Liquid nitrogen tank is a common equipment for low-temperature storage in the laboratory. It can be divided into transport type liquid nitrogen tank and storage liquid nitrogen tank according to its use. It is also a kind of equipment often used in medical, biological, scientific research and other industries. After adding a small amount of liquid nitrogen to the liquid nitrogen tank, some black spots appear on the bottom. What's the reason?

If black spots appear after a small amount of liquid nitrogen is added to the new liquid nitrogen container, it is actually a symptom of impurities frozen in liquid nitrogen and attached to the metal surface. Generally speaking, they enter together with liquid nitrogen. This situation is mostly more obvious to observe after adding a small amount of liquid nitrogen to a new liquid nitrogen tank and the liquid nitrogen has volatilized. If it is not a new liquid nitrogen tank and there is still a little liquid nitrogen inside, it is more difficult to observe the internal impurities after adding liquid nitrogen to the liquid nitrogen tank in use, and the black spots are not obvious.

Therefore, if add liquid nitrogen to the liquid nitrogen biological container constantly for a long time, some precipitated impurities will gradually appear, which are the so-called black spots. So, it is recommended to clean the inside of the liquid nitrogen tank once after using it for a period of time.