内掺Ca(OH)_2对碱矿渣混凝土水化进程的影响

以钠水玻璃为激发剂,用Ca(OH)_2等量取代矿渣,研究了不同水胶比下Ca(OH)_2对碱矿渣混凝土早期性能的影响.使用水化动力学分析、X射线衍射(XRD)及扫描电子显微镜(SEM)分析了碱矿渣混凝土的水化过程.结果表明:掺入Ca(OH)_2后,碱矿渣混凝土的凝结速率增大并造成快速坍落度损失;当Ca(OH)_2掺量(质量分数)分别为5%和10%时,碱矿渣混凝土中水泥加速期的水化反应速率常数(K)由4.76×10~(-5)分别增长至5.60×10~(-3)和1.56×10~(-2),水泥水化诱导期显著缩短,Ca(OH)_2主要作用于水化加速期,同时水化加速期反应级数(N)由2.89分别减小至1.26和0.98,意味着加速期反应由反应物通过致密层生成物扩散控制逐渐转变成反应物沉积控制;Ca(OH)_2加快了24h内碱矿渣水泥的水化,并生成了C_2ASH_8及C_4AH_(13)等水化产物.     

Facile synthesis of multiblock copolymers composed of poly(tetramethylene oxide) and polystyrene using living free-radical polymerization macroinitiator

A facile synthetic strategy for well-defined multiblock copolymers utilizing ‘living’ free-radical polymerization macroinitiator has been presented. Polyurethane composed of alkoxyamine initiating units and poly(tetramethylene oxide) (PTMO) segments was prepared by polyaddition of tolylene 2,4-diisocyanate terminated PTMO with an alkoxyamine-based diol. Polymerization of styrene with the polyurethane macroinitiator was carried out under nitroxide-mediated free-radical polymerization (NMRP) condition. GPC, NMR, and IR data revealed that the polymerization was accurately controlled and well-defined polystyrene chains were inserted in the main chain of macroinitiator to give the poly(tetramethylene oxide)-b-polystyrene multiblock copolymers. The synthesized multiblock copolymers were characterized by tensile test, differential scanning calorimetry, and dynamic mechanical analysis. Mechanical properties of the multiblock copolymers can be tuned by the sufficient molecular weight control of PS chains. Soft segment of PTMO and hard segment of PS were apparently compatible due to the multiblock structure of low molecular weight segments and polar urethane groups.     

Homogeneous ZrO2–Al2O3 Composite Prepared by Nano-ZrO2 Particle Multilayer-Coated Al2O3 Particles

ZrO₂–Al₂O₃ nanocomposite particles were synthesized by coating nano-ZrO₂ particles on the surface of Al₂O₃ particles via the layer-by-layer (LBL) method. Polyacrylic acid (PAA) adsorption successfully modified the Al₂O₃ surface charge. Multilayer coating was successfully implemented, which was characterized by ξ potential, particle size. X-ray diffraction patterns showed that the content of ZrO₂ in the final powders could be well controlled by the LBL method. The powders coated with three layers of nano-ZrO₂ particles, which contained about 12 wt% ZrO₂, were compacted by dry press and cold isostatically pressed methods. After sintering the compact at 1450°C for 2 h under atmosphere, a sintered body with a low pore microstructure was obtained. Scanning electron microscopy micrographs of the sintered body indicated that ZrO₂ was well dispersed in the Al₂O₃ matrix.     

Reactivity of surface isocyanate species with NO, O2 and NO+O2 in selective reduction of NOχ over Ag/Al2O3 and Al2O3 catalysts

Reactivity of surface isocyanate (NCO(a)) species with NO, O₂ and NO+O₂ in selective reduction of NOχ over Ag/Al₂O₃ and Al₂O₃ catalysts was studied by a pulse reaction technique and an in situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. The NCO(a) species on Ag/Al₂O₃ reacted with O₂ or NO+O₂ mixture gas to produce N₂ effectively above 200°C, while the reaction of NCO(a) with NO hardly produced N₂ even at 350°C. In the case of Al₂O₃ alone, less N₂ was detected in the reaction of NCO(a) with NO+O₂, indicating that silver plays an important role in the N₂ formation from NCO(a). These behaviors of the reactivity of NCO(a) species with reactant gases were in good agreement with the changes in NCO(a) bands shown by in situ DRIFT measurements. Based on these findings, the role of NCO(a) species in the selective reduction of NOχ on Ag/Al₂O₃ and Al₂O₃ catalysts is discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

FTIR studies of the effects of outdoor exposure on varnish-coated wood pretreated with CCB or water repellents

Scots pine (Pinus sylvestris L.)and chestnut (Castanea sativa Mill.) panels were coated with a polyurethane or an alkyd-based synthetic varnish. Some of the panels were impregnated with chromium-copper-boron (CCB) or the varnishes themselves before coating, as preservative-coating or water repellent (WR)-coating combination treatments, respectively. Earlier drastic changes in the intensity of the bands assigned to lignin and their shifts to some other stretching points were mostly attributed to chemical modification of lignin with the chromium in CCB, as well as the previously reported high color stability of CCB-impregnated wood. IR spectra of the nine months of weathering indicated that the synthetic varnish coating of non-impregnated or CCB-impregnated wood limited the reactions in lignin compared with polyurethane coating. Wood density and structural difference also seemed to play an important role since changes in lignin were mostly observed after six months of exposure for chestnut wood. Therefore, chemical reactions of CCB-wood cell wall components on the surface appeared likely to be affected from varnish type (their relative absorbency and distribution of sunlight), wood species (density and extractive substances), and exposure time and conditions. Technical Education Faculty, Mugla, 48000 Turkey. Faculty of Forestry, Trabzon, 61080 Turkey.     

Enzymatic enrichment of arachidonic acid from Mortierella single-cell oil

An attempt was made to enrich arachidonic acid (AA) from Mortierella single-cell oil, which had an AA content of 25%. The first step involved the hydrolysis of the oil with Pseudomonas sp. lipase. A mixture of 2.5 g oil, 2.5 g water, and 4000 units (U) Pseudomonas lipase was incubated at 40°C for 40 h with stirring at 500 rpm. The hydrolysis was 90% complete after 40 h, and the resulting free fatty acids (FFA) were extracted with n-hexane (AA content, 25%; recovery of AA, 91%). The second step involved the selective esterification of the fatty acids with lauryl alcohol and Candida rugosa lipase. A mixture of 3.5 g fatty acids/lauryl alcohol (1:1, mol/mol), 1.5 g water, and 1000 U Candida lipase was incubated at 30°C for 16 h with stirring at 500 rpm. Under these conditions, 55% of the fatty acids were esterified, and the AA content in the FFA fraction was raised to 51% with a 92% yield. The long-chain saturated fatty acids in the FFA fraction were eliminated as urea adducts. This procedure raised the AA content to 63%. To further elevate the AA content, the fatty acids were esterified again in the same manner with Candida lipase. The repeated esterification raised the AA content to 75% with a recovery of 71% of its initial content.     

Revisiting the Mechanism of β-O-4 Bond Cleavage During Acidolysis of Lignin. Part 3: Search for the Rate-Determining Step of a Non-Phenolic C6-C3 Type Model Compound

Abstract

The rate-determining step of a C₆-C₃ dimeric non-phenolic β-O-4 type lignin model compound, 2-(2-methoxyphenoxy)-1-(3,4-dimethoxyphenyl)propane-1,3-diol (veratrylglycerol-β-guaiacyl ether, VG), was evaluated under acidolysis conditions (0.2 mol/l HBr in 82% aqueous 1,4-dioxane at 85°C) by comparing the disappearances between VG and the corresponding compound labeled at the β-position of VG, 2-(2-methoxyphenoxy)-1-(3,4-dimethoxyphenyl)(2–²H)propane-1,3-diol. The disappearance of VG occurred more rapidly than that of the latter compound, and a primary kinetic isotope effect was clearly observed. This result indicates that the C-H bond at the β-position of VG is broken in the rate-determining step. Two possible mechanisms are presented as the rate-determining step: (1) A base abstracts the β-proton of a benzyl cation-type intermediate produced from VG affording an enol ether compound, 2-(2-methoxyphenoxy)-3-(3,4-dimethoxyphenyl)prop-2-en-1-ol; (2) The hydride transfers from the β- to the α-position of the benzyl cation. It was confirmed that both mechanisms certainly exist and that the latter seems to contribute more than has generally been considered.     

Fractionation and Characterization of Wood Cell Wall Components of Fagus crenata Blume Using LiCl/DMSO Solvent System

Abstract

The fractionation of wood cell wall components was achieved by the application of the LiCl/DMSO solvent system developed in our previous study. Various soluble and insoluble fractions were prepared from beech milled wood by extractions with DMSO containing different amounts of lithium chloride (LiCl) for the study of a lignin-carbohydrate complex (LCC). Nitrobenzene oxidation (NO) analyses demonstrated that the lignin in the soluble fractions always has lower yields of NO products consisting of syringaldehyde + syringic acid (S_y) and vanillin + vanillic acid (V_a). The syringyl ratios, S_y/(S_y+V_a), were also lower than in insoluble fractions. Accordingly, lignins with lower syringyl ratios are better soluble than those with higher syringyl ratios. The former is typical in the primary wall and the latter in the secondary wall. Solubilization of glucan is significantly dependent on the LiCl concentration in DMSO. In the absence of LiCl, only about 6% of glucan was found in the soluble fraction, but about 40% of lignin and xylan were solubilized. The additional 40% of lignin and xylan became soluble together with glucan solubilization, which increased at 3% LiCl concentration. However, a fraction amounting to 13% (based on the whole wood) still remained as a residue under these conditions. Glucan solubilization could not be the reason for this observation as ball-milled cellulose is soluble in 3% LiCl/DMSO. It is likely that strong interactions between lignin and carbohydrates prevent solubilization of this fraction, which has never been isolated and analyzed in previous studies.     

The differences in conformation between {alpha}-human atrial natriuretic polypeptide, {alpha}-hANP, and its derivative, Met(O)-{alpha}-hANP, in solution

The differences in conformation between -human atrial natriureticpolypeptide (-hANP) and its inactive analog, Met(O)--hANP, havebeen analyzed by nuclear magnetic resonance spectroscopy. Allproton resonances for both peptides were assigned by means ofthe sequential assignment procedure. The three-dimensional structureof -hANP in solution had previously been determined by distancegeometry calculation using distance constraints derived fromnuclear Overhauser effects (NOEs). Here, the three-dimensionalstructure of Met(O)--hANP was determined. The conformationaldifferences between these two molecules were as follows: threesegments of -hANP, Serl–Cys7, Arg11–Ala17 and Gln18–Tyr28,have some ordered structures. In Met(O)--hANP the Gln18-Tyr28region has a similar conformation, while the remaining two regionsdo not have the ordered structure found in -hANP. It is suggestedthat the conserved conformation of the Gln18–Tyr28 regionis required for binding to the ANP receptor and that the slightbiological activity of Met(O)-a-hANP is due to loss of the orderedstructures evoked in the Serl–Cys7 and Arg11–Ala17regions of -hANP.     

Crack propagation analysis of SiCf/SiC composites by gas permeability measurement

Permeability of helium gas through the NITE-SiC_f/SiC composites after applying tensile stress was measured experimentally in a vacuum apparatus. Tensile stress equal to 1.1-1.2 times the proportional limit stress (PLS) was applied parallel to the direction of the reinforced fiber. Results of the permeability experiments revealed that the permeability rapidly increased when threshold stress was applied on the specimens. The permeability of helium gas was governed by the narrowest diameter of the permeation pathway. In the case of NITE composites, the diameter of the pathway was calculated to be below 0.65 μm. The NITE composites exhibited superior performance even when the applied stress was greater than 1.2 times the PLS. Fiber bundles considerably magnified the permeability of helium gas because of the relatively large pore size of the intra-fiber bundles. Transverse cracks propagated with increasing stress and they connected fiber bundles when the applied stress was 1.10-1.15 times the PLS.