Inorganic fluorine compounds play an outstanding role in the aluminum industry. They are frequently encountered not only in the manufacture, but also in the processing and finishing of aluminum.
The manufacture of aluminum on a commercial scale was first made possible with the introduction of cryolite at the end of the 19th century. Cryolite as the essential component of the electrolyte (85 – 90 %) decreases the temperature of the smelting flux electrolysis.
Other important additions to electrolytes in current commercial use are aluminum fluoride, calcium fluoride and lithium fluoride. These fluorides increase the conductivity of the electrolyte and improve the efficiency of the used energy. The aluminum so produced has a purity of between 99.5 and 99.9 %. Refining, that is to say the thorough cleaning and improvement of aluminum, is carried out for example by a process of three-layer fused-salt electrolysis. This method represents the only commercially viable process for the production of pure aluminum. Further electrolyte components from our product range which may be used are barium fluoride or calcium fluoride. Aluminum produced by this method has a purity of between 99.99 and 99.999 %.
In the aluminum industry, salt covers are used as an aid in casting. The salt covers are a mixture of substances which protect molten aluminum alloys from oxidizing. The molten salt mixture also prevents gases from entering the bath, reduces heat losses from the surface of the molten metal and absorbs impurities which rise to the surface of the melt. Suitable salt covers are fluxes containing cryolite or sodium fluorosilicate. The melting points of these fluxes are reduced by the addition of, for instance, sodium chloride or potassium chloride to such an extent that they liquefy at the prevailing working temperatures.
Hydrofluoric acid and ammonium bifluoride are the bath constituents for the surface treatment of pure aluminum. Bright reflective surface on the aluminum is achieved by chemical polishing. Inorganic fluorides are also of critical importance in the flux brazing of aluminum and aluminum alloys, acting to remove the oxide layer.
In recent decades there has been a steady increase in the quality of abrasives. This is especially true for elastically and fixed bonded abrasives, and is due in no small part to the use of abrasively active filler materials such as Solvay-Cryolite. Abrasively active fillers are today encountered in almost all high performance abrasives employed in the grinding of metals. Fixed bonded abrasives are abrasive bodies which are produced in a wide variety of forms. Examples of abrasives held on substrates are abrasive papers (generally without abrasively active filler materials), abrasive belts and abrasive fibers. Aluminum oxide and silicon carbide, produced by fusion processes in electric furnaces, are the main abrasive grains employed.
As a manufacturer of soda ash, Solvay is an acknowledged partner of the glass industry. It is less well known that a whole range of inorganic fluorine compounds plays an important role both in the manufacture of glass and in its processing.
In the manufacture of opaque glass, also known as milk or cloud glass, the cloudiness is achieved by the addition of inorganic fluorides. These are added to the glass melt as so-called “white opacifier”.
In small amounts, fluorides act as fluxes, and only the addition of larger quantities brings about the clouding effect. This clouding effect is caused mainly by the precipitation of small crystals of calcium and sodium fluoride. A typical fluoro- opaque glass will have a fluoride content of approx. 3.5 – 4.0 %.
Metal Surface Treatment
Hydrofluoric acid is the primary product of the fluorochemical industry, and is the most produced of all inorganic fluoro compounds. It also enjoys a prominent status in the surface treatment of metals .
The requirements for innovative braking systems that can be used worldwide are extremely high. With regard to the braking process they include:
- Performance stability
- Comfort properties
- Noise emission
Aspects relevant to the environment will become even more important in the future. At the same time it will be necessary to meet the increasingly stringent specifications of the automobile industry and other sectors with regard to standardization and cost minimization.
Synthetic calcium fluoride from Solvay fulfils these requirements and has proved to be outstandingly good in high performance brakes.