The magnesium fluoride it is a colorless inorganic salt whose chemical formula is MgF₂. It is found in nature as the mineral sellaite. It has a very high melting point and is very poorly soluble in water. It is relatively inert, since, for example, its reaction with sulfuric acid is slow and incomplete and it resists hydrolysis with hydrofluoric acid (HF) up to 750ºC..
It is a compound little affected by high energy radiation. In addition, it has a low refractive index, high corrosion resistance, good thermal stability, significant hardness, and excellent visible, UV (ultraviolet) and IR (infrared) light transmission properties..
These properties make it have excellent performance in the optical field and, in addition, make it a useful material as a catalyst support, coatings element, anti-reflective lenses and windows for infrared transmission, among other applications..
Article index
The crystalline structure of chemically prepared magnesium fluoride is of the same type as that of the natural mineral sellaite. Crystallizes in the dipyramidal class of the tetragonal system.
Magnesium ions (Mg2 +) are located in a centered tetragonal lattice-space, while fluoride ions (F-) are found in the same plane as and associated with their Mg2 + neighbors, grouped in pairs with each other. The distance between the Mg2 + and F- ions is 2.07 Å (angstroms) (2.07 × 10-10m).
Its crystal coordination is 6: 3. This means that each Mg2 + ion is surrounded by 6 F- ions and each F- ion, in turn, is surrounded by 3 Mg2 + 5 ions..
The structure is very similar to that of the mineral rutile, which is the natural form of titanium dioxide (TiO2), with which it has several crystallographic properties in common..
During its production, magnesium fluoride does not precipitate as an amorphous solid, because the Mg2 + and F- ions do not tend to form polymeric complexes in solution..
Interestingly, magnesium fluoride is a birefringent material. This is an optical property that allows an incident light ray to be split into two separate rays that propagate at different speeds and wavelengths..
Table 1 shows some of its properties.
Table 1. Physical and chemical properties of magnesium fluoride.
It can be prepared in various ways, including the following:
1-Through the reaction between magnesium oxide (MgO) or magnesium carbonate (MgCO3) with hydrofluoric acid (HF) 2:
MgO + 2 HF MgF2 + H2O
MgCO3 + 2 HF MgF2 + CO2 + H2O
2-By reaction between magnesium carbonate and ammonium bifluoride (NH4HF2), both in solid state, at a temperature between 150 and 400ºC2:
150-400ºC
MgCO3 + NH4HF2 MgF2 + NH3 + CO2 + H2O
3-Heating an aqueous solution of magnesium carbonate and ammonium fluoride (NH4F) in the presence of ammonium hydroxide (NH4OH) at 60ºC 2:
60 ° C, NH4OH
MgCO3 + 3 NH4F NH4MgF3 + (NH4) 2CO3
The resulting precipitate of magnesium ammonium fluoride (NH4MgF3) is then heated at 620 ° C for 4 hours to obtain magnesium fluoride:
620ºC
NH4MgF3 MgF2 + NH3 + HF
4-As a by-product of obtaining beryllium (Be) and uranium (U). The fluoride of the desired element is heated with metallic magnesium in a crucible coated with MgF2 2:
BeF2 + Mg Be + MgF2
5-Reacting magnesium chloride (MgCl2) with ammonium fluoride (NH4F) in aqueous solution at room temperature 3:
25 ° C, H2O
MgCl2 + 2 NH4F MgF2 + 2NH4Cl
Since the methods of preparing MgF2 are expensive, there are attempts to obtain it more economically, among which the method of producing it starting from seawater stands out..
This is characterized by adding a sufficient amount of fluoride ions (F-) to seawater, which has an abundant concentration of magnesium ions (Mg2 +), thus favoring the precipitation of MgF2..
Magnesium fluoride optical crystals are obtained by hot pressing of high quality MgF2 powder, obtained, for example, by the NH4HF2 method.
There are many techniques for preparing magnesium fluoride materials, such as single crystal growth, sintering (compaction to mold or shaping) without pressure, hot pressing, and microwave sintering..
MgF2 crystals are suitable for optical applications because they are transparent from the UV region to the middle IR region 2.10.
As an inert film it is used to alter the light transmission properties of optical and electronic materials. One of the main applications is in VUV optics for space exploration technology.
Due to its birefringence property, this material is useful in polarization optics, in windows and prisms of the Excimer Laser (a type of ultraviolet laser used in eye surgery)..
It should be noted that the magnesium fluoride used in the manufacture of thin film optical materials must be free of impurities or compounds that are a source of oxide, such as water (H2O), hydroxide ions (OH-), carbonate ions (CO3 = ), sulfate ions (SO4 =), and the like 12.
MgF2 has been successfully used as a catalyst support for the reaction of elimination of chlorine and addition of hydrogen in CFCs (chlorofluorocarbons), known refrigerants and aerosol propellants, and responsible for the damage to the ozone layer of the atmosphere.
The resulting compounds, HFC (hydrofluorocarbons) and HCFC (hydrochlorofluorocarbons), do not have this harmful effect on the atmosphere 5.
It has also been useful as a catalyst support for the hydrodesulfurization (removal of sulfur) of organic compounds..
The materials generated by the intercalation of graphite, fluorine and MgF2 present high electrical conductivity, which is why they have been proposed for use in cathodes and as electroconductive materials..
The eutectic formed by NaF and MgF2 has energy storage properties in the form of latent heat, which is why it has been considered for use in solar energy systems..
In the area of biochemistry, magnesium fluoride, along with other metal fluorides, is used to inhibit phosphoryl transfer reactions in enzymes.
Recently, MgF2 nanoparticles have been successfully tested as drug delivery vectors in diseased cells for the treatment of cancer..
Yet No Comments