sodium tetraborate decahydrate borax

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Comprehensive Analysis of Sodium Tetraborate Decahydrate (Borax): Chemical Name and Basic Properties Sodium tetraborate decahydrate, commonly known as borax, is an important inorganic compound with the chemical formula Na₂B₄O₇·10H₂O, a molecular weight of 381.37, and a CAS registry number of 1303-96-4. This compound typically exists as colorless translucent crystals or white crystalline powder, is odorless, tastes salty, and is easily soluble in water, with notably increased solubility in hot water, but almost 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.

Physical Properties: Borax has a density of 1.73 g/cm³ at room temperature, a melting point of 75℃, and a boiling point of approximately 320℃ (decomposition temperature of decahydrate). It is prone to weathering in dry air, losing some crystal water and becoming opaque. This characteristic requires attention to environmental humidity during storage. In addition, borax loses eight crystal waters at 60℃ and completely dehydrates at higher temperatures, forming a colorless glassy substance after melting. This property has important applications in glass manufacturing.

The chemical properties of borax are manifested in its ability to react with acids in aqueous solution to form boric acid. For example, it can react with sulfuric acid to form a borax sulfate solution, which is commonly used in the preparation of buffer solutions in laboratories. Its strong complexing ability enables it to form stable complexes with metal ions, making it a flux used in metal processing and welding to effectively lower the melting point of metal oxides and improve welding efficiency. Borax also exhibits a pronounced flame reaction, and when hydrochloric acid is added to its aqueous solution, a turmeric reaction occurs. These characteristics are used to identify borates in chemical analysis.

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

Carbon-soda process: Mix pre-treated boron ore powder with sodium carbonate solution, and introduce carbon dioxide into a carbonator for reaction to produce borax. This method optimizes the utilization rate of raw materials and the purity of the product by controlling the reaction pressure (0.5-0.6 MPa) and temperature (130-135°C).

Pressurized alkaline hydrolysis method: This method involves reacting sodium hydroxide solution with boron-magnesium ore powder under high temperature and pressure to produce sodium metaborate solution, which is then subjected to carbonization treatment to obtain borax. This method is suitable for the production of high-purity borax and is widely used in the fields of electronics and optical materials.

Soda ash alkali hydrolysis method: This method involves mixing well salt brine or ulexite with soda ash and boiling them together. Through precipitation and crystallization processes, borax is produced. This method is relatively low-cost and suitable for large-scale industrial production, but attention must be paid to impurity removal.

Borax finds extensive applications in various fields, spanning industry, medicine, and daily life:

Industrial use: As a cleaning agent, insecticide, and preservative, it is used in glass, enamel glaze, non-ferrous metal welding agents, and capacitor manufacturing. Its aqueous solution has inhibitory activity against microorganisms and can be used for soil sterilization and wood preservation. In agriculture, it serves as a herbicide, achieving weed control in non-cultivated areas by disrupting plant cell structure.

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 it also has astringent and protective effects on the skin and mucous membranes. However, its toxicity should be noted, and long-term or excessive use should be avoided.

Daily Life: As a laundry detergent booster, it softens water quality and enhances cleaning efficiency. It is used in household cleaning, such as dishwasher detergent, floor and wall cleaners, and for removing stains from stainless steel surfaces. Its eco-friendly properties make it a preferred alternative to traditional chemical cleaners.

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, such as wearing protective gloves and glasses, to prevent skin and eye contact.

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, thereby promoting the development of borate chemistry. Borax is also known by other names such as moonstone and yellow moonstone, reflecting its diversity in different cultures and application scenarios. Its applications have continuously expanded and deepened, ranging from ancient medicine to modern industry.

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