stannate

Stannate refers to salts and esters of the stannate(IV) anion, containing tin in the +4 oxidation state. The principal anion is orthostannate, [SnO3]2−, which forms when tin(IV) oxide dissolves in strongly basic solutions, for example SnO2 + 2 NaOH → Na2SnO3 + H2O. In aqueous solution, the tin–oxygen system can exist as various hydroxy-stannate species that depend on pH, such as [Sn(OH)6]2− under highly basic conditions.

Stannates are typically basic and form soluble alkali metal salts (for instance, sodium or potassium stannates). They may hydrolyze and rearrange with changes in pH, and on heating they can decompose to tin(IV) oxide or hydrated tin oxides. In acidic solutions, stannates are converted to tin(IV) oxyacids and eventually to tin dioxide hydrates.

Common uses of stannates include corrosion inhibition and protection in metal systems, where sodium stannate acts as a passivating agent in coolants and pretreatment baths. They also serve as fluxes in soldering and brazing, stabilizers in certain glazes and ceramic formulations, and as additives in glass processing to improve durability and resistance to corrosion.

Safety and handling guidelines for stannates follow general practices for inorganic salts: they are typically of low to moderate toxicity, with standard precautions for powder handling and routine laboratory or industrial hygiene practices.

See also: stannic acid, stannates in ceramics, poly-stannates.