摘要:
IntroductionBarium sulfate is a white pigment used in cosmetics and as a filler in papermaking or as a coating material. When synthesizing barium sulfate as a powder, controlling its morphology is very important. However, conventional processes do not control the morphology of sedimentary barium sulfate. There has been a great deal of research on the morphology control of barium sulfate using various additives,1,2including organic acids3–7such as alkyldiphosphonates. The morphology changes that occur during the synthesis of barium sulfate with added organic acids seem to be governed by the inhibition of the growth of specific crystal surfaces. This results from either the substitution of an organic acid ion for a sulfate ion or the binding of an organic acid ion to a barium ion.The interaction between the barite crystal surface and the solution or chelating reagent has also been studied. Molecular model calculations have demonstrated that the crystal growth rate of the barite surfaces differ with the surface energy or attachment energy.8,9EDTA, a typical chelating agent, dissolves barite effectively by forming BaII–EDTA surface complexes; their desorption results in an increased etch pit formation rate.10Research on barite dissolution in aqueous diethylenetriaminepentaacetic acid (DTPA) suggested that the active sites of the DTPA molecule bind to Ba2+cations exposed on the (001) surface.11Kinetic studies on the dissolution of barium sulfate in aqueous EDTA and DTPA indicate that the surface reaction is the ratecontrolling step in the dissolution process and not the mass transfer.12The synthesis of monodispersed particles of slightly soluble inorganic materials, such as barium sulfate,13,14metal oxides15and phosphate salts,16–18by homogeneous precipitation using the dissociation or decomposition of the metal–EDTA complexes has been reported. Preparation of powder by hydrothermal synthesis uses the metal–aminocarboxylate complex as a precursor. This method can be used to control the morphology, and even occurs at low temperatures. Although the mechanism by which aminocarboxylates regulate the morphology of the powder is not clear, they appear to contribute to the supply of metal ions by the dissociation of metal complex. They also affect the flocculation control of primary particles and the adsorption or binding to specific particle surfaces.In this study, barium sulfate was synthesized by a hydrothermal method using BaII–aminocarboxylic acid complex as a precursor. The effect of the chelating agent on the morphology of barium sulfate was examined. The effect of the type of aminocarboxylic acid on the morphology of barium sulfate is discussed from two perspectives: (1) dissociation reactions involving the BaII–aminocarboxylic acid complex that influences the supply of Ba2+ions and (2) adsorption reactions involving the aminocarboxylic acids that affect the growth and flocculation of the BaSO4crystal.
ISSN:1466-8033
DOI:10.1039/b009571k
出版商:RSC
年代:2000
数据来源: RSC