铁基触媒的组织结构对合成金刚石的影响

采用粉末冶金铁基触媒在六面顶压机上高温高压合成金刚石.使用高性能金相显微镜,扫描电子显微镜和X射线衍射仪对合成之后触媒的组织结构进行系统的表征.试验发现,触媒组织主要由粗大的板条状初生渗碳体和细密的共晶莱氏体构成;金刚石生长效果不好时,触媒组织中夹杂有团絮状石墨.分析认为,初生渗碳体极有可能就是金刚石生长的直接碳源,即高温高压下溶解于触媒熔体的石墨首先与触媒合金形成碳化物,在触媒的催化作用下,碳原子自渗碳体脱溶,沉积到金刚石表面,完成金刚石的生长.     

合成金刚石的碳源石墨

本文论述了碳源石墨的特性对静压溶剂-触媒法合成金刚石的影响,提出了静压溶剂-触媒法合成金刚石的机理,包括热力学模型、触媒合金的作用、金刚石的成核和成长、P-T条件对合成的影响。论述了碳源石墨的晶体完善程度、织构、颗粒大小、杂质含量及其他性能对金刚石的成核、长大和物理性质的影响。本文还介绍了几种国外碳源石墨的理化性质。     

高温高压合成含硼金刚石单晶制备工艺初探

本文以掺入不同含量硼铁的铁基合金为触媒,以石墨为碳源,在高温高压条件下合成了含硼金刚石单晶体.利用扫描电镜(SEM)观察了金刚石及触媒的组织形貌;利用金相显微镜观察了金刚石颗粒的颜色和形态;利用拉曼光谱仪(RS)确认了人造金刚石单晶体中硼的存在;利用低温电阻测量仪验证了合成的含硼金刚石单晶颗粒具有半导体性能.实验结果表明,在金刚石的合成中,触媒中硼铁含量为2wt%的合成效果相对最好.     

测定含硼金刚石单晶颗粒电阻的方法

以铁基舍金掺杂FeB或B4C为触媒、石墨为碳源，在高温高压条件下合成了含硼金刚石单晶。测定了金刚石单晶颗粒在不同温度下的电阻并绘制出两参数之间的变化曲线。结果表明，当金刚石单晶中掺入硼时，其电阻大幅度降低，且电阻随温度的升高而下降，即存在负的电阻温度系数，表现出半导体材料的特性。     

低压下用CO H_2气体制备人造金刚石的相图计算

用非平衡热力学耦合模型计算了低压下由CO＋H2气体制备人造金刚石的相图．这些相图与经典的平衡热力学理论计算的相图不同，都有一个金刚石生长区．金刚石生长区的存在是实现用CO＋H2气体制备人造金刚石的热力学基础．本文认为相图中的金刚石生长区是体系中超平衡氢原子和超平衡氧原子对金刚石相和石墨相不同作用的结果．不同压力下相图中金刚石生长区的范围稍有不同，压力降低时，金刚石生长区将向低CO浓度的方向移动．本文还将计算的结果与报道的实验结果进行了对比分析，两者基本相符．     

Fe+Ni+C体系合成粗颗粒金刚石单晶的生长特征

在配备有高精密化控制系统SPD6×1670T型国产六面顶压机上,采用Fe80Ni20粉末触媒和高纯石墨开展粗颗粒金刚石单晶的生长特征研究。在粉末触媒技术合成金刚石的基础上,引入旁热式组装,以及采用优选粒度的触媒,特别是通过优化合成工艺严格地控制了合成腔体内晶体的成核量及生长速度。最终,在高温高压条件下(约5.4GPa、1435℃)成功合成出尺寸达到0.95mm(18/20目)的优质的粗颗粒金刚石单晶,分析了粗颗粒金刚石的生长特征和晶体缺陷,期待研究的结果有助于我国高品级粗颗粒金刚石的发展。     

粉末触媒合成金刚石体系的温度稳定性问题

就不同粉末触媒、石墨粉配比体系的金刚石单晶在高温高压条件下生长过程中,合成腔体内温度场的变化进行分析,指出合理的粉末触媒合成金刚石体系的粉末触媒及石墨粉的分布状态。     

铱衬底上金刚石外延形核与生长:第一性原理计算

异质外延为金刚石晶圆合成提供了一个有效的实现路径,而Ir衬底上金刚石形核生长技术经过20多年的发展已经有能力制备最大直径为3.5英寸的晶体,开启了金刚石作为终极半导体在电子信息产业应用的大门。然而,表面形核、偏压技术窗口、金刚石外延生长等一系列发生在异质衬底上的问题都需要从生长热力学的角度给予解释。本研究针对化学气相沉积气氛中金刚石如何实现外延形核与生长这一关键问题,利用第一性原理计算从原子尺度对金刚石形核生长过程展开了系列探究。研究结果如下:C原子在Ir衬底表面位点吸附比在体相位点吸附更稳定,表明无偏压条件下金刚石形核只能在衬底表面发生;离子轰击作用下非晶氢化碳层中sp3杂化C原子个数随着离子动能的增加呈现先增大后减小的变化规律,证实了金刚石高密度形核存在一定的离子动能与偏压大小窗口;金刚石沿着Ir衬底外延生长时界面结合能最低(约为–0.58 eV/C),意味着界面结合能是决定外延形核生长的主要热力学因素。本研究阐明了偏压辅助离子轰击促进金刚石单晶外延生长的热力学机制,对于指导金刚石及其他碳基半导体生长具有重要意义。     

微晶石墨对Ⅱa型宝石级金刚石单晶生长的影响

将除氮剂Ti(Cu)添加到FeNiCo合金触媒中在高温高压下合成出优质Ⅱa型宝石级金刚石单晶.在压力5.4GPa、温度1600K的条件下沿{111)面合成Ⅱa型宝石级金刚石过程中伴随有黑色粉末析出.采用X射线衍射(XRD)和扫描电子显微镜(SEM)对该黑色石墨粉末的测试表明其为微晶石墨.随着生长时间的延长,这种微晶石墨...     

温度场对金刚石薄膜质量的影响

在引进的韩国微波等离子化学气相沉积（MPCVD）设备中,利用氢气和甲烷作为气源,在单面抛光的（100）单晶硅片上研究了不同的形核温度和生长温度条件下制备出金刚石薄膜。通过Raman光谱、XRD光谱和扫描电子显微镜（SEM）对制备的金刚石膜的质量进行表征。研究结果表明,形核温度和生长温度对金刚石膜的生长均有影响。形核温度过低会增大薄膜中的非金刚石相的含量,促使二次形核增加,降低了金刚石薄膜质量。随着生长温度的升高,金刚石中非金刚石相含量越少,金刚石的质量提高,但金刚石的晶面同时也被大量刻蚀。     

Fe-PPy-TsOH/C用作质子交换膜燃料电池氧电极催化剂的研究

氧电极催化剂是制约质子交换膜燃料电池(PEMFCs)发展和应用的一个重要因素, 开发低价高效的非贵金属催化剂对PEMFCs来说已成为当务之急。本研究选择氮掺杂的碳载过渡金属(M-N/C)类催化剂为研究对象, 以铁盐作为金属前驱体, BP2000为碳源, 聚吡咯(PPy)为氮源, 对甲基苯磺酸(TsOH)为掺杂剂, 合成了非贵金属催化剂Fe-PPy-TsOH/C, 探究了不同的热处理温度及钴原子的掺杂对其氧还原催化性能的影响。研究结果表明: 800℃制备的Fe-PPy-TsOH/C催化剂因结晶度高、颗粒大小适中且分布均匀而具有最佳的氧还原催化性能; 一定量的钴原子取代可以改善Fe-PPy-TsOH/C的氧还原催化性能, 当钴的掺杂量为33.33%时(铁钴原子比为2︰1), 催化剂的性能达到最优。     

Endofullerenes with metal atoms inside as precursors of nuclei of single-walled carbon nanotubes

Thermodynamic estimations have been made which show that amorphous carbon cannot be the source of single-walled carbon nanotube growth during carbon/metal vapor condensation. Thus the source of carbon material for nanotube growth seems to be small carbon clusters into gas phase or clusters in the adsorbed state on the nanotube surface. Kinetic analysis of carbon/metal vapor condensation in the arc process was performed and showed that metal vapor becomes supersaturated at temperatures that are close to the temperature of the highest rate of fullerene shell formation. A new model of the nucleation of single-walled carbon nanotubes is proposed. In the model an endometallofullerene serves as the precursor of a nanotube nucleus, and the nucleus itself forms as an adduct arising after metal atoms attach to the endofullerene shell. The relative efficiencies of La/Ni, Gd/Ni, Ce/Ni, and Pr/Ni catalysts, in comparison with Y/Ni catalyst, were measured, and their high efficiency in buckytube formation was demonstrated. This fact was explained by the double action of a metal catalyst in buckytube nucleus formation. First, metal takes part in the formation of endometallofullerenes. Second, the metal atoms attach to the endofullerene shell to transform an endofullerene into a nanotube nucleus. The high performance of bimetallic catalysts lies in adjusting the values of two metal concentrations separately for each of these purposes. In accordance with observations, the proposed model predicts increasing size of endofullerenes with increasing concentration of the metal that controls endofullerene formation.     

以超临界和亚临界水活化掺金属化合物的酚醛树脂制备球形活性炭(英文)

以掺稀土金属化合物氯化铈的酚醛树脂为原料,采用超临界和亚临界水活化制备了具有较好中孔结构和机械强度的球形活性炭。通过77K氮气吸附对所制球形活性炭进行表征,并研究不同活化方法、活化条件对其孔隙结构的影响。结果表明:氯化铈具有催化作用,在超临界水环境下促进了孔结构的发展,优势中孔分布于4nm和7nm;而活化方法和活化压力对孔结构的影响较小。     

General rules governing carbon nanomaterial growth directly on metal support by chemical vapor deposition

Growing carbon nanotubes and relative nanomaterials directly on metal support has attracted increasing attention due to its applications in nanoelectronics and composites. In order to reveal the effect of metal support on the catalytic property of the catalyst, several metal powders were selected as catalyst carrier for carbon nanomaterial growth by chemical vapor deposition (CVD). The results show that the interaction between metal support and catalyst plays a key role for the activity of the catalyst, while, the metal support itself has a relative little effect. By critically controlling their interactions, all metal powders are extrapolated to be used as catalyst supports for the carbon nanomaterial growth by CVD.     

Stabilizing High Density Cu Active Sites with ZrO2 Quantum Dots as Chemical Ligand in N-doped Porous Carbon Nanofibers for Efficient ORR

The emerging transition metal-nitrogen-carbon (M N C) materials are considered as a promising oxygen reduction reaction (ORR) catalyst system to substitute expensive Pt/C catalysts due to their high surface area and potential high catalytic activity. However, M N C catalysts are easy to be attacked by the ORR byproducts that easily lead to the deactivation of metal active sites. Moreover, a high metal loading affects the mass transfer and stability, but a low loading delivers inferior catalytic activity. Here, a new strategy of designing ZrO₂ quantum dots and N-complex as dual chemical ligands in N-doped bubble-like porous carbon nanofibers (N-BPCNFs) to stabilize copper (Cu) by forming Cu ZrO_3-x/ZrO₂ heterostructures and Cu N ligands with a high loading of 40.5 wt.% is reported. While the highly porous architecture design of N-BPCNFs builds a large solidelectrolytegas phase interface and promotes mass transfer. The preliminary results show that the half-wave potential of the catalyst reaches 0.856 V, and only decreases 0.026 V after 10 000 cycles, exhibiting excellent stability. The proposed strategy of stabilizing metal active sites with both heterostructures and Cu N ligands is feasible and scalable for developing high metal loading ORR catalyst.     

Influence of the nanoscale support on carbon deposition and carbon elimination over Ni/gamma-Al2O3 catalyst for CH4 conversion

Characteristics of carbon deposition by CH4 and carbon elimination by CO2 over conventional and nanoscale Ni/gamma-Al2O3 catalysts were investigated by using a pulse reaction, as well as by TGA, TEM, TPO-MS, H2-TPR and H2-chemisorption techniques. It was found that the behaviors of carbon deposition by CH4 decomposition and carbon elimination by CO2 depend on the active metal dispersion and the metal-support interaction. The filamentous carbon was formed on the conventional Ni/gamma-Al2O3 catalyst with low metal dispersion and relatively large particles, this type of filamentous carbon was far from the active centers and difficult to eliminate by CO2. On the other hand, the carbon deposition originated from CH4 decomposition on the nanoscale Ni/gamma-Al2O3 catalyst would mainly cover the surface of active centers, this type of highly active carbon was easily eliminated by CO2 because it is close to the active center Ni atoms. As a result, the improvement of coking-resistance was ascribed to the high metal dispersion and strong metal-support interaction, a model of CH4 decomposition carbon deposition on Ni/gamma-Al2O3 catalyst was proposed.     

调变Ni／Mo／MgO催化剂中Ni／Mo比例可控合成薄壁碳纳米管

采用摩尔分数1%Ni及负载少量Mo的Ni/MO/MgO催化剂裂解甲烷合成薄壁碳纳米管.通过SEM、TEM、XRD和Raman光谱表征方法研究了碳纳米管直径和催化剂中Ni/Mo比例关系.实验发现:通过控制Ni/Mo比例可以调变催化剂颗粒大小以及活性相.TEM及XRD表征发现,随着Ni/Mo比例的降低,金属Mo相逐渐从NiMo合金相中析出.NiMo合金相对应的活性组分颗粒很小,容易催化裂解甲烷形成薄壁碳纳米管;而后析出的Mo相则主要形成了大管径厚壁的碳纳米管.当Ni/Mo比例为6时可以高选择性地获得窄分布,内径为1.3nm,外径为3.0nm的溥壁碳纳米管.Raman光谱进一步验证了碳纳米管含有较少的缺陷.薄壁碳纳米管形成的关键因素主要体现为碳在其表而的快速扩散以及小颗粒的碳纳米管催化剂活性相控制.     

Comparison studies between hydrogenation and oxidation of MWNTs followed by acid treatment

MWNTs obtained using iron catalyst and ethylene as a carbon source were submitted to a purification procedure. To purify these materials from amorphous carbon two parallel methods--based on either hydrogen or air treatment--were applied. At the second purification stage iron particles were removed using 1 M or 5 M nitric or hydrochloric acids. The phase composition of the samples was determined using X-ray diffraction method. The sample morphology was characterized using a high resolution transmission electron microscopy. The relative fraction of impurities in the samples was estimated by Raman spectroscopy and the quantitative analysis of metal impurity content was validated by means of thermogravimetric analysis.     

In situ observations of catalyst dynamics during surface-bound carbon nanotube nucleation

We present atomic-scale, video-rate environmental transmission electron microscopy and in situ time-resolved X-ray photoelectron spectroscopy of surface-bound catalytic chemical vapor deposition of single-walled carbon nanotubes and nanofibers. We observe that transition metal catalyst nanoparticles on SiOx support show crystalline lattice fringe contrast and high deformability before and during nanotube formation. A single-walled carbon nanotube nucleates by lift-off of a carbon cap. Cap stabilization and nanotube growth involve the dynamic reshaping of the catalyst nanocrystal itself. For a carbon nanofiber, the graphene layer stacking is determined by the successive elongation and contraction of the catalyst nanoparticle at its tip.     

非贵金属/碳氮复合材料电催化析氧反应的研究进展

析氧反应(OER)是一种复杂的四电子转移反应,其动力学缓慢、所需能量高,制约了电解水制氢等新型能源技术的发展.近年来,非贵金属复合材料因其优异的催化活性以及相比于贵金属基催化剂的成本优势而受到广泛关注.本文概述了这一研究领域的最新进展,首先简要介绍析氧反应的机理以及材料催化性能的评价方法,重点关注非贵金属/碳氮复合材料...