4 crystals are recorded and the vibrational assignments have been made with possible explanations. Thermo gravimetrical analysis is undertaken to study the thermal stability of the grown crystals.The photoluminescence measurement shows that the material is suitable for photonic devices. The crystals grown were characterized by Laser Raman spectrum, TG/DTA, EDAX and Photoluminescence. Keywords: Gel technique, TG/DTA, EDAX, Laser Raman, and Photoluminescence. |
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Abstract: The paper presents some new technological sequences of electron beam evaporation and deposition of high-temperature metal-ceramic coatings. The main attention is given to two-layer Me-Cr-Al-Y/ZrO2-Y2O3 coatings with transition layers of the total thickness of up to 0.2 mm. Chemical composition and structures of the main layers (metal, ceramics) and substrate/metal and metal/ceramics transition layers, as well as the respective physico-mechanical properties are considered. A method of deposition of these coatings in one technological cycle of evaporation and condensation with application of evaporation composite ingot is proposed. Examples of coating “design” and respective equipment for practical application in gas turbine construction are given. Keywords: Electron-beam evaporation and deposition (EB-PVD), high-temperature coating, multilayered thermal-barrier coating, crucible-evaporator, gas turbine blades. |
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Abstract: Nanocrystalline silicon (nc-Si:H) thin films were deposited by capacitive coupled radio-frequency plasmaenhanced chemical vapor deposition (RF-PECVD) system with direct current (DC) bias applied. Raman, XRD and ultraviolet-visible transmission spectra were employed to investigate their microstructure and optical properties, respectively. Both the crystalline volume fraction and the average crystalline size increase with the substrate temperature. With the increase of silane concentration, the crystalline volume fraction increases, while the average crystalline size decreases. With the increase of the radio frequency (RF) power or the DC negative bias voltage, the crystalline volume fraction and the average crystalline size increase firstly, then decreases. Finally, the optical band gaps were discussed in detail. Keywords: PECVD,process conditions, optical property, microstructure. |
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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. |
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Abstract: The paper presents the results of survey, dedicated to synthesis of metal oxide coatings on porous materials applied for implant surgery (stainless steel 12X18H9T, titanium alloy and high-purity niobium VT5). This article examines kinetic features of electrochemical formation of anodic oxide coatings on steel, niobium and titanium. It is shown that for steel anodic treatment method does not provide a reliable surface passivation (no current decay, the surface indicates the transition to the passive state). Analysis of polarization dependences obtained on niobium and titanium in electrolytes with an activator (F-), indicates surface passivation (current slump), and at potentials above 2 on the surface of a transition curves in transpassive state (as evidenced by the current increase). Consequently, it can be concluded that presence of F- results surface activation of titanium and niobium electrode (F- oxide reacts to form water-soluble complexes) that promotes nucleation and formation of pores of the porous structure of the oxide coating. SEM results verify the presence of self-organized porous oxide film synthesized on titanium and niobium in solutions containing F-. Keywords: Oxidation, anodic film, coating, implantant. |