| 摘要 |
1488159 Silicon nitride and carbide compositions NORTON CO 20 Nov 1974 [23 Nov 1973] 50279/74 Headings ClA and ClJ [Also in Divisions H5 and C7] A ceramic heating element is formed of a sintered resistive mixture of from 10 to 60% by weight of silicon carbide and 90 to 40% by weight of silicon nitride, silicon oxynitride, silicon aluminium oxynitride and mixtures thereof, the sintered mixture being substantially impervious. An insulating layer of sintered silicon nitride, silicon oxynitride, silicon aluminium oxynitride or mixtures thereof may be applied to the surface or surfaces of the heating resistor. In manufacture a layer of the insulating particles is placed in a mould, then a layer of the particulate resistive mixture, and finally a further layer of insulating particles. The centre of the resistive layer may be partially removed prior to the addition of the further insulating layer so that after hot pressing at 2000 p.s.i. at 1750‹ C. for 60 minutes an insulated heating resistor having a hot zone and integral cold ends is formed. Cold ends can alternatively be formed by impregnating or coating the element ends with metal, e.g. Si or a mixture of Si and C or by increasing the cross-sectional area at the ends. The element may be perforated for heating air or liquids passing therethrough, it may be planar to form a hot plate, it may be shaped as a crucible or it may be rod shaped. It may be used to form the walls of a furnace. |
