Environmental Barrier Coating Sintering Aids
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Solution Overview
Problem
Current environmental barrier coatings for high temperature ceramic components in gas turbine engines are inadequate in protecting against high temperature steam environments, leading to oxidation and volatilization issues, and existing coating processes often require high temperatures that can damage the components.
Innovation Solution
A method involving the use of sintering aids, such as rare earth nitrate and ammonium phosphate, to create a densified environmental barrier coating with a transition layer and an outer layer, applied via a slurry deposition process that lowers the sintering temperature and promotes a hermetic seal, using a combination of mullite and BSAS with specific porosity levels to enhance durability and resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If standard industrial coating processes (plasma spray, vapor deposition) are used to apply EBCs, then the coating can be applied to ceramic components, but the process requires high temperatures that can damage the components and the coating may not provide adequate protection against high temperature steam
Solution Approach 1:
A transition layer comprising mullite or a mullite/BSAS mixture is applied between the ceramic component and the outer BSAS layer. This intermediary layer enables the coating system to function at lower sintering temperatures while providing adequate protection against oxidation and steam attack, resolving the contradiction between protection reliability and temperature requirements.
Solution Approach 2:
The invention changes the chemical composition parameters of the coating system by incorporating specific sintering aids (rare earth oxides, phosphates, borates) in controlled amounts. These compositional changes enable densification and hermetic sealing at reduced sintering temperatures, achieving both protection reliability and lower temperature processing.
2Reliability
If the coating is made highly dense to prevent oxidation and volatilization, then protection against corrosive gases is improved, but the manufacturing process becomes more complex and costly
Solution Approach 1:
Chemical composition parameters are optimized by incorporating sintering aids (rare earth oxides, phosphates, borates) in specific amounts (0.1-10 wt% of primary material). These compositional changes enable the coating to achieve hermetic density through a simplified slurry deposition and sintering process, reducing manufacturing complexity while maintaining protection reliability.
3Reliability
If the coating is made highly dense to prevent oxidation and volatilization, then protection against corrosive gases is improved, but the manufacturing cost increases
Solution Approach 1:
The invention optimizes chemical composition parameters by using relatively small amounts of sintering aids (0.1-10 wt% of primary material) combined with common, cost-effective materials like mullite and BSAS. This parameter optimization achieves hermetic sealing at lower sintering temperatures through slurry deposition, reducing manufacturing cost while maintaining protection reliability.
Solution Approach 2:
The invention replaces complex mechanical coating processes (plasma spray, vapor deposition) with a chemical slurry deposition process. This substitution simplifies manufacturing operations and reduces equipment costs while achieving the same hermetic sealing function through chemical composition control and lower temperature sintering.
4Adaptability or versatility
If conventional coating materials are used, then the coating can be applied using existing processes, but the coating does not provide adequate protection against high temperature steam environments
Solution Approach 1:
The chemical composition parameters of conventional coating materials are modified by incorporating sintering aids (rare earth oxides, phosphates, borates) in optimized amounts. These parameter changes enhance the coating's resistance to steam attack and enable hermetic sealing at lower temperatures, improving protection reliability while maintaining compatibility with existing slurry deposition and sintering processes.
Solution Approach 2:
The invention creates a composite coating system consisting of a transition layer (mullite or mullite/BSAS mixture) and an outer layer (BSAS with sintering aids). This composite structure combines the benefits of conventional materials with enhanced steam resistance, achieving both adaptability to existing processes and improved protection reliability.
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 method results in a highly dense coating that effectively seals against high temperature steam, preventing oxidation and volatilization, while reducing the risk of mechanical property degradation and offering cost savings through the slurry deposition process, with improved uniformity and ability to apply to complex geometries.
Implementation Method 1
sintering the component to produce the environmental barrier coating having at least a transition layer and an outer layer
Implementation Method 2
the remaining insoluble portion reacts with the primary material of the least one of the transition layer slurry or the outer layer slurry to form a secondary material
Implementation Method 3
the slurry sintering aid exceeding the amount of slurry sintering aid soluble in the primary material of the at least one of the transition layer slurry or the outer layer slurry to leave a remaining insoluble portion
Implementation Method 4
EBCs can provide a dense, hermetic seal against the corrosive gases in the hot combustion environment, which can rapidly oxidize silicon-containing CMCs and monolithic ceramics
Implementation Method 5
silicon oxide is not stable in high temperature steam, but is converted to volatile (gaseous) silicon hydroxide species. Thus, EBCs can help prevent dimensional changes in the ceramic component due to such oxidation and volatilization processes
Data Source
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AI summary
A method for making an environmental barrier coating (12) using a sintering aid comprising: combining at least water, and a primary transition material comprising mullite, BSAS, or a mullite/BSAS mixture to produce a transition layer slurry; applying the transition layer slurry to a ceramic component (10); combining at least water, and a primary outer material comprising BSAS to produce an outer layer slurry; applying the outer layer slurry to the component having the applied transition layer slurry; and sintering the component to produce the environmental barrier coating having at least a transition layer (16) and an outer layer (18) wherein at least one of the transition layer slurry or the outer layer slurry comprises a slurry sintering aid and wherein the transition layer comprises a porosity of from 0% to about 30% by volume of the transition layer, and the outer layer comprises a porosity of from 0% to about 15% by volume of the outer layer.