Volume 9, Issue 4
November 1987, pages 249-308
pp 249-253 November 1987
Pyroelectric properties of poled solid solutions of lead-barium titanate and leadstrontium titanate have been investigated in the temperature range covering their transition points. The values of pyroelectric current and coefficients of (Pbx − Ba1 −x)TiO3 and (Pbx − Sr1 −x)TiO3(x = 0·8 − 0·5) show a sharp peak at the Curie temperature. It is observed that these values change with Ba or Sr concentration in the respective solid solutions.
pp 255-262 November 1987
Glasses with varying molar ratios of PbO/BaO in the system BaO-PbO-TiO2-B2O3-SiO2 were prepared keeping (BaO + PbO)/TiO2 ratio equal to one. The glasses were ceramized by two-stage heat treatment. X-ray diffraction indicates that PbTiO3 crystallizes in lead-rich glasses while BaTiO3 precipitates in barium-rich compositions. Solid solution (Ba, Pb)TiO3 does not seem to crystallize over the entire range of compositions. Simultaneous presence of PbO and BaO in the initial glass composition reduces the yield of ferroelectric phase. Dielectric properties have been interpreted in terms of microstructural features.
pp 263-267 November 1987
Aliovalent sulphates were selected for substitution in β-Li2SO4 at 6% vacancy concentration. The results show that if the guest ions are substituted on the basis of the criteria given for the formation of a solid solution, then it is possible to achieve a considerable enhancement in conductivity especially in the case of isostructural materials.
pp 269-275 November 1987
Differential scanning calorimetry (DSC) technique has been employed to study the crystallization kinetics of a Fe74Co10B16 glass. Crystallization of Fe74Co10B16 glass is known to occur in two distinct stages. It was possible to separate out the isothermal kinetics of both the crystallization stages through a thermal treatment scheme in the DSC. The crystallization processes are interpreted in the light of the kinetic data obtained.
pp 277-285 November 1987
In the zinc-bismuth system, a monotectic reaction occurs at 689 K and 0·6 at.% Bi composition. Rapid solidification of the as-cast monotectic alloy led to a micromorphology in which bismuth was uniformly and bimodally distributed as small droplets in the zinc matrix. Statistical analysis of the electron micrographs obtained from different transparent regions of the foils revealed that the size of most of the droplets was about 6 nm. These droplets undercooled by 132 K. An analysis of the nucleation rate measurements shows that the activation energy barrier to nucleation is of the order of 39·8 kcal/mol at the maximum undercooling.
pp 287-294 November 1987
The load dependence of Vicker’s indentation hardness has been measured in some non-metallic materials and thin foils. A load of 100 g appears to be appropriate for comparing materials. Foil thickness, especially for soft metals like copper, must be at least twenty times the impression diagonal to get a correct value of hardness. The Meyer index varies for materials and can be used for comparison because it seems to pertain to the nature of chemical bonds. The index for boron carbide is similar to glass as was expected by Rice.
pp 295-303 November 1987
Favourable conditions for the growth of good quality silicon carbide (SiC) whiskers from rice husk have been discussed in the light of available evidence on the probable growth mechanism and the theoretical understanding of the same. Preliminary results indicate an increase in whisker yield at lower temperatures and coarsening of whiskers with longer duration of conversion.
pp 305-308 November 1987
A high pressure and high temperature Sievert’s type gas doping apparatus using indigenous components has been designed and fabricated for preparing metal hydrides. This has been tested by preparing vanadium hydride VH0·8. Proton NMR of this hydride has been observed and compared with earlier reports.
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