Making temperature-stable protectively coated graphite molded body

摘要

In order to prevent a protective carbide layer on a graphitic molded article from splitting off under thermal stress, an external carbide layer is provided on a graphitic molded article having a graded content of silicon or zirconium (in the carbide state) that increases from near zero at the interior boundary of the layer to about 50 atomic percent at the exterior. Such a layer is produced either by dipping the graphitic molded article into melted silicon, dipping it into a succession of suspensions of carbon and either silicon or zirconium, with a greater silicon or zirconium content in each successive dip, the suspensions also including a binder resin, or by applying layers of a paste of carbon and either silicon or zirconium, also with some resin, each successive layer having a higher silicon or zirconium content. In the case of the successive dipping into suspensions, the article is dried after each dip and then heated to harden the binder, and in the case of application of successive paste layers, the binder is likewise hardened each time. In each case, the treatment terminates with heating to a coking temperature, followed by a rapid rise of temperature to a value at which silicon carbide or zirconium carbide will be formed, followed by cooling to room temperature.