【作者】 陆静；

【导师】 王艳辉； 臧建兵；

【作者基本信息】 燕山大学 ， 材料学， 2009， 博士

【摘要】 纳米金刚石和碳纳米管具备碳材料和纳米材料的双重特性,在众多研究领域拥有巨大的应用潜力。但是它们也同时具备了碳材料热稳定性差和纳米材料易团聚的特点,严重阻碍了它们的广泛应用。采用合适的沉积方法对其进行表面改性是解决这一问题的有效途径。此外,还能赋予纳米金刚石和碳纳米管新的物化性能,扩宽其应用范围。本论文在纳米金刚石和碳纳米管表面准原子层沉积镀硅、镀钛,并通过直接氧化处理钛镀层和ZrOCl2?8H2O恒温水解制备氧化钛和氧化锆涂层,实现了纳米金刚石和碳纳米管表面纳米涂层的均匀沉积改性。以SiH4为前驱体在纳米金刚石和碳纳米管表面准原子层沉积硅镀层。反应温度从400 ?C升高到500 ?C,硅镀层由晶态变为非晶态,沉积温度提高到600 ?C,镀层又由非晶态变为晶态。500 ?C时,镀层完全由非晶态硅组成,非常均匀光滑,与基体的同形性也最好。单次循环反应周期的镀层平均厚度为1-2 nm,随着循环次数的增加,镀层逐渐增厚。硅镀层完整连续,能显著提高纳米金刚石和碳纳米管在空气中的抗氧化性能,5 nm金刚石和碳纳米管循环沉积10次镀硅后,加热到1300 ?C的氧化失重仅有1.23%和6.68%。采用准原子层沉积方法通过H2还原TiCl4在纳米金刚石和碳纳米管表面镀钛。温度较低为650 ?C时,镀层主要是六方相金属钛,棒状纳米晶均匀分布。反应温度升高至750 ?C时,界面反应更容易,镀层主要为立方相碳化钛,由不规则几何形的纳米颗粒组成,镀层比较光滑。随循环次数的增加镀层逐渐增厚,但结构形貌变化不大。纳米金刚石和碳纳米管镀钛后在乙醇溶液中的分散性变好,悬浮液可稳定存放半年不发生明显分层。700 ?C、循环沉积5次镀钛的纳米金刚石和碳纳米管在空气中氧化处理20 min获得氧化钛镀层。温度从500 ?C升高到900 ?C时,氧化钛层的结构由锐钛矿逐渐转变为更加稳定的金红石。涂层由球形氧化钛晶粒组成,均匀连续,完整覆盖基体表面,晶粒大小均在10 nm以下。以ZrOCl2?8H2O为前驱体,90 ?C长时间恒温水解,在纳米金刚石和碳纳米管表面沉积完全同形的氧化锆涂层,制备出核壳结构的纳米金刚石(碳纳米管)/氧化锆纳米复合材料。氧化锆壳层为单斜相晶体,且涂层厚度随反应时间的延长而增加。选用不同循环次数准原子层沉积镀硅和镀钛的纳米金刚石为原料,在1300 ?C、5 GPa准等静压短时烧结90 s,得到SiC、TiC中介结合的纳米金刚石烧结体。循环沉积10次镀硅、镀钛的样品,镀层厚度适中,抗拉强度值也最高。原位反应形成的中介相在纳米金刚石颗粒周围均匀分布,不仅能抑制纳米晶粒的异常长大,而且有利于获得致密的烧结体。纳米金刚石表面涂覆氧化钛或氧化锆涂层有效提高了纳米金刚石电极的电化学活性。锐钛矿结构氧化钛涂覆的纳米金刚石粉末电极对NO2?的氧化有明显的催化作用,在污染物的检测和处理方面有很大的应用潜力。Pt-ZrO2/ND电极则能催化甲醇的氧化,比Pt/ND电极具有更好的电催化活性和稳定性,在直接甲醇燃料电池领域非常有发展前景。更多还原

【Abstract】 Nanodiamonds and carbon nanotubes, which are nano carbon materials, possess great potential in a variety of application fields. However, they also have the poor thermal stability of carbon and the aggregation of nanopowder, significantly embarrassing their application. Modifying the surface of nanodiamonds and carbon nanotubes with proper deposition methods could effectively resolve the above problems. Besides, the nano-coating with new properties would also broaden the application of nanodiamonds and carbon nanotubes. In this thesis, quasi atomic layer deposition method has been used to coat nanodiamonds and carbon nanotubes with silicon and titanium. Titania and zirconia nano-coatings have also been acquired by oxidizing of titanium and hydrolyzing of ZrOCl2?8H2O, respectively.Silicon film was coated on nanodiamonds and carbon nanotubes by quasi atomic layer deposition from SiH4. With deposition temperature increasing from 400 to 500 ?C, the structure of the film changes from polycrystalline to amorphous. When the temperature continues to go up from 500 to 600 ?C, the film converts from amorphous to polycrystalline. At 500 ?C, the almost amorphous film is much more even and conformal. The thickness of the coating deposited per cycle is 1-2 nm on average. By repeating the deposition cycle, the thickness of the coating increases. Continuous silicon film could effectively protect nanodiamonds and carbon nanotubes from oxidation. After heating in air to 1300 ?C, the weight loss of 10 times Si-coated 5 nm diamonds and carbon nanotubes are only 1.23% and 6.68%.Quasi atomic layer deposition was also utilized to coat nanodiamonds and carbon nanotubes with titanium from gaseous H2 and TiCl4. The coating deposited at 650 ?C is mainly hexagonal phase Ti, consisting of stick-like nanoparticles. While the relatively smooth coating deposited at 750 ?C is almost cubic phase TiC, for higher temperature promotes the interface reaction. By repeating the deposition cycle, the thickness of the coating increases, but the structure and morphology of the coating does not change much. With titanium coating, the dispersible stability of nanodiamonds and carbon nanotubes in ethanol improves dramatically. By oxidizing Ti-coated (700 ?C, 5 cycles) nanodiamonds and carbon nanotubes in air for 20 min, titania coating was obtained on the surface. With the oxidizing temperature increasing from 500 to 900 ?C, the structure of the coating changes from anatase to more stable rutile. The entire surface of nanodiamonds and carbon nanotubes is covered by continuous titania coating, which is composed of spherical nanoparticles less than 10 nm.Extremely conformal zirconia coating was deposited on nanodiamonds and carbon nanotubes by long time isothermal hydrolyzing of ZrOCl2?8H2O at 90 ?C. Core-shell structural nanodiamonds (carbon nanotubes) / zirconia nanocomposites were successfully prepared. The thickness of the monoclinic phase zirconia coating increases with the hydrolyzing time.SiC and TiC bonded nanodiamond compacts were sintered at 1300 ?C, 5 GPa for 90 s from silicon and titanium coated nanodiamonds deposited by different cycles. The tensile strength of the compacts sintered from 10 times deposited samples is the highest for the proper thickness of the coating. The bonding phase formed in situ distributes homogeneously among the nanodiamond particles, which could not only prevent the nanoparticle from abnormal grain growth but also lead to the sintering of the compact.Coating nanodiamonds with titania or zirconia could improve the electrochemical activity of nanodiamond electrodes. Anatase coated nanodiamond powder electrode could catalyse the oxidation of NO2?, which would possess great potential in detecting and treating pollutant. Pt-ZrO2/ND electrode, more active and stable than Pt/ND electrode, could catalyse the oxidation of methanol, which would be candidate in direct methanol fuel cells.更多还原