(GB2237801-B)      Analogues of beta''alumina (i.e. of formula Na2O.5Al2O3) with layered spinel type structure where at least some of the Na+ ions in Na+ ion layers sepd. by layers of Al3+ and O ions are replaced by cations of a mono, di and/or trivalent metal (I) are obtd. by (i) dispensing an oxide of metal (I) or its precursor in a boehmite (II) then (ii) heating to convert at least some of the mixt. obtd. to analogue prod. Boehmite (II) is defined as having an average crystal size of 100 Angstroms at least, average basal plane spacing of 6.8 Angstroms, mass loss on heating from 20 to 700 deg.C of below 20wt.% with max. loss above 400 deg.C. Spinel stabilisers may be added in (i) e.g. Li2O or MgO. (I) is e.g. Li, K, Be, Mg, Ga, As or Bi etc.    USE/ADVANTAGE -   Prods. can be formed as artefacts for use as separators in electrochemical cells or as solid electrolytes (III) when heating in (ii) is at 1610-1620 deg.C. (III) are used in fuel cells or gas sensors e.g. for vehicle exhaust gases. Powder or particulate prods. are mfd. when in (ii) is to 1200 deg.C.    (US5458868-A)      Prodn. of sinterable solid electrolyte which is a conductor of alkali metal cations is claimed. The solid electrolyte has a layered beta''-alumina spinel structure in which the alkali metal cations are present as discrete layers sepd. by layers of aluminium ions and oxygen ions.    Method comprises dispersing in Al2O3 or precursor an oxide of alkali metal cations or precursor to form a starting mixt.; and heating this mixt. to above 1000 deg.C. The alkali metal cations are of K opt. mixed with Na. The Al2O3 (precursor) is a boehmite having crystal size of at least 100 A, basal plane spacing of at most 6.8 A, and a mass loss upon heating at 10 degC/min. in air from 20 degC up to 700 degC of at most 20%. Max. loss rate occurs at at least 400 degC.    USE/ADVANTAGE -   Prod. is used in electrochemical or fuel cells, gas sensing devices, etc. Prod. has a well ordered highly crystallised structure.    (JP3037397-B2)      Analogues of beta"alumina (i.e. of formula Na2O.5Al2O3) with layered spinel type structure where at least some of the Na+ ions in Na+ ion layers sepd. by layers of Al3+ and O ions are replaced by cations of a mono, di and/or trivalent metal (I) are obtd. by (i) dispensing an oxide of metal (I) or its prescursor in a boehmite (II) then (ii) heating to convert at least some of the mixt. obtd. to analogue prod. Boehmite (II) is defined as having an average crystal size of 100 Angstroms at least, average basal plane spacing of 6.8 Angstroms, mass loss on heating from 20 to 700 deg.C of below 20wt.% with max. loss above 400 deg.C. Spinel stabilisers may be added in (i) e.g. Li2O or MgO. (I) is e.g. Li, K, Be, Mg, Ga, As or Bi etc.    USE/ADVANTAGE -   Prods. can be formed as artefacts for use as separators in electrochemical cells or as solid electrolytes (III) when heating in (ii) is at 1610-1620 deg.C. (III) are used in fuel cells or gas sensors e.g. for vehicle exhaust gases. Powder or particulate prods. are mfd. when in (ii) is to 1200 deg.C.