火山ガラスの電気的性質と水熱反応性

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Hydrothermal reactivity of basaltic glass was investigated under various chemical conditions using Morey-type autoclave. Basaltic glass, similar to andesitic glass, is less reactive to crystallize in hydrothermal media compared with the case of more siliceous volcanic glass, such as obsidian.To clarify relationships among chemical compositions, hydrothermal stabilities and some electrical properties, the dielectric dispersions and the d. c. conductivities were carefully measured.The results are as follows.1) The discrimination between ionic charge carriers and electronic one in the glass sample could be attained by the analysis of low frequency dispersions less than 30c/sec. The rate of the electronic to the ionic conductivity is strongly depended on the iron content. Obsidian is an essentially ionic conductor at high temperatures and no electronic conduction is observable, but in Sanukite, an andesitic glass, electronic conduction is a few fraction of the total, and the result for basaltic glass shows far larger amount of electronic conduction than that of the andesitic one.2) The d. c. conductivity of volcanic glasses are determined by the use of interfacial polarization arised introducing a barrier of known demensions purposely, in the form of thin sheet of mica. The activation energies for d. c. conduction are: 19.2kcal/mole (obsidian), 20.5kcal/mole (Sanukite) and 30.8kcal/mole (basaltic glass). These values should be ascribed to ionic transfer in the glass-structures.3) The ratio of the number of mobile Na+ions derived from the d. c. conductivity to the total decreases in the following order: obsidian Sanukite, basaltic glass. The greater part of Na+ ions in obsidian contribute to the d. c. conduction, so that the network seems to be rather loose resulting in the low activation energy for conduction and also in the low resistivity. On the other hand, in andesitic or basaltic glass, a large number of Na+ ions will be situated in deep potential wells and take little part in the conduction, so that the activation energy and the net resistivity increase. This means that the mobility of Na+ ions is restricted or they are even imprisoned by immobile network modifiers. It is concluded that the network of volcanic glasses contains a large number of immobile Na+ ions bound in the glass-structures.4) It was demonstrated that the chemical stability under hydrothermal condition was closely related to the ratio between mobile Na+ ions and immobile Na+ ions. Increase of the number of mobile Na+ ions give rise to a decrease in chemical stability of volcanic glasses, such as obsidian. It was observed experimentally, however, that the amout of silica content had almostly no effect on crystallization in basic hydrothermal media. This results indicate that the crystallization of volcanic glass is is mainly determined by the rate of the decondensation of the framework contracted by framework modifieres.5) An interesting aspect of basaltic glass is that the mobility of Na+ ions is grately hampered by the increasing number of immobile ions, which manifests itself in an considerable increase of the activation energy for the d. c. conduction. This behavior is entirely different from that of other volcanic glasses investigated. Moreover, the chemical composition of basaltic glass are characterized by such a low content of network-forming ions that the coherence of the structure units becomes inadequate to form a spatial network and the amorphous pattern of X-ray diffraction is shift to higher angle compared with Sanukite and obsidian. This fact and the low content of silica suggest that the SiO4-tetrahedra in basaltic glass are mainly in the form of tangled chains of different lenghs and not in three-dimensional silica-like structure.
社団法人日本セラミックス協会の論文
1966-08-01

火山ガラスの電気的性質と水熱反応性

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