电化学法制备镁盐晶须及第一性原理研究

发布时间：2018-04-23 18:12

  本文选题：阳极氧化 + 晶须　； 参考：《太原理工大学》2011年硕士论文

【摘要】：一维材料是本世纪高新技术领域的一种新型功能材料,是材料领域中非常重要的部分。其中镁盐晶须有优良的耐高温、耐腐蚀性能、电绝缘、高强度、高硬度等特性,作为塑料、金属、陶瓷等材料的增强剂时显示出极佳的物理、化学性能和优异的机械性能,在生产和技术领域有着广阔的应用前景。因此,晶须的制备具有重要的学术意义和应用价值。 本文采用常温常压的电化学方法成功制备了硼酸镁晶须和硅酸镁晶须,克服了传统制备方法存在的高温高压高能耗的不足,主要研究内容为：①采用电化学阳极直接氧化法制备硼酸镁晶须,首先利用SEM、XRD、EDS、IR和TG-DTA等手段对晶须的表面形貌、结构以及元素组成等进行了表征,其次采用三电极体系测定了反应的循环伏安曲线,研究了其电化学过程,同时考察了温度、毒化剂和电流密度等因素的影响,并探讨了其毒化机理；②采用电化学阳极直接氧化法制备硅酸镁晶须,利用SEM、XRD、EDS、IR和TG-DTA等手段对其表面形貌、结构和元素组成等进行了分析；③采用基于密度泛函理论的第一性原理对晶须微观结构进行了计算。结果表明： 1、通过SEM观察可得,硼酸镁晶须长为6～8μm,直径约为500 nm,长径比为12:1～16:1;XRD、EDS和IR分析可知其为硼酸镁(Mg2B2O5)晶须；由TG-DTA分析可得硼酸镁晶须中不含有结晶水；从循环伏安图看出,阳极在2.0 V附近发生氧化反应,Mg2+在阴极没有发生还原反应；制备硼酸镁晶须的最佳条件为：0.20mol/L毒化剂,电流密度为0.06A/cm2,温度为20℃左右,乙醇和水体积比为1:3,通电时间1h,硼酸的浓度为0.44mol/L,氯化钠的浓度为0.20mol/L,平均电流效率约为35%。 2、通过SEM分析可知硅酸镁晶须长度为5-6μm,直径约为500 nm,长径比为10:1～12:1,符合晶须的定义；其XRD谱分析表明出现正交晶系结构的硅酸镁的特征峰,还含有少量的氧化镁,其衍射峰强度大,说明结晶良好；EDS和IR分析可得其构成为Mg2SiO4;由TG可知该产品不含结晶水；制备硅酸晶须的最佳电流密度为0.6A/cm2。 3、通过第一性原理计算可得,Mg2B2O5和Mg2SiO4原胞的带隙宽度分别为4.9eV和5.0eV,均接近于绝缘体。Mg2B2O5晶胞价带主要为氧的2p、镁的3s和硼的2s、2p态的贡献,导带主要是硼的2p态的贡献。Mg2SiO4原胞价带主要由氧的2p、镁的3s态和硅的3s、3p态的贡献,导带主要由硅的3p和少量镁的3s态的贡献。Mg2B2O5和Mg2SiO4原胞结合能分别为-1444.1990eV和-1646.0148eV,其中Mg2SiO4原胞稳定性较大。 总之,本文采用电化学阳极直接氧化法成功地制备出了硼酸镁晶须和硅酸镁晶须,该方法在国内外还未见报道(已申请两项发明专利)。该研究将为其它晶须的制备提供一条新的途径。
[Abstract]:One-dimensional material is a new functional material in the field of high-tech in this century, and it is a very important part in the field of material. Magnesium salt whiskers have excellent properties of high temperature resistance, corrosion resistance, electrical insulation, high strength, high hardness and so on. As reinforcements for plastics, metals and ceramics, magnesium whiskers show excellent physical and chemical properties and excellent mechanical properties. It has a broad application prospect in the field of production and technology. Therefore, the preparation of whiskers has important academic significance and application value. In this paper, magnesium borate whisker and magnesium silicate whisker were successfully prepared by electrochemical method at room temperature and atmospheric pressure. The main content of this study is to prepare magnesium borate whiskers by electrochemical anodic direct oxidation. Firstly, the surface morphology, structure and elemental composition of the whiskers were characterized by SEM-XRDX EDSI-IR and TG-DTA. Secondly, the cyclic voltammetry curve of the reaction was measured by three-electrode system, the electrochemical process was studied, and the effects of temperature, toxicant and current density were investigated, and the toxic mechanism was discussed. (2) magnesium silicate whiskers were prepared by electrochemical anodic direct oxidation method. The surface morphology, structure and elemental composition of the whiskers were analyzed by means of SEMXRDX EDS-IR and TG-DTA. (3) the microstructure of whisker was calculated by using the first principle based on density functional theory (DFT). The results show that: 1. By SEM observation, magnesium borate whisker is 6 8 渭 m in length, 500 nm in diameter, and aspect ratio is 12: 1 1: 1 X RDX DS and IR analysis shows that it is magnesium borate mg 2B 2O 5) whisker; magnesium borate whisker does not contain crystal water by TG-DTA analysis; the cyclic voltammetry shows that there is no crystal water in magnesium borate whisker. The anodic oxidation reaction happened near 2.0 V and Mg2 did not deoxidize at the cathode, the optimum conditions for preparing magnesium borate whisker were as follows: 0.20mol / L toxic agent, current density 0.06A / cm ~ 2 and temperature about 20 鈩，

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