Historical Background

Aluminum powder was first used commercially as flakelike pigment products called aluminum bronze powder in the United States around 1900. It was made from aluminum sheet by the Bessemer dry stamping process developed fifty years earlier for the manufacture of gold powders. Stamping mills were both inefficient and dangerous to operate, because, unlike gold powders, aluminum powder forms an explosive mixture with air over a wide range of metal-to-air ratios (Ref 3). Several fatal fires and explosions marred the early days of the aluminum powder industry.

Two major breakthroughs developed by Hall (Ref 4) occurred in aluminum powder production in the late 1920s. First, the development of safer ball mill production processes that are still employed today for milling powders into flakes. Second, the introduction of the atomization process, which allowed the manufacture of the forerunners of today's atomized powders. Atomized aluminum powder was used initially only as raw material to produce aluminum flake pigments by ball milling. After World War II and the development of aluminized high explosives, a major market for atomized aluminum was created. The application of atomized powders broadened in postwar years from military explosives to commercial markets listed above.

To meet the individual needs of each of these markets, manufacturers now produce many grades of aluminum powders in several different general categories: granules, regular and coated atomized powders, spherical powders, high-purity powders, alloy powders, blended powders, and dedusted atomized powders. All are produced by the same basic gas atomization technique, but starting materials may differ and, as with flake powders, further processing may be required. Powders atomized in inert gas (nitrogen, argon, and helium), which have a spherical shape, are preferred for some applications. Water atomization of aluminum is not practiced because it is dangerous, due to the creation of hydrogen and the potential presence of rust in the equipment. The latter can lead to explosions through thermite reaction with the dry powder. Some manufacturers still use the dry stamping process for converting foil scrap into coarse particulate (granules), although it is now a very small percentage.

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