不同金属催化炭纤维原位生长纳米炭纤维/纳米碳管的研究

为了选择合适的催化剂，来催化炭纤维生长纳米炭纤维／纳米碳管，分别以Fe、Co、Ni和Mo的金属盐为催化剂前驱体，H2为还原气体，N2为载气，采用浸渍-还原法在炭纤维表面制备纳米催化剂颗粒，再以CO为碳源，催化热解生长纳米炭纤维／纳米碳管。用扫描电镜观察了纳米催化剂颗粒的形貌和粒径及纳米炭纤维／纳米碳管的形貌，并探讨了四种金属的催化生长机制，发现四种金属的催化效果为：Ni最好，Co次之，Fe较差，Mo最差。     

镍催化制备炭/炭复合材料

利用催化化学气相沉积法制备炭／炭复合材料，研究了反应温度、前驱体气体含量、催化剂含量和时间对所制备的炭／炭复合材料密度的影响，采用扫描电镜观察分析了基体碳的形貌。结果表明，利用催化剂镍可制取密度达1．594g／cm^3的炭／炭复合材料，并有晶须状基体碳生成。在各种工艺参数中，对炭／炭复合材料的密度影响最大的是温度和前驱体气体，其次为催化剂含量，最后是时间。     

负载型Pd催化剂催化苯酚原位加氢反应研究

以氯钯酸为前驱体,采用浸渍共沉淀还原法制备Pd/纳米碳管(CNTs)和Pd/活性炭(AC)催化剂。在493 K,3.5 MPa下,考察催化剂在"苯酚+甲醇+水"原位加氢反应中的催化活性。实验结果表明,Pd/CNTs对苯酚原位加氢制环己酮有更高的选择性。通过COTPD,TEM表征结果表明,这主要是由于Pd/CNTs催化剂独特的中孔结构和内腔孔道。     

双金属纳米颗粒在硅基底上直接催化生长碳纳米管

以甲烷为碳源,双金属纳米颗粒Fe／Ru（1：1）、Fe／Ru（1：1）、Ru／Fe（1：1）为催化剂,在含有加厚氧化层的硅基底上,于875-950℃制备纳米碳管,并用原子力显微镜（atomic force micmscopr——AFM）和拉曼光谱进行表征,发现随着反应温度的降低,3种催化剂的催化效果具有明显的不同程度的降低,最佳反应温度为925℃;所制备的纳米碳管都是单壁的,并且高度都约是1．25nm;对催化剂进行预处理（925℃,1min）后,其催化效果会有显著的提高,这对实现碳纳米管的定点生长具有重要的意义。     

新型炭纤维/泡沫炭预制体的制备及致密化研究

由炭纤维/酚醛树脂经过发泡、固化和炭化制备出4种不同炭纤维含量(3%,7%,10%和15%)的泡沫炭作为制备炭/炭复合材料新型预制体,通过等温化学气相沉积对预制体进行致密化处理。研究了炭纤维含量对预制体微观结构、致密化过程及力学性能的影响。结果表明:炭纤维含量增加,使预制体产生更多的微裂纹,并有更多的炭纤维裸露在泡沫炭韧带外,有助于提高化学气相沉积的沉积速率。炭纤维/泡沫炭预制体炭/炭复合材料压缩强度随着预制体中炭纤维含量的增加而增加,当炭纤维体积分数为10%时,压缩强度达到峰值,为43MPa。     

化学气相沉积法合成纳米碳管阵列研究

研究以环己烷为前驱体采用化学气相沉积法制备纳米碳管阵列。将催化剂二茂铁定量溶解在环己烷中，通过载气夹带进入反应器中，采用化学气相沉积方法定向生长出炭纳米管阵列，此法有效地控制反应体系中的催化剂含量，使生产稳定性及重现性较好。并通过透射电子显微镜、扫描电子显微镜、拉曼光谱及X射线衍射对产品形态和结构进行分析和表征，所制备出的纳米碳管阵列形态比较规整，纯度较高，具有较好的石墨微晶结构；并对纳米碳管的生长机理进行了详细讨论。     

单壁纳米碳管的纯化及其储氢特性

针对半连续氢电弧法制备的单壁纳米碳管提出了一种纯化方法。采用HNO3和H2O2回流水煮的方法对单壁纳米碳管进行了纯化处理，透射电镜观察及热重分析表明样品中的无定形炭、纳米碳颗粒及金属催化剂颗粒等杂质可被有效去除，提纯后单壁纳米碳管的收率约为35％，纯度在95％以上；研究发现该纯化方法对单壁纳米碳管的孔径分布和比表面积有较大影响。采用体积法测定了纯化前后单壁纳米碳管样品的储氢容量，结果表明纯化样品的储氢量为1．65％，比未提纯样品（0．56％）有较大提高。     

纳米镍／炭复合材料的制备研究

采用阳离子交换树脂作为炭载体的前驱体,经过镍离子交换,再经热解后制备了一种纳米镍／炭（n—Ni／C）复合材料。以XRD、SEM、TEM、EDS为主要分析手段研究了热解条件对纳米镍在n—Ni／C复合材料中的形貌、大小和分布情况的影响。结果表明：通过热解条件可以控制n—Ni／C复合材料中纳米镍的粒径;TEM和SEM—EDS观察表明热解所得n—Ni／C复合材料中的纳米镍颗粒大小均匀、分散性好。差热分析（DTA）研究结果表明加入n-Ni／C可增加高氯酸铵（AP）的表观放热量,降低AP的高温分解峰,最大可达95℃。     

纳米炭载PbO·CuO复合催化剂的制备及其应用

采用三元溶胶-凝胶技术和超临界干燥法制备出纳米炭载PbO·CuO复合催化剂,用扫描电镜和元素分析仪对其颗粒表面进行形貌表征和元素分析;将其应用至交联改性双基推进剂中,研究了该复合催化剂对推进剂燃烧性能及火焰结构的影响,并与同配比的微米级PbO/CuO/CB混合催化剂进行了对比。结果表明,采用该方法制备的纳米炭载PbO·CuO复合催化剂颗粒分布均匀,单组分含量可以有效控制,PbO和CuO均匀负载在纳米炭上,颗粒尺寸为30~60nm,可有效改善交联改性双基推进剂的燃烧性能;当PbO、CuO、CB的摩尔比为5∶10∶3时,推进剂在10~20 MPa内的燃速压强指数可降至0.36;与含微米级PbO/CuO/CB混合催化剂的推进剂相比,含纳米炭载PbO·CuO复合催化剂的推进剂火焰燃面更不规则,火焰亮度和亮黄丝线明显增加,燃烧更为剧烈,表明纳米炭载PbO·CuO复合催化剂对交联改性双基推进剂催化效果明显优于微米级PbO/CuO/CB混合催化剂。     

Ni/SiO2催化制备炭/炭复合材料研究

利用常规化学气相渗透工艺，在针刺炭布预制体中添加3．5％，4．O％Ni／SiO2负载型金属催化剂，以丙烯作碳源气体，在750-900℃下，经过100h的沉积，炭／炭（C／C）复合材料的密度达到1．65g／cm^3，其催化沉积炭的速率比不舍催化剂时提高了3倍以上。该材料经高温处理后，氧化失重率低，氧化起始温度高。应用扫描电镜（SEM），X射线衍射分析（XRD）和光学显微镜观察了基体炭的形貌，分析了催化沉积炭和抗氧化机理。实验结果证明，用该催化化学气相渗透法制备C／C复合材料，周期短，成本低，抗氧化性能好。     

硝酸铁为催化剂大量制备离散Mn2O3纳米管/纤维

采用简单的液相催化法实现了完全离散的Mn2O3纳米管/纤维的大规模制备. TEM电镜观察表明,Mn2O3纳米管外径约30~50 nm,长度约0.2~1.0 mm, Mn2O3纳米纤维直径约10~30 nm,长度约0.4~2.0 mm. 通过控制KMnO4和Fe(NO3)3的用量和比例可以分别得到管状、纤维状和颗粒状等不同微观形态的纳米Mn2O3. Fe(NO3)3是制备Mn2O3纳米管/纤维的理想催化剂,以Co(NO3)2和Ni(NO3)2作催化剂只能制得无定形颗粒. XRD分析表明,Mn2O3纳米管具有不同于已知的o-Mn2O3, t-Mn2O3, h-Mn2O3和g-Mn2O3的晶体结构.     

Differences between carbon nanofibers produced using Fe and Ni catalysts in a floating catalyst reactor

Carbon nanofibers were produced by the catalytic CVD process by the floating catalyst method, in semi-industrial systems at temperatures above 1350 K. Iron-derived carbon nanofibers were produced from natural gas and xylene, using ferrocene as catalyst source, yielding a thickened submicron vapor grown carbon fibers with a core of multi-wall nanotubes. For the production of Ni derived nanofibers, natural gas was used as the carbon feedstock, and the Ni was added in a nickel compound solution. When no sulfur is used, only soot was obtained, but when sulfur is added to the reactive feedstock, a highly graphitic and very nice stacked-cup-type nanofibers with no free-CVD thickened layer were produced. TEM-EDS analysis confirms that this type of stacked-cup carbon nanofiber is produced only with a partially molten catalyst and methane as hydrocarbon source. In fact, very few fibers have either a particle tip at the end or trapped metal particle inside the wide hollow core of this type of produced carbon material.     

Synthesis of carbon nanotubes on Ni/carbon-fiber catalysts under mild conditions

Methane, n-hexane, benzene, and cyclopentadiene were decomposed at a relatively mild temperature (773 K) over a Ni catalyst supported on either vapor grown carbon fibers (VGCF) or graphitized carbon fibers (GCF). Transmission electron microscopy showed that the morphology of the fibers changed according to hydrocarbon and particle size. Decomposition of methane and n-hexane produced fishbone-type fibers. The fibers from n-hexane sometimes showed intermittent hollow structures but the diameters of the fibers were widely distributed. Decomposition of benzene and cyclopentadiene mainly produced winding type carbon nanotubes of relatively uniform diameters (10-20 nm). Bidirectional fishbone-type fibers (fibers growing outward from a central catalyst particle) were also observed as a by-product. Small Ni particles (10-20 nm) with stretched tails were present on the tips of tubular fibers, some of which frequently changed growth direction. The varying tubular morphologies can be ascribed to liquid-like Ni particles resulting from the freezing point depression due to a fast dissolution of carbons during decomposition of benzene or cyclopentadiene. The formation of bidirectional fibers was also observed in the decomposition of n-hexane. Relatively large well-faceted Ni particles (diameter 50-110 nm) grew bidirectional fibers.     

Production of Carbon Nanotube by Ethylene Decomposition over Silica-Coated Metal Catalysts

Formation of carbon nanofibers (CNFs) and carbon nanotubes (CNTs) through the decomposition of ethylene at 973 K was achieved using various metal catalysts covered with silica layers. CNFs of various diameters were formed by ethylene decomposition over a Co metal catalyst supported on the outer surface of the silica. In contrast, silica-coated Co catalysts formed CNTs with uniform diameters by ethylene decomposition. Silica-coated Ni/SiO₂ and Pt/carbon black also formed CNTs with uniform diameters, while CNFs and CNTs with various diameters were formed over Ni/SiO₂ and Pt/carbon black without a silica coating. These results indicate that silica layers that envelop metal particles prevent sintering of the metal particles during ethylene decomposition. This results in the preferential formation of CNTs with a uniform diameter.     

气体流速对La／Co／Ni／MgO催化剂CVD法制备碳纳米管的影响

我们在400℃下利用溶胶一凝胶法制备了La／Co／Ni／MgO催化剂,用化学气相沉积法（CVD）在650—600℃下裂解乙炔气体生长碳纳米管,研究了载气、还原气体和碳源气体流速对碳纳米管产量的影响。其中,载气流速N2是100mL／min,还原气体流速H2是30mL／min,碳源气体流速c2H4是60mL／min时,催化剂聚合物团簇分散效果最佳,碳纳米管的产量和形貌达到最大。     

Multi-wall carbon nanotubes by catalytic decomposition of carbon monoxide on Ni/MgO

The redox behavior of the catalyst and the catalytic decomposition of carbon monoxide (CO) were investigated in the synthesis process of multi-wall carbon nanotubes (MWCNT) using Ni/MgO catalyst. The surface morphology of the heated Ni layer was observed by TEM to confirm the formation of NiO particles (50 nm or less) and NiO (222). The chemical reaction behavior of the catalyst in CO the atmosphere was displayed via TG-DSC analysis, and the reduction of NiO was revealed due to the mass decrease of 2.71 wt% and the exothermic peak at around 400°C. The deposition of carbon was identified with an increase in mass and the exothermic peak near 600°C. Ni (111) and carbon (002) facets was taken place in a diffraction pattern of carbon deposited catalyst, indicating the reduction in NiO and the graphitic carbon deposition. The crystallinity of the graphitic carbon was analyzed as the ratios of 0.998 for I_D/I_G and 0.26 for sp³/sp² in Raman and photoelectron spectra. The encapsulated Ni in MWCNT was observed through TEM-EDS, verifying the activation of the catalyst by CO.     

CNTs／TMO复合催化剂对含高氯酸钾烟火药剂分解反应速率的影响

采用化学沉淀法制备沉积于碳纳米管(CNTs)表面上的CuO、Fe2O3复合催化剂.用光电子能谱(XPS)对复合催化剂进行表征,研究了CuO/CNTs和Fe2O3/CNTs复合催化剂对含高氯酸钾烟火药剂分解反应的影响.结果表明,CuO和Fe2O3颗粒均匀地附着在碳纳米管表面上,Cuo/CNTs和Fe3O3/CNTs复合催化剂能够提高含高氯酸钾烟火药剂的反应速率,复合催化剂对高氯酸钾烟火药剂的催化性能明显优于Fe2O3和CuO混合物的催化性能.     

乙醇裂解制备碳纳米管及其生长机理研究

以乙醇作为碳源,Mo-Co/C和Mo-Fe/C作为催化剂,采用化学气相沉积法,高温裂解乙醇制备碳纳米管.利用SEM和TEM对碳纳米管形貌和结构进行表征.结果表明:乙醇在催化剂Mo-Co/C和Mo-Fe/C裂解产生的碳纳米管遵循顶部生长机理.并建立了乙醇制备碳纳米管的生长模型.     

旋涂分布催化剂制备直立单壁碳纳米管

采用聚乙二醇和铁盐、钴盐的乙醇溶液,通过旋涂法在硅基底表面分散得到制备单壁碳纳米管的催化剂颗粒,并用水汽辅助化学气相沉积法制备了直立生长的单壁碳纳米管。考察了不同旋涂速度、聚合物用量和Fe/Co用量对基底表面催化剂分布的影响,用SEM、Raman光谱对相应催化剂分布条件下生长的碳纳米管进行了表征。结果表明,旋涂的转速高时形成的催化剂颗粒分布均匀、粒径小,有利于单壁碳纳米管的生长,而较高Fe、Co和聚乙二醇(PEG)用量能使催化剂密集分布,有利于碳纳米管的直立生长;在7 000 r/min成膜时,质量分数为1.25%的PEG和质量分数均为0.05%的Fe和Co,是单壁碳纳米管直立生长的适宜催化剂条件。     

Low temperature growth mechanisms of vertically aligned carbon nanofibers and nanotubes by radio frequency-plasma enhanced chemical vapor deposition

Using radio frequency-plasma enhanced chemical vapor deposition (RF-PECVD), carbon nanofibers (CNFs) and carbon nanotubes (CNTs) were synthesized at low temperature. Base growth vertical turbostratic CNFs were grown using a sputtered 8 nm Ni thin film catalyst on Si substrates at 140 °C. Tip growth vertical platelet nanofibers were grown using a Ni nanocatalyst in 8 nm Ni films on TiN/Si at 180 °C. Using a Ni catalyst on glass substrate at 180 °C a transformation of the structure from CNFs to CNTs was observed. By adding hydrogen, tip growth vertical multi-walled carbon nanotubes were produced at 180 °C using FeNi nanocatalyst in 8 nm FeNi films on glass substrates. Compared to the most widely used thermal CVD method, in which the synthesis temperature was 400–850 °C, RF-PECVD had a huge advantage in low temperature growth and control of other deposition parameters. Despite significant progress in CNT synthesis by PECVD, the low temperature growth mechanisms are not clearly understood. Here, low temperature growth mechanisms of CNFs and CNTs in RF-PECVD are discussed based on plasma physics and chemistry, catalyst, substrate characteristics, temperature, and type of gas.