THALLIUM(I) IODIDE

Thallium (I) iodide is a yellow solid, nearly insoluble in water. It is used as infrared radiation transmitter (crystals mixed with thallium bromide).

Yellow powder. Insoluble in alcohol; slightly soluble in water; soluble in aqua regia.

Mixed crystals with thallium bromide for infrared radiation transmitters.

Thallium(I) iodide is used in mercury lamp to enhance its performance. It is mainly used for underwater lighting, since the blue green light produced has least absorption in water. Scintillator made by using iodide salt of thallium, sodium and cesium is utilized for radiation scintillation detectors.

Poison by ingestion and subcutaneous routes. Human systemic effects: blood pressure lowering, change in motor activity, muscle weakness. When heated to decomposition it emits very toxic fumes of T1 and I-. See also IODIDES and THALLIUM COMPOUNDS.

T1I, also known as thallium(I) iodide can be made using a direct reaction between thallium and iodine, but it is usually precipitated by adding thallium salts (sulfates, perchlorates) to an aqueous solution of potassium iodide or hydriodic acid, washed with water, and then dried at 110 C. Thallium iodide has two homogeneous isomers that will undergo reversible phase transfer at 175C or 4.7 GPa. The high-temperature type is an isometric crystalline system with a cesium chloride-type body-centered cubic lattice, called β-T1I quasi-stable phase, and is red in color. The low-temperature type α-T1I is a rhombohedral crystal system and is yellow in color. It fluoresces by X-rays or light. Above 160 GPa it shows metallic conductivity. Although stable in dilute hydrochloric and dilute sulfuric acids, it reacts with nitric acid to form iodine and thallium nitrate.

Reflux it for 2-3hours with water containing HI, then wash it until acid-free, and dry it at 120o. Store it in brown bottles. [D.nges in Handbook of Preparative Inorganic Chemistry (Ed. Brauer) Academic Press Vol I p 870 1963]. POISONOUS.