Calcium fluoride


Calcium fluoride is the inorganic compound of the elements calcium and fluorine with the formula CaF2. It is a white solid that is practically insoluble in water. It occurs as the mineral fluorite, which is often deeply coloured owing to impurities.

Chemical structure

The compound crystallizes in a cubic motif called the fluorite structure.
Ca2+ centres are eight-coordinate, being centred in a cube of eight F− centres. Each F− centre is coordinated to four Ca2+ centres in the shape of a tetrahedron. Although perfectly packed crystalline samples are colorless, the mineral is often deeply colored due to the presence of F-centers.
The same crystal structure is found in numerous ionic compounds with formula AB2, such as CeO2, cubic ZrO2, UO2, ThO2, and PuO2. In the corresponding anti-structure, called the antifluorite structure, anions and cations are swapped, such as Be2C.

Gas phase

The gas phase is noteworthy for failing the predictions of VSEPR theory; the molecule is not linear like, but bent with a bond angle of approximately 145°; the strontium and barium dihalides also have a bent geometry. It has been proposed that this is due to the fluoride ligands interacting with the electron core or the d-subshell of the calcium atom.

Preparation

Naturally occurring mineral fluoriteis the principal source of hydrogen fluoride, a commodity chemical used to produce a wide range of materials. Calcium fluoride in the fluorite state is of significant commercial importance as a fluoride source. Hydrogen fluoride is liberated from the mineral by the action of concentrated sulfuric acid:
High purity CaF2 is produced from the HF in the above reaction by treating calcium carbonate with hydrofluoric acid:

Waste Product

Separately, calcium fluoride can be generated as a waste product via ion exchange of PFAS rich water using a durable layered double hydroxide membrane of copper and aluminum heated to 500C.

Commercial Uses of Calcium Fluoride

Optical Applications

Lenses and Windows: Calcium fluoride is transparent over a broad range from ultraviolet to infrared frequencies. Its low refractive index reduces the need for anti-reflection coatings. Its insolubility in water is convenient as well. It also allows much smaller wavelengths to pass through. Calcium fluoride is used to manufacture optical components such as windows and lenses used in:
  • thermal imaging systems
  • spectroscopy
  • telescopes
  • excimer lasers.

    Metallurgical Applications

  • Flux in Metal Production: Acts as a flux in the production of aluminum and steel, helping to remove impurities and improve metal quality.
  • Cement and Concrete: Enhances properties in cement production, reducing melting points and improving energy efficiency.

    Chemical Industry

  • Source of Hydrogen Fluoride: Serves as a precursor for producing hydrogen fluoride, which is essential in various chemical processes:
  1. Feedstock for the creation of fluorochemical refrigerants
  • Pesticides and Fungicides: Used in formulations to stabilize products and protect crops.
  • Certain well-categorized molecular calcium fluorides can serve as reagents for nucleophilic fluoride addition to organic compounds. Well-characterized molecular calcium fluorides are clusters are formed by treating CaF2 with large, multidentate ligands.

    Glass and Ceramics

  • Specialty Glass Manufacturing: Contributes to the production of glasses with improved thermal and chemical resistance.
  • Ceramics: Enhances the mechanical properties of ceramic materials.

    Dental and Health Products

  • Fluoride Supplements: Incorporated into dental products to strengthen tooth enamel and prevent decay.

    Medical Applications

  • Doped calcium fluoride, like natural fluorite, exhibits thermoluminescence and is used in thermoluminescent dosimeters. It forms when fluorine combines with calcium.durability.

    Other Applications

  • Paints and Coatings: Functions as an opacifying agent in paints, improving brightness and durability.
  • Sealants and Adhesives: Used as an inert filler in sealants, enhancing performance.

    Safety

CaF2 is classified as "not dangerous", although reacting it with sulfuric acid produces hydrofluoric acid, which is highly corrosive and toxic. With regards to inhalation, the NIOSH-recommended concentration of fluorine-containing dusts is 2.5 mg/m3 in air.