HfO2-Y2O3 Refractory Ceramic for Thermal Cycling Stability
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Solution Overview
Problem
Hafnium dioxide (HfO2) based refractory ceramic materials used in nuclear reactor simulations experience cracking due to thermal cycling between 1500° C. and 1800° C. due to allotropic transformations, and existing stabilization methods lower the solidus temperature, making them unsuitable for high-temperature applications.
Innovation Solution
A refractory ceramic material with a solidus temperature between 2500° C. and 2800° C., comprising hafnium dioxide grains in both monoclinic and cubic structures stabilized by yttrium oxide (Y2O3) with 0.5 mol % to 8 mol % Y2O3, and a powder metallurgy process involving granulation by pelletization with polyvinyl alcohol and polyethylene glycol to achieve a compact and dense microstructure with closed and non-interconnected pores.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hafnium dioxide is stabilized in cubic phase using 8-12 mol% yttrium oxide, then thermal stability during cycling is improved, but solidus temperature decreases below 2500°C making it unsuitable for high-temperature applications
Solution Approach 1:
The patent changes the concentration parameter of yttrium oxide from the conventional 8-12 mol% range to a lower range of 0.5-8 mol%, which fundamentally alters the material's phase stability behavior and solidus temperature while still providing sufficient thermal cycling stability
Solution Approach 2:
The patent creates a composite microstructure containing both monoclinic and cubic phases of hafnium dioxide, where the cubic phase provides thermal stability during cycling and the monoclinic phase maintains high solidus temperature, achieving synergistic properties not possible with a single phase
2Stability of the object's composition
If hafnium dioxide undergoes allotropic transformation from monoclinic to quadratic phase during thermal cycling, then material density changes, but cracking occurs due to 3.4% volume shrinkage
Solution Approach 1:
The patent modifies the compositional parameter by adding yttrium oxide to change the phase transformation behavior of hafnium dioxide, stabilizing the cubic phase and preventing the harmful monoclinic-to-quadratic transformation that causes cracking
Solution Approach 2:
The patent utilizes controlled phase transitions by stabilizing the cubic phase of hafnium dioxide, which has better thermal stability and avoids the damaging volume changes associated with monoclinic-quadratic phase transformations during thermal cycling
3Temperature
If thorium dioxide is used as refractory material, then high melting temperature of 3380°C is achieved, but radioactivity makes it difficult to implement
Solution Approach 1:
The patent replaces the radioactive but high-performance thorium dioxide with non-radioactive hafnium dioxide modified by yttrium oxide, sacrificing some absolute melting temperature (2500-2800°C vs 3380°C) but eliminating radioactivity while maintaining sufficient performance for the application
Solution Approach 2:
The patent uses yttrium oxide as an intermediary additive to bridge the performance gap between pure hafnium dioxide and thorium dioxide, enabling hafnium dioxide to achieve thermal stability and structural integrity comparable to thorium dioxide without the radioactive hazard
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 material maintains high mechanical strength and chemical resistance, avoids cracking during thermal cycling, and preserves a solidus temperature close to pure HfO2's melting point without using sintering aids, ensuring appropriate mechanical strength and gas tightness for high-temperature applications.
Implementation Method 1
hafnium dioxide grains having a cubic structure which is stabilized by yttrium oxide Y2O3
Implementation Method 2
during thermal cycling (increasing/decreasing temperature), its allotropic transformation from the monoclinic phase to the quadratic phase is accompanied by a 3.4% shrinkage (or a volume expansion during the opposite transformation) between 1500° C. and 1800° C.
Implementation Method 3
granulation by pelletization with polyvinyl alcohol and polyethylene glycol
Implementation Method 4
a powder metallurgy process involving granulation by pelletization
Implementation Method 5
achieve a compact and dense microstructure with closed and non-interconnected pores
Implementation Method 6
chemical resistance to corrosion and/or high temperature ablation, which may be caused by baths consisting of oxides and metals
Data Source
AI summary
A refractory ceramic material possessing a solidus temperature between 2500° C. and 2800° C., having a compactness greater than 85%, and a microstructure such that the material is composite of: (a) hafnium dioxide HfO2 grains having a monoclinic structure (1); (b) hafnium dioxide HfO2 grains having a cubic structure (2) which is stabilized by yttrium oxide Y2O3, the yttrium oxide Y2O3 representing 0.5 mol % to 8 mol % relative to the total number of moles of hafnium dioxide HfO2; (c) closed pores (3); (d) non-interconnected open pores. The process of manufacturing the material and a structural part incorporating the material are also set forth.