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51.
The simultaneous rising temperature (DTA-TG) technique and the gas evolution method are adopted for studying the thermal decomposition of unirradiated and irradiated MgC2O4 and MgC2O4 + TiO2 mixtures. The data are applied to theories of different solid state reaction models and the best fit is obtained for the Avrami-Erofeev mechanism (n=2) suggesting that both the nucleation and growth processes occur at the reactant product interface in a two dimensional chain branching manner. Low irradiation doses decrease the rate of reaction remarkably whereas the reverse phenomenon takes place at higher doses. The n-type semiconducting oxide, TiO2 (5-40 mol%) enhances the rate of decomposition which increases with increasing concentration of the catalyst. The influence of n -irradiation is explained in the light of defects, dislocations and electron-hole (e?, h+) pairs generated in the lattice, whereas the influence of TiO2 is understood on the basis of electron transfer process involved in the reaction. 相似文献
52.
Considerable changes were observed in the X-ray diffraction pattern of ammonium zinc chloride after doping with Sr2+ in different concentrations and after irradiating with γ rays at different doses. The effect of γ-radiation and Sr2+ content on optical parameters of (NH4)2ZnCl4: x Sr2+ single crystals (x?=?0.00, 0.020, 0.039, 0.087 or 0.144?wt.%) has been investigated. The transmittance near the absorption edge of unirradiated crystals and crystals irradiated with different γ-doses has been measured, hence the absorption coefficient (α) was calculated. The values of α at room temperature increased under the influence of γ-irradiation. The rate by which α increases with photon energy just before the absorption edge is strongly inhibited by higher γ-doses. The type of intraband transition in (NH4)2ZnCl4: x Sr2+ single crystals was found to be of the allowed indirect transition, and γ-irradiation had no effect on the type of transition. The values of the optical energy gap (E g ) were calculated as a function of γ-dose. The effect of γ-irradiation was found to be more pronounced on samples doped with x?=?0.087 or 0.144?wt.% Sr2+. The results can be discussed on the basis of γ-irradiation-induced defects and Sr2+ concentration. A diagram representing probable transitions to the created bands due to irradiation could be constructed. 相似文献
53.
54.
The electron paramagnetic resonance spectra of γ-irradiated powders of α-(methylamino)isobutyric acid – CH3NHC(CH3)2COOH, α -aminoisobutyric acid methyl ester hydrochloride – NH2(CH3)2CCOOCH3 HCl, and diethylmalonic acid – (CH3CH2)2C(COOH)2 have been investigated at room temperature. It has been found that γ -irradiation produces the (CH3)2C˙COOH radical in the first, the (CH3)2C˙COOCH3 radical in the second and the (CH3CH2)2C˙COOH radical in the third compound. The spectra were computer-simulated. The g values and the hyperfine coupling constants of the unpaired electron with the environmental methyl, methylene protons and OH proton were determined. The results were found to be in good agreement with the existing literature data and theoretical predictions. 相似文献
55.
It has been observed on the oxidized V2 O5/γ-Al2 O3 that C3H6 form alkoxides which were converted to acetone during the desorption of adsorbate phase at 373 K. C3 H8 may form π-complexes on the reduced form of the same catalyst. However, the intensities of the bands in the adadsorption of C3 H8 were very weak as compared with the case of C3 H6 adsorption. Therefore, it was not reasonable to assign these bands clearly as any of the surface type species. 相似文献
56.
An investigation by high-resolution transmission electron microscopy of the precipitation process during ageing a Cu–1.2?wt%Be–0.1?wt%Co alloy at 320°C has revealed that the transition phases follow a γ″→ γ″?+?γ′?→?γ sequence. The γ′ phase heterogeneously precipitates on the γ″ phase. The effects of an external stress on the nucleation and growth of disc-shaped γ″ and plate-shaped γ′ precipitates have been examined for the alloy aged at 320°C. A compressive stress applied in the [001] direction during ageing preferentially accelerates the nucleation and growth of the γ″ variant normal to the [001] axis among three crystallographically equivalent variants and the specific four γ′ variants formed on the γ″ variant normal to the [001] axis. A tensile stress does not significantly affect those of γ″ and γ′ precipitates. The critical diameter of the disc-shaped γ″ nucleus is estimated as about 1?nm from evaluation of the interaction energy between the applied stress and the misfit strains of γ″ precipitates. It is proposed that applied external stress does not affect the diffusion rate but the interphase boundary velocity. 相似文献
57.
《Journal of Macromolecular Science: Physics》2013,52(4-6):1091-1104
The influence of cooling rate from the melt on the polymorphism and crystallinity is investigated as a function of isotacticity and stereo-defect distribution in polypropylenes. Detailed analysis of wide angle x-ray diffraction patterns shows that crystallinity in the materials used is nearly independent of the experimental cooling rates (0.5–40°C/min). At high cooling rates, the materials exist mainly in the α-phase, whereas the amount of the γ-phase increases at the lower cooling rates. With an increasing amount of stereo-defects, this cooling-rate dependence of the polymorphism is enhanced. The effect of different stereo-defect distributions, as observed in metallocene-(random) and Ziegler–Natta (blocklike) derived isotactic polypropylenes, was investigated. The formation of the γ-phase is more prevalent in materials with a random defect distribution compared to the materials in which the stereo-defects have a blocklike distribution. The crystallinity decreases more rapidly as a function of the tacticity in the random defect-distributed materials. 相似文献
58.
A new technique of determining Be content in samples using 4.66 MeV γ-rays is proposed. This energy range is sufficient to knock out the neutron from the 9Be nucleaus and to excite the first 2.9 MeV level of the 8Be nuclei. 1.5 MeV alpha particles are registered by means of CR-39 or cellulose nitrate detectors. Alpha particles produced in the reaction of γ-rays with Li nuclei which are contained in samples may cause the background. The latter is excluded by heating of samples before irradiation for Li molecules to be evaporated. 11B nuclei do not produce alpha particles at the energy range of γ-rays presented above.The results obtained in the experiments of determining Be content in natural beryl crystal samples are in good agreement with their known chemical composition. Microparticles containing Beryllium were found in soil samples from the Ust-Kamenogorsk are deposit region, which contains 10−3 − 10−4 g/g of Be. The sensitivity of the method is 10−6 g/g of Be in solids. 相似文献
59.
60.
Takamasa Suzuki 《Tetrahedron letters》2008,49(32):4701-4703
The enantioselective allylation of aldehydes using a variety of β-amido functionalized allyltributylstannanes proceeded smoothly with good to high yields and enantioselectivities in the presence of 10 mol % of a chiral catalytic complex prepared from In(OTf)3 and 2,6-bis[(S)-4-isopropyloxazolin-2-yl]pyridine {(S)-i-Pr-pybox}, providing the corresponding chiral γ-hydroxy amides. 相似文献