Calcium fluoride is the inorganic compound of the elements calcium and fluorine with the formula CaF<sub>2</sub>. It is a white solid that is practically insoluble in water. It occurs as the mineral fluorite (also called fluorspar), which is often deeply coloured owing to impurities.
The compound crystallizes in a cubic motif called the fluorite structure.
Ca<sup>2+</sup> centres are eight-coordinate, being centred in a cube of eight F<sup>âÂÂ</sup> centres. Each F<sup>âÂÂ</sup> centre is coordinated to four Ca<sup>2+</sup> 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 AB<sub>2</sub>, such as CeO<sub>2</sub>, cubic ZrO<sub>2</sub>, UO<sub>2</sub>, ThO<sub>2</sub>, and PuO<sub>2</sub>. In the corresponding anti-structure, called the antifluorite structure, anions and cations are swapped, such as Be<sub>2</sub>C.
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 145ð; 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.
Naturally occurring mineral fluorite(CaF<sub>2</sub>)is 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 CaF<sub>2</sub> is produced from the HF in the above reaction by treating calcium carbonate with hydrofluoric acid:
Separately, calcium fluoride can be generated as a waste product via ion exchange of PFAS rich water using a durable layered double hydroxide(LDH) membrane of copper and aluminum heated to 500C.
Lenses and Windows: Calcium fluoride is transparent over a broad range from ultraviolet (UV) to infrared (IR) 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:
CaF<sub>2</sub> 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/m<sup>3</sup> in air.