Effect of Heat Treatment on Band Gap of V2O5

The most stable oxide of the vanadium oxide family is V2O5. A lot of research effort is focused on it because it has a multitude of functional applications. Here we report on how the heat treatment (600°C, 5 h, air) affects the microstructure and hence, the band gap of V2O5. The V2O5 powders, initially obtained by simple thermal dissociation (500 °C, 3 h, air) of ammonium metavanadate, followed by heat treatment of pellets; were studied. The structural and optical studies performed using X-ray diffraction (XRD), FESEM and UV-Vis techniques, provide uniquely interesting results which indicate the possibility of band gap tuning by controlling the microstructure

Influence of Impurity on the Properties of Chemically Synthesized Calcium Hydroxide

Here we report synthesis and characterization of chemically synthesized calcium hydroxide (Ca(OH)2) with and without deliberate presence of NaNO3 as an impurity. Calcium nitrate tetrahydrate (Ca(NO3)2.4H2O) is used as precursor and alkaline NaOH solution is used as precipitant to synthesize the Ca(OH)2 samples. The samples were characterized by XRD, FESEM, FTIR spectroscopy, DTA, TGA and UV-Vis spectroscopy techniques. From the UV-Vis spectroscopy results, it is found that the Ca(OH)2 with NaNO3 impurity has higher bandgap than the sample without NaNO3. The weight loss in TGA is also more for the Ca(OH)2 with impurity than the one for without impurity. The results are discussed in terms of composition formed during synthesis process

Nanocolumnar Crystalline Vanadium Oxide-Molybdenum Oxide Antireflective Smart Thin Films with Superior Nanomechanical Properties

Vanadium oxide-molybdenum oxide (VO-MO) thin (21-475 nm) films were grown on quartz and silicon substrates by pulsed RF magnetron sputtering technique by altering the RF power from 100 to 600 W. Crystalline VO-MO thin films showed the mixed phases of vanadium oxides e.g., V2O5, V2O3 and VO2 along with MoO3. Reversible or smart transition was found to occur just above the room temperature i.e., at similar to 45-50 degrees C. The VO-MO films deposited on quartz showed a gradual decrease in transmittance with increase in film thickness. But, the VO-MO films on silicon exhibited reflectance that was significantly lower than that of the substrate. Further, the effect of low temperature (i.e., 100 degrees C) vacuum (10(-5) mbar) annealing on optical properties e.g., solar absorptance, transmittance and reflectance as well as the optical constants e.g., optical band gap, refractive index and extinction coefficient were studied. Sheet resistance, oxidation state and nanomechanical properties e.g., nanohardness and elastic modulus of the VO-MO thin films were also investigated in as-deposited condition as well as after the vacuum annealing treatment. Finally, the combination of the nanoindentation technique and the finite element modeling (FEM) was employed to investigate yield stress and von Mises stress distribution of the VO-MO thin films

Microplasma sprayed hydroxyapatite coating: emerging technology for biomedical application

Highly crystalline (similar to 80%) yet porous (similar to 20%) hydroxyapatite (HAp) coating was developed on surgical grade SS316L substrate by the microplasma spraying (MIPS) technique. Phase analysis and microstructural characterisations were carried out by X-ray diffraction, scanning electron microscopy and field emission scanning electron microscopy. Nanohardness and Young's modulus were measured by the nanoindentation technique at 100 mN load. Further, the HAp coatings were immersed in simulated body fluid (SBF) environment for 1-14 days to investigate their in vitro properties. Finally, single pass microscratch test was also conducted on the MIPS-HAp coatings after immersion in SBF

On the microhardness of silicon nitride and sialon ceramics

Influences of relative density, grain size, Young's modulus, flexural strength and fracture toughness on microhardness characteristics of hot-pressed silicon nitride, sintered silicon nitride, reaction-sintered sialon and liquid-phase sintered sialon have been discussed. Three new semi-empirical equations have been proposed to correlate microhardness to relative density. Indentation size effects on microhardness measurement have also been discussed

Fracture toughness of structural ceramics

A comparative study of fracture toughness evaluation at room temperature of three different structural ceramics viz. sintered alumina, silicon carbide and silicon nitride is reported. Four methods of fracture toughness evaluation such as the single edge notched beam (SENB) technique, chevron notched beam (CNB) technique, indentation fracture (IF) technique and fractographic methods (FM) were compared. In addition, for a given method, the influence of several experimental parameters, e.g. blade width, notch tip radius, normalised notch length and the loading rate on the measured value of fracture toughness was investigated in the cases of the aforesaid materials. (C) 1999 Elsevier Science Limited and Techna S.r.l. All rights reserved

Assessment of strength by Youngs modulus and porosity - a critical-evaluation

Literature data on strength, porosity, and Young's modulus at room temperature of reaction-bonded silicon nitride, sintered silicon nitride, and hot-pressed silicon nitride have been fitted into available and proposed strength-porosity relationships. In general, the Lewis method of iterative least-squares fitting in these relationships has been found to be better than conventional linearized least-squares fitting. Further a semiempirically proposed strength–Young's modulus relationship has been found to predict strength more precisely than the conventional strength-porosity relationship

High temperature strength and fractography of sintered silicon-nitride

Influences of the sintering liquid system, temperature, microstructure and post sintering heat treatment on high temperature (30-1250-degrees-C) strength, Young's modulus and fracture toughness of sintered silicon nitride (SSN) have been studied. Based on quantitative fractography, typical fracture origin statistics has been presented for SSN. The measured strength of the SSN is in good agreement with the fractographically predicted strength

Tribological studies of microplasma sprayed hydroxyapatite coating at low load

For bioactive prosthetic implant applications, the present work reports the tribolgical behaviour of the recently developed, microplasma (e.g. plasmatron power < 1.5 kW) sprayed (MIPS) hydroxyapatite (HAp) coatings on Ti6Al4V substrates at low constant normal load, e. g. 200 mN. Conventionally, the macroplasma (e. g. plasmatron power < 25 kW) sprayed (MAPS) HAp coatings are used for such purpose. The phase analysis and microstructural studies of the HAp coatings were carried out by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. Further, the single pass scratch tests were conducted on both the bare substrates and the HAp coatings at an applied normal load of 200 mN. The average coefficient of friction (COF, mu) of the HAp coatings developed by MIPS (e.g. mu similar to 0.7) was slightly higher than that (e.g. mu similar to 0.5) of the bare Ti6Al4V substrates. The characteristic, high variability of the m data of the HAp coatings developed by MIPS; was explained in terms of the intrinsic microstructural heterogeneity and the local differences in orientations of the splats

Mechanical behaviour of glass fibre reinforced composite at varying strain rates

Here we report the results of compressive split Hopkinson pressure bar experiments (SHPB) conducted on unidirectional glass fibre reinforced polymer (GFRP) in the strain rate regime 5 x 10(2)-1.3 x 10(3) s(-1). The maximum compressive strength of GFRP was found to increase by as much as 55% with increase in strain rate. However, the corresponding relative strain to failure response was measured to increase only marginally with increase in strain rates. Based on the experimental results and photomicrographs obtained from FE-SEM based post mortem examinations, the failure phenomena are suggested to be associated with increase in absorption of energy from low to high strain rates. Attempts have been made to explain these observations in terms of changes in deformation mechanisms primarily as a function of strain rates