Ammonium polyphosphate is a compound that is widely used for the production of fertilizers and paints with fire retardant properties. Its structure is formed by the fusion of monomeric orthophosphates into one polymer chain. The starting material for the preparation of the substance is phosphoric acid and ammonia.
Description
Ammonium polyphosphate (or ammonium polyphosphate, according to the international name) is a high molecular weight inorganic salt derived from phosphoric acid.
Chemical formula of the substance: (NH 4 PO 3 ) n . Its crystalline structure can be of two types:
Type I (the number of monomer units n = 100-200).
Type II (n> 1000). Such a compound has a more complex structure, greater molecular weight and thermal stability, it dissolves worse in water compared to the first type. Particles have sizes of 10-40 microns or more. Most often, this salt is used in industry.
The structural formula of ammonium polyphosphate has the form, as in the picture below.
Physical and chemical characteristics
The connection is characterized by the following properties:
- stability and non-volatility;
- melting point - 180-185 ° C;
- when diluted in water (solubility is 0.5 g / cm 3 ) exhibits the properties of a polyelectrolyte and increases the viscosity of the liquid;
- when heated to 300 ° C, active decomposition into polyphosphoric acid and ammonia occurs;
- the acidity level in a 10% aqueous solution is 5.5-7.5 pH;
- density - 1.9 g / cm 3 ;
- appearance - white granular substance.
Release form - in the form of powder or small granules. In relation to living organisms, the compound is environmentally friendly. The hazard class of ammonium polyphosphate is IV according to GOST 12.1.007.
Getting
The production of this substance in the chemical industry is carried out in several ways:
- The 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 NH 3 ammonium polyphosphate, monoamidopyrophosphoric and diamidopyrophosphoric acids are formed.
- Neutralization of polyphosphoric acid with ammonia.
- Thermal dehydration of ammonium phosphates.
- Neutralization of H₃PO₄ ammonia and dehydration of the resulting ammonium orthophosphate.
The exact chemical composition of ammonium polyphosphate depends on the parameters of the process. The nitrogen content can be 14-17%, phosphorus - 30-32%, the degree of polymerization - 40-77%.
Ammonium Polyphosphate: Application
The compound 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;
- manufacturing of insulating sheaths of electric cables;
- use as an antipyretic in paints and varnishes (varnishes, enamels), sealants, technical lubricants, adhesives and other compositions;
- fertilizer production for agriculture.
Ammonium polyphosphate can be used to enrich all types of soil and fertilize all types of cultivated plants. Fertilizer shows the best efficiency on sierozem 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, which are obtained by hot or cold mixing. Most often, this substance is part of complex top dressings along with nitrate or potassium chloride, urea. This compound also combines well with trace elements and pesticides.
Fire retardant coatings
Due to its special properties, when exposed to open fire, ammonium polyphosphate is the main component of modern flame retardant coatings for both non-combustible (metal, concrete) and combustible (wood, fabric, plastic) materials. When ignited, salt does not release 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 the composition of fire retardant coatings is as follows:
- Under the influence of high temperature, the paint with antipyretic swells (without melting).
- Due to dehydration and heating, polyphosphate acid is formed on the main material (wood, metal).
- A carbon film appears on the surface of the latter.
- A large volume of non-combustible gases is released.
- A foamed layer forms 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 coatings.