The process of depositing the required covering layer on the substrate (after pretreatment) by electrolysis is called electroplating. Electroplating is a very ancient traditional technique, widely used for permanent decoration and protection. Electroplating can be divided into single metal electroplating, multi-layer composite electroplating and alloy electroplating. There are many factors affecting the quality of coating, such as: plating pretreatment, plating solution purification method and degree, the rationality of the way to the plating, plating solution, the determination of composition and thickness, system setting process parameters (PH, temperature, current density), additive (brightener, leveling agent, in addition to the stress agent, wetting agent, dispersant), analysis of plating solution and the complement system, operating system, post-treatment of plating (to hydrogen, closed), etc. Because electroplating three wastes to the environment pollution and the influence health, each district environmental protection department management is increasingly strict, many enterprises do not set up their own electroplating workshop, but to the specialized factory (workshop) commissioned processing. In order to ensure the quality of electroplating parts, the appearance, adhesion, thickness, porosity, corrosion resistance and other specific requirements should be put forward according to relevant standards and regulations. In case of quality problems in acceptance or use, it is convenient for quality accident analysis and improvement.
Oxidation treatment can be divided into ferrous metal oxidation treatment and non-ferrous metal oxidation treatment.
Oxidation treatment of steel and alloy, also known as blue or black treatment. Due to its low cost, high efficiency, quick effect, stable process, convenient operation and simple equipment, it is widely used.
Alkaline chemical oxidation
Alkaline oxidation is the most common method, which is carried out at high temperature in sodium hydroxide solution containing certain oxidant. Oxidizing agent and hydroxide steel react with metal iron to form oxide film with iron oxide (Fe3O4) as main component. The color of the film depends on the surface condition of the part, the alloy composition and the process condition of oxidation treatment. Film thickness 0.6 ~ 0.8 um.
The order of chemical reaction is no formation of sodium ferrous (Na2Fe02) and sodium ferrite (Na2Fe204), and then the reaction of sodium ferrite and sodium ferrite forms the oxide film Fe304. The equation is as follows:
Fe 3 + Na02 + 5 na0h - > 3 na2fe02 + H20 + NH3 write
6 na2fe02 + NaN02 + 5 h20 - > 3 na2fe204 + 7 na0h + NH3 write
Na2Fe02 + Na2Fe204 + 2 h20 - Fe304 na0h + 4