The Crystal Structure of Synthetic Boehmite

Abstract

Crystal structure computations have been made for synthetic boehmite, the α‐modification of aluminum oxide monohydrate, using the powder method. The experimental data were found to fit an orthorhombic lattice with constants a₀ = 2.85₉A, b₀ = 12.2₄A, and c₀ = 3.69₁A. The assignment of four AlO (OH) groups to this unit cell gives a calculated density of 3.06₃ g/cc. The observed density is 2.97₇ g/cc. The general space group extinctions were found to agree with those of D_2h¹⁷. Generalized atomic coordinates were roughly determined by application of Pauling's coordination theory for ionic crystals and the determinations refined by the usual intensity computations. The parameter values selected were u_Al = −0.334, uO_I = 0.287, uO_II = 0.067. It is suggested that the inconsistencies which exist between the experimental and computed intensity data may be explained by the occurrence of a small quantity of γ—Al₂O₃ in the synthetic samples used. The value of 2.47±0.07A obtained for the hydrogen bridge distance is discussed. This value is less than that observed for any previously determined structure.