Synthesis of precursor ceramics

Ion exchange of Na for K (cq for P -Al203 increases from 3.339 to 3.412 nm) induces 0.005 positive strain, resulting in c. 400 MPa stress. There are three possible solutions  

The spinel and aluminate cause failure during H30 ion exchange. Further time reverses this reaction and sintering samples achieve the same /(P) value twice. 

The discovery of the second low-/(P) value led to reproducible polycrystals. The final grain-size of the new ceramic is still fine (=3 pm), the evident grain-boundary immobility being due to pinning by the slowly assimilating spinel. 

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