无砂大孔贫混凝土在百色水利枢纽专用公路中的应用

无砂大孔贫混凝土是应用于公路基层的新技术 ,具有加快施工进度 ,提高生产效率 ,延长路面混凝土的使用寿命 ,节约施工成本等优点。根据施工经验对其技术要求、配合比设计、施工方法、质量控制与检测等方面进行介绍。     

Soret Diffusion and Non‐Ideal Dufour Conduction in Macroporous Catalysts with Exothermic Chemical Reaction at Large Intrapellet Damköhler Numbers

The adiabatic temperature rise in catalytic pellets is predicted from a modified version of the Prater equation. Onsager reciprocal relations for coupled heat and mass transfer are violated in an analysis of thermal diffusion in macroporous catalysts with exothermic chemical reaction when Dufour conduction (i.e., the diffusion‐thermo effect) is neglected. In this contribution, Dufour conduction is analyzed for both ideal and non‐ideal pseudo‐binary gas mixtures that simulate the production of methanol from carbon monoxide and hydrogen. In the diffusion‐controlled regime at large intrapellet Damköhler numbers where intermolecular collisions provide the dominant resistance to mass transfer within the catalytic pores, temperatures in the catalytic core could be much greater than predictions based on the original Prater equation when the Prater number exceeds 0.30. The molecular flux of thermal energy includes Fourier's law, the interdiffusional flux, and Dufour conduction. Diffusional mass flux includes Fick's law and the Soret effect. All physicochemical properties of the reactive gas mixture exhibit temperature dependence. There is essentially no difference between maximum intrapellet temperature predictions that include or neglect ideal Dufour conduction when external catalytic surface temperatures range from 300‐400 K and thermal diffusion enhances the flux of “smaller” reactants toward the centre of the catalyst. For “large‐molecule reactants” that participate in exothermic reactions, thermal diffusion opposes Fick's law and Dufour conduction opposes Fourier's law. Under these conditions, it is demonstrated that core temperatures are overestimated by neglecting both off‐diagonal coupling mechanisms (i.e., Soret diffusion and Dufour conduction). Prater numbers greater than unity and unrealistically high gas pressures are required to distinguish between maximum intrapellet temperatures for ideal and real gas simulations, where the latter consider two‐body interactions for Lennard‐Jones molecules in the virial equation of state.     

Fast speed pore formation via strong oxidizers

It is difficult to produce nice macropores at high speed with strong oxidants via the breakdown mechanism on low doped n-Si. In this letter, HF-containing electrolytes were modified with strong oxidants; galvanostatically anodizing in the dark, macropores with depths upto 80 μm and pore-diameters between 100 and 1000 nm were fast produced on low doped substrate. Two new phenomena were observed: pore tips could be tumefied simultaneously and macropores could be filled with a uniform microporous layer under dark conditions. Mild short-range ordering of pores was observed. The macropores are rather nice while the etching rate could reach the highest of its kind, 1800 μm/h. The underlying mechanism was in the framework of the current-burst-model combined with avalanche breakdown; both pore pitch and pore-wall thickness could be significantly less than SCR (space charge region) width.     

Modelling water flow,nitrogen uptake and production for wheat

Soil water and temperature conditions were simulated for three years at three sites in the Netherlands, using a model named SOIL. Observed water table depths from one site with a sandy loam soil indicated bypass flow in macropores. Nitrogen turnover was simulated using the output of SOIL as input to a nitrogen model. To improve the nitrogen model, a crop-growth submodel was introduced, and simulations were compared with measured data for two seasons and three fertilizer treatments at the three sites. Mineral-N in the soil after application of fertilizer was substantially higher in the simulation than indicated by measurements in 4 out of 18 simulations. Regression analyses showed that simulated mineral-N content in the uppermost metre explained 64% of the observed variation. The corresponding values for nitrogen content (N _ta) and biomass (W _ta) of aboveground tissues were 86 and 93%, respectively. With a few exceptions annual values ofW _ta andN _ta were simulated with an accuracy of approximately 20%. A sensitivity test showed that growth parameters and especially the light use efficiency parameter strongly influenced biomass production for fertilized treatments whereas the control of nitrogen uptake from soil was most important for non-fertilized treatments.     

A facile synthesis method for millimeter polyacrylonitrile-based activated carbon spheres with radiate tunnel-like macropores

A facile approach was employed to prepare polyacrylonitrile-based activated carbon spheres (PAN-ACS) through Rayleigh instability, double diffusion and catalytic activation. The obtained PAN-ACS were characterized by nitrogen adsorption-desorption and scanning electron microscopy (SEM). PAN-ACS had a better sphericity, and its average diameter was about 1.75 mm. And it displayed a novel hierarchical porous structure, in which macropores were tunnel-like and meso- and micropores existed in the wall of tunnels. The diameter of the tunnels was about 10 μm. And the tunnels arrayed regularly, radiating from the core. The distribution peak of mesopores mainly located at about 4.0 nm.     

Analysis of p-Si macropore etching using FFT-impedance spectroscopy

The dependence of the etch mechanism of lithographically seeded macropores in low-doped p-type silicon on water and hydrofluoric acid (HF) concentrations has been investigated. Using different HF concentrations (prepared from 48 and 73 wt.% HF) in organic electrolytes, the pore morphologies of etched samples have been related to in situ impedance spectra (IS) obtained by Fast Fourier Transform (FFT) technique. It will be shown that most of the data can be fitted with a simple equivalent circuit model. The model predicts that the HF concentration is responsible for the net silicon dissolution rate, while the dissolution rate selectivity at the pore tips and walls that ultimately enables pore etching depends on the water content. The ‘quality’ of the pores increases with decreasing water content in HF/organic electrolytes.     

富氮多孔碳纤维的制备及其在超级电容器中的应用

以聚丙烯腈（PAN）为前驱体,制备具有发达三维网络结构的大/中孔PAN纤维,采用水合肼和盐酸羟胺处理使PAN纤维在产生交联反应的同时进一步引入氮原子,制备了富氮多孔碳纤维,并考察了富氮多孔碳纤维的形貌结构、孔结构特征及电化学性能。结果表明：富氮多孔碳纤维中的N和O原子含量分别为13.53%和8.01%,在电流密度为0.1 A/g时,比电容为222 F/g,比表面电容达0.80 F/m²。