NOPR Collection:

Microstructure and glass transition temperature determination of styrene-methyl acrylate copolymers by 13C-NMR spectroscopy

Tue, 01 Dec 1992 00:00:00 GMT

Title: Microstructure and glass transition temperature determination of styrene-methyl acrylate copolymers by 13C-NMR spectroscopy Authors: Brar, A S; Sunita Abstract: Styrene-methyl acrylate (S/M) copolymers of different monomer compositions have been prepared by bulk polymerization using benzoyl peroxide as an initiator. Copolymer composition is determined from NMR spectrum and comonomer reactivity ratios have been determined by the method of Kelen-Tudos. The copolymerization parameters such as terminal, penultimate reactivity ratios, diad concentrations, conditional probabilities, number-average sequence lengths and run number in the copolymers have been calculated from the observed triad sequence distribution determined from ¹³C[¹H]-NMR spectra. The observed triad sequence concentrations as determined from ¹³C[¹H]-NMR spectroscopy are in good agreement with those calculated from reactivity ratios. Glass transition

temperature (T_g) values of various copolymers calculated from NMR spectra (using Barton's equation) give good agreement with the values obtained from DSC. Page(s): 903-908

Investigation of Cr3+ substituted γ-Fe2O3 catalyst in its active form

Tue, 01 Dec 1992 00:00:00 GMT

Title: Investigation of Cr3+ substituted γ-Fe2O3 catalyst in its active form Authors: Sengupta, A C; Kundu, M L; Maiti, G C; Sen, B; Ghosh, S K; Banerjee, P; Ganguli, S; Bhattacharya, M Abstract: The Cr³⁺ ion substituted γ-Fe₂O₃ catalysts after reduction in their active states for water gas shift reaction, prepared by three different routes have been investigated using TG, XRD, IR and Mossbauer techniques. The TG and XRD results indicate that Cr³⁺ could be substituted in the magnetite lattice and the IR and Mossbauer investigations reveal that Cr³⁺ gets included in the octahedral sites of γ-Fe₂O₃. The inclusion of Cr³⁺ produces ultrafine particles indicative of lattice instability which depends on the method of preparation. Ultrafine particles have been registered through the average crystallite size measurement by XRD and the super paramagnetic doublet in Mossbauer spectra. On the basis of correlation between relative abundance of ultrafine particles and the concentration of Cr³⁺ ions, the criteria for the best catalytic function have been suggested invoking ordering of Cr³⁺ ions/vacancies and the electron hopping between Fe²⁺ and Fe³⁺ in the magnetite lattice. Page(s): 909-914

Effect of alkali halide additives on the gamma radiolysis of thorium nitrate

Tue, 01 Dec 1992 00:00:00 GMT

Title: Effect of alkali halide additives on the gamma radiolysis of thorium nitrate Authors: Joshi, (MIss) N G; Garg, AN Abstract: Gamma radiolytic decomposition of thorium nitrate and its binary mixtures with potassium halides has been studied over a wide absorbed dose range (upto 600 kGy) and at different compositions. G(NO) values decrease on the addition of halides, except for several fold enhancement at 75% composition in low dose region. A part of the energy is taken up by the additive and later transferred to the nitrate thus affecting its decomposition. Reflectance spectra of irradiated binary mixtures show characteristic bands corresponding to the formation of X and colour centres (V and F). Thermoluminescence (TL) studies of pure halides and its binary mixtures with thorium nitrate suggest the formation of radical species affecting the decomposition. EPR measurements on γ-irradiated thorium nitrate indicate the presence of NO₂, O and O. A plausible mechanism has been proposed. Page(s): 915-920

Conversion of methanol over metal salts of 12-molybdophosphoric acid

Tue, 01 Dec 1992 00:00:00 GMT

Title: Conversion of methanol over metal salts of 12-molybdophosphoric acid Authors: Ebeid, Fikry M; AIi, Laila I; Amin, Nabil H; Abd-AIla, Fawzia F Abstract: The effect of ionic size of the counter cation and its electronegativity on the 'conversion of methanol to dimethyl ether and methane over sodium, calcium, magnesium and zinc salts of dodecamolybdophosphoric acid has been studied. The reaction has been carried out in a flow system. It has been found that the zinc salt which has the highest electronegativity and the smallest cation radius is the most active catalyst. The higher activity observed at lower calcination temperatures may be explained by the concept of pseudo liquid phase. The results indicate that methane is formed by a consecutive reaction. The effect of pyridine on both products has also been studied. It is found that the formation of ether is more inhibited by pyridine than methane. Ether formation follows a second order equation of Langmuir-Hinshelwood type, whereas methane formation follows a first order equation. Page(s): 921-928