粗糙集属性约简在尾矿坝浸润线预测模型中的应用

在建立尾矿坝浸润线支持向量回归机（SVR）模型的过程中,预测精度低、计算时间长等问题较难解决,并且严重制约SVR模型的推广应用。为了解决以上问题,尝试引入粗糙集（RS）算法对训练样本的输入属性进行约简,同SVR算法共同建立浸润线预测模型。实例证明,RS-SVR模型有效降低了SVR模型在迭代时的计算难度,并使浸润线的预测精度得到了提高。由此可得,RS-SVR结合无论在理论上还是在实例应用中都具有可行性。     

Inhibition of tungsten particle growth during reduction of V-doped WO3 nanoparticles prepared by co-precipitation method

The effect of vanadium on the tungsten particle growth during hydrogen reduction has been discussed. The nanostructured V-doped WO₃ powder was synthesized by co-precipitation method with ammonium tungstate and ammonium metavanadate as its starting materials and was then reduced in hydrogen atmosphere. The products were characterized by X-ray diffractometry, scanning electron microscopy, thermogravimetric analysis and small angle X-ray scattering. It was observed that the vanadium added to tungsten oxide formed tungsta-vanadate solid solution and was then reduced to V–O–W bronze, V_xWO_3−y, during the early stage of hydrogen reduction and decomposed continuously to α-W and V₂O₃ during the entire WO₂ → W transition. The results of particle size measurement and morphological analysis showed that the addition of vanadium could effectively inhibit the particle growth of tungsten powder during the reduction process. The addition of vanadium mainly effects on nucleation of tungsten at the lower temperatures below 850 °C because the slow decomposition of V–O–W bronze continuously provides the nucleation sites on the surface of WO₂ particles during reduction via impeding the formation of WO₂(OH)₂ and providing of nucleation aids for W deposition from the surrounding WO₂.     

Synthesis of chromium carbide by reduction of chromium oxide with methane

In the present work, production of the chromium carbide was investigated by reduction of chromium oxide with methane-containing gas mixture. The experiments were conducted on the chromium oxide powder and methane gas at different temperatures, times, and gas mixtures. X-ray diffraction (XRD) analysis was used to characterize the products at different stages of reduction. The morphology of the starting chromium oxide powder and Cr₃C₂ were studied by electron microscopy technique. The results showed that the minimum temperature and time for carbide formation in 30%-methane gas mixture is about 850 °C and 20 min, respectively. X-ray diffraction analysis showed that Cr₃C₂ is the only carbide product. The formation of chromium carbide in 30%-methane gas mixture was completed at 1000 °C and 60 min.     

Structures of thermally and chemically reduced graphene

This study investigated the structures and compositions of two types of graphene (GP) produced by the reduction of graphene oxide (GO): GP_TR, produced by thermal reduction at 1073 K in N₂; and GP_CR, chemically reduced with hyrdazine. GP_TR and GP_CR have a small number of surface oxide groups with the compositions C₁₀₀O_3 ± 1 and C₁₀₀O_6.5 ± 2 and consist of six layers and three layers, respectively. The interlayer spaces are slightly larger than those in typical graphene produced by “top-down” exfoliation from graphite. These structures and compositions are intrinsic properties of graphene produced by the “bottom-up” layer-by-layer stacking process.     

Controlled reduction of Cu to Cu with an N,O-type chelate under hydrothermal conditions to produce Cu2O nanoparticles

N,O-type organic chelates reduced coordinated Cu²⁺ ions under hydrothermal reaction conditions to produce Cu₂O/CuO nanoparticles. Chelates in which the N and O atoms are closely spaced produced smaller amounts of CuO nanoparticles, indicating their higher ability to reduce Cu²⁺ ions to Cu⁺ ions. [Cu(Gly)₂]² with the shortest ligand chain length produced only Cu₂O nanoparticles and, therefore, can be used as a single molecule precursor for the synthesis of Cu₂O nanoparticles.     

Forming of tailor blanks having local thickening for control of wall thickness of stamped products

A two-stage forming process of tailor blanks having local thickening for controlling the distribution of wall thickness of stamped parts was developed. In the 1st stage, the target portion of the sheet for the local thickening is drawn into the die cavity, and then the bulging ring is compressed with the flat die under the clamping of the flange portion in the 2nd stage. The effects of the punch stroke, the clearance between the punch projection and die, and the projection width on the amount of the location thickening were examined. A 12% increase in thickness of the blank was obtained in an experiment. The tailor-formed blank having local thickening was applied to increase the wall thickness at the inner corner of a wheel disk. An 11% increase in wall thickness at the inner corner was successfully obtained in the experiment. The tailor blanks having local thickening obtained by the two-stage forming process are effective in controlling the distribution of wall thickness of the stamped parts.     

碳、硅铁及碳化硅对白钨矿还原动力学的影响

在实验室用15 kW碳管炉进行碳粉、硅铁粉(75％Si)、碳化硅粉对白钨矿粉(67．25％WO3)还原动力学影响的研究。结果表明,碳还原白钨矿的反应级数为二级,反应表观活化能为234．6 kJ／mol;碳在较低温度下,反应性能差,当温度达到1 400℃时,反应剧烈;随温度升高,硅铁的还原性能比较平稳,反应产生SiO₂,使渣量增加;碳化硅高温反应性能好(≥1 400℃);碳和硅铁适合较低合金化率(3％W),碳化硅适宜用于较高的合金化率(≥5％W)。     

使用双燃料发动机与普通柴油机作钻机动力的经济性分析

本文简要介绍2000型柴油／天然气双燃料发动机的技术特点,以及双燃料发动机与普通柴油机的区别,并以配备DJ40钻机动力为例,从经济效益方面对双燃料发动机与普通柴油机进行了对比分析,最终为优选双燃料发动机提供依据。     

Preparation and electrochemical properties of Co–Si3N4 nanocomposites

Cobalt nanoparticles on an amorphous Si₃N₄ matrix were synthesized by direct ball-milling of Co and Si₃N₄ powders for an improvement of their electrochemical performance. The microstructure, morphology and chemical state of the ball-milled Co–Si₃N₄ composites are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The electrochemical performance of Co–Si₃N₄ composites was investigated by galvanostatic charge–discharge process and cyclic voltammetry (CV) technique. It is found that metallic Co nanoparticles of 10–20 nm in size are highly dispersed on the amorphous inactive Si₃N₄ matrix after the ball-milling. The composite with a Co/Si molar ratio of 2/1 shows the optimized electrochemical performance, including discharge capacity and cycle stability. The formation of Co nanoparticles with a good reaction activity is responsible for the discharge capacity of the composites. The reversible faradic reaction between Co and β-Co(OH)₂ is dominant for ball-milled Co–Si₃N₄ composite. The surface modification of the hydrogen storage PrMg₁₂–Ni composites using Co–Si₃N₄ composites can enhance the initial discharge capacity based on the hydrogen electrochemical oxidation and Co redox reaction.     

Relative rates of various steps of NO–CH4–O2 reaction catalyzed by Pd/H-ZSM-5

Reaction mechanism of the reduction of nitrogen monoxide by methane in an oxygen excess atmosphere (NO–CH₄–O₂ reaction) catalyzed by Pd/H-ZSM-5 has been studied at 623–703 K in the absence of water vapor, in comparison with the mechanism for Co-ZSM-5. Kinetic isotope effect for the N₂ formation in NO–CH₄–O₂ vs. NO–CD₄–O₂ reactions was 1.65 at 673 K and decreased with a decrease in the reaction temperature. In addition, H–D isotopic exchange took place significantly in NO–(CH₄+CD₄)–O₂ reaction. These results are in marked contrast with the case of Co-ZSM-5, for which the C–H dissociation of methane is the only rate-determining step, and show that the C–H dissociation is slow but not the only rate-determining step in the case of Pd/H-ZSM-5.

A reaction scheme was proposed, in which the relative rates of the three steps ((i)–(iii) below) vary depending on the reaction conditions.

Further, in contrast to Co-ZSM-5, NO_x–CH₄–O₂ reaction was much slower than CH₄–O₂ reaction for Pd/H-ZSM-5; the presence of NO_x retards the reaction of CH₄ over the latter catalyst, while it accelerates the reaction over the former. It is suggested that CH₄ is activated directly by the Pd atoms in the case of Pd/H-ZSM-5, but by NO₂ strongly adsorbed on Co ion for Co-ZSM-5. The reaction order of the NO–CH₄–O₂ reaction with respect to NO pressure was consistent with this mechanism; 1.05 for Pd/H-ZSM-5 and 0.11 for Co-ZSM-5.