Diammonium phosphate

Detailed Explanation of Diammonium Phosphate (DAP)

Chemical Formula: (NH₄)₂HPO₄  

Alias: Diammonium Phosphate

1. Basic Properties

(1) Physical Properties

- Appearance: White crystals or granules (commonly grayish-brown granules for agricultural use).  

- Solubility: Highly soluble in water (57.5 g/100 mL, 20°C), aqueous solution is weakly alkaline (pH≈8).  

- Density: 1.62 g/cm³.  

- Melting Point: 155°C (decomposes).  

(2) Chemical Properties 

- Thermal Decomposition: Decomposes when heated above 155°C, forming ammonium dihydrogen phosphate (NH₄H₂PO₄) and ammonia gas (NH₃):  

 2. Main Applications

(1) Agricultural Fertilizer (Core Use)

- High nitrogen-phosphorus compound fertilizer (N: 18%, P₂O₅: 46%), suitable for neutral or slightly alkaline soils.  

- Advantages:  

  - Balanced nitrogen-phosphorus ratio (1:1), ideal for mid-growth stage topdressing.  

  - Fast dissolution, suitable for drip irrigation and foliar spraying.  

(2) Industrial Applications

- Flame Retardant: Used in wood, paper, and textiles, decomposes to form a phosphoric acid glass layer that isolates oxygen.  

- Food Additive: Acts as a leavening agent and yeast nutrient (requires food-grade quality).  

- Water Treatment: Serves as a corrosion inhibitor to control boiler water pH.  

(3) Scientific Research and Chemical Industry 

- Preparation of buffer solutions (pH 7.5~8.5).  

- Laboratory ammonia source for synthesizing other ammonium salts.  

3. Safety and Storage  

- Health Hazards: Dust irritates eyes and respiratory tract; protective equipment is required during handling.  

- Environmental Risks: Overuse may lead to soil compaction or water eutrophication.  

- Storage Conditions:  

  - Seal to prevent moisture (hygroscopic and prone to caking).  

  - Keep away from strong acids

4. Precautions

- Agricultural Use: Avoid mixing with alkaline fertilizers (e.g., plant ash) to prevent ammonia volatilization loss.  

- Industrial Grade vs. Food Grade: Food additives must comply with GB 25560-2010 standards.