Disodium hydrogen phosphate

Disodium hydrogen phosphate (Na2HPO4, CAS 7558-79-4) is a water-soluble, hygroscopic, colorless, granular powder. It readily absorbs moisture forming hydrated salts including the dihydrate (Na2HPO4·2H2O, CAS 10028-24-7), heptahydrate (Na2HPO4·7H2O, CAS 7782-85-6), or dodecahydrate (Na2HPO4·12H2O, CAS 10039-32-4). The dodecahydrate is heat responsive where it absorbs or releases a large amount of latent heat while changing from crystalline to molten phase or vice versa. Due its agile phase change associated with heat absorption or release, disodium hydrogen phosphate dodecahydrate finds wide applications in the fields of solar thermal storage, waste heat recovery, building temperature control and electric power peak adjustment. In general, Na2HPO4 forms composites with other phase change hydrate salts such as sodium carbonate decahydrate (Na2CO3·10H2O), sodium sulfate decahydrate (Na2SO4·10H2O), sodium acetate trihydrate (CH3CO2Na·3H2O), calcium chloride hexahydrate (CaCl2·6H2O), sodium thiosulfate pentahydrate (Na2S2O3·5H2O), etc.
In solution, dissolved disodium hydrogen phosphate forms basic solutions with pH ranging from 8.5 to 9.5, which makes it an alkaline phosphate salt. Alkaline phosphates such as di- and tri-sodium phosphate are effective water binders, surface treating agents, dispersants, antifreeze agents, mordants, etc.
Other useful applications of Na2HPO4 include:
·       cement ingredient
·       emulsifier
·       solar thermal energy storage
·       fabric weighting agent,
·       fire retardant,
·       borax substitute in welding 
·       stabilizer for hydrogen peroxide bleaching
·       acidity regulator