The different particle shapes of copper powder and their methods of production

The most common ways for producing granular copper powder include atomization, electrolysis, hydrometallurgy, and solid state reduction. Each process produces a powder with distinct characteristics.

The properties are also influenced by the characteristics of a mass of powder. The average particle size is the statistical average of all particles in the mass, and it can vary across a large range. The flow and packing of powders are influenced by the particle size distribution.

The weight of a unit volume of powder under specific conditions is known as apparent density. It is influenced by the relative surface area and packing characteristics of the powders, as well as their size, shape, and particle size distribution. Because the die is typically filled by volume, apparent density is essential in pressing operations.

Flow is the amount of time it takes for a given amount of powder to flow through a given aperture of a given size. It is determined by particle size distribution and form, as well as friction and other factors. Flow affects the amount of time it takes to fill a die and, as a result, the maximum output rate that may be reached.

Green strength is measured by compacting and breaking a mass of powder under certain circumstances. The strength is determined using the compact’s dimensions and the breaking load. It is a measurement of the compact’s strength prior to sintering.

As seen in the table below, the different production methods can produce significant differences in characteristics. Individual features offer some powders significant benefits in particular applications, despite the fact that they may be employed interchangeably. Click here to learn more about the applications of copper powders.

Acicular (1D) – chemical decompositions	Dendritic (2D) – electrolysis	Spherical (3D) – atomization – carbonyl (Fe) precipitation from a liquid
Irregular Rod-like (1D) – chemical decompositions – mechanical comminution	Flake (2D) – mechanical comminution	Irregular Rod-like (3D) – atomization – chemical decomposition
Porous (3D) – reduction of oxides	Angular (3D) – mechanical disintegration carbonyl (Ni)	Irregular (3D) – atomization – chemical decompositions

Atomization

Copper is typically heated and then passed through an aperture where it is hit by a high-velocity jet of gas or liquid, generally water, shattering the molten metal into small particles that solidify quickly. The atomizing medium, pressure, and flow rate all have an impact on particle size and form. Deoxidizing elements, such as phosphorus, are added in tiny amounts to control particle size and form. The product is milled, categorized, and mixed to obtain the particle size distribution necessary after atomization and annealing in a reducing environment to reduce any surface oxide generated during atomization.

Electrolysis

Electrolytic copper powder is made by using electroplating principles but changing the circumstances to generate a loose powdery deposit rather than a smooth adherently solid coating. Low copper ion concentration in the electrolyte, high acid concentration, and high cathode current density encourage the development of powder deposits that cling loosely to the cathode. The inclusion of colloids, such as glucose, causes a homogeneous copper deposit to develop. Pure cathode copper is used as the starting material. The concentration of sulfuric acid and copper sulfate, the kind and quantity of the addition agent, the temperature of the electrolyte, the current density, and the frequency of brush-down are all factors that affect the powder’s properties. The powder is cleaned to remove all traces of the electrolyte, annealed in a reducing environment, fed through high-velocity impact mills to break up clusters, screened, categorized, and blended to the appropriate particle size distribution after deposition. The temperature at which the powder is reduced has an impact on its characteristics.

Hydrometallurgy

Copper powder can be made via the hydrometallurgy method from cement copper, concentrates, or scrap copper. Sulfuric acid or ammoniacal solutions are used to leach copper from these materials, and the pregnant solution is separated from the residue by filtering. By reducing the copper in solution with hydrogen under pressure, the copper is precipitated. For example, in one technique, reduction is carried out in an autoclave at 225-280F (107-138C) for one hour at 400 psig partial pressure of hydrogen (total pressure 425 psig) with a thickening agent added to reduce plating and regulate particle size. 90% to 95% of the copper is precipitated as powder during the reduction process. A slurry of powder is pumped to a centrifuge, where it is separated from the liquid and cleaned. To obtain the appropriate particle size distribution, the wet copper powder is dried in a reducing environment, milled, categorized, and mixed. The powder’s physical properties may be altered in a wide range of ways. The amount of acrysol used, as well as the temperature and duration of reduction, have a significant impact on the powder characteristics.

Solid State Reduction

This process involves grinding oxides, including mill scale, to regulate particle size before reducing them with a gas, generally carbon monoxide, hydrogen, or split natural gas, at temperatures below the melting point of copper. By changing the particle size and shape of the oxides, as well as lowering the temperature, pressure, and velocity of the gas, particle size and shape may be adjusted within fairly broad ranges. The powder is then processed, categorized, and mixed according to the standards.

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