I. Definition and Chemical Properties
1, Chemical Formula and Structure
Dibasic calcium phosphate dihydrate （DCPD）(Cas No. 7789-77-7.)has the chemical formula CaHPO4·2H2O.
Calcium hydrogen phosphate dihydrate has two ionic molecular crystal structures:
a, Monoclinic crystal system
The most common crystal structure of calcium hydrogen phosphate dihydrate is monoclinic crystal system, whose chemical formula is CaHPO4-2H2O.The molecular structure of monoclinic crystal system is ionic, which is composed of calcium ions, phosphate ions and water molecules. Its cell parameters are a=6.995 Å, b=17.919 Å, c=6.870 Å, β=100.5°. This crystal structure is more common in medical use and is often used as a dental material and bone marrow transplant scaffold.
b, Triclinic crystal system
Another crystal structure of calcium hydrogen phosphate dihydrate is the triclinic crystal system, whose chemical formula is CaHPO4-2H2O.The molecular structure of the triclinic crystal system is also ionic, similar to the structure of the monoclinic crystal system, but its cellular parameters are a=6.576 Å, b=11.938 Å, c=13.911 Å, α=92.53°, β=97.33°, γ=110.07°. 110.07°. This crystal structure is less common and is often used as a fertilizer additive and feed additive.
We could find that dibasic calcium phosphate dihydrate is not the same as dibasic calcium phosphate anhydrous. The dibasic calcium phosphate dihydrate can be produced from anhydrous dibasic calcium phosphate. The specific process involves heating anhydrous dibasic calcium phosphate at a certain temperature so that it absorbs water, which converts it into dibasic calcium phosphate dihydrate
2, Physical Traits
Dibasic calcium phosphate dihydrate appears as a white monoclinal crystalline powder. It is odorless and tasteless, which makes it suitable for various applications where these properties are desired.
a, The solubility of Calcium Hydrogen Phosphate Dihydrate is as follows:
- Solubility: Calcium Hydrogen Phosphate Dihydrate is slightly soluble in water, insoluble in ethanol, but soluble in dilute hydrochloric acid and nitric acid.
- Dissolving speed: Calcium Hydrogen Phosphate Dihydrate dissolves slowly in water, which belongs to slow dissolution.
- Solubility: At 25°C, the solubility of Calcium Hydrogen Phosphate Dihydrate in water is 0.1 g/L.
This property makes Calcium Hydrogen Phosphate Dihydrate an excellent performer in a wide variety of applications.
b, Stability and Transformation
This compound is relatively stable in the air under normal conditions. However, when heated to around 75℃, it undergoes a significant transformation. It loses its crystallization water during this heating process and becomes anhydrous dibasic calcium phosphate (CaHPO4). This change in its hydration state can alter its physical and chemical properties to some extent. For instance, the loss of water molecules might affect its solubility characteristics or its reactivity in certain chemical reactions. Additionally, in other environmental conditions or in the presence of specific substances, its stability might also be influenced, but the change at 75℃ is one of the most notable aspects regarding its stability and transformation behavior.
II. Production and Sources
1, Industrial Production Methods
Dibasic calcium phosphate dihydrate can be produced through several common industrial methods. One typical approach is the reaction between calcium hydroxide（Ca(OH)₂） or calcium carbonate（CaCO₃） with phosphoric acid（H₃PO₄）. For instance, when calcium carbonate reacts with phosphoric acid in an appropriate reaction vessel under controlled temperature and agitation conditions, the chemical reaction proceeds as follows:
CaCO₃ + H₃PO₄ → CaHPO₄·2H₂O + CO₂↑.
Here, the calcium carbonate gradually dissolves in the phosphoric acid solution and reacts to form dibasic calcium phosphate dihydrate while carbon dioxide gas is liberated. The reaction temperature usually needs to be maintained within a certain range, typically around room temperature to moderately elevated temperatures like 40 – 60℃, to ensure a reasonable reaction rate and good product quality. Another method might involve using calcium oxide as the starting material. Calcium oxide is first slaked to form calcium hydroxide and then reacts with phosphoric acid in a similar manner to yield the target compound. After the reaction is completed, the resulting mixture undergoes processes such as filtration to separate the solid dibasic calcium phosphate dihydrate from the reaction solution. Subsequently, it is often washed with water to remove impurities and then dried to obtain the final product in a powder form suitable for various applications.
2, Natural Occurrence
In nature, dibasic calcium phosphate dihydrate can be found in certain geological formations. It is sometimes present in phosphate rock deposits, although it may not be the dominant component. It can occur in association with other calcium phosphate minerals and substances. For example, in some sedimentary rocks that have accumulated phosphorus-containing materials over long periods of time, dibasic calcium phosphate dihydrate might be formed through natural chemical reactions involving calcium, phosphorus, and water. In addition, it can also be found in some biological systems to a limited extent. In the remains of organisms, such as bones and teeth that are in the process of decomposition or fossilization in specific environmental conditions, small amounts of dibasic calcium phosphate dihydrate might be present as part of the complex mixture of minerals. However, compared to other more common minerals in nature, its occurrence is relatively less widespread and is usually in specific locales where the right combination of chemical elements and environmental factors exist.
III. Applications in Different Fields
1, Pharmaceutical Field
Scope of Dibasic calcium phosphate dihydrate is widely used in various types of preparations such as tablets, capsules, granules, injections and so on. Its application is particularly common in drugs such as anti-infectives, anti-gout drugs, vitamins and calcium supplements. In these preparations, the application of calcium phosphate dihydrate makes the drug easier to be absorbed and utilized by the body, thus enhancing its efficacy.
a. pH regulation of drugs
Dibasic calcium phosphate dihydrate, as an acidic salt, can be used in pharmaceutical formulations to regulate the pH value. In some drugs which need to maintain stability and activity, the pH value of the drug can be adjusted by adding appropriate amount of calcium phosphate dihydrate, which can improve the stability and solubility of the drug, and thus enhance the efficacy of the drug.
b. Improve the solubility of the drug
Calcium phosphate dihydrate has good solubility in water, so it can help the drug dissolve better in the drug preparation. This is especially important for some drugs with low solubility, which can improve the bioavailability of the drug in the body and increase the efficacy of the drug.
c. Stabilize drug formulation
In the drug production process, calcium phosphate dihydrate can also play a role in stabilizing the formulation. It can help drugs in the preparation, storage and use of the process to maintain a certain degree of stability, to extend the effective period of the drug, and reduce the degradation of drugs and the production of undesirable substances.
2, Food Industry
Dibasic calcium phosphate dihydrate has a variety of roles in food, mainly as a calcium fortifier, emulsion stabilizer, dough conditioner, nutritional supplement and antioxidant synergist.
- Calcium fortification: Dibasic calcium phosphate dihydrate can increase the calcium content in food to meet the human body’s demand for calcium.
- Emulsion stabilizer: It can help stabilize the emulsion system in food products, prevent the separation of fats and oils, and maintain the uniformity and stability of food products.
- Dough conditioner: In the process of making pasta products such as bread and noodles, dibasic calcium phosphate dihydrate can improve the texture and elasticity of the dough and enhance the quality of the products.
- Nutritional supplement: Due to its calcium content, it can be used as a nutritional supplement to increase the nutritional value of food.
- Antioxidant booster: In the process of food preservation, dibasic calcium phosphate dihydrate can delay the oxidation reaction and extend the shelf life of food. Commonly used in jam, chocolate, bread, cookies and other foods.
3, In Agriculture
Calcium hydrogen phosphate dihydrate is used as a soil conditioner and fertilizer to raise soil pH and improve acidic soils. It also provides the phosphorus needed for crop growth, but overuse can lead to problems such as soil crusting.
4, Animal feed
It is added as an important additive. For example, in livestock and poultry feed, it provides essential calcium and phosphorus nutrients that are crucial for animal growth, bone development, and overall health. The presence of these elements in an appropriate form helps animals grow faster and maintain good physiological conditions.
In addition, it also has the effect of improving the taste of feed and promoting the appetite of animals.
5, Chemical industry
Calcium Hydrogen Phosphate Dihydrate is an important chemical reagent that can be used in a variety of chemical reactions. Such as the preparation of other phosphates, treatment of heavy metal ions and so on.
6, Water treatment industry
Dibasic calcium phosphate dihydrate can be used as a softener and scale inhibitor, by combining with calcium ions in hard water, it can soften the water quality. At the same time, it can inhibit scale formation and improve the efficiency of thermal equipment and cooling systems.
7, Other uses
In industrial products like ceramic production, it can be incorporated into the ceramic materials. It may influence the properties of the ceramic during the firing process, such as improving its hardness or altering its structural integrity. Calcium hydrogen phosphate dihydrate is also used in petroleum, as an additive to drilling fluids and so on. Additionally, in some specialized applications where controlled release of calcium or phosphorus is needed, or where certain physical and chemical properties related to these elements are desired, dibasic calcium phosphate dihydrate can also play a valuable role.
IV. Quality Standards and Precautions
1, Quality Assessment Standards
In different application scenarios, dibasic calcium phosphate dihydrate needs to meet specific quality parameters and standards. In the pharmaceutical field, a high level of purity is crucial. Generally, it should have a purity of over 97% or even higher depending on the specific requirements of the drug formulation. Impurities such as heavy metals like lead, mercury, and arsenic need to be strictly controlled and kept within extremely low limits, usually in the parts per million (ppm) range, to ensure the safety and efficacy of the final pharmaceutical products.
For its use in the food industry as an anti-caking agent or moisture retainer, it must comply with food-grade quality standards. For example, it should meet the requirements set by regulatory authorities regarding its chemical composition and absence of harmful contaminants. The content of dibasic calcium phosphate dihydrate in the final food product also has to be within the permitted dosage range specified for different food categories to avoid any potential adverse effects on human health.
In industrial applications like ceramic production or animal feed, the quality requirements focus on aspects such as particle size distribution. In ceramic production, a consistent and appropriate particle size helps in achieving better mixing with other ceramic materials and influences the quality of the final ceramic product. In animal feed, the bioavailability of the calcium and phosphorus it provides is an important quality factor, which is related to its chemical form and purity to ensure proper absorption by animals for their growth and health.
2, Storage and Handling Precautions
Proper storage conditions are essential to maintain the quality of dibasic calcium phosphate dihydrate. It should be stored in a cool and dry place. The ideal temperature range is usually between 15℃ and 25℃. High temperatures can accelerate chemical reactions or cause changes in its physical properties, such as the potential loss of crystallization water if stored above its dehydration temperature around 75℃.
Humidity also needs to be carefully controlled as excessive moisture can lead to caking or agglomeration of the powder, especially in its use as a free-flowing additive in products like food powders. It is recommended to store it in sealed containers to prevent moisture absorption from the air.
During handling, appropriate protective measures should be taken. Workers should wear gloves and masks to avoid direct contact with the powder and inhalation of dust particles. When transferring or measuring the compound, use clean and dry tools to prevent contamination. In case of accidental spillage, it should be carefully cleaned up using proper cleaning agents and following safety procedures to avoid slipping hazards due to the powdery nature of the substance and also to prevent any potential environmental pollution if it enters waterways or soil.
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