Classifications

• • 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
  • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
• • 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
  • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
  • B22F1/05—Metallic powder characterised by the size or surface area of the particles
• • 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
  • B22F9/00—Making metallic powder or suspensions thereof
  • B22F9/02—Making metallic powder or suspensions thereof using physical processes
  • B22F9/04—Making metallic powder or suspensions thereof using physical processes starting from solid material, e.g. by crushing, grinding or milling
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C27/00—Alloys based on rhenium or a refractory metal not mentioned in groups C22C14/00 or C22C16/00
  • C22C27/04—Alloys based on tungsten or molybdenum

Definitions

• the present disclosure relates to powders containing molybdenum.
• This application claims priority from Japanese Patent Application No. 2021-168283 filed on October 13, 2021. All the contents described in the Japanese patent application are incorporated herein by reference.
• Patent Document 1 Japanese Patent Application Laid-Open No. 11-36006
• the molybdenum-containing powder of the present disclosure has an average particle size of 0.5 ⁇ m or more and 3.0 ⁇ m or less by the Fsss method, and a BET specific surface area of 0.3 m 2 /g or more and 5.5 m 2 /g or less by the gas absorption method. It has an aggregation coefficient of 5.5 or less calculated from the average particle diameter and BET specific surface area by the Fsss method, and an apparent density of 2.13 g/cm 3 or less measured according to JISZ2504 (2012).
• ammonium molybdate or MoO 3 (molybdenum trioxide) powder is filled in a reduction boat (for example, a heat-resistant alloy boat), inserted into a reduction furnace in a hydrogen atmosphere, and reduced at a constant temperature. , to produce intermediate products.
• the intermediate product is further heated at a high temperature to produce Mo powder.
• a sintering temperature of about 1800 ° C to 2000 ° C is required to obtain a dense molybdenum sintered body by a general powder metallurgy method, and sintering at a high temperature is required. This leads to high sintering costs for molybdenum-containing powders produced by conventional methods.
• the sintering (joining) temperature with materials containing molybdenum powder is generally higher than 1000 ° C.
• Thermal expansion with ceramics other than molybdenum Due to the difference, problems such as warping of the fired workpiece may occur. The reason for this is considered to be the problem of shrinkage characteristics during sintering caused by variations in particle size of molybdenum powder and aggregation of particles.
• molybdenum powder which has fine grains, less agglomeration, and good sinterability at low temperatures, is useful.
• Patent Document 1 In the powder metallurgy method of Patent Document 1, an intermediate product produced when powder of ammonium molybdate or MoO 3 (molybdenum trioxide) is reduced is doped with K and P and reduced in a hydrogen atmosphere. A method for producing molybdenum powder having uniform grains having an apparent density of 2.2 or more and having no particles of 22 ⁇ m or less in the grain size distribution is described.
• the Mo powder obtained by the method of Patent Document 1 has less agglomeration than the conventional molybdenum-containing powder, but is considered to have poor sinterability due to its large particle size. Further, Patent Document 1 describes improvement of the packing density of Mo powder, but does not mention sinterability at all.
• the powder containing molybdenum of the present disclosure has an average particle size (hereinafter also referred to as Fsss average particle size) of 0.5 ⁇ m or more and 3.0 ⁇ m or less by the Fsss method, and a BET specific surface area (hereinafter, BET specific surface area ) is 0.3 m 2 /g or more and 5.5 m 2 /g or less, and the cohesion coefficient calculated from the average particle size by the Fsss method and the BET specific surface area is 5.5 or less.
• Fsss average particle size average particle size
• BET specific surface area a BET specific surface area
• the present disclosure relates to a molybdenum-containing powder that is less agglomerated and has excellent sinterability, and it was found that an effect can be obtained by setting the following characteristic values within a predetermined range.
• the required ranges are Fsss average particle size of 0.5 ⁇ m or more and 3.0 ⁇ m or less, BET specific surface area of 0.3 m 2 /g or more and 5.5 m 2 /g or less, aggregation The coefficient is 5.5 or less.
• the aggregation coefficient ⁇ is expressed by the following formula.
• d the BET particle diameter calculated from the BET specific surface area
• ⁇ the density
• a more preferable range is an Fsss average particle size of 0.5 ⁇ m or more and 3.0 ⁇ m or less, a BET specific surface area of 0.3 m 2 /g or more and 5.5 m 2 /g or less, and an aggregation coefficient of 1.5 or more and 5.1 or less. .
• a preferred range of molybdenum purity is 99.5% by mass or more.
• a more preferable range is molybdenum purity of 99.9% by mass or more. Within this range, impurities are less likely to affect sinterability.
• At least one of Al, Ca, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Sn, Si, Na, K, As, P, and W can be included as a composition other than molybdenum.
• the proportion of each composition is less than 0.1% by mass.
• the analysis method is JISH1404 (2001) for Fe, Ca, Si, Al, and Mg, atomic absorption spectrometry for K, Na, and As (manufactured by Analytic Jena Japan: contrAA300), and ICP emission spectroscopy for P and other metals (manufactured by Shimadzu Corporation). : ICPS-8100) can be used.
• the preferred range of particle size distribution is D90/D10 of 4.3 or less.
• a more preferable range of D90/D10 is 1.5 or more and 4.0 or less. Within this range, the sinterability is further improved.
• D90 represents the D90% diameter, and refers to the particle size at which the cumulative frequency of particles below this particle size in the particle size distribution graph is 90%.
• D10 represents the D10% diameter, and refers to the particle size at which the cumulative frequency of particles smaller than this particle size in the particle size distribution graph is 10%. Within this range, the sinterability is further improved.
• a preferable range of crystallite size is 1000 nm or less.
• a more preferable range is a crystallite size of 75 nm or more and 980 nm or less. Within this range, the sinterability is further improved.
• a preferable range of lattice strain is 0.018% or more.
• a more preferable range is a lattice strain of 0.02% or more. Within this range, the sinterability is further improved.
• a relative density of 70% or more can be achieved when sintered at 800°C, and a relative density of 85% or more can be achieved when sintered at 1400°C.
• the apparent density measured according to JISZ2504 (2012) is 2.13 g/cm 3 or less, preferably the tap density measured according to JISZ2512 (2012) is 4.34 g/cm 3 or less.
• Step 1 raw material sieving
• step 2 single-step reduction
• step 3 intermediate sieving
• step 4 two-step reduction
• step 5 final sieving
• step 6 mortar crushing
• Step 1 Raw material sieving The raw material MoO3 powder is sieved. The raw material is passed through a sieve with a predetermined mesh size to remove coarse particles and agglomerated powder, and to collect under-sieves. The opening of the sieve mesh is appropriately changed depending on the raw material and the target molybdenum powder particle size.
• Step 2 One-step reduction (MoO 3 ⁇ MoO 2 )
• MoO 3 sieved in step 1 is charged into a heat-resistant alloy boat, reduced to MoO 3 ⁇ MoO 2 and taken out.
• Optimal reduction conditions temperature, hydrogen flow rate, boat filling amount, equipment to be used, etc. are appropriately selected according to the target particle size of the powder.
• Step 3 Intermediate sieving The MoO 2 powder obtained in step 2 is sieved.
• the MoO 2 powder is passed through a sieve with a predetermined mesh size to remove coarse particles and agglomerated powder, and the under-sieves are recovered.
• the opening of the sieve mesh is appropriately changed according to the MoO 2 powder and the target molybdenum powder particle size.
• Step 4 Two-step reduction ( MoO2 ⁇ Mo)
• MoO2 ⁇ Mo The MoO 2 sieved in step 3 is charged into a heat-resistant alloy boat, reduced to MoO 2 ⁇ Mo and taken out.
• Optimal reduction conditions temperature, hydrogen flow rate, boat filling amount, equipment to be used, etc. are appropriately selected according to the target particle size of the powder. Thus, a powder containing molybdenum is obtained.
• Step 5 Final sieving The molybdenum-containing powder obtained in step 4 is sieved.
• the molybdenum-containing powder is passed through a sieve with a predetermined mesh size to remove coarse particles and agglomerated powder, and to collect under-sieves.
• the opening of the sieve mesh is appropriately changed according to the powder containing molybdenum and the target particle size of the molybdenum powder.
• Step 6 Mortar Grinding The molybdenum-containing powder obtained in Step 5 is ground in a mortar. As a result, the slightly remaining agglomerated powder is crushed and lattice strain is introduced.
• Step 1 Raw material sieving MoO3 powder with Fsss average particle size of 4 ⁇ m and molybdenum purity in MoO3 of 66.33% or more (99.5% or more in terms of Mo powder) is used as the raw material.
• the Fsss average particle diameter is preferably 0.5 ⁇ m or more and 50 ⁇ m or less. If it exceeds this, the Fsss average particle size of the molybdenum-containing powder may become 3.0 ⁇ m or more. It should be noted that "possible” indicates that there is a slight possibility that such an event will occur, and does not mean that such an event will occur with a high probability.
• Molybdenum purity in MoO 3 is preferably 66.33% or more (99.5% or more in terms of Mo powder).
• the molybdenum purity in MoO 3 is 66.6% or higher (99.9% or higher in terms of Mo powder). This is because the more impurities contained in molybdenum, the more likely it is to affect the sinterability of molybdenum.
• the opening is preferably 300 ⁇ m or less. If it exceeds this, coarse particles or agglomerated powder may not be removed.
• Step 2 One-step reduction (MoO 3 ⁇ MoO 2 ) MoO 3 sieved in step 1 is packed into a heat-resistant alloy boat with a thickness of 35 mm. Using a pusher-type reducing furnace, MoO 2 is obtained by carrying out a reduction treatment under the conditions of a hydrogen flow rate of 5 m 3 /h and a reduction temperature of 500°C.
• the thickness of MoO3 filled in the alloy boat is preferably 50 mm or less. If this is exceeded, the reduction of MoO 3 in the boat may not progress.
• a hydrogen flow rate of 3 m 3 /h or more is preferable. If it is less than this, reduction of MoO 3 in the boat may not progress.
• the reduction temperature is preferably 450° C. or higher and 650° C. or lower. If this is exceeded, the MoO3 raw material may melt because it approaches the melting point. If it is less than this, reduction of MoO 3 in the boat may not progress.
• Step 3 Intermediate sieving The MoO 2 obtained in Step 2 is sieved with a mesh size of 75 ⁇ m to remove coarse particles and agglomerated powder, and to collect undersieving.
• the opening is preferably 150 ⁇ m or less. If it exceeds this, coarse particles or agglomerated powder may not be removed.
• Step 4 Two-stage reduction (reduction of MoO2 )
• the MoO 2 after intermediate sieving in step 3 is packed into a heat-resistant alloy boat with a thickness of 20 mm.
• a powder containing molybdenum is obtained by reduction treatment using a pusher-type reducing furnace under the conditions of a hydrogen flow rate of 10 m 3 /h and a reduction temperature of about 600 to 920°C.
• the thickness of MoO2 filled in the heat-resistant alloy boat is preferably 50 mm or less. If this is exceeded, the reduction of MoO 2 in the boat may not progress.
• a hydrogen flow rate of 5 m 3 /h or more is preferable. If it is less than this, reduction of MoO 2 in the boat may not progress.
• the reduction temperature is preferably 600° C. or higher and 950° C. or lower. If it exceeds this, the Fsss average particle size of the molybdenum-containing powder may become 3.0 ⁇ m or more. If it is less than this, reduction of MoO 2 in the boat may not progress.
• Step 5 Final sieving The obtained powder containing molybdenum is sieved with a mesh size of 45 ⁇ m or less (20 ⁇ m for sample No. 1) to remove coarse particles and agglomerated powder, and to collect undersieving.
• the opening is 45 ⁇ m or less. If it exceeds this, coarse particles or aggregated powder may not be removed.
• Step 6 Mortar Pulverization Mo powder obtained by the final sieving is pulverized in an automatic mortar. Add 500 g per batch and perform for 10 minutes.
• step 4 two-stage reduction and the opening of the sieve mesh in step 5 final sieving were changed, and step 6 mortar pulverization was omitted. This gave powders containing molybdenum of sample numbers 1 to 33 and 41 to 60.
• Powders containing molybdenum were evaluated as follows. ⁇ Method for measuring Fsss average particle size> The Fsss average particle diameter is measured by the Fisher method.
• the equipment used is Fisher Scientific's Fisher Sub-Sieve Sizer Model 95. Fill the sample tube with a sample of true density, determine the porosity from the height of the sample, pass air of 1 MPa pressure through it, read the manometer water level with the numerical value on the calculator chart, and take the value as Fsss average particle size in ⁇ m. show.
• the Fsss average particle size represents the average particle size of the powder, and the lower the value, the smaller the average particle size.
• the BET specific surface area is measured by a gas adsorption method.
• the device used is Macsorb HM Model-1208 manufactured by MOUNTECH. Nitrogen gas is adsorbed on the powder, and the BET specific surface area of the powder is measured from the amount of adsorbed gas molecules.
• the unit of the BET specific surface area is m 2 /g, and the smaller the Fsss average particle size, the larger the BET specific surface area.
• the aggregation coefficient is represented by the ratio of the Fsss average particle size ( ⁇ m) and the BET particle size ( ⁇ m) obtained from the BET specific surface area. The closer the cohesion coefficient is to 1, the less cohesion there is, and the larger the cohesion coefficient, the more cohesion there is. In principle, the cohesion coefficient takes a value of ⁇ 1.
• the Fsss average particle diameter means the secondary particle diameter including aggregation, while the BET particle diameter obtained from the BET specific surface area means a value close to the primary particle diameter not including aggregation.
• ⁇ Particle size distribution measurement method The particle size distribution is measured by a laser diffraction/scattering method. D90 and D10 are thus obtained.
• the equipment used is Microtrack Bell's MT3300EX2, laser light diffraction/scattering type. Pure water was used as a solvent with a particle refractive index of 2.76 and a solvent refractive index of 1.33.
• a larger value for D90/D10 indicates a broader particle size distribution, and a smaller value indicates a sharper (uniform particle) particle size distribution.
• Lattice strain and crystallite size are measured by the X-ray diffraction method.
• the equipment used is PANalytical's EMPYREAM.
• EMPYREAM EMPYREAM.
• the scattered X-rays show a diffraction pattern peculiar to the material depending on the arrangement state of the atoms and molecules of the material, and Rietveld analysis is performed by fitting this diffraction pattern using the nonlinear least-squares method. Obtain lattice strain and crystallite size.
• the crystallite size indicates the smallest unit of a crystal grain that can be regarded as a single crystal. Smaller crystallite sizes tend to result in smaller particle diameters, while smaller particle diameters tend to increase the contact area between grains. Since sintering proceeds easily, the relative density of the sintered body can be improved.
• “Final sieve opening” in Tables 1 and 2 refers to the sieve opening used in the final sieving in step 5.
• “Pulverization in a mortar” indicates the presence or absence of the mortar crushing in step 6.
• “Fsss”, “BET”, “aggregation coefficient”, “particle size distribution”, and “crystallite size” are the Fsss average particle size, BET specific surface area, and aggregation coefficient of the molybdenum-containing powder obtained through step 5 or 6. , particle size distribution D90/D10 and crystallite size.
• a sintered body was produced using the molybdenum-containing powder shown in Tables 1 and 2, and the density was determined.
• the method for measuring the density of the sintered body is as follows.
• the sintered body for density measurement was produced by first putting 10 g of molybdenum-containing powder into a ⁇ 20 mm mold and press-molding it with a 30-t press so that a pressure of 50 MPa was applied. Next, sintering was performed in a hydrogen atmosphere at a sintering temperature of 800° C. for 2 hours or at a sintering temperature of 1400° C. for 2 hours to obtain a sintered body. After impregnating the sintered body with paraffin for about 10 minutes to fill voids in the sintered body, the density of the sintered body was measured using the Archimedes method.
• Relative density after sintering at 800°C in Tables 3 and 4 refers to the relative density of the sintered body after sintering at a temperature of 800°C.
• “Relative density after sintering at 1400°C” refers to the relative density of the sintered body after sintering at a temperature of 1400°C.
• sample numbers 1 to 33 are powders containing molybdenum that are less agglomerated, have fine and uniform grains, and have a lot of lattice distortion, so they are easier to sinter at a lower temperature than before. This reduces the cost of sintering and also reduces the energy used, thus solving the energy problem.
• the shrinkage rate can be controlled by the sintering temperature.
• a sintered body that can be plastically worked by rolling or forging is required to have a relative density of 85% or more, and in order to manufacture it, it was necessary to sinter a molybdenum compact at 1800 ° C. or more. Since it can be manufactured at a temperature of 1400° C., it is possible to reduce the manufacturing cost.
• sample numbers 28, 29, 30, 31, 32, and 33 where the Fsss average grain size exceeds 2.5 ⁇ m, it was determined that the relative density after sintering at 800° C. and the relative density after sintering at 1400° C. are effective in the present disclosure. It becomes a value close to the lower limit of 70% or more and 85% or more. Furthermore, in sample numbers 30 and 33, which have an Fsss average grain size of 2.5 ⁇ m and a BET specific surface area of less than 0.5, relative density after sintering at 800°C is 72% or less and It can be seen that the sinterability is lowered to a relative density of 85% or less after binding.
• the Fsss average particle diameter is 0.5 ⁇ m or more and 2.5 ⁇ m or less
• the BET specific surface area is 0.4 m 2 /g or more and 5.5 m 2 /g or less
• the aggregation coefficient is 1.5 or more and 5.1 or less. more preferred.
• Sample Nos. 8, 18, and 28, in which the particle size distribution D90/D10 exceeds 4.3, are slightly less sinterable than the samples in Tables 1 and 3, which have the same Fsss average particle size or BET specific surface area. It can be seen that it is declining. Therefore, the particle size distribution D90/D10 is preferably 4.3 or less.
• the particle size distribution D90/D10 is more preferably 4.3 or less.
• Sample Nos. 31 and 32 with a crystallite size exceeding 1000 nm have slightly lower sinterability than the samples in Tables 1 and 3 having the same Fsss average particle size or BET specific surface area. I understand. Therefore, the crystallite size is preferably 1000 nm or less.
• sample number 33 whose crystallite size exceeds 980 nm, has slightly decreased sinterability compared to the samples in Tables 1 and 3, which have the same Fsss average particle size or BET specific surface area. I understand. Therefore, the crystallite size is more preferably 75 nm or more and 980 nm or less.
• sample numbers 11, 17, 22, 24, and 32 with lattice strain less than 0.018% are slightly less than the samples in Tables 1 and 3, which have equivalent Fsss average grain sizes or BET specific surface areas. It can be seen that the sinterability is degraded. Therefore, the lattice strain is preferably 0.018% or more.
• sample numbers 18, 28, and 31 with lattice strain less than 0.020% are slightly sinterable compared to the samples in Tables 1 and 3, which have comparable Fsss average grain size or BET specific surface area. is found to be declining. Therefore, the lattice strain is more preferably 0.020% or more.
• the apparent density measured according to JISZ2504 (2012) is less than 1.96 g/ cm3 .
• the tap density measured according to JISZ2512 (2012) is preferably 4.34 g/cm 3 or less.

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• 2022
  • 2022-10-06 JP JP2023554461A patent/JP7684414B2/ja active Active
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