What is Trisodium phosphate?

Trisodium phosphate (TSP, E339) is a cleaning agent, food additive, stain remover and degreaser. It is a white, granular or crystalline solid, highly soluble in water producing an alkaline solution. The item of commerce is often partially hydrated and may range from anhydrous trisodium phosphate, Na3PO4, to the dodecahydrate, Na3PO4·12H2O. Most often found in white powder form, it can also be called trisodium orthophosphate or just plain sodium phosphate. Trisodium phosphate was at one time extensively used in formulations for a wide variety of consumer grade soaps and detergents, but ecological problems have largely ended that practice, at least in the western world. Substitutes are not as effective, but the raw chemical can be bought in bulk to add to underpowered detergents.
Uses
Cleaning
The major use for trisodium phosphate is in cleaning agents. The pH of a 1% solution is 12, and the solution is sufficiently alkaline to saponify grease and oils. In combination with surfactants, TSP is an excellent agent for cleaning everything from laundry to concrete driveways. This versatility and low manufacturing price, made TSP the preferred basis for a plethora of cleaning products sold in the mid-20th century. TSP is still sold, and used, as a cleaning agent, but during the late 1960s in the United States,[citation needed] government regulators in seventeen states determined that overuse led to a series of ecological problems.
By the end of the 20th century, many products that formerly contained TSP were manufactured with TSP Substitutes, which consist mainly of sodium carbonate along with various admixtures of nonionic surfactants and a limited percentage of sodium phosphates.
Trisodium phosphate is commonly used after cleaning with mineral spirits in order to remove hydrocarbon residues. TSP may be used with household chlorine bleach in the same solution without hazardous reactions. This mixture is particularly good for removing mildew.
Although it is still the active ingredient in some toilet bowl cleaning tablets, TSP is generally not good for cleaning bathrooms, because it can stain metal and can damage grout.
Flux
In the United States, trisodium phosphate is an approved flux for use in hard soldering joints in medical grade copper plumbing. The flux is applied as a concentrated water solution and dissolves copper oxides at the temperature used in copper brazing. Residues are fully water soluble and can be rinsed out of plumbing before it is put in service.
Trisodium phosphate is used as an ingredient in fluxes designed to deoxygenate nonferrous metals for casting.
TSP can be used in ceramic production to lower the flow point of glazes.
Painting enhancement
TSP is still in common use for the cleaning, degreasing and deglossing of walls prior to painting. Trisodium phosphate breaks the gloss of oil based paints and opens the pores of latex based paint providing a surface better suited for the adhesion of the subsequent layer of paint.
Food additive
Trisodium phosphate is approved as a food additive in the EU.
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