In the prodn. of AlH3(PO4)2.3H2O (I) the improvement comprises allowing (I) to crystallise from a soln. contg. Al phosphate (II), water and a water-miscible organic solvent (III), the Al2O3:P2O5 molar ratio in the soln. being 1:2-6. It is pref. to add seed crystals and to filter the soln. (to remove small amts. of amorphous phosphate) before adding these. The process is generally applicable and not confined to addn. of (III) to an aq. (II) soln. as in the parent patent. Thus (III) can be added to an aq. (II) soln. or water added to a soln. of Al(H2PO4)3 in (III) e.g. EtOH. It is also possible to use a soln. obtd. by reacting Al(OH)3 with H3PO4 in the presence of (III) or to start from Al and H3PO4. (II) is pref. an ortho-phosphate. The seed crystals can be (I) or an isomorphous cpd. e.g. FeH3(PO4)2.3H2O. (III) should be added slowly to minimise the formation of an amorphous prod.
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