Patent ID: 8133378

Claim:
A solid polycrystalline potassium ion conductor having a β″-Al 2 O 3 structure and being free of chlorine and comprising at least 90% by weight of potassium β″-Al 2 O 3 , obtainable by means of ion exchange of the alkali metal ions of a polycrystalline alkali metal β″-Al 2 O 3 moulding, in which the alkali metal ions are sodium ions or a mixture of sodium and potassium ions and the molar ratio M 2 O (M=alkali metal) to Al 2 O 3 is 1:x, x being an integer or non-integer number within the range 5 to 11, for potassium ions, the ion exchange being effected by a process wherein neither chloride-containing nor liquid potassium ion sources are used, the process comprising the steps of: embedding the polycrystalline alkali metal β″-Al 2 O 3 moulding in an oxidic powder containing potassium and aluminium of a molar K 2 O to Al 2 O 3 ratio within the range 1:(x−1) to 1:(x+1), the weight of oxidic powder amounting to at least two times the weight of the moulding; heating the embedded moulding at a rate of at least 100° C. per hour to at least 1100° C.; and further heating to at least 1300° C., this temperature being maintained for at least one hour prior to cooling.