Citric acid is divided into two types: anhydrous and monohydrate. Translucent crystal or white fine powder crystal. Odorless, with a strong sour taste. It becomes anhydrous when dried or heated to 40-50°C. Anhydrous is easy to weather in dry air and is slightly deliquescent. It becomes soft at 75ºC. Melting at 100ºC. The relative density is 1.542 (-hydrate) and 1.67 (anhydrate). Easily soluble in water (monohydrate 209g] 100mL, 25°C; anhydrous 59.2g/100mL, 20°C; pH value of 1% solution is 2.31) and ethanol, soluble in ether. The natural product is found in citrus fruits such as lemons. Powder and air can form explosive mixtures. In case of open flame, high heat or contact with oxidants, there is a risk of combustion and explosion.
Citric acid has a strong chelating effect. It can complex Fe3+ and weaken the promotion effect of Fe3+ on corrosion. It can remove iron, copper and other metal oxide scales. It is easy and safe to operate and is suitable for a variety of materials. Since there is no c1- in the molecule, it will not cause stress corrosion of equipment. It is used as a cleaning agent. Citric acid has a smaller corrosion rate on steel than hydrochloric acid. Citric acid mainly removes rust and has poor solubility in calcium, magnesium and silicon scale, so it is mainly used to clean newly built large-scale equipment. Citric acid cannot remove calcium magnesium scale and silicate scale. However, citric acid mixed with sulfamic acid, glycolic acid or formic acid can be used to clean rust and calcium magnesium scale. Citric acid mixed with EDTA can be used to clean heat exchangers. The corrosion inhibitor added to the citric acid cleaning solution is mainly thiourea, with a dosage of 0.1%. You can also use 0.06% thiourea mixed with other corrosion inhibitors. In addition, it can also be used in the medical field. The sodium citrate salt can prevent blood coagulation, the calcium salt can be used as an antacid for the stomach, and the barium salt is toxic.