Evolution of Pore Structure in Compacts Produced from Nickel Carbonyl Powders during Sintering

The influence of pore structure evolution in compacts sintered from nickel carbonyl powder with an average particle size of 1.4 μm in the temperature range 200–1000°C on local and bulk shrinkage was analyzed. The pore structure of the samples was characterized by the maximum and average diameters of pore channel constrictions determined by the Barus–Bechhold method. To minimize local (incoherent) shrinkage in the sintering of fine nickel powders, a criterion for pore structure homogeneity in compacts, α ≤ 0.03, was selected. The criterion was determined by the difference between the maximum and average diameters of pore channel constrictions. The influence of pore structure evolution on local and bulk shrinkage during sintering of compacts produced from nickel carbonyl powder with an average particle size of 1.4 and 4 μm was experimentally confirmed. The local shrinkage was due to the three-level structure and wide particle size distribution of the nickel carbonyl powders. A method was proposed to determine the average diameter of particles (agglomerates) in nickel carbonyl powders using the Kozeny equation, establishing a relationship between the particle diameter, the maximum diameter of pore channel constrictions, and the porosity of the compacts, varying from 0.25 to 0.45.