- Structure
- Nomenclature
- Properties
- Physical state
- Molecular weight
- Melting point
- Boiling point
- Density
- Refractive index
- Solubility
- Chemical properties
- Presence in nature
- Applications
- - In obtaining fluorine compounds
- - In the care of teeth
- CaF nanoparticles
- - In lenses for optical equipment
- In cameras
- - In the metallurgical industry
- - In detectors of radioactivity or dangerous radiation
- - Other uses
- References
The calcium fluoride is an inorganic solid comprises a calcium atom (Ca) and two fluorine atoms (F). Its chemical formula is CaF 2 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.
Solid CaF 2 calcium fluoride. w: User: Walkerma in June 2005. Source: Wikimedia Commons.
In addition, CaF 2 is used to prevent tooth decay, which is why it is added to materials used by dentists to cure them. In fact, calcium fluoride is also added to drinking water (drinking water) so that the population benefits from drinking it and brushing their teeth.
CaF 2 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.
Structure
Calcium fluoride CaF 2 is an ionic compound formed by a calcium Ca 2+ cation and two fluoride F - anions. However, some sources of information indicate that their links have a certain covalent character.
Structure of calcium fluoride CaF 2. Blue: calcium; Yellow fluorine. Claudio Pistilli. Source: Wikimedia Commons.
Nomenclature
Calcium fluoride
Properties
Physical state
Colorless to greyish-white solid with cubic crystalline structure.
Cubic crystal structure of CaF 2. Benjah-bmm27. Source: Wikimedia Commons.
Molecular weight
78.07 g / mol
Melting point
1418 ºC
Boiling point
2533 ºC
Density
3.18 g / cm 3 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. It dissolves slowly in nitric acid HNO 3.
It is not flammable. It 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
Calcium fluoride CaF 2 is found naturally in the mineral fluorite or fluorspar.
Although pure CaF 2 is colorless, the mineral fluorite is often colored by the presence of electrons trapped in the "holes" in the crystal 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."
Fluorite from a mine in France. Muséum de Toulouse. Source: Wikimedia Commons.
Fluorite (blue crystals) from the Natural Museum of Milan. Giovanni Dall'Orto. Source: Wikimedia Commons.
Fluorite from a mine in England. Didier Descouens. Source: Wikimedia Commons.
Fluorite from a mine in France. Didier Descouens. Source: Wikimedia Commons.
Fluorite from a mine in the USA. Author: Jurema Oliveira. Source: Wikimedia Commons.
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 2 is the basic or majority source of fluorine worldwide. It is the raw material for preparing 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 - is released from the mineral by reacting it with concentrated sulfuric acid H 2 SO 4:
CaF 2 (solid) + H 2 SO 4 (liquid) → CaSO 4 (solid) + 2 HF (gas)
- In the care of teeth
CaF 2 calcium fluoride is an agent for the prevention of cavities. It is used to fluoridate drinking water (water that can be drunk) for this purpose.
In addition, the 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 caries preventive dental care.
Calcium fluoride helps in the prevention of cavities. Author: Annalize Batista. Source: Pixabay.
CaF nanoparticles
Although fluorides are used in toothpastes and rinses, the low concentration of calcium (Ca) in saliva means that CaF 2 deposits are not formed on the teeth as effectively as possible.
That is why a way to obtain CaF 2 powder as nanoparticles has been devised.
For this, a spray dryer (from English spray-dryer) is used where two solutions (one of calcium hydroxide Ca (OH) 2 and one of ammonium fluoride NH 4 F) are mixed while they are sprayed in a chamber with flow of hot air.
Then the following reaction occurs:
Ca (OH) 2 + NH 4 F → CaF 2 (solid) + NH 4 OH
NH 4 OH volatilizes as NH 3 and H 2 O and the CaF 2 nanoparticles remain.
They 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.
CaF 2 is transparent in such regions of the light spectrum, has a refractive index extremely low and enables a more efficient resolution than that of the NaCl in the range 1500-4000 cm - 1.
Thanks to its chemical stability, it can withstand adverse conditions, so the CaF 2 optical elements are not attacked. It also has a high hardness.
In cameras
Some photographic camera manufacturers use artificially crystallized CaF 2 lenses to reduce light scattering and achieve excellent correction of color distortion.
Some cameras have calcium fluoride CaF 2 lenses to reduce color distortion. Bill Ebbesen. Source: Wikimedia Commons.
- In the metallurgical industry
CaF 2 is used as a fluxing agent in the metallurgical industry, since 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
CaF 2 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.
That is why CaF 2 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 chemical reactions of dehydration and dehydrogenation 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).
Man welding. CaF 2 calcium fluoride electrodes form stronger welds. William M. Plate Jr.. Source: Wikimedia Commons.
References
- Pirmoradian, M. and Hooshmand, T. (2019). Remineralization and antibacterial capabilities of resin-based dental nanocomposites. Synthesis and characterization of calcium fluoride (CaF 2). In Applications of Nanocomposite Materials in Dentistry. Recovered from sciencedirect.com.
- US National Library of Medicine. (2019). Calcium fluoride. Recovered from pubchem.ncbi.nlm.nih.gov.
- Weman, K. (2012). Manual metal arc (MMA) welding with coated electrodes. In Welding Processes Handbook (Second Edition). Recovered from sciencedirect.com.
- Hanning, M. and Hanning, C. (2013). Nanobiomaterials in Preventive Dentistry. Nanosized calcium fluoride. In Nanobiomaterials in Clinical Dentistry. Recovered from sciencedirect.com.
- Ropp, RC (2013). Group 17 (H, F, Cl, Br, I) Alkaline Earth Compounds. Calcium Fluoride. In Encyclopedia of the Alkaline Earth Compounds. Recovered from sciencedirect.com.
- Cotton, F. Albert and Wilkinson, Geoffrey. (1980). Advanced Inorganic Chemistry. Fourth Edition. John Wiley & Sons.
- Valkovic, V. (2000). Measurements of Radioactivity. In Radioactivity in the Environment. Thermoluminescent detectors (TLDs). Recovered from sciencedirect.com.