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、開車投料后需要使用氮氣密封設備

1. Nitrogen sealing equipment is needed after start-up and feeding

當設備處于微正壓狀態的時候，可以有效的避免空氣進入到系統當中。所以制作的時候開車投料后用氮氣密封設備，保持通入的氮氣處裝置始終處于高溫強堿狀態，氧氣進入從而會加劇鎳材腐蝕，進而增加其中的鎳含量，從而導致顏色發黑。

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、能力控制

2. Capability control

能力需要控制在額定產量的60%~100%的范圍內。在蒸發器中，如果進料量太小，蒸發器中液膜就會因為太薄以致斷裂，從而出現干壁區，這樣就會使管子承受更大的的熱應力，從而加劇應力腐蝕。當液體的進料量太大時，液體就無法正常成膜或者膜太厚，在升溫過程中，液體經常不能得以充分的熱量傳遞，從而達不到沸騰所需要的溫度，因此不能全部的進行蒸發，就會導致濃縮過程不能很好地進行，甚會發生無法進行的情況。流量太大或太小都會損壞設備，腐蝕鎳材，這樣就會增加氫氧化鉀中的鎳含量，使其發黑。

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、減少開、停車次數

3. Reduce the number of driving and stopping

盡量減少設備開停車的次數，因為每一次開車，進料堿液都會沖掉一層鎳材表面起保護作用的氧化鎳層，然后繼續沖刷腐蝕下層鎳材，所以開車過程中難免產生黑堿。可以進行延長蒸氣吹掃系統的時間等措施，盡量的降低開車黑堿量。

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、開車前用蒸氣吹掃設備

4. Purge the equipment with steam before start-up

開車前用蒸氣吹掃干凈系統，保證有足夠的壓力和吹掃時間。吹掃既可以預熱設備，降低投料時的熱應力，又能在吹掃過程中把管路中的殘留堿吹掃干凈；還可以通過吹掃把系統中的空氣排出，盡量減少氧氣含量；同時可以減少投料時對鎳材設備的沖刷和腐蝕，降低其中的鎳含量，防止發黑。

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.

上面介紹的就是氫氧化鉀在制作時顏色發黑的原因，主要是因為制作時候的產量的控制不好，以及設備可以沒有清理干凈，導致的產品在制作時顏色發黑。

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.