Magnesium Aluminate Spinel Ceramics Without Sintering Aids
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Solution Overview
Problem
There is a need for a cost-effective manufacturing method to produce large ceramic sintered bodies of high purity (>99.999%) and high density comprising magnesium aluminate spinel (MgAl2O4) with dimensions ranging from 100 mm to 600 mm, which are free of sintering aids and exhibit high mechanical strength, chemical resistance, and resistance to plasma corrosion and erosion, suitable for applications in semiconductor processing and other harsh environments.
Innovation Solution
A method involving the combination of high-purity magnesium oxide and aluminum oxide powders, calcination, and pressure-assisted sintering at controlled temperatures (1000 to 1700°C) without sintering aids, followed by optional annealing and machining, to produce a ceramic sintered body with 90-100% cubic crystallographic structure and densities of 3.47 to 3.58 g/cc, achieving high purity and density with minimal porosity and grain size control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional sintering methods are used to produce large spinel ceramic bodies, then high density can be achieved, but the manufacturing cost increases significantly and production time extends to several days
Solution Approach 1:
The patent applies preliminary action by performing cold isostatic pressing (CIP) before sintering to pre-densify the green body. This preliminary densification step reduces the porosity and improves the packing density of the compact, allowing for shorter sintering times and lower sintering temperatures while achieving the same final density, thereby reducing overall production time and energy consumption
Solution Approach 2:
The patent employs parameter changes by optimizing the sintering temperature range (1400-1700°C) and time duration (2-24 hours) based on the pre-densified state of the green body. The CIP pressure (100-300 MPa) is also optimized to achieve the desired green density before sintering. These parameter adjustments enable faster production cycles while maintaining high final density
2Manufacturing precision
If high pressures (80 MPa and greater) are applied to promote densification, then density improves, but expensive sintering equipment is required
Solution Approach 1:
The patent segments the densification process into two distinct stages: (1) cold isostatic pressing at room temperature to achieve initial green density, and (2) sintering at elevated temperature to achieve final density. This segmentation allows the use of relatively lower pressures during CIP (100-300 MPa) compared to traditional single-stage high-pressure sintering (80 MPa and greater), reducing equipment cost while achieving the same densification effect
Solution Approach 2:
The patent introduces cold isostatic pressing as an intermediary process between powder compaction and sintering. This intermediary step creates a pre-densified green body with improved particle packing and reduced porosity, which then requires lower pressure and temperature during the subsequent sintering stage, thereby reducing the complexity and cost of the sintering equipment required
3Temperature
If sintering aids are used to promote densification, then sintering temperature can be reduced, but the purity of the ceramic decreases and mechanical strength is compromised
Solution Approach 1:
The patent extracts and eliminates sintering aids from the formulation by using high-purity starting powders (99.99% and greater) and optimizing the cold isostatic pressing and sintering parameters to achieve adequate densification without any additives. This extraction of harmful elements (sintering aids) maintains the high purity (>99.99%) and mechanical strength requirements while still achieving the desired density through the CIP-sintering combination
4Manufacturing precision
If prolonged sintering durations are used to achieve high density, then porosity is reduced, but grain growth is exaggerated and mechanical strength decreases
Solution Approach 1:
The patent applies preliminary cold isostatic pressing to achieve significant densification before sintering, reducing the initial porosity of the green body. This preliminary action means that the subsequent sintering duration can be shortened (2-24 hours) while still achieving the target density, thereby limiting the time available for grain growth and preserving mechanical strength
Solution Approach 2:
The patent optimizes the sintering temperature (1400-1700°C) and time (2-24 hours) parameters to achieve the desired density while controlling grain growth. The combination of pre-densification by CIP and optimized sintering parameters creates a synergistic effect that achieves high density with minimal grain growth, maintaining mechanical strength
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 method enables the production of large, high-purity, high-density ceramic sintered bodies with enhanced mechanical strength, chemical resistance, and erosion resistance, suitable for semiconductor processing components, reducing costs and improving handling and performance in harsh environments.
Implementation Method 1
calcining the powder mixture by applying heat to raise the temperature of the powder mixture to a temperature of from 600° C. to 1000° C. and maintaining the calcination temperature for a duration of from 4 to 12 hours
Implementation Method 2
applying from 5 to 60 MPa of pressure to the calcined powder mixture while heating to a sintering temperature of from 1000 to 1700° C. and performing sintering to form the ceramic sintered body
Implementation Method 3
disposing the calcined powder mixture inside a volume defined by a tool set of a sintering apparatus and creating vacuum conditions inside the volume
Data Source
AI summary
Disclosed is a ceramic sintered body comprising magnesium aluminate spinel of composition MgAl2O4 having from 90 to 100% by volume of a cubic crystallographic structure and a density of from 3.47 to 3.58 g/cc, wherein the ceramic sintered body is free of sintering aids. A method of making the ceramic sintered body comprising spinel is also disclosed.