Aluminum powder, found in products ranging from suntan lotion to lightweight concrete to solar panels, is produced by melting aluminum ingot in a gas furnace and spraying the molten metal under high pressure into a fine granular powder. Two types of powder can be produced from this process, depending on the atomizing gas used to "blow" the molten aluminum from a nozzle tip.
Aluminum pigments are used in applications ranging from graphic arts and inks, to automotive paints and protective coating for bridges and buildings. Pigments are produced from aluminum powder and almost exclusively manufactured through a wet-milling process. Mineral spirits, an acid lubricant and aluminum powder are placed in a mill. When the mill is rotated, balls within the rotation chamber cascade the aluminum slurry in a manner that flattens and breaks the resultant flakes on impact.
Aluminum powder was originally produced by using a stamp mill to create flakes. In the 1920s, E. J. Hall pioneered the process of spraying molten aluminum to make powder droplets. Today, molten aluminum is sprayed under high pressure to produce a fine granular powder. Two types of powder (nodular and spherical) can be produced, depending on the type of atomizing gas that is used to "blow" the molten aluminum from a nozzle tip.
Aluminum powder is also a key ingredient in the production of "fly ash bricks" (bricks made from fly ash, water, quicklime, cement and gypsum). Builders save about 30 to 35 percent of the weight of structural steel and concrete, as these blocks significantly reduce the load placed on the building’s frame.
Aluminum powder plays a vital role in the fabrication and performance of solar cells. A film paste made from aluminum is applied to the back side of silicon to be used in solar cells. The paste is metallized and screen-printed to create the electrical conduction properties necessary for the solar cell to function properly. Continuing improvements to reduce the granular size of powder (referred to as "superfine") will increase solar cell efficiency and reduce manufacturing costs.
Aluminum pigments are produced almost exclusively using a wet-milling process that involves mineral spirits or other solvents. When aluminum powder is milled into a pigment, the geometry of the particles forms different shapes. For example, pigments used in plastics come in three different shapes. They resemble a flat cornflake, a flat ellipse and a sphere. Mirror-like pigments are produced through a vapor deposition process when a thin aluminum layer is deposited on a carrier film. The metallized film is run through a solvent tank where the release coating is dissolved. The remaining aluminum layer is removed to form coarse reflective aluminum pigment flakes.
Aluminum pigments appear to have color because they absorb some wavelengths of light more readily than other wavelengths (selective absorption). In contrast to a dye, a pigment generally is insoluble and will not combine with the substrate. This is a vital advantage when absorption-prone materials are used. The appearances created by aluminum pigment range from metallescence (a colored pearlescent effect), a "liquid metal" appearance, a high or pinpoint sparkle and the glitter effect. Pigments can appear low-sheen or exceptionally bright, depending on the surface polish. These light-absorption and reflective factors contribute to the different appearances of paints and coatings used in the automotive industry.
Aluminum powder was used in early photography to create the bright flashes necessary to take pictures. Today, it is one of the key materials used in the manufacturing of fireworks.
Christmas tree ornaments are commonly accented with aluminum pigments. Their metallescent, liquid metal, pinpoint sparkle and glitter effects are created by aluminum pigments (with some help from Santa, of course).