Non-solvated aluminum hydride. Crystallization from diethyl ether-benzene solutions

Abstract

Crystallization of non solvated aluminum hydride from a diethyl ether-benzene mixed solvent was studied. The desolvation of AlH 3 •(Et 2 O) x etherate in solution and the crystalliza tion of α AlH 3 during polythermal heating of the solution occur only in the presence of ≥10 wt.% LiAlH 4 . The process is multistage, and the crystallization begins with the formation of the AlH 3 •0.25Et 2 O solvate, which recrystallizes in the solid phase into γ AlH 3 and then α AlH 3 . Four crystalline modifications of aluminum hydride were characterized by X ray diffraction and electron microscopy.

Aluminum hydride as a hydrogen and energy storage material: Past, present and future

“…Previous work of Brower et al indicated that the etherated AlH 3 forms translucent spheres after precipitating from solution. According to Bulychev et al [18] the etherated material has a chemical composition close to AlH 3 ·0.25Et 2 O and although it is generally amorphous, it may form a crystalline phase with an orthorhombic structure and unit cell parameters a = 9.90Å; b = 8.54Å, c = 12.05 (±0.01)Å.…”

“One-step” synthesis of nonsolvated aluminum hydride

“…However, the stoichiometry of this reaction differs substantially from that of the "classical" Schlesinger reaction, which diminishes the economical effect of the increase in С eff AlH 3 . In addition, the product formed is multiphase and decomposes rapidly to elements even at 60-70 °С.…”

“…Presently, the most popular method for the syn thesis of this hydride is the thermal cleavage of etherate {AlH 3 •xEt 2 O}, which was obtained by the Schlesinger reaction 1 (Eq. (1)) in the presence of small amounts of lithium tetrahydridoaluminate and tetrahydridoborate (10)(11)(12)(13)(14)(15) wt.% of aluminum hydride) followed by crystal lization of nonsolvated aluminum hydride (hereinafter, NAH) from solutions in an ether-ArH mixed solvent.…”

“…(1)) in the presence of small amounts of lithium tetrahydridoaluminate and tetrahydridoborate (10)(11)(12)(13)(14)(15) wt.% of aluminum hydride) followed by crystal lization of nonsolvated aluminum hydride (hereinafter, NAH) from solutions in an ether-ArH mixed solvent. 2 3 LiAlH 4 solv + AlCl 3 (1) It has been shown 3 that the concentration of alumi num hydride in a 1 : 1 (v/v) Et 2 O-ArH solution should not exceed 4 g L -1 for the process to occur successfully. The concentration can be increased to 5-6 g L -1 with addition of a large amount of LiAlH 4 and LiBH 4 (up to 25-45 wt.% each of aluminum hydride).…”

“…The concentration can be increased to 5-6 g L -1 with addition of a large amount of LiAlH 4 and LiBH 4 (up to 25-45 wt.% each of aluminum hydride). 3 All further attempts to increase the concentration resulted in the spontaneous precipitation of the "dead" solvate {AlH 3 •0.33 Et 2 O} n (see Ref. 4) and a simultaneous decrease in the yield of the nonsolvated material and deterioration of its quality.…”