Variation of Glass-Forming Regions with Cooling Rate in the SiO<sub>2</sub>-Li<sub>2</sub>O System

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  • OTA Rikuo
    Department of Industrial Chemistry, Faculty of Engineering, Kyoto University
  • KOZUKA Hiromitsu
    Department of Industrial Chemistry, Faculty of Engineering, Kyoto University
  • SOGA Naohiro
    Department of Industrial Chemistry, Faculty of Engineering, Kyoto University

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Other Title
  • SiO<sub>2</sub>-Li<sub>2</sub>O系融液の冷却速度によるガラス化領域の変化
  • GeO2 Na2Oケイ ユウエキ ノ レイキャク ソクド ニ ヨル ガラス
  • SiO2 Li2Oケイ ユウエキ ノ レイキャク ソクド ニ ヨル ガラスカ

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The glass-forming regions in the SiO2-Li2O system have been determined by cooling the melts containing 35-81mol% SiO2 from liquidus temperature to room temperature at cooling rates; Q1=4×10-2, Q2=1.4×10-1, Q3=4×10-1, Q4=3, Q5=19, Q6=4.4×102 and Q7≅105K/s. In the composition range SiO2=35-75mol%, the glass-forming region expanded with increasing cooling rate, and the critical cooling rate Q* decreased with increasing silica content, and reached a minimum at SiO2=75mol%. Phase separation was observed in the composition range SiO2>70mol% at cooling rates Q2-Q5. However, the region in which the phase separation takes place decreased with increasing cooling rate, yet persisting in high silica compositions. A linear dependence was found in the log-log plot of liquidus viscosity ηL against Q*. When the logQ*-logηL diagrams are compared with the system B2O3-Li2O, the system SiO2-Li2O system was found to have a higher liquidus viscosity than B2O3-Li2O system for a given critical cooling rate. The difference in the glass-forming ability between the two systems was analyzed in terms of kinetic parameters based on the crystallization formula, and the poor glass-forming ability in the system SiO2-Li2O in comparison with B2O3-Li2O system was elucidated to be due to a smaller fusion entropy in the former. This implies a smaller structural difference upon crystallization of the silicate in comparison with that of the borate.

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