NOPR Collection:

Dielectric properties of different varieties of rapeseed-mustard oil at different temperatures

Wed, 01 Aug 2001 00:00:00 GMT

Title: Dielectric properties of different varieties of rapeseed-mustard oil at different temperatures Authors: Bansal, A K; Singh, P J; Sharma, K S; Kumar, Satyanshu; Kumar, P R Abstract: Dielectric properties of five rapeseed-mustard oil samples having different percentage of erucic acid have been studied at 100 kHz, 8.93GHz and optical frequency of sodium light. The dielectric constant at optical frequency (є_∞) is almost the same for all the five samples, while the dielectric constant at 100 kHz (є₀), the dielectric constant at 8.93 GHz (є) and the loss factor (є) show dependence on erucic acid content, but no systematic variation with change in erucic acid is obtained which may be attributed to the presence of other fatty acids in these samples. Temperature variation of dielectric properties has also been investigated in the range 303 to 333 K. є₀ and є_∞ decrease regularly with increase in temperature while є′ and ″ do not show a regular variation with temperature, except for Hyola-401, which contains zero level of erucic acid. In other samples є′ and є″ show a maximum or minimum type of behaviour at about 313 K, which may be attributed to the presence of some type of molecular resonance/antiresonance at this temperature. The molar free energy 'of activation, (ΔFє) and the macroscopic relaxation time (_m) have also been worked out whose temperature dependence requires consideration of other fatty acids also. Page(s): 532-540

Quantum mechanical structural studies on 2-butanone in the ground and excited electronic states and electronic spectra of its conformers

Wed, 01 Aug 2001 00:00:00 GMT

Title: Quantum mechanical structural studies on 2-butanone in the ground and excited electronic states and electronic spectra of its conformers Authors: Sharma, Archna; Gupta, V P; Virdi, Ajit; Thakur, Sheela Abstract: 2-Butanone (ethyl methyl ketone) may be considered as a two rotor system in which internal rotation may take place about C-C single bond connecting the ethyl and O=CCH₃ moieties and also about C-CCH₃ bond leading to hindered rotation of the methyl group. Results of ab initio quantum chemical calculations using STO-3G,4-31 G, 6-31G and 6-31 G** basis sets and semi-empirical calculations in MNDO approximation using modified AM1 Hamiltonian and CNDO/2 approximations are reported .The calculations were undertaken for understanding the structural and spectroscopic characteristics of the rotational isomers of 2-butanone in the electronic ground (S₀) and n-π* excited (S₁) states and for plotting the potential energy curves for these states. It was found that while in S₀ state, the molecule may exist in two stable isomeric forms- transand gauche, it may exist in only one isomeric form- gauche in the S₁ state. Completely optimized geometries of the conformers in the two states are reported. In the ground state the trans conformer is more stable than gauche by an enthalpy difference of about 1.5 kcal/mol. Ab initio calculations predict a shallow potential well for the gauche conformer with rotational barrier height of 1.56 kcal/mol for trans-gauche and 0.025kcal/mol (0.35 kcal/mol in AM1) for the gauche-trans conformers. The S₀ state of 2-butanone has about 93% trans-conformer, which wholly changes to gauche in the S₁ state. The methyl group shows hindered rotation both in the S₀ and S₁ states with rotational barriers of 0.97 kcal/mol (trans) and 1.36 kcal/mol (gauche) in the S₀ state and 1.30 kcal/mol (gauche) in the S₁ states. The ionisation potentials of the transand gauche conformers in the S₀ state are 11.01±0.06 eV and 11.03±0.08 eV, respectively, while that of the gauche conformer in S₁ state is 8.78 eV. Calculations confirm the assignment of experimental band at 278.0 nm to n-π* transition and predict transitions near 155 nm,142 nm and 131 nm corresponding to π-π* transition, both for the trans and gauche conformers. The blue shift of n-π* transition in polar solvent is explained by less polar character of the molecule in the S₁ state than in the S₀ state. Page(s): 525-531

Chemical resistance of some irradiated ceramic-glazes

Wed, 01 Aug 2001 00:00:00 GMT

Title: Chemical resistance of some irradiated ceramic-glazes Authors: Ezz-Eldin, F M; Nageeb, W M Abstract: The effect of neutrons irradiation on the chemical durability of some ceramic-glazes with different compositions has been investigated with particular attention to the change in the corrosion rate. Different factors have been studied such as glaze composition, irradiation dose, concentration of the leaching solution, immersion time and temperature of leaching solution. It was found that zircon improved the chemical durability. Corrosion rate increased with increasing concentration of immersion solution up to 2N HNO₃ then decreased, also it increased with increasing immersion time and raising the temperature of leaching solution. The amount of the silica released in solution showed a maximum weight loss percent up to 2N HNO3, and then decreased dramatically with increasing the concentration of the tested solution. The corrosion results have been explained in relation to the hydration, diffusion and selective dissolution. The density increases with successive increase of zirconium oxide content reaching the highest value of 2.59 g/cm³. The induced defects obtained on irradiating a glaze, either in the surface or in the bulk, have been assumed to result from neutron irradiation which decreases both the chemical durability and the density. Page(s): 514-524

Ultrasonic attenuation in semi-metallie GdX single crystals (X=P,As,Sb and Bi) in the temperature range 10 to 300 K

Wed, 01 Aug 2001 00:00:00 GMT

Title: Ultrasonic attenuation in semi-metallie GdX single crystals (X=P,As,Sb and Bi) in the temperature range 10 to 300 K Authors: Kor, S K; Pandey, Govind; Singh, Devraj Abstract: Ultrasonic attenuation studies have been made in semi-metallic GdX single crystals (X= P, As, Sb and Bi) in the temperature range 10-300 K. Attenuation due to e-p interaction has been studied from 10 to 80K and due to p-p interaction between 100-300 K. Morse potential has been used to evaluate second and third order elastic constants at 0 K and then at higher temperatures. Mason's approach has been used to evaluate ultrasonic attenuation. Results have been discussed, at neel-temperature slight kink in ultrasonic attenuation is observed in all the cases. Page(s): 510-513