Propriedades estruturais e eletricas dos carvões minerais brasileiros

AUTOR(ES)
DATA DE PUBLICAÇÃO

1980

RESUMO

Inspection of X-ray diffraction patterns revealed that the amorphous structure of Brazilian natural coals evolue towards a more ordered state after heat treatment at high temperatures. The structure of samples carbonized in vacuum above 2000 ºC is similar to that of commercial graphite. The microscopic particles with graphitic structure which characterized the carbonaceous matrix of heat treated samples were parametrized in terms of Warren s theory for random layer structures. The pore diameter and Internal Surface Area were used in order to characterize the porosity of natural and heat treated samples, according with Porod s theory. Electronic transport studies were carried out on natural and carbonized coals. The room temperature electrical resistivity of natural coals (~ 1010 W-cm)decreased almost twelve orders of magnitude after heat treated in vacuum at 2000 ºC. This was attributed, as suggested by the X-ray data to irreversibles changes in the coal structure. Resistivity measurements at low temperatures (77 to 300 ºK) in natural coal samples, showed that the temperature dependence of the conductivity at low applied field was of the type predicted by Mott for non-crystalline materials. Heat treated coals, according to our diffraction data are formed by small particles(~ 50 Þ). Resistivity measurements from room temperature down to 77 ºK in these samples indicated that the conduction process at low applied fields is characterized by thermally activated charge carriers involving charge transfer between initially neutral particles and also by the drift velocity of these charges in an applied field. The mechanism of charge transfer between particles is tunneling. The temperature dependence of the electrical resistivity "r" was of the type, lnr ~ A/ÖT where "A" is a constant depending on the structure

ASSUNTO(S)

carvão - minas e mineração - brasil

ACESSO AO ARTIGO

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