水泥石孔结构的X射线小角度散射研究

本文着重讨论了X射线小角度散射(SAXS)用于水泥石孔结构研究的方法以及相关的理论与实验问题。在大量实验的基础上,对国外同类工作中的某些有影响的结论提出了质疑。根据所得到的实验数据从一个侧面揭示了水泥石内比表面积与水灰比、相对湿度及干燥条件之间的关系。讨论了引起基件电子密度起伏不均的可能原因。实验结果对目前流行的孔结构模型中的某些观点提出了重新认识。本工作与其它实验研究手段相互补充有助于较全面和深入地了解水泥石的孔结构。     

水泥石与石灰石集料界面过渡区孔结构及其CH晶体亚微观结构的研究

本文采用SAXS法研究了水泥石和石灰石界面过渡区在10—300(?)区间的孔分布,并用XRD法研究了界面过渡区CH晶体的取向性和平均尺寸。综合讨论了混凝土界面过渡区亚微观结构的形成机理。从微观结构的角度探讨了掺加硅灰和降低水灰比对界面过渡区的改进。     

Concerning voids in polyimide

Small angle X-ray scattering (SAXS) has been used to evaluate the size and concentration of voids in poly(N,N′-bis-(phenoxyphenyl)pyromellitimide), PMDA-ODA. Analysis of the angular dependence of the scattering indicates the presence of voids ranging from 50 to 150 Å in radius. Integrated SAXS demonstrated that the volume fraction of voids was 7 × 10^?4. These results were supported by measurements of the attenuation factor as a function of the sample thickness.     

The application of small angle scattering techniques to porosity characterization in carbons

Small angle scattering (SAS) techniques offer a number of advantages for the investigation of the nature and behavior of porous materials. In particular, with respect to carbons, the essentially non-intrusive nature of SAS means that along with the more traditional, pre- and post-treatment characterization of carbons, in principle, characterization can also be performed in situ during adsorption and activation processes. In the current communication, the application of the techniques of small angle X-ray (SAXS) and neutron (SANS) scattering is reviewed specifically with respect to porosity characterization in carbons. First, the basis of these techniques is presented. More recent applications of SAXS and SANS to carbon porosity are presented, and their relative attributes are contrasted, including the related technique of contrast matching with SANS to distinguish “closed” from “open” porosity, and its application to elucidation of pore development mechanisms. Applications of other related techniques, such as μSAXS and TGA/SAXS, to carbon characterization and porosity development are also discussed.     

透水混凝土冻融剥蚀成因分析

为探究透水混凝土冻融剥蚀是否来自水泥浆体劣化,选取2.5~10.0 mm粒径骨料,制备了水灰比为0.31的透水混凝土及同水灰比的水泥石,测量二者冻融循环下质量、强度及透水混凝土相对动弹性模量变化。采用压汞法(MIP)测量水泥石冻融循环下孔结构特征参数及孔径分布变化,并通过扫描电镜(SEM)观察透水混凝土骨料水泥界面形貌演变。结果表明,在水冻与盐冻环境下透水混凝土宏观性能指标均有不同程度下降,骨料水泥界面产生裂缝并随冻融次数增加不断扩展,而水泥石强度、质量及微观孔隙结构均无明显变化。这表明透水混凝土冻融劣化与骨料水泥界面劣化相关。     

ODTMA+ and HDTMA+ organo-montmorillonites characterization: New insight by WAXS,SAXS and surface charge

In this work we investigate the microstructure and properties of organo-montmorillonites (OMts) synthesized by intercalation of a Patagonian Mt with different surfactant/CEC ratios (0.5, 1 and 2) of octadecyl trimethylammonium (ODTMA⁺) and hexadecyl trimethylammonium (HDTMA⁺) cations. X-ray diffraction (XRD) patterns showed that in all OMt samples d₀₀₁ value increases with respect to raw Mt (1.258 nm). Small angle and wide angle X-ray scattering (SAXS and WAXS) curves, particle apparent diameters (determined by laser), zeta potential values and scanning electron microscopy (SEM) images, showed the presence of assorted d₀₀₁ values (which depend on storage conditions), aggregate formation and charge reversal (which varied with loading and cation length) for samples obtained with 1 and 2 CEC. However, for samples intercalated with 0.5 CEC, we found evidence of smaller aggregate formation, no charge reversal, and similar d₀₀₁ and zeta potential values (both higher than those of Mt). Findings reported here will help attain better conditions to functionalize highly charged Mt making them suitable to be used as nanocomposite precursors for different applications.     

杂化介孔二氧化硅陈化过程中结构的演变及其SAXS表征

运用小角X-射线散射(SAXS)技术,定量地分析了杂化介孔二氧化硅产物SiO2骨架、介观孔洞以及纳米结构整体的分形维数在陈化处理过程中的演变过程。结果表明,SiO2骨架电子不平均区尺度(E)、孔洞回旋半径(Rg)和整体质量分形(DM)尺度数目都呈逐渐减少的趋势,标志着在陈化处理过程中产物整体结构规整程度逐步得到提高。     

SAXS方法及其在多孔材料研究中的应用

小角X射线散射（SAXS）是一种有效，重要的亚微结构分析手段。本文主要介绍了SAXS对于非理想两相体系的解析方法及其在多孔材料中的应用。     

Evidence of the vital role of the pore network on various catalytic conversions of N2O over Fe-silicalite and Fe-SBA-15 with the same iron constitution

Fe-silicalite and Fe-SBA-15 with similar iron content have been characterized by N₂ adsorption, small angle X-ray scattering (SAXS), wide-angle X-ray scattering (WAXS), scanning electron microscopy (SEM), high-resolution transmission electron micrographs (HRTEM), UV–vis–DRS and EPR, and tested in direct N₂O decomposition, N₂O reduction by CO and N₂O-mediated propane oxidative dehydrogenation. Both catalysts contain almost exclusively isolated Fe³⁺ sites of similar concentration and structure, which are, however, stabilized in markedly different pore geometries (intersecting channels of ca. 0.55 nm diameter in Fe-silicalite versus parallel linear pores of ca. 7.5 nm diameter in Fe-SBA-15). This aspect is of vital importance in order to exclusively ascribe different catalytic performances to the environment where the iron species are stabilized. Fe-silicalite revealed to be much more active than Fe-SBA-15 in all reactions studied. This clearly illustrates that the confinement of the iron species in pores of suitable geometry (structure and size) is essential to originate their remarkable catalytic properties. The large pores in ordered mesoporous materials apparently do not generate the required intimate contact between potentially active Fe sites and reactant molecules.     

Nuclear magnetic resonance characterization of high- and ultrahigh-performance concrete: Application to the study of water leaching

In the present study, we show that high-resolution ²⁹Si and ²⁷Al magic angle spinning (MAS) nuclear magnetic resonance (NMR) can be a powerful tool for analyzing actual concrete mixes. The influence of the amount of silica fume and of the type of cement in high-performance concrete (HPC), as well as the influence of the type of silica fume and of the granular packing in ultrahigh-performance concrete (UHPC) were investigated. Significant effects on the amount and shape of C-S-H, on the incorporation of aluminum in the C-S-H structure, and on the distribution of aluminum-containing hydrates were observed. Nuclear magnetic relaxation of protons was also performed and it showed the fractal feature of the pore size distribution in UHPC and the higher amount of larger pores in HPC. The microstructure of the surface of these same formulations leached by mineral water for up to 1 year exhibits slight modifications.     

Phase distribution and microstructural changes of self-compacting cement paste at elevated temperature

Self-compacting concrete, as a new smart building material with various advanced properties, has been used for a wide range of structures and infrastructures. However little investigation have been reported on the properties of Self-compacting when it is exposed to elevated temperatures. Previous experiments on fire test have shown the differences between high performance concrete and traditional concrete at elevated temperature. This difference is largely depending on the microstructural properties of concrete matrix, i.e. the cement paste, especially on the porosity, pore size distribution and the connectivity of pores in cement pastes.In this contribution, the investigations are focused on the cement paste. The phase distribution and microstructural changes of self-compacting cement paste at elevated temperatures are examined by mercury intrusion porosimetry and scanning electron microscopy. The chemical decomposition of self-compacting cement paste at different temperatures is determined by thermogravimetric analysis. The experimental results of self-compacting cement paste are compared with those of high performance cement paste and traditional cement paste. It was found that self-compacting cement paste shows a higher change of the total porosity in comparison with high performance cement paste. When the temperature is higher than 700 °C, a dramatic loss of mass was observed in the self-compacting cement paste samples with addition of limestone filler. This implies that the SCC made by this type of self-compacting cement paste will probably show larger damage once exposed to fire. Investigation has shown that 0.5 kg/m³ of Polypropylene fibers in the self-compacting cement paste can avoid the damage efficiently.     

Structural Investigation of Resorcinol Formaldehyde and Carbon Aerogels Using SAXS and BET

The structure of organic RF aerogels (RF Recorcinol Formaldehyde) and carbon aerogels, their pyrolized counterparts, can be modified upon variation of the resorcinol to catalyst (RC) ratio. RF aerogels with RC ratios between 100 and 1500 have been produced in steps of 100. The densities for the organic aerogels were kept in the range of 350 to 390 kg m^-3. After pyrolysis, these samples have nearly the same density as their RF precursors, except the ones with very low RC ratios. This is due to the combined shrinkage and mass loss during the heat treatment. All samples were investigated using small angle X-ray scattering (SAXS) and nitrogen sorption (BET) as well as transmission electron microscopy (TEM). Two main effects have been observed. On the one hand, the particle/pore diameter distribution widens with increasing RC ratio, i.e., decreasing catalyst concentration. The average pore diameter increases from 20 nm to about 100 nm. On the other hand the pyrolysis generates a considerable amount of micropores in the particles.     

Small and wide angle X-ray studies of impregnated activated carbons

Small angle X-ray scattering (SAXS) and powder X-ray diffraction (XRD) measurements were made on CuO-impregnated activated carbons, prepared with and without an HNO₃ co-impregnant, in order to determine the effect of impregnant loading and HNO₃ content on impregnant distribution. A comprehensive matrix of 30 CuO-impregnated samples with five HNO₃ concentrations and six impregnant loadings was prepared and studied. As a highlight, in Cu-based samples prepared with no HNO₃, relatively small particle size CuO impregnant (approximately 3 nm) was observed at low impregnant loading and additional CuO appeared in large particles (>10 nm diameter) in meso and macropores as the impregnant loading increased. By contrast, when 4 M HNO₃ was present during the impregnation, the largest impregnant particles found were less than 4 nm. Results from SAXS data were shown to be in good agreement with XRD and data obtained from nitrogen gas adsorption isotherms. The combination of SAXS and XRD is shown to be a powerful combination in elucidating the nanostructure of impregnated activated carbons.     

Heterogenized Molybdovanadophosphoric Acid on Amine-Functionalized SBA-15 for Selective Oxidation of Alkenes

Mono-vanadium substituted molybdovanadophosphoric acid has been immobilized on amine-functionalized SBA-15 and characterized by different techniques. Small angle X-ray scattering (SAXS) analysis and SEM technique provide evidence for the structural integrity of the amine-functionalized SBA-15 and for the molybdovanadophosphoric acid immobilized sample. Diffuse reflectance UV–vis, ³¹P, ⁵¹V-NMR and FT-IR data confirm the incorporation of molybdovanadophosphoric acid onto the amine-functionalized SBA-15. The textural properties of these materials were studied by nitrogen sorption studies. Oxidation of selected substrates, norbornene, cyclooctene, cyclohexene and styrene with aqueous hydrogen peroxide was carried out with the immobilized molybdovanadophosphoric acid catalyst (heterogenized) and the results were compared with that of the neat molybdovanadophosphoric acid catalyst (homogeneous). The selectivity of the desired products was higher with the immobilized catalyst. The immobilized catalyst could be separated after the reaction and the reusability of the catalyst has also been demonstrated.     

Entrapment of Immature Amyloid Protofilaments in the Hydrophobic Domain of Schizophyllan

β-1,3-glucan schizophyllan (SPG) is known to adopt a triple helical structure in nature and a random coil conformation in alkaline solutions which forms a hydrophobic domain when its random coil is renatured. This paper presents the complexation of amyloid with SPG, presumably owing to hydrophobic interactions between the β-sheets and the SPG hydrophobic domain. Circular dichroism (CD) showed that complex had a negative band at 225 nm, indicating the presence of the stacked β-sheets. However, wide angle X-ray scattering (WAXS) showed no clear inter β-sheet diffractions that are generally observed at 1.0 nm in matured amyloid. Combining WAXS and CD, it can be concluded that lysozyme in complex has β-sheets but the β-sheets are not well stacked to give diffraction. Small angle X-ray scattering (SAXS) profile from complex can be reproduced using a combination of the cross-sectional Gunier and Debye-Bueche functions.     

小角Ｘ射线散射模糊数据解析方法

小角Ｘ射线散射（ＳＡＸＳ）是研究多孔材料结构的一种有效方法，可得到孔径分布、平均孔径、比表面、界面层厚度、分形维数等许多微结构住处、ＳＡＸＳ理论公式基于点状光源（针孔准直），但实践中则大多采用长狭准直条件，简要综述了ＳＡＸＳ在长狭缝准直条件下直接应用模糊强度进行煤、炭、干凝胶、分子筛等多孔材料结构解析的方法，并与针孔准直进行了对比。     

Analysis of iron oxides accumulating at the interface between aggregates and cement paste

Iron oxides formed by the corrosion of a steel reinforcing bar were found to accumulate at interfaces between aggregate and cement paste in Portland cement-based concrete. Microstructural characterization of the zones of oxide was carried out using optical microscopy, scanning electron microscopy (SEM), and energy dispersive X-ray (EDX) spectroscopy. The study showed that the oxide layer has an average thickness of about 1.5 mm, and consists of inner and outer layers with different types of oxides in each layer. A mechanism based on the Schikorr reaction is proposed for the preferential formation of iron oxides in the two layers taking into account local variations in pH of the pore solution during the early ages of the cement paste.     

小角X-射线散射法测定Pd-Al_2O_3催化剂上钯颗粒尺寸

用小角X-射线散射法测定了Pd-Al2O3。催化剂上金属钯粒子的大小。使用少量电子密度与Al2O3。相似的有机液体──CH2I2，消除了载体氧化铝微孔的背景干涉散射，CH2I2的适宜用量与样品的比孔容有关。SAXS的分析结果与SEM结果对照认为二者基本上是吻合的。     

Insights into the formation of microporous materials by in situ X-ray scattering techniques

Here we demonstrate the power of in situ scattering techniques in the understanding of formation of nanoporous aluminosilicate and aluminophosphate materials. We utilised a number of X-ray techniques, in particular, in situ energy dispersive X-ray diffraction (EDXRD) and small angle and wide angle X-ray scattering (SAXS/WAXS) techniques for this purpose. The in situ SAXS measurements show the formation of homogeneous precursors in the size of ca. 10 nm, prior to the crystallization of LTA. The crystal size is estimated by fitting the SAXS patterns with an equation for a cubic particle, and it is revealed that the final crystal size of the LTA depends on the synthesis temperature. Whereas, the crystallisation of CoAlPO-5, occurs through the formation of poly-dispersed particles with an average size of the precursor particle of ca. 50 nm. Also shown the effect of temperature and structure directing organic cations on the production of CoAlPO-5 materials.     

Analysis of C-S-H gel and cement paste by small-angle neutron scattering

The role of small-angle X-ray and neutron scattering (SAXS and SANS) in the characterization of cement is briefly reviewed. The unique information obtainable from SANS analysis of C-S-H gel in hydrating cement is compared with that obtainable by other neutron methods. Implications for the nature of C-S-H gel, as detected by SANS, are considered in relation to current models. Finally, the application of the SANS method to cement paste is demonstrated by analyzing the effects of calcium chloride acceleration and sucrose retardation on the resulting hydrated microstructure.