Fe-Oxide-Assisted κ-Phase Formation in CeO2–ZrO2 Oxygen Storage Material
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Solution Overview
Problem
The high-temperature heat treatment required for synthesizing the κ phase in CeO2—ZrO2-based oxygen storage materials leads to a significant decrease in specific surface area, making it difficult to utilize this phase effectively in practical applications.
Innovation Solution
A method involving the addition of a Fe oxide during reduction treatment of CeO2—ZrO2 oxide at a lower temperature, allowing the formation of a κ phase with a larger specific surface area, preventing crystal grain growth and maintaining high surface area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-temperature heat treatment (1200°C or higher) is performed to synthesize the κ phase, then the oxygen storage capacity is improved, but the specific surface area decreases significantly
Solution Approach 1:
The patent applies parameter changes by modifying the heat treatment temperature from the conventional 1200°C or higher to a lower range of 900-1100°C. This temperature parameter change enables the formation of the κ phase while preventing excessive crystal grain growth, thereby maintaining a high specific surface area (5-20 m²/g) while achieving sufficient oxygen storage capacity. The reduced temperature parameter resolves the contradiction between oxygen storage capacity and specific surface area preservation.
2Stability of the object's composition
If high-temperature heat treatment is performed to form the κ phase, then the phase structure is improved, but the crystal grain growth increases leading to reduced surface area
Solution Approach 1:
The patent changes the temperature parameter from conventional high temperatures (1200°C+) to a optimized lower range (900-1100°C). This parameter modification allows the κ phase to form with proper structural stability while limiting crystal grain size growth. The lower temperature parameter enables phase structure improvement without the harmful side effect of excessive crystal grain enlargement that would reduce surface area.
3Stability of the object's composition
If conventional synthesis methods are used, then the κ phase can be formed, but the specific surface area becomes too small for practical application
Solution Approach 1:
The patent implements a parameter change in the heat treatment temperature, reducing it from conventional 1200°C or higher to 900-1100°C. This temperature parameter adjustment maintains the ability to form the desired κ phase structure while preventing the excessive crystal grain growth that occurs at higher temperatures. The result is a material with sufficient phase stability and clinically useful specific surface area (5-20 m²/g), resolving the contradiction between phase formation and surface area preservation.
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 a CeO2—ZrO2 oxide with a κ phase having a specific surface area greater than that in existing methods, enhancing its practical applicability as an oxygen storage material.
Implementation Method 1
a first step (reduction step) and a second step (oxidation step) thereafter. In the first step (reduction step), a precursor of CeO2—ZrO2 is subjected to a heat treatment at a high temperature of, for example, 1200° C. or higher in a reduction atmosphere to synthesize pyrochlore phase Ce2Zr2O7 in which Ce and Zr are arranged in order. Next, in the second step (oxidation step), a heat treatment is performed at, for example, about 600° C., and oxygen is introduced, thereby synthesizing κ-Ce2Zr2O8.
Implementation Method 2
a heat treatment at a high temperature of, for example, 1200° C. or higher in a reduction atmosphere to synthesize pyrochlore phase Ce2Zr2O7
Implementation Method 3
CeO2 stores and releases oxygen according to the following reaction formula with a change in valence of Ce ions. Ce ions of CeO2 are Ce4+, and when all Ce4+ are reduced to Ce3+, δ becomes the largest. At this time, δ=0.5.
Implementation Method 4
since an ion radius is increased by about 1.2 times during the reduction from Ce4+ to Ce3+, a strain of a crystal lattice occurs, and the lattice becomes unstable. Therefore, the strain is relaxed by introducing Zr4+ having an ion radius smaller than that of the Ce ions.
Data Source
AI summary
This oxygen storage material has a chemical composition represented by Ce1-xZrxO2-δ (0.45≤x≤0.65, 0≤δ), has a peak attributed to a cubic pyrochlore-like structure (κ phase) near 14.5° in an XRD pattern, and has a specific surface area of 3 [m2/g] or more.