Variation of the oxidation state of iron in sodium borate glasses caused by the external magnetic field applied during sample preparation

摘要

Sodium borate glass containing iron and cobalt oxides, (Na_2B_4O_7)_(0.750)(Fe_2O_3)_(0.125)(CoO_2)_(0.125) was prepared by melting the reagent mixture at 1000 deg C for half an hour in air. Part of the melt was poured onto a stainless steel plate kept at room temperature under an external magnetic field (about 1 kOe). For comparison, the other part of the melt was also poured on a stainless steel plate at room temperature without applying the external magnetic field. Room-temperature Mossbauer and magnetic susceptibility measurements of the pulverized glass samples at one-week interval, starting from the time of preparation, show a gradual change of the oxidation state of iron with time from Fe(II) to Fe(III) for the sample which was subjected to an external magnetic field; sample (A). The sample prepared without the magnetic field, sample (B), showed no change of the oxidation states of iron with time; it showed almost a constant value of the oxidation state as indicated from the isomer shift values in the Mossbauer spectra and from the magnetic susceptibility measurement. Effect of the magnetic field on the redox of iron in the melt is discussed together with the time-dependent oxidation state of the iron in sodium borate glasses.