Obtaining Red Phosphate Coatings on Steel at Room Temperature

The article discusses the aspects of obtaining red-colored phosphate coatings on the surface of steel at low temperature. The solution for color phosphating is based on a modified composition based on the chemical «Majef» with sodium nitrite as an accelerator, organic additives of glycerin and Trilon B to improve the quality of precipitated phosphate coatings, and the preparation OS-20 for emulsifying and wetting the surface. To precipitate red phosphate coatings, it is proposed to introduce a copper salt into the composition of the phosphating solution. In the phosphating solution with the addition of copper salt, contact deposition of copper occurs before the formation of a phosphate film on the surface of the steel. This copper layer stains the resulting phosphate coating, but does not adhere to the steel surface. To obtain a red phosphate coating of satisfactory quality, it is recommended to first soak the steel product in a modified cold phosphating solution for 15 minutes, and after the formation of a thin layer of phosphate film on the surface of the steel, introduce copper salt into the solution. Red phosphate coatings are much inferior in protective abilities to unpainted phosphate films, they have greater roughness and high porosity. To increase the protective properties and improve the appearance, it is recommended to additionally coat phosphate coatings with varnish.