Properties of electrolytic nickel powders and porous permeable strips produced from them

Résumé fourni par la source

The particle size distribution, apparent density, tap density, flowability, particle morphology, and specific surface area (BET) were determined for fractions of electrolytic nickel powders differing in particle shape and surface morphology. Despite similar particle size distributions, differences in particle morphology and surface condition were found to have a decisive effect on powder processing properties. Powders with highly developed particle surfaces exhibited lower apparent density and flowability and a higher specific surface area than powders with smoother particles. The powders were ranked using a particle-shape criterion that accounts for both particle geometry and surface condition. Adding 15–20 wt. % of a fine powder with a highly developed surface imparted roll-formability to powders with rounded particles that otherwise could not be cold-rolled into highly porous strips. This effect is attributed to the formation of a load-bearing framework that promotes particle interlocking during deformation. Highly porous strips were produced both from a nickel powder with a roll-formable particle morphology and from an otherwise non-roll-formable powder blended with a fine powder having a highly developed surface. After sintering, shrinkage, strength, and pore-structure parameters were determined. Higher sintering temperatures were found to be preferable for powder blends containing this additive. The pore structure of strips produced from a blend of smooth, rounded powder and fine powder with a highly developed surface was governed by the additive content. As the additive fraction increased, pore size and permeability decreased, whereas tortuosity remained nearly unchanged. At the optimum additive content, the resulting pore structure was comparable to that of strips produced from a powder with an inherently favorable particle morphology. At lower additive contents, higher permeability was achieved, but the roll-formability of the blend decreased substantially.

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