Self-Healing Coating for C/C Composites Above 1450°C
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Solution Overview
Problem
Current protective coatings for thermostructural composite materials, particularly those containing carbon, lose effectiveness above 1450°C due to the volatilization of B2O3, leading to insufficient wettability and the inability to form a continuous protective film, necessitating additional complex steps like silicon carbide underlayer formation.
Innovation Solution
A single-step method for applying a self-healing composition comprising a borosilicate system, silicon carbide grains, and ultra-refractory oxides, which forms a continuous protective film at temperatures above 1450°C by transitioning from a borosilicate to a silicate self-healing phase, ensuring effective oxidation protection without the need for a silicon carbide underlayer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a borosilicate-based self-healing coating is used to protect carbon composite parts, then effective oxidation protection is achieved at temperatures up to 1450°C, but above 1450°C the B2O3 volatilizes completely causing loss of wettability and inability to form a continuous protective film
Solution Approach 1:
The patent modifies the chemical composition parameters of the protective coating by incorporating specific ratios of B2O3 (20-40 wt%), SiO2 (30-50 wt%), and ultra-refractory oxides (10-30 wt%). This parameter adjustment allows the coating to maintain protective properties at temperatures above 1450°C where conventional borosilicate coatings fail due to complete B2O3 volatilization.
Solution Approach 2:
The patent creates a composite protective coating system combining borosilicate glass (for self-healing properties below 1450°C), silica (for high-temperature stability), and ultra-refractory oxides (for maintaining structural integrity above 1450°C). This composite approach allows the coating to function effectively across a broader temperature range by leveraging the complementary properties of different materials.
2Duration of action of stationary object
If metallic borides like TiB2 or ZrB2 are added to regenerate B2O3, then protection is extended to 1350°C, but above 1450°C complete volatilization of B2O3 still occurs leading to loss of protective effectiveness
Solution Approach 1:
The patent adjusts the composition parameters to include ultra-refractory oxides (10-30 wt%) such as Al2O3, ZrO2, or HfO2 with melting points above 2000°C. These materials do not volatilize at temperatures above 1450°C and provide a stable structural framework that maintains coating integrity even when B2O3 is completely volatilized, thereby extending the maximum effective temperature beyond 1450°C.
3Reliability
If a silicon carbide underlayer is formed to enable protection above 1450°C, then high-temperature protection is achieved, but the manufacturing process becomes more complex requiring additional shaping steps
Solution Approach 1:
The patent merges the functions of the underlayer and topcoat by incorporating ultra-refractory oxide particles directly into the borosilicate-based self-healing coating formulation. This single-layer composite structure eliminates the need for separate underlayer formation steps while providing both adhesion to the carbon substrate and high-temperature stability above 1450°C, thereby reducing manufacturing complexity.
Solution Approach 2:
The patent creates a universal protective coating that performs multiple functions: (1) provides self-healing properties through borosilicate glass below 1450°C, (2) maintains structural integrity through ultra-refractory oxides above 1450°C, and (3) ensures adhesion to carbon substrates through B2O3-mediated wettability. This multi-functional coating eliminates the need for separate specialized layers for different temperature ranges.
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 provides sustained protection against oxidation at high temperatures by maintaining wettability and forming a continuous film, even after B2O3 disappearance, with the silicon carbide grains ensuring protection above 1450°C and the ultra-refractory oxides adapting the glass composition for optimal viscosity and barrier performance.
Implementation Method 1
Boron oxide (B2O3) is the essential component of boron-based protective compositions. It has a relatively low melting point (approximately 450°C) and its presence ensures proper wettability of the carbon surface to be protected.
Implementation Method 2
A self-healing composition is defined as one that, by becoming viscous at the part's operating temperature, can seal cracks that may form in the coating or protective layer.
Implementation Method 3
These borides are capable of gradually reforming B2O3 through oxidation as it volatilizes.
Implementation Method 4
titanium diboride (TiB2) acts as a regenerator of B2O3, since, following its progressive oxidation starting at 550°C and accelerating from 1100°C, TiB2 compensates for the loss of B2O3 by generating B2O3 + TiO2.
Implementation Method 5
protection against oxidation is essential to prevent rapid deterioration of parts made from such composite materials when these parts are used in oxidizing atmospheres at temperatures exceeding 350°C
Data Source
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AI summary
In order to produce a self-healing layer on a part made of a composite, a composition is applied to the part, which composition contains: - a colloidal silica suspension, - boron or a boron compound in powder form, - silicon carbide in powder form, and - at least one ultra-refractory oxide.