A quimica dos atomos dopantes de 51Cr (III) em K2CrO4

AUTOR(ES)
DATA DE PUBLICAÇÃO

1988

RESUMO

Several investigations have been published in which Cr(III) was incorporated into K2CrO4 as dopant in order to study annealing reactions. However, the control of specific doping methods for obtaining doped material preferentially exhibiting one of the radiolabelled species has never been performed. Furthermore, in most of the studies carried out thus far, the most discussed reaction is that involving the oxidation of Cr (III) to Cr (VI), while the reactions involving monomeric, dimeric and polymeric species are not properly considered. Thus, one of the objectives of the present study was to obtain crystals of K2CrO4 doped with Cr(III) predominantly exhibiting one of the radiolabelled species. To this end, the effects of temperature, pH and time of dopant contact with the host solution were studied. Another objective was to study the thermal annealing reactions of the doped material preferentially exhibiting a given radiolabelled species. Thermal annealing of crystals predominantly exhibi ting the monomeric Cr (III) species was perforrned with two different batches. Comparison of the curves for the yields in ead1 situation permitted, the identification of the following processes: M D; M P; M VI and D VI. By mathematical treatment based on work by VAND and PRIMAK we obtained the initial distributions of the activation energy for the processes that resulted in consumption of the monomeric species and related them. In the thermal annealing of K2CrO4 doped with Cr(III), preferentially exhibiting the dimeric species, we compared the results for the same batch in different sampling environments and the resul ts for two different batches in the same environment. On the basis of the yields of the radiolabelled species and of their ratios it was possible to identify the following processes: DP; DVI; MVI e PVI. In order to identify the reactions occurring in solid mixtures of inactive K2CrO4 with radiolabelled chrome hydroxide prepared under two different sets of conditions, we studied the effect of pressure application on the variation in yields of radiolabelled species and on isothermal annealing of the mixture. The results showed that the only process that could be distinguished in isothermal annealing in this case was the conversion of the dimeric species to the polymeric species, which is retarded by the application of pressure. The results of the above studies were useful for the elucidation of some processes occurring between Cr(III) and K2CrO4 .

ASSUNTO(S)

potassio - compostos cromo - compostos

ACESSO AO ARTIGO

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