熔盐法制备氧化镁及含镁尖晶石粉体的研究

发布时间：2018-05-04 02:25

本文选题：熔盐法 + 氧化镁粉体　；参考：《武汉科技大学》2010年博士论文

【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。
[Abstract]:The synthetic method of molten salt synthesis is an inorganic material synthesis method developed in modern times. It uses one or several kinds of low melting point salts as reaction medium to complete synthesis reaction in high temperature molten salt, then dissolve salt with suitable solvent, filter and wash the synthetic products. Because of the simple process and low cost of the molten salt synthesis process. Low temperature, short heat preservation time and stable and uniform chemical composition of synthetic products have been widely used in the synthesis of high melting point oxide powder, electronic ceramic powder and other functional powder materials.
In this paper, magnesia powder was synthesized in LiCl molten salt medium. The influence of the variety of raw materials, reaction temperature and holding time, the relative content of molten salt on the properties of Magnesium Oxide products was studied. It was found that in molten salt medium, magnesia powder was synthesized by using MgCl2, CaCO3 materials, Mg2+ ions and Ca2+ ions were replaced, and magnesium carbonate was formed. The intermediate product has a higher degree of crystallization than the natural magnesite. The reaction series of the decomposition reaction is close to 1 and the average apparent activation energy is Ea=221.23kJ/mol. The size distribution of magnesia powders prepared by MgCl2, CaCO3 raw materials and MgCl2, CaO raw materials is more uniform, mainly composed of particles similar to spherical morphology, using MgCl2 6H2O, CaCO3 raw materials and MgCl2, MgCa (CO3). The morphology of magnesia powder prepared by 2 raw materials is different and the size distribution is uneven. Among the four kinds of raw materials, MgCl2. 6H2O and CaCO3 are relatively good in the activity of Magnesium Oxide. The increase of the reaction temperature and the prolongation of the heat preservation time are beneficial to the growth of the Magnesium Oxide crystal, the smaller the size of the Magnesium Oxide product, the increase of the true density, the decrease of the activity, and the increase of the LiCl. The addition of Magnesium Oxide is beneficial to the growth of Magnesium Oxide crystals, the crystallinity of Magnesium Oxide products increases, the average particle size increases, and the activity decreases.
The Magnesium Oxide hydrolysate in the molten salt medium was prepared by adding different surface active agents to control the morphology of magnesium hydroxide precursor, thus preparing different morphologies of magnesia powder. The effect of different morphologies of magnesia powder on the properties of silicon steel body was studied. The results showed that after the heat treatment of MgCl2. 6H2O, CaCO3, LiCl reaction system, PEG solution was used. Magnesium hydroxide was soaked in EDTA-PEG solution, and magnesium hydroxide was soaked in tetrahedron. The fibrous magnesium hydroxide was decomposed to the chain shape Magnesium Oxide. The tetrahedral magnesium hydroxide was decomposed to Magnesium Oxide to retain the tetrahedral morphology, and the MgCl2, CaCO3, LiCl reaction system was soaked in PEG solution after heat treatment. Magnesium hydroxide is soaked in EDTA-PEG solution, and the sheet shape magnesium hydroxide is obtained. The fibrous magnesium hydroxide is decomposed into a porous Magnesium Oxide. The sheet shape magnesium hydroxide is decomposed to Magnesium Oxide and remains flaky. Four different morphologies of magnesia powder are sprayed on the surface of the silicon steel body. After annealing, the magnesium hydroxide has been annealed. The microstructure of the coating of silicon steel body and the magnetic properties of silicon steel body have been detected. It is found that the quality of the porous silicon steel body is better than that of the porous bar shape Magnesium Oxide, and the quality of the silicon steel body with the tetrahedral morphology of Magnesium Oxide is poor.
Magnesium chromium spinel and magnesium aluminum spinel were synthesized on the basis of the preparation of Magnesium Oxide by molten salt method. The effects of raw material and molten salt on the formation and growth of magnesium chromium spinel and magnesia spinel were studied. NaCl-KCl composite molten salt is used as reaction medium, and MgCl2, MgCl2, 6H20 and CaCO3 are used to react with MgO as raw materials to react with Cr2O3. The synthesized magnesium chromium spinel crystal is well developed. The increase of reaction temperature and prolongation of heat preservation time are beneficial to the growth of magnesium chromium spinel crystal, and the crystallinity of magnesia chromium spinel products increases, and the true density is true. The morphology of magnesium aluminum spinel products is related to the morphology of alumina, and the effect of the variety of molten salt on the products of magnesia aluminum spinel is mainly achieved by the difference of the solubility of the reactants in different molten salt medium. The increase of reaction temperature and the prolongation of the heat preservation time are beneficial to the growth of magnesium aluminum spinel crystal. The crystallinity of Al spinel increased, the true density increased, and the average particle size increased.
Compared with the single molten salt of NaCl and Na2C03, the NaCl-KCl compound molten salt is more beneficial to the formation of magnesium chromium spinel and magnesium aluminum spinel crystals and the synthesis of magnesium chromium spinel and magnesia spinel in the.NaCl-KCl compound molten salt medium. The mechanism of "template growth" and the "dissolution precipitation" mechanism coexist at the same time. However, the synthesis of magnesium chromium spinel crystals has been found in the synthesis of magnesium chromium spinel crystals. The mechanism of "dissolution precipitation" plays a dominant role in the process. In the process of synthesizing mg Al spinel crystal, the "template growth" mechanism plays a major role.

【学位授予单位】：武汉科技大学
【学位级别】：博士
【学位授予年份】：2010
【分类号】：TB383.3

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