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  • Author or Editor: M. Pospíšil x
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Abstract  

This paper describes a study on some physico-chemical properties of CuO−Bi2O3 mixed oxides of various composition and their reactivity during hydrogen reduction in the range 290–460°C. Depending on the composition, the changes in the morphology of the samples, their specific surface areas, phase composition of Bi2O3 as well as the change in the amount of chemisorbed surface oxygen (specific surface oxidation ability) were found. The last mentioned parameter is strongly affected positively or negatively (depending on the dose absorbed) by the pre-irradiation with gamma-rays and accelerated electrons. Either reduction of CuO or consecutive reduction of both components with a maximum rate on the surface or sub-surface layers of grain, proceed in different temperature ranges. The retarding effect of liquid bismuth is partially compensated for by the sponging and trapping effects, so that the overall reduction rate changes non-monotonously with the composition of the samples. Pre-irradiation leads in all cases to the lowering of reduction rate, which can be correlated with the increase in the concentration of strongly bound oxygen forms, creating centres of donor hydrogen chemisorption. The effect of gamma-radiation appears to be function of the threshold dose absorbed.

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Abstract  

Some physico-chemical properties and reactivity in their reduction with hydrogen of NiO—Y2O3 mixed oxides prepared in a dry way have been studied using isothermal thermogravimetry in the range of 320–410°C and temperature-programmed reduction. It was found that addition of small amounts of chloride and acetate anions retarded the reduction of nickel oxide and accelerated the reduction of mixed oxides. The presence of oxalate and formate ions manifests itself by a small positive effect. Introduction of platinum activator or heat treatment of the samples in various atmospheres led to a pronounced increase in the reduction rate. The efficiency of the spill-over effect increases with increasing proportion of non-reducible Y2O3. The pre-irradiation of the samples by accelerated electrons and gamma rays at a dose of 1 MGy results in a negative kinetic effect only with the samples containing an excess of nickel oxide.

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The reduction of cadmium oxide and zinc oxide mixtures of various compositions with hydrogen at 410–450° was studied with thermogravimetry. The reduction kinetics, which depends markedly on the composition in the whole composition range, can be described by the equation (α+0.3)/(1−α)=A·e kt. Preliminary irradiation of the samples with60Coγ-rays (applied doseD γ=105 Gy) causes an increase in the rate of reduction of samples containing an excess of CdO and decrease in the rate of reduction in the region with excess of non-reducible ZnO. Fast neutron irradiation with a flux density of 1.18·1017 n/m2 (total doseD n=4.5·102 Gy) from a252Cf source retards the reduction in the whole range of composition. The probable mechanism of mutual interaction of both components and of the applied ionizing radiation is discussed.

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Abstract  

The physico-chemical properties and reactivity tested by hydrogen reduction have been studied for two series of NiO-ZnO mixed oxides of various composition. The solid nickel oxide or zinc oxide in interaction with the solution of nitrate of the second component were used as the precursors in each series. The differences in some physico-chemical parameters of the samples in both series were correlated with their reduction behaviour, followed both in iso- and non-isothermal regime. Moreower, the influence of various factors modifying the reactivity of mixed oxides was also investigated and the results were compared with those obtained from earlier studied analogous systems of quite different origin.

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Abstract  

A Doppler broadening is described of the 4438 keV spectral gamma-line observed by means of a Ge(Li) detector during the deexcitation of nuclei of12C in an inelastic scattering12C(n, n′γ)12C using an241Am−Be source as well as during the reaction9Be(α, nγ)12C taking place in the Am−Be source. The FWHM of the spectral line is equal to (90±4) keV in the latter reaction and (64±8) keV in the former process. Experimental values agree well with theoretical ones.

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Abstract  

Some physico-chemical properties of NiO–ThO2 mixed oxides of various compositions have been investigated. The presence of strongly bound constitutional water in the hydrogel of reactive forms of thorium dioxide, determined by their origin (thermal decomposition of mixed hydroxides) caused the different reduction behaviour as compared with other mixed oxide systems containing the only, thermodynamically less stabile reducible component. The significant effects of the thermal treatment in oxygen atmosphere, pre-irradiation by the gamma rays or accelerated electrons under various conditions (in air or in water suspension) as well as of surface chemical activation with a platinum complex on the reactivity of mixed oxides or reoxidized samples during their hydrogen reduction have been also proved.

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Abstract  

The possibilities were studied of the analytical application of high energy primary gamma rays from the radiative capture of slow neutrons (the NCGA-HE method) to a rapid nondestructive determination of technologically important elements (Ni, Cr, Fe, Si) in large volumes of nickel ores. Neutron source was a241Am–Be (10 Ci) isotopic source, prompt gamma radiation was detected by high resolution gamma-ray spectrometer. Detection limit for nickel was 0.2% for chromium 0.25%.

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