Fluorapatite
Encyclopedia
Fluorapatite, often with the alternate spelling of fluoroapatite, is a mineral
with the formula Ca5(PO4)3F (calcium fluorophosphate). Fluorapatite is a hard crystalline solid. Although samples can have various color (green, brown, blue, violet, or colorless), the pure mineral is colorless as expected for a material lacking transition metals. It is an important constituent of tooth enamel
.
Fluorapatite crystallizes in a hexagonal crystal system. It is often combined as a solid solution
with hydroxylapatite
(Ca5(PO4)3OH) in biological matrices. Chlorapatite (Ca5(PO4)3Cl) is another related structure. Industrially, the mineral is an important source of both phosphoric
and hydrofluoric acid
s.
Fluorapatite as a mineral is the most common phosphate mineral. It occurs widely as an accessory mineral in igneous rocks and in calcium rich metamorphic rocks. It commonly occurs as a detrital or diagenic
mineral in sedimentary rocks and is an essential component of phosphorite
ore deposits. It occurs as a residual mineral in lateritic soils
.
Fluorapatite can be synthesized in a two step process. First, calcium phosphate
is generated by combining calcium and phosphate salt
s at neutral pH
.This material then reacts further with fluoride sources (often sodium monofluorophosphate
or calcium fluoride
(CaF2)) to give the mineral. This reaction is integral in the global phosphorus cycle
.
generates hyrodrogen fluoride as a byproduct during the production of phosphoric acid
, as apatite is digested by sulfuric acid
. The hydrogen fluoride
byproduct is now one of the industrial sources of hydrofluoric acid
, which in turn is used as a starting reagent for synthesis of a range of important industrial and pharmaceutical fluorine
compounds.
Synthetic fluorapatite doped with manganese
-II and antimony
-V formed the basis for the second generation of fluorescent tube phosphor
s referred to as halophosphors. When irradiated with 253.7 nm mercury
resonance radiation they fluoresced
with broad emission which appeared within the range of acceptable whites. The antimony-V acted as the primary activator and produced a broad blue emission. Addition of manganese-II produced a second broad peak to appear at the red end of the emission spectrum at the expense of the antimony peak, excitation energy being transferred from the antimony to the manganese by a non radiative process and making the emitted light appear less blue and more pink. Replacement of some of the fluoride ions with chloride ions in the lattice caused a general shift of the emission bands to the longer wavelength red end of the spectrum. These alterations allowed phosphors for Warm White, White and Daylight tubes, (with corrected color temperatures of 2900, 4100 and 6500 K respectively), to be made. The amounts of the manganese and antimony activators vary between 0.05 and 0.5 mole percent.
The reaction used to create halophosphor is shown below. The antimony and manganese must be incorporated in the correct trace amounts if the product is to be fluorescent.
Sometimes some of the calcium was substituted with strontium
giving narrower emission peaks. For special purpose or colored tubes the halophosphor was mixed with small quantities of other phosphors, particularly in De-Luxe tubes with higher color rendering index for use in food market or art studio lighting.
Prior to the development of halophosphor in 1942, the first generation willemite
latticed, manganese-II activated zinc orthosilicate and zinc beryllium orthosilicate phosphors were used in fluorescent tubes. Due to the respiratory toxicity of beryllium compounds the obselescence of these early phosphor types were advantageous to health.
Since about 1990 the third generation TriPhosphors, three separate red, blue and green phosphors activated with rare earth ions and mixed in proportions to produce acceptable whites, have largely replaced halophosphors.
Fluorapatite can be used as a precursor for the production of phosphorus
. It can be reduced by carbon
in the presence of quartz
:
Upon cooling, white phosphorus (P4) is generated:
Mineral
A mineral is a naturally occurring solid chemical substance formed through biogeochemical processes, having characteristic chemical composition, highly ordered atomic structure, and specific physical properties. By comparison, a rock is an aggregate of minerals and/or mineraloids and does not...
with the formula Ca5(PO4)3F (calcium fluorophosphate). Fluorapatite is a hard crystalline solid. Although samples can have various color (green, brown, blue, violet, or colorless), the pure mineral is colorless as expected for a material lacking transition metals. It is an important constituent of tooth enamel
Tooth enamel
Tooth enamel, along with dentin, cementum, and dental pulp is one of the four major tissues that make up the tooth in vertebrates. It is the hardest and most highly mineralized substance in the human body. Tooth enamel is also found in the dermal denticles of sharks...
.
Fluorapatite crystallizes in a hexagonal crystal system. It is often combined as a solid solution
Solid solution
A solid solution is a solid-state solution of one or more solutes in a solvent. Such a mixture is considered a solution rather than a compound when the crystal structure of the solvent remains unchanged by addition of the solutes, and when the mixture remains in a single homogeneous phase...
with hydroxylapatite
Hydroxylapatite
Hydroxylapatite, also called hydroxyapatite , is a naturally occurring mineral form of calcium apatite with the formula Ca53, but is usually written Ca1062 to denote that the crystal unit cell comprises two entities. Hydroxylapatite is the hydroxyl endmember of the complex apatite group...
(Ca5(PO4)3OH) in biological matrices. Chlorapatite (Ca5(PO4)3Cl) is another related structure. Industrially, the mineral is an important source of both phosphoric
Phosphoric acid
Phosphoric acid, also known as orthophosphoric acid or phosphoric acid, is a mineral acid having the chemical formula H3PO4. Orthophosphoric acid molecules can combine with themselves to form a variety of compounds which are also referred to as phosphoric acids, but in a more general way...
and hydrofluoric acid
Hydrofluoric acid
Hydrofluoric acid is a solution of hydrogen fluoride in water. It is a valued source of fluorine and is the precursor to numerous pharmaceuticals such as fluoxetine and diverse materials such as PTFE ....
s.
Fluorapatite as a mineral is the most common phosphate mineral. It occurs widely as an accessory mineral in igneous rocks and in calcium rich metamorphic rocks. It commonly occurs as a detrital or diagenic
Diagenesis
In geology and oceanography, diagenesis is any chemical, physical, or biological change undergone by a sediment after its initial deposition and during and after its lithification, exclusive of surface alteration and metamorphism. These changes happen at relatively low temperatures and pressures...
mineral in sedimentary rocks and is an essential component of phosphorite
Phosphorite
Phosphorite, phosphate rock or rock phosphate is a non-detrital sedimentary rock which contains high amounts of phosphate bearing minerals. The phosphate content of phosphorite is at least 15 to 20% which is a large enrichment over the typical sedimentary rock content of less than 0.2%...
ore deposits. It occurs as a residual mineral in lateritic soils
Laterite
Laterites are soil types rich in iron and aluminium, formed in hot and wet tropical areas. Nearly all laterites are rusty-red because of iron oxides. They develop by intensive and long-lasting weathering of the underlying parent rock...
.
Synthesis
Calcium phosphate
Calcium phosphate is the name given to a family of minerals containing calcium ions together with orthophosphates , metaphosphates or pyrophosphates and occasionally hydrogen or hydroxide ions ....
is generated by combining calcium and phosphate salt
Salt
In chemistry, salts are ionic compounds that result from the neutralization reaction of an acid and a base. They are composed of cations and anions so that the product is electrically neutral...
s at neutral pH
PH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
.This material then reacts further with fluoride sources (often sodium monofluorophosphate
Sodium monofluorophosphate
Sodium monofluorophosphate, commonly abbreviated MFP, is the inorganic compound with the formula Na2PO3F. Typical for a salt, MFP is odourless, colourless, and water-soluble. This salt is an ingredient in some toothpastes.-Uses of MFP:...
or calcium fluoride
Calcium fluoride
Calcium fluoride is the inorganic compound with the formula CaF2. This ionic compound of calcium and fluorine occurs naturally as the mineral fluorite . It is the source of most of the world's fluorine. This insoluble solid adopts a cubic structure wherein calcium is coordinated to eight fluoride...
(CaF2)) to give the mineral. This reaction is integral in the global phosphorus cycle
Phosphorus cycle
The phosphorus cycle is the biogeochemical cycle that describes the movement of phosphorus through the lithosphere, hydrosphere, and biosphere. Unlike many other biogeochemical cycles, the atmosphere does not play a significant role in the movement of phosphorus, because phosphorus and...
.
- 3 + 2 →
- 3 + → 2
Applications
Fluorapatite as a naturally occurring impurity in apatiteApatite
Apatite is a group of phosphate minerals, usually referring to hydroxylapatite, fluorapatite, chlorapatite and bromapatite, named for high concentrations of OH−, F−, Cl− or Br− ions, respectively, in the crystal...
generates hyrodrogen fluoride as a byproduct during the production of phosphoric acid
Phosphoric acid
Phosphoric acid, also known as orthophosphoric acid or phosphoric acid, is a mineral acid having the chemical formula H3PO4. Orthophosphoric acid molecules can combine with themselves to form a variety of compounds which are also referred to as phosphoric acids, but in a more general way...
, as apatite is digested by sulfuric acid
Sulfuric acid
Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...
. The hydrogen fluoride
Hydrogen fluoride
Hydrogen fluoride is a chemical compound with the formula HF. This colorless gas is the principal industrial source of fluorine, often in the aqueous form as hydrofluoric acid, and thus is the precursor to many important compounds including pharmaceuticals and polymers . HF is widely used in the...
byproduct is now one of the industrial sources of hydrofluoric acid
Hydrofluoric acid
Hydrofluoric acid is a solution of hydrogen fluoride in water. It is a valued source of fluorine and is the precursor to numerous pharmaceuticals such as fluoxetine and diverse materials such as PTFE ....
, which in turn is used as a starting reagent for synthesis of a range of important industrial and pharmaceutical fluorine
Fluorine
Fluorine is the chemical element with atomic number 9, represented by the symbol F. It is the lightest element of the halogen column of the periodic table and has a single stable isotope, fluorine-19. At standard pressure and temperature, fluorine is a pale yellow gas composed of diatomic...
compounds.
Synthetic fluorapatite doped with manganese
Manganese
Manganese is a chemical element, designated by the symbol Mn. It has the atomic number 25. It is found as a free element in nature , and in many minerals...
-II and antimony
Antimony
Antimony is a toxic chemical element with the symbol Sb and an atomic number of 51. A lustrous grey metalloid, it is found in nature mainly as the sulfide mineral stibnite...
-V formed the basis for the second generation of fluorescent tube phosphor
Phosphor
A phosphor, most generally, is a substance that exhibits the phenomenon of luminescence. Somewhat confusingly, this includes both phosphorescent materials, which show a slow decay in brightness , and fluorescent materials, where the emission decay takes place over tens of nanoseconds...
s referred to as halophosphors. When irradiated with 253.7 nm mercury
Mercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...
resonance radiation they fluoresced
Fluorescence
Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation of a different wavelength. It is a form of luminescence. In most cases, emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation...
with broad emission which appeared within the range of acceptable whites. The antimony-V acted as the primary activator and produced a broad blue emission. Addition of manganese-II produced a second broad peak to appear at the red end of the emission spectrum at the expense of the antimony peak, excitation energy being transferred from the antimony to the manganese by a non radiative process and making the emitted light appear less blue and more pink. Replacement of some of the fluoride ions with chloride ions in the lattice caused a general shift of the emission bands to the longer wavelength red end of the spectrum. These alterations allowed phosphors for Warm White, White and Daylight tubes, (with corrected color temperatures of 2900, 4100 and 6500 K respectively), to be made. The amounts of the manganese and antimony activators vary between 0.05 and 0.5 mole percent.
The reaction used to create halophosphor is shown below. The antimony and manganese must be incorporated in the correct trace amounts if the product is to be fluorescent.
- 6 + (3+x) + (1-x) + (2x) → 2 + (3+x) + (3+x)+ (2x)
Sometimes some of the calcium was substituted with strontium
Strontium
Strontium is a chemical element with the symbol Sr and the atomic number 38. An alkaline earth metal, strontium is a soft silver-white or yellowish metallic element that is highly reactive chemically. The metal turns yellow when exposed to air. It occurs naturally in the minerals celestine and...
giving narrower emission peaks. For special purpose or colored tubes the halophosphor was mixed with small quantities of other phosphors, particularly in De-Luxe tubes with higher color rendering index for use in food market or art studio lighting.
Prior to the development of halophosphor in 1942, the first generation willemite
Willemite
Willemite is a zinc silicate mineral and a minor ore of zinc. It is highly fluorescent under shortwave ultraviolet light.It occurs in all different colors in daylight, in fibrous masses, solid brown masses , and apple green gemmy masses.It was discovered in 1830 and named after William I of the...
latticed, manganese-II activated zinc orthosilicate and zinc beryllium orthosilicate phosphors were used in fluorescent tubes. Due to the respiratory toxicity of beryllium compounds the obselescence of these early phosphor types were advantageous to health.
Since about 1990 the third generation TriPhosphors, three separate red, blue and green phosphors activated with rare earth ions and mixed in proportions to produce acceptable whites, have largely replaced halophosphors.
Fluorapatite can be used as a precursor for the production of phosphorus
Phosphorus
Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...
. It can be reduced by carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
in the presence of quartz
Quartz
Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...
:
- 4 + 21 + 30 C → 20 + 30 CO + + 6
Upon cooling, white phosphorus (P4) is generated:
- 2 →