甲烷浓度对金刚石薄膜(100)织构生长的影响

以H2和CH4的混合气体为气源,用微波等离子体辅助化学气相沉积法(MPECVD)在1 cm×1 cm S i(100)基体上沉积了金刚石薄膜。研究了不同的甲烷浓度对金刚石薄膜(100)织构生长趋势的影响。分别采用扫描电子显微镜(SEM),Ram an光谱对金刚石膜的表面形貌、质量进行了分析。结果表明,当基体温度为750℃,气压为4.8×103Pa,甲烷浓度为1.4%时,薄膜表面为(100)织构。     

Hydrogen evolution during the oxidation of formaldehyde on Au:: The influence of single crystal structure and Tl-upd

Hydrogen evolution during formaldehyde oxidation in alkaline solution has been monitored by Differential Electrochemical Mass Spectrometry on Au(111) and polycrystalline gold. The current efficiency for hydrogen evolution increases with higher concentration and is in the same range on both, polycrystalline Au and Au(111) electrode. The onset potentials and half-wave potentials are higher on Au(111). Reaction orders for the faradaic current on the bare gold electrodes have been determined as 0.21 for higher and 0.76 for lower concentrations. Reaction orders for hydrogen evolution during formaldehyde oxidation are 1.4 times higher in each case. Tafel slopes in the range of 140-160 mV are found. This signifies that the first reaction step involving the formation of adsorbed hydrogen is largely determining the overall reaction rate. In the presence of thallium adlayers hydrogen evolution from formaldehyde oxidation is largely suppressed. On the thallium modified polycrystalline Au, formaldehyde oxidation is shifted for 100 mV to higher potentials where Tl is partially desorbed and hydroxide is coadsorbed on the modified surface. On thallium modified Au(111), a similar process takes place, but in the same potential region as the onset of formaldehyde oxidation on the bare surface and therefore the formaldehyde oxidation is only slightly shifted. Tafel slopes are decreased to 80 mV/dec in the presence of thallium. In the presence of adsorbed thallium, the first reaction step is in equilibrium, the coverage with adsorbed hydrogen is smaller and its recombination to H₂ is largely suppressed.     

High quality double wall carbon nanotubes with a defined diameter distribution by chemical vapor deposition from alcohol

We have synthesized double wall carbon nanotubes (DWNTs) with few defects and little amorphous carbon by hot wall chemical vapor deposition (CVD) of alcohol. Catalysts for the DWNT growth were made from cobalt and molybdenum acetates. Scanning electron microscopy, transmission electron microscopy, multi frequency resonance Raman spectroscopy and optical absorption spectroscopy were used for characterization of the product with regard to DWNT yield, the nanotube diameter distribution, defect concentration and amorphous carbon content. Base pressures lower than 1 × 10⁻⁵ mbar in the CVD reactor considerably suppress defects in the DWNTs. Optimized growth conditions for DWNT formation are presented.     

溶液中钙离子对玻璃颗粒电泳沉积的影响

研究了玻璃颗粒在乙醇溶液中对Ca^2 的选择吸附，反转了玻璃颗粒在乙醇中的荷电性质，使玻璃颗粒能够在乙醇中与羟基磷灰石发生共沉积。讨论了不同离子浓度下电泳沉积的沉积量与沉积电流的变化情况，并以此对Ca^2 在电泳沉积中的作用进行了分析。实验结果证实：悬浮液中Ca^2 或吸附到玻璃颗粒上，改变其荷电性质；或留在溶液中，作为电泳沉积过程中电流的主要承载者。离子浓度对电泳沉积的效果有重要的影响，离子浓度太低或太高都易使涂层出现缺陷。分析了不同沉积条件下电泳沉积所得涂层的各种缺陷及其成因。     

Strong influence of buffer layer type on carbon nanotube characteristics

Carbon nanotubes (CNTs) have been grown by chemical vapor deposition in a vacuum chamber equipped with in situ photoelectron spectroscopy technique that allows for precise characterization of the chemical state of substrate and catalyst before the CNTs growth. The CNTs were grown onto Si wafers covered with thin buffer layers of Al, Al₂O₃, TiN, and TiO₂, using Fe as catalyst. Marked differences were observed both in growth rate and nanotube characteristics, as determined by SEM, TEM and micro-Raman spectroscopy, depending on the choice of buffer layer.     

电站取水河段长时段的泥沙淤积特性研究（注：研究生论坛）

摘 要:为解决将数学模型运用于电站取水口长时段内的河床演变问题,从而引起计算效率与精度不足的缺陷。本文采用基于隐式与显式结合的算法,探索河道长时段的泥沙淤积特性,建立能模拟长时段河床演变的水沙数学模型,并将该模型应用于昭化电站取水河段泥沙冲淤模拟。通过物理模型与数学模型在不同频率洪水下取水口水位和流速的比较结果,表明此数学模型可以较好模拟取水口水流特性;通过预测昭化电站拉沙方案与不拉沙方案下取水河段运行多年后的河床演变,结果表明此数学模型模拟结果与实际工程结果相似,符合客观规律,能较好模拟河段的泥沙问题。     

Performance of fluorine-added CoMoS/Al2O3 prepared by sonochemical and chemical vapor deposition methods in the hydrodesulfurization of dibenzothiophene and 4,6-dimethyldibenzothiophene

The performance of a new type of CoMoS/Al₂O₃ catalyst, with added fluorine and prepared by sonochemical and chemical vapor deposition (CVD) methods, was investigated in the hydrodesulfurization (HDS) of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT). The catalyst, which was designed to contain optimum amounts of fluorine and cobalt, exhibited a higher activity, ca. 4.6 times higher activity particularly in the HDS of 4,6-DMDBT, than a fluorine-free catalyst prepared by a conventional impregnation method. The enhanced activity of the new catalyst can be attributed to the cumulative effects of individual factors involved in the catalyst preparation. That is, the use of a sonochemical synthesis led to a high dispersion of small MoS₂ crystallites on the alumina, and the addition of the Co species to the catalyst by CVD caused a close interaction between the Co species and the MoS₂ crystallites to produce numerous CoMoS species, which are the catalytically active species for HDS. The addition of fluorine increased the amounts of acidic sites in the catalyst, which promoted hydrogenation (HYD) route to a greater extent than the direct desulfurization (DDS) route in DBT HDS and both HYD and DDS routes to similar extents in the case of 4,6-DMDBT HDS. Accordingly, the addition of fluorine led to a greater increase in catalytic activity for 4,6-DMDBT HDS than for DBT HDS.     

Mass production of high-quality multi-walled carbon nanotube bundles on a Ni/Mo/MgO catalyst

A new catalyst (Ni/Mo/MgO) is reported, with which one can synthesize multi-walled carbon nanotube (MWNT) bundles with a yield of more than 45 times the amount of the pristine catalyst, using a methane-hydrogen mixture as precursor. Powder X-ray diffraction, Raman spectroscopy and thermal gravimetric analysis show that the purity of the as-prepared MWNTs is over 97%. The diameter of the carbon nanotubes is 9-20 nm, measured by high-resolution electron microscopy on 421 individual MWNTs. The high purity of the as-prepared MWNTs allows us to omit the usual complex purification process required for carbon nanotubes synthesized by chemical vapor deposition. Because of its durable high activity, the Ni/Mo/MgO catalyst in its pristine state is ideal for mass production of high-quality MWNTs. The synergism of nickel and molybdenum is considered the main reason for the high yield of carbon nanotubes.     

碳沉积法制富氮用炭分子筛的研究

本文提出的碳沉积法是用煤焦油馏分油的有机溶液浸渍煤炭化物,然后热解以进行“孔调变”。确定了最佳工艺条件,制得富氮性能良好的炭分子筛。并用D-A方程求取了各种样品的微孔结构参数。     

Syngas production from methane reforming with CO2/H2O and O2 over NiO–MgO solid solution catalyst in fluidized bed reactors

Catalyst performance of NiO–MgO solid solution catalysts for methane reforming with CO₂ and H₂O in the presence of oxygen using fluidized and fixed bed reactors under atmospheric and pressurized conditions was investigated. Especially, methane and CO₂ conversion in the fluidized bed reactor in methane reforming with CO₂ and O₂ was higher than those in the fixed bed reactor over Ni_0.15Mg_0.85O catalyst under 1.0 MPa. In contrast, conversion levels in the fluidized and fixed bed reactor were almost the same over MgO-supported Ni and Pt catalysts. It is suggested that the promoting effect of catalyst fluidization on the activity is related to the catalyst reducibility. On a catalyst with suitable reducibility, the oxidized and deactivated catalyst can be reduced with the produced syngas and the reforming activity regenerates in the fluidized bed reactor during the catalyst fluidization. In addition, the catalyst fluidization inhibited the carbon deposition.