SOFC Air Electrode Powder With High Crystallinity and Low Impurities
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Solution Overview
Problem
The synthesis of powder materials for air electrodes in solid oxide fuel cells faces challenges in achieving high crystallinity while minimizing impurities, as high crystallinity leads to increased hardness and faster wear of pulverization media, and existing methods like the citric acid and solid-phase methods have low yield and productivity issues, respectively.
Innovation Solution
A powder material with a perovskite crystal structure represented by the formula A1(1-x)A2xBO3-δ, where A1 is La or Sm, A2 is Ca, Sr, or Ba, and B is Mn, Fe, Co, or Ni, with a specific surface area of 20 m2/g or more, and a crystallite diameter to specific surface area-based particle diameter ratio ≥0.3, is produced using a method involving a preparation step and a pulverization step with aluminum oxide beads to reduce impurity content.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the metal composite oxide is synthesized at a high temperature to achieve high crystallinity, then the crystallinity is improved, but the hardness increases and the pulverization medium wears faster
Solution Approach 1:
The patent applies preliminary action by conducting a pre-pulverization step before the main pulverization process. The pre-pulverized powder is then subjected to classification to separate fine particles from coarse particles. This preliminary treatment reduces the size and hardness of particles before the main pulverization, thereby reducing wear on the pulverization medium while maintaining high crystallinity of the final product.
Solution Approach 2:
The patent segments the pulverization process into multiple stages: pre-pulverization, classification, and main pulverization. This segmentation allows the process to handle different particle size ranges and hardness levels at appropriate stages, reducing overall wear on equipment while achieving the desired fine particle size and high crystallinity.
2Length of moving object
If a medium stirring-type pulverizer is used to pulverize the metal composite oxide, then the particle size is reduced, but impurities from the pulverization medium are included in the powder
Solution Approach 1:
The patent applies the taking out principle by removing and separating fine particles from the pre-pulverized powder through classification before the main pulverization step. By extracting and setting aside the finest particles early in the process, the method prevents these particles from being re-contaminated with impurities during subsequent pulverization steps, thereby reducing impurity content in the final product.
Solution Approach 2:
The patent uses classification as an intermediary step between pre-pulverization and main pulverization. This intermediary process separates particles by size and removes potential contaminants, acting as a mediator that prevents impurity transfer from the pulverization medium to the final powder product.
3Stability of the object's composition
If the citric acid method is used to synthesize the metal composite oxide, then the composition uniformity is improved, but the yield is low and productivity is poor
Solution Approach 1:
The patent applies parameter changes by optimizing the synthesis temperature and duration parameters in the solid-phase method. By conducting synthesis at 900-1500°C for 1-24 hours, the method achieves both high composition uniformity and high yield, overcoming the limitations of the citric acid method while maintaining the advantages of the solid-phase method.
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 resulting powder is fine, highly crystalline, and contains almost no impurities, improving electrical conductivity and reaction efficiency of the air electrode.
Implementation Method 1
the metal composite oxide is stirred together with a pulverization medium, so that it is pulverized by the collision with the pulverization medium
Data Source
AI summary
A powder material for an air electrode in a solid oxide fuel cell, the powder material being a powder of a metal composite oxide having a perovskite crystal structure represented by:A11-xA2xBO3-δ,where the element A1 is at least one selected from the group consisting of La and Sm, the element A2 is at least one selected from the group consisting of Ca, Sr, and Ba, the element B is at least one selected from the group consisting of Mn, Fe, Co, and Ni, x satisfies 0<x<1, and δ is an oxygen deficiency amount. The powder has a specific surface area of 20 m2/g or more, satisfies (Crystallite diameter/Specific surface area-based particle diameter)≥0.3, and contains elements M in an amount of 300 ppm or less in terms of atoms, the elements M being other than the elements A1, A2 and B, and oxygen.