Effects of Borosilicate Glass on Densification and Properties of Borosilicate Glass + TiO 2 Ceramics
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Effects of borosilicate glass on densification and properties of borosilicate glass 1 TiO2 ceramics Jau-Ho Jean and Shih-Chun Lin Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu, Taiwan, Republic of China (Received 19 December 1997; accepted 28 September 1998)
Effects of borosilicate glass (BSG) on densification and dielectric and thermal expansion properties of a binary composite of BSG 1 TiO2 ceramics have been investigated. Two different phases of TiO2 including anatase and rutile are used. A much greater densification is observed with anatase because it has a much better wetting with BSG than rutile. With increasing BSG content, the densification of BSG 1 TiO2 increased. Activation analysis shows that the densification is controlled by viscous flow of BSG. Both dielectric constant and coefficient of thermal expansion of the binary composite of BSG 1 TiO2 increase with decreasing BSG content and increasing the degree of anatase-to-rutile transformation, as well.
I. INTRODUCTION
It has been previously demonstrated that the densification of glass 1 ceramics can be described by conventional three-stage liquid phase sintering,1–9 i.e., particle rearrangement, dissolution and precipitation, and solid state sintering. Depending upon the reactivity between glass and ceramics, the densification of glass 1 ceramics can be further classified as nonreactive, partially reactive, and completely reactive systems. Little dissolution of ceramic filler in glass during firing is observed for nonreactive systems, such as borosilicate glass (BSG) 1 cordierite6 in which the densification is mainly achieved by particle rearrangement. The required amount of glass content to achieve densification decreases with increasing the particle size ratio between ceramic filler and glass.7 For partially reactive systems such as BSG 1 alumina,8 the dissolution of ceramic filler in glass is localized and limited, and no particle growth and shape accommodation are observed. The required BSG content to achieve densification is close to that of nonreactive systems such as BSG 1 cordierite.6,7 A global dissolution of ceramic filler in a low-softening glass is found for completely reactive systems including BSG 1 high silica glass (HSG)9 in which the required BSG content, i.e., 20 –40 vol%, to obtain high densification is much lower than that needed for nonreactive and partially reactive systems, i.e., 40 –60 vol%.6–8 A lower and slower densification results when larger BSG or ceramic filler particle is used for a completely reactive system.9 In this study, which is an extension of an earlier effort on the densification kinetics and mechanism of nonreactive (BSG 1 cordierite6,7 ), partially reactive (BSG 1 alumina8 ) and reactive (BSG 1 HSG9 ) glass 1 ceramics systems, a nonreactive system of BSG 1 TiO2 J. Mater. Res., Vol. 14, No. 4, Apr 1999
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is investigated. To densify TiO2 ceramics at temperatures lower tha
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