【作者】 牛永效；

【导师】 王恩德；

【作者基本信息】 东北大学 ， 矿产普查与勘探， 2010， 博士

【摘要】 水镁石是迄今为止发现的含镁量最高的一种矿物,在世界上分布不广,产出比较稀少,我国具有丰富的水镁石资源。作为一种工业矿物,水镁石在耐火材料、环境保护、建材、陶瓷和核工业等领域得到了广泛应用。但是,由于技术比较落后,目前我国的水镁石的开发利用还处于原矿的出口及生产耐火材料等低附加值产品的初级阶段,这对水镁石资源造成了极大的浪费并限制了水镁石的高效利用。为了避免这种浪费,应将其用于高附加值、具有高技术含量的功能材料的生产与加工上。用水镁石制备环境友好型的氢氧化镁无机阻燃剂受到了广泛的关注,近年来,随着人们环保意识的日益增强,氢氧化镁作为环境友好型的无机阻燃剂,由于其阻燃、抑烟、无毒、热稳定性高等特点,在聚合物、电缆、建筑和装饰材料等领域得到了广泛的应用。氢氧化镁的晶形和粒度对其性能有十分显著的影响,具有优良阻燃性能的氢氧化镁应为纤维状和片状,纯度大于97%,厚度大于80nm,颗粒的平均尺寸为0.5-1μm,(101)极性面的微观应变小于3.0×10-3。但是,以水镁石为原料采用物理法所制得产品的纯度不高、晶形难以控制,严重影响了其阻燃性能。目前,优质氢氧化镁主要是以金属镁和镁盐为原料,采用化学法制备所得,成本较高。因此,利用水镁石资源制备高纯、超细的氢氧化镁对提高我国优势镁资源的市场竞争力具有十分重要的意义。本文以水镁石为原料,通过水热合成和水热处理法制备出了超细、高纯、颗粒均一、分散均匀的具有不同形貌的氢氧化镁颗粒,利用X-射线衍射仪(XRD)和扫描电子显微镜(SEM)对所制得氢氧化镁颗粒的晶相、形貌和颗粒尺寸进行了表征,结合实验结果,对水热条件下晶粒的形成机理进行了研究。本文取得了以下研究成果：(1)通过现场调研和大量的资料分析,研究了辽宁省水镁石矿床形成的地质条件、不同形态水镁石的形成及其矿物学性质,为水镁石的开发利用提供了地质依据。同时,结合辽宁省水镁石资源特点,提出制备定形氢氧化镁晶体的技术方法。(2)采用水热合成法和水热处理法分别制备出了高纯、分散均匀、厚度为80-100nm、直径为200-400nm的六方片状和直径为100-500nm、长度为1-20μm纤维状氢氧化镁。所得产物的特征峰值与氢氧化镁的标准峰值完全一致,没有杂峰出现,(101)晶面的微形变小于3.0×10-3,这表明,所得产物为高端无机阻燃剂。(3)系统研究了搅拌速度、填充度、前驱物浓度、反应温度、反应时间、pH值、氢氧化钾、硫酸根离子、溶剂和表面活性剂等对氢氧化镁晶形的影响。通过计算(001)晶面和(101)晶面的衍射强度比值I001/I101,对比了不同晶面的优先生长方向。(4)研究了晶体的晶形和结晶度与过滤性能的关系,发现六方片状晶体与纤维状晶体相比,具有较好的过滤性能,通过控制晶体的晶形和结晶度可以显著改善其过滤性能。(5)根据大量的实验数据,结合现代物理学、溶液化学和结晶学知识,以“负离子配位多面体模型”为基础,发现晶体的形貌和尺寸由其内部结构和外在生长条件共同决定,晶体生长过程是生长基元在其界面叠加的过程。生长基元在晶体晶面的叠加过程受晶面结构和外在生长条件的共同影响。Mg(OH)64为氢氧化镁晶体的生长基元,根据键价理论模型计算表明,氢氧化镁的理想生长形态为正六边形。Mg(OH)64生长基元在不同晶面的叠加过程受晶面上Mg-O-Mg键桥和位于“三配位”位置OH基团数目的影响。外在生长条件通过影响生长基元的形成和生长基元在晶面的叠加过程来影响晶体的形成。通过理论分析得到了和实验结果相一致的结论。通过本文的工作,可以看出,生长基元模型把晶体生长过程中晶体的结构、外在生长条件和晶体的生长形态紧密的联系起来,具有很强的生命力。本文研究为水镁石制备定形氢氧化镁晶体提供了理论基础和技术方法。更多还原

【Abstract】 Brucite is a high-grade mineral, only few countries have brucite mineral resources, which have been found in China. Brucite has been widely in refractory, environmental protection, building materials, ceramics and nuclear industry, as an industrial mineral. Brucite is mainly used to be exported as a raw material and prepare refractory in China, due to undeveloped technology, which is a great waste and limit high efficiency utilization of brucite. Brucite should be used to prepare high value-added and high technological functional materials to avoid waste.More and more attention has been paid to prepare magnesium hydroxide by brucite. In recent years, Magnesium hydroxide has been widely used in polymers, electric cables, building and decoration materials, as an economic and environment-friendly inorganic flame retardant, due to flame retardency, smoke-repressive property, low or zero evolution of toxic or hazardous byproducts and high decomposition temperature. The morphology and particles size of crystals play an important role in flame retardency of Mg(OH)2.It was reported that preferred flame retardant features Mg(OH)2 purity>97%, particles thickness>80nm, average particle size at 0.5-1μm, the microstain of (101) polar plane is small. However, products prepared with brucite as raw materials by physical method have bad flame retardency, due to low purity and irregular morphology. Good magnesium hydroxide was mainly prepared by chemical methods, with magnesium and magnesium salts as raw materials, which is high cost. So, preparation of magnesium hydroxide by brucite can remarkably improve competitiveness of magnesium resource of China.Superfine high pure, different morphological Mg(OH)2 particles with uniform particle size and good dispersion were prepared by hydrothermal synthesis and treatment with brucite as raw materials in this paper. The crystal phase, morphology and particles size of the Mg(OH)2 particles as prepared were characterized with X-ray(XRD) and scanning electron microscopy(SEM). Mechanistic interpretation of crystal growth was postulated based on experiment result. Conclusions can be drawn as follow:(1)Geological conditions of brucite deposit in Liaoning Province, formation of different morphological brucite and mineralogical characterization were researched through field investigation and data analysis, which provide geological proof for utilization of brucite. Technological methods of preparing form stable magnesium hydroxide were presented based on characterization of brucite resources in Liaoning Province.(2)The high pure Mg(OH)2 crystals of good dispersion were prepared by hydrothermal synthesis and hydrothermal treatment, which exhibited hexagonal lamellar morphology with thickness of 80-100nm and diameter of 200-400nm and fibrous morphology of diameter of 100-500nm and lengths of 1-20μm. All the diffractive peaks of each sample were in agreement with the standard data, no peaks arising from impurities were observed, the microstain of (101)polar plane<3.0×10-3, which indicated the obtained Mg(OH)2 particles were preferred inorganic flame retardant.(3)The influence of speed of stirring, degree of filling, precursor concentration, time, temperature, pH values, KOH, SO42-, solvent and surfactant on Mg(OH)2 particles were systemically researched. The preferential orientations of different crystal facet were estimated by calculating I001/I101.(4)The relationship of filtration efficiencies and crystal morphology and crystallinity was discussed. The results indicated that hexagonal lamellar morphological crystals had better filtration efficiencies than whiskers, which indicated controlling crystal morphology and crystallinity of Mg(OH)2 could satisfy filtration efficiency.(5)Based on the experimental data, started from knowledge of modern physics, solution chemistry and crystallography, according to the theoretical model of anionic coordination polyhedron growth units, the growth mechanism of Mg(OH)2 crystals under hydrothermal conditions were investigated. It concluded that the final morphology of a crystal was dependent on the intrinsic crystal structure and external growth conditions, growth units connected to crystal facet determined the process of crystal growth, which was affected by crystal structures and external growth conditions.Mg(OH)64- is the basic growth unit of Mg(OH)2 crystals. The intrinsic crystal structure make Mg(OH)2 be in favor of formation of hexagonal lamellar crystals, according to bond valence model. The process of Mg(OH)64- growth units connected to crystal facet is determinated by the number of Mg-O-Mg and OH groups at the three-centered bringing position.The formation of growth units and process of growth units connected to facet are affected with external growth conditions, which play an important role on crystal growth.Theoretical analysis is in agreement with experimental result. The work of this paper shows that growth unit connects the crystal structure, external growth conditions and growth morphology together for a better understanding of intrinsic relationships between them. Therefore, growth unit model is correct and thus is powerful.This study provides theoretic basis and technological method for preparation of form stable magnesium hydroxide crystals by brucite.更多还原