| 摘要 |
1339112 Modified MgO PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 8 May 1972 [7 May 1971] 21356/72 Heading C1A [Also in Division H1] A material having a positive temperature coefficient of resistance is produced by sintering in a reducing atmosphere a mixture of MgO containing 0À25 to 1À5 mol. per cent TiO 2 , 0À35 to 2À5 mol. per cent SiO 2 and 0À35 to 2À5 mol. per cent CaO. The starting mixture may utilize other compounds of Mg, Ti, Si and Ca which are reduced by heat to the specified composition, e.g. MgCO 3 , MgTiO 3 , MgSiO 3 and CaCO 3 . Methyl cellulose or nitrocellulose may be used as a binder. In a specific embodiment a pulverulent mixture of 97À1 mol. per cent MgO, 1À1 mol. per cent CaCO 3 , 0À7 mol. per cent TiO 2 and 1À1 mol. per cent SiO 2 is mixed with a binder of 4À8 wt. per cent methyl cellulose and 95À2 wt. per cent water and moulded into bars which are dried and heated at 1350‹ C. to remove the binder. The bars are then sintered for 15 min. at 1800‹ C. in an atmosphere of 92 vol. per cent N 2 , 8 vol. per cent H 2 and electrodes are then applied. |
