Reaction Bonded Silicon Carbide Production via Laser Sintering and Carbon Impregnation
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Solution Overview
Problem
The existing selective laser sintering (SLS) process for producing reaction-bonded silicon carbide (RBSiC) members results in low fillability and density due to lack of pressure, leading to poor strength and handleability, and previous methods to address this have not successfully produced members with large size and complicated shapes while maintaining excellent ceramic properties.
Innovation Solution
A process involving the use of silicon carbide particles and a binder with a specific weight ratio, laser sintering to form thin layers, impregnation with a carbon source, and subsequent reaction sintering to achieve a RBSiC member with enhanced strength and ceramic properties, where the fired body contains 8% to 30% carbon by weight and uses thermoplastic resins like nylon as binders.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If a green body of silicon carbide is obtained by SLS process using silicon carbide particles and binder as raw materials, then the green body can be formed with complicated shape, but the fillability is low and density is low due to no pressure application
Solution Approach 1:
The patent changes the physical and chemical parameters of the binder system by using a two-stage process: first forming a green body with a thermoplastic binder, then impregnating with a phenolic resin that undergoes curing and carbonization. This transforms the binder from a simple binding agent to a carbon source, enabling both shape retention and high silicon carbide content in the final product.
Solution Approach 2:
The phenolic resin acts as an intermediary material that serves dual purposes: it strengthens the green body structure during handling and provides carbon during subsequent carbonization. This intermediary substance bridges the gap between the need for shape retention and the need for high silicon carbide content.
2Quantity of substance
If the green body is heated to remove the binder, then the binder disappears or shrinks, but the shape of the green body cannot be kept and handleability is poor
Solution Approach 1:
The patent applies preliminary action by impregnating the green body with phenolic resin before the binder removal step. The phenolic resin penetrates the porous structure and provides structural support during subsequent heating and carbonization, preventing shape collapse that would occur with simple binder evaporation.
Solution Approach 2:
The phenolic resin undergoes phase transitions including curing (chemical crosslinking), carbonization (conversion to carbon), and potential graphitization. These phase transitions transform the resin from a liquid impregnation medium to a solid structural component that maintains green body integrity during heating.
3Strength
If epoxy resin is used for impregnation and sintering, then the green body strength is improved, but the RBSiC member does not possess excellent ceramic properties such as rigidity and strength
Solution Approach 1:
The patent changes the chemical composition parameter by replacing epoxy resin with phenolic resin as the impregnation medium. Phenolic resin, when carbonized, provides carbon that reacts with silicon to form silicon carbide, thereby improving the ceramic properties of the final RBSiC member while maintaining green body strength during processing.
Solution Approach 2:
The final RBSiC member is a composite material consisting of silicon carbide particles, carbon from the phenolic resin, and silicon matrix. This composite structure provides excellent ceramic properties including high rigidity, strength, and thermal stability, unlike epoxy-based composites.
4Quantity of substance
If the amount of carbon impregnated is not controlled, then silicon infiltration is insufficient or cracking occurs during reaction sintering, but excellent RBSiC member cannot be obtained
Solution Approach 1:
The patent implements feedback control by carefully controlling the carbon content from phenolic resin impregnation to be within 8-30 wt%, which optimizes the subsequent silicon infiltration and reaction sintering processes. This controlled carbon amount ensures complete silicon infiltration and prevents cracking during the exothermic reaction sintering process.
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 enables the production of RBSiC members with high density, rigidity, and strength, suitable for large and complex shapes, while preventing cracking and maintaining excellent ceramic properties, making them suitable for high-temperature and high-rigidity applications.
Implementation Method 1
forming a thin layer of the raw material, and sintering the thin layer by irradiating a desired area in the thin layer with laser
Implementation Method 2
sintering the thin layer by irradiating a desired area in the thin layer with laser to form a sintered thin layer
Implementation Method 3
impregnating the green body with an assisting agent containing a carbon source
Implementation Method 4
carbonizing organic compound components contained in the cured body to give a fired body
Implementation Method 5
infiltrating the fired body with silicon
Implementation Method 6
subjecting the fired body infiltrated with silicon to reaction sintering
Data Source
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AI summary
Disclosed is a process for producing a RBSiC member that has a large size and a complicated shape and possesses ceramic properties. The process is a Selective Laser Sintering process which includes providing a raw material containing silicon carbide particles and a binder, forming a thin layer of the raw material, and sintering the thin layer by irradiating a desired area in the thin layer with laser to form a sintered thin layer, repeating the step of forming the sintered thin layer to obtain a green body, impregnating the green body with a carbon source and curing the green body impregnated with the carbon source to give a cured body, carbonizing an organic compound component in the cured body to give a fired body, infiltrating the fired body with silicon, and subjecting the fired body to reaction sintering to give a RBSiC member, wherein the fired body contains 8% to 30% by weight of carbon.