News

The main component of cryolite is sodium hexafluoroaluminate or sodium aluminum fluoride, with a molecular formula of Na3AlF6. It is a small white crystal with no odor, a specific gravity of 3, a hardness of 2-3, a melting point of 1009 degrees Celsius, and is prone to water absorption and moisture. Cryolite is mainly used as a flux for aluminum electrolysis, wear-resistant filler for rubber and grinding wheels, enamel whitening agent, glass shading agent and metal flux, insecticide for crops, etc. The Hall Heroult method is a method of producing metallic aluminum using fluoride melt based on cryolite as a solvent, and no other compound has been found to replace cryolite so far. This is because cryolite not only has the ability to dissolve alumina, but also has other essential properties, such as not containing elements with higher electrical conductivity than aluminum, good stability, no decomposition, volatilization, or deliquescence under general conditions, a melting point higher than aluminum, good conductivity, and energy savings. It can be said that without cryolite, the world may not have such a large-scale aluminum industry, prices would not be so low, and applications would not be so widespread. The west coast of Greenland is the main source of cryolite, which was mined in 1987. At present, sodium hexafluoroaluminate is mostly synthesized artificially from fluorite for industrial use. Spain, Russia, and the United States also produce.

Theoretical composition (wB%): Na 32.8, Al 12.8, F 54.4. Named after its similarity to ice. The ingredients are usually pure, sometimes containing trace amounts of Ca, Fe, Mn, and organic matter.

Structural form

cryolite

Monoclinic crystal system, a0=0.547nm，b0=0.562nm，c0=0.782nm，β=9011’； Z=2。 The crystal structure consists of slightly modified [AlF6], [NaF6] octahedra, and [NaF12] cubic octahedra; Two types of octahedra are connected to form chains with a c-axis extension, and the interchain is filled with 2/3 of Na, with a coordination number of 12. The [AlF6] octahedron is located at the corner top and center of the unit cell, while the [NaF6] octahedron is located at the center of the bottom surface and the middle of the vertical edge of the unit cell. Among the 6 [NaF12] octahedra, 4 are on the unit cell surface, and the remaining 2 are inside the unit cell. At around 500 ℃, β - cryolite belongs to the equiaxed crystal system, Oh3-Fm3m； a0=0.795nm； Z=4。 (NH4) 3AlF6 type structure, similar to potassium sodium cryolite structure. Due to the small radius of Na+distributed in cubic octahedra, it cannot fill the space of cubic octahedra. Therefore, under cooling conditions, the polyhedron tilts and transforms into a monoclinic crystal system.

Rhombohedral crystals, C2h-2/m(L2PC)。 Common simplices: parallel double-sided a {100}, b {010}, c {001}, and diagonal column s {111}. Due to the well-developed crystal planes of {001} and {010}, the crystal appearance resembles a cube. Twin crystals often rely on (110). Usually in the form of dense blocks, sometimes in the form of flakes or granules.

property

Colorless, white, sometimes light gray, light brown, light red or brick red. The stripes are white. Glass gloss to grease gloss. Transparent to semi transparent. No cleavage, with {001} and {110} cracks. Sexual fragility. The fracture surface is uneven. Hardness of 2-3. The relative density is 2.95-3.1.

Under polarizing lens: colorless and transparent. Two axis crystal (+), 2V=43?. Ng=1.3396，Nm=1.3389，Np=1.3385。

cryolite

purpose

Mainly used as a flux for aluminum electrolysis; Also used as a wear-resistant additive for grinding products, it can effectively improve the wear resistance, cutting force, and extend the service life and storage time of grinding wheels; Industries such as fluxes for ferroalloys and boiling steel, non-ferrous metal fluxes, deoxidizers for casting, catalysts for olefin polymerization, emulsifiers for glass anti reflective coatings, enamel, opalescent agents for glass, fluxing agents for welding materials, fillers for ceramics, insecticides for pesticides, etc