Characteristics: Soft gray, lead-like metal that is not found free in nature. Thallium is extremely soft, malleable and soft enough to be cut with a knife at room temperature. It has a metallic luster that, when exposed to air, quickly tarnishes to a bluish-gray tinge, resembling lead. A heavy layer of oxide builds up on thallium if left in air. It may be preserved by immersion in oil. In the presence of water, thallium hydroxide is formed. Sulfuric and nitric acid dissolve thallium rapidly to make the sulfate and nitrate salts, while hydrochloric acid forms an insoluble thallium chloride layer. Soluble in nitric and sulfuric acids. Insoluble in water, but readily forms soluble compounds when exposed to air or water.
Derivation: Commercially thallium is produced as a byproduct from the refining of heavy metal sulfide ores.
60–70% of thallium production is used in the electronics industry such as: infrared optical applications, doping selenium semiconductors, high-temperature superconducting materials for applications like magnetic resonance imaging, storage of magnetic energy, magnetic propulsion, electric power generation and transmission, infrared detectors. The remainder finds its use in medical applications for nuclear cardiography and the pharmaceutical industry for treatment of ringworm and other skin infections.
Hazards: Thallium and its compounds are extremely toxic and should be handled with great care. Numerous cases of fatal thallium poisoning have been documented. Adequate ventilation should be provided when melting this metal. Thallium compounds have a high aqueous solubility and are readily absorbed through the skin. Exposure by inhalation should not exceed 0.1 mg per cubic metre in an 8-hour time-weighted average.