GB595759A - Improvements in or relating to the production of useful articles from coal - Google Patents

Abstract

Moulded products are made from bituminous coal by firing to a temperature above 550 DEG C. under non-oxidizing conditions a moulded intimate mixture of finely-powdered coal having a swelling number, as determined by B.S. 1016, of 2-10 and preferably 6-10 with a finely-divided solid agent which inhibits swelling during heating and which does not melt during firing. The product is not swollen, has a greater density than the coal used, no cellular structure visible to the naked eye, is not affected by boiling toluene or aniline, a tensile strength above 3,000 lbs. per square inch, a modulus of rupture above 5000 lbs. per square inch, and a porosity in methyl alcohol not above 15 per cent. is not affected by heating in a non-oxidizing atmosphere up to 2600 DEG C., and may have good electrical conductivity. The coal is preferably a bituminous variety having 13-30 per cent., and perferably 22-28 per cent. volatile matter calculated on a dry ash-free basis, and a carbon content of 80-90 per cent. The swell-inhibiting agent may be a carbonaceous material, e.g., pitch coke, a weakly-coking or non-coking coal, cuprene, or, if a product of good electrical properties is required, graphite, or a non-carbonaceous material such as silica, silicates, alumina, magnesia, metals or their oxides or salts, silicon, ball clay, bentonite or similar argillaceous material, or, for a product resistant to high temperatures, zirconia. Between 5 and 30 per cent. by weight of the agent may be included, but allowance should be made when a coal having a high non-bituminous content is employed. The constituents are ground so that over 95 per cent. passes a 200 B.S. sieve, and preferably 60 per cent. are smaller than 10 microns. Thorough mixing of the ingredients is essential. Moulding may be effected without the use of a bonding-agent by simple pressing at 1/2 to 10 tons per square inch for 10-15 p seconds normally at atmospheric temperature, extrusion, slip casting, or other process. The non-oxidizing firing atmosphere may be obtained by packing the moulded article in a mass of powdered material which evolves non-oxidizing gases, e.g., a coal of high volatile content and low caking capacity such as Warwickshire brights. Alternatively, an atmosphere of hydrogen, carbon monoxide, coal gas (from which any oxidizing gas has been removed), or hydrocarbon vapours may be maintained in the furnace, the article being placed on a support of fine loose granular material such as sand or charcoal. When a hydrogen or hydrogen-containing atmosphere is used the minimum amount possible should be used in order to avoid any hydrogenation of the coal constituents resulting in the reduction of the elementary carbon normally deposited in the pores of the article. Preferably the atmosphere contains an unsaturated hydrocarbon such as ethylene or other olefine, or a readily-cracked hydrocarbon such as benzene, particularly when a coal of low volatile content and agglutinating property is used. Firing is carried out at above 550 DEG C. and preferably above 700 DEG C. Firing should be sufficiently slow between 300 and 500 DEG C. to avoid intumescence, but may be speeded up later. Increased strength and electrical conductivity result from firing up to 1500 DEG C. When an atmosphere of ethylene is used, firing up to 450 DEG C. may be effected in a cheaper non-oxidizing atmosphere so as to avoid contamination of the ethylene which can then be recycled, and also to produce satisfactory deposition of carbon in the pores of the article. The products may be electroplated or glazed; in the latter case, the swell-inhibiting agent may be of such a nature as to ensure the product will take the glass, and the product may be treated with a wetting-agent. Certain of the Provisional Specifications describe (a) an experimental procedure for determining the correct amounts of the ingredients and firing temperatures; (b) a pore-filling treatment similar to that described in Specification 593,079, or in which a liquid monomer of a polymerizable organic compound is filled into the pores and subsequently polymerized; (c) the use of boron or germanium or their compounds other than the saturated oxides, chlorides or fluorides as swell-inhibiting agents; (d) the swell-inhibiting agent in liquid or gaseous state, in which latter case it is introduced into the firing atmosphere; (e) the use of throwing, jolleying and jiggering processes for moulding the article when bentonite or ball-clay is used as the swell-inhibiting agent; (f) drying of the moulded article before firing when a wet-moulding process has been employed, to avoid cracking during firing; and (g) the introduction of acetylene into the firing-atmosphere. Specifications 561,498, 561,546, 595,760 and 595,763 also are referred to.