Gunnar Nordberg
Occurrence and Uses
Germanium (Ge) is always found in combination with other elements and never in the free state. Among the most common germanium-bearing minerals are argyrodite (Ag8GeS6), containing 5.7% germanium, and germanite (CuS·FeS·GeS2), containing up to 10% Ge. Extensive deposits of germanium minerals are rare, but the element is widely distributed within the structure of other minerals, especially in sulphides (most commonly in zinc sulphide and in silicates). Small quantities are also found in different types of coal.
The largest end use of germanium is the production of infrared sensing and identification systems. Its use in fibre-optical systems has increased, while consumption for semiconductors has continued to decline due to advances in silicon semiconductor technology. Germanium is also used in electroplating and in the production of alloys, one of which, germanium-bronze, is characterized by high corrosion resistance. Germanium tetrachloride (GeCl4) is an intermediate in the preparation of germanium dioxide and organogermanium compounds. Germanium dioxide (GeO2) is used in the manufacture of optical glass and in cathodes.
Hazards
Occupational health problems may arise from the dispersion of dust during the loading of germanium concentrate, breaking up and loading of the dioxide for reduction to metallic germanium, and loading of powdered germanium for melting into ingots. In the process of producing metal, during chlorination of the concentrate, distillation, rectification and hydrolysis of germanium tetrachloride, the fumes of germanium tetrachloride, chlorine and germanium chloride pyrolysis products may also present a health hazard. Other sources of health hazards are the production of radiant heat from tube furnaces for GeO2 reduction and during melting of germanium powder into ingots, and the formation of carbon monoxide during GeO2 reduction with carbon.
The production of single crystals of germanium for the manufacture of semiconductors brings about high air temperatures (up to 45 ºC), electromagnetic radiation with field strengths of more than 100 V/m and magnetic radiation of more than 25 A/m, and pollution of the workplace air with metal hydrides. When alloying germanium with arsenic, arsine may form in the air (1 to 3 mg/m3), and when alloying it with antimony, stibine or antimonous hydride may be present (1.5 to 3.5 mg/m3). Germanium hydride, which is used for the production of high-purity germanium, may also be a pollutant of the workplace air. The frequently required cleaning of the vertical furnaces causes the formation of dust, which contains, apart from germanium, silicon dioxide, antimony and other substances.
Machining and grinding of germanium crystals also give rise to dust. Concentrations of up to 5 mg/m3 have been measured during dry machining.
Absorbed germanium is rapidly excreted, mainly in urine. There is little information on the toxicity of inorganic germanium compounds to humans. Germanium tetrachloride may produce skin irritation. In clinical trials and other long-term oral exposures to cumulative doses exceeding 16 g of spirogermanium, an organogermanium antitumour agent or other germanium compounds have been shown to be neurotoxic and nephrotoxic. Such doses are not usually absorbed in the occupational setting. Animal experiments on the effects of germanium and its compounds have shown that dust of metallic germanium and germanium dioxide causes general health impairment (inhibition of body weight increase) when inhaled in high concentrations. The lungs of the animals presented morphological changes of the type of proliferative reactions, such as thickening of the alveolar partitions and hyperplasia of the lymphatic vessels around the bronchi and blood vessels. Germanium dioxide does not irritate the skin, but if it comes into contact with the moist conjunctiva it forms germanic acid, which acts as an eye irritant. Prolonged intra-abdominal administration in doses of 10 mg/kg leads to peripheral blood changes.
The effects of germanium concentrate dust are not due to germanium, but to a number of other dust constituents, in particular silica (SiO2). The concentrate dust exerts a pronounced fibrogenic effect resulting in the development of connective tissue and formation of nodules in the lungs similar to those observed in silicosis.
The most harmful germanium compounds are germanium hydride (GeH4) and germanium chloride. The hydride may provoke acute poisoning. Morphological examinations of organs of animals which died during the acute phase revealed circulatory disorders and degenerative cell changes in the parenchymatous organs. Thus the hydride appears to be a multi-system poison that may affect the nervous functions and peripheral blood.
Germanium tetrachloride is a strong irritant of the respiratory system, skin and eyes. Its threshold of irritation is 13 mg/m3. In this concentration it depresses the pulmonary cell reaction in experimental animals. In stronger concentrations it leads to irritation of the upper airways and conjunctivitis, and to changes in respiratory rate and rhythm. Animals which survive acute poisoning develop catarrhal-desquamative bronchitis and interstitial pneumonia a few days later. Germanium chloride also exerts general toxic effects. Morphological changes have been observed in the liver, kidneys and other organs of the animals.
Safety and Health Measures
Basic measures during the manufacture and use of germanium should be aimed at preventing the contamination of the air by dust or fumes. In the production of metal, continuity of the process and enclosure of the apparatus is advisable. Adequate exhaust ventilation should be provided in areas where the dust of metallic germanium, the dioxide or the concentrate is dispersed. Local exhaust ventilation should be provided near the melting furnaces during the manufacture of semiconductors, for example on zone-refining furnaces, and during the cleaning of the furnaces. The process of manufacturing and alloying monocrystals of germanium should be carried out in a vacuum, followed by the evacuation of the formed compounds under reduced pressure. Local exhaust ventilation is essential in operations such as dry cutting and grinding of germanium crystals. Exhaust ventilation is also important in premises for the chlorination, rectification and hydrolysis of germanium tetrachloride. Appliances, connections and fittings in these premises should be made of corrosion-proof material. The workers should wear acid-proof clothing and footwear. Respirators should be worn during the cleaning of appliances.
Workers exposed to dust, concentrated hydrochloric acid, germanium hydride and germanium chloride and its hydrolysis products should undergo regular medical examinations.