Chromium, chemical symbol Cr, atomic number 24, is a silver and shiny metal. It is ductile. Chromium containing impurities is hard and brittle. Chromium is soluble in strong alkali solution. It has a very high corrosion resistance.
The most important use of chromium is to make alloys. Stainless steel contains more than 12% of chromium. It has very good toughness, mechanical strength and corrosion resistance. In a watch, chromium-containing stainless steel accounts for almost over 60% of the total weight, because the watch case and machines are mostly made of stainless steel. The so-called “all-steel watch”, refers to the fact that the watch case and the back cover are made of stainless steel. And “semi-steel watch”, refers to the fact that the back cover of the watch is made of stainless steel while the watch case is made of brass or other metals. Some medical devices, such as scalpels, syringe needles and scissors, are mostly made of chromium alloys. They are clean, beautiful, and durable. Ships and motorboats made of chromium alloys don’t even need to be painted.
Chromium is the essential trace element for human body. It plays a special role in the sugar metabolism and lipid metabolism of human body. The physiological functions of chromium work together with other substances that control metabolism, such as hormones, insulin, various enzymes, genetic materials of cell (DNA and RNA) and so on. The human body’s absorption and utilization rate of inorganic chromium is very low, which is less than 1%; the human body’s utilization rate of organic chromium can be up to 10-25%. The content of chromium in natural food is relatively low, and it is present in trivalent form. The toxicity of chromium is related to the valence of its existence. Metallic chromium has almost no hazardous effect on human body, and there has been no report of it causing industrial poisoning. Trivalent chromium is an element that is beneficial to the human body, while hexavalent chromium is toxic. Hexavalent chromium is 100 times more toxic than trivalent chromium and is easily absorbed by human body and accumulated inside the body. Trivalent chromium and hexavalent chromium can be converted into each other.