Industrial pure titanium tube pickling process
In the industrial production process of pure titanium tube, pickling is a very important process, must be forgotten. Because the titanium tube in the heat treatment or heat treatment process, in the absence of protective atmosphere with the furnace gas and other gases in the chemical generated by the role of the oxide layer. Titanium tube surface of the oxide layer by pickling after the process, or the quality of the final product is very harmful.
If the titanium tube with an oxide layer of rolling, will make the pipe defects, but also because of the existence of an oxide layer, so that the oxide layer into the pipe surface, resulting in unsatisfactory surface. Directly affect the titanium tube product quality, material consumption, productivity and economic efficiency are good or bad. It is common knowledge that the soaking of acid is the process of removing the surface oxide layer in the treatment of acids, bases, salts and their solutions.
There are numerous ways to remove the oxide layer. The traditional method is to use inorganic strong acids such as sulfuric acid (H2SO4), hydrochloric acid (HCI), nitric acid (HNO3) and hydrochloric acid (HF). This method is the point of oxide and acid chemical reaction to remove the oxide layer. For different materials according to their performance characteristics of the corresponding one of them.
Industrial titanium tube oxide layer, mainly titanium dioxide (TiO2), followed by various low-priced titanium oxides, such as TiO, Ti2O3, TiO5. In addition, there is titanium high-priced oxides, such as TiO3 and so on. Studies have shown that, at room temperature, the titanium tube in <5% dilute sulfuric acid pickling liquid pickling in the titanium tube surface to generate protective oxide layer to protect the titanium is not dilute sulfuric acid continue to erode, but> 5% sulfuric acid The pickling has a significant reaction with titanium.
At room temperature, about 40% of the sulfuric acid corrosion of titanium corrosion rates of the fastest. Concentration <5% of hydrochloric acid at room temperature does not react with titanium, when the temperature increases, even if dilute hydrochloric acid will also corrosion of titanium, but> 10% hydrochloric acid at 70 ℃ and 1% hydrochloric acid at 100 ℃ on the titanium Significant corrosion occurs. However, when the hydrochloric acid solution in the presence of oxide or metal ions (such as copper, etc.), you can reduce the corrosion of hydrochloric acid on titanium. Hydrochloric acid (HF) is the strongest solvent for titanium. Even if the concentration of 1% of hydrochloric acid, but also with titanium reaction: 2Ti + 6HF = 2TiF3 + 3H2 when the hydrochloric acid solution in the presence of iron, copper and other metal ions, can accelerate the dissolution of titanium. The surface roughness of the titanium tube is most likely to react with cold, boiling nitric acid (HNO3): 3Ti + 4HNO3 + 4H2O = 3H4TiO4 + 4NO3Ti + 4HNO3 + H2O = 3H2TiO3 + 4NO.
In view of the corrosion characteristics of various nitrates on the titanium tube, in order to effectively remove the titanium oxide surface of the oxide layer, the relevant information on the use of nitric acid nitric acid hydrochloric acid, its formula and process are as follows: solution concentration ratio: (35% ~ 40%) HNO3 + (5% ~ 7%) HF + residual H2O solution temperature: 30 ℃ ~ 50 ℃ test proved that the above formula and process there are some deficiencies: First, titanium tube into the acid reaction is too intense, so that acid temperature Rapid rise, and even can make the acid boiling, this situation can easily lead to oxidation of titanium tube combustion, resulting in increased loss of titanium tube matrix; Second, in such a violent reaction process spilled acid, for the operator With considerable harm; Third, the operating environment of workers is poor, too much pollution.
In view of the above reasons, the titanium tube pickling formula and process were adjusted as follows:
(25% ~ 28%) HNO3 + (3% ~ 5%) HF + residual H2O solution temperature: ≤ 30 ℃ Pickling time: (1) The reaction temperature of the solution (HNO3) + hydrochloric acid (HF) 10 minutes to 20 minutes Practice has proved that the adjustment of the pickling situation is better, titanium tube into the acid reaction is more stable, titanium tube base pickling loss rate can be reduced by 30% to 50%.
It should be noted that the pickled titanium tube must be washed and did. Because the titanium tube in the acid solution after pickling, although the purpose of removing the oxide layer, but the titanium tube surface by the erosion of acid or more part of the residual acid, this part of the residual acid if not removed, will be due to The chemical effect of residual acid, so that part of the hydrogen diffusion to the titanium tube matrix, titanium tube plasticity reduced. At the same time, the presence of residual acid on the surface of the titanium tube will cause the roll to be prematurely rolled during rolling and the waste of the titanium tube.
Therefore, the surface of the titanium tube after pickling does not permit the existence of residual acid. The purpose of drying is to promptly drive out the metal atoms in the metal lattice, in order to prevent the formation of titanium tube in the rolling hydrogen embrittlement phenomenon, while improving the lubrication performance.
