Sodium hexametaphosphate is also known as “sodium polymetaphosphate”, “sodium polymetaphosphate”, “glassy sodium metaphosphate”, and “Gram’s salt”. Mixture of sodium polymetaphosphate. It is one of the polymers of sodium metaphosphate (NaPO3). The chemical formula is expressed as (NaPO3)n, where n is 10 to 23. It is a commonly used complexing agent in elimination solutions. Sodium hexametaphosphate is white flake or powdery crystal, easily soluble in water but insoluble in organic solvents. It is easy to deliquesce and should be stored in a dry and ventilated warehouse. The storage period is preferably 6 months. Sodium hexametaphosphate is usually used in conjunction with detergents, and the dosage is generally 1%.
Physical and chemical properties
Sodium hexametaphosphate is a colorless glassy solid with the molecular formula (NaPO3)5. Molecular weight 611.17. The melting point is 616℃ (decomposition), and the refractive index is 1.482±0.002. It is insoluble in organic solvents and soluble in water, but dissolves very slowly at low temperatures and dissolves quickly in warm water at 30 to 40°C. Water-soluble poloxamer 188 liquid is weakly acidic (pH value = 6.0~6.8). It is used as a dispersant for non-weighted water-based mud to remove Ca2+ and Mg2+ ions by forming chelated phosphates. Therefore, it can effectively prevent mud flocculation caused by Ca2+ and Mg2+, and is very effective in resisting cement invasion and gypsum invasion in mud treatment. But it is not suitable for high temperature, high salt and high calcium conditions. Its main function in industry is to soften hard water.
Physical and chemical properties
(1) Sodium polymetaphosphate was once mistakenly called sodium hexametaphosphate, and it is still used today because people once thought it had the composition of (NaPO3)6, but in fact it does not have (PO3)66-units. Research in recent years has shown that sodium polymetaphosphate is a linear polyphosphate sodium salt vitreous body, and its molecular formula is best written as (NaPO3)x.
(2) Colorless transparent glass flakes or white powder, relative density 2.48, melting point 628℃.
(3) The aqueous solution is weakly alkaline, with a pH of 8 to 8.6.
(4) Soluble in water, insoluble in organic solvents.
(5) It is highly hygroscopic and can gradually absorb water and turn into a sticky substance in humid air.
Functions and features
(1) Sodium polymetaphosphate used in vegetable tanning can block the alkaline base of collagen (fixation), reduce the combination of vegetable tannins and collagen proteins, and is beneficial to accelerating tanning.
(2) It can form soluble complexes with Ca2+, Mg2+ plasma in water, and can also prevent the deposition of boiler scale such as Ca3 (stearic acid 1801PO4)2.
(3) Its anions have a blocking effect.
Purpose and usage
Sodium hexametaphosphate is mainly used as a quality improver and pH regulator for food additives, metal ion chelating agent, adhesive and expanding agent. my country’s GB2760-1996 stipulates that it is a food additive (moisture retaining agent) that is allowed to be used, and can be used in cans, fruit drinks, dairy products, and soy products; it is also used as a dye dispersant and water treatment agent.
In mineral processing, drilling, electroplating, papermaking, printing and dyeing, textile and tanning, it is used as flotation agent, mud conditioner, metal surface treatment agent, copperplate paper brightener, leveling agent and tanning auxiliary, etc. . In the photography industry, it is used to prevent hard salts or heavy metal ions in water from causing spots on the film. In food processing, it is used as dispersant, water retaining agent, anti-sedimentant, bacteriostatic agent and emulsifier. Mainly used as corrosion inhibitor and scale inhibitor in cooling water treatment.
(1) Pre-tanning agent for rapid vegetable tanning. If pre-treated with sodium hexametaphosphate and then treated with anhydrous sodium sulfate, the effect will be better.
(2) Pretreatment agent before chrome tanning.
(3) Neutralizing agent for chrome tanned leather.
(4) Water softener for boiler water and descaler for boiler scale.
Product quality standards
Preparation
It is obtained by heating sodium dihydrogen phosphate to 300°C until H2O is completely eliminated.
It can be prepared by sodium dihydrogen phosphate method and phosphoric anhydride method. The sodium dihydrogen phosphate method uses soda ash to neutralize phosphoric acid to produce sodium dihydrogen phosphate, which is then heated and dehydrated to produce sodium metaphosphate, which is then melted and polymerized. The phosphorus anhydride method uses phosphorus pentoxide and soda ash as raw materials, which are heated and polymerized at high temperature (750-850°C) and then quenched to form a glassy product.
