Arsenic

Arsenic in it’s pure elemental form is a silver-gray brittle, crystalline solid. Only about 3% of the world demand for arsenic is for arsenic metal. Arsenic is used as an alloying element in lead and copper alloys. In quantities of 0.5 to 2%, arsenic improves the sphericity of lead shot. Arsenic is a semi-conductor with low thermal conductivity. High purity arsenic, 4N purity or greater, is used in the semi-conductor industry.

Toxicity:

Arsenic is probably found throughout the universe; it is found in meteorites in percentages of .00005 to 0.1. The occurrence in the earth’s crust is 0.0005%. Extremely small amounts of arsenic are common in the air and in water supplies. The toxicity of arsenic is related to it’s chemical state and can be extremely high. The degree of toxicity of arsenic in the elemental state is relatively low. Metallic arsenic on exposure to the atmosphere will develop an oxide coating, and, for this reason, care must be taken not to ingest or handle it. Arsenic trioxide is very toxic and inhalation of dust and fumes is to be avoided. Controlled exhaust ventilation of work areas and careful handling is required to comply with the OSHA standard of 10 µm (As)/m³.

Typical Properties:

• Crystal Structure: Hexagonal (rhombohedral equivalent); at 26 ^oC, a = 0.3760 nm and c = 1.0548 nm
• Atomic Weight: 74.9216
• Density: 5.778 gm/cm³ at 26 ^oC
• Melting Point: 816 ^oC at 3.91 MPa
• Boiling Point: Sublimes at 615 ^oC (Vaporization apparent at 100 ^oC and is rapid at 450 ^oC)
• Coefficient of Thermal Expansion: 5.6 µm/m ⋅ K at 20 ^oC
• Specific Heat: 0.328 kJ/kg ⋅ ^oK
• Latent Heat of Fusion: 370.3 kJ/kg
• Latent Heat of Sublimation: 426.77 kJ/kg
• Electrical Resistivity: α-metallic form, 260 nΩ ⋅ m at 0 ^oC
• Electrochemical Equivalent: Valence 3, 0.15254 mg/^oC; Valence 5, 0.25876 mg/^oC
• Magnetic Susceptibility: Volume: -3.9 x 10^-6 mks at 18 ^oC
• Hardness (Mohs): 3.5
• Solubility: Insoluble in water, caustic acids, and nonoxidizing acids. Attacked by hydrochloric acid in presence of oxidant. Reacts with nitric acid.