Carbon-Carbon Antioxidant Coating for High-Temperature Oxidation
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Solution Overview
Problem
Carbon-carbon composite materials used in high-temperature applications, such as aircraft brake discs, are susceptible to oxidation and deterioration of physio-mechanical properties, particularly due to external oxidation and internal oxidant ingress.
Innovation Solution
A carbon-carbon composite substrate is treated with an antioxidant coating including ytterbium disilicate and a sintering aid, applied on a bond coat disposed on the non-friction surface, which reduces oxidation at the external surface and prevents internal oxidation by matching the coefficient of thermal expansion with the substrate and bond coat, ensuring thermal stability up to 3000°F (1645°C).
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If carbon-carbon composite is used in high temperature applications, then high temperature performance is improved, but oxidation resistance deteriorates
Solution Approach 1:
The patent applies a multi-layer coating system comprising a bond coat and an antioxidant top coat on the carbon-carbon composite substrate. This composite material approach combines different materials with complementary properties: the bond coat provides thermal stability and adhesion, while the antioxidant top coat (containing materials like B4O3, B2O3, SiO2, and Al2O3) provides oxidation resistance at high temperatures, thus resolving the contradiction between high temperature performance and oxidation resistance.
Solution Approach 2:
The antioxidant top coat creates a protective barrier that effectively creates an inert environment around the carbon-carbon composite substrate. The coating materials (particularly the borates and silicates) form stable oxide layers that prevent oxygen from reaching and oxidizing the underlying carbon substrate, thereby protecting the material in a chemically inert environment even at high temperatures.
2Reliability
If antioxidant coating is applied to prevent oxidation, then oxidation resistance is improved, but coating adhesion deteriorates
Solution Approach 1:
The bond coat serves as an intermediary layer between the carbon-carbon composite substrate and the antioxidant top coat. This intermediate layer provides chemical compatibility and strong adhesion to both the substrate and the top coat, ensuring that the antioxidant coating remains firmly attached while providing its protective function. The bond coat acts as a mediator that bridges the interface between dissimilar materials.
Solution Approach 2:
The multi-layer coating structure itself is a composite material system designed to combine adhesion properties with oxidation resistance. The bond coat is formulated with materials that adhere well to carbon substrates, while the top coat provides oxidation protection, and together they form a composite coating system where each layer contributes its specific functional properties.
3Reliability
If thick antioxidant coating is applied to prevent internal oxidation, then oxidation protection is improved, but thermal stress resistance deteriorates
Solution Approach 1:
The antioxidant top coat is applied as a relatively thin layer (typically 1-10 micrometers) rather than a thick coating, providing sufficient oxidation protection while minimizing thermal mass and thermal stress accumulation. The protective function is achieved with minimal coating thickness, maintaining local quality where protection is needed without the adverse effects of excessive thickness.
Solution Approach 2:
The coating system is designed with specific material compositions and thickness parameters optimized for thermal stress resistance. The bond coat and top coat materials are selected and formulated to have thermal expansion coefficients compatible with the carbon-carbon substrate, and the layer thicknesses are controlled to minimize thermal stress while maintaining adequate protection.
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 antioxidant coating effectively prevents oxidation and maintains the mechanical integrity of carbon-carbon composite materials at high temperatures, reducing the risk of delamination, spallation, and cracking, thereby extending the usable life of components like brake discs.
Implementation Method 1
the antioxidant coating may be configured to reduce oxidation at an external surface of the C-C composition
Implementation Method 2
reduce ingress of oxidants into pores or other open passages defined by the C-C composite substrate to avoid internal oxidation
Implementation Method 3
The antioxidant coating includes ytterbium disilicate and a sintering aid
Data Source
Figure 1~2
Figure 3
AI summary
An article including carbon-carbon composite substrate is treated with an antioxidant coating prior to use in an oxidizing environment. The antioxidant coating is configured to reduce oxidation at an external surface of the C-C composite and reduce ingress of oxidants into pores or other open passages defined by the C-C composite substrate to avoid internal oxidation. The article includes a C-C composite substrate, a bond coat, and an antioxidant coating. The C-C composite substrate defines a friction surface and a non-friction surface. The bond coat is disposed on the non-friction surface. The antioxidant coating is disposed on at least a portion of the bond coat. The antioxidant coating includes ytterbium disilicate and a sintering aid.