Type of Document Dissertation Author Lee, Kyoung-Ho URN etd-06192006-125732 Title Synthesis and characterization of in situ whisker-reinforced glass-ceramics Degree PhD Department Materials Engineering Science Advisory Committee
Advisor Name Title No Advisors Found Keywords
- Glass-ceramics Mechanical properties
- Glass-ceramics Thermal properties
- Glass-ceramics Synthesis
Date of Defense 1993-04-05 Availability restricted Abstract
The effects of in situ Ti02 whisker reinforcement on mechanical and thermal properties of glass-ceramics in the Li2O-Al203-P206-Si02 system were investigated.
When Ti02 whiskers, having an average aspect ratio of 28, are precipitated from the glass-ceramic matrix, (Lio,4,Cao.o5)AI(Si0.75>/sub>,P0.5)04.5, flexural strength is improved from 72 to 134 MPa. Fracture toughness, KIc, is increased from the 1.1 to 1.6 MPa·m1/2 due to crack deflection by the Ti02 whiskers. In situ Ti0sub>2 whisker-reinforced glass-ceramic exhibits rising fracture resistance, KR, with increasing crack extension. The fracture resistance, KR, is increased from 1.89 to 2.5 MPa·m1/2 over the crack extension range range of 40 to 200 μm. The composite shows a narrow failure strength distribution compared to the glass-ceramic without Ti02 whisker precipitation. The coefficient of thermal expansion (CTE) changes from -2.8x10-7/∘C to -1.7xl0-7/∘C due to the precipitation of Ti02 phase which has a positive CTE (7.3xl0-6/∘C).
With the matrix composition, (Li0.41,Mg0.035)AI(Si00.48,PO.52)O4, a three-fold increase in flexural strength was observed with a Ti02 content of 12 wt%. CTE value of the composite increases linearly from a negative to a positive value with increasing Ti02 content up to 12 wt%. The in situ composite containing 8-10 wt% Ti02 exhibits near zero CTE values up to l000°C.
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