Process for producing highly ion-conductive porcelain

Claim 1

A process for producing a highly ion-conductive procelain with a low specific resistivity not more than 10 ohm-cm at 300° C and with good stability in air, which comprises (a) mixing about 87 to about 95% by weight of Al 2 O 3 of a particle size of about 0.3 to about 5 microns with about 5 to about 13% by weight, as Na 2 O, of a sodium salt of a particle size of about 5 to about 50 microns, wherein the sodium salt is a compound which decomposes to Na 2 O at a temperature higher than about 700° C; (b) heat-treating the mixture obtained in (a) at a temperature of about 900° to about 1500° C in an oxidizing atmosphere for a time of from about 10 minutes to about 7 hours to produce a powder which in the X-ray powder diffraction pattern has a β-Al 2 O 3 /β"-Al 2 O 3 ratio such that the ratio of Iβ:Iβ" is about 1.0 to about 0.25:1 where Iβ is the peak intensity of β-Al 2 O 3 in the (017) planes with d=2.69 A and Iβ" is the peak intensity of β"-Al 2 O 3 in the (01,11) planes with d=2.60 A in which d is the lattice distance; (c) mixing 100 parts by weight of the resulting heat-treated powder obtained in (b) with 0.2 to about 3 parts by weight, as the oxide, of at least one compound capable of providing a monovalent or divalent metal ion, said ion increasing the ion conductivity of the sintered β-alumina in step (e) in combination with the Na ion in the alkaline atmosphere used in step (e); (d) molding the mixture obtained in (c); and (e) sintering the molding in Na 2 O alkaline atmosphere at a temperature of about 1500° to about 1750° C for about 5 to about 90 minutes.