Ammonium Phosphate is a widely used nitrogen–phosphorus (NP) fertilizer produced by reacting ammonia (derived from petrochemical natural gas processing) with phosphoric acid. Because ammonia is synthesized from petrochemical feedstocks, ammonium phosphate is classified as a partially petrochemical fertilizer. It supplies nitrogen for vegetative growth and phosphorus for root development, flowering, and energy transfer.
Major Commercial Types
| Type | Chemical Formula | Common Name |
|---|---|---|
| MAP | NH₄H₂PO₄ | Monoammonium Phosphate |
| DAP | (NH₄)₂HPO₄ | Diammonium Phosphate |
| APP | (NH₄PO₃)ₙ | Ammonium Polyphosphate |
Chemical Composition
Monoammonium Phosphate (MAP)
Nitrogen (N): ~11–12%
P₂O₅: ~50–52%
Acidic in solution
Diammonium Phosphate (DAP)
Nitrogen (N): ~18%
P₂O₅: ~46%
Slightly alkaline in solution
Ammonium Polyphosphate (APP)
Nitrogen (N): 10–17%
P₂O₅: 40–70%
Polymerized phosphate chains
Key Physical Properties
| Property | Typical Behavior |
|---|---|
| Physical State | Crystalline solid / Granular |
| Color | White to off-white |
| Odor | Odorless |
| Density | 1.6–1.8 g/cm³ |
| Melting Point | Decomposes (>155–190 °C) |
| Solubility in Water | High (MAP & DAP) |
| Hygroscopicity | Low–Moderate |
| Thermal Stability | Moderate |
| Electrical Conductivity | High (solution) |
Mechanical Properties
| Property | Performance |
|---|---|
| Hardness | Moderate |
| Crush Strength | High (granulated grades) |
| Abrasion Resistance | Moderate |
| Flowability | Excellent |
| Caking Tendency | Low |
| Dust Generation | Low (granular) |
✔ Excellent mechanical stability
✔ Suitable for long-distance transport
Metallurgical & Thermal Behavior
Ammonium phosphates function chemically rather than mechanically:
✔ Form protective phosphate layers
✔ Release phosphoric acid upon heating
✔ Act as fire-retardant precursors
✔ Promote char formation on metals and polymers
✔ Used in metal surface passivation
APP is widely used in intumescent coatings, while MAP is used in metal surface treatments.
Available Forms
Granules (fertilizer grade)
Crystalline powder
Water-soluble powder
Liquid ammonium polyphosphate
Food-grade refined crystals
Technical / industrial grades
Fire-retardant formulations
Applications
Agriculture: Primary phosphorus fertilizer, starter fertilizer, drip irrigation, blended NPKs
Fire Retardants: Dry chemical extinguishers (MAP), intumescent coatings (APP)
Metallurgy: Phosphate coatings, corrosion inhibition, surface passivation
Chemical & Food: Buffer systems, pH control, regulated food additives
Water Treatment: Scale control, corrosion inhibition
Advantages
✔ High nutrient concentration
✔ Immediate phosphorus availability
✔ Non-explosive and safe to handle
✔ Excellent storage stability
✔ Multi-industry usability
✔ Cost-effective large-scale production
MAP vs DAP vs APP
| Property | MAP | DAP | APP |
|---|---|---|---|
| Nitrogen % | ~11% | ~18% | 10–17% |
| pH Reaction | Acidic | Alkaline | Neutral–Acidic |
| Solubility | High | High | Very High |
| Fertilizer Use | Starter | Bulk | Liquid |
| Fire Retardant | Medium | Low | Excellent |
Limitations & Considerations
Ammonia loss at high temperatures
Phosphate impurities from rock sources
Moisture control required during storage
Over-application may cause eutrophication