Reaction of zirconium powder with oxygen:

Dense metal zirconium is very stable in air, but with the increase of temperature, it absorbs oxygen, nitrogen and hydrogen, and reacts with CO and CO2 at high temperature. In air, the oxide film formed on the surface of zirconium will protect zirconium, but the protective effect of oxide film will disappear when the temperature is higher than 400 ℃. The solubility of oxygen in zirconium can reach 29%. However, the effect of zirconium powder on oxygen is different. Because zirconium powder has large specific surface and surface energy, it acts rapidly with oxygen. For example, when the average particle size of zirconium powder is less than 10 μ  M and in suspension, it will spontaneous combustion and explosion. The study of zirconium powder with different particle size shows that the minimum energy required to ignite zirconium powder is 5 mJ ~ 40 MJ. If the particle size of dispersed zirconium powder is 2 μ  m～10  μ  M, the minimum energy required for ignition is 125 μ  J;  When the particle size is 10 μ  m～44  μ  M, the minimum energy required to ignite zirconium powder is 20 MJ, while when the particle size is 44 μ  m～75  μ  M, 12.5 J. For non dispersive zirconium powder (the average particle size is 2.05 μ  m) , the minimum energy required for ignition is 45 μ  J。  The particle size, concentration and surface state of zirconium powder determine its explosive force. The maximum explosive force per gram of zirconium powder in the above samples is 0.63 MPa.