The zinc phosphate is an inorganic compound whose chemical formula is Zn3(PO4)two, but it occurs in nature in its tetrahydrate form, Zn3(PO4)two4HtwoOr, in the hopeíta and parahopeíta minerals. Likewise, a basic variety of it is found in the mineral tarbutite, Zntwo(PO4) (OH). These minerals are formed by the oxidation of sphalerite in phosphate-rich waters.
All known uses for this compound are based on Zn3(PO4)two4HtwoOr, because its water molecules give it the property of being a good fixing agent. Therefore, its anhydrous form as such lacks uses of great economic demand..
As can be seen in the image above, zinc phosphate is a white solid, present as a powder or caked in small fragments. Its white color has been used in the formulation of cosmetic products, as well as in the preparation of dental cements and phosphate pozzolanic cements..
Zinc phosphate is an anticorrosive agent that has been used in processes for the electrodeposition of zinc minerals (hopeite and phosphophyllite) on the surface of steels..
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The Zn formula3(PO4)two indicates that Zn ionstwo+ and PO43- make up salt in a 3: 2 ratio, which means that for every three Zn cationstwo+ there are two PO anions43-. These ions interact with each other electrostatically, thus establishing a strong ionic bond due to the magnitude of their charges. Both ions are polyvalent.
Thus, the Zntwo+ and PO43- they end up orienting themselves in space until they define an orderly and repetitive structure: a crystal of zinc phosphate. This crystal adopts a monoclinic structure, α-Zn3(PO4)two. It appears to be capable of undergoing phase transitions to other polymorphic forms: β-Zn3(PO4)two and γ- Zn3(PO4)two, all dependent on temperature.
The three polymorphs are isostructural, differing only in the spatial orientation of their ions; that is, they have different spatial groups.
On the other hand, zinc phosphate tends to appear mainly as a hydrate: Zn3(PO4)two4HtwoOr, whose crystal structure is also monoclinic. This time the ions are accompanied by four water molecules, which interact with them through dipole-ion forces and hydrogen bonds..
Dusty white solid.
454.11 g / mol
900 ºC
No information. This could be due to possible thermal decomposition, or the unavailability of pressure conditions for the saline liquid to boil..
3.998 g / cm3
1,595.
Insoluble. This is due in part to the ionic bond between the Zn ionstwo+ and PO43-, which increases the crystalline lattice energy against dissolution of the salt in water.
Zinc phosphate is a non-flammable substance.
The uses of zinc phosphate correspond to those of its tetrahydrate, Zn3(PO4)two4HtwoOr, since it is its predominant form and it is even found in the hopeite and parahopeite minerals. Therefore, it is unknown whether its anhydrous form, Zn3(PO4)two, have a specific use.
Zinc phosphate has been used as a white pigment, replacing zinc and titanium oxides in cosmetic and beauty products. The material, soft to the touch, of small and round particles to cover the surface of the skin without seeping through its pores, is synthesized from a mixture of phosphoric acid, H3PO4, and zinc nitrate, Zn (NO3)two.
Thus, zinc phosphate white pigments are prepared by varying the Zn / P ratios. For this, when mixing the reagents, variable amounts of H are added.3PO4 and Zn (NO3)two, until obtaining the product with the best cosmetic properties.
In a study carried out by the Kyoto Prefectural University, they found that pigments prepared with a Zn / P ratio equal to 2/1, 1/1 and 3/2 showed the best reflectances; therefore, they illuminated the faces of those who applied the cosmetic more compared to the brightness of other formulations.
Zinc phosphate nanoparticles are in the arsenal destined to fight microbes and, thus, be an alternative to the use of antibiotics. In this way, the constant and progressive resistance that bacteria develop towards antibiotics is reduced, while it seeks to reduce expenses in the treatment of infectious diseases.
These nanoparticles have shown great antibacterial activity against coliform bacteria, a study that was verified in rats without causing oxidative stress.
Zinc phosphate is used to prepare phosphate cement, which is used in restorations of many materials; among them, our own teeth, behaving like a dental cement that has been quite popular in dentistry for a long time. This phosphate cement is used to fix and join several solids at the same time.
It is prepared by dissolving zinc and magnesium oxides in phosphoric acid, which is why Zn ions are presenttwo+ and Mgtwo+, forming complex structures. This dental cement is essential for the final cementation of the teeth. However, due to its acidity, polycarboxylate cement is used instead for patients who are too sensitive to it..
Similar to cement, the surface of steels can also be phosphated.
To do this, the steel pieces are introduced into an alkalinized phosphoric acid bath, and after supplying an electric current, a protective film composed of hopeite (Zn3(PO4)two4HtwoO) and phosphophyllite (ZntwoFaith (PO4)two4HtwoO), the latter compound being the most resistant against strongly alkaline media.
The chemical reactions involved are the following:
3Zntwo+ + 2HtwoPO4- + 4HtwoO → Zn3(PO4)two4HtwoO + 4H+
2Zntwo+ + Faithtwo+ + 2HtwoPO4- + 4HtwoO → ZntwoFaith (PO4)two4HtwoO + 4H+
The problem with these coatings lies in their degree of porosity, as it leaves exposed flanks where the steel can suffer corrosion..
On the other hand, pozzolanic cement containing zinc phosphate has been used for the development of more corrosion-resistant concretes..
In general, the anticorrosive property of zinc phosphate has been used to serve as coatings for the walls before applying the layers of paint, so that they are longer lasting and show better colors.
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