Due to exposure to water or high humidity during storage, as well as the high content of aluminum, calcium and phosphorus impurities in ferrosilicon, a phenomenon called "shedding" occurs after a while. This is accompanied by the release of toxic gases phosphine (PH3) and hydrogen (ASH3), and in severe cases, even a fire can occur.
Improper content of aluminum, phosphorus and calcium in ferrosilicon can contribute to the shedding of ferrosilicon. With a simultaneous increase in the content of aluminum and phosphorus to a certain value, this type of ferrosilicon is prone to crumbling in humid air. Some sources indicate that ferrosilicon containing less than 0.04% phosphorus and less than 3% aluminum is not subject to shedding.
Initially, it is believed that ferrosilicon with a low silicon content is more prone to shedding. This may be because the temperature-dependent bulk expansion of silicon and iron compounds, such as FeSi and FeSi2 in ferrosilicon, causes it to sputter. Ferrosilicon containing aluminum forms aluminum hydroxide and gas when in contact with water, which is the main cause of pulverization of ferrosilicon.
The cooling rate after pouring also affects the degree of grinding of ferrosilicon. If the cooling rate is fast, silicon segregation is low and pulverization is unlikely; If the cooling rate is slow, silicon segregation is large and pulverization is likely. Similarly, if the thickness of the ferrosilicon ingot is large, then pulverization can occur, and if it is small, then pulverization is unlikely.
In order to prevent the pulverization of ferrosilicon, you need to pay attention to the following three points:
1. The thickness of the ferrosilicon ingot should not be too large to reduce the segregation of silicon in ferrosilicon.
2. Strictly control the silicon content of ferrosilicon and prevent it from being too low. Control the aluminum, phosphorus and calcium content of ferrosilicon by using the best raw materials, especially not using coke with high ash content to reduce the aluminum and phosphorus content, and minimize the addition of lime during smelting to reduce the calcium content of ferrosilicon.