【作者】 陈浩；

【导师】 王玺堂；

【作者基本信息】 武汉科技大学 ， 材料学， 2010， 博士

【摘要】 熔盐合成法是近代发展起来的一种无机材料合成方法。它采用一种或几种低熔点的盐类作为反应介质,在高温熔融盐中完成合成反应,然后采用合适的溶剂将盐类溶解,经过滤、洗涤得到合成产物。由于熔盐合成法具有工艺简单、成本低廉、合成温度低、保温时间短、合成产物的化学成分稳定均匀等优点,因而在合成高熔点氧化物粉体和电子陶瓷粉体及其它功能粉体材料等领域广泛应用。本论文在LiCl熔盐介质中合成了氧化镁粉体,研究了原料种类、反应温度和保温时间、熔盐的相对含量对氧化镁产物性能的影响,研究发现：熔盐介质中,采用MgCl2、CaCO3原料合成氧化镁粉体,Mg2+离子与Ca2+离子发生置换反应,生成碳酸镁等中间产物,其结晶程度比天然菱镁矿高,分解反应的反应级数接近1,平均表观活化能Ea=221.23kJ/mol;采用MgCl2、CaCO3原料和MgCl2、CaO原料制备的氧化镁粉体,大小分布较均匀,主要由近似球状形貌的颗粒组成,采用MgCl2·6H2O、CaCO3原料和MgCl2、MgCa(CO3)2原料制备的氧化镁粉体形貌不一,大小分布不均匀,四种原料中,MgCl2·6H2O、CaCO3原料制备的氧化镁活性相对较好；反应温度的升高和保温时间的延长有利于氧化镁晶体的生长,氧化镁产物晶胞体积变小,真密度增大,活性降低；增大LiCl的加入量有利于氧化镁晶体的生长,氧化镁产物的结晶度增大,平均粒径增大,活性降低。将熔盐介质中合成的氧化镁水解,通过加入不同表面活性剂控制氢氧化镁前驱体的形貌,从而制备不同形貌的氧化镁粉体,研究了不同形貌氧化镁粉体对硅钢坯体性能的影响,结果表明：MgCl2·6H2O、CaCO3、LiCl反应体系热处理后,经PEG溶液浸泡得到纤维状氢氧化镁,经EDTA-PEG溶液浸泡得到四面体形貌氢氧化镁,纤维状的氢氧化镁分解得到链状形貌氧化镁,四面体形貌的氢氧化镁分解为氧化镁后仍保持四面体形貌；MgCl2、CaCO3、LiCl反应体系热处理后,经PEG溶液浸泡得到纤维状氢氧化镁,经EDTA-PEG溶液浸泡,得到片状形貌氢氧化镁,纤维状的氢氧化镁分解得到多孔棒状形貌氧化镁,片状形貌氢氧化镁分解为氧化镁后仍保持片状形貌。分别将四种不同形貌的氧化镁粉体喷涂于硅钢坯体表面,经退火处理后,通过对硅钢坯体涂层的显微结构和硅钢坯体磁性性能检测发现,多孔棒状形貌氧化镁喷涂的硅钢坯体质量较好,四面体形貌氧化镁喷涂的硅钢坯体质量较差。以熔盐法制备氧化镁为基础,在熔盐介质中合成了镁铬尖晶石和镁铝尖晶石,研究了原料和熔盐种类、反应温度和保温时间对镁铬尖晶石和镁铝尖晶石形成与生长的影响。研究发现：原料和熔盐种类对镁铬尖晶石形成与生长影响显著,选用NaCl-KCl复合熔盐作为反应介质,分别采用MgCl2、MgCl2·6H20和CaCO3原料替代MgO原料与Cr2O3反应,所合成的镁铬尖晶石晶体发育良好；反应温度的升高和保温时间的延长有利于镁铬尖晶石晶体的生长,镁铬尖晶石产物结晶程度增大,真密度增大,平均粒径增大。镁铝尖晶石产物的形貌则与氧化铝的形貌有关,熔盐种类对镁铝尖晶石产物的影响主要通过反应物在不同熔盐介质中溶解度的不同来实现；反应温度的升高和保温时间的延长有利于镁铝尖晶石晶体的生长,镁铝尖晶石产物结晶程度增大,真密度增大,平均粒径变大。与NaCl和Na2C03单一熔盐相比,NaCl-KCl复合熔盐更有利于镁铬尖晶石和镁铝尖晶石晶体的形成与生长。NaCl-KCl复合熔盐介质中合成镁铬尖晶石和镁铝尖晶石,“模板生长”机理和“溶解-析出”机理同时并存,然而在合成镁铬尖晶石晶体过程中“溶解-析出”机理占主导地位,合成镁铝尖晶石晶体过程中,“模板生长”机理起主要作用。更多还原

【Abstract】 Molten salt method is recently developed as a novel synthetic method for inorganic materials. Based on one or more low melting point salts as a reaction medium, which can be dissolved by the appropriate solvent, the reaction is easily carried out via the media and pure product can be obtained after filtering and washing. Due the advantages of the simple process, low cost and synthetic temperature, short reaction time and high stability in chemical compositions, molten salt method has been widely applied in different fields, such as in the synthesis of high melting point oxide powders, electronic ceramic powders and other functional powder materials.Magnesium oxide powders were synthesized in LiCl molten salt media. The effects of different raw materials, such as reaction temperature, holding time and the relative content of molten salt on the performances of the products have been studied. The results indicated that Ca2+ ions were replaced by Mg2+ ions and produced magnesium carbonate and other intermediate products with MgCl2 and CaCO3 raw materials. Compared to natural magnesite, the as-prepared magnesium carbonate had a higher degree of crystallinity and its order of decomposition closed to 1, and the average apparent activation energy, Ea, is 221.23 kJ/mol. Using MgCl2 and CaCO3, and MgCl2 and CaO as raw materials respectively, the prepared magnesium oxides were characterized with a uniform size distribution and a near sphere-like morphology. Whereas using MgCl2·6H2O and CaCO3, and MgCl2 and MgCa(CO3)2 as raw materials, the both prepared products had the mixed morphologies and uneven size distributions, in which the former product has a relatively better reactive activity, a higher reaction temperature and longer holding time were favorable for the growth of magnesium oxide crystals, resulting in the decrease of crystal cell volume and reactive activity, and the increase of true density. The increase of LiCl addition content was favorable for the growth of magnesium oxide crystals, leading to the increase of crystalinity degree and mean particle size and the decrease of reactive activity.By adding different surfactants, the morphologies of the magnesium hydroxide are controlled to yield the corresponding morphologies of MgO powders. As for the MgCl2·6H2O, CaCO3 and LiCl reaction system, fibrous magnesium hydroxide was produced after the heat treatment and soaking of the PEG solution and it can be decomposed to form chain-like morphology of magnesium oxide. Accordingly, tetrahedral shape magnesium hydroxide by EDTA-PEG magnesium hydroxide can produce tetrahedron magnesium oxide. Seemly, as for MgCl2, CaCO3 and LiCl reaction system, fiber-like and flake-like magnesium hydroxide can be respectively obtained under the soaking of PEG and EDTA-PEG solutions, which can be transformed into porous rod and flake magnesium oxide, accordingly. The four different morphologic magnesium oxide powers were spayed on the surfaces of Si-steel billet respectively. The results of the microstructures and magnetic examinations showed that Si-steel billets were of high performance coated by porous rod-like Magnesium oxide powders, while they were of poor performance by tetrahedron magnesium oxide.Furthermore, MgCr2O4 and MgAl2O4 spinel powders were synthesized in molten salt media. The effects of different raw materials, salts, heating temperature and holding time on the performances of the final products have been studied respectively. It is found that both raw materials and salts played an important role in the formation of MgCr2O4 and its crystal growth. They were well-developed by using MgCl2, MgCl2·6H2O and CaCO3 as raw materials in NaCl-KCl mixture molten salt. Further research has found that a higher reaction temperature and longer holding time were favorable for the growth of MgCr2O4 spinel crystals, resulting in the increase of MgCr2O4 spinel crystallinity, true density and average particle size. The morphology of MgAl2O4 spinel powder was closely related to alumina materials. A higher reaction temperature and holding time favored the growth of MgAl2O4 spinel crystals, resulting in the increase of its crystallinity, true density and average particle size.Compared with single NaCl and single Na2CO3 salt, NaCl-KCl mixture salts were more favorable for the formation and growth of MgCr2O4 and MgAl2O4 spinel crystals. The two mechanisms, "dissolution-precipitation" and "template formation", were involved in MgCr2O4 or MgAl2O4 spinel formation. "dissolution-precipitation" mechanism acted a leading role in the course of MgCr2O4 synthesis while "template formation" was dominant in MgAl2O4 formation.更多还原