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Basic Research On Synthesis And Application Performance Of Micro-crystal Of Mg-Al Layered Double Hydroxides

Posted on:2006-10-19Degree:DoctorType:Dissertation
Country:ChinaCandidate:G J GouFull Text:PDF
GTID:1101360155468208Subject:Inorganic Chemistry
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Clays are among the most common minerals on the Earth's surface and indispensable to our existence. Generally speaking, clays can be divided into two broad groups: cationic clays and anionic clays. The anionic clays are natural or synthetic layered double hydroxides (LDH) with interlayer spaces containing exchangeable anions. LDH can be structurally characterized as containing brucite-like (magnesium hydroxide - like) layers in which some divalent metal ions have been substituted by trivalent ions to form positive charge sheets. The positive charges created in the layers are compensated by the presence of hydrated anions between the stacked sheets. The anionic clays of LDH are very versatile materials, and have been investigated for applications in four areas: 1) catalysts and catalyst precursors, 2) ion exchangers and absorbers, 3) medical applications, and 4) flame retardant and PVC stabilizer.The abundant chloride salt lakes of Qinghai-Xizang plateau can supply a cheap raw material (MgCl2·6H2O) for preparation of LDH-Cl. A fundamental research on synthesis, properties, and application performance of LDH-Cl will be beneficial to the sustainable exploitation of salt lake resources. We have completed a great deal of works on LDH-Cl as the followings.1. In order to study the effect of preparation conditions on composition, structure, and property of LDH-Cl, a series of LDH-Cl samples were prepared under different crystallization patterns, and were characterized with EDS, XRD, FTIR, TEM, TG-DTA, and BET-N2 surface area measurement. Our results demonstrate that the particles of LDH-Cl exhibit different crystal growth habits in different crystallizationcourses; the nanometer micro-crystal of LDH-C1 show different degree of crystallinity under different preparation conditions.2. The coprecipitation mechanism and kinetic characteristics of synthesis LDH-C1 were studied by monitoring and testing the solution concentration, and structural characterization of samples produced from different reaction courses. Our results show that the synthetic reaction of LDH-C1 is controlled by polynuclear layer surface reaction mechanism. The stability of layer structure, and strength of interaction between the layer of LDH and gallery Cl" increases with the reaction courses.3. The dynamics feature of intercalation and assembly of B4Os(OH)42" into LDH-C1" was investigated on the results of monitoring for variation of solution concentration during reaction course, and the results of EDS, IR, XRD, TEM and TG-DTA characterization for the samples produced from different reaction courses. The results testified that the displacement of Cl" accorded with Stumm's kinetic pattern, the intercalation of B4Os(OH)42" was controlled by diffusion course pattern. Our investigation proved that the brucite layer structure and micropore structure feature of precursor remained intact after ionic exchange, but the intercalation of bulky complicated B4Os(OH)42" resulted in volume expansion of unit cell in c axial, decreasing of grain size, increasing of micropore specific surface area, and varying of thermodynamic action.4. Based on a study of the coprecipitation course, unit cell structure, surface property, and thermal stability of different LDH-An" intercalated with different anions such as Cl', NO3', CO32", B4O5(OH)42', and SO42', we suggest that the coprecipitation kinetic character of LDH-A"" is not related to the type of anions, while the structural character of LDH unite cell and the laminar character of LDH particles are evidently effected by the symmetry of An'. The micropore characteristics, adsorbabilities, and thermal stabilities of LDH-A"" are determined to certain extent by the modes of pillar-layer interaction of An".5. In order to study the effect of the anion types, preparation conditions, and surfaction method on the effectiveness of recombination LDH grains intothermoplastic vulcanizate (TPV), we prepared the composite materials ( TPV-LDH) through banburying LDH into TPV, and tested their mechanical properties such as tensile strength and hardness, and combustion characteristic parameters such as oxygen index, vertically burning velocities, and levelly burning velocities. We find that the LDH micro-crystal dispersed homogeneously in TPV can exhibit evident inflame retarding effectiveness without remarkably decreasing machining property of composite materials.
Keywords/Search Tags:LDH, micro-crystal, coprecipitation, composite material, inflaming retard
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