Influence of Sodium Fluoride on the Crystallization Behavior of Machinable MgO-Al2O3-SiO2 Glass-Ceramics.

• Main Authors: CHEN CHIEN-TING, 陳建庭
• Other Authors: Shun-tian Lin
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/66137980746204035557

碩士 === 國立臺灣科技大學 === 材料科技研究所 === 92 === Abstract Mica-containing glass-ceramics are unique because they possess the unusual property of machinability, they can be machined to precise tolerance and surface finish with conventional metal-working tools. Transparent and clear glasses were prepared from the MAS system (based on MgO-Al2O3-SiO2) with different fluorine contents. Their crystallization behavior to giving mica glass-ceramics upon heat treatment was studied as a function of the source of fluorine and its concentration. For this study, glasses having weight-percentage compositions of；SiO2 34.7-38.1；B2O3 10.2-11.3；Al2O3 14.8-16.3；MgO 22.5-24.7；K2CO3 4.1- 4.5；CaCO3 0.1 and sodium fluoride (NaF) as additive, and added with 5wt﹪，9.5wt﹪，13.6wt﹪separately，The batch ingredients were gotten together and thereafter melt in close crucible for about 5 hours in an electrically fired furnace operating at 1450℃. Preparing three groups all contained those samples, and having two of them expose to heat treatment for four hours at 700℃ and 1100℃ individually, while the other one maintained the original form. Trying to find out influence of sodium fluoride on crystallization behavior machinable glass-ceramics. SEM observation shows that sample contained crystalline mica platelets that range in diameter from about 1.2μm to 2.5μm. The Vickers hardness data clearly show that the hardness of these glass-ceramics decrease as the mica platelets increased. The sodium fluoride (NaF) contents increased while the values of thermal expansion coefficient increased. Temperature of heat treatment also increased while the values of thermal expansion coefficient increased. Two kinds of content（9.5wt﹪,13.6wt﹪） heat treated for 4 hours at 1100℃.It can be found that the experimental samples have machineability, or the fluorophlogopite mica crystals make the material machinable.