Sodium phosphite ( Na₂HPO₃) is an inorganic compound that usually exists in a white or yellowish solid form, and can also be an aqueous solution. Sodium phosphite is a sodium salt of phosphorous acid, which has a variety of uses in industry, mainly as a reducing agent, preservative, buffer and detergent, etc.

1. Metal surface treatment: Sodium phosphite can be used as a corrosion inhibitor in metal processing, especially in the processing of steel, aluminum, and copper. It can also be used for the cleaning of metals and the removal of oxides from surfaces.

2. Water treatment: In cooling water and other industrial water systems, sodium phosphite acts as a corrosion inhibitor and scale inhibitor to reduce the corrosion of metal pipes and equipment and the formation of scale.

3. Food industry: Sodium phosphite can be used as a food additive, as a preservative and antioxidant, to extend the shelf life of food, and prevent food from deteriorating due to oxidation.

4. Textile and paper handling: In the textile and paper industry, sodium phosphite can be used as a bleaching and dechlorinating agent, as well as to prevent oxidative damage to fibers.

5. Petrochemical: Sodium phosphite can be used as a catalyst and accelerator in the petrochemical process to synthesize certain chemicals.

6. Detergents and detergents: Sodium phosphite can be used as an ingredient in detergents and detergents to help remove hard water and metal ions and improve the cleaning effect.

7. Fertilizer: Sodium phosphite can be used as a component of phosphate fertilizer to provide phosphorus that plants can absorb.

8. Chemical synthesis: In organic synthesis, sodium phosphite can be used as a raw material for phosphite to synthesize a variety of organic compounds.

9. Pharmaceutical intermediates: Sodium phosphite is used as an intermediate in the production of some drugs.

10. Wood preservative: Sodium phosphite can also be used for wood preservative treatment to prevent wood from rotting due to fungal and insect attacks.