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  • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
  • C04B35/622—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
  • C04B35/626—Preparing or treating the powders individually or as batches ; preparing or treating macroscopic reinforcing agents for ceramic products, e.g. fibres; mechanical aspects section B
  • C04B35/63—Preparing or treating the powders individually or as batches ; preparing or treating macroscopic reinforcing agents for ceramic products, e.g. fibres; mechanical aspects section B using additives specially adapted for forming the products, e.g.. binder binders
  • C04B35/632—Organic additives
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
  • B22F3/22—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces for producing castings from a slip
  • B22F3/225—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces for producing castings from a slip by injection molding
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  • 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
  • C04B35/56—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 carbides or oxycarbides
  • C04B35/5607—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 carbides or oxycarbides based on refractory metal carbides
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  • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
  • C04B2235/02—Composition of constituents of the starting material or of secondary phases of the final product
  • C04B2235/50—Constituents or additives of the starting mixture chosen for their shape or used because of their shape or their physical appearance
  • C04B2235/54—Particle size related information
  • C04B2235/5418—Particle size related information expressed by the size of the particles or aggregates thereof
  • C04B2235/5436—Particle size related information expressed by the size of the particles or aggregates thereof micrometer sized, i.e. from 1 to 100 micron
• • C—CHEMISTRY; METALLURGY
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  • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
  • C04B2235/60—Aspects relating to the preparation, properties or mechanical treatment of green bodies or pre-forms
  • C04B2235/602—Making the green bodies or pre-forms by moulding
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  • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
  • C04B2235/65—Aspects relating to heat treatments of ceramic bodies such as green ceramics or pre-sintered ceramics, e.g. burning, sintering or melting processes
  • C04B2235/656—Aspects relating to heat treatments of ceramic bodies such as green ceramics or pre-sintered ceramics, e.g. burning, sintering or melting processes characterised by specific heating conditions during heat treatment
  • C04B2235/6562—Heating rate
• • C—CHEMISTRY; METALLURGY
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  • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
  • C04B2235/70—Aspects relating to sintered or melt-casted ceramic products
  • C04B2235/74—Physical characteristics
  • C04B2235/77—Density
• • C—CHEMISTRY; METALLURGY
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  • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
  • C04B2235/70—Aspects relating to sintered or melt-casted ceramic products
  • C04B2235/94—Products characterised by their shape
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
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  • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
  • C04B2235/70—Aspects relating to sintered or melt-casted ceramic products
  • C04B2235/95—Products characterised by their size, e.g. microceramics

Definitions

• This invention relates to the method of producing finished and semi-finished products of molybdenum carbide and to products resulting from same.
• Molybdenum carbide embodies many interesting properties including a high melting point temperature of 2600 C.; an electrical conductivity which is about ten times that of graphite; and a heat conductivity which is about one-fifth that of graphite.
• molybdenum carbide finds many important applications in metallurgical processes including use as a refractory material for high temperature applications and as an electrical resistance for furnaces .and the like.
• the molybdenum carbide, in aqueous suspension, embodying a suspension agent of high viscosity such as sodium alginate is injected into a plaster mold and then fritted. It is impractical to make use of the first method in the formation of thin tubular members or of shaped elements of substantial lengths and the paste of the second method has only an insufficient initial strength and is incapable of use to form tubular elements.
• composition formed of powdered or finely divided molybdenum carbide in admixture with a wax present in an amount within the range of 1 to percent by weight of the carbide and an aliphatic saturated hydrocarbon present in an amount within the range of 5 to percent by volume of the carbide.
• the mixture is heated and formed int-o a paste which can be cast when hot and which sets upon cooling.
• the hot mixture can be shaped into the desired product by one or more of the methods, such as simple molding in the form of compression molding, or molding and extrusion, in which the hot mixture is cast or compressed into a mold, cooled, dried and finally removed fro-m the mold, or it may be formed to the desired shape by centrifugal molding in which the mixture is introduced into a preheated mold and formed cen-trifugally by rotation of the mold at high speed and then frit-ted by heating to high temperature, preferably in an oxidizing or inert atmosphere.
• the methods such as simple molding in the form of compression molding, or molding and extrusion, in which the hot mixture is cast or compressed into a mold, cooled, dried and finally removed fro-m the mold, or it may be formed to the desired shape by centrifugal molding in which the mixture is introduced into a preheated mold and formed cen-trifugally by rotation of the mold at high speed and then frit-ted by heating to high temperature, preferably in an oxidizing or inert atmosphere.
• the waxy component of the described mixture may be selected of bees wax or carnauba wax, and as the saturated aliphatic hydrocarbon it is preferred to make use of a halogenated 3,277,222 Patented Oct. 4, 1966 ice aliphatic hydrocarbon such as carbon tetrachloride or trichlorethylene.
• the paste in a heated state of about 60 C., is then shaped, depending upon the form of the product, either in a single process step of simple moulding or centrifugal molding, or else in a two step process wherein the hot paste is first formed preferably by simple moulding into a billet which is there-after drawn or extruded to shape.
• the hot paste at about 60 C. is cast or pressed into the mold and'then chilled. Thereafter the cast material is dried in air or under vacuum prior to removal from the mold.
• the hot paste at about 5070 C., is placed in a mold heated to elevated temperature, such as 40-50 C.
• the mold is rotated at high speed, such as 5004500 r.p.m. depending somewhat upon the diameter of the product to be molded. After rotation for about one to two hours, the molded product is removed from the mold.
• the paste is introduced and compressed into billets, preferably using a mold formed of steel or other easily shaped material, and more preferably one which can provide a polished or smooth surface to ease removal of the billet from the mold and the forming or drawing operation.
• a mold formed of steel or other easily shaped material preferably one which can provide a polished or smooth surface to ease removal of the billet from the mold and the forming or drawing operation.
• Particular care is required in the drying in order to preserve sufi'icient plasticity in the mold while excessive drying may lead to the formation of cracks in the drawn product.
• the shaping and the drying of the paste is followed by fritting.
• the fritting operation may be performed in two stages-namely, a pre-fritting "stage which covers the temperature range from ambient temperature to about 1350 C. during which little, if any, shrinkage of the heated product is observed.
• a pre-fritting "stage which covers the temperature range from ambient temperature to about 1350 C. during which little, if any, shrinkage of the heated product is observed.
• the temperature is increased rapidly from ambient tempera ture to from 250-300 C., usually in less than 30 minutes, and thereafter the temperature is increased steadily at a rate of about 40 C. per hour until the temperature of 1350 C. is reached.
• the rise in temperature is achieved at a higher rate, such as at a rate of 50-100 C. per hour, until the final fritting temperature is reached which is generally within the range of 1600-2300 C.
• the molded product is maintained at fritting temperature for a number of hours after which the product is cooled down slowly.
• the density of the fritted product will depend greatly upon the temperature and the time that the product is maintained at fritting temperature. Fritting is desirably carried out in the absence of oxygen: it is generally effected in a neutral atmosphere, preferably under vacuum conditions.
• the paste is molded preferably by simple compression molding, optionally followed by drawing or extrusion instead of by centrifugal molding because otherwise the centrifugal forces would tend to cause classification or separation between the heavier fritted particles and the unfritted powders.
• the rapid rate in the initial rise in temperature during the pre-fritting stage would no longer be necessary.
• fritted material reduced to granular size within the range of 1 to 2 millimeters in cross-section and the fritted material can be employed in the mixture in an amount up to 70 percent of the mixture but it is preferred to limit the use of the fritted component to an amount within the ranke of to 50 percent by weight of the combined fritted and unfritt'ed molybdenum carbide component.
• Example 2 Preparation of a bar having a diameter of 30 millimeters and a length of 1000 millimeters
• the bar is obtained by drawing or drafting a billet formed in a steel mold having a diameter of 97 millimeters and a length of 90 millimeters.
• the billet is molded of a paste formed of a mixture of molybdenum carbide kneaded wit-h 3 parts by weight of carnauba wax per 100 parts by weight of the molybdenum carbide and 12 percent by volume of carbon tetrachloride.
• the cast material is partially dried by exhaustion to the atmosphere for about two hours.
• the pre-fritting step is carried out by increasing the temperature to 300 C. in 20 minutes followed by increasing the temperature from 300 to 1350 C. under vacuum at a rate of 40 C. per hour.
• the fritting step is carried out by increasing the temperature from 1350 to 1650 C. at a rate of 60 C. per hour, in an atmosphere of nitrogen, after which it is held at 1650 C. for about six hours.
• the pre-fritting and fritting cycle is the same as that of Example 2 except that the final fritting temperature is at 2100 C. at which temperature the product is maintained for about six hours.
• the final density is 8.1.
• Example 4.Preparati0n 0 a molded tubing having an outer diameter of 350 millimeters, an inside diameter of 320 millimeters, and a length of 400 millimeters
• a mold and core formed of graphite For this purpose, use is made of a mold and core formed of graphite.
• the tubing is retained in its mold and the temperature is increased from room temperature to l350 C. at the rate of about 40 C. per hour, under vacuum, and thereafter the tubing is removed from the mold.
• the temperature is increased from 1350 C. to 2000 C. at a rate of 60 C. per hour, and then held at this temperature for six hours in an atmosphere of nitrogen.
• the density is raised from a density of 5 for the crude paste to a density of 7 for the fritted product.
• Example 5 Preparati0n of molded tubing having an outside diameter of 245 millimetens, and inside diameter of 215 millimeters, and a length of 530 millimeters Fritted molybdenum carbide reground into granules of l2 millimeters is introduced dry to fill the mold. The mold is heated to a temperature of 60 C. and the following hot fluid mixture is then cast into the mold:
• the tubing formed by extrusion of the paste into the mold filled with the fritted molybdenum carbide has a green density of 5.8 and results in a tubing density of 7 after the fritting steps.
• the results can be improved further by vibration of the paste during molding for purposes of densification and before removal of the product from the mold.
• use can be made of a shaker table on which the mold is placed during or after it is filled with the paste. Under such conditions, a green density of 6.2 instead of 5.8 is possible with a corresponding increase in the density of the final product from 7 to a level of about 7.5.
• the fritting and cure can be carried out in a single fritting cycle, the complete cycle comprising drying for several hours preferably by exhaustion under vacuum and then fritting by increasing the temperature at a rate of 30-70 C. and preferably 50 C. per hour until a temperature of 1600-2200 C. and preferably 2000 C. is reached. This results in a savings in time and power and any cracking in the first phase of the process is greatly minimized.
• the solvent employed in the moldable composition may comprise other aliphatic saturated hydrocarbons in addition to or instead of trichlorethylene and carbon tetrachloride.
• a composition for use in the preparation of molded products of molybdenum carbide comprising a mixture of unfritted molybdenum carbide powder and granules of molybdenum carbide which has been heated to a temperature within the range of 16002300 C. and in which the latter makes up to 70 percent by weight of the carbide mixture and in which the carbides are mixed to form a paste consisting essentially of the carbide, a wax present in an amount within the range of 1 to percent by weight of the carbide and a saturated organic hydrocarbon liquid present in an amount within the range of 5 to 20 percent by volume of the carbide.
• composition as claimed in claim 1 in which the wax is selected from the group consisting of carnauba wax and bees wax.
• the method of producing finished and semi-finished products of molybdenum carbide comprising the steps of providing the carbide in finely divided form, mixing the carbide to form a paste consisting essentially of the carbide, a wax and a saturated organic hydrocarbon solvent, said wax being present in the paste in an amount within the range of 1 to 10 percent by weight of the carbide, and said hydrocarbon being present in an amount within the range of 5 to 20 percent by volume of the carbide, molding the paste into a product of the desired shape, drying the molded product, heating to a temperature Within the range of 250300 C. and then heating more slowly at a rate of 40-60 C. per hour to a temperature of 1350-4600 C., and thereafter heating the product to a temperature within the range of 16002300 C.
• Wax component is selected from the group consisting of carnauba wax and bees wax.
• the method of producing finished and semi-finished "products of molybdenum carbide comprising the steps of providing the carbide in finely divide-d form, said carbide consisting of unfritted molybdenum carbide powder and molybdenum carbide which has been heated to a temperature within the range of 1600-2300 C.

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Citations (7)

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• 1962
  • 1962-11-06 FR FR914471A patent/FR1367431A/fr not_active Expired
• 1963
  • 1963-05-09 FR FR934250A patent/FR83931E/fr not_active Expired
  • 1963-11-04 GB GB4341863A patent/GB1051449A/en not_active Expired
  • 1963-11-05 NL NL300107A patent/NL300107A/xx unknown
  • 1963-11-05 US US321398A patent/US3277222A/en not_active Expired - Lifetime
  • 1963-11-05 CH CH1356263A patent/CH428540A/fr unknown
  • 1963-11-05 DE DEP32918A patent/DE1245827B/de active Pending
  • 1963-11-06 BE BE639587A patent/BE639587A/xx unknown

Patent Citations (7)

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