GB595760A - Improvements in or relating to the production of useful articles from coal - Google Patents

Abstract

Moulded products are produced from bituminous coal without the use of a binding-agent by finely grinding a coal having good agglutinating properties, moulding to the desired shape and firing, in the presence of a chemical swell-inhibiting agent, above 550 DEG C., and preferably above 700 DEG C., in a non-oxidizing atmosphere and under such conditions that the product is not swollen, has a greater density than that of the coal used and has no visible cellular structure. The product is also resistant to boiling toluene and aniline, has a tensile strength exceeding 3000 lbs. per square inch and a modulus of rupture exceeding 5000 lbs. per square inch, has a porosity in methyl alcohol not exceeding 15 per cent., is unaffected by heat in a non-oxidizing atmosphere up to 2600 DEG C., and has good electrical conductivity. The swell-inhibiting agent is one which effects a chemical decomposition of some of the coal constituents during firing, generates a volatile hydride in the presence of hydrogen or hydrocarbon, and, by reason of its action on the coal constituents prevents intumescence and facilitates the evolution of gas. The agent, if solid, is finely ground and intimately mixed with the ground coal; if liquid, it may be mixed with the coal before moulding or may be applied, as by spraying, to the moulded article before firing; or, if a volatile liquid or a gas, it may be introduced into the firing atmosphere. It may be (a) a halogen, or a compound which, during firing, generates a halogen or halogen halide without other elements which act to oxidise the coal or affect the strength or distortion of the product; (b) a member of the sixth group of the periodic system other than oxygen or the metallic elements, or a compound thereof which exists as or can generate a volatile hydride in the presence of hydrogen or a hydrocarbon during firing, provided that other deleterious elements such as oxygen and chlorine are not evolved; or (c) an element other than those of the vanadium sub-group, of the fifth group of the periodic table, or a compound thereof which exists as or generates a volatile hydride under the firing conditions. The coal is one having a swelling-number of 2-10, preferably 6-10, the higher values being employed when a tough product is desired; low ash-content is necessary if the product is to be of good electrical conductivity. The coal and inhibiting-agent, if solid, are ground so that 95 per cent. pass a 200 B.S. sieve, and 60 per cent. of the particles are smaller than 10 microns. Mixing is effected in a blending mill of the type known under the Registered Trade Mark "Kek." Moulding may be effected under a pressure from 1/2 to 10 tons per square inch, normally for only a short time at atmospheric temperature. Moulding may be effected in an ordinary press or by extrusion. The non-oxidizing firing atmosphere may be obtained by embedding the article in granular material which evolves non-oxidizing gases, e.g., a coal of high volatile content and little coking property, or by passing a stream of gas through the furnace. If hydrogen is used, the flow should be as small as possible provided a non-oxidizing atmosphere is maintained to avoid interaction with the unsaturated constituents of the coal and thus to produce a greater deposition of carbon in the pores of the article. If town gas is employed, any oxidizing constituents should be removed. Preferably the atmosphere contains an unsaturated hydrocarbon such as ethylene or other olefine, or a readily-cracked hydrocarbon such as benzene, particularly in the temperature range 450-850 DEG C., whereby carbon deposition is increased and a harder, less porous product is obtained. Firing is at a controlled rate, and must be relatively slow in the range 300-450 DEG C. to avoid intumescence. The products may be electroplated or glazed; in the latter case, they are preferably first treated with a wetting agent. According to examples (a) 2 per cent. of crystallized iodine is added to the coal; (b) 1.5 per cent. of sulphur is employed; (c) firing is conducted in an atmosphere of ammonia. According to the Provisional Specifications, the product may be treated to a pore-filling operation as described in Specification 593,079 or by treating with a liquid monomer and subsequent polymerization. Specifications 512,882, [Group XII], and 595,759 also are referred to.