Volume 19, Issue 4
August 1996, pages 607-715
pp 607-613 August 1996
A series of oxides LnBaCuCoO5 (Ln=Pr, Nd, Sm, Dy, Gd, Ho and Er) have been synthesized by ceramic method. The oxides crystallize in a tetragonal structure, isostructural to YBaCuCoO5. All the oxides in the series are semiconducting. IR spectra of these oxides show distinct absorption bands at 630 cm−1, 550 cm−1 and 330 cm−1 which are assigned toE,A2 andA1 modes respectively. Doping of holes in these oxides, by calcium substitution in Er1−xCaxBaCuCoO5−x (up tox ⋍ 0·3) was done but, these oxides did not show metallic behaviour.
pp 615-622 August 1996
In the present paper, a modified self-flux technique has been successfully employed for the growth of pure and praseodymium substituted (partially) large single crystals of high temperature superconducting Y1−xPrxBa2Cu3O7−δ (x = 0·0,0·2,0·4). Typical sizes of the platy and bulky crystals of pure YBCO(123) material are ≈ 2 × 2 × 0·1 mm3 and 4 × 1 × 1 mm3, respectively. In case of Pr-substitution, the typical sizes of platy and bulky crystals of Y0·8Pr0·2Ba2Cu3O7−δ and Y0·6Pr0·4Ba2Cu3O7−δ materials are ≈ 2 × 3 × 0·1 mm3 and 5 × 1 × 1 mm3 and ≈ 1 × 1·5 × 0·1 mm3 and 7 × 0·2 × 0·1 mm3, respectively. The morphology and growth habit of the as-grown single crystals and the critical transition temperature (Tc) of the oxygenated crystals were found to depend on the Pr-content.
pp 623-629 August 1996
Optical fibres were coated with polypyromellitimide (PPM) using their precursor polyamic acid to study the application of optical fibres at elevated temperatures. Normally optical fibres can withstand temperatures in the range of 100–200°C but our studies have indicated that optical fibre coated with PPM can easily withstand temperatures up to 400°C without any loss. Interaction of silica with polyamic acid has been suggested with the formation of water and thus it is presumed that damaging hydrogen is not being formed. Characterization of the coated optical fibre has been done with the help of FT-IR and TG analysis.
pp 631-637 August 1996
Dielectric properties of nanophase AgI are studied over the frequency range from 100 kHz to 3 MHz at different temperatures. The values ofε, tanδ andσac are considerably larger than those reported for crystalline pellets of AgI, but they show a similar trend in variation with frequency and temperature. The increase in these values are attributed to the defect structure of the nano-particles.
pp 639-643 August 1996
CoxCd1−xC2O44H2O crystals grown by gel technique are characterized for dielectric properties by optical absorption measurements. Loss curve shows a relaxation peak at 500 KHz corresponding to a relaxation time of 0·3 µs. Cole-Cole diagrams give exponent of universal power law to be equal to 0·22. Optical absorption shows peaks due to Co+2 ion and water of hydration. An attempt is made to understand the results.
pp 645-649 August 1996
Vacuum deposited MoO3-V2O5 films of different molar concentrations have been used for DC electrical conductivity studies at different temperatures. The optical absorption spectra of MoO3-V2O5 films of different molar concentrations have been measured. From these measurements it is found that optical band gap and activation energy vary with molar concentration of MoO3-V2O5 films.
pp 651-656 August 1996
WO3 thin films have been prepared by employing spray pyrolysis technique. Photoelectrochemical (PEC) cell was formed using WO3 thin film as a photoanode and 0·1 M Na2SO4 as an electrolyte. Different physical parameters of the PEC cell such as flat band potential, donor density, hole diffusion length and band gap energy were determined by using Gartner’s model.
pp 657-660 August 1996
Thermomechanical properties like thermal expansion (αc) and electrostriction along with ΔH and transition temperature are reported for the KNO2-H3BO3 binary phase. The transition is classified as second order phase transition. Some of these properties were compared with those of its pure compound. On the basis of thermodynamic properties it is predicted that binary phase is more stable rather than its pure phase.
pp 661-669 August 1996
Titanium alloys, because of their excellent specific strength/density ratio result in significant weight reduction in airborne vehicles thus improving their performance and fuel efficiency. In addition, excellent corrosion resistance, high fracture toughness, creep strength up to ∼ 600°C make them a wanted material for aeroengine applications. Though a number of alloys are in use, Ti-8Al-1Mo-1V alloy, due to its advantageous characteristics has been selected for HP compressor blades for Adour engine (JAGUAR Aircraft) applications. Optimization of chemical composition, forging technology and heat treatment were the main objectives to obtain best combination of properties for the end use. The alloy has been successfully evaluated in accordance with mandatory airworthiness requirements.
pp 671-675 August 1996
Local stress and strain variations in the deformation zone can be ascertained by measuring hardness. Hardness is correlated with strain and stress. The expressions discussed later are useful in determining the local variations in stress and strain from hardness measurement. It is a simple method compared to visioplasticity. One can estimate the forces required for a forming process. It helps in the choice of equipment, design of tooling and selection of lubricant for the particular process.
pp 677-698 August 1996
Three distinct trends in the modeling of hot working behavior of metallic materials are identified. These are respectively (a) analytical and numerical methods to characterize the material flow behavior and related macroscopic properties, (b) metallurgical models to predict microstructural parameters at each step in a multi-step processing operation, and (c) hot workability models to predict optimum conditions of temperature and strain rate for a single step deformation. Important features of the models are critically examined and some possible directions for future work indicated.
pp 699-711 August 1996
The temperature dependence of the viscosity of the undercooled melts exhibits an important role in the study of nucleation, crystal growth and the glass-forming ability of materials. Several attempts have been made to study the viscous behaviour of the glass-forming melts and these investigations are mainly based on free volume theory as well as on the configurational entropy model. In the present investigation, an attempt has been made to correlate the thermodynamic parameters with the viscosity of the glass-forming melts and to study the temperature dependence of the viscosity of undercooled liquids on the basis of the free volume theory as well as on the basis of the configurational entropy model of Adam and Gibbs. The entire study is confined on the expression for thermodynamic parameters reported by the authors recently. The expression obtained has been successfully applied to study the temperature dependence of the viscosity of the metallic, molecular and oxide glass-forming liquids.
pp 713-715 August 1996 Rapid Communication
A new ceramic voltage sensor based on SnO2 doped with Co, Nb and Al has been successfully synthesized by ceramic route. The ceramic compact exhibited excellent non-linear current-voltage (I-V) characteristics withα ≈ 24 andE1mA ≈ 700 V/mm.
Volume 42 | Issue 6
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