| Today, there is growing interest in using copper powders for thick film application in the place of precious metals. Copper powders with particle size less than 5 {dollar}mu{dollar}m, narrow size distribution, spheroidal shape and very low oxygen content (high purity) are required for this kind of application where high electrical conductivity is of primary consideration.; In this work a novel method of preparing copper powder having the above requirements was investigated. This method involves the precipitation of copper powder from an organic medium by hydrogen reduction under pressure. The organic medium used, Kelex 100{dollar}spcircler{dollar} - decanol - kerosene, is one of the solvent mixtures used in solvent extraction of metals.; The work was conducted in two parts. In part (I), all the parameters affecting the precipitation of copper were studied. The parameters studied were temperature (473-573 K), hydrogen pressure (1.03-3.79 MPa), time, use of additives, solvent composition, etc. In particular, the investigation focused on the underlying correlation between the reduction kinetic parameters of the system and the physical properties of the powder. Powders with the following excellent properties were produced: d = 1 {dollar}mu{dollar}m, spread 80% {dollar}-{dollar}1.2 + 0.6 {dollar}mu{dollar}m, specific surface area = 1 {dollar}pm{dollar} 0.2 m{dollar}sp2{dollar}/g, spheroidal shape, and 0.056 wt% oxygen content. This powder was produced by separating homogeneous nucleation (here induced by an intramolecular redox reaction) from growth (H{dollar}sb2{dollar} reduction), and using a tertiary carboxylic acid additive to bring about steric stabilization.; The kinetic results were analyzed with the help of the Avrami-Erofeev model and the parameters of the model were correlated to the morphology of the copper powder. The chemically controlled growth process was found to exhibit 10 kcal/mol activation energy and a complex dependency (from first order to fractional/zero order) on hydrogen pressure.; In part (II) the best powder produced was processed by compaction and sintering and its electrical conductivity was measured. |
