Volume 13, Issue 3
June 1990, pages 161-234
pp 161-164 June 1990
Na3BaCl5·2H2O crystals were prepared by the slow evaporation of an aqueous solution of a mixture of sodium chloride and barium chloride in stoichiometric ratio. Crystals were found to possess platelet habit. Crystals were analysed by infrared spectrophotometry, thermogravimetry and X-ray diffraction. The appearance of bands due to stretching and bending modes of water molecules in the IR spectra showed that the grown crystals were hydrated. X-ray oscillation and Weissenberg photographs were used to measure the dimensions of the unit cell.
pp 165-171 June 1990
The authors examine the boric oxide—ammonia route with special stress on the yield and composition of the intermediate addition compound (BN)x(B2O3)y(NH3)z. It has been concluded that B2O3 and NH3 present in the addition compound formed between 350°C and 900°C cannot be further reacted to convert the B2O3 into BN and the BN yield remains at around 66%. A formula (BN)12·7(B2O3)7·5NH3 has been suggested for the addition compound.
pp 173-178 June 1990
Silicon nitride-silicon carbide (Si3N4-SiC) composites were prepared by varying the percentage of silicon nitride at temperatures of 1350 to 1450°C. The mechanical and thermal properties of these composites were determined. The modulus of rupture of the composites increases with increase of temperature whereas the thermal expansion decreases. Composites with 10% and 50% Si3N4 have modulus of rupture of 49 and 86 MPa at 1400°C and thermal expansion coefficients (25°–1000°C) of 4·4 × 10−6 and 3·2 × 10−6°C−1 respectively.
pp 179-189 June 1990
Fine particle fluorescent aluminous oxide materials like Cr3+-doped α-Al2O3 (ruby), MgAl2O4, LaAlO3, Y3Al5O12 and Ce3+-doped Y3Al5O12, LaMgAl11O19, CaAl12O19 and CeMgAl11O19 have been prepared by the combustion of the corresponding metal nitrate-aluminium nitrate-urea/carbohydrazide mixtures at 500°C in less than 5 min. Formation of these Cr3+- and Ce3+-doped aluminous oxides has been confirmed by their characteristic XRD, colour, UV-visible and fluorescence spectra as well as decay time measurements. Ruby (Cr3+/α-Al2O3) powder showed characteristic excitation bands at 406 and 548 nm and emission band at 695 nm with the decay time of 3·6 ms.
pp 191-195 June 1990
The structural study of ZnCuTiO4, ZnCuSnO4 and ZnCuGeO4 reveals that while the cooperativeJ-T effect of Sn4+ is responsible for the orthorhombic symmetry of ZnCuSnO4, the hexagonal influence of Ge4+ is more predominant in ZnCuGeO4. Ti4+ is uninfluential either in initiating the distortive tendency or cooperating with other ions for the same. The XRD,ρRT, ΔE and the nature of the charge carriers, all suggest that the air oxidation of metallic copper leads to the minority concentration of Cu+ along with a majority concentration of Cu2+, as demanded by the stoichiometric considerations of these compositions.
pp 197-204 June 1990
The temperature dependence of DC electrical conductivityσ of sodium acetylacetonate compound Na(ac,ac) is studied for fresh and polarized samples. Both samples show semiconductor behaviour, but the value ofσ for the fresh sample is higher than that of the polarized sample. Three distinct regions are observed in the temperature conductivity curves. The conduction mechanism of each region is discussed. Anomalous conductivity phenomena are observed above 105°C and attributed to unidirectional intermolecular or phase transformation. The results are discussed on the basis of ionic conduction and some conduction parameters such as conduction energyEc, transport energyEu, ion mobilityu, free ion densityn, are calculated.
pp 205-210 June 1990
The transmission behaviour of manganese containing alkali-lime-silica glasses have been investigated with and without CeO2 and As2O3 as dopants. The changes taking place owing to irradiation with solar and ultra-violet conditions are reported and the roles of arsenic and ceria in causing the observed changes are discussed.
pp 211-216 June 1990
Positron annihilation studies were carried out on the Nasicon analogue Na2(La, Al)Zr(PO4)3 compound for three different concentrations (2·2, 2·8 and 5·2 by wt.%) of ZrO2 in the nutrient. Angular correlation study of annihilated photons reveals that the defect concentration is maximum for 2·8 (wt.%) of ZrO2. Further, positron lifetime studies indicate that the positrons are trapped at cation vacancies. Application of a two-state trapping model to this system made it possible to evaluate the lifetime of positrons in the Bloch state and of positrons trapped at cation vacancies.
pp 217-225 June 1990
An equation for contact area between powder particles in a powder compact, in terms of the porosity, has been derived using a geometry representing spherical voids of different sizes distributed in a material matrix. This equation is verified using experimental data as well as results obtained from computer simulation of powder compaction using a finite element method.
pp 227-234 June 1990
A full factorial 23 matrix was designed to study the bending strength, permeability and hoop-stress of investment moulds. A novel method of ethyl-silicate hydrolysis; two-step hydrolysis, was used. The results indicate that the bending strength is directly proportional to the quantity of filler material in the slurry. Grain size of stucco material appears to exert the least effect on bending and hoop strength, whereas permeability increases slightly when coarser grain is used.
Volume 42 | Issue 6
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