Metal pretreatment steps, we must have been familiar with, today, we popularize, we should be how to choose the metal rust remover?
Author: Marisa
Metal pretreatment steps, we must have been familiar with, today, we popularize, we should be how to choose the metal rust remover?
First of all, we need to understand, we are in the pickling descaling, usually using a diluted solution, diluted solvent plus other corrosion inhibitors and other raw materials, both to improve the solution's ability to remove rust, but also to protect us in the process of descaling agent used in the safety of the metal descaling agent commonly used in the main sulfuric acid, phosphoric acid, hydrochloric acid, urolithiophosphate, bentonite clay and other raw materials, the mixing of modulation, the better descaling effect is hydrochloric acid and sulfuric acid, also are strong, the same are strong. Rust removal effect is better hydrochloric acid and sulfuric acid, the same are strong acids, what kind of difference between the two of them? For this we did an experiment.
We put the same number of rusty screws were put into the concentration of 10% hydrochloric acid solvent and sulfuric acid solvent, hydrochloric acid solvent quickly produced a large number of bubbles and loose purple-red solids, and exothermic, the solution by the blue colorless: while the sulfuric acid solvent is no obvious chemical changes, and then we will be the two solvents after a period of time, and found that, dilute hydrochloric acid solvent in the removal of rust effect is more satisfactory, while the dilute sulfuric acid solution Rust removal effect is not obvious, taking into account the characteristics of sulfuric acid, we will also sulfuric acid solution for heating, after heating the solution rust removal effect is more obvious, but because of the heating temperature is too high, resulting in screws were slightly corroded.
It is worth mentioning that when the solution was diluted before the experiment, we found that hydrochloric acid with a large solute mass fraction was volatile and the hydrogen chloride gas emitted was strongly irritating and corrosive to the human body, while hydrochloric acid with a low solute mass fraction was relatively stable. Concentrated sulfuric acid needs to be diluted before use, the dilution will produce a lot of heat, easy to cause burns, and concentrated sulfuric acid is far more corrosive than concentrated hydrochloric acid. It can be seen that hydrochloric acid is safer to use.
Summary: Hydrochloric acid pickling has the following characteristics compared with sulfuric acid pickling.
1, hydrochloric acid pickling rate is higher. Hydrochloric acid pickling reaction rate is not subject to neither the loose degree of iron oxide in the pickling before, also not subject to the relative composition of the iron oxide, hydrochloric acid solution can dissolve 3 layers of iron oxide at the same time at a greater rate, the dissolution rate is much greater than in sulfuric acid solution.
2, hydrochloric acid pickling surface silver, smooth, clean. This is due to the characteristics of hydrochloric acid, basic non-corrosive metal matrix; on the other hand, due to the oxides are easily dissolved in hydrochloric acid, pickling products are easy to remove, so it will not cause the surface of the casein, and make the surface and clean; sulfuric acid pickling of pickling products produced by the sulfuric acid, iron sulfate, is a kind of difficult to dissolve the hydrate, often in the surface of the acid spot and other problems.
3, hydrochloric acid pickling defects less, less chemical acid loss. Because hydrochloric acid basically does not corrode the metal matrix, so hydrochloric acid pickling acid loss than sulfuric acid pickling low hydrochloric acid will not occur over the pickling, but also seldom produces hydrogen embrittlement, and sulfuric acid due to casein corrosion of the metal matrix to release hydrogen, part of the hydrogen atoms diffuse into the metal interior leading to hydrogen embrittlement;.
4. Hydrochloric acid pickling does not produce pickling residue, and in the case of sulfuric acid pickling must be frequently cleaned and neutralize the acid and mucus-like residue
5, copper in the steel does not affect the quality of pickling. In hydrochloric acid, copper does not form a carburizer, so the surface flatness and brightness will not be reduced due to the inclusion of copper and in sulfuric acid pickling, due to the precipitation of steel carburizer will lead to the surface of the dark, reducing the surface quality.
6. Hydrochloric acid pickling waste acid and cleaning waste liquid can be completely regenerated and recycled; while the sulfuric acid pickling waste liquid can not be recycled and waste liquid treatment is more troublesome.
After reading the above analysis, we must have a clear understanding of how to choose the rust remover, but we need to remind you again, although hydrochloric acid is safer than sulfuric acid, but after all, it is also a veritable strong acid, we use hydrochloric acid for the operation, you need to add an appropriate amount of corrosion inhibitors, but also need to do a good job of personal protection.