Aluminate alkali substitution

There is wide agreement that substitution of alkali metal ions retards the early reaction of the aluminate phase, which is thus less for the orthorhombic than for the cubic polymorphs (S35,B43,RI3). The effect has been attributed to structural differences, but the early reaction of pure C, A is also retarded by adding NaOH to the solution, and the OH ion concentration in the solution may be the determining factor (S35). The reaction of C,A is also retarded by iron substitution and by close admixture with ferrite phase formation of a surface layer of reaction products may be a determining factor, at least in later stages of reaction, and the retarding effect of such a layer may be greater if it contains Fe (B44). 

Of these, the P- and P"-aluminas have been studied most extensively. The isostructural sodium gallates, potassium, rubidium and cesium gallates, aluminates, and ferrites are also known. The ideal formulas for the p and P" structures are AMuOn and A2M11O17, respectively, but all of the compounds are intrinsically nonstoichiometric and the actual alkali content is always greater than unity but less than 2. The most obvious charge compensation mechanism is alower-valence cation substitution for trivalent M , namely Ai, )Oi7 (M = Mg, Co, Ni, Zn) and... 

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