Abstract: Growth of scale on the wall surfaces of high-temperature furnaces is prevented, or the damaged portions are repaired. In addition, the inner wall surfaces of furnaces such as coke furnaces and carbon-firing furnaces, and attachments to furnaces (furnace lids and gas pipes) are protected from deposition of carbon.Glazing layers are formed by application to the refractory surfaces of furnaces of a glazing agent which comprises as a glaze, on an oxide basis, 0-10% by weight of Li.sub.2 O, 0-10% by weight of B.sub.2 O.sub.3, 10-40% by weight of R.sub.2 O (R represents Na or K) and SiO.sub.2 as the balance, wherein the glaze has a melting point of 900.degree. C. or below.

Abstract: A process for producing an aluminum nitride sintered body is disclosed, comprising mixing an aluminum nitride powder with (a) a calcium compound and (b) a copper compound, and, if desired, (c) a yttrium compound as sintering aids; molding the mixture; and sintering the molded article in a non-oxidative atmosphere. The resulting sintered body has a high density (3.10 g/cm.sup.3 or higher) and a high thermal conductivity (110 W/mK or higher) even by sintering at a low temperature (1500.degree. to 2000.degree. C.).

Abstract: An aluminum nitride powder obtained by firing and reacting a mixture of alumina and carbon in a nitrogen-containing atmosphere is disclosed, the aluminum nitride powder having an oxygen content of not more than 2.0% by weight, an iron content of not more than 20 ppm, a silicon content of not more than 100 ppm, and a titanium content of not more than 20 ppm and having has a tapped density of at least 1.0 g/cm.sup.3. An aluminum nitride powder containing from 0.01% to 10% by weight of a sintering aid is also disclosed, the aluminum nitride powder having an oleophilic surface and having a tapped density of at least 1.0 g/cm.sup.3. The aluminum nitride powder of the present invention has excellent moldability, has a high tapped density, is less in formation of coagulated particles, and has a sharp particle size distribution.

Abstract: In a furnace which allows a feed powder or granules in a stack of trays on a base plate to be reacted with a reactive gas, the improvement wherein each of the trays has a cutout or an opening providing a passage for the reactive gas or the produced gas both at the top of one side wall and in the bottom wall to the opposite side of the tray, the base plate having an opening through which the reactive gas is introduced or the produced gas is discharged.