What is cryolite?

What is Cryolite?

Cryolite is also known as sodium hexafluoroaluminate or sodium aluminum fluoride, the molecular formula is Na3AlF6, white fine crystal, odorless, solubility is larger than natural cryolite, specific gravity is 3, hardness 2~3, melting point, easy to absorb water and be affected by moisture.  Crcrite is mainly used as flux for aluminum electrolysis, wear-resisting filler for rubber and grinding wheel, enamel opalescent agent, glass sunshield and metal flux, pesticide for crops and so on.  The Hall-Heroult method uses cryolite as a base fluoride melt as the solvent to produce metallic aluminum. So far, no alternative compound has been found to replace cryolite.  This is because cryolite in addition to be able to dissolve alumina also has some other indispensable properties, such as no electrical elements than aluminum, good stability, under general conditions, no decomposition, no volatilization, no deliquescence, melting point is higher than aluminum, good conductivity, save electricity and so on.  It can be said that without cryolite, the world would not have such a large aluminum industry, the price would not be so low, and the application would not be so widespread.

Theoretical composition (wB%) : Na 32.8, Al 12.8, F 54.4.  Named for its resemblance to ice.  The composition is usually very pure, sometimes can contain very small amounts of Ca, Fe, Mn and organic matter.  

Structure form of Cryolite

Monocline system, A0 =0.547nm, B0 =0.562nm, C0 =0.782nm, β=9011 ';  Z = 2.  The crystal structure is composed of [AlF6], [NaF6] octahedron and [NaF12] cubic octahedron.  The two octahedrons are connected to form chains with c-axis extension, and the interchains are filled with other 2/3 Na, and the coordination number is 12.  The [AlF6] octahedron is located at the angular apex and center of the cell, the [NaF6] octahedron is located at the base center of the cell and the middle of the vertical edge, 4 of the 6 [NaF12] are on the cell surface, and the remaining 2 are in the cell.  At about 500℃, β -cryolite is equiaxed, OH3-FM3m;  A0 = 0.795 nm;  Z = 4.  The structure of (NH4)3AlF6 is similar to that of potassium sodium cryolite.  Due to the small radius of Na+ distributed in the cubic octahedron, it cannot fill the space of the cubic octahedron, so the polyhedron tilts and transforms into monoclinic system under cooling condition.  

Rhombic column, C2H-2 / M (L2PC).  Common simplex: parallel double-sided A {100}, B {010}, C {001} and rhombus S {111}.  Because {001} and {010} crystal planes are relatively developed, the crystal shape is similar to a cube.  Twin crystals chang Yi (110).  Usually dense massive, sometimes flake or granular.  The physical and chemical properties  

Colorless, white, sometimes light gray, light brown, light red or brick red.  Streaks white.  Glass luster to grease luster.  Transparent to translucent.  No cleavage, {001}, {110} split.  Crispy.  The fracture is uneven.  Hardness is 2 ~ 3.  Relative density 2.95~3.1.  

Polarizing lens: colorless transparent.  Biaxial crystal (+), 2V=43?  .  Ng=1.3396, Nm=1.3389, Np=1.3385  

Application of cryolite

Mainly used as flux for aluminum electrolysis;  Also used as wear-resisting additive of grinding products, can effectively improve the abrasion resistance, cutting, cutting force of grinding wheel, prolong the service life and storage time of grinding wheel;  Ferroalloy and boiling steel flux, non-ferrous metal flux, casting deoxidizer, chain olefin polymerization catalyst, as well as for glass anti-reflection coating, enamel emulsifier, glass opalescent agent, welding material flux ceramic fillers, pesticides and other industry enterprises.  

Application advantages of cryolite

1.  Compared with cryolite, the use of polymer in the new starter tank has the advantages of stable electrolyte level, slower shrinkage and gentle change of molecular ratio, which is conducive to the stable maintenance of electrolyte composition.  

2.  It can greatly save the dosage of sodium fluoride or soda and reduce the production cost.  

3.  Adding method is simple and easy to operate.  

In addition to industrial cryolite, there is a special abrasive cryolite in the market, the cryolite is mainly suitable for abrasive/flux industry, the product is pure white powder.  It is not suitable for electrolytic aluminum, and 30% of customers in the welding industry report that there will be smoke.