At room temperature, hydrochloric acid has a strong chemical dissolution of metal oxides, but the dissolution of the steel matrix is relatively slow, the use of hydrochloric acid etching is not easy to occur over corrosion and hydrogen embrittlement phenomenon. Hydrochloric acid can effectively etch a variety of metals at room temperature. When the concentration, the same temperature, hydrochloric
Commonly used etching agents for plating pretreatment
Author: Robby
I. Sulfuric acid
At room temperature, sulfuric acid solution has a weak ability to dissolve metal oxides. Increasing the concentration of the solution can not significantly improve the etching ability of sulfuric acid. When its concentration reaches 40% or more, the solubility of iron oxide is significantly reduced, and when it reaches 60% or more, the oxide skin can hardly be dissolved. Hot sulfuric acid on the steel matrix corrosion ability is stronger, the oxide skin has a greater peeling effect. But when the temperature is too high, it is easy to cause excessive corrosion, and make the steel matrix produce hydrogen embrittlement. Therefore - generally only heated to 50 ~ 60C, should not exceed 75C, but also add appropriate corrosion inhibitors. Iron and steel parts are generally in 10% 20% (v/v) sulfuric acid solution in the etching, the temperature is 40 ° C. When the solution contains more than 80g / L of iron, ferrous sulfate more than 215g / L, should be replaced with an etching solution.
Sulfuric acid solution is widely used for the etching of steel, copper and brass parts. It is used with chromic acid and dichromate as de-oxidizer and de-hanging ash agent for aluminum. It is used with hydrofluoric acid, nitric acid or a mixture of the two - for the removal of oxidized skin on stainless steel. Sulfuric acid anodic etching is an effective way to remove the oxide skin of steel and hanging ash.
II, hydrochloric acid
At room temperature, hydrochloric acid has a strong chemical dissolution of metal oxides, but the dissolution of the steel matrix is relatively slow, the use of hydrochloric acid etching is not easy to occur over corrosion and hydrogen embrittlement phenomenon. Hydrochloric acid can effectively etch a variety of metals at room temperature. When the concentration, the same temperature, hydrochloric acid etching speed than sulfuric acid 1.5 ~ 2 times faster. The concentration of hydrochloric acid etching solution is usually 20% ~
80% (v/v) hydrochloric acid solution at room temperature. Some departments] also use concentrated hydrochloric acid and properly heated.
III. Nitric acid
Nitric acid is an important component of many bright etching solutions. A mixture of nitric acid and hydrofluoric acid is widely used to remove heat-treated oxidized skin on lead, stainless steel, nickel- and iron-based alloys, titanium, zirconium and certain cobalt-based alloys. Nitric acid and sulfuric acid mixed acid can be used for copper and copper alloy parts glossy etching.
IV. Hydrofluoric acid
Hydrofluoric acid can dissolve compounds containing silicon. The oxides of chromium and aluminum also have good solubility. Therefore, hydrofluoric acid can be used for castings and stainless steel and other special materials parts of the etching. However, hydrofluoric acid is highly toxic and volatile, it should be used carefully to prevent contact with human skin.
V. Phosphoric acid
Phosphoric acid is widely used in descaling steel parts, mainly in the combination of steel weldments before coating rust. For example, 2% phosphoric acid, at a temperature of 80 ° C, used in steel parts rust. Phosphoric acid mixed with nitric acid, sulfuric acid, acetic acid or chromic anhydride, can be used for aluminum, copper, steel and other metals bright etching.
VI. Sodium bisulfate
Sodium bisulfate is an acid salt used in most dry etching liquids, which can replace sulfuric acid and make the treatment more convenient. In addition, for aluminum-based, zinc-based parts, can be used in alkaline etching.