Microstructural Development and Creep Deformation in an Alumina-5% Yttrium Aluminum Garnet Composite

An alumina-5 vol% yttrium aluminum garnet (YAG) composite was obtained through in situ reaction of alumina and yttria during sintering.Analysis of creep experiments together with microstructural data indicated that both pure alumina and alumina-5 vol% YAG composite deform by a Coble grain boundary diffusion creep process. Comparison with other data suggests that at temperatures greater than similar to1650 K, an isolated or interconnected fine-grained YAG phase does not significantly affect creep in alumina. However, an isolated YAG phase retards both static and dynamic grain growth in the composite

Role of small amount of MgO and ZrO2ZrO_{2} on creep behaviour of high purity Al2O3Al_{2}O_{3}

Small levels of various dopants have a significant effect on creep in polycrystalline alumina. While most previous studies have examined the effect of ionic size, the influence of valency of dopants on creep hasnot yet been completely characterized. The present detailed experimental study, utilizing magnesia and zirconia with a similar ionic size, demonstrates that the ionic valency of dopants also plays a crucial role in creep since magnesia does not significantly alter creep whereas zirconia retards creep substantially. Magnesia doped aluminade forms by Coble diffusion creep where as zirconia doped alumina deforms by an interface controlled diffusion creep process

Effect of spinel second phase on high temperature deformation in alumina

Constant stress compression creep experiments were carried out on high purity alumina composites with spinel contents of 8 and 30%, corresponding to a situation with isolated and interconnected second phases. The creep experiments were conducted over a stress and temperature range of 10 to 150 MPa and 1623 to 1723 K, respectively. Analysis of the experimental data indicated that the variation in spinel content did not have any influence on high temperature deformation in the composite. The spinel phase retards grain growth, and this may enhance superplasticity in alumina-spinel composites

Tuning the fluorescence behavior of liquid crystal molecules containing Schiff-base: Effect of solvent polarity

We report the influence of intermolecular and intramolecular hydrogen bonding on the excited state proton transfer (ESPT) emission behavior of two bent core liquid crystal (BLC) molecules, C 54 H 63 NO 9 (BLC3) and C 60 H 75 NO 9 (BLC4), having a Schiff-base and two long alkyl chains at its two ends. Fluorescence spectra of these BLC molecules dispersed in different solvents show dual emission (at � 365 nm and �425 nm) from the keto and enol tautomers. We observed that the population of these keto and enol tautomers and the corresponding intensities of fluorescence emission are strongly influenced by the solvent polarity. In protic solvents, formation of intermolecular hydrogen bond with the Schiff-base of the BLC molecules is highly favoured than the intramolecular hydrogen bonding. This intermolecular hydrogen bonding drastically reduces the population of the keto tautomers in the excited state, resulting in enhanced enol fluoroscence band along with a weak keto emission band. The observed intensity of the enol fluorescence band is the highest for the most studied polar solvent (methanol). On the other hand, in aprotic solvents, the intramolecular hydrogen bonding is highly favoured, which leads to the formation of keto tautomers in the excited state. Hence, an intense keto emission band is observed for the aprotic solvents along with a weak enol emission band. From the time resolved fluorescence studies we observed a longer life time for the keto band than that for the enol band. This is also related to the delayed emission associated with the vibrational bands resulting from the bulky alkyl chains attached to the ends of the BLC molecules. © 2019 Elsevier B.V

Effect of substrate roughness on growth of diamond by hot filament CVD

Polycrystalline diamond coatings are grown on Si (100) substrate by hot filament CVD technique. We investigate here the effect of substrate roughening on the substrate temperature and methane concentration required to maintain high quality, high growth rate and faceted morphology of the diamond coatings. It has been shown that as we increase the substrate roughness from 0.05 mu m to 0.91 mu m (centre line average or CLA) there is enhancement in deposited film quality (Raman peak intensity ratio of sp (3) to non-sp (3) content increases from 1.65 to 7.13) and the substrate temperature can be brought down to 640A degrees C without any additional substrate heating. The coatings grown at adverse conditions for sp (3) deposition has cauliflower morphology with nanocrystalline grains and coatings grown under favourable sp (3) condition gives clear faceted grains