|Monthly Tech-Tip |
Occurs in nature as the minerals bauxite, bayerite, corundum, diaspore, gibbsite.
This oxide exists in several forms
In the production of aluminum, refractory materials, synthetic abrasives etc, such as
In spite of its high m.p. (2050°C), alumina can be fused in an oxy-hydrogen flame or in an electric arc. By the former method, large single crystals (boules) can be produced; they are used as bearings, and as dies for wire-drawing, and for other purposes demanding high abrasion resistance. Fused alumina made in electric arc furnaces is usually crushed, bonded with fine alumina powder, shaped and then sintered.
Alumina, sometimes containing a small amount of clay or of a mineralizer and fired at a high temperature to form a dense ceramic. Sintered alumina has great strength and abrasion resistance, high dielectric strength, and low power factor.
The only form of alumina that remains stable when heated above about 1000 C, also known as alpha-alumina. It occurs naturally, but impure, in S. Africa and elsewhere but generally it is produced by extraction from bauxite followed by a firing process at high temperature.
In general, aluminas are efficiently eliminated from the lung and are considered to be nuisance dusts; their role in fibrogenic lung disease remains unclear.
High aluminum levels (between 400 and 1080 mg/kg of wet pulmonary tissue) have been found in the lungs of subjects exposed during 10 to 37 years to alumina dust. Animal experiments indicate that prolonged inhalation of alumina involves a rise in the concentration of aluminum in the brain.
A review of the literature (1957), on the pulmonary toxicity of aluminum carried out in the USA concluded that aluminum, aluminum oxide and aluminum hydroxyde Al(OH)3 do not cause pulmonary effects; the lesions reported by some authors would result from the presence of other substances.
A number of epidemiologic studies of aluminum smelter workers have confirmed either minimal or absent fibronodular disease and no excess mortality associated with pneumoconiosis.
The risk associated with chronic exposure to alumina dust (Al2O3) is not entirely elucidated. Some authors think that alumina can generate a pneumoconiosis (aluminosis) while others have recommended the use of powdered alumina by inhalation as a therapeutic and preventive method in the case of silicosis.
Italian studies suggest that chronic exposure to high concentrations of alumina can causea light pulmonary fibrogenic reaction and the presence of small opacities on the chest X-ray.
A few cases of fibrosis due to prolonged exposure to alumina during the production of abrasives were reported. It does not seem that these workers were exposed to silica or asbestos.
Studies seem to indicate that, independently from exposures to other pneumotoxicants, massive inhalation of aluminum or alumina can favor the development of interstitial fibrosis.
Excessive protracted nuisance dust exposure (100 mg/year for more than 20 years) has been accompanied by findings consistent with a minor degree of nonspecific chronic industrial bronchitis.
An asthmatiform syndrome has been described among potroom workers attributed by some authors to exposure to volatile fluorides. A respiratory obstructive syndrome has also been described among workers involved in the manufacture of aluminum fluoride.
|Aluminium, oxide expressed as Al||10mg/m3||Poussière Totale (Total Dust), without asbestos fibers, and <1% crystalline silica.|
By Edouard Bastarache
Article by Edouard Bastarache
Edouard Bastarache is a well known doctor that has written many articles on the subject of toxicity of ceramic materials and books on technical aspects of ceramics. He writes in both English and French.