| Co-Investigator(Kenkyū-buntansha) |
MAEDA Yonezo Kyushu University, Department of Chemistry, Faculty of Science, Professor, 理学部, 教授 (30037262)
HARA Kazuhiro Kyushu University, Department of Applied Science, Faculy of Engineering, Associa, 工学部, 助教授 (00180993)
ICHIKAWA Fusao Kyushu University, Department of Physics, Faculty of Science, Research Associate, 理学部, 助手 (30223085)
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| Research Abstract |
Heat treatment of glass causes a structural change from glass to glass-ceramics, in which several crystalline particles with 'nanometer size' are precipitated. This structural change, I.e., crystallization of glass, brings about a drastic change of electrical conductivity, magnetism, optical transparency, etc. The present study was carried out in order to elucidate the mechanism of crystallization and the correlation between the structure and physical prperties of glass-ceramics by means of Mossbauer effect, FT-IR,magnetic susceptibility, XRD,and DTA.As a result, following conclusions could be obtained :
1) Heat treatment of semiconducting 25K_2O・65V_2O_5・10Fe_2O_3 glass at around the crystallization temperature (Tc) for a short time (10-30 min) results in a jump of the electrical conductivity from the order of 10^<-8> S・cm^<-1> to the order of 10^<-4> S・cm^<-1>, owing to the structural relaxation. After a prolonged heat treatment, the electrical conductivity decreases owing to the prec
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ipitation of an insulating crystalline phase.
2) Heat treatment of IR-transmitting aluminate glasses, 60CaO・27Al_2O_3・13Fe_2O_3 and 60CaO・10BaO・17Al_2O_3・13Fe_2O_3, at around the Tc causes a decrease in the IR-transmittance and that of magnetic susceptibility owing to the precipitation of 'nanoparticles' of antiferromagnetic Ca_2Fe_2O_5.
3) Activation energy (Ea) required for the crystallization is equal to the bond energies of the structural units (e.g., Ca-O and Al-O bonds), indicating that cleavage of the chemical bonds triggers the crystallization. The value of Ea is reduced to 2.6 eV in the case of vanadate and tungstate glsses containing iron (Fe (III), being equal to the Fe-O bond energy.
4) Glass transition temperature (Tg) is in proportion to the magnitude of quadrupole splitting (DELTA), one of the Mossbauer parameters, as discovered by Nishida et a1. ("Tg-DELTA rule", 1990). Heat treatment of silicate glass at around the Tg results in a concordant decrease of Tg with the DELTA of Fe (IlI), owing to the structural relaxation associated with a decrease in the distortion of SiO_4 and FeO_4 tetrahedra.
5) The " Tg-DELTA rule", originally discovered for several inorganic glasses containing several mol% of Fe_2O_3, holds for the 'ferrate glasses containing a large amount (-30 mol%) of Fe_2O_3. Less
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