Provided is a method for producing high density nickel powder particularly having a median diameter of 100 to 160 m by controlling a particle size of nickel powder. The method includes: performing an initial operation by charging a pressure vessel equipped with a stirrer with a nickel ammine complex solution containing nickel in the concentration of 5 to 75 g/L together with seed crystals in the amount of 5 to 200 g per liter of the solution, increasing the temperature of the solution, and performing a reduction reaction with hydrogen by blowing hydrogen gas into the pressure vessel, thereby obtaining the nickel contained in the nickel ammine complex solution as nickel powder; and thereafter, performing a specified operation A repeatedly at least once to obtain the nickel powder having the median diameter of 100 to 160 m and a bulk density of 1 to 4.5 g/cm.sup.3.

Provided is a method for producing high density nickel powder particularly having a median diameter of 100 to 160 m by controlling a particle size of nickel powder. The method includes: performing an initial operation by charging a pressure vessel equipped with a stirrer with a nickel ammine complex solution containing nickel in the concentration of 5 to 75 g/L together with seed crystals in the amount of 5 to 200 g per liter of the solution, increasing the temperature of the solution, and performing a reduction reaction with hydrogen by blowing hydrogen gas into the pressure vessel, thereby obtaining the nickel contained in the nickel ammine complex solution as nickel powder; and thereafter, performing a specified operation A repeatedly at least once to obtain the nickel powder having the median diameter of 100 to 160 m and a bulk density of 1 to 4.5 g/cm.sup.3.

The present invention provides a method to achieve full densification and grain size control for sintering metal materials. First, raw material powder is deagglomerated to obtain deagglomerated powder with dispersion. The deagglomerated powder is granulated by spray granulation. The granulated particles are processed by high-pressure die pressing and cold isostatic pressing. The powder compact is sintered by two-step pressureless sintering. The first step is to heat up the powder compact to a higher temperature and hold for a short time to obtain 75-85% theoretical density; the second step is to cool down powder compact to a lower temperature and hold for a long time. The two-step sintering can decrease the sintering temperature, so that the powder compact can be densified at a lower temperature. Thus, the obtained refractory metal product is densified, with ultrafine grains, uniform grain size distribution, and outstanding mechanical properties.

Provided is a method for efficiently manufacturing fine metal particles applicable as a fuel cell electrode catalyst. Provided is a method of manufacturing fine metal particles, including the step of: a hydrogen bubbling step to perform bubbling to a reaction solution, wherein: the reaction solution is prepared by allowing seeds of fine metal particles in a dispersed state and a water soluble noble metal precursor to co-exist in a water-containing solvent; and the bubbling is performed with a reaction gas containing a hydrogen gas, is provided.

Provided is a method for efficiently manufacturing fine metal particles applicable as a fuel cell electrode catalyst. Provided is a method of manufacturing fine metal particles, including the step of: a hydrogen bubbling step to perform bubbling to a reaction solution, wherein: the reaction solution is prepared by allowing seeds of fine metal particles in a dispersed state and a water soluble noble metal precursor to co-exist in a water-containing solvent; and the bubbling is performed with a reaction gas containing a hydrogen gas, is provided.

A method for producing nickel powder sequentially includes: a mixing step of adding, to a nickel ammine sulfate complex solution, an insoluble solid as seed crystals and a polyacrylate or lignosulfonate as a dispersant to form a mixed slurry; and a reduction and precipitation step of charging a reaction vessel with the mixed slurry and blowing hydrogen gas into the mixed slurry in the reaction vessel to reduce nickel complex ions in the mixed slurry to form nickel precipitate on the surface of the insoluble solid, wherein the amount of the dispersant added in the mixing step is controlled to control the number of the nickel powder obtained by formation of the nickel precipitate in the reduction and precipitation step.

A method for producing nickel powder sequentially includes: a mixing step of adding, to a nickel ammine sulfate complex solution, an insoluble solid as seed crystals and a polyacrylate or lignosulfonate as a dispersant to form a mixed slurry; and a reduction and precipitation step of charging a reaction vessel with the mixed slurry and blowing hydrogen gas into the mixed slurry in the reaction vessel to reduce nickel complex ions in the mixed slurry to form nickel precipitate on the surface of the insoluble solid, wherein the amount of the dispersant added in the mixing step is controlled to control the number of the nickel powder obtained by formation of the nickel precipitate in the reduction and precipitation step.

A nickel sulfate amine complex liquid and nickel powder having a particle diameter of 0.1 m to 300 m are supplied to a reaction container, hydrogen gas is continuously supplied while the inside of the reaction container is maintained at 150 C. to 250 C., and the pressure is set to 2.5 MPa to 3.5 MPa, whereby nickel ions in the nickel sulfate amine complex liquid are reduced to nickel and deposited on the surfaces of the nickel powder supplied to the reaction container, a reacted slurry including the nickel sulfate amine complex liquid and the nickel powder is then transferred to a pressurized storage container at the same or slightly lower pressure than the internal pressure of the reaction container, and the pressure of the pressurized storage container to which the reacted slurry is transferred is then reduced, after which the reacted slurry is extracted from the pressurized storage container.

A nickel sulfate amine complex liquid and nickel powder having a particle diameter of 0.1 m to 300 m are supplied to a reaction container, hydrogen gas is continuously supplied while the inside of the reaction container is maintained at 150 C. to 250 C., and the pressure is set to 2.5 MPa to 3.5 MPa, whereby nickel ions in the nickel sulfate amine complex liquid are reduced to nickel and deposited on the surfaces of the nickel powder supplied to the reaction container, a reacted slurry including the nickel sulfate amine complex liquid and the nickel powder is then transferred to a pressurized storage container at the same or slightly lower pressure than the internal pressure of the reaction container, and the pressure of the pressurized storage container to which the reacted slurry is transferred is then reduced, after which the reacted slurry is extracted from the pressurized storage container.

Provided a production method for reducing the content level of sulfur and carbon which are impurities in nickel powder to improve the quality of nickel powder produced by a complexing reduction method. The method of producing nickel powder having low carbon and sulfur concentrations includes: a complexing treatment of adding a complexing agent to a nickel sulfate aqueous solution to form a solution containing nickel complex ions; maintaining the solution containing nickel complex ions at a solution temperature of 150 to 250 C. in a pressure vessel and blowing hydrogen gas into the solution containing nickel complex ions to perform hydrogen reduction to produce nickel powder; washing the nickel powder with water; and then roasting the nickel powder washed with water in a mixed gas atmosphere of nitrogen and hydrogen.