Systems Based on AlAs
Some quaternary compounds are formed in the Al–H–O–As system. AlAsO 4 ·2H 2 O crystallizes in the orthorhombic structure with the lattice parameters a = 882.18 + 0.05, b = 982.52 + 0.06, and c = 1011.63 + 0.06 pm and experimental and calculated densities of 3.031 [for mineral mansfieldite (Allen et al. 1948)] and 3.06 g·cm−3, respectively (Harrison 2000). To prepare this compound, a starting mixture of KOH (1 M, 4 mL), Al(NO3)3 (0.5 M, 8 mL), and H3AsO4 (1 M, 4 mL) was heated to 170°C in a 23 mL capacity Teflon-lined hydrothermal bomb for 4 days (Harrison 2000). Upon cooling the bomb to ambient temperature over a period of 2–3 h, a crop of small blocks and octahedra of the title compound was recovered by vacuum filtration and washing with water and acetone.