[Alias]Orthoboric acid
［Molecular Formula］H3BO3
[Properties]Boric acid is essentially a hydrate of boron oxide (H3BO3·3H2O), which is colorless scales with a slight pearly luster. It is in the form of oblique crystals or white powder, odorless and smooth to the touch. The taste is slightly sour and sweet. The relative density is 1.435 (15℃), the melting point is 170℃, and it decomposes at the same time. It is heated and dehydrated sequentially. At 107°C, it loses water and becomes metaboric acid. At 140-160°C, it generates pyroboric acid. At 300°C, it becomes boric anhydride. Boric acid tends to form or harden when it gets wet. It is soluble in water, ethanol, glycerin, ethers and flavors. Its solubility in water increases with the increase of temperature and can evaporate with water vapor. 1g of boric acid can be dissolved in 4mL of boiling water, 18mL of ethanol, and glycerin. Dissolve in 4 mL. The acidity of boric acid is very weak. The 1:50 aqueous solution was tested with dextromethrin test paper and showed a weak acidic reaction. The acidity of boric acid is greatly increased by adding mannitol or glycerin. It has a disinfecting effect, but it is toxic to the human body. Oral administration will affect the nerve center, upper respiratory tract and liver.
Use of boric acid
Boric acid is the basic raw material for the production of borides and borates. It is widely used in the glass industry to produce optical glass, acid-resistant glass, organic boron glass and other high-grade glasses and glass fibers. It is used in the production of glazes in the ceramics and enamel industries, and as additives and fluxes in the metallurgical industry. In the pharmaceutical industry, it is used to produce disinfectants, astringents, preservatives and boric acid ointments. Used as fabric fire-retardant finishing agent in the printing and dyeing industry. In the leather industry, it is used for deliming the surface of bare leather. The cosmetics industry is used to produce boric acid medicated soaps and pH regulators. It can also be used as wood preservatives, pesticides, catalysts, antifungal agents, tackifiers for starch glue, and buffer solutions for electronics, rare metal smelting, photography, artificial gemstones and other industries.
Brief preparation method of boric acid
① There are many industrial methods for producing boric acid, including ammonium bicarbonate method, borax sulfuric acid neutralization method, hydrochloric acid method, sodium polyborate method, electrolytic electrodialysis method and well salt method Brine hydrochloric acid method, etc. Among them, the borax sulfuric acid neutralization method is relatively simple. Heating a solution of sulfuric acid and borax produces boric acid. The reaction is as follows:
After the reaction solution is cooled, crystallized, separated and dried, the finished product of boric acid is obtained.
②A small amount of pure boric acid for laboratory use can be obtained by recrystallization of industrial boric acid. That is, mix 1 part of industrial boric acid and 2 parts of deionized water and heat it to melt the boric acid, then filter it while it is hot, and the filtrate will be cooled and crystallized. The finished product is obtained by drying.
Safety and Protection
Boric acid is packed in plastic woven bags lined with polyethylene plastic film, with a net weight of 50kg per bag. Avoid rain or moisture during storage and transportation.
Boric acid is toxic to the human body. Symptoms such as nausea, vomiting, abdominal pain and collapse may occur during poisoning. The lowest lethal dose is: 640mg/kg orally administered to humans and 8600mg/kg administered to human skin. If it comes into contact with skin or eyes, rinse with water.
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