Several chemical substances that have an erosive effect on refractory fibers include: fluorine, fluoride, vanadium and other heavy metals, phosphoric acid, strong alkali, etc.
(1) Fluorine and fluoride. There is no doubt that fluorine is the most corrosive to refractory fibers. Below 10C, the reaction of fluorine and water with refractory fibers will cause great damage to the fiber structure. Even at lower concentrations, hydrofluoric acid will first react with alumina to form AIE, and AIF, .H20, resulting in severe damage to the fiber structure. Hydrofluoric acid reacts most easily with SiO2. At lower temperatures (below 980C), the fluorine-rich environment may promote low-temperature recrystallization, resulting in slight damage to the fiber structure. At temperatures where substantial recrystallization occurs, fluorine has the potential to form reactants on the fiber surface, causing structural changes in the fiber and the apparent formation of a thin crust on the fiber surface. Fluorine reacts with all aluminosilicate materials, including mullite. After reacting with fluorine, the reactants often vaporize, making it difficult to determine the cause of refractory fiber damage.
(2) Vanadium and other heavy metals. Vanadium and other heavy metals present in inferior fuel oil can attack refractory fibers when burned. This corrosive substance comes from vanadium pentoxide which is solid at room temperature but melts at about 690C. This liquid slag adsorbs in the pore structure of the fibers and reacts with the aluminum silicate in the fibers. After the reaction, a hardened shell will be formed on the hot side of the fiber lining. After a period of time, the hardened shell will detach from the unreacted fiber layer of the fiber blanket, and the chemical reaction will continue on the exposed fresh fiber surface. The reaction rate depends on factors such as: heavy metal concentration (1 x10~), time, porosity of the material, and temperature. There is no clear concentration boundary that defines whether a reaction occurs or not. Generally, it is the high concentration of heavy metals over a long period of time that shortens the life of the refractory material. Vanadium pentoxide will react with fibers when the temperature is higher than 690C, but the reaction speed is affected by the above factors. As the chemical reaction continues, it is necessary to replace the hot surface material regularly. It is important to note that vanadium pentoxide is corrosive to the fibers, but vanadium in the presence of an alkaline compound forms a more corrosive slag at very low temperatures, resulting in faster degradation of the refractory fibers. In the case of chanting, the fuel with high content of heavy metal also contains alkali at the same time.