Microprobe state analysis of PbO, B2O3, SiO2 and of their molten mixtures by X-ray OK- and BK-emission band spectra.

Abstract

OK and BK band spectra of some simple oxides and their molten mixtures were measured by an electron probe microanalyzer (EPMA) with a special attention to the characterization of the heterogeneous and glassy materials. OK spectra of PbO, B2O3 and SiO2 changed in spectral features with excitation voltage when they were coated with beryllium at about 1×10-4 Torr. When they were coated with carbon instead of beryllium at 1×10-4 Torr or with beryllium at about 2×10-5 Torr, OK spectra did not show any clear changes in features with the excitation voltage. Then it was considered that the formation of BeO during the evaporation in a low vacuum was the major cause for the spectral changes. Any significant differences were not observed in OK spectra of SiO2 among all the crystalline forms. OK spectra of binary molten mixtures were the averaged ones of component oxides. BK spectra of oxides accompanied satellite bands at the both sides of the main band and these satellite bands showed distinct changes in features with chemical combinations in molten mixtures. PbO-B2O3 system showed remarkable changes in spectral features such as the intensity and wavelength of satellite bands and the width of the main band depending on the mutual concentrations of the components. It was found that the strong intensity of the high energy satellite band was characteristic to the B2O3-SiO2 system and the small intensity of the high energy one was to PbO-B2O3 system.These spectral changes in features among oxides and binary molten mixtures were used for the microanalysis of the molten mixture of PbO⋅1.8B2O3⋅3.2SiO2 in which a phase separation was clearly observed. It was found by the X-ray elemental and microscopic analysis that the bright field region in the secondary electron image of the fracture, surface of the sample corresponded to the region rich in PbO and the dark field to the one rich in SiO2. The BK spectra were measured at each region and the spectral features were compared with those of oxides and binary molten mixtures. It was presumed that some PbO-B2O3 compound was formed in the bright field region and that B2O3⋅SiO2 was formed in addition to SiO2 as a major component in the dark field region.It was concluded that the microanalysis of heterogeneous and glassy or amorphous materials by an EPMA was especially useful for the characterization of materials in microregion in combination with the conventional X-ray elemental and microscopic observation and the valence or chemical state analysis by ultrasoft X-ray emission band spectra.