borax sodium tetraborate decahydrate

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Detailed introduction to borax (sodium tetraborate decahydrate) Borax, with the chemical name sodium tetraborate decahydrate, is an important boron-containing mineral and boron compound, widely used in industry, medicine, and daily life. Its chemical formula is Na₂B₄O₇·10H₂O, with a molecular weight of 381.37 and a CAS registry number of 1303-96-4.

Physical Properties Borax is typically a colorless translucent crystal or white crystalline powder, odorless, and has a salty taste. At room temperature, its density is 1.73 g/cm³, melting point is 75℃, and boiling point is approximately 320℃ (decahydrate). Borax is easily soluble in water, especially with higher solubility in hot water, but insoluble in ethanol. Its aqueous solution is weakly alkaline, with a pH value of approximately 9.5, and exhibits an alkaline reaction to litmus and phenolphthalein indicators.

Chemical properties: Borax is prone to weathering in the air, losing some of its crystal water and becoming opaque. Its aqueous solution can react with acids to form boric acid, such as reacting with sulfuric acid to form a borax sulfate solution, which is commonly used for the preparation of buffer solutions in the laboratory. Borax also has strong complexing ability and can form stable complexes with metal ions, making it a flux used in metal processing and welding.

Preparation methods: There are various industrial preparation methods for borax, mainly including:

Carbon-soda process: Mix the pretreated boron ore powder with sodium carbonate solution, and introduce carbon dioxide into the carbonator for reaction to produce borax.

Pressurized alkaline hydrolysis method: A reaction is conducted between sodium hydroxide solution and boron-magnesium ore powder under high temperature and pressure, producing sodium metaborate solution. This solution is then subjected to carbonization treatment to obtain borax.

Soda ash alkali digestion method: The process involves boiling a mixture of well salt brine or ulexite with soda ash, and then obtaining borax through precipitation and crystallization.

Borax finds extensive applications across multiple industries:

Industrial use: As a cleaning agent, insecticide, and preservative, it is used in the manufacture of glass, enamel glazes, non-ferrous metal welding agents, and capacitors. Its aqueous solution has inhibitory activity against microorganisms and can be used for soil sterilization and wood preservation.

Pharmaceutical Use: In traditional medicine, borax is used as an external antipyretic and detoxifying agent to treat conditions such as sore throat and oral ulcers, while when taken internally, it can clear the lungs and reduce phlegm. Modern research has shown that borax has inhibitory effects on various bacteria and fungi, and also has astringent and protective effects on the skin and mucous membranes.

Daily life: As a laundry detergent booster, it softens water quality and enhances cleaning effectiveness. It is used in household cleaning, such as dishwasher detergent, floor and wall cleaners, and for removing stains from stainless steel surfaces.

Safety and toxicity Borax has a certain degree of toxicity. Long-term or excessive intake may pose a risk to human health, especially to the reproductive system and developing fetuses. Therefore, since 2008, borax has been listed as a prohibited additive in food, and illegal addition will face legal consequences. When storing and using, it is necessary to pay attention to ventilation and dryness, avoid contact with strong acids, and take appropriate protective measures.

History and Background The research on the chemical processing of borax began in the early 18th century, when G. Holmberg first obtained boric acid by reacting natural borax ore with ferrous sulfate. Subsequently, several scientists further studied the properties of borax by heating its aqueous solution with acid. Borax is also known by various names such as moonstone and yellow moonstone, reflecting its diversity in different cultures and application scenarios.

Through the above elaboration, the comprehensive characteristics and applications of borax (sodium tetraborate decahydrate) are clearly demonstrated, highlighting its importance in science, industry, and daily life.