Classification of Copper Powders and Moisture Testing Methods

Copper powder is made by grinding copper into a powder and is widely used in powder metallurgy, electro-carbon products, electronic materials, metallic coatings, chemical catalysts, filters, heat-dissipation tubes, and other electromechanical parts and in the electronics and aerospace fields. Copper powder is soluble in nitric acid and hot concentrated sulfuric acid, and slightly soluble in hydrochloric acid. Heated in oxygen, copper reacts to form copper oxide—this is not combustion but, strictly speaking, an oxidation-reduction reaction. Pure copper is rose-red with a metallic luster, but oxidation forms an oxide film that gives it a purple appearance, hence the common name 'purple copper'. Physical properties of copper powder: density:8.89g/cm3 melting point:1083°C; boiling point: approximately2500°C. Copper powder has excellent electrical and thermal conductivity and is widely used in conductive and heat-transfer materials; it is tough and wear-resistant.

I. Classification of copper powders:

1.Atomized copper powder: a light rose-red irregular powder produced by atomization, widely used in diamond tools, powder metallurgy parts, chemical catalysts, carbon brushes, friction materials, and welding electrodes.

2.Electrolytic copper powder: purple copper powder / pure copper powder, a rose-red dendritic powder that oxidizes readily in humid air and dissolves in hot sulfuric acid or nitric acid; widely used in diamond tools, electro-carbon products, friction materials, conductive inks, and other powder metallurgy products.

3.Copper oxide powder: the particle size of copper oxide powder refers to a particle size of100mesh.

4.Bronze powder: a bluish spherical powder,Sn5-7％Zn5-7%Pb2-7%CUbalance, widely used in powder metallurgy oil-impregnated bearings and diamond tools.

5.Brass powder: a yellow irregular powder used in bearing materials, diamond products, and powder metallurgy products.

6.Purple copper powder: a leafing flake pigment made from copper powder, zinc powder, and aluminum alloy powder in given proportions by smelting, grinding, and classification. The coarser the particles, the stronger and more sparkling the metallic effect, but the poorer the coverage; conversely, very fine particles give a weaker metallic effect and softer color with better coverage. With its pure, brilliant color and strong metallic character, purple copper powder can be tailored to different applications and desired metallic effects by selecting particle diameter and color tone.

7.Atomized copper alloy powder: with copper as the base material,alloyed with tin, lead, zinc, and other elements, smelted at high temperature, and then high-pressure atomized using water (or gas) as the medium.depending on the alloy composition and production process,there are many varieties and specifications,with differing performance and uses,widely used in powder metallurgy, chemicals, electrical alloys, and many other industries.

8.Copper gold powder: mainly alloyed with copper and zinc, with the traditional golden color of Chinese culture. The particle size range is micron-scale, with an average particle diameter ofd50of4~40microns; the particles have a flake-like morphology under the microscope. Thanks to advanced anti-oxidation, classification, and surface modification technologies in the production process, copper gold powder offers high coverage, a strong metallic effect, and excellent temperature and weather resistance.

 II. Moisture testing methods for copper powder

（1) Karl Fischer method

In the Karl Fischer method, a water-containing sample is injected once the Karl Fischer reagent in the instrument's electrolytic cell has reached equilibrium. The water participates in the oxidation-reduction reaction of iodine and sulfur dioxide; in the presence of pyridine and methanol, pyridine hydroiodide and methyl sulfate pyridine are formed. The consumed iodine is regenerated electrolytically at the anode, so the reaction continues until all the water is consumed. According to Faraday's law of electrolysis, the iodine generated electrolytically is proportional to the quantity of electricity consumed. A Karl Fischer moisture analyzer in its best state can measure down to10-4level;；consumables((reagents) are)expensive, and；measurement time is rather long.

（2) Oven method

Based on loss-on-drying, the sample is dried in an oven, weighed, and the moisture value calculated. The oven method takes a long time.

（3) Rapid moisture analyzer method

Based on loss-on-drying, the sample is heated and dried in a sample pan—short measurement time with strong stability.

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