Potassium hydroxide is a strong alkali, can be widely used for electroplating or as chemical raw materials for use, but we will find that the color of some products is blackened when we use it. This is because there are some mistakes in the steps when the products are made. Let's have a detailed understanding of the reasons for the black color of the products.
1. Nitrogen sealing equipment is needed after start-up and feeding
When the equipment is in micro positive pressure state, it can effectively avoid air entering into the system. Therefore, the equipment is sealed with nitrogen after the start-up and feeding, and the device is always in the high temperature and strong alkali state at the nitrogen inlet. The oxygen entering will aggravate the corrosion of nickel material, and then increase the nickel content in it, resulting in black color.
2. Capability control
The capacity should be controlled in the range of 60% ~ 100% of the rated output. In the evaporator, if the feed rate is too small, the liquid film in the evaporator will break because of its thin thickness, resulting in dry wall area, which will make the pipe bear greater thermal stress, thus aggravating stress corrosion. When the amount of liquid feed is too large, the liquid can not be normal film-forming or the film is too thick. In the process of heating, the liquid can not be fully heat transferred, which can not reach the required temperature for boiling. Therefore, it can not be fully evaporated, which will lead to the concentration process can not be carried out well, and even can not be carried out. If the flow rate is too large or too small, it will damage the equipment and corrode the nickel material, which will increase the nickel content in potassium hydroxide and make it blackened.
3. Reduce the number of driving and stopping
The number of start-up and shut-down of the equipment should be reduced as much as possible, because each time the feeding alkali liquor will wash away a layer of nickel oxide layer which plays a protective role on the surface of nickel material, and then continue to wash and corrode the nickel material at the lower layer, so it is inevitable to produce black alkali during the start-up process. Measures such as prolonging the time of steam purging system can be taken to reduce the black alkali content as much as possible.
4. Purge the equipment with steam before start-up
Clean the system with steam before start-up to ensure sufficient pressure and purging time. Purging can not only preheat the equipment, reduce the thermal stress when feeding, but also purge the residual alkali in the pipeline during the purging process; it can also exhaust the air in the system by blowing to reduce the oxygen content as far as possible; at the same time, it can reduce the scouring and corrosion of nickel equipment during feeding, reduce the nickel content in it and prevent blackening.
The above is the reason why the color of potassium hydroxide turns black in the production. The main reason is that the production is not well controlled, and the equipment can not be cleaned up, resulting in the black color of the product during production.