The phosphates are used primarily for their water softening action. Phospates also contribute to soil dispersion of peptization, efficient rinsing, and scale control. In the phosphate family are the orthophosphates, trisodium, and monosodium. Trisodium phosphate (Na3PO4. 12 H2O) is sometimes used alone as a soak or spray cleaner. Disodium phosphate is used when a cleaner needs to be buffered in the 8 to 10 pH range and monosodium phosphate is widely used in iron phosphating compounds.
Tetrasodium pyrophosphate has excellent sequestering of chelating action for zinc, copper and magenesium, but is not very good for calcium. It is difficult to dissolve and has lower solubility than most of the other sodium phosphate.
Sodium tripolyphosphate (Na5P3O10) comes close to being the best all round phosphate. Its consumption by the detergent and cleaning industry exceeds the combined total of all of the other sodium phosphates. "Tripoly" has excellent water softening action, sequester or chelates some metal ions, stores and compounds well, and contributes to good rinsing because of its threshold effect where a few parts per million prevent precipitation and scaling in the rinses.
Silicates are excellent buffers and when compounded with surfactants are the best wetting, emulsifying, and deflocculating agents of all the alkalis. The silicates are excellent inhibitors for metal to be necessary for heavy duty, long life cleaners. Sodium metasilicate is widely used in cleaners both as the pentahydrate (Na2SiO3. 5 H2O) and as the anhydrous sodium metasilicate (Na2SiO4). Sodium orthosilicate (Na2SiO4) is widely used in steel cleaners. Silicates can be a source of trouble in subsequent specifications may call for nonsilicated cleaners to avoid trouble.
Various chelating agents have become prime importance in recent years because of the demand for low or non phosphated cleaners. The most widely used are sodium gluconate, sodium heptagluconate, sodium citrate NTA (trisodium-nitrilo-triethanolamine) EDTA (tetrasodium ethylenediamine tetraacetate), and triethanolamine. These chemicals, because of their capacity to soften water and tie up various metal ions, are finding a place in non phosphated metal cleaners, aluminum etchants, alkaline derusters and descalers, and in electrocleaning compounds.
There are about 700 commercially available surface active agents and it takes experience to select the proper anionic, nonionic, cationic, or amphoteric detergent for specific metal cleaning compounds. The anionics are widely used in electrocleaning compounds. The nonionic or combinations of the nonionics with anionics have been useful in soak and spray cleaners. Some nonionics have defoaming properties so it is possible to control the amount of foam by property selecting and compounding nonionic and anionic surface active agents. The cationics and amphoterics are useful for leaving a film on the metal surface to prevent rusting or oxidation.
The most widely used surface active agents in metal cleaning are the sodium linear alkylate sulfonates and the fatty alcohol sulfates in electrocleaning compounds, the sodium linear alkylate sulfonates and the oxyethylated alcohol type of nonionics in soak cleaners, and the low foaming nonionics in spray cleaners.