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Li_2O-Al_2O_3-SiO_2 system low thermal expansion glass

Author: LiuShuJiang
Tutor: LuAnXian
School: Central South University
Course: Materials Science
Keywords: glass-ceramics nucleating agent thermal treatment phase-separation thermal expansion coefficient mechanics property
CLC: TQ171
Type: Master's thesis
Year: 2004
Downloads: 402
Quote: 1
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Abstract


According to Rusum Roy and E.F.Osborn’s Li2O-Al2O3-SiO2 system glass phase diagram, a set of compositions of LAS system glass-ceramics doped P2O5; TiO2 as nucleating agent were designed. The homogeneous and colorless base glasses were prepared at the lower temperature of 1450 σ for Ih, and the glass-ceramic materials were obtained by using of the one-stage and two-stage heating treatment way. The microstructure of the glass-ceramics was studied by DTA, IR, XRD, SEM etc. The result shows that, as far as the two-stage heating treatment, the crystalline phase of glass-ceramics with TiO2is same as that of the glass-ceramics with P2Os, the main crystals are -quartz S.S, which contributed to the lower thermal expansion coefficient of these glass-ceramics; but the crystallization conduct, appearance, microstructure and mechanics properties of two kinds of glass are different. The glass with TiO2 crystallizes rapidly, the particles are isolated, with small particle size, as a result, the glass-ceramics’ mechanics property is very poor. While the mechanics property of glass-ceramics with P2O5 is better than that of the glass with TiO2, and the crystals grow slowly. Its particle size is bigger and these particles form denser microstructure, therefore it possesses excellent mechanics properties. As far as the one-stage heating treatment, appearance, microstructure and physical properties of the glass with P2O5 changed with the increasing of thermal treatment temperature. During the initial stage, namely when the temperature is very low, phase-separation arises, and the activation energy of the glass crystallization is lowered. Phase-separation provides good condition for the growth of nucleus. Then sub-stable phase 13 -quartz S.S. with low coefficient of thermal expansion appeared. The transparent or semi-transparent glass-ceramics can be easily obtained by controlling the particle size of micro-crystals in the glasses. With the increasing of thermal treatment temperature, sub-stable phase begins to gather together and transforms into stable phase -spodumene S.S.. The size of particles grows bigger and the transparent property of glass-ceramics disappeared. The glass-ceramics withexcellent strength can be easily obtained by controlling the transform of micro-crystals.

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