Tricalcium phosphate (TCP), chemical formula Ca₃(PO₄)₂, is a calcium salt of phosphoric acid, appearing as a white, odorless, tasteless powder. It is also known as tribasic calcium phosphate and bone phosphate of lime (BPL). It is a white solid of low solubility. Most commercial samples of “tricalcium phosphate” are in fact hydroxyapatite. It’s naturally found in cow milk and as a mineral in bone and teeth. TCP is widely used in food, pharmaceutical, and industrial applications due to its biocompatibility and versatility.
In food, TCP serves as an anticaking agent, stabilizer, or calcium supplement in products like powdered spices, beverages, and cereals, enhancing texture and shelf life (E341 in the EU). In pharmaceuticals, it’s a common excipient in tablets and a source of calcium and phosphorus in nutritional supplements. Its bone-like composition makes it valuable in medical applications, such as bone grafts and dental implants, promoting bone regeneration. It exists as three crystalline polymorphs α, α′, and β. The α and α′ states are stable at high temperatures.
Properties
TCP is insoluble in water but soluble in acidic environments, like the stomach, aiding nutrient absorption. It’s produced by reacting calcium carbonate or hydroxide with phosphoric acid. While generally safe, excessive intake may lead to hypercalcemia or kidney issues. Industrially, it’s used in ceramics and fertilizers. Its biocompatibility, low toxicity, and nutritional benefits make TCP a critical compound across multiple fields, with ongoing research into its biomedical applications.
- Chemical formula: Ca3(PO4)2
- Molar mass: 310.18 g/mol
- Appearance: White amorphous powder
- Density: 3.14 g/cm3
- Melting point: 1,670 °C (3,040 °F; 1,940 K)
- Solubility in water: 1.2 mg/kg
- Solubility product (Ksp): 2.07×10−33
Natural Occurrences
Tricalcium phosphate is a major constituent of phosphate rock, a naturally occurring mineral deposit primarily composed of apatite minerals (e.g., hydroxyapatite, fluorapatite). It is found in igneous, metamorphic, and sedimentary rocks, often in association with other phosphate minerals.
Preparation
Tricalcium phosphate is produced commercially by treating hydroxyapatite with phosphoric acid and slaked lime.
It cannot be precipitated directly from aqueous solution. Typically double decomposition reactions are employed, involving a soluble phosphate and calcium salts, e.g. (NH4)2HPO4 + Ca(NO3)2.[6] is performed under carefully controlled pH conditions. The precipitate will either be “amorphous tricalcium phosphate”, ATCP, or calcium deficient hydroxyapatite, CDHA, Ca9(HPO4)(PO4)5(OH), (note CDHA is sometimes termed apatitic calcium triphosphate).
An alternative to the wet procedure entails heating a mixture of a calcium pyrophosphate and calcium carbonate:
CaCO3 + Ca2P2O7 → Ca3(PO4)2 + CO2
Biological Occurrences
Tricalcium phosphate is a key component of bone and teeth in humans and animals. It is present in the form of hydroxyapatite [Ca₅(PO₄)₃(OH)], a closely related compound. It contributes to the mineral matrix of bone, providing strength and rigidity.
Synthetic Production
TCP is synthesized industrially by reacting calcium carbonate (CaCO₃) or calcium hydroxide (Ca(OH)₂) with phosphoric acid (H₃PO₄).
Example reaction:
3Ca(OH)₂ + 2H₃PO₄ → Ca₃(PO₄)₂ + 6H₂O
It is also produced as a byproduct in the processing of phosphate ores for fertilizers.
Applications
- Biomedical: Used in bone grafts, dental cements, and drug delivery systems due to its biocompatibility and bioresorbability.
- Food Industry: Acts as an anticaking agent, stabilizer, or calcium supplement (E341 in food labeling).
- Agriculture: Used in fertilizers as a source of phosphorus and calcium.
- Industrial: Component in ceramics, polishing agents, and as a raw material in phosphate production.
