Tricalcium phosphate, or, going by its IUPAC name, tricalcium diphosphate, is a calcium salt of phosphoric acid. Its molecular formula is Ca3O8P2.
Did You Know?Tricalcium phosphate is found in two crystal forms. One of them, however, is only formed in high-temperature conditions.
It is found in the form of whitlockite fragments in rocks in countries such as Egypt, Israel, and Morocco. This naturally occurring form is not pure, and can contain up to 40% phosphorus pentoxide by weight.
It is a naturally occurring chemical, found in the bones and teeth of all vertebrates. As a result, it is a primary product of the combustion of bones. It is also found in the milk of various mammals, particularly cows. It performs the function of holding together quasi-micelles of proteins in milk.
Tricalcium diphosphate molecules consist, as the name makes obvious, of two ions of phosphates (PO43-) linked to three Ca2+ ions. Each phosphate ion contains four oxygen atoms, one of which is joined to the phosphorus atom by a double bond. The other three oxygen atoms are linked by single bonds, which leaves them with a valency of 1 (since oxygen needs 2 electrons to attain a stable configuration). The six oxygen atoms in the two phosphate ions constitute a net negative charge of 6. This is neutralized by three Ca2+ ions, each with a positive charge of 2. Here's a representation of the structure of tricalcium diphosphate.
For those of you who may have difficulty grasping this structure, here's a simpler illustration. The following is not an accurate representation, and is only meant to represent the distribution of the bonds in a rudimentary way.
Tricalcium phosphate is a white amorphous powder, with a density of 3.14 g/cm3.
It is largely unaffected by heat, and doesn't melt until 2535°F (1391°C). Even at such high temperature, it needs heavy pressures to melt.
It is not readily soluble in water, due to its complicated structure and division of polarity. It has a solubility of 0.002 g/100 g (for comparison, table salt has a solubility of 36 g/100 g).
Tricalcium phosphate is found naturally in the most commonly consumed type of milk in the world: Cow milk. As mentioned before, it helps bind 'casein micelles'. Though at least two competing hypotheses have been proposed negating or minimizing the role of calcium phosphates in the structure of milk, this is still the conventionally held theory.
It also occurs naturally in bone ash. As a consequence, vegans and others following strict no-animal diets have to be particularly careful, since tricalcium phosphate obtained from bone ash may be present in foods they do otherwise eat.
► It is also sometimes used as a nutritional supplement and an antacid, both due to its calcium content. Calcium carbonate is, by far, the more common calcium compound used for these purposes, but the phosphate is also used. The benefit of tricalcium phosphate (as well as calcium carbonate) is that it increases dietary calcium, though it is doubtful how much effect this has on its absorption into the body, and negates the acidic components in the stomach thanks to the alkaline nature of calcium.
► It is used in the production of phosphate fertilizers.
► It is also used in dental powders and porcelain.
► It is used in medication that improves bones health.
Its normal dietary consumption―naturally occurring or as a nutritional supplement recommended by a doctor―doesn't have any side effects. If large amounts come in contact with the skin, rashes may form. However, it is difficult for the overwhelming majority among the population to encounter harmful amounts of pure tricalcium phosphate, and is thus no matter of concern.