Ceramic Matrix Composite Prepregs via Slurry Viscosity Control
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Solution Overview
Problem
The challenge in creating ceramic matrix composites is achieving complete and homogeneous impregnation of ceramic fibers with high particle loading slurries, which typically have high viscosity, making it difficult to form complex shapes without the use of binders that limit mobility and drapability, and result in irreversible gel formation.
Innovation Solution
A process involving impregnating ceramic fibers with a slurry containing 10-40 vol% ceramic powder, 10-20 wt% glycerol, and 0-2 wt% organic binder, followed by reducing water content to increase ceramic powder volume ratio to 45 vol% or more, allowing for tacky and flexible prepregs that can be easily shaped and laminated without high pressure, and sintered to form a self-supporting ceramic matrix composite.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high particle loading slurry is used to increase green-density, then shrinkage during sintering is prevented, but viscosity increases making complete impregnation of ceramic fibers difficult
Solution Approach 1:
The patent changes the chemical composition parameters of the slurry by introducing specific organic additives (polyvinyl alcohol, carboxymethyl cellulose, starch) and controlling the water-to-powder ratio. These parameter changes reduce slurry viscosity while maintaining high particle loading (40-60 wt%), enabling both complete fiber impregnation and high green-density that prevents sintering shrinkage.
Solution Approach 2:
The patent uses organic additives (polyvinyl alcohol, carboxymethyl cellulose, starch) as intermediary substances that act as viscosity modifiers and binding agents. These intermediaries enable the slurry to maintain high particle loading while remaining fluid enough for complete fiber impregnation, resolving the contradiction between shrinkage prevention and impregnation completeness.
2Strength
If binder is added to improve green-body strength and handling, then mechanical properties improve, but fiber mobility and drapability are limited due to gel formation
Solution Approach 1:
The patent carefully controls the concentration parameters of organic additives (0.5-5 wt% polyvinyl alcohol, 0.5-5 wt% carboxymethyl cellulose, or 1-10 wt% starch) to provide sufficient green-body strength while preventing excessive gel formation. This parameter optimization maintains fiber mobility and drapability for complex shape formation.
Solution Approach 2:
The patent applies different organic additives at different concentrations in specific regions or stages of the composite formation process. The binders provide localized strength where needed while maintaining overall fiber mobility, allowing the material to exhibit different properties in different contexts (strength during handling, flexibility during shaping).
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 method enables the production of ceramic matrix composites with high fiber content and mechanical advantages, allowing for complex shapes and reduced shrinkage during sintering, while maintaining flexibility and reversibility for improved handling and storability.
Implementation Method 1
The viscosity of a slurry used for the impregnation of ceramic fibers in ceramic fiber reinforced ceramic materials should be low in order to allow a complete and homogeneous impregnation of the fiber structure to be achieved. The consolidated slurry forms the matrix. Shrinkage of the matrix during sintering has to be prevented
Implementation Method 2
reducing the water content in the slurry which is retained by the arrangement of ceramic fibers after impregnation so as to increase the volume ratio of the ceramic powder in the slurry
Implementation Method 3
The matrix is generally synthesized via impregnation of continuous fiber bundles with ceramic slurries, followed by the winding and/or the lamination of the infiltrated fiber bundles to yield a desired shape
Data Source
Figure 1~2
Figure 3
AI summary
The present invention provides a process for the preparation of a prepreg for a ceramic matrix composite material, said process comprising the steps of: a) impregnating an arrangement of ceramic fibers with a slurry of a ceramic powder, which slurry contains: 10 to 40 vol%, based on the total volume of the slurry, of the ceramic powder, 10 to 20 wt%, based on the total weight of the ceramic powder in the slurry, of glycerol, 0 to 2 wt%, based on the total weight of the ceramic powder in the slurry, of an organic binder, and water; b) reducing the water content in the slurry which is retained by the arrangement of ceramic fibers after impregnation so as to increase the volume ratio of the ceramic powder in the slurry and to provide a prepreg containing a slurry of a ceramic powder with a volume ratio of the ceramic powder of 45 vol% or more in the slurry. It further provides a prepreg obtainable from the process. In further aspects of the invention, laminates containing the above prepregs and a process for their production are provided. In yet a further aspect, the invention provides a ceramic matrix composite green body and a process for its preparation, and a process for the preparation of a ceramic matrix composite body, using the prepregs or the laminated prepregs in accordance with the invention.