Classifications

• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
  • C01F11/00—Compounds of calcium, strontium, or barium
  • C01F11/02—Oxides or hydroxides
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B21/00—Nitrogen; Compounds thereof
  • C01B21/06—Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron
  • C01B21/076—Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron with titanium or zirconium or hafnium
  • C01B21/0765—Preparation by carboreductive nitridation
• • 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
  • C01B32/90—Carbides
• • 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
  • C01B32/90—Carbides
  • C01B32/907—Oxycarbides; Sulfocarbides; Mixture of carbides
• • 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
  • C01B32/90—Carbides
  • C01B32/914—Carbides of single elements
• • 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
  • C01B32/90—Carbides
  • C01B32/914—Carbides of single elements
  • C01B32/921—Titanium carbide
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2002/00—Crystal-structural characteristics
  • C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
  • C01P2002/72—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data by d-values or two theta-values, e.g. as X-ray diagram
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2002/00—Crystal-structural characteristics
  • C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
  • C01P2002/77—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data by unit-cell parameters, atom positions or structure diagrams
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2004/00—Particle morphology
  • C01P2004/01—Particle morphology depicted by an image
  • C01P2004/03—Particle morphology depicted by an image obtained by SEM
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2004/00—Particle morphology
  • C01P2004/50—Agglomerated particles
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2004/00—Particle morphology
  • C01P2004/60—Particles characterised by their size
  • C01P2004/62—Submicrometer sized, i.e. from 0.1-1 micrometer
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2006/00—Physical properties of inorganic compounds
  • C01P2006/80—Compositional purity

Definitions

• the present invention relates to a process for the synthesis of certain powdery complex ceramics of refractory metals, according to which an oxide of at least one of these metals is mixed with a reducing metal and with a pure or combined metalloid in solid form, and heats the resulting mixture to a threshold temperature for initiating a self-propelled reaction, in order to obtain the synthesis of a powdery ceramic.
• Complex ceramics are compounds comprising a metallic network of these metals in which are inserted metalloid atoms.
• the advantage of such compounds is that of combining both the properties of metals and ceramics. Due to their hardness, these materials are particularly resistant to wear and are suitable for entering, for example, in the manufacture of cutting tools or polishing products. Their good resistance to chemical attacks and their good electrical conductivity also allow interesting applications in certain fields of chemistry, electronics and electrochemistry.
• Magnesium has the disadvantage of having a boiling point at 1103 ° C, which is low compared to the adiabatic temperature of the reaction. This therefore has an almost explosive character, which makes industrial production problematic.
• the difficulty of attacking a magnesia having been heated to high temperature complicates the final rinsing of the powder with an acid solution.
• a process for the synthesis of nitrides has already been proposed in US Pat. No. 4,459,363, which consists in reducing the oxide of a metal with Mg or Ca and supplying the necessary nitrogen by adding azides, preferably NaN. 3 .
• the use of azide is more in the explosives industry than in the ceramics industry.
• the object of the present invention is to remedy at least in part, the drawbacks of the abovementioned methods in order to allow the production in a controlled manner of powdery complex ceramics using self-propelled combustion starting from reactants in solid phases available industrially and not requiring a pressurized enclosure.
• the subject of this invention is a method of synthesis of the aforementioned type, according to claim 1.
• This invention also relates to a carbide, nitride, carbo-nitride, oxy-carbide, oxy-nitride, nitride or mixed carbide, obtained according to one of the processes defined below. More particularly and advantageously, the mixed carbides are TiC / HfC in a molar ratio typically 40/60.
• the advantage of bringing the refractory metals in the form of oxide lies in the fact that it is an inexpensive chemical form, which can generally be found in very fine powder.
• the carbon powder has the advantage of being available at a very fine particle size which allows a very intimate mixing with the other reactants. Its complete separation from the ceramic powder resulting from the synthesis in the event of an excess balance is however delicate. This disadvantage is palliated by putting an excess of Ca which combines with the carbon.
• Calcium carbide has the advantage of providing a portion of the reducing calcium necessary for the reaction in a very economical form. In addition, in the event of an excess balance at the end of the reaction, it decomposes during the acid rinsing into C 2 H 4 gas and into CaO and therefore leaves no residue in the synthesized ceramic powder.
• the nitrogen necessary for the synthesis of nitrides is advantageously provided in the form of calcium nitride Ca 3 N 2 , which is a pulverulent product, which can be obtained in fine powder, easy to handle and which does not risk breaking down. explosively. It is an easy product to prepare by simple reaction of nitrogen gas on calcium in a temperature-controlled oven. It also makes it possible to provide part of the reducing calcium.
• calcium can be provided in the form of CaCN 2 , also readily available in powder form. It is also possible to synthesize carbonitrides by mixing CaC and Ca 3 N 2 in suitable proportions.
• M is a refractory metal.
• the single oxide M0 2 can be replaced by a mixture of two different refractory metal oxides aM'0 + (la) M "0 2 in predetermined molar proportions a and (1-a) , making it possible to obtain ceramics mixed of two metals.
• This type of reaction can be interesting, because we know of "Material selection for hard coatings" of H. Holleck, Journal Vac. SCI.
• the size of the starting metal oxide particles will preferably also be submicron.
• oxides can be used, such as, for example, ilmenite or zircon sands.
• oxides formed with the reducing metal must then be removed by a selective chemical attack. It is also possible, when it is favorable for the intended use of the ceramic powder produced, to leave the oxides formed.
• FIG. 1 illustrates the diagram of the first embodiment
• FIG. 2 illustrates the diagram of the second embodiment
• Figures 3 and 4 are two SEM photos of two ceramic powders obtained by the process
• FIG. 5 is the X-ray diffraction spectrum making it possible to analyze the exact composition and the content of impurities in a ceramic powder such as TiN
• FIG. 6 is the X-ray diffraction spectrum of a mixed titanium and hafnium carbide
• FIG. 7 is a diagram showing the hardness of mixed carbons as a function of the respective concentrations of two metals extracted from the article by H. Holleck mentioned above.
• the operating method used for implementing the process consists first of all in intimately mixing, in an industrial mixer, a stoichiometric proportion of metal oxide powder with, depending on the case, either a carbon or calcium carbide powder. or a powder of calcium nitride. To avoid untimely reactions during this mixing, it is important to make sure beforehand that the metal oxide powder is perfectly dry, which can be obtained by baking at 110 ° C for one hour.
• an amount of calcium powder is added which exceeds by about 10% the theoretical stoichiometric amount, to obtain the final mixture.
• the reaction is triggered by moderate heating of all or part of the mass. Indeed, the reaction being strongly exothermic, it propagates quickly, as soon as a part of the mixture is brought to a threshold temperature T s for triggering the reaction. Heating can be performed using an oven, torch, induction or any other suitable way.
• the schematic diagram of the installation for the implementation of the process illustrated in FIG. 1 shows a crucible 1 made of current steel XC38, for receiving the mixture of reactants 2.
• This crucible 1 is placed in a closed enclosure 3, made of steel refractory stainless steel, connected by a supply duct 4 to a source of neutral gas, in particular nitrogen for nitrides and argon for carbides.
• a thermocouple is inserted in a housing formed in the bottom of the crucible 1.
• This closed enclosure 3 is placed in the muffle 5 of an electric furnace of 3.3 kW.
• the volume of the enclosure 3 was 3 liters and that of the crucible 1 about 500 cm 3 .
• FIG. 2 a simplified mode of carrying out the reaction was tested using the installation shown diagrammatically in FIG. 2.
• Approximately 1 kg of reactive charge 6 was placed in a flat ingot mold. 7 made of carbon steel 9 cm wide by 50 cm long and 3 cm deep, giving a volume of approximately 1350 cm 3 , closed by a cover 8.
• This ingot mold 7 is placed in a parallelepiped enclosure 9 in steel closed by a cover 10.
• An intake duct 11 opens at one end of the enclosure 9 and is connected to a source of neutral gas 12 such as nitrogen or argon.
• a deflector 11a directs this gas towards the bottom of the enclosure 9.
• a discharge opening 13 is formed at the other end of this enclosure 9 , directly above the end of the mold 7. This opening 13 also serves to light the charge 6 and it can then be closed during cooling to avoid oxidation. After ignition, the reaction propagates at a variable speed, depending on the nature of the charge, the thermal characteristics of the mold 7 and the flow of neutral gas.
• the charge is gradually immersed in a stainless steel conical bottom reactor (not shown) fitted with an agitator containing approximately 10 l of tap water.
• the agitator is started and the acetic acid is gradually added while monitoring the pH continuously.
• neutrality is reached, the mixture is left to settle, the supernatant solution is drawn off and replaced with tap water. If necessary, the acetic acid is added again until neutrality is obtained.
• the powder is stirred with this water for two hours and the powder is decanted which is withdrawn from the bottom of the reactor after removal of the supernatant water.
• the powder is finally filtered and dried in a vacuum reactor.
• Ti0 2 + 2Ca + C ⁇ 2CaO + TiC We use 480 g of Ti0 2 in dehydrated sub icronic powder, 72 g of carbon black and 530 g of Ca in beads of diameter less than 500 ⁇ m (i.e. an excess of calcium of about 10% on the theoretical stoichiometric quantity).
• 349 g of TiC are collected in the form of a well crystallized submicron powder and having an average particle size of 0.7 ⁇ m.
• the oxygen content is 0.6%.
• Hf0 2 + 2Ca + C ⁇ HfC + 2Ca0 737 g of Hf0 2 , 42 g of carbon and 310 g of calcium are used. We proceed as before. The amount of HfC collected is then 650 g. The well-crystallized powder has an average particle size of 0.5 ⁇ m.
• Example 4 The procedure is as in Example 4, under a stream of nitrogen.
• the amount of ZrN collected is 460 g with an average particle size of 0.7 ⁇ m.
• the elements are probably in the form of highly reactive ionized gas in which it is not possible to differentiate the metals from each other any more than the metalloids, which makes it possible to '' consider the production of any combination comprising several metals and several metalloids.
• the final composition is determined by the initial composition of the reactants. This opens up the possibility of synthesis not only of mixed carbides, but also of carbonitrides in all proportions.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Inorganic Chemistry (AREA)
• Life Sciences & Earth Sciences (AREA)
• Geology (AREA)
• Carbon And Carbon Compounds (AREA)
• Compositions Of Oxide Ceramics (AREA)
• Inorganic Compounds Of Heavy Metals (AREA)
• Ceramic Products (AREA)
• Oxygen, Ozone, And Oxides In General (AREA)

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• 1999
  • 1999-03-16 AU AU26352/99A patent/AU2635299A/en not_active Abandoned
  • 1999-03-16 CN CNB998039403A patent/CN1204043C/zh not_active Expired - Fee Related
  • 1999-03-16 EP EP99906402A patent/EP1064224B1/fr not_active Expired - Lifetime
  • 1999-03-16 RU RU2000125557/15A patent/RU2225837C2/ru not_active IP Right Cessation
  • 1999-03-16 AT AT99906402T patent/ATE267768T1/de active
  • 1999-03-16 WO PCT/IB1999/000441 patent/WO1999047454A1/fr not_active Ceased
  • 1999-03-16 ES ES99906402T patent/ES2218996T3/es not_active Expired - Lifetime
  • 1999-03-16 JP JP2000536653A patent/JP4541544B2/ja not_active Expired - Fee Related
  • 1999-03-16 DE DE69917613T patent/DE69917613T2/de not_active Expired - Lifetime
  • 1999-03-16 CA CA002322707A patent/CA2322707C/fr not_active Expired - Fee Related

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