alphasulfur

Alpha-sulfur, or orthorhombic sulfur, is the most stable allotrope of elemental sulfur at ambient conditions. It consists of S8 ring molecules arranged in an orthorhombic crystal lattice, forming pale yellow crystals or grains. The form is commonly encountered as a bright, naturally occurring crystalline material and as a component of elemental sulfur samples.

Properties and structure are defined by the S8 ring motif. The orthorhombic arrangement gives alpha-sulfur its characteristic crystalline habit and color. It is insoluble in water and has limited solubility in many common solvents, but dissolves in nonpolar solvents such as carbon disulfide, benzene, and toluene. Its melting point is about 115°C, but its stable form at room temperature is alpha-sulfur rather than the higher-temperature forms.

Phase behavior is notable for sulfur. At temperatures below roughly 95–96°C, alpha-sulfur is the stable form. As temperature increases into this range, alpha-sulfur converts to beta-sulfur, the monoclinic modification. The beta form remains stable up to its own melting range, after which liquid sulfur is obtained. Upon cooling, beta-sulfur reversibly transforms back to alpha-sulfur as temperatures fall below about 95°C.

Occurrence and uses are tied to elemental sulfur in general. Alpha-sulfur is commonly sourced from natural sulfur deposits and is a key raw material in industries such as vulcanization of rubber, fertilizer production, and chemical synthesis. Safety considerations for handling sulfur include avoiding inhalation of dust and avoiding overheating to prevent irritant vapors.