Thermostructural Composite Siliciding via Aerogel Pore Segmentation
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Solution Overview
Problem
Thermostructural composite materials face challenges in achieving uniform and controllable siliciding due to random pore filling and the formation of inaccessible pores, leading to irregular thermal diffusivity and leakproofing.
Innovation Solution
The method involves forming an aerogel or xerogel precursor within the pores of the composite material, which is then pyrolyzed to create a refractory material, allowing for regular and reproducible siliciding by impregnating with a molten silicon phase that penetrates uniformly through the subdivided pores.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If molten silicon is used to impregnate the composite material, then the fluidity and wetting ability improve, but the pore filling becomes random and uncontrollable
Solution Approach 1:
The invention divides the pore space into two distinct zones: a macroporous outer phase that allows silicon infiltration and a microporous inner phase that prevents uncontrolled silicon penetration. This segmentation is achieved by forming a carbonaceous material in the microporous phase that acts as a barrier, thereby controlling the extent and uniformity of silicon filling while maintaining good wetting properties.
Solution Approach 2:
The invention applies different properties to different regions of the composite material. The outer macroporous phase maintains high porosity for silicon access, while the inner microporous phase is filled with carbonaceous material to restrict silicon penetration. This local differentiation of pore characteristics enables controlled silicon impregnation with uniform distribution.
2Manufacturing precision
If conventional liquid technique or gas technique is used for densification, then the material can be densified, but the process requires extended time to achieve maximum density
Solution Approach 1:
The invention performs preliminary action by forming a carbonaceous material in the microporous inner phase before silicon impregnation. This pre-formed barrier structure enables subsequent rapid silicon infiltration into the macroporous phase without requiring extended processing time to achieve maximum density, as the silicon is directed to the appropriate regions where it can efficiently densify the material.
3Ease of operation
If molten silicon flows along macropore surfaces, then the fluid flow is maintained, but the macropores remain unfilled and thermal diffusivity cannot be controlled
Solution Approach 1:
The invention segments the pore structure into macroporous and microporous phases with distinct functions. The microporous inner phase is filled with carbonaceous material that restricts silicon flow, forcing silicon to fill the macropores rather than merely flowing along their surfaces. This segmentation enables both maintained fluid flow during impregnation and controlled thermal diffusivity in the final product.
4Shape
If carbon grains are formed in micropores or constrictions, then the pore structure is modified, but the silicon reacts with carbon increasing grain volume and closing pores
Solution Approach 1:
The invention applies local quality by selectively forming carbonaceous material only in the microporous inner phase, while keeping the macroporous outer phase free of carbon grains that would block silicon access. This spatial differentiation ensures that silicon can freely access and fill macropores without reacting with carbon in constriction zones, maintaining pore accessibility while achieving desired structural modification.
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
This approach results in uniform thermal conductivity, leakproofing, and tribological properties, eliminating oxidizable carbon phases and forming a nanoarray of ceramic particles, enhancing the material's mechanical and thermal characteristics.
Implementation Method 1
which is then pyrolyzed to create a refractory material
Implementation Method 2
impregnating with a molten silicon phase that penetrates uniformly through the subdivided pores
Implementation Method 3
in impregnating it with molten silicon that then reacts with the carbon in order to form silicon carbide
Data Source
AI summary
Within the pores of a porous thermostructural composite material, there is form an aerogel or xerogel made up of a precursor for a refractory material, the precursor is transformed by pyrolysis to obtain an aerogel or xerogel of refractory material, and then it is silicided by being impregnated with a molten silicon type phase. The aerogel or xerogel is formed by impregnating the composite material with a composition containing at least one organic, organometalloid, or organometallic compound in solution, followed by in situ gelling. The method is applicable to improving the tribological properties or the thermal conductivity of C/C or C/SiC composite material parts, or to making such parts leakproof.