Morphology observation of carbon deposition by CH4 decomposition over Ni-based catalysts

We found a novel morphology variation of carbon deposition derived from CH4 decomposition over NI-based catalysts. By altering the chemical composition and particle size of Ni-based catalysts, carbon filaments, nanofibres and nanotubes were observed over conventional Ni/y-Al2O3, Ni-Co/gamma-Al2O3 and nanoscale Ni-Co/gamma-Al2O3 catalysts, respectively. The simple introduction of Co into a conventional Ni/gamma-Al2O3 catalyst can vary the carbon deposition from amorphous filamentous carbon to ordered carbon fibres. Moreover, carbon nanotubes with uniform diameter distribution can be obtained over nanosized Ni-Co/gamma-Al2O3 catalyst particles. In addition, the oxidation behaviour of the different deposited carbon was studied by using a temperature-programmed oxidation technique. This work provides a simple strategy to control over the size and morphology of the carbon deposition from catalytic decomposition of CH4.

活性炭纤维(ACF)吸附法处理河流突发污染事故模拟研究

环境突发污染事故给人民生活、经济发展和生态环境造成重大影响，研究污染物泄漏造成河流突发污染事故的应急处理方法十分必要。本论文选取苯酚、苯胺和亚甲基蓝等典型污染物为实验对象，采用吸附容量大、密度与水接近的活性炭纤维(ACF)为吸附剂。在自制的河流模型中，研究了ACF以苯酚、苯胺和亚甲基蓝为典型污染物的吸附过程，考察了吸附剂投加量、污染物浓度、吸附剂比表面积、吸附剂投加方式、水流速度与水质等对吸附速率与吸附效果的影响。实验结果表明，ACF能以较快的速率吸附苯酚、苯胺和亚甲基蓝，吸附率都在95％以上； ACF投加量是影响吸附速率最重要的因素，当一次性投加ACF质量之比为 1:2:4时，吸附速率常数之比近似为1:2:4；污染物浓度对吸附速率的影响显著，浓度较低时吸附速率较高。苯酚初始浓度为7mg·L-1时，经过86分钟的吸附，处理后的浓度可以达到地表水Ⅴ类水中挥发酚的限值要求(0.1mg·L-1)；在吸附11分钟左右追加适量的ACF，能够明显提高吸附速率；河水流速和河流中的天然有机物、浊度、河水硬度对ACF吸附都不产生显著影响，这说明ACF作为河流突发污染事故应急处理的吸附剂，有广泛的适应性。在实际河水中，ACF对苯酚的吸附过程与在模拟河水中相似，吸附效果显著。实验结果还表明，ACF对苯酚的吸附是放热反应，符合Freundlich模型和Langmuir模型。事故应急处理后，应该及时将吸附了污染物的ACF打捞上来，有利于进行后续处理。 Emergency environmental pollution accidents pose significant impacts on our living, economic development and ecological environment. The study on the approach of emergency control for the contingency caused by leakage of pollutants in rivers is very necessary. In the experiment, phenol, aniline and methylene blue were selected as representative pollutant and activated carbon fiber (ACF) was selected as adsorbent, which has strong adsorption capacity and similar density to water. In the self-made river model, the effects of ACF dosage, pollutant concentration, ACF surface area, ACF adding ways, water flow rate and water quality on adsorption courses were investigated. The experimental results showed that ACF could adsorb pollutant quickly and effectively. The ACF dosage was the most important factor that affected adsorption rate .When the ACF dosage rate was 1:2:4, the constants of adsorption rate was approximately 1:2:4. The effect of pollutant concentrations on the adsorption rate was notable. Faster adsorption rates were achieved at low pollutant concentrations. Phenol concentration reached the limits of volatile phenol in Category Ⅴ surface water (0.1 mg·L-1) after 86 minutes of adsorption with initial phenol concentration of 7 mg·L-1. After 11 minutes of adsorption, certain amount of ACF was added and the adsorption rate was improved significantly. River flow rate and water quality have little effect on the adsorption rate. The adsorption results obtained in actual river water were comparable with that in simulating river water. The results also showed that, ACF on the absorption of phenol is exothermic reaction, witch matched with the Freundlich model and the Langmuir model. After emergency treatment, the ACF absorbed pollutants should be promptly salvaged for follow-up treatment.

The effect of formulated molecular weight on temperature resistance and mechanical properties in polyimide based composites

This experimental study examines the role of formulated molecular weight between crosslink sites on the temperature resistance and mechanical properties of composites based on a polyimide containing a diphenyl thioether unit (PTI). The composites are fabricated by in situ polymerization of monomer reactants (PMR) using three monomeric ingredients: bis(3,4-dicarboxyphenyl) sulfide dianhydride (TDPA); 4,4'-methylene dianiline (MDA); and the monomethyl ester of norbornene anhydride (NE). By changing monomeric molar ratio, three formulations are prepared, in which formulated molecular weight between crosslink sites varies from 1487 to 3446 g mol(-1). Unidirectional composite laminates from each formulation and T300 carbon fibres are compression moulded and cut into a series of test specimens. By measuring the glass transition temperature (T-g), Mode I interlaminar fracture toughness (G(IC)) and other mechanical properties at room and elevated temperatures, the influences of formulated molecular weight on the temperature resistance and mechanical properties of PTI-based composites are investigated.

Single-crystalline nanowires of SiC synthesized by carbothermal reduction of electrospun PVP/TEOS composite fibres

Nanowires of SiC were synthesized by carbothermally reducing PVP/TEOS composite fibres obtained by electrospinning. High-resolution transmission electron microscopy (HRTEM) and selected-area electron diffraction (SAED) indicated that the SiC nanowires are single crystalline in nature. Both Fourier-transformed infrared spectroscopy and HRTEM indicated that a thin layer of SiO2 was formed on the outer surface of the nanowire as a result of post-heat treatment for the removal of residual carbon. Such SiO2 layer protects the inner SiC fibre from further oxidation. The formation mechanism of single-crystalline SiC nanowires was proposed based on our understanding and characterizations. The growth of the nanowire is believed to be along the ( 111) of its cubic cell.

Pull-in Instability Study of Carbon Nanotube Tweezers Under the Influence of Van der Waals Forces

The pull-in instability of two nanotubes under van der Waals force is studied. The cantilever beam with large deformation model is used. The influence of nanotube parameters such as the interior radius, the gap distance between the two nanotubes, etc, on the pull-in instability is studied. The critical nanotube length is determined for each specific set of nanotube parameters. The Galerkin method is applied to discretize the governing equations, and it shows good convergence.

Experimental investigation of the shear strength of a unidirectional carbon/aluminum composite under dynamic torsional loading

In this paper, the dynamic shear strength of a unidirectional C/A356.0 composite and A356.0 alloy, respectively, are measured with a split Hopkinson torsional bar (SHTB) technique. The results indicate that the carbon fibers make very little contribution to the enhancement of the shear strength of the matrix material. The microscopic inspections on the fracture surface of the composite show a multi-scale zigzag feature. This implies that there is a complicated shear failure mechanism in the unidirectional carbon/aluminum composite.