Why can't aluminum powder be bought
Because aluminum powder is a regulated metal. Commonly known as silver powder, that is, silver metallic pigment, pure aluminum foil with a small amount of lubricant, crushed into a scaly powder after mashing, and then polished. It is light in weight, high in floating power, strong in hiding power, and good in light and heat reflection. .
The aluminum powder is oxidized when it is not available in the reagent store. You need to buy the milled aluminum powder produced under protective gas to be the purest. Ordinary aluminum powder is produced by the gas spraying method after melting. The reagent store sells it for a long time, so it is generally not bright. Grinding is not easy to control and not oxidize. The pure aluminum powder you mentioned is metal aluminum powder, which can be ordered online, or you can go directly to the reagent sales department for sodium and potassium metal.
Light metals (mainly aluminum powder, iron powder, aluminum powder, etc.) are used to chemically react with alkaline cement to produce hydrogen, which will increase the volume of the cement and improve the strength of the cement.
Similarly, the chemical reaction between aluminum powder and cement causes cement bubbles. The intuitive phenomenon is that sand will form after being stepped on. Aluminum powder is generally not recommended now. One is because the dosage is too small, the laboratory is OK, and the production is not easy to control; the second is the expansion is unstable, the reaction of aluminum and alkali is very sensitive to temperature, the expansion is almost completed within a few minutes in summer, and there is almost no reaction in winter ; The third is that the hydrogen released by the reaction is easy to form "hydrogen embrittlement", which has a destructive effect on steel bars.
Aluminum powder with a certain degree of fineness (called mesh in jargon, 200-300 mesh, the larger the mesh, the smaller the particle) can be used as rocket fuel, so this type of thing may be developed by some countries for medium and short-range ballistic missiles. If necessary, export is restricted. According to the Export Control List of Missiles and Related Items and Technologies of the People's Republic of China, the export of aluminum powder with a particle size of less than 500 microns is prohibited because the fine-grained aluminum powder may be used by non-skeletal purchasers as missile fuel. Foreign parties often claim that the purpose of aluminum powder is to paint heating equipment.