Patent GB-1152494-A (GB)
Title: Improvements in or relating to Refractory Products
IPC: B28B3/00
Filed: 1966-06-21
Abstract: 1,152,494. Refractory bodies; carbon bodies. GULF GENERAL ATOMIC Inc. 21 June, 1966 [23 June, 1965], No. 27595/66. Heading C1A. [Also in Division C7] A refractory body is produced from a body formed of a refractory matrix material and a liquefiable dispersant which melts or reacts with said refractory material to form a liquid phase at a temperature below the vaporization or melting temperature of said refractory material, by heating this body to a temperature sufficient to melt and maintain the dispersant in a liquid state whilst applying a compressive stress to the body, which is left free to expand in a direction perpendicular to the direction of stress. A permanent true strain of 15-65% is preferably induced by said compression, and the product upon cooling is a crystalline refractory material matrix with a crystalline dispersant distributed throughout the pores of said matrix. The refractory matrix material may be carbon (including graphite), beryllia, alumina, zirconia, titania or mixtures thereof. The liquefiable dispersant for use in a carbon matrix may be the metals Zr, Mo, U, Nb, Th, Ti, Ta, V, W or Al, the carbides thereof, or other compounds thereof which form a carbide on thermal treatment. The temperature of heating may be 2600-3200‹ C. and the compressive stress is generally 2000-10,000 p.s.i. The body to be treated may be fabricated from a mixture consisting of particulate refractory material (e.g. of particle size 5-100 microns when carbon is used) and particulate liquefiable dispersant (e.g. of particle size less than 60 microns when zirconium carbide or molybdenum carbide is used) and preferably containing a binder (e.g. coal tar pitch) by any suitable forming process (e.g. hot-pressing, extrusion) optionally followed by heating in an inert atmosphere. When the dispersant is ZrC and the matrix material is carbon, the initial mixture preferably contains 10-50 wt. % of ZrC. The process of the invention leads to refractory products having a controlled degree of crystal orientation, and thus a controlled degree of anisotropy, including the special case of an isotropic product. In comparative examples the heating to 2600-3200‹ C. is carried out without any compression. Graphite bodies are prepared (Samples 1, 2 and 5) by mixing graphite or carbon filler of particle size 5-100 microns with coal tar pitch (in amounts of 20, 25 and 10 wt. per cent respectively). In Sample 1 the pitch contains added trichlorethylene which is subsequently evaporated and the mixture hot-pressed at 800‹ C. for one hour to obtain a cylinder. In Sample 2 the mixture also contains 2 wt. per cent cellulose and 2 wt. per cent stearic acid and is extruded at 110‹ C. to form a rod which is then baked under restraint at 900‹ C. In Sample 5 the mixture is hot-pressed. Each Sample is then heated to 2600-2800‹ C. with or without compression as described above to yield products having specified density, porosity, helium permeability, compressive strength, modulus of rupture, coefficient of thermal expansion at 400‹ C. and thermal diffusivity.