Oxidation inhibition effects of phosphorus and boron in different carbon fabrics

To improve oxidation inhibition, elemental boron and two phosphorus compounds were doped into an activated carbon cloth and a carbon felt. The hypothesis was that P can block active sites by virtue of the formation of C-P-O or C-O-P bonds at graphene edges while substitutional B can alter the chemical reactivity of the residual free active sites by reducing the electron density in the graphene layer. To increase the final dopant concentration, the carbon felt was activated in nitric acid. The crystallinity of activated carbon cloth was improved by heat treatment and substitutional B; that of carbon felt was also improved, but not necessarily due to substitutional B. In all cases the oxidation reactivity is suppressed by heat treatment and in the presence of dopants. The oxidation inhibition mechanism in P-doped samples appears to be active sites blockage because of a proportional increase of oxidation inhibition with increasing P loading. The results for B-doped samples are consistent with our previous studies in which B was found to exhibit both a catalytic and an inhibiting effect on carbon oxidation. Samples doped with both P and B showed the most effective oxidation inhibition and their oxidation behavior is described in detail.     

Adsorption of H2S or SO2 on an activated carbon cloth modified by ammonia treatment

The aim of this research is to investigate how ammonia treatment of the surface can influence the activity of a viscose-based activated carbon cloth (ACC) for the oxidative retention of H₂S and SO₂ in humid air at 25 °C. Surface basic nitrogen groups were introduced either by treatment with ammonia/air at 300 °C or with ammonia/steam at 800 °C. The pore structure of the samples so prepared was examined by adsorption measurements. Changes in the surface chemistry were assessed by X-ray photoelectron spectroscopy, X-ray absorption spectroscopy and temperature programmed desorption (TPD). The change of ACC activity could not be merely attributed to surface nitrogen groups but to other changes in the support. Ammonia/steam treatment improved ACC performance the most, not only by introducing nitrogen surface groups, but also by extending the microporosity and by modifying the distribution of surface oxygen groups. Successive adsorption-regeneration cycles showed important differences between oxidative retention of H₂S and SO₂ and the subsequent catalyst/support regeneration process.     

Carbon nanotubes and onions from carbon monoxide using Ni(acac)2 and Cu(acac)2 as catalyst precursors

New catalyst precursors (copper and nickel acetylacetonates) have been used successfully for the synthesis of carbon nanotubes and onion particles from carbon monoxide. Catalyst nanoparticles and carbon products were produced by metal-organic precursor vapour decomposition and catalytic disproportionation of carbon monoxide in a laminar flow reactor at temperatures between 705 and 1216 °C. Carbon nanotubes (CNTs) were formed in the presence of nickel particles at 923-1216 °C. The CNTs were single-walled, 1-3 nm in diameter and up to 90 nm long. Hollow carbon onion particles (COPs) were produced in the presence of copper particles at 1216 °C. The COPs were from 5 to 30 nm in diameter and consisted of several concentric carbon layers surrounding a hollow core. The results of computational fluid dynamics calculations to determine the temperature and velocity profiles and mixing conditions of the species in the reactor are presented. The mechanisms for the formation of both CNTs and COPs are discussed on the basis of the experimental and computational results.     

Carbon coating of anatase-type TiO2 through their precipitation in PVA aqueous solution

Fine particles of photocatalytic anatase-type TiO₂ prepared through hydrolysis of titanium-tetraisopropoxide were coated by carbon through their precipitation in poly(vinyl alcohol) (PVA) aqueous solution, followed by heat treatment at high temperatures of 400-1000 °C in a flow of high purity Ar. Without carbon coating, the phase transformation from anatase to rutile started above 600 °C, but it was suppressed up to 800 °C with carbon coating. Suppression of the phase transformation depended on the amount of carbon coated, apparent suppression being observed with carbon content above 5 mass%. The amount of carbon coated on anatase was controlled by changing the concentration of PVA in the solution. In order to have a carbon content of about 5 mass%, a PVA solution with more than 2 mass% had to be used.     

Preparation and characterization of trilobal activated carbon fibers

The objective of this research was to evaluate the effectiveness of several different methods for controlling the pore size and pore size distribution in activated carbon fibers. Variables studied included fiber shape, activation time, and the addition of small amounts of silver nitrate. Pure isotropic pitch and the same isotropic pitch containing 1 wt.% silver were melt spun to form fibers with round and trilobal cross sections. These fibers were then stabilized, carbonized, and activated in carbon dioxide. Field emission scanning electron microscopy (FE SEM), electron dispersive spectra (EDS), and wavelength dispersive spectra (WDS) were used to monitor the size and distribution of the silver particles in the fibers before and after activation. Each of these analyses showed that the distribution of silver particles was extremely uniform before and after activation. The fibers were also weighed before and after activation to determine the percent burn-off. The BET specific surface areas of the activated fibers were determined from N₂ adsorption isotherms measured at −196 °C. The results showed that round and trilobal fibers with equivalent cross-sectional areas yielded similar burn-off values and specific surface areas after activation. Also, activation rates were found to be independent of CO₂ flow rate. The porosity of the activated fibers depended on the total time of activation and the cross-sectional area of fibers. The N₂ adsorption measurements showed that the activated fibers had extremely high specific surface areas (greater than 3000 m²/g) and high degrees of meso- and macro-porosity. FE SEM was also used to investigate surface texture and size of pore openings on the surfaces of the activated fibers. The photos showed that silver particles generated surface macro- and mesopores, in agreement with the inferences from N₂ adsorption measurements.     

A multiscale model for effective moduli of concrete incorporating ITZ water-cement ratio gradients, aggregate size distributions, and entrapped voids

This paper develops a model for the effective elastic properties of concrete, which is a function of the volume fractions, size distributions, and elastic properties of fine aggregate (FA) and coarse aggregate (FA) and entrapped voids. Furthermore, the model is a function of the overall water-cement ratio and specific gravity of cement. Explicitly modeled are the water-cement ratio gradients through the interfacial transition zone (ITZ), which, in turn, affect the variation of the cement paste elastic properties through the ITZ, while maintaining the total fractions of cement and water consistent with the overall water-cement ratio. The ITZ volume is also conserved.     

Influence of aggregates on chloride diffusion coefficient into mortar

In order to determine the influence of aggregates on chloride ion ingress, mortar specimens were cast with different aggregate size distribution and the same aggregate volume content. One side of the specimen was in contact with alkaline solution containing sodium chloride. The process of chloride ingress is due to diffusion. The effect of the interfacial transition zone (ITZ) around aggregate and of the tortuosity due to aggregates have been taken into account for interpreting the experimental data obtained. These two competing effects have been quantified by using the theory of composite materials. It appears that the diffusion coefficient varies as a function of the ITZ volume content and of the tortuosity.     

银杏内酯A和B的分离纯化研究

In this paper a simple preparative method for isolation and purification of ginkgolides A and B was developed,As starting material,a commercially available standardized ginkgo extract (EGb761,containing 24% flavonoid and 6% terpene trilactones) was used,After a pretreatment step,optimized by the uniform design method ,the concentrated intermediate extract with high content of GA and gb( 90%) was separated into the individual terpenes by preparative liquid chromatography eluted with petroleum ether-ethylacetate,Analysis of products was carried out by means of HPLC-ELSD(evaporative light -scattering detector),The results show that ginkgolides A and B are obtained in higher yield and better purity.