Ammonium polyphosphate is a compound that is widely used in the production of fertilizers and paints with flame retardant properties. Its structure is formed by the fusion of monomeric orthophosphates into one polymer chain. The raw materials for obtaining the substance are phosphoric acid and ammonia.
Description
Ammonium polyphosphate (or ammonium polyphosphate, according to its international name) is a high molecular weight inorganic s alt derived from phosphoric acid.
The chemical formula of the substance: (NH4PO3). Its crystal structure can be of two kinds:
- I type (number of monomer units n=100-200).
- II type (n > 1000). Such a compound has a more complex structure, greater molecular weight and thermal stability, and is less soluble in water than the first type. Particles have sizes of 10-40 microns or more. Most often, this s alt is used in industry.
The structural formula of ammonium polyphosphate looks like in the picturebelow.
Physical and chemical characteristics
The following properties are typical for a connection:
- stability and non-volatility;
- melting point - 180-185 °C;
- when diluted in water (solubility is 0.5g/cm3) exhibits polyelectrolyte properties and increases liquid viscosity;
- when heated to 300 °C, active decomposition into polyphosphoric acid and ammonia occurs;
- acidity level in 10% aqueous solution - 5, 5-7, 5 pH;
- density– 1.9 g/cm3;
- appearance - white free-flowing substance.
Release form - in the form of powder or small granules. In relation to living organisms, the compound is environmentally friendly. Ammonium polyphosphate hazard class - IV according to GOST 12.1.007.
Receive
The production of this substance in the chemical industry is carried out in several ways:
- Interaction of gaseous phosphoric anhydride, ammonia and water vapor. Phosphorus is burned at a temperature of 3000-3500 °C, anhydride vapor enters a special chamber, where, when heated to 400-500 °C in the presence of NH3, ammonium polyphosphate, monoamidopyrophosphoric and diamidopyrophosphoric acids are formed.
- Neutralization of polyphosphoric acid with ammonia.
- Thermal dehydration of ammonium phosphates.
- Neutralization of H₃PO₄ with ammonia and dehydration of the resulting orthophosphateammonium.
The exact chemical composition of ammonium polyphosphate depends on the process parameters. The content of nitrogen can be 14-17%, phosphorus - 30-32%, the degree of polymerization - 40-77%.
Ammonium polyphosphate: application
The connection is used in the following industries:
- use as an additive in the manufacture of plastics, thermoplastic polyurethane, foams, foam insulation and polymer resins;
- production of chipboard, fiberboard, plywood;
- production of insulating sheaths of electric cables;
- application as an antipyretic in paints and varnishes (varnishes, enamels), sealants, technical lubricants, adhesives and other compounds;
- production of fertilizers for agriculture.
Ammonium polyphosphate can be used to enrich all types of soil and feed any kind of cultivated plants. Fertilizer shows the best efficiency on gray soils. Due to its high solubility in water, the substance is better absorbed by plants than similar top dressings based on phosphorus phosphates. Fertilizers with ammonium polyphosphate are used in the form of solutions that are obtained by hot or cold mixing. Most often, this substance is part of complex dressings along with potassium nitrate or chloride, urea. This compound also pairs well with micronutrients and pesticides.
Fire retardant coatings
Due to its special properties, when exposed to open fireAmmonium polyphosphate is the main component of modern flame retardant paints and varnishes for both non-combustible (metal, concrete) and combustible (wood, fabrics, plastic) materials. When ignited, the s alt does not emit toxic fumes into the air and slows down the spread of fire, which makes it possible to increase the fire resistance of structures.
The principle of operation of this polymer compound in fire retardant coatings is as follows:
- Under the influence of high temperature, the paint with antipyretic puffs up (without melting).
- Due to dehydration and heating, polyphosphate acid is formed on the base material (wood, metal).
- A carbon film appears on the surface of the latter.
- A large amount of non-flammable gases are released.
- A foam layer is formed that insulates the base material and prevents further flame propagation in the building structure.
At the same time, low-toxic gases are released during combustion, which are safer for humans than when using traditional paint and varnish coatings.
