1、 Aluminum powder self coating process (core internal factor)
a. Resin/silica coating (high-end non floating type): A dense protective layer is formed on the surface of the aluminum flakes, which isolates water vapor and oxygen, has strong oxidation resistance, and has a long shelf life (up to 24 months). It is also the mainstream type of aluminum powder used for dipping aluminum paste.
b. Stearic acid coating (ordinary non floating aluminum powder): The protective film is weak and easily damaged by water vapor. The aluminum sheet is prone to oxidation and blackening, and the shelf life is generally only 12 months.
c. Aluminum powder particle size: Fine grained aluminum powder has a larger specific surface area, higher reactivity, and is more prone to oxidation. Under the same conditions, its shelf life is shorter than that of coarse aluminum powder.
2、 Packaging conditions
a. Sealing performance: The original barrel is well sealed, with an inner bag/aluminum foil bag to isolate water vapor and air, and the shelf life meets the standard; The bucket lid is damaged, the inner bag is leaking, and water vapor enters and quickly becomes ineffective.
b. Packaging material: Aluminum foil lining, galvanized iron drum superior to ordinary plastic drum, better moisture barrier effect.
3、 Storage environment (main external factors)
a. Temperature: High temperature will accelerate the aging of the coating layer and the aluminum oxidation reaction. Long term storage above 30 ℃ significantly shortens the shelf life; The most ideal environment is cool (≤ 25 ℃). Avoid direct sunlight exposure.
b. Humidity: A high humidity environment (relative humidity>60%) is the primary cause of aluminum powder oxidation. When aluminum comes into contact with water, it undergoes hydrolysis: (2Al+3H2O=Al2O3+3H2 ↑), resulting in blackening, gas production, and agglomeration.
c. Environmental medium: There is acid mist, ammonia gas, and corrosive gases in the warehouse that can corrode aluminum scales and accelerate failure.
d. Stacking: When the bottom of the ground becomes damp, the buckets can be stacked directly on the ground, and the bottom of the buckets is prone to moisture.
4、 Operational factors after opening
a. Kaifeng exposure: Once the packaging is opened, air and water vapor continue to enter, and the surface of the powder gradually oxidizes. Kaifeng dry powder is recommended to be used up within 3 months.
b. Material retrieval method: Wet tools or spoons with water droplets inserted into the bucket will directly bring in moisture, causing local clumping and oxidation.
c. Repeatedly opening and closing the lid: repeatedly taking and opening and closing the lid, continuously introducing moisture and accelerating aging.