(19)

(11)

EP 0 549 657 A1

(12)

(43) Date of publication: 07.07.1993 Bulletin 1993/27 (21) Application number: 91916669.0 (22) Date of filing: 13.09.1991

(51) International Patent Classification (IPC):  C01G 1/ 00( . ) C04B 35/ 00( . ) C04B 35/ 46( . ) H01L 39/ 12( . ) C01G 23/ 00( . ) C04B 35/ 45( . ) C04B 35/ 465( . ) (86) International application number: PCT/GB1991/001572 (87) International publication number: WO 1992/005125 (02.04.1992 Gazette 1992/08)

(84) Designated Contracting States: CH DE FR GB IT LI NL SE (30) Priority: 14.09.1990 GB 19900020115 (71) Applicant: BRITISH TECHNOLOGY GROUP LIMITED London SE1 6BU (GB)	(72) Inventors: BINKS, John Henry Aberdeen AB1 9JA (GB) IRVINE, John Thomas Sirr Inverurie, Aberdeenshire AB51 0AX (GB) COGLE, Trevor James St. Margarets Hope, Orkney KW17 2RN (GB) SERENO MATEUS, Carlos, Alexandre P-1500 Lisbon (PT) (74) Representative: Cullis, Roger  Patents Department British Technology Group Ltd 101 Newington Causeway London SE1 6BU London SE1 6BU (GB)