| Materials, which have become the core of advances in modern science and technology, are imposing significant influences on the economy of every country. For both the US and Japan, the costs by rupture, weariness and corrosion of materials are over 200 billion dollars per year.'In the field of materials there is no other material like magnesium showing such remarkable inversion between potential and reality', especially the contrast between exploitation and resource quality of magnesium in the salt lakes of China. Materials whose microscopic images appear to be morphologically mesoscopic are micron or nanoscale powders in a macroscopic view. For most of these materials, the microscopic morphology or bonding form among the atoms are still uncertain. The research focused on the microscale magnesium materials.The hydrothermal preparation of fibrous basic magnesium sulfate as well as its thermal decomposition has been intensively studied in this paper. The thermal decomposition procedure of fibrous 513MOS was discussed based on the combination of its thermal analysis patterns and the temperature programmed XRD patterns. The high-resolution micrographs of the final product of thermal decomposition of fibrous 513MOS proved that the obtained fibrous MgO was not of single crystals, thus could not be whisker. After the hydrothermal reaction completed, the products would be different under different conditions of lowering temperature. Further study indicated that the initial product should be 512MOS, whereas 513MOS was converted from 512MOS during temperature lowering procedure. Meanwhile, zeolite water was found in 513MOS. The IR spectra of the products during thermal decomposition of fibrous 513MOS exhibited persistent existence of hydrogen radicals up to 1100℃.Through systematical analysis with the literature, it was considered as a common feature of Mg(OH)2 and its derivatives. In view of the problem that the preparation of MgO by thermal decomposition of precursor MOS entails the release of corrosive gases, a tentative revised reaction procedure that obtaining MgO from Mg(OH)2 prepared from MOS and bases was proposed and corresponding experiments were carried out, but theresults were not much satisfactory.It was discovered that, even if fibrous magnesium materials undergo a non-crystal stage before growing to crystals during heat treatments, the product MgO could still retain the same fibrous morphology as the original species. The key is how to manipulating the operating conditions. Therefore, the'in-situ-conversion'crystallization mechanism was introduced into thermal treating processes and extended for treating mesoscale materials. Thus, a universal method for preparing mesoscale MgO materials was proposed involving aforehand precursor decomposition followed by"in-situ-conversion"crystallization. This was confirmed by experiments for preparing MgO materials of different morphological appearances. SEM images showed that the MgO prepared were fibrous, lamellar, lump and porous materials, quite corresponding to the prepared carbonate precursors. Environmental efficiency were fully considered in the experimental designs: the precursor of lamellar MgO was Mg(OH)2·4MgCO3·4H2O, whereas that of lump MgO was artificially synthesized magnesite.Currently, many repetitive and unsystematic studies have been done about basic magnesium compounds. Based on sufficient analytical comparisons, the author proposed that these compounds could be attributed as derivatives of Mg(OH)2. Firstly, a systematic denomination method and the logogram rules for Mg(OH)2 derivatives was presented. Further, a homologous hypothesis was suggested utilizing some basic principles, thus establishing the theoretical foundation for studying Mg(OH)2 and its derivatives. Finally, possible structures were described for typical one-dimensional fibrous compounds, namely, 318MOCl, 518MOCl, 512MOS and 513MOS.
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