The catalyst is the key to artificial rainfall. The selection of the catalyst should not be casual. It is necessary to consider the effectiveness, economy and the ecological environment can not be affected. According to the nature of the cloud, the catalyst can be divided into catalyst in cold clouds and catalyst in warm clouds.
1. Catalyst in cold clouds
Catalyst in cold clouds also include refrigerant, inorganic ice nucleus and organic ice nucleus. Inorganic ice nucleus and organic ice nucleus are collectively called artificial ice nucleus.
Refrigerant: It can cool some areas in the cloud rapidly, so that the cooling water droplets can spontaneously condense into ice crystals. There are dry ice, liquid petroleum gas, liquid nitrogen, liquid air and so on. The dry ice is usually spread by the airplane.
Inorganic ice nucleus: There are mainly silver iodide, leaching iodide and copper sulfide. Silver iodide is considered to be very effective, which is suitable for - 4 ℃ - 15 ℃ cold cloud catalysis, there are many sowing methods.
Organic ice nucleus: There are mainly metaldehyde, copper acetylacetonate, phthalic anhydride and so on. The metaldehyde is a kind of high quality ice nucleus, which is non - toxic, and can be decompose at the temperature above 80 ℃. But it has the disadvantages of slow create velocity, easy decomposition vaporization, and the effect is not as good as the silver iodide.
2. Catalyst in warm clouds
It is mainly some hygroscopic matter, such as salt, calcium chloride, urea, ammonium nitrate and so on. The price is cheaper. They are usually milled into 100 - 101um particles, and then scatter into the clouds through the plane. Because of their strong hygroscopicity, they can quickly form large cloud droplets, while stimulating the gravity collision and coalescence processes. But the amount required is large, which requires a large load of the aircraft.http://www.wxytgas.com/