Millable Boron Nitride Paste for Collapse-Resistant Ceramic Cavities
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Solution Overview
Problem
Existing methods for creating cavity structures in ceramic components face issues such as collapse during sintering due to the use of polymers that decompose, and materials like alumina are not suitable for further processing, leading to inadequate mechanical stability and chemical resistance.
Innovation Solution
A millable paste comprising boron nitride, a binding agent, solvent, and a pore-forming agent is used to create cavity structures in ceramic components, which hardens and can be machined, then removed without residue, ensuring internal structures remain open during silicon infiltration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If polymers are used to define patterns and cavities in ceramic material, then the cavity shape is defined during lamination, but the polymer decomposes and volatilizes during sintering causing cavity collapse
Solution Approach 1:
The patent introduces a two-stage system: first a polymer defines the initial cavity shape during lamination, then a refractory material (alumina or silica) is applied as an intermediary shell that maintains the cavity shape during sintering. The polymer serves its purpose and is removed, but the refractory intermediary remains to prevent collapse, solving the contradiction between temporary shape definition and permanent structural support.
Solution Approach 2:
The refractory material is applied in advance before sintering to create a protective shell around the cavity. This preliminary action ensures that when sintering occurs, the cavity is already protected by the refractory material that will prevent collapse, rather than relying on the polymer to withstand the high temperatures.
2Reliability
If alumina is used to define cavity configuration, then the cavity shape is retained during sintering, but the material is not suitable for further processing
Solution Approach 1:
The patent separates the functions of shape definition and final cavity formation. The alumina or silica serves temporarily as a support structure during sintering, then is extracted (removed) after sintering to reveal the final cavity. This allows the material to provide structural support when needed, then be removed when no longer needed, solving the contradiction between shape retention and processing flexibility.
3Strength
If non-sinterable material is used to provide supporting structure, then the shape is guaranteed during sintering, but the material cannot be removed easily
Solution Approach 1:
The patent changes the physical state and properties of the support material through controlled heating. The alumina or silica shell is heated to sintering temperatures, which strengthens it for support during the process, then is subsequently removed through thermal decomposition or mechanical means. The parameter changes (temperature, strength) are controlled to achieve both strong support during sintering and easy removal afterward.
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 paste maintains cavity structures during sintering and allows for further processing, providing ceramic components with internal channels and coils that are mechanically and chemically stable, suitable for applications like heat exchange systems.
Implementation Method 1
a pore-forming agent is present in 20-40 wt%, wherein the sum of all ingredients adds up to 100 wt%
Implementation Method 2
the paste comprises 20-60 wt% of boron nitride, 20-30 wt% of a binding agent
Data Source
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AI summary
The present invention relates to a millable paste for obtaining cavity structures in a ceramic substrate comprising 20-60 wt% of boron nitride, 20-30 wt% of a binding agent, 0-30 wt% of a solvent, 20-40 wt% of a pore-forming agent, wherein the sum of all ingredients always adds up to 100 wt%. The present invention relates further to a method for obtaining said paste, a method for forming said cavity structures in a ceramic component using said paste.