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
  • C04B35/56—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
  • C04B35/563—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 boron carbide
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
  • B01J19/08—Processes employing the direct application of electric or wave energy, or particle radiation; Apparatus therefor
  • B01J19/12—Processes employing the direct application of electric or wave energy, or particle radiation; Apparatus therefor employing electromagnetic waves
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
  • B01J19/08—Processes employing the direct application of electric or wave energy, or particle radiation; Apparatus therefor
  • B01J19/12—Processes employing the direct application of electric or wave energy, or particle radiation; Apparatus therefor employing electromagnetic waves
  • B01J19/121—Coherent waves, e.g. laser beams
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
• • 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
  • C01B32/991—Boron carbide
• • 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
  • C04B35/622—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
  • C04B35/64—Burning or sintering processes
  • C04B35/645—Pressure sintering
• • 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
  • 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
  • C01P2004/00—Particle morphology
  • C01P2004/60—Particles characterised by their size
  • C01P2004/64—Nanometer sized, i.e. from 1-100 nanometer
• • 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
  • C01P2006/10—Solid density
• • 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
  • C01P2006/12—Surface area
• • 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
  • C01P2006/60—Optical properties, e.g. expressed in CIELAB-values
• • 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
  • C01P2006/90—Other properties not specified above

Definitions

• the present invention concerns an improved process for the preparation of ultrafine high purity- boron carbide powders, and its product, useful as a relatively high cost refractory material in the manu- facture of ceramic parts.
• the grain size is governed by the particle size of the powder from which the part is prepared. In other words, the grain size is necessarily larger than the crystalites from which a part is sintered. Thus, the sintering of finer particles presents the opportunity to produce fine-grained bodies.
• the gas-phase synthesis of boron carbide powders typically involves the reaction of a boron halide with a hydrocarbon as the carbon source in the presence of hydrogen.
• a boron halide with a hydrocarbon as the carbon source in the presence of hydrogen.
• I. M. MacKinnon and B. G. Reuben, "The Synthesis of Boron Carbide in an RF Plasma", J. Electrochem. Soc. 122(6), 806 (1975) utilize a radio-frequency induced argon plasma to heat a stream of boron trichloride, methane and hydrogen.
• the boron o carbide powders formed are about 200-300 A in diameter.
• British Patent 1,069,748 and U.S. Patent 3,340,020 describe the reaction of boron trichloride-methane mixtures in a hydrogen plasma jet to produce boron o carbide powders of 200 A average particle size.
• a C0 2 laser is an acceptable energy source for the reaction of boron trichloride, hydrogen and a hydrocarbon for the production of high purity boron carbide but only under certain reaction conditions.
• the present invention provides a process for the preparation of high purity ultrafine boron carbide powder. Also, the present process produces relatively monodispersed ultra-high purity boron carbide powders.
• ultrafine high purity boron carbide powder is produced by subjecting a continuous stream of reactant gases consisting essentially of a volatile boron source, less than the stoichiometric amount, calculated on the boron in the boron source, of a volatile carbon source and at least a stoichiometric amount, calculated on the boron in the boron source, of a source of hydrogen, at an absolute pressure of at least about 300 Torr, to an amount of C0 2 laser radiation effective to convert at least a portion of the volatile boron source to B 4 C.
• reactant gases consisting essentially of a volatile boron source, less than the stoichiometric amount, calculated on the boron in the boron source, of a volatile carbon source and at least a stoichiometric amount, calculated on the boron in the boron source, of a source of hydrogen, at an absolute pressure of at least about 300 Torr, to an amount of C0 2 laser radiation effective to convert at least a portion
• This invention also concerns the boron carbide powder product prepared by the present present process.
• the product (B 4 C) powder has several unique properties compared to known B 4 C powders.
• the present B 4 C powder can be hot-pressed to parts of theoretical density at temperatures substantially below those required for conventionally prepared B 4 C powders.
• the microstructure of the pressed parts reveals pure, uniform grains, which are required in high strength ceramic parts.
• this inven- tion also concerns boron carbide having the follow ⁇ ing characteristics: a) B/C ratio of 3.9 to 4.2; b) metal impurities of less than 10 ppm per metal; o c) particle size range of 100 to 1300 A; d) monodispersed powder; e) surface area of at least 50 f) microcrystalline structure; and g) capable of being densified to theo ⁇ retical density (2.52 g/cm 3 ).
• Figure 1 is a schematic drawing of apparatus suitable for practicing the process of the invention.
• Figure 2 is the X-ray diffraction pattern of boron carbide obtained by the process of the invention.
• high purity means B 4 C which is at least about 94 percent pure.
• a source of hydrogen means a source capable of releasing hydrogen, such as in reac- tion with the volatile boron and carbon sources or when subjected to heat.
• ultra-fine particle means par ⁇ ticles having a diameter of less than I ⁇ m.
• volatile boron source means a boron-containing material which is gaseous at the temperature at which the material is injected into the reactant stream.
• volatile boron sources for use in the present process include absorbing boron sources such as, trimethyl borate.
• Other volatile boron sources include alkyl borons, such as trimethyl boron, alkyl borates, such as trimethyl borate, boron hydrides, such as diborane, and boron halides, such as boron trifluoride.
• a preferred boron source is boron trichloride.
• reactant gases means the gases which are employed, because of their carbon, boron, and/or hydrogen content, to form B 4 C when subjected to low power laser irradiation.
• a reactor suitable for effecting the reaction is illustrated schematically in Figure 1.
• the reactor proper is a cylindrical Pyrex glass tube or reactor 10 with KCl windows 11 and 12 firmly attached at either end.
• the reactor has a centrally located entrance port 13 and a centrally located exit port.14 positioned opposite entrance port 13.
• a glass inlet tube 5 is fitted in gas tight connection in entrance port 13 and to the argon source 1.
• a smaller gas inlet tube 6 is mounted concentrically in inlet tube 5 with an open end thereof extending into reactor 10 and the other end in gas tight connection with the source of reaction gases.
• a gas outlet tube 7 is mounted in gas tight connection to exit port 14 and the other is fitted in gas tight connection into the top of a Pyrex Buchner funnel 20, which has a glass frit filter 21 and a collection tube 22, by a rubber stopper 30. Smaller gas inlet ports 15 and 16 are located proximate the KCl windows 11 and 12.
• the reactor is designed ' to inhibit the B 4 C solids formed from adhering to the inside of the reactor and/or fusing together to form larger agglomerates.
• reactors can be used within the scope and teachings of the instant invention, for instance, a reactor with germanium or zinc selenide windows would be acceptable.
• An argon gas purge is introduced proximate each window via ports 15 and 16 and also concentric to the reactant gas stream via tube 1 and inner tube 6 into entrance port 13.
• the window purge serves to prevent both window overheating and the accumulation of material on the window surfaces.
• the concentric flow of argon serves to entrain the boron carbide particles in the gas stream as they are formed.
• the reactant gases, H 2 , BC1-, and CH 4 or C 2 H 4 are introduced into reactor 10 through aluminum tubes 2, 4 and 3, respectively. All gas flow rates are monitored with gas flow controllers.
• a typical gas flow meter can be a calibrated Matheson flow meter.
• the reactant gases are premixed prior to entering the reactor via the inner tube of entrance port 13.
• the pressure within the reactor is monitored by a conventional Bourdon gauge (not shown) and is regulated by regulating both gas input flow rate and vacuum pumping rate.
• a gas scrubber can be in fluid communication with the vaccum pump.
• the scrubber can be in direct connection with the fil ⁇ tration device to eliminate undesirable materials from the gas stream.
• the out ⁇ put of a C0 2 laser 60 100W cw (Coherent model 40), operating multimode at 10.6 microns at a power of about 80 watts, is focused at about 1-10 kw/cm 2 into the jet of reactant gases entering the reactor 10.
• the beam travels through the front KCl window 11 and out the rear KCl window 12.
• An AR-coated germanium lens 62 with a 200 mm focal length is used to focus the beam.
• a defocused beam is used; that is, the beam is focused so that the focal point of the beam is located either in front of or behind the flame produced where the laser beam intersects the gaseous mixture (boron carbide powder nucleates and forms in the flame).
• the preferred distance between the combustion nozzle formed by the open end of inlet tube 6 projecting into entrance port 13 and the laser focal point is about 3 cm.
• the size of the laser spot where it impacts the reactant gases is pre- ferably the same diameter as the diameter of the react ⁇ ant gas stream, however the diameter of the laser spot can be less than the diameter of the reactant gas stream or alternatively, greater than the diameter of the react ⁇ ant gas stream.
• the power of the laser could be increased, operating at up to 25 kw.
• a low power laser at less than 25 watts could be used, e.g., 10 watts.
• the reactor 10 and accompanying optics, such as the lens 62, mirrors and windows 11 and 12, would require some modifications known to one skilled in the art.
• the yield and purity of the B 4 C obtained in the process of this invention is determined by a number of inter-related process variables.
• the purity of B 4 C obtained is significantly affected by the ratio of hydrocarbon to boron source in the starting gas mixture particularly when using conventional low power lasers, e.g., about 25 watts. Ordinarily, that ratio is less and desirably substan ⁇ tially less than stoichiometric, i.e., up to about 60 percent thereof. Conversely, too little of the carbon source can lower purity and, of course, yield.
• the adverse effect of an amount of carbon source in the reaction gas mixture in excess of about 60 percent of stoichiometric can be compensated for at least partially by using a higher powered laser. With higher powered lasers, up to about stoichiometric amounts of the carbon source can probably be employed without seriously affecting the purity of the B 4 C produced.
• At least the stoichiometric amount of hydro ⁇ gen which would be required if all of the boron source reacted is preferably employed, e.g., from about 100 percent to 1,000 percent, preferably about 200 percent to 800 percent, and most preferably about 300 percent to 400 percent of the stoichiometric amount of H 2 is employed.
• the power of the laser affects yield and, as noted above, can also affect purity. Laser powers of from about 25 watts have utility. However, powers of greater than 25 watts are preferred.
• the laser spot size near the reactant nozzle also affects yield and can affect purity. The distance between the focusing lens and the reactant gas stream is fixed such that the laser spot size is comparable to the diameter of the reactant gas stream.
• the pressure at which the reaction is conducted also can affect purity and/or yield.
• a pressure of about 300 to 1,500 Torr and most preferably about 600 to 700 Torr is therefore employed.
• the optimal pressure above 600 Torr is determined by the desired particle size of the boron carbide powder produced.
• a pressure of about 600 Torr is preferred for the synthe- o sis of 200-300 A boron carbide particles.
• an inert gas diluent e.g., argon or helium
• any carbon source which is gaseous at the temperature at which it is mixed with the BC1_ and H- can be employed.
• volatile hydrocarbons e.g., methane, ethane, ethylene, isooctane, acetylene and butylene
• contemplated equivalents are other volatile carbon sources which contain another element, e.g., chlorine or nitrogen, e.g., volatile halocarbons, provided they react comparably to the corresponding hydrocarbon.
• the carbon source comprises a member of the group consisting of methane, ethylene and carbon tetrachloride.
• a volatile boron source can be used in conjunction with boron trichloride or either an absorbing hydrocarbon, such as ethylene, or an absorbing boron source, such as trimethyl borate.
• Other volatile boron sources include alkyl borons, such as trimethyl borate, boron hydrides, such as diborane, and boron halides, such as boron trifluoride.
• the boron source comprises a member of the group of an alkyl boron, an alkyl borate, a boron hydride or a boron halide.
• the reaction is endothermic, lower laser power is required if the starting gaseous mixture is heated, e.g., up to about 1,400 °C (but below the temperature at which the stream of reactant gases react in the absence of laser engergy) .
• the unreacted BC1 3 is preferably recycled to the reactor, after separation of the HC1 therefrom in any conventional manner.
• an electrostatic precipitator or cyclone to col ⁇ lect the B 4 C the reaction can be conducted continuously, thereby ensuring steady state conditions.
• the B 4 C produced according to the process of this invention is very pure, i.e. it contains less than 6 percent, preferably less than 1 percent, and most preferably less than 0.1 percent each of elemental carbon and boron.
• the B 4 C produced has extremely fine particles, for example, ranging from about 100 to 1,300 A.
• the reactor pressure was fixed at approximately 600 Torr. The laser beam was then allowed to enter the cell with the concomitant appear- ance of a luminescent flame.
• the product is gray ⁇ ish black, indicative of an amorphous carbon impurity.
• the BC1 3 /C 2 H 4 ratio is increased from 8 to 16 the color of the sample changes from gray-black to gray.
• Use of an amount of ethylene up to about half the stoichiometric amount results in boron carbide product of good purity.
• the yield and purity of product increases with increasing laser power.
• the product contains a substantial carbon impurity. Accordingly, operation at 50W incident radiation or above is preferred.
• Optimal pressure in the reactor for the pro- duction of particles with diameters between 200 and 300 A ranges from about 600-700 Torr. Increasing amounts of carbon are formed as the pressure is lowered further. As noted previously, pressure within the reactor is con ⁇ trolled both by controlling the flow rate of the react- ants and by controlling the vacuum applied to the reactor.
• the quantum yield for the boron carbide synthesis i.e., molecules of boron carbide per photon absorbed, can be estimated from the weight of recovered product and the laser power absorbed.
• Run 51 a 48 percent yield of boron carbide at 9W power absorbed, the quantum yield is 0.0041. This value corresponds to 240 photons per boron carbide molecule.
• the ⁇ H values for the reactions shown above correspond to 34 (ethylene) and 42 (methane) photons.
• the yield of boron car ⁇ bide obtained depends on the incident laser intensity.
• a laser spot diameter substantially similar to the diameter of the stream of reactant gases favors higher yields.
• the power densities in the focused and slightly defocused configurations were approxi ⁇ mately 10 kw/cm 2 and 1.5 kw/cm 2 , respectively, at 80W incident power. If one extrapolates yield vs. laser power employed in this example, incident laser inten ⁇ sity of about 340W should give a 100 percent yield.
• the properties of the B 4 C powder prepared by the present process and the properties of commer ⁇ cially available B 4 C powders are shown in Table IV.
• the powders produced by the present process are ultra ⁇ fine, equiaxed, and monodispersed.
• ND means not detectable
• Example 1 is a product of this invention
• Example A is ESK 1200 from Elektroschmelzwerk Kempten GmbH
• Example B is ESK 1500 from Elektroschmelzwerk Kempten GmbH
• Example C is from Callery Chemical Co.
• Example D is Norbide from Norton.
• B 4 C is hot pressed at about 5,000 psi and 2,200°C.
• the B.C of the present invention has been densified at temperatures significantly below those reported in the literature.
• Table IV are summarized some properties of hot pressed B 4 C powders of the present invention and commercially available powders, all pressed at 2,200°C.
• Example 1 is a product of this invention
• Example A is ESK 1200 from Elektroschmelzwerk Kempten GmbH
• Example B is ESK 1500 from Elektroschmelzwerk Kempten GmbH
• Example C is from Callery Chemical Co.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Organic Chemistry (AREA)
• Ceramic Engineering (AREA)
• Manufacturing & Machinery (AREA)
• Materials Engineering (AREA)
• Physics & Mathematics (AREA)
• Inorganic Chemistry (AREA)
• Structural Engineering (AREA)
• Electromagnetism (AREA)
• Health & Medical Sciences (AREA)
• General Health & Medical Sciences (AREA)
• Toxicology (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Nanotechnology (AREA)
• Optics & Photonics (AREA)
• Composite Materials (AREA)
• Condensed Matter Physics & Semiconductors (AREA)
• General Physics & Mathematics (AREA)
• Crystallography & Structural Chemistry (AREA)
• Carbon And Carbon Compounds (AREA)

Applications Claiming Priority (2)

Publications (2)

Family

ID=24815094

Family Applications (1)

Country Status (4)

Families Citing this family (8)

Citations (1)

Family Cites Families (3)

• 1986
  • 1986-02-12 JP JP61501339A patent/JPS62501838A/ja active Pending
  • 1986-02-12 WO PCT/US1986/000322 patent/WO1986004524A1/en not_active Application Discontinuation
  • 1986-02-12 EP EP19860901635 patent/EP0211948A4/en not_active Ceased
  • 1986-02-12 KR KR1019860700706A patent/KR870700028A/ko not_active Application Discontinuation

Patent Citations (1)

Non-Patent Citations (2)

Also Published As

Similar Documents

Legal Events