1432184 Coated thermal regenerator NISSAN MOTOR CO LTD 13 Aug 1973 [15 Aug 1972] 38288/73 Heading B2E [Also in Division F4] The surface of a rubbing seal member 1 contacting the end face of a rotary matrix 2 in a gas turbine engine thermal regenerator includes a porous layer 1e impregnated with a heat resisting lubricant. The porous layer of the seal member 1 is formed and impregnated as follows : an undercoating material such as powdered nickel aluminite is first sprayed on to the surface of the seal member. Then a mixture of powders comprising a first material selected from nickel oxide and cobalt oxide and a second material selected from alkaline earth metal fluorides, phosphates and borates, e.g. CaF 2 is sprayed on to the undercoated surface. The content of nickel oxide or cobalt oxide is preferably 75 to 90% by weight and that of CaF 2 is preferably 10 to 25% by weight. The porous layer is impregnated with a heat resisting lubricant such as graphite, molybdenum disulphide, tungsten disulphide, boron nitride and soricite. The matrix, which may be ceramic, has a honeycomb structure 2a consisting of flat and corrugated plates. A ceramic matrix may be directly impregnated with the lubricant, e.g. by immersing in an ethanolicsolution of boron nitride.