Cyclosilicate Glass-Ceramic Sealing with Tailored Thermal Expansion
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Solution Overview
Problem
Current sealing materials and coatings for metals and ceramics lack high thermal stability, mechanical strength, and tailored thermal expansion coefficients, which are essential for high-temperature applications and hermetic seals.
Innovation Solution
Development of highly crystallized frit-sintered glass-ceramics with cyclosilicate crystal structures, specifically compositions containing silicon dioxide, calcium, barium, and strontium oxides, which offer high thermal expansion coefficients and stability up to 1450°C, and can be tailored to match the thermal expansion of various substrates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional sealing materials are used, then ease of manufacture is maintained, but thermal stability and mechanical strength are insufficient for high-temperature applications
Solution Approach 1:
The patent employs glass-ceramic composite materials that combine glassy phases with crystalline phases (specifically cyclosilicate crystals). This composite structure provides both high thermal stability and reliable sealing performance, resolving the contradiction between temperature resistance and sealing reliability. The glassy matrix binds the crystalline phases while providing chemical stability and sealability.
Solution Approach 2:
The patent systematically varies compositional parameters (ratios of SiO2, Al2O3, CaO, MgO, and other oxides) and processing parameters (heating rates, holding temperatures, and cooling rates) to achieve glass-ceramics with tailored thermal expansion coefficients and high-temperature stability. This parameter optimization enables the material to maintain sealing integrity at elevated temperatures.
2Adaptability or versatility
If high thermal expansion coefficients are desired for matching substrates, then adaptability improves, but material complexity increases
Solution Approach 1:
The patent utilizes compositional parameter changes within a defined system (SiO2-Al2O3-CaO-MgO with specific oxide ranges) to achieve a wide spectrum of thermal expansion coefficients. By adjusting the proportions of network formers, modifiers, and intermediates, the material can be tailored to match various substrates without requiring fundamentally different material systems.
Solution Approach 2:
The patent creates local compositional variations through the formation of different crystalline phases (walstromite, cyclo-wollastonite, μ-(Ca,Sr)SiO3) within the glass-ceramic matrix. Each phase contributes differently to thermal expansion, allowing localized adjustment of the overall thermal properties to achieve substrate matching.
3Strength
If high crystallinity is achieved to reduce porosity, then mechanical strength improves, but processing difficulty increases
Solution Approach 1:
The patent incorporates nucleating agents in the glass composition before firing, which create pre-formed nucleation sites that facilitate uniform crystal growth during heat treatment. This preliminary action ensures high crystallinity and mechanical strength while simplifying the processing by reducing the required holding time and temperature control complexity.
Solution Approach 2:
The patent employs multi-stage heat treatment schedules with periodic temperature variations (rapid heating to crystallization temperature, holding period for crystal growth, then controlled cooling). This periodic thermal processing achieves high crystallinity and strength while managing the complexity through standardized cycle patterns.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The glass-ceramic materials provide zero or near-zero porosity, minimal residual glass, and linear thermal expansion curves, ensuring no softening or dimensional changes during thermal cycling, making them suitable for high-temperature applications and hermetic seals with superior mechanical properties.
Implementation Method 1
Glass-ceramics are polycrystalline materials formed by controlled crystallization of a precursor glass article. A glass-ceramic may be prepared by exposing a glass monolith to a thermal treatment for conversion to a crystalline state.
Implementation Method 2
The glass composition, particle size, and processing conditions are chosen such that the glass softens prior to crystallization and undergoes viscous sintering to maximum density just before the crystallization process is completed.
Implementation Method 3
The glass-ceramic materials of the invention can be used as sealing agents and as high performance coating for metals, metal alloys and ceramics... with high thermal expansion coefficients and stability up to 1450°C, and can be tailored to match the thermal expansion of various substrates
Data Source
AI summary
The invention is directed to highly crystalline, frit-sintered glass-ceramic compositions having a coefficient of thermal expansion in the range of 85-115×10−7° C. The primary crystal phases of the glass-ceramics of the invention possess a cyclosilicate structure. The glass-ceramic of the invention are useful as metal-to-metal, metal-to-ceramic and ceramic-to-ceramic sealing agents, and also as high-performance coating for metals and ceramics. In their broadest composition the glass-ceramic contain, in weight percent, 30-55% SiO2, 5-40% CaO, 0-50% BaO, 0.1-10% Al2O3, and 0-40% SrO, wherein the sum of CaO+BaO+SrO is in the range of 35-65 wt. %. Optionally, the glass-ceramic compositions may contain at least one from the group of >0-15 wt. % MgO and >0-10 wt. % ZnO. Also optionally, the glass ceramic compositions may contain >0-10 wt. % of at least one transition metal or rare earth metal oxide.