Abstract:

Ca oxalate was crystd. in the presence of the anionic surfactant diisooctyl sulfosuccinate, AOT, and the phase compn. of the ppts. (by x-ray diffraction powder patterns and thermal anal.) and their crystal growth morphol. (by SEM and electron diffraction) were detd. In the control systems and in the presence of low concns. of AOT (below the crit. micellar concn., CMC) Ca oxalate monohydrate (CaC2O4·H2O, COM) was the dominant crystal phase. Crystals grown in the presence of C(AOT)\textgreater0.75 CMC were thinner and more elongated than in the controls, indicating preferential adsorption of the surfactant at the 1̅01 and \010\ crystal faces. When the AOT concn. exceeded the crit. micellar concn., the morphol. changes in COM crystals became more intense and the compn. of the ppts. abruptly changed to mixts. of COM and Ca oxalate dihydrate (CaC2O4·(2+x)H2O, x\textless0.5; COD) with a COM/COD ratio up to 50%. The morphol. of the COD crystals was mostly unaffected. The phase change was attributed to preferential adsorption of AOT - as surface aggregates - at the crystal faces of COM with the consequence of strong inhibition of nucleation and crystal growth of this crystal type and growth of the kinetically less favored COD crystals. [on SciFinder(R)]