Zinc oxide is an inorganic substance with the chemical formula ZnO, an oxide of zinc. It is insoluble in water and soluble in acids and strong bases. Zinc oxide is a commonly used chemical additive and is widely used in the production of plastics, silicate products, synthetic rubber, lubricants, paints and coatings, ointments, adhesives, food, batteries, flame retardants and other products. With a large energy band gap and exciton binding energy, high transparency, and excellent room temperature luminescence, zinc oxide is used in the semiconductor field for liquid crystal displays, thin film transistors, light emitting diodes, and other products. In addition, microparticulate ZnO is beginning to play a role in related fields as a nanomaterial. Zinc oxide is also a well-known white pigment, commonly known as zinc white. It has the advantage that it does not turn black when encountering H2S gas, as ZnS is also white. When heated, ZnO gradually changes from white and light yellow to lemon yellow, and when cooled the yellow color recedes. Using this property, it is mixed into paints or added to thermometers to make color-changing paints or color-changing thermometers. Because ZnO has astringent and certain bactericidal ability, it is often used as ointment in medicine.