The interface reactions between oxide glasses and magnetic alloy, Fe-AI-Si (so-called Sendust), were analysed. The oxide glasses used were Si02-PbO, Si02-Na20, Si02-Li20 and B203-Na20 binary glasses. It was observed that the lattice constant of the alloy decreases and the saturation magnetic-flux density of the alloy increases on reaction with the glasses. It was found that the aluminium atoms in the alloy diffuse to the interface and dissolve into the glass melt as AI 3 § ions, leading to the iron-rich composition of the alloy. On the other hand, Pb 2 § Na + and H + ions in the molten glasses were reduced at the interface. Metallic lead particles about 20 I-tm in diameter were found to be dispersed in the Si02~-PbO melt. Reduced sodium was thought to evaporate from the Si02-Na20 melt, and H 2 gas bubbles were observed at the interface between B203-Na20 melt and the alloy. These reactions were analysed based on the standard free energy diagrams of oxidation-reduction reaction, and expressed as 3Pb2+g ass -'I-2AlaHoy-* 3Pb + 2AI31+ss 3Na~ass + AlaHoy~ 3Na + AI 3+ glass 6H;ass + 2Ala,,ov~ 3H2 + 2AI3+ss IntroductionMost devices are composed of many materials. As the chemical reactions at the interfaces affect the properties of the devices, it is important to determine the mechanism of the interface reactions thoroughly in order to develop composite devices with excellent properties. Oxide glasses have been extensively used for electromagnetic devices, such as integrated circuits and magnetic he~lds.There has been little attention devoted to the chemical reactions between oxide glasses and different materials. Pask and co-workers [1-9] studied the interface reaction between metals and glasses based on the concept of wettability. Takashio [10][11][12][13] studied the interface reactions between metals and glasses from the view point of thermodynamics. Tanigawa et al. [14,15] reported the reactions of Mn-Zn ferrite with lead silicate glasses and found PbO'2FezO3 is deposited during the heat treatment. Mino and Watanabe [16] studied the interface reaction between Mn-Zn ferrite and lead silicate glasses and observed that intermediate layers with many pores were formed at the interface, depending on the surface condition of the ferrite after polishing.
The interface reactions between Si02-Pb0 melt and Mn-Zn ferrite were studied using electron probe microanalysis (EPMA) and X-ray diffraction (XRD). Intermediate layers were formed at the interface between the glass and the Mn-Zn ferrite which were heated at 800" and 900"C, although those layers were not found in specimens heated at 1000°C. Using EPMA and XRD, the intermediate layers were found to be Pb2(Mn, Fe)2Siz09 and Pb8(Mn, Fe)Si60zl. The mechanisms of interface reactions are discussed, related to glassforming regions. It was concluded that the interface reactions between Si02-Pb0 melt and Mn-Zn ferrite are controlled by the dissolution of Zn ions and Mn ions from the Mn-Zn ferrite. [
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...
Enhancement of photoexcited charge separation in semiconductor photocatalysts is one of the important subjects to improve the efficiency of energy conversion for photocatalytic overall water splitting into H2 and O2. In this study, we report an efficient separation of photoexcited charge at the interface between non-doped pure CeO2 and Y3+-doped CeO2 phases on particle surfaces with heterogeneous doping structure. Neither non-doped pure CeO2 and homogeneously Y3+-doped CeO2 gave activities for photocatalytic H2 and O2 production under ultraviolet light irradiation, meaning that both single phases showed little activity. On the other hand, Y3+-heterogeneously doped CeO2 of which the surface was composed of non-doped pure CeO2, and Y3+-doped CeO2 phases exhibited remarkable photocatalytic activities, indicating that the interfacial heterostructure between non-doped pure CeO2 and Y3+-doped CeO2 phases plays an important role for the activation process. The role of the interface between two different phases for activated expression was investigated by selective photo-reduction and oxidation deposition techniques of metal ion, resulting that the interface between two phases become an efficient separation site of photoexcited charge. Electronic band structures of both phases were investigated by the spectroscopic method, and then a mechanism of charge separation is discussed.
The interface reactions between Mn-Zn ferrites and SiO2-PbO-MO ternary melts were studied using electron probe microanalysis and x-ray diffraction. In interface reaction between Mn-Zn ferrite and 55SiO2-40PbO-5MnO (in mol %), the intermediate layers were observed in close vicinity to the interface. It was found that these layers were mixtures of Pb2(Mn,Fe)2Si2O9 and Pb8(Mn,Fe)Si6O21 crystals. But no intermediate layers were observed at the interface between the ferrite and 55SiO2-40PbO-5ZnO (in mol %) heat-treated at various temperatures. The two kinds of the intermediate layers were observed at the interface between the ferrite and 55SiO2-40PbO-5FeO1.5 glass. It was found that one of the intermediates was a mixture of Pb2(Mn,Fe)2Si2O9 and Pb8(Mn,Fe)Si6O21, and the other was α-Fe2O3. The interface reaction mechanisms were proposed in this study.
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