| 摘要 |
1280078 Ceramics; alumina sheets INTERNATIONAL BUSINESS MACHINES CORP 25 March 1970 [28 April 1969] 14469/70 Headings C1A and C1J Ceramic sheets are formed by extruding a viscous sol containing a particulate ceramic material, e.g. alumina, through an elongated opening, coagulating the extrudate and severing the coagulated extrudate at separate points along its length. The sol is suitably a weakly alkaline or non-alkaline aqueous suspension of a ceramic powder containing a linking agent which is activated by a relatively strong alkaline medium and the extrudate is coagulated by passage into a relatively strong alkaline medium, e.g. ammonium, potassium or sodium hydroxide or gaseous ammonia. Suitable linking agents are polyvalent cations or complexes of Ca<SP>2+</SP>, Al<SP>3+</SP>, borate and chromate. The sol can also contain a copolymer of mannose and galactose and glycerol as a humectant, in which case the relatively strong alkaline medium can contain 5-20% of glycerol. Fig. 1 shows a sol 2 being extruded into a bath of strongly alkaline medium 4 and then being dried at 10 and sliced at 11. A separation can be maintained between the nozzle 3 and the coagulant 4 by providing an air space, a layer of xylene or silicone oil floating on the coagulant, by extruding the sol upward through a layer of trichloroethylene either into a liquid coagulant floating on the trichloroethylene or to float on the surface where it is exposed to ammonia vapour. |
