Abstract
M.Tech.
The study into the effect of additives used in nickel powder precipitation by sodium
hypophosphite has been carried out. Reduction experiments were conducted in a 10 L stainless
steel batch reactor fitted with 3 baffles, 4-bladed axial impeller, heating element, thermocouple
and thermostat. Nickel seed was used to initiate the reduction process, sodium hypophosphite
was used as a reducing agent, and ammonia solution was used to adjust pH, poly(ethylene-comaleic
anhydride) (EMA) was used as the first additive and poly(acrylic acid) (PA) as the second
additive. Reduction experiments were conducted at a temperature between 60oC to 70oC, pH
around 8 and a reaction time of 3 min. Synthetic nickel sulfate solution and sodium
hypophosphite solutions at concentration of 0.5 g/L were used as nickel feed solution and
reducing agent, respectively. Additives were investigated at high and low concentrations of 5
mg/L and 10 mg/L. The effect of additives on reduction behavior of nickel was investigated by
studying the evolution of the volume distribution, moments, specific surface area, and rate of
reduction and purity of the powder product. EMA was found to be a growth promoter and PA
was found to be a growth inhibitor. The highest reduction rate was observed in the presence of
EMA and the lowest in the presence of PA. The SEM micrographs of the powder obtained in the
presence of EMA and PA showed that the powder was spherical shaped, open, dentritic and
more porous compared with that of the seed particles. Both additives were found to increase the
pore size of the powder particles. The presence of particle fragments observed in the scanning
electron micrographs confirmed breakage as one of the major particulate process. The addition of
additives significantly affected the volume distribution at lower concentrations of 5 mg/L. The
extent of aggregation increased with increasing dosages of PA and decreased with increasing
dosages of EMA. The highest specific surface area was obtained in the presence of 5 mg/L of
EMA.