铬硼化合物的高温高压制备及物性研究

发布时间：2018-02-24 08:05

本文关键词： 铬硼化合物硬质材料维氏硬度高温高压多功能材料　出处：《吉林大学》2017年硕士论文　论文类型：学位论文

【摘要】：过渡金属具有较高的价电子密度,具有极强的抵抗体积压缩的能力,但是由于抗剪切能力不强,导致硬度值较低,在过渡金属当中引入方向性极强的硼-硼共价键,其所形成的化合物可具有极强的抵抗体积形变能力与较高的抗剪切形变能力,是一种潜在的超硬材料。过渡金属硼化物以其较高的硬度、强抗氧化性、抗磨损性、化学惰性、导电和导热等多种优良性能已经广泛应用于生产生活中。本论文通过高温高压合成系统研究了几种铬硼化合物的制备,并且对铬硼化合物的结构、硬度、磁性、抗氧化性进行了深入的研究,得到了以下结果:通过高温高压的方法探索了不同配比的铬硼化合物的合成条件,在5.0 GPa、15 min、不同的温度、不同摩尔比的条件下成功合成出了高质量的Cr B、Cr_3B_4和Cr B_2多晶样品。对Cr B、Cr_3B_4和Cr B_2样品的X射线衍射结果进行了Rietveld精修。通过对合成块体多晶样品的密度、扫描、抗氧化性、硬度、磁性等物性表征,发现随着硼浓度的升高,铬硼化合物中的硼原子亚结构依次经历了以下的变化:Cr B晶体中的“Z”字形链→Cr_3B_4晶体中的聚合硼“Z”字形双链→Cr B_2晶体中的类石墨烯状硼层结构→Cr B4晶体中的三维笼状结构。硬度测试结果表明随着硼原子骨架引入铬金属骨架当中,铬硼化合物的硬度值相比铬金属得到了极大的提升,达到了硬质材料的标准。随着硼浓度的提升,铬硼化物的硬度呈现先升高、后降低、再升高的变化规律,从而证明过渡金属轻元素化合物的硬度值除与轻元素浓度有关外,还与轻元素所构成的亚结构有关。磁性测试结果表明随着硼原子骨架引入铬金属骨架当中,由于硼原子亚结构对铬金属原子间的扩展,使得Cr B、Cr_3B_4和Cr B_2的磁性发生了一定的变化。其分别经历了顺磁性、超顺磁性、反铁磁性、顺磁性的变化。热重-差热测试表明Cr B、Cr_3B_4和Cr B_2的抗氧化能力要比金刚石及工业中广泛应用的硬质材料碳化钨等强许多,达到了1000℃以上。利用高压原位同步辐射的测量方法对Cr_3B_4的晶体结构变化进行了研究。分析了Cr_3B_4晶胞的抗压缩性、晶格常数轴向的压缩情况。我们发现正交结构的Cr_3B_4晶体结构在压力达到25 GPa左右时,其晶体结构依然保持稳定,并没有发生结构相变,说明该结构具有强稳定性。正交结构Cr_3B_4晶体结构当中的聚合“Z”字形链具有极强的共价性,所以Cr_3B_4在c轴方向具有强抗压缩能力。通过与常见的硬质(超硬)材料的抗压缩性对比发现,Cr_3B_4较低的体弹性模量导致其硬度值并没有达到超硬材料的标准,但是由于其中加入了强共价性的聚合“Z”字形链,导致其硬度相对于铬金属有较大的提高。
[Abstract]:Transition metals have high valence electron density and strong resistance to volume compression. However, due to the low shear resistance, the hardness of transition metals is lower, so the highly directional boron-boron covalent bond is introduced into the transition metals. The resulting compounds have a strong resistance to volume deformation and high shear deformation resistance, and are potential superhard materials. Transition metal boride is characterized by its high hardness, strong oxidation resistance, wear resistance and chemical inertia. Many excellent properties, such as conductive and thermal conductivity, have been widely used in production and life. In this paper, the preparation of several kinds of chromium-boron compounds has been studied by high-temperature and high-pressure synthesis system, and the structure, hardness, magnetic properties of chromium-boron compounds have been studied. The oxidation resistance was studied in depth. The following results were obtained: the synthesis conditions of different ratios of chromium and boron compounds were explored by high temperature and high pressure method, at 5. 0 GPA for 15 min, at different temperatures, High quality polycrystalline samples of CrBX Cr3B4 and CrB2 have been successfully synthesized under different molar ratios. The X-ray diffraction results of CrBX Cr3B4 and CrBST2 samples have been refined by Rietveld. The density, scanning and oxidation resistance of the synthesized bulk polycrystalline samples have been studied. Hardness, magnetism and other physical properties were characterized. It was found that with the increase of boron concentration, the substructure of boron atoms in chromium-boron compounds underwent the following changes in turn: "Z" zigzag chain in the crystal of "Cr B" 鈫抁igzag double chains of Polyboron "Z" in Cr_3B_4 crystals. 鈫扴tructure of graphene like boron layer in Cr BZ _ 2 crystal. 鈫扵he hardness test results show that with the introduction of the boron atomic skeleton into the chromium metal skeleton, the hardness of the chromium-boron compounds is greatly improved than that of the chromium metal. With the increase of boron concentration, the hardness of chromium boride increases first, then decreases, and then increases. It is proved that the hardness of transition metal light element compounds is related to the concentration of light elements. The magnetic test results show that with the introduction of the boron atomic skeleton into the chromium metal skeleton, the boron atomic substructure extends to the chromium metal atom. The magnetic properties of CrBX and CrB2 have changed to some extent. They have undergone paramagnetism, superparamagnetism and antiferromagnetism, respectively. The change of paramagnetism. Thermogravimetry and differential thermal analysis showed that the oxidation resistance of Cr BX CrS 3B4 and Cr BSP 2 was much stronger than that of diamond and tungsten carbide, a hard material widely used in industry. The crystal structure changes of Cr_3B_4 were studied by means of high voltage in situ synchrotron radiation measurement. The compressibility of Cr_3B_4 cell was analyzed. The axial compression of lattice constants. We find that the structure of Cr_3B_4 crystal with orthogonal structure remains stable and no phase transition occurs when the pressure reaches about 25 GPa. It shows that the structure has strong stability, and the polymerized "Z" zigzag chain in the Cr_3B_4 crystal structure of orthogonal structure has very strong covalent property. So Cr_3B_4 has strong compression resistance in the c-axis direction. By comparing it with the compression resistance of common hard (superhard) materials, it is found that the lower bulk elastic modulus of Cr3B4 results in a hardness value that is not up to the standard of superhard materials. However, due to the addition of a strong covalent "Z" zigzag chain, the hardness of the zigzag chain is higher than that of chromium metal.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O52

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