Classifications

• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
  • C04B35/515—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics
  • C04B35/52—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on carbon, e.g. graphite
  • C04B35/528—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on carbon, e.g. graphite obtained from carbonaceous particles with or without other non-organic components
  • C04B35/532—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on carbon, e.g. graphite obtained from carbonaceous particles with or without other non-organic components containing a carbonisable binder
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B32/00—Carbon; Compounds thereof
  • C01B32/05—Preparation or purification of carbon not covered by groups C01B32/15, C01B32/20, C01B32/25, C01B32/30
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
  • C04B35/515—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics
  • C04B35/52—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on carbon, e.g. graphite
  • C04B35/522—Graphite

Definitions

• the invention relates to processes for the production from bituminous coal of shaped articles, predominantly carbon in composition with a density greater than that of the original coal and with properties which render such articles useful in various arts and industries.
• the product may be made by the processes herein described to have a tensile strength of 3,000- 6,000 lbs.
• articles of the character referred to are made from bituminous coal, without requiring the use of an added binding material, by taking advantage of the agglutinating power of suitable coals themselves (particularly suitable coking coals), to effect the binding of the material and to promote its strength.
• the process comprises moulding followed by carbonization, and involves fine comminution and intimate mixture of the material, the moulding of the same to shape under pressure which usually is considerable, and subsequent carbonizatio-n of the shaped article in a non-oxidizing atmosphere, under a carefully controlled firing schedule.
• Successful results are obtained by adjustment and regulation of certainfactors ofthe process particularly of the firing rate, as will presently be explained.
• the process, it may be added may involve the feature that the non-oxidizing atmosphere consists of or contains one or another gas or vapour, thecharacter of which may considerably affect the properties of the-final product.
• This 4 firing may be carried out at a very slow rate of increase, particularly in passing through the plastic range, so that the volatile matters are not generated too rapidly and can escape without setting up critical internal pressures. It is important, also, that the comminution ofthe material should be neither too coarse nor too.
• the factors'whi ch promote strength in the degree of fineness, so that the individual par ticles can-be brought into the closest possible contact; to compressthe mass under very pressure-into a desired shape, analogous to the process of powder metallurgy to conduct the fir ingat a rate of: temperature rise as rapid as possible; and during the carbonization, to errsure that the atmosphere surrounding-the article is rich in hydrocarbons, especially unsaturated hydrocarbons. But it so happens that all these strength-promoting factors tend, whether separately or in combination,. to produce swelling if they are allowed to operate without restriction.
• the object of the invention is the provision of methods, for the production of articles of the character referred to, which shall-be eifective, readily controllable, and comparatively inexpensive and speedy.
• the process may involve the use of a swell-inhibiting agent, under certain conditions, as when the tendency to intumesce of the coal operated upon exceeds a certain value, or it may be practised without the use of such agent under other conditions, as when the swelling tendency is below such value or when the rate of firing is considerably reduced.
• Possible swell-inhibiting agents may be of various characters.
• One type consists of materials which appear to be inert. These appear to have little or no effect beyond that which follows from a reduction of the amount of volatile matter as a fraction of the weight of the preformed product. This type will be referred to as diluents.
• diluents sists of a weakly caking coal. This acts to some extent as a diluent, but'it contributes its own small agglutinating power to the mixture, and evolves gaseous products during the firing, (the temperature range at which the most rapid evolution takes place being, however, somewhat different for the two coals).
• Such materials as the above may be employed in the present invention, when required, but in other cases no inhibitor will be used within the scope of the present invention.
• the invention is based on a number of discoveries and observations of a more detailed character than those mentioned above, and, to said understanding of the process, these will now be referred to briefly.
• coal having a higher percentage of volatiles can be diluted by the addition of enough of an inert material of the character described or of a weakly caking coal to bring the volatile percentage down to about the same figure, with very much the same effect, the diluent being ground to about the same degree of fineness as the coal, and the rate of firing and the other steps of the process being similar to those practised in the case in which no diluent was used.
• the specially favourable percentage range referred to is 18/22.
• the material to be moulded must be finely comminuted and intimately mixed, and the mixture must be moulded under a pressure at least sufficient to enable the shaped article to be handled and transferred undamaged from the mould to the furnace in which it is fired, and preferably under a pressure of at least 2 tons per square inch.
• a Welsh coal suitable for the process is found to consist mainly of a constituent (Seylers No. 6) having an optical reflectance in oil immersion of 1.62%.
• Anthracite which has the highest optical reflectance of naturally occurring coals, has an optical reflectance in oil of 2.34%.
• the product made in accordance with the process of the invention is found to contain a substantial proportion of a material having optical reflectance in oil from 4.95% up to 5.2% (hereinafter referred to as alpha material) which is not found in any naturally occurring coal. It has, moreover, been found that the presence of this material of high optical reflectance is an important factor in conferring strength and other desired properties.
• the material of high reflectance referred to is carbon in an elementary form which, when the process is carried out in a preferred manner, occurs in a proportion of at least 30% by weight of the product, or of the carbonaceous material contained in the product in case a substantial proportion of the product is non-carbonaceous, as when a non-carbonaceous swell-inhibiting agent is used in the process, as is hereinafter described.
• the rate of firing must be sufficiently slow during that temperature range in which the coal is plastic and is also evolving gases, to avoid swelling, and likewise during that temperature range in which the coal is no longer plastic but is still evolving gases, i. e., above about 500 C. sufiiciently slow to avoid formation of cracks.
• the firing rate should be substantially as rapid as possible, conformably with avoidance of swelling, through the range in which the coal is both plastic and is evolving gases. This firing rate must be slower when the powder is comminuted more finely, or when a higher moulding pressure is used, or when articles of thicker section are made, than when less fine comminution or less pressure are used or thinner section articles are made.
• useful articles for some purposes can be produced by firing only to about 550? 0., but for articles of considerable toughness and strength, the firing should be continued to at least about 650 C.-850 C.
• the gas envelope in which the article is surrounded during carbonization exerts a marked influence on the process, which varies considerably with dii erent gases.
• excellent results are obtained in some cases when carbonizing in an envelope composed of or containing ethylene or other unsaturated hydrocarenemas bon gas or vapour, with deposition of carbonwithin the interstices and on the internal faces of particles within the body, and in some cases an article which is defective, for example, in tensile strength, can be improved considerably by re-firing it in such a selected atmosphere.
• the first consideration is choice of a suitable coal.
• Mechanically strong bodies may be produced from bituminous coal by carbonization, as a general principle, provided that the coal agglutinates into a coherent mass during carbonization.
• Different coals vary considerably in agglutinating power, and when this is below a certain figure the addition of an agglutinating agent or binder may be used to produce suitable co-- hesion, such binders being, for example, the products of coke manufacture, tars, pitches, etc.
• Such additions are not required in the present process and generally are not desired, for a number of reasons.
• the coal chosen must be one in which the temperature ranges in which softening and thermal decomposition occur are suitably related to each other.
• coals which have been found to be best adapted for use in the present invention are bituminous coals, having a volatile matter content which lies between about 13 and 39 per cent, calculated on a dry ash-free basis. Differences exist between coals of this type sufficiently Wide to predetermine the treatment to be employed. A gradation of such coals in composition with increasing rank will usually show a steady decrease in the intensity of the anti-swelling factors required to produce unswollen products. Thus considering the following strongly swelling coals:v
• coal 0 the'percentage of volatiles is 20, while in coal A, when diluted by mixing 90 per cent coal with 10 per cent of, say, pitch coke, the percentage is 2 1.6,
• the coal selected is first cornminuted to a fine powder, so that, for example, more than 95 ,per cent byweight of the particles pass through a 200 mesh B. S. sieve. This is fairly close to the optimum fineness for the prevention of swelling, it being believed that the optimum for a typical coking coal is 80-90% through 260 mesh B. S. S. This is optimum because with coarser particles internal pressures are set up inside the particles, on carbonizatiomand with finer particles having a greater surface volume ratio pressures are set up between the particles, with effects tending. to make the mass swell.
• the coal may be so comminuted that at least 69 per cent by weight of the particles are smaller than 16 microns, or so that the specific surface exceeds 15,009 sq. ems. per
• the swell-inhibiting agent which maybe required when theswelling tendency of the coalis greater than desired, may be an inert filler, which seems to act solely as a diluent, or it may be a weakly-coking coal, or even a non-colring coal. 0f the last two, each contributes a small agglutinating power. e
• the agent is of the inert type,it may be a carbonaceous material such as pitch coke, or coke breeze.
• Graphite may be used, and is of particular value for special purposes; as when good electrical conductivity is wanted, or when special shapes are required which require fluidity in the moulding stage, in which case graphite may be added and be useful both as a lubricant and as a swell-inhibitor.
• Higher rank coals. such as anthracite, which seem to approximate to an inert filler, may also be used.
• the diluent may be a non-carbonaceous material, as for example, a solid pulverulent' material which does not melt within thefiring temperature range, such as, for example, silica in any of its'nurnerous forms, siliceous minerals such as clays, mica, granite, etc nietallic oxides such as alumina, and metal powders.
• a solid pulverulent' material which does not melt within thefiring temperature range
• silica in any of its'nurnerous forms
• siliceous minerals such as clays, mica, granite, etc nietallic oxides such as alumina, and metal powders.
• the selected agent is ground in any suitable grinder to a degree of sub-division which may be determined experimentally to be best in a particular case, and which usually is atleast sufficient to pass 90-95 per cent by weight of the particles through a 200 mesh B. S. sieve.
• the agent may be further comminuted so that at least 60 per cent by weight of the particles are smaller than 10 microns or so that the specific surface exceeds at least 15,000 sq. ems. per gramme, with a resulting increase of tensile strength of the product.
• the grading of the particle sizes when comminuted to pass will generally be such as to secure a satisfactory degree of close packing, but if desired the coal and/or agent may be further graded as to particle size, in accordance with known principles, to obtain an improved degree of close packing.
• the moulding is normally carried out at room temperature, but for certain mixtures it may be desirable to mould Warm, say up to As alternatives to moulding, extrusion or similar techniques usedin the plastics and ceramics industries may be employed.
• the ordinary technique which is used for the moulding of synthetic resins and of dry powders is suitable, except that temperatures higher than atmospheric need not be used.
• the mould is designed with slightly greater clearance for the plunger than is customary with the usual moulding powders of the plastics industry.
• firing totemperatures higher than 850 C. increased electrical conductivity is obtained.
• the firing schedule above 1000 C. may be as rapid as is convenient.
• a further matter of considerable importance in the process is that of the firing atmosphere.
• the heating of the shaped articles and their subsequent cooling must be conducted under nonoxidizing conditions, not only to prevent the coal from burning, but also because oxidation may tend to weaken the agglutinating power of the compacted mass.
• This may conveniently be achieved by packing the article within a protective mass of granular or powdered material which evolves non-oxidizin gas or vapours during the firing operation.
• a suitable material for this purpose is a coal of high volatile content with little or no caliing property, such as the British coal, Warwickshire Brights.
• a bed of this powdered material is made and may be slightly compressed, and the moulded article may then be laid in a depression within the bed which has been made, for example by tamping with a solid former of the same shape as the article. If the moulded article is hollow, the interior of the article is filled with the same powdered material. The exposed surface or surfaces of the articles are then covered with the powder, the latter being firmly but gently pressed down.
• 1+ is also possible to secure the necessary protection by passing a gas stream through the furnace, for example, hydrogen, carbon monoxide, ordinary town gas, or hydro-carbon vapours.
• a gas stream for example, hydrogen, carbon monoxide, ordinary town gas, or hydro-carbon vapours.
• the article should be placed on an even support, preferably of fine, loose, granular ma terial such as sand 01' charcoal. And care should be taken to see that the gas composition all round the article is as uniform as possible.
• This atmosphere may be maintained at normal pressure, or a part or the whole of the firing operation may be conducted with the atmosphere at pressure either above or below normal.
• the mixture was then moulded cold into small howls about 1% deep by 5%" diameter at the rim, under a pressure of 3 tons per square inch,
• the pressure being applied slowly (for example, a travel of 1 inch in seconds) and then immediately released.
• the bowls were then placed in a copper box insidean electrical furnace and covered all over with a high-volatile non-caking coal of a size to pass through a inch mesh B. S. sieve.
• the temperature of the furnace was raised to 800 C. at a rate of 1 C. per minute, the furnace was then allowed to cool, and the bowls were removed from the furnace when the temperature had fallen to about 250 0.
• Example 2 80 parts of the same coal as in Example 1 was comminuted the same as in. Example 1.
• parts of pitch coke and 10 parts of powdered cuprene were taken, the pitch coke being comminuted so as to pass 100% through a 200 mesh B. S. sieve and 90% through a 240 mesh B. S. sieve, and the powdered cuprene being made by allowing gaseous acetylene to deposit on metallic copper at an elevated tem perature.
• Example 3 As an example of the process whenemployinc a weakly caking coal as the swell-inhibiting agent, 70 parts of the strongly coking Welsh coal described in connection with Example 1 was comminuted as in Example 1 and mixed, the same as in Example 1, with 30 parts of a Yorkshire weakly caking coal having a volatile content of 34% and separately comminuted so that per cent passed through a 200 mesh B. S. sieve. The mixture was pressed into flat plates having a thickness of at a moulding pres-sure of 4 tons per square inch, the procedure as to moulding being the same as in Example 1, and also the arrangement to produce the non-oxidizing atmosphere. The rate of firing was, however, different, the temperature of the furnace being raised at the rate of 2 per minute to 300 C'., then at per minute to 500 C. and thereafter at 1 per minute to 700 C. The product was about the same as thatof Example 1.
• thi coal volatiles 20%, swelling number 9, ash 1.1% (90.9% carbon, 4.6% hydrogen, 1.6% nitrogen, 2.9% oxygen and errors on Parrs basis).
• the mixture was moulded the same as in Examh ple 2, into bars of the same size, andthese were subjected to a non-oxidizing atmosphere in an electric furnace in the same way as in Example 1.
• the furnace was raised to 850 C'Qat the rate of 2 C. per minute, and the bars removed when the temperature had fallen to 200 C.
• the product was exceptionally hard, strong, unswollen and undistorted.
• This example is the'same as No. 4 in all respects except that 60 parts of the coal were taken, with 40 parts of elemental silicon, of about the same degree of fineness as the coal, and that the firing rate was 3 C. per minute.
• the product was a strong, hard undistorted material, throughout the mass of which were distributed small, highly reflective facies. This material had a hardness exceeding 5on the Moh scale.
• Example 2 As an example of the use of the higher volatile coal without an anti-swell agent, the same Welsh coking coal as in Example 1 was comminuted so that per cent passed through a 200 .mesh B. S. sieve. The coal powder was pressed into flat plates having a thickness of A at a moulding pressureof 2 tons per square inch,
• Example 3 in which a weakly-caking coal is used to inhibit swelling, the conditions are somewhat different from those in the other examples.
• the inhibitor seems to act merely as a diluent, and materials which behave in that way may be used throughout a wide range, provided that they do not introduce complications into the process, as by decomposing and oxidizing the coal substance.
• a weakly caking coal is not merely a diluent, since it has a small agglutinating value of its own.
• the volatiles of coals of difierent "rank are not evolved over exactly the same temperature range.
• Example 3 the firing rate through the plastic temperature range was substantially as rapid as possible, with the avoidance of swelling, as determined by test, while the degree of comminution and the pressure applied in moulding were similarly determined experimentally, in accordance with the contrasting necessities of providing strength and avoiding swelling, in each case.
• the eifect of variation in each factor can be determined for any particular case, and adjustments made by further tests for combinations of factors. For instance, test pieces are made and fired with a standardized procedure except that different proportions of a particular anti-swelling agent are mixed with a given coal, and the tensile strength, shatter resistance, and other desirable qualities of the product determined, to ascertain the effect of varying such proportions, other conditions being equal.
• the non-oxidizing atmosphere should consist of or contain an unsaturated hydrocarbon gas or vapour such for example as ethylene or other olefine or benzene, or other readily cracked hydrocarbons (whether saturated or unsaturated). Whilst such vapours may scour away certain unsaturated constituents evolved from the coal, the latter will be replaced by another unsaturated substance such as ethylene, which eiiect would not be obtained when the nonoxidizing atmosphere is provided by a gas such as hydrogen or methane.
• an unsaturated hydrocarbon gas or vapour such for example as ethylene or other olefine or benzene, or other readily cracked hydrocarbons (whether saturated or unsaturated). Whilst such vapours may scour away certain unsaturated constituents evolved from the coal, the latter will be replaced by another unsaturated substance such as ethylene, which eiiect would not be obtained when the nonoxidizing atmosphere is provided by a gas such as hydrogen or methane.
• such an atmosphere can suitably consist of or contain an unsaturated hydro carbon gas or vapour such for example as ethyl-- ene or other olefine or benzene, or other readily cracked hydrocarbons, whether unsaturated or saturated.
• This latter method in addition to yielding an article which has an especially low porosity, provides for improved control over the process.
• the non-oxidizing means in the first stage is a gas such as hydrogen or ordinary town gas
• the hydrogenation and the scouring away of unsaturated constituents both of the coal substance and of the surrounding atmosphere can be tolerated, and hence the volume flow of the gas may be sufficient to remove any danger of burning of the article as the result of the ingress of atmospheric oxygen.
• the ethylene or other gas or vapour which is used in the second stage will be relatively free from contamination and therefore may be recycled, thus re ducing the cost of the process.
• the two stages of firing above-described are especially suitable for the treatment of coal of high volatile content.
• the shaped articles may lack sufficient strength to withstand a firing operation unless the hydrocarbon gas or vapour is introduced at the outset.
• the deposition of carbon on the inner surfaces of the material or in the voids between them will not be seriously interfered with. nor will it be necessary to use an excessive quantity of gas or vapour.
• the process of producing useful shaped articles which comprises preparing an intimate mixture of finely comminuted material composed at least predominantly of coal which contains volatiles in the proportion of about 13 to 30% on a dry ash-free basis, moulding from the resultant mixture an article of the desired shape under a pressure of the order of at least two tons per square inch, at least sufficient to enable the shaped article to be transferred undamaged from the moulding machine to a furnace, releasing the pressure, producing test pieces from said mixture, firing the test pieces in a non-oxidising atmosphere to a temperature of at least 550 C.
• the process of producing useful shaped articles which comprises preparing an intimate mixture of finely cc-inminuted material containat least a major proportion of coal which contains Volatiles in the proportion of about 13 to 38% on a dry ash-free basis, moulding test pieces from said mixture under a pressure of the order a of at least two tons per square inch, firing said test pieces in a non-oxidising atmosphere to a temperature of at least 556 0., controlling'the rate of firing of said test pieces in such manner as to produce afired test piece free from cracks and free from cellular structure visible to the naked eye, moulding some of the mixture of which said last named test piece was made to desired shape, under a pressure of the order of at least two tons per square inch, releasing the pressure, transferring the moulded article from the moulding machine to a furnace, firing the same in a like atmosphere and at the rate at which the last named test piece was fired to a temperature of about 550 C. and continuing the firing to temperaturecf at least between 650 C. and 850 0.,
• the process of producing useful shaped articles which comprises preparing an intimate mixture of finely comminuted coal which contains volatiles inthe proportion of about 13 to 30% on a dry ash-free basis with finely 00111- rninuted coal of less agglutineting power, mould ing from the resultant mixture an article of the desired shape under a pressure of the order of at least two tons per square inch, at least sufficient to enable the shaped article to be trans- 1 ferred undamaged from the moulding machine to a furnace, releasing the pressure, producing test pieces from said mixture, firing the test pieces in a non-oxidising atmosphere to a temperature of at least 550 C. and controlling the rate of firing in such manner as to produce a fired test piece free from cracks and free from .a cellular structure visible to the naked eye,
• the process of producing useful shaped articles which comprises, preparing an intimate mixture of finely comminutecl material containing at least a major proportion of coal which contains volatiles in the proportion of about 13 to 30% on a dry ash-free basis, moulding from the resultant mixture an article of the desired shape under a pressure of the order of at least two tons per square inch, at least sufiicient to enable the shaped article to be transferred undamaged from the moulding machine to a furnace, releasing the pressure, producing test pieces from said mixture, firing the test pieces in a non-oxidising atmosphere containing a gaseous hydrocarbon decomposable at temperatures attained in firing, to a temperature of at least 550 C.
• the process of producing useful shaped articles which comprises, preparing an intimate mixture of finely cornminuted material containing at least a major proportion of coal which contains volatiles in the proportion of about 13 to 30% on a dry ash-free basis, moulding from the resultant mixture an article or the desired shape under a pressure of the order of at least two tons to the square inch, at least sufiicient to enable the shaped article to be transferred undamaged from the moulding machine to a furnace, releasing the pressure, transferring the said article to a furnace, firing it in a non-oxidising atmosphere to a temperature of at least 550 C.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Organic Chemistry (AREA)
• Ceramic Engineering (AREA)
• Manufacturing & Machinery (AREA)
• Materials Engineering (AREA)
• Structural Engineering (AREA)
• Inorganic Chemistry (AREA)
• Carbon And Carbon Compounds (AREA)
• Solid Fuels And Fuel-Associated Substances (AREA)

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Cited By (9)

Citations (5)

• 0
  • BE BE467198D patent/BE467198A/xx unknown
• 1945
  • 1945-10-17 US US622934A patent/US2461365A/en not_active Expired - Lifetime

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