what's the difference between fused zirconia and chemical grade zirconia,

The term fused zirconia refers to the zirconia grains which are melted by heating above their melting point therefore the surface of these grains is in a fused state and it is nearly theoretically dense. One would expect better thermo mechanical properties from fused grains. Where as chemical grade is generally refered to zirconia prepared by chemical precipitation or decomposition of zirconium salts and such grains show high surface porosity hence they are prone to liquid metal wetting.


 Refractoriness is all about purity. A fused grade will contain fewer of the glass forming impurities which reduce the refractoriness of high melting point materials like zirconia. Hence you will have cleaner grain boundaries less prone to chemical attack, high temperature creep etc. In extreme applications, go for fused grade every time. Of course there are grades of fused materials as well, so you have to go by the quantities and types of impurities present in the chemical analysis to be sure that you're getting a quality product.


Price wise:
It can expected the fused grade to be more expensive. But there are different grades of fused zirconia, as with any other fused material. The fused material obtained from the centre of the melted mass is expected to contain the least contaminants and companies will often sell this material at the highest price whilst sell the material obtained from the outside of the melt at a lower price.
Whether it's better depends upon what use of it and how essential the place it is. That is, it could be cost effective to use the lower grade of zirconia in certain applications. Usually any containment vessel is zoned and the highest grade, fused materials only used in the high wear areas.


Crystal Size :
Cristal size is a major difference. Fused ZrO2 is slowly cooled, thus allowing for better formed and larger crystals than chemical ZrO2.


Lattice Size: 
There can not be major difference in the lattice parameters of the fused and chemical grade calcined zirconia but it may vary by from 5to 6% because the chemical grade is expected to have high vacancy or interstitial concentration hence it may show larger lattice parameter.Since in the fused zirconia the imputities are segregated to the surface of grains during solidification therefore it show lattice corresponding to that of pure zirconia crystal.