| 摘要 |
<p>The base plate of a rectifier may consist of bismuth, cadmium or tin (which sinter at a temperature below the melting point of selenium) either singly or in combination, or together with one or more of the metals nickel, aluminium, pure iron, chromium, magnesium, platinum, silver, zinc, palladium, antimony, which sinter at a temperature above the melting point of selenium. The base plate preferably comprises an alloy of 61 per cent tin and 39 per cent cadmium or 89 per cent tin and 11 per cent antimony, each of which sinter at about 216 DEG C. The former alloy is also suitable for the counterelectrode. Powders of between 60 mesh and 300 mesh may be employed. In one method, the base plate powder is compressed in a mould at a pressure of thirty tons per square inch and a layer of semi-conducting powder 14 is applied. The temperature is raised to between 130 DEG C. and 140 DEG C. by a heating coil and the two layers are compressed for about two minutes at a pressure of 2,500 pounds per square inch. This consolidates the powders and forms the nuclei of selenium crystals. Alternatively both powders may be simultaneously compressed in the mould and in either case the pressed discs may be removed from the mould for the first heat treatment, four or five hours then being necessary at the above stated temperatures. After the first heat treatment, the discs are subjected to a second heat treatment at a temperature just below the melting point of selenium to complete the conversion of the selenium to the grey crystalline metallic form. This takes from fifteen minutes to one hour and during this treatment, the base metal is further sintered. The operation may be carried out in a non-oxidising atmosphere.</p> |
