Dolomite Preparation Of Nano-magnesium Hydroxide, And Special Morphology Of Nano-magnesium Oxide

The preparing process and the crystal growth mechanism of nanometer MgO with special shapes and nanometer Mg(OH)₂ flakes processed from dolomites were systematically studied in this article. Rhombus flower like MgO flakes with multi interspaces and coral-twig like, shutter like MgO with high activities were prepared by calcining Mg(OH)₂ powders in different process conditions. The evenly growth hexagon Mg(OH)₂ flakes, the precursor of MgO, could be obtained via twice-acid immersing and ammonia depositing method from dolomites. The process conditions, growth mechanism and shape impact factors were studied in this paper.The best processing condition of max Mg²⁺ extraction rate was: calcine dolomite at 1050℃for 2h; 70℃processed in water for 30 mins; the hydrochloric acid consumption ratio was 2: 1(nHCl/nCa²⁺) in first acid immersing process; the vitriol acid consumption ratio was 1:1 (nH₂SO₄/nMg²⁺); ammonia consumption ration was 4:1(nNH₃/nMg²⁺). The max Mg²⁺ extraction rate was 94.64%, Mg(OH)₂ purity was 99.79% above, MgO purity was 99.73% above, Ca²⁺ content was 0.16% below, all the other impurity content were 0.05% below.The structure, morphology and composition of MgO and its precursor Mg(OH)₂ were characterized by means of XRD, SEM, TEM, HRTEM and FT-IR spectra analysis methods. The results analysis indicated that the Mg(OH)₂ are radial epitaxial growth fine crystal hexagon flakes with 10～20 nm in thickness and 200～600 nm in landscape orientation size. The nanometer flower like magnesia flakes with 10～20 nm in thickness and up to 1μm² in acreage are single crystal with cubic crystal fabric. The distortion of crystal lattice which leads to the variety of the phase difference and the abnormal infrared behavior of nanometer MgO flakes could be observed.The analysis results indicated that the deposition features and the micro shape of Mg(OH)₂ are affected by process conditions.The EDTA, PEG and alcohol molecules are endow with the effect which could improve the interface features and reduce the surfaceζelectric potential and surface energy. The EDTA, PEG improved the uniformity of crystal growth of Mg(OH)₂, and enabled Mg(OH)₂ arrangements to have the certain regularity.Water heating process and low content ammonia could be preferred to the evenly growth of Mg(OH)₂.The form process and the thermal decomposition of nanometer Mg(OH)₂ crystal and the growth mechanism of Mg(OH)₂ and MgO were analyzed with Zetaζelectric potential, DSC-TGA, SEM and FT-IR analysis methods. The crystal growth of Mg(OH)₂ flakes was controlled by the form of max greatly stable energy which could be obtained through the form of hexagon growth element which constituted with 7 Mg-O₆ octahedron. The thermal decomposition process of nanometer Mg(OH)₂ crystal could be two steps, the inflexion temperature was 397℃.In the earlier and middle period of decomposition of Mg(OH)₂, the control step was core forming and after-growth mechanism; when the temperature was higher than 397℃,the control step was diffuse control mechanism. Based on the Gibbs-Wulff theory, when the surface energy was in the scope of best energy steady state and accorded with the energy smallest principle, MgO growth elements will orderly grow along [100] direction by the way of crystal face to face...