Calcium fluoride (CaF2) structure, properties, uses

The calcium fluoride It is an inorganic solid formed by one calcium atom (Ca) and two fluorine atoms (F). Its chemical formula is CaF_two and it is a crystalline grayish-white solid.

In nature it is found in the mineral fluorite or fluorspar. It exists naturally in bones and teeth. The mineral fluorite is the main source used to obtain other fluorine compounds.

In addition, the CaF_two It is used for the prevention of cavities in teeth, so it is added to materials used by dentists to cure them. In fact, calcium fluoride is also added to drinking water (water that can be drunk) so that the population benefits from ingesting it and brushing their teeth..

The CaF_two It is used in the form of large crystals in optical equipment and cameras. It is also used in small devices that are used to detect how much a person has been exposed to radioactivity.

Article index

• 1 Structure
• 2 Nomenclature
• 3 Properties
  • 3.1 Physical state
  • 3.2 Molecular weight
  • 3.3 Melting point
  • 3.4 Boiling point
  • 3.5 Density
  • 3.6 Refractive index
  • 3.7 Solubility
  • 3.8 Chemical properties
• 4 Presence in nature
• 5 Uses
  • 5.1 - In obtaining fluorine compounds
  • 5.2 - In the care of teeth
  • 5.3 - In lenses for optical equipment
  • 5.4 - In the metallurgical industry
  • 5.5 - In detectors of radioactivity or dangerous radiation
  • 5.6 - Other uses
• 6 References

Structure

CaF calcium fluoride_two is an ionic compound formed by a calcium cation Ca^two+ and two fluoride anions F^-. However, some sources of information indicate that their links have a certain covalent character.

Nomenclature

Calcium fluoride

Properties

Physical state

Colorless to greyish-white solid with cubic crystal structure.

Molecular weight

78.07 g / mol

Melting point

1418 ºC

Boiling point

2533 ºC

Density

3.18 g / cm³ at 20 ° C.

Refractive index

1.4328

Solubility

It is insoluble in water at 20 ° C. Almost insoluble at 25 ° C: 0.002 g / 100 mL of water. Slightly soluble in acids.

Chemical properties

Its oxidizing or reducing properties are very weak, however, these reactions can occur. Although, in general, in very few cases.

It is inert to organic chemicals and many acids, including HF hydrofluoric acid. Dissolves slowly in nitric acid HNO₃.

It is not flammable. Does not react quickly with air or water.

Due to its low affinity for water, even if it is exposed to a high percentage of humidity, it does not affect it even for up to a month at normal room temperature..

In the presence of humidity the walls of its crystals dissolve slowly at temperatures above 600 ° C. In dry environments it can be used up to about 1000 ° C without being affected appreciably.

Presence in nature

CaF calcium fluoride_two found naturally in the mineral fluorite or fluorspar.

Although the CaF_two pure is colorless the mineral fluorite, it is often colored by the presence of electrons trapped in the "holes" of the crystalline structure.

This mineral is highly prized for its glassy luster and variety of colors (purple, blue, green, yellow, colorless, brown, pink, black, and reddish orange). It is said to be "the most colored mineral in the world".

Calcium fluoride is also found in the bones in amounts between 0.2 and 0.65%, and also in the enamel of the teeth in 0.33-0.59%.

Applications

- In obtaining fluorine compounds

The mineral fluorite CaF_two it is the basic or majority source of fluorine worldwide. It is the raw material to prepare almost all fluorine compounds.

The most important of these is hydrofluoric acid HF, from which the other fluorinated compounds are prepared. The fluoride ion F^- released from the mineral by reacting it with concentrated sulfuric acid H_twoSW₄:

CaF_two (solid) + H_twoSW₄ (liquid) → CaSO₄ (solid) + 2 HF (gas)

- In the care of teeth

CaF calcium fluoride_two it is an agent for the prevention of cavities. It is used to fluoridate drinking water (water that can be drunk) for this purpose.

Furthermore, low concentrations of fluoride F^- (on the order of 0.1 parts per million) used in toothpastes and mouthwashes have been shown to have a profound positive effect on cavities preventive dental care.

CaF nanoparticles_two more effective

Although fluorides are used in toothpastes and rinses, the low concentration of calcium (Ca) in saliva means that CaF deposits do not form._two on the teeth as effectively as possible.

That is why a way to obtain CaF powder has been devised._two as nanoparticles.

For this, a spray dryer is used (from the English spray-dryer) where two solutions (one of calcium hydroxide Ca (OH)_two and one of ammonium fluoride NH₄F) are mixed while being sprayed in a chamber with hot air flow.

Then the following reaction occurs:

Ca (OH)_two + NH₄F → CaF_two (solid) + NH₄Oh

NH₄OH volatilizes as NH₃ and H_twoOr and the CaF nanoparticles remain_two.

These have high reactivity and greater solubility, which makes them more effective for remineralizing teeth and as anticaries.

- In lenses for optical equipment

Calcium fluoride is used to build optical elements such as the prisms and windows of infrared and ultraviolet (UV) light spectrophotometers..

These devices allow us to measure the amount of light absorbed by a material when it passes through it..

The CaF_two It is transparent in these regions of the light spectrum, has an extremely low refractive index and allows a more efficient resolution than NaCl in the 1500-4000 cm range.^-1.

Thanks to its chemical stability, it can withstand adverse conditions, which is why CaF optical elements_two they are not attacked. It also has a high hardness.

In cameras

Some camera manufacturers use CaF lenses_two artificially crystallized to reduce light scattering and achieve excellent color distortion correction.

- In the metallurgical industry

The CaF_two It is used as a fluxing agent in the metallurgical industry, as it is a source of calcium insoluble in water and therefore effective in oxygen sensitive applications..

It is used to melt and process iron and steel in liquid form. This is based on the fact that it has a melting point similar to that of iron and also that it can dissolve oxides and metals..

- In detectors of radioactivity or dangerous radiation

The CaF_two it is a thermoluminescent material. This means that it can absorb radiation in the electrons of its crystalline structure and later, when heated, release it in the form of light..

This emitted light can be measured by an electrical signal. This signal is proportional to the amount of radiation the material received. It means that the greater the amount of radiation received, the greater the amount of light that it will emit after being heated..

For this reason the CaF_two It is used in so-called personal dosimeters, which are used by people who are exposed to dangerous radiation and want to know how much radiation they have received in a period of time.

- Other uses

- It is used as a catalyst in dehydration and dehydrogenation chemical reactions for the synthesis of organic compounds.

- It is used in alkaline welding electrodes. A stronger weld is obtained than with acid electrodes. These electrodes are useful in the manufacture of ships and high pressure steel vessels..

- As a dietary supplement in extremely low amounts (ppm or parts per million).

References

1. Pirmoradian, M. and Hooshmand, T. (2019). Remineralization and antibacterial capabilities of resin-based dental nanocomposites. Synthesis and characterization of calcium fluoride (CaF_two). In Applications of Nanocomposite Materials in Dentistry. Recovered from sciencedirect.com.
2. U.S. National Library of Medicine. (2019). Calcium fluoride. Recovered from pubchem.ncbi.nlm.nih.gov.
3. Weman, K. (2012). Manual metal arc (MMA) welding with coated electrodes. In Welding Processes Handbook (Second Edition). Recovered from sciencedirect.com.
4. Hanning, M. and Hanning, C. (2013). Nanobiomaterials in Preventive Dentistry. Nanosized calcium fluoride. In Nanobiomaterials in Clinical Dentistry. Recovered from sciencedirect.com.
5. Ropp, R.C. (2013). Group 17 (H, F, Cl, Br, I) Alkaline Earth Compounds. Calcium Fluoride. In Encyclopedia of the Alkaline Earth Compounds. Recovered from sciencedirect.com.
6. Cotton, F. Albert and Wilkinson, Geoffrey. (1980). Advanced Inorganic Chemistry. Fourth Edition. John Wiley & Sons.
7. Valkovic, V. (2000). Measurements of Radioactivity. In Radioactivity in the Environment. Thermoluminescent detectors (TLDs). Recovered from sciencedirect.com.