Glass forming regions, valence states, and viscosities in Si0,-PbO systems containing various transition-metal oxides as a third component were investigated. The glasses were prepared by melting in an open atmosphere. The glass-forming regions ranged as follows: MnO~ZnO>Fe0,,5>Ni0. The ratios Fe2+/(Fe2' +Fe3') and Mn3+/(Mn3+ +Mn2+) in the glasses were determined by chemical analysis. The Fe2'/(Fe2' +Fe3+) ratio in SiO,-PbO-FeO,,, glasses ranged from 0.016 to 0.050. The Mn3'/(Mn3'+ Mn") ratio in SiO,-PbO-MnO glasses rangedfrom 0.056 to 0.30. The fraction of manganese (III) ions in the glasses varies considerably with the glass composition. The effects of transitionmetal oxides on the viscosity are discussed. (Key words: glass, silica, lead oxide, transition metals, manganese oxide .I LASSES that contain transitionmetal because of their unique optical,' mag- G .oxides have attracted much attention A 0 (mol%) PbO Fig. 1. Glass-forming region in the system SiO,-PbO-ZnO: (0) glass, (a) glass+crystal, ( 0 ) crystal, and (W) not melted at 1400°C.n e t i~, , -~ and redox5 properties. The valence states of transition elements in glasses have been investigated by various techniques, such as visible absorption,'26 Mo~sbauer,~-" electron spin resonance," electron spectroscopy for chemical analy-&,I3 and chemical analyses. However, the concentration of transition-metal oxides in most of the studies hitherto reported was < 10 mol% and only a few studies reported compositions containing larger amounts of transition-metal oxides. Matusita et al. l4 and Kamiya and c o -w o r k e r~'~~'~ reported low values of thermal expansivity for glasses containing 17.5 mol% copper oxides. Imaoka and Y a m a~a k i '~-~' reported the same glass-forming regions in systems containing transition-metal oxides. Glasses based on SO2-PbO are of potential interest in the fabrication of magnetic devices,', but there have been few studies of the glass-forming regions in the system SO,-PbO containing transition-metal oxides.The purpose of the present communication is to investigate the glass-forming regions, valence-state ratios, and viscosities in the system SO,-PbO containing transition-metal oxides, especially iron oxide, manganese oxide, and nickel oxide. EXPERIMENTAL PROCEDUREThe raw materials used were reagentgrade SiOz, Pb,O,, MnO,, Fe203, and NiO. Batches producing 50-g glass samples were placed in platinum crucibles and melted in an electric furnace in an ZnO m 0 0 . U P b O m 0 0 0 0 0 . . 20 LO 60 80 (mol%l SiOz Fig. 2. Glass-forming region in the system SiO,-PbO-MnO: (0) glass, (a) glass+crystal, ( 0 ) crystal, and (W) not melted at 1400°C.open atmosphere at 1000" to 1400°C for 2 h depending on the composition. The melts were cast onto a hot steel plate and annealed in an electric furnace preheated to the glass transition temperature. The surface of the melt hardened 50 s after casting; therefore, the cooling rate was estimated to be =20 K/s. The glass formation was determined visually or by XRD analysis. The DTA measurements were made under f...
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