Research On Crystal Morphology Control And Growth Mechanism Of Basic Magnesium Carbonate

The morphology and properties of materials are closely related,so there has been the research topic in controlled preparation of structure with desirable morphology and size.Basic magnesium carbonate?Mg₅?CO₃?₄?OH?₂.4H₂O?is a kind of important magnesium inorganic material.With higher decomposition temperature,excellent dispersion and fluidity,it could be used as flame retardant and strengthening agent to fill in polymer materials.Mg₅?CO₃?₄?OH?₂.4H₂O materials have been widely used in lots of industrial fields,such as pharmaceuticals,food industry and rubber industry.Using magnesium chloride hexahydrate?MgCl₂.6H₂O?as magnesium source,urea?CO?NH₂?₂?as precipitant,basic magnesium carbonate plate-like whiskers were obtained successfully by the template-mediated/homogeneous precipitation method.While flower-like basic magnesium carbonate microspheres with porous microstructure were prepared using MgCl₂.6H₂O and ammonium bicarbonate?NH₄HCO₃?as raw materials.The changes of crystal structure and crystal morphology were studied systematically in this paper.Phase and morphology of the samples in different experiment condition were characterized by X-ray diffraction?XRD?,scanning electron microscopy?SEM?,fourier infrared spectroscopy?FT-IR?,and atomic force microscopy?AFM?respectively.Furthermore,the growth mechanism of the basic magnesium carbonate was discussed preliminary.The contents and results are mainly as follows:?1?Using MgCl₂.6H₂O and CO?NH₂?₂ as raw materials,organic template agent as sorbic alcohol,basic magnesium carbonate plate-like whiskers were obtained successfully at 85?by the template-mediated/homogeneous precipitation method.And the average length to diameter ratio of whiskers with single phase was greater than 26.According to the phase analysis and group analysis,the crystal structure of the basic magnesium carbonate could be inferred and drawn.?2?The investigations on the organic template mediated mechanism and the homogeneous precipitation mechanism show that the template affects the crystal morphology by changing surface energy and growth rate of different crystal plane,to realize the one-dimensional orientation growth of the crystal.Through the two-dimensional nucleation-step growth mechanism,the growth of basic magnesium carbonate plate-like whiskers could be explained in the homogeneous system with organic template agent.?3?The magnesium carbonate trihydrate?MgCO₃.3H₂O?whiskers as intermediate phase and flower-like basic magnesium carbonate?Mg₅?CO₃?₄?OH?₂.4H₂O?materials with porous microstructure were obtained successfully using MgCl₂.6H₂O and NH₄HCO₃ as raw materials.Through the analysis of the morphology of whisker,MgCO₃.3H₂O whiskers growth is in line with“steps growth”mechanism.?4?The influence of different reaction time on the the crystal phase and morphology were discussed.When reaction time was less than 6 hours,the sample was basically MgCO₃.3H₂O whiskers.In addition,with the extension of time,aspect ratio of MgCO₃.3H₂O whiskers increased first and then decreased,and the surface became more rough.In 7 to 9 hours,flower-like basic magnesium carbonate microspheres began to appear.And the proportion of whiskers among all products was reduced.Eventually all samples became into flower-like microspheres.?5?The effects of different reaction temperature on the the crystal phase and morphology were also investigated.The MgCO₃.3H₂O whiskers could be obtained in30⁵0?.And as the reaction temperature rose,length to diameter ratio of MgCO₃.3H₂O whiskers increased first and then decreased.When reaction occurred on 60⁸0?of temperature,there were flower-like lamellae crystal on the head of whisker.When reaction system was on the relatively high temperature,unstable magnesium carbonate trihydrate whiskers began to dissolve.More stable flower-like basic magnesium carbonate microspheres with porous structure became to appear.When temperature varied from 80?to 95?,all products were the flower-like Mg₅?CO₃?₄?OH?₂.4H₂O microspheres.Moreover,with the temperature going up,the pore size was smaller gradually.?6?It was analysed about the formation mechanism of porous microstructure.The gathering and growth of the CO₂ bubbles which could to be seen as a novel template led to generate the porous structure of Mg₅?CO₃?₄?OH?₂.4H₂O in the transformation process.From MgCO₃.3H₂O whiskers growing into the flower-like basic magnesium carbonate microspheres,this formation process was demonstrated by building“the bubble template growth”model.