Polymorphism of tricalcium silicate, the major compound of Portland cement clinker: 2. Modelling alite for Rietveld analysis, an industrial challenge

A comprehensive quantification of the various phases of clinkers by X-ray diffraction with a Rietveld-like analysis is an important industrial challenge. Various available structural models are used for the most frequent M1 and M3 polymorphs of alite usually found in industrial clinkers, referred to as M1- or M3-based clinkers. In this paper, the effect of C₃S structural model is investigated. Four models are tested and compared using either synthetic M1 and M3 alites or M1- and M3-based clinkers. The comparison validates the available models for M1 and M3 alites and an average model, given here, derived from our recently proposed M1 structure as a catch-all model when the nature of the clinker is unknown. The latter model is meant to be used for industrial on-line quantification.     

Surface Chemical Modification of Poly(Methylphenylphosphazene)

Summary The surface reactivity of poly(methylphenylphosphazene), PMPP, and its derivatives containing silane, PMPP-SiH, and alcohol, PMPP-OH, substituents was investigated. These polymers were fabricated into films by casting from THF solutions and reactions were carried out at the interface between solid film samples and solutions. The surface of PMPP was successfully modified by deprotonation under dilute conditions followed by reactions with RMe₂SiCl [where R = CH=CH₂, and H]. While surfaces of PMPP-OH were not readily modified, those containing Si-H groups reacted with oxygen when heated and with carbon tetrachloride. The polymer surfaces were examined by contact angle measurements, attenuated total reflectance infrared spectroscopy (ATR-IR), and scanning electron microscopy (SEM). We dedicate the paper to Christopher W. Allen in recognition of his outstanding contributions to inorganic ring and polymer chemistry.     

Cu/SBA-15 as adsorbent for propane/propylene separation

Samples of mesoporous silica SBA-15 were prepared under hydrothermal conditions where Cu cations were incorporated to the structure by impregnation in order to compare the adsorption behavior in the presence and absence of this element. The adsorption/desorption equilibrium isotherms of propylene, propane, and N₂ were measured to evaluate their usefulness in the propane/propylene separation. All the adsorption isotherms of SBA-15 measured in the absence of Cu cations were described by the Freundlich equation, while the adsorption isotherms of propane on Cu/SBA-15 were better represented by the Henry equation and those of propylene were satisfactorily described by the Langmuir model in the range P < 100 Torr. The adsorption uptake of propylene increased and that of propane decreased in Cu/SBA-15 as compared to the amounts observed in the SBA-15 sample. The presence of Cu atoms in the adsorbent lattice increased the selectivity towards propylene. Under some working conditions the adsorbed amount of propylene in Cu/SBA-15 sample was totally reversible and the propane uptake, negligible.     

不规则面积测算方法及精度分析

面积测量有多种方法,采取何种方法取决于测区的环境条件、测量要求及仪器设备情况,不同的测量方法对面积的测量精度会产生不同的影响。本文结合实例介绍了对土地面积测量的方法和精度分析。     

NO reduction by CH4 over Pd/Co-sulfated zirconia catalysts

A series of sulfated zirconia supported Pd/Co catalysts was synthesized by the sol–gel method and examined for NO_x reduction by methane. The NO conversion increased up to a Co/S ratio of 0.43, and then decreased at a higher Co loading (Co/S = 0.95). Sulfate content was also essential for obtaining high selectivity to molecular nitrogen. A catalyst loaded with 0.06 wt.% Pd, 2.1 wt.% Co and 2.1 wt.% S (Pd/Co-SZ-2) exhibited remarkable performance under lean conditions and displayed stability in a long-term durability test using a synthetic reaction mixture containing 10% water vapor. This catalyst exhibited the highest sulfur retention most probably as cobalt sulfide. Besides, the catalytic oxidation of NO to NO_y groups was confirmed by FT-IR, in agreement with the general mechanism for the SCR of NO by hydrocarbons. In the absence of oxygen in the feed stream, the catalyst was highly active for NO reduction with methane. IR stretching bands assigned to N₂O and adsorbed nitro groups were identified upon adsorbing NO on Pd/Co-SZ-2. This indicates that under rich conditions disproportionation of NO to N₂O and NO₂ occurs and confirms that the formation of NO₂ species is an essential step for NO reduction by CH₄.     

In vivo aging of gutta‐percha dental cone

Gutta‐percha cone is the most widely used material for root canal filling. The in vivo aging of this cone focus on the degradation of its main organic component, trans‐1,4‐polyisoprene, was studied. Aged cones (25 samples) from 2 to 30 years of root canal filling were extracted from different patients in the occasion of retreatment by mechanical way. The information about the aging time was given by the patients. Gel‐permeation chromatography (GPC) and infrared spectroscopy (FTIR) were the analytical techniques used. Polyisoprene degrades with time of aging, but in a slow process. Decrease in polymer molar mass from 5.7 × 10⁵ to 1.7 × 10⁵ g/mol was observed in polyisoprene from cone after 30 years of root canal filling and inside a noninfected tooth. In tooth with caries and periodontal infection, the decrease in molar mass is higher (4.6 × 10⁴ g/mol in cone with 10 years of aging). The production of carbonyl and hydroxyl groups in the aged material indicates that the process is oxidative, even in closed teeth. In these cases, the oxygen could be provided from tissue fluid. The degradation mechanism is complex and depends on many factors, besides time of root canal filling. The dental problem caused by the aging could be the production and migration of cytotoxic substances to periodontal ligament and the reduction on the canal sealing property due to the polymer weight loss. Both of them could contribute to the root canal treatment failure. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100:4082–4088, 2006     

Electrical and optical study of Cu(In, Ga)Se2 co-evaporated thin films

Co-evaporation technique from three sources was used to prepare Cu(In, Ga)Se₂ polycrystalline thin films for photovoltaic conversion. Their conductivity was studied in the range 20–300 K. The grain boundary scattering mechanism is mainly responsible for the diffusion process in the latter materials. In the low temperature region, we interpret the data in terms of Mott law and the analysis is very consistent with the variable range hopping. However, thermoionic emission is predominant at high temperatures. When the conductivity deviates from the classical grain boundary conduction models, inhomogeneity is then considered and parameters such as the standard deviation and the mean potential barrier height are derived. Transmittance measurements yielded band gap values of 1.07 and 1.64 eV for CuInSe₂ and CuGaSe₂, respectively.     

Selective hydrogenation of soybean oil in the presence of copper catalysts

Many investigators associate the poor keeping properties of soybean oil with its linolenic acid content. On the other hand the high linoleic acid content is a desired property from a nutritional point of view. We have therefore developed a process for the preferential reduction of the linolenic acid content by selective hydrogenation. Conventional catalysts for the hydrogenation of fats have a rather low selectivity in this respect. When linolenic acid in soybean oil is hardened (e.g., with a nickel catalyst), most of the linoleic acid is converted into less unsaturated acids. It was found that linolenic acid is hydrogenated much more preferentially in the presence of copper catalysts than in that of nickel and other hydrogenation catalysts. At a linolenic acid content of 2%, soybean oil hardened with nickel catalyst contained about 28% linoleic acid, whereas with copper catalyst the hardened soybean oil contained 49% linoleic acid. By means of our process it is possible to manufacture a good keepable oil of, e.g., I.V. 115 and containing 1% linolenic acid and 46% linoleic acid. The storage stability of this product is comparable with that of sunflower-seed oil. A liquid phase yield of 86% is obtained after winterization at 5C for 18 hr. The high selectivity for linolenate reduction of copper catalysts must be ascribed to the copper part of the catalyst. Investigations into the structure of the catalyst indicate that the active center consists of copper metal crystallites; whether these centers are promoted by the carrier or traces of other substances is under investigation.     

配合物Zn(Him)2(OAc)2的室温固相合成及表征

乙酸锌与咪唑 (Him)通过室温固相反应一步合成配合物Zn(Him) 2 (OAc) 2 ,反应不需溶剂 ,2 0min即可完成 ,产率达 96% ,并用元素分析、红外光谱、热重分析、X -射线粉末衍射和X -射线单晶衍射对产物进行了表征。     

Nile blue adsorbed onto silica gel modified with niobium oxide for electrocatalytic oxidation of NADH

A study of modified carbon paste electrode employing Nile blue (NB) adsorbed on silica gel modified with niobium oxide (SN) for electrocatalytic oxidation of reduced nicotinamide adenine dinucleotide (NADH) is described. The adsorbed organic dye on SN was used to prepare a modified carbon paste electrode to investigate its electrochemical properties. The formal potential (E°′) of the adsorbed NB (−230 mV vs. saturated calomel electrode, SCE) showed a shift of 70 mV towards a more positive potential value, compared to NB dissolved in aqueous solution. In solutions with pH between 6.0 and 8.0 did stability and E°′ remained almost constant. However, for a solution pH lower than 6.0 the E°′ was affected by the acidity of the contacting solution, shifting the E°′ towards more positive values. For the solution pHs between 6.0 and 8.0 the electrocatalytic activity remained almost constant. A linear response range for NADH between 1.0×10⁻⁵ and 5.2×10⁻⁴ mol l⁻¹, at pH 7.0, was observed for the electrode, with an applied potential of −200 mV versus SCE. The formation of an intermediate charge transfer (CT) complex was proposed to the CT reaction between NADH and adsorbed NB. The heterogeneous electron transfer rate, k_obs, was 1400 M⁻¹ s⁻¹ and the apparent Michaelis-Menten constant, was 0.21 mM at pH 7.0 evaluated from rotating disk electrode (RDE) experiments with an electrode coverage of about 5.2×10⁻⁹ mol cm⁻². The increase in the reaction rate between NADH and the immobilized NB compared to those obtained with dissolved NB was assigned to the shift of the E°′ towards more positive values.