Refractory Crucible Fabrication via Green Stage Machining
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Solution Overview
Problem
Existing methods for fabricating crucibles for bulk crystal growth, such as plasma-spray processes, face limitations in precision machining, high material yield, shape and thickness constraints, and uniform material properties, particularly when dealing with refractory materials at elevated temperatures.
Innovation Solution
A two-stage process involving initial sintering of refractory material powder in a mold under controlled temperature and pressure to create a shape-sustaining, machinable form, followed by final sintering to achieve high density and low porosity, allowing for precise shaping and enhanced material properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If plasma-spray processes are used to form crucibles, then refractory material can be deposited onto substrate surface, but precise machining of shapes is not allowed before densification
Solution Approach 1:
The patent applies preliminary action by forming the crucible shape during the green stage before final sintering, while the material is still machinable. The green crucible is formed by compacting refractory powder in a mold, allowing precise machining of the desired shape before the material becomes too hard for conventional tools after full sintering.
Solution Approach 2:
The patent segments the manufacturing process into distinct stages: forming the green crucible shape, machining the precise shape while still machinable, and then performing final sintering to achieve full density. This segmentation allows each operation to be performed when the material is in the appropriate state.
2Productivity
If plasma-spray processes are used, then crucibles can be formed, but material yield is relatively low
Solution Approach 1:
The patent changes the processing parameters by using controlled compacting and sintering conditions that maximize material utilization. The green crucible is formed with precise control over powder compaction, and the final sintering is performed under optimized temperature and atmosphere conditions to achieve high density with minimal material loss.
3Adaptability or versatility
If plasma-spray processes are used, then coatings can be formed, but thickness and shape constraints are limited
Solution Approach 1:
The patent uses preliminary action by forming the complete crucible shape during the green stage before sintering, rather than forming thin coatings. The mold is designed to create the full desired geometry, and the green crucible retains this shape, allowing for complex geometries and various thicknesses without the constraints of plasma-spray coating limitations.
4Stability of the object's composition
If plasma-spray processes are used, then refractory material can be deposited, but uniform material properties are not achieved
Solution Approach 1:
The patent applies parameter changes by controlling the sintering process parameters (temperature, time, atmosphere) to achieve uniform material properties throughout the crucible. The controlled compaction during green formation and optimized sintering conditions ensure homogeneous density and composition throughout the final product.
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 process enables the production of dense, refractory-shaped articles with high density and low porosity, overcoming the limitations of existing methods by allowing precise machining and uniform material properties, and extending the life and durability of crucibles for high-temperature applications.
Implementation Method 1
the mold containing the powder is treated at a temperature and a pressure sufficient to form a self-supporting and shape-sustaining molded powder that conforms to the shape of the mold
Implementation Method 2
the shape-sustaining molded powder is sintered at a temperature and for a time sufficient to produce a dense, shaped article having a density of greater than about 90%, a total porosity of no more than about 10%, and a total open porosity of no more than about 1%
Data Source
AI summary
The invention provides a method of forming a dense, shaped article, such as a crucible, formed of a refractory material, the method comprising the steps of placing a refractory material having a melting point of at least about 2900° C. in a mold configured to form the powder into an approximation of the desired shape. The mold containing the powder is treated at a temperature and pressure sufficient to form a shape-sustaining molded powder that conforms to the shape of the mold, wherein the treating step involves sintering or isostatic pressing. The shape-sustaining molded powder can be machined into the final desired shape and then sintered at a temperature and for a time sufficient to produce a dense, shaped article having a density of greater than about 90% and very low open porosity. Preferred refractory materials include tantalum carbide and niobium carbide.