Sealing glass-ceramics with near linear thermal strain, Part II: Sequence of crystallization and phase stability

Journal Article · Wed Jun 01 00:00:00 EDT 2016 · Journal of the American Ceramic Society

DOI:https://doi.org/10.1111/jace.14364· OSTI ID:1253125

Dai, Steve Xunhu ^[1]; Rodriguez, Mark A. ^[1]; Griego, James M. ^[1]

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1. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

A widely adopted approach to form matched seals in metals having high coefficient of thermal expansion (CTE), e.g. stainless steel, is the use of high CTE glass-ceramics. With the nucleation and growth of Cristobalite as the main high-expansion crystalline phase, the CTE of recrystallizable lithium silicate Li₂O–SiO₂–Al₂O₃–K₂O–B₂O₃–P₂O₅–ZnO glass-ceramic can approach 18 ppm/°C, matching closely to the 18 ppm/°C–20 ppm/°C CTE of 304L stainless steel. However, a large volume change induced by the α-β inversion between the low- and high- Cristobalite, a 1^st order displacive phase transition, results in a nonlinear step-like change in the thermal strain of glass-ceramics. The sudden change in the thermal strain causes a substantial transient mismatch between the glass-ceramic and stainless steel. In this study, we developed new thermal profiles based on the SiO2 phase diagram to crystallize both Quartz and Cristobalite as high expansion crystalline phases in the glass-ceramics. A key step in the thermal profile is the rapid cooling of glass-ceramic from the peak sealing temperature to suppress crystallization of Cristobalite. The rapid cooling of the glass-ceramic to an initial lower hold temperature is conducive to Quartz crystallization. After Quartz formation, a subsequent crystallization of Cristobalite is performed at a higher hold temperature. Quantitative X-ray diffraction analysis of a series of quenched glass-ceramic samples clearly revealed the sequence of crystallization in the new thermal profile. In conclusion, the coexistence of two significantly reduced volume changes, one at ~220°C from Cristobalite inversion and the other at ~470°C from Quartz inversion, greatly improves the linearity of the thermal strains of the glass-ceramics, and is expected to improve the thermal strain match between glass-ceramics and stainless steel over the sealing cycle.

• Research Organization: Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA)
• Grant/Contract Number: AC04-94AL85000
• OSTI ID: 1253125
• Alternate ID(s): OSTI ID: 1253126; OSTI ID: 1325915; OSTI ID: 1401691
• Report Number(s): SAND-2016-1103J; SAND-2016-1104J; SAND-2016-9015J; 619184
• Journal Information: Journal of the American Ceramic Society, Journal Name: Journal of the American Ceramic Society; ISSN 0002-7820
• Publisher: American Ceramic Society
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
glass-ceramics
crystals/crystallization
thermal expansion
thermal treatment
phase transformations
phase/transformations