Espectroscopia Mossbauer em vidros e vitro-cerâmicos ferro-alcaninos -silenciosos

Abstract

Môssbauer spectroscopy is used to study two types of silicate glasses: a) quaternary glasses with cornpositions (1 -x) (O, 50SiO O, 45Na O. O, 05CaO) xFe O where 0.0l<x<0.47, (b) ternary glasses with cornposition (1 - x)[(l - y) SiO yCaO] xFe O where x takes values of 0,084 and 0,154 e y values such that the ratio SiO /CaO is equal to 2/3, 1, 4/3, 3/2 and 2. For quaternary glasses, the presence of only Fe3 + ln the Mõssbauer spectra reveal both octahedral and tetrahedral coordinations. For glasses with x 2: O, 28 the Móssbauer spectra reveal the presence of an iron oxide, identified as haernatite (Fe O ) Fo r t ernary g l asses, th e iron occurs as Fe3 + and Fe2 + at octahedral and tetrahedral sites and also as rnetalic iron (a-Fe) and magnetite (Fe O ) . Reduction processes in these glass-forrning melts are discussed. Crystallization processes, for annealead sarnples glass-cerarnics, are observed and qualitatively analized based on ciassical volume nucleation thopry in glasses.