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Friday, 11 February 2011 21:55

Titanium

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Gunnar Nordberg

Occurrence and Uses

Titanium (Ti) is contained in many minerals, but only a few of them are of industrial significance. These include ilmenite (FeTiO3), which contains 52.65% Ti and 47.4% FeO; rutile (TiO2), with admixtures of ferrous oxide; perovskite (CaTiO3), which contains 58.7% TiO2 and 41.3% CaO; and sphene, or titanite, (CaOTiO2·SiO2), which contains 38.8% TiO2. Some heterogeneous minerals, such as loparite, pyrochlor, and tailings from bauxite and copper ore processing may also be sources of titanium.

Titanium is used as a pure metal, in alloys, and in the form of various compounds. The bulk of titanium is needed in the iron and steel industry, in shipbuilding, for aircraft and rocket construction, and for the fabrication of chemical plants. Titanium is used as a protective surface on mixers in the pulp and paper industry. It is also found in surgical appliances. Titanium has been employed for the manufacture of electrodes, lamp filaments, paints, dyes and welding rods. Titanium powder is used in pyrotechnics and in vacuum engineering. Titanium is also used in dentistry and in surgery for implants or prostheses.

Titanium carbide and titanium nitride are used in powder metallurgy. Barium titanate is used for making heavy-duty capacitors. Titanium dioxide is utilized as a white pigment in paints, floor coverings, upholstery, electronics, adhesives, roofing, plastics and in cosmetics. It is also useful as a component of porcelain enamels and glazes, as a shrinking agent for glass fibres, and as a delustering agent for synthetic fibre. Titanium tetrachloride acts as an intermediate in the production of titanium metal and titanium pigments, and as a catalyst in the chemical industry.

Hazards

The formation of titanium dioxide (TiO2) and concentrate dust, pitch briquette dust arising from crushing, mixing and charging of bulk raw materials, and radiant heat from coking furnaces are hazards in titanium production. There may be chlorine, titanium tetrachloride (TiCl4) vapours and their pyrolysis products in the air of the chlorination and rectification plants, arising from leaking or corroded equipment. Magnesium oxide may be present in the air of the reduction area. Titanium dust becomes airborne when titanium sponge is knocked out, crushed, separated and bagged. Exposure to heat and infrared radiation occurs in the arc furnace area (up to 3 to 5 cal/cm2 per min).

Maintenance and repair of the chlorination and rectification installations, which includes disassembly and cleaning of the equipment and pipework, create particularly adverse conditions of work: high concentrations of TiCl4 vapours and hydrolysis products (HCl, Ti(OH)4), which are highly toxic and irritant. Workers in these plants often suffer from upper-airway disease and acute or chronic bronchitis. Liquid TiCl4 splashed on the skin causes irritation and burns. Even very short contact of the conjunctiva with TiCl4 leads to suppurative conjunctivitis and keratitis, which may result in corneal opacities. Animal experiments have shown that dust of metallic titanium, titanium concentrates, titanium dioxide and titanium carbide is slightly toxic. While titanium dioxide has not been found to be fibrogenic in animals, it seems to increase the fibrogenicity of quartz when given as combined exposure. Long-term exposure to titanium-containing dust may result in mild forms of chronic lung disease (fibrosis). There is radiological evidence that workers who have handled TiO2 for long periods develop lung changes resembling those observed in mild forms of silicosis. In one worker who had worked in contact with titanium dioxide for several years and died from brain cancer, the lungs displayed accumulations of TiO2 and changes analogous to anthracosis. Medical examinations of powder metallurgy workers in various countries have disclosed cases of chronic pneumonitis due to mixed dust including titanium carbide. The degree of this disease varied according to conditions of work, length of dust exposure and individual factors.

Workers who have been chronically exposed to titanium and titanium dioxide dust show a high incidence of chronic bronchitis (endobronchitis and peribronchitis). The early stages of the disease are characterized by impaired pulmonary respiration and ventilatory capacity, and by reduced blood alkalinity. Electrocardiographic tracings of these titanium workers revealed cardiac changes characteristic of pulmonary disease with hypertrophy of the right auricle. A considerable number of these cases presented myocardial hypoxia of various degrees, inhibited atrioventricular and intraventricular conductivity, and bradycardia.

Airborne metallic titanium dust is explosive.

Other hazards in titanium production are carbon monoxide exposures at the coking and arc furnaces, and burns.

Safety and Health Measures

Control dust during ore crushing by moistening the material to be processed (up to 6 to 8% moisture content), and by adopting a continuous process, which enables the equipment to be enclosed with exhaust devices at all points where dust may form; the dust-laden air exhausted should be filtered and the dust collected should be recycled. Dust exhaust systems must be provided at the knock-out stations; crushers, separators and baggers in the titanium sponge plant. Knocking out with pneumatic chipping hammers should be replaced by machining out on special milling or turning machines.

 

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Read 2882 times Last modified on Thursday, 19 May 2011 10:35