镁渣晶体结构对脱硫活性影响实验

研究了激冷水合过程中镁渣晶体结构的变化,结合钙转化率研究了晶体结构对镁渣脱硫活性的影响。借助X射线衍射和透射电镜分析了镁渣的晶体结构和形貌特征。结果表明：β-C₂S中的Ca²⁺配位不规则是其水合活性高于γ-C₂S的原因。随着镁渣激冷温度升高,β-C₂S增加,促进了具有发达孔隙结构的C－S－H生成,提高了物理吸附能力;晶粒细化程度增大,晶胞参数变化引起的晶格缺陷增多,增强了化学吸附能力。950℃激冷温度下镁渣脱硫活性最高,钙转化率达到24.6%。     

Identification of structural defects in graphitic materials by gas-phase anisotropic etching

We developed a method of identifying the structural defects in graphitic materials by an anisotropic etching technique. Intrinsic and oxygen- or argon- plasma induced artificial defects' density and domain size can be obtained easily and precisely. It was inferred, through our investigations, that the grade ZYA highly oriented pyrolytic graphite (HOPG) sample has a better crystal quality, with a lower defect density, while the Kish graphite has a larger grain size and higher defect density. Defect types and lattice orientations can also be extracted by this technique. Furthermore, this method could apply to various graphitic materials including graphene.     

Effect of titanium chelating compound on hydration resistance of CaO material

The hydration resistance of CaO materials prepared by Ca(OH)₂ calcination with titanium chelating compounds is investigated in this paper. The crystalline phases and microstructure characteristics of sintered specimens were studied by X-ray diffraction (XRD), define FTIR spectroscopy, scanning electron microscopy (SEM), and energy dispersive spectrometer (EDS). The results showed that the hydration resistance of CaO samples was improved significantly, especially for samples with 9 wt% Ti chelating compound. The specimens with Ti chelating compound showed an increase in bulk density and a decrease in apparent porosity after heating when compared to the specimens without additive. The grain surface of CaO grain and the gaps between the CaO grain boundaries were covered with calcium phosphate glass phase, calcium phosphate showed two different shapes: irregular shape and rod shape. The formation and distribution of these two forms were the key factors that affecting the hydration resistance of CaO samples.     

多组分组合作用下Al2O3掺杂对阿利特结构及活性的影响

采用X射线衍射结合Rietveld方法、热释光及微量热分析,研究了在Na、K等熟料阿利特中常见固溶组分作用下,Al2O3掺杂对阿利特结构、缺陷及水化活性的影响。结果表明:约1/3Al取代Ca,2/3Al取代Si;少量Al2O3即可将阿利特稳定为M3型,且M3晶格常数随Al2O3含量增加呈线性变化,直至达到Al2O3固溶极限1%(质量分数),符合Vegard固溶体定律;Al2O3进入阿利特,形成杂质缺陷,使其热释光性及水化反应动力学特征随之发生显著变化,且缺陷类型对水化的影响比浓度的影响更为显著;阿利特原始热释光强度与其水化反应活性大小一致,这与阿利特中以俘获电子形式亚稳储藏的能量有关。     

Crystal lattice defects in di-calcium silicate

It is well documented that the impurity content of C₂S has a marked effect on its hydration properties. It is also a fact that pure C₂S at room temperature exists in a crystal configuration, γ, which is completely different from the clinker C₂S. Incorporation of impurity ions into pure C₂S inhibits the β → γ transition on cooling, even at impurity levels as low as 0.1%. Currently, there is no fully accepted model for the mechanism of the stabilization of the β phase over the γ phase by impurities. The presence of these trace impurities naturally raises the question of the location and role of the impurities in producing this marked stabilizing effect. A quantitative solution to this problem requires that the lattice defect disorder of C₂S be defined and related to the phase stabilization properties of the impurities. Definition of crystal defect disorder can be achieved through detailed measurements of the electrical conductance of the solid with the data being interpreted in terms of solid state physics. Data for the electrical conductance of pure and “intentionally” impure (doped) C₂S over the temperature range 300 to 1100°C is presented. These data are interpreted in terms of crystal defects, their formation, location and kinetics. Models are presented to account for the stabilizing action of impurity ions within the crystal lattice of C₂S.     

Distribution of chain defects and microstructure of melt crystallized polyethylene

A combined study using wide-angle X-ray diffraction (WAXD) and small-angle X-ray diffraction (SAXD) of a series of mostly low density polyethylenes with a wide range of chain defect concentrations (0.1–7%) crystallized from the melt is reported. The data presented here complement the earlier results obtained by Swan⁷ and Holdsworth and Keller⁸ for copolymers. The concurrent unit cell expansion and long period decrease with increasing chain defect concentration leads to a picture of chain defects (branches, unsaturations) being distributed between the crystalline lamellae and the surface layer. Based on a model which assumes inclusion of defects within the lattice by means of a generation of 2gl kinks, (supported by the parallel increase of paracrystallinity) an estimation of the concentration of chain defects, ?_c, incorporated into the crystal lattice (<1%) is attempted. The density of defects in the non-crystalline regions, ?_a, turns out to be substantially larger than ?_c and supports the view of a clustering of defects, ?_c and ?_a are both increasing functions of ? with a tendency to level off for ? > 6. According to this model, the fraction of defects incorporated into the lattice does not exceed 20% of the total number of defects in any of the samples investigated. The fraction of defects excluded from the lattice (>80%), on the other hand, sets a higher permissable limit to the crystal thickness value achieved.     

高炉镍铁渣粉在水泥基复合胶凝材料中的水化特性研究

通过对不同高炉镍铁渣掺量的水泥-高炉镍铁渣粉复合胶凝材料水化放热速率、高炉镍铁渣粉的反应程度、硬化浆体化学结合水含量以及水化产物中C-S-H凝胶Ca/Si的测定,分别研究了水泥-高炉镍铁渣粉复合胶凝材料的早期、中长期水化进程、浆体微观形貌以及水化产物特点等水化特性.研究结果表明:高炉镍铁渣的掺入会降低水化放热速率,并推迟水化加速期放热峰的出现时间;在复合胶凝体系中,随着高炉镍铁渣粉掺量的增大,其反应程度和硬化浆体中化学结合水含量将降低.复合胶凝材料水化生成的C-S-H凝胶的Ca/Si低于水泥,且随着水化的进行呈降低趋势;高炉镍铁渣粉中的Al,在水化过程中会取代部分Si进入C-S-H凝胶中,形成C-A-S-H凝胶.     

Intrinsic defects,Mo-related defects,and complexes in transition-metal carbide VC: A first-principles study

Intrinsic defects and Mo-related defects in vanadium carbide VC, as well as the defect complexes between vacancies and Mo defects were investigated by means of first-principles calculations within the framework of density functional theory. In addition, Mo diffusion in VC was also studied using LST/QST method. The formation energies of defects have clearly shown that except C vacancy (V_C) all other point defects are not energetic favorable compared to perfect VC. V_C can exist in the lattice forming nonstoichiometric carbide VC_x (x < 1), and also can stabilize the Mo-related defects (S_Mo-V, S_Mo-C, and T_Mo). Free Mo atoms have the strong tendency to enter the already formed V_V and occupy the lattice position of V atoms. Meanwhile, Mo atom in C lattice (S_Mo-C) and interstitial Mo (I_Mo) atom can also enter the V_V position stabilizing the lattice structure. S_Mo-C + V_V will transform into S_Mo-V + V_C and I_Mo + V_V will transform into S_Mo-V during optimization, and large binding energy makes Mo atom tend to exist in the interstitial position. From the perspective of energy, Mo atom tends to diffuse through the interstitial position.     

A1N陶瓷中的晶格缺陷

用透射电镜观察了不同热导率的Ａ１Ｎ陶瓷中存在的晶格缺陷，这类缺陷主要以位错线形式呈现，分布不均匀，大多集中在晶界处。一些晶粒中存在反相畴界。热导率不同的试样其缺陷密度明显不同，氧杂质进入Ａ１Ｎ晶格并形成铝空位是产生晶格缺陷的主要原因，也对晶格参数有显著影响。分析了抑制晶格缺陷形成、提高热导率的工艺措施。     

Role of defects in tailoring optical,electronic, and luminescent properties of Cu-doped ZnO films

We present a detailed characterization study on copper-doped ZnO films to correlate the films' electronic and optical properties with the existing native defects in the lattice. In addition, we describe the variation in the concentration of these defects with Cu dopant and temperature. The results of XRD confirmed the single-phase würtzite-structure of the synthesized films. The SEM images showed a homogeneous and dense grain morphology with a granular form and a signature for a hexagonal-like shape. The EDX, XPS, and UV–Vis spectra showed the proper doping of Cu ions into the lattice. The XPS analysis indicated mixed electronic states of both Cu²⁺ and Cu¹⁺ and showed a clear increase in the Cu²⁺ intensity relative to Cu¹⁺, with Cu dopant. The transmittance spectra exhibited an average value above 80% in all doped films in the visible and infrared regions. The overall results indicated a clear link between the films’ optical and electronic responses and the level of the intrinsic defects in the lattice. By increasing the Cu dopant, we find a slight reduction in the energy bandgap (E_g). This is correlated with a clear reduction in the blue emission luminescence band associated with the V_Zn and in the yellow emission band associated with the O_i. On the other hand, we observed a clear enhancement in the green emission band originating from the V_O, and in the emission band related to possible transitions from Zn_i levels to O_i levels. The slight reduction in the E_g signals a weak sp-d hybridization between the ZnO conduction band electrons and the Cu²⁺ ions, which is mediated by the intrinsic defects. With reducing the temperature, the photoluminescence temperature profiles indicated a slight increase in the E_g values and a negligible effect on the distribution of the native defects.     

Preparing tungsten carbide with highly defective crystal lattice

The preparation of tungsten carbide was studied with the aim of obtaining a product combining the minimum grain size with the maximum concentration of defects in the crystal lattice. It was confirmed that crystal defectivity can be obtained by one of the following procedures: (a) using white modification of tungstic acid as raw material; (b) adding chlorides to initial material; (c) adding lattice promoters; (d) oxidizing the product prior to use.     

环境扫描电镜用于硅酸盐水泥早期水化的研究

采用环境扫描电镜对硅酸盐水泥的早期水化过程进行了连续观察。将硅酸盐水泥早期水化过程分为预诱导期、诱导期、加速期、减速期和稳定期个阶段加以描述。预诱导期阶段水泥开始水解,释放出离子,硅酸三钙(C3S)颗粒表面形成低n(Ca)／n(Si)层,第一批水化产物产生,水泥颗粒表面生成一层水化物的保护膜,使水化反应速度降低。诱导期阶段保护膜逐渐推进直至覆盖整个颗粒表面,膜内外产生渗透压力差。当渗透压力大到足以使薄膜在薄弱处破裂,缺钙的硅酸盐离子就被挤入液相,并和钙离子结合,生成各种不定形的C—C—H。加速期阶段钙离子和硅酸盐离子浓度相对于C—S—H来说达到过饱和,C—S—H高速生长,在颗粒表面附近形成类似于网状形貌的产物(高密度C—S—H),而在颗粒间的原充水空间里形成近球状形貌的产物(低密度C—S—H)。减速期阶段水化产物继续生长,由不定形富水的凝胶状转变为不定形的颗粒状,显微结构继续发展。稳定期阶段水化产物颗粒个数几乎保持不变,但单个颗粒均逐渐生长变大,显微结构逐渐致密化。保护膜的形成和破裂分别可以解释诱导期的产生和结束。C—S—H的生长速度是加速期水化反应速度控制的主要因素。     

The composition of the C-S-H phases in portland cement pastes

The composition of the calcium silicate hydrate (C-S-H) present in Portland cement pastes from eight days to five years old, and in concrete samples ten years old, has been determined by electron probe micro-analysis. The dependence of C-S-H composition on water/cement ratios has also been studied. When the cement is only partially hydrated inner and outer hydrate layers are seen around alite grains. These hydrates have different chemical compositions. With progressive hydration it becomes impossible to distinguish the inner from outer hydrates without a reference alite grain. At this stage two distinct C-S-H compositions can still be found by microanalysis. After further hydration a single CSH composition predominates. The calcium content of C-S-H varies significantly with water/cement ratio and there is new evidence to suggest that in the C-S-H structure Mg replaces Ca, and that Al, S and Fe replace Si.     

Reactions of fly ash with calcium aluminate cement and calcium sulphate

The hydration processes in the ternary system fly ash/calcium aluminate cement/calcium sulphate (FA/CAC/C$) at 20 °C were investigated; six compositions from the ternary system FA/CAC/C$ were selected for this study. The nature of the reaction products in these pastes were analysed by X-ray diffraction (XRD) and infrared spectroscopy (FTIR). At four days reaction time, the main hydration reaction product in these pastes was ettringite and the samples with major initial CAC presented minor ettringite but calcium aluminates hydrates. The amount of ettringite developed in the systems has no direct relation with the initial components.     

Evolution microstructurale des composites du systeme ciment alumineux-granulat calcaire. I. Mode de propagation de la fissure

The transitional layer, formed at the interface between a calcareous aggregate and an aluminous cement paste, changes versus the hydration time and leads to a zone rich in hydrated carboaluminate, which is formed by epitaxic growth on calcium carbonate. This phenomenon is responsible for a noticeable change in the crack propagation process in the solid. In the system calcium aluminate - siliceous aggregates, the process is always intergranular. In the case of aluminate - calcareous aggregate it is intergranular at the beginning of hydration and becomes transgranular after some months. Then the crack propagation concerns the carbonate grain itself but neither the surrounding zone nor the interface aggregate - transitional zone.     

Combined effect of MgO sintering additive and stoichiometry deviation on YAG crystal lattice defects

This study aims to investigate the combined effect of the magnesium oxide (MgO) sintering additive and the deviations of the yttrium aluminum garnet (YAG) stoichiometry towards the excess of Al³⁺ and Y³⁺ on crystal lattice defects. YAG ceramic powders with an excess of aluminum (up to 4.79 mol.%) or yttrium (up to 2.87 mol.%) and various concentrations of the MgO sintering additive (from 0 to 0.2 wt%) were obtained using a two-stage co-precipitation method. The samples calcined at 1600 °C were studied by X-ray powder diffraction (XRD), scanning electron microscopy, diffuse reflectance, Raman and IR-spectroscopy.The cumulative analysis of theoretical calculations of the composition of the samples was performed based on a change in the lattice parameters. Experimental data obtained suggested that, depending on the YAG stoichiometry, magnesium can substitute both the dodecahedral positions of yttrium (in the case of aluminum excess), as well as the octahedral positions of aluminum (in the case of yttrium excess). The resulting substitution defects give pronounced absorption bands in the diffuse reflectance spectra. An increase in the concentration of introduced magnesium leads to a shift in the IR-transmission maximum of ≈620 cm⁻¹ towards wave numbers increasing with an excess of aluminum and towards wave numbers decreasing with an excess of yttrium. In addition, when magnesium was introduced, a decrease in the intensity of incidental peaks in the Raman spectra was observed, which may be due to the relaxation of stresses due to a decrease in the number of intrinsic crystal lattice defects.     

Chemical Expansion of Yttrium‐Doped Barium Zirconate and Correlation with Proton Concentration and Conductivity

Y‐doped BaZrO₃ (BZY) is a promising candidate as an electrolyte in fuel cells, and attracts increasing attention. In this work, a systematic investigation was performed on microstructure, proton concentration, proton conductivity, and hydration induced chemical expansion in Y‐doped BaZrO₃. The results revealed that the bimodal microstructure in BaZr_0.85Y_0.15O_3?δ was composed of large grains with composition close to the nominal value, and fine grains with large compositional discrepancy. This property is considered to be one of the evidences of phase separation at lower temperature than sintering temperature (1600°C), which hinders the grain growth. Thermal expansion coefficient of BZY was measured for various dopant level, and was determined to be around 10^?5 K^?1 in wet and dry argon atmosphere. In addition, chemical expansion effect due to hydration was confirmed by HT‐XRD in dry and wet Ar atmospheres, and suggests an interesting relationship between the lattice change ratio and proton concentration, in the BZY system with different Y content. The change ratio of lattice constant due to hydration increased obviously with the proton concentration for the sample containing the Y content of 0.02 and 0.05, but only changed slightly when the Y content was increased to 0.1 and 0.15. However, when the Y content was further increased over 0.2, the change ratio of lattice constant due to hydration starts to increase obviously again. Such results indicate a high possibility that the stable sites of protons in BZY changed with the variation in Y content.     

One-dimensional extended lines of divacancy defects in graphene

Since the outstanding transport properties of graphene originate from its specific structure, modification at the atomic level of the graphene lattice is needed in order to change its electronic properties. Thus, topological defects play an important role in graphene and related structures. In this work, one-dimensional (1D) arrangement of topological defects in graphene are investigated within a density functional theory framework. These 1D extended lines of pentagons, heptagons and octagons are found to arise either from the reconstruction of divacancies, or from the epitaxial growth of graphene. The energetic stability and the electronic structure of different ideal extended lines of defects are calculated using a first-principles approach. Ab initio scanning tunneling microscopy (STM) images are predicted and compared to recent experiments on epitaxial graphene. Finally, local density of states and quantum transport calculations reveal that these extended lines of defects behave as quasi-1D metallic wires, suggesting their possible role as reactive tracks to anchor molecules or atoms for chemical or sensing applications.     

Precipitation potential of some BI-univalent electrolytes

Precipitation potentials of chlorides, bromides, and iodides of barium, calcium and magnesium are measured. The phase potentials of these electrolytes have been estimated from the decay curves. True precipitation potentials computed thereby show a linear relationship (for each set of halides) with (i) lattice energy; (ii) ratio of ionic radii of cation and anion; and (iii) ratio of real hydration energies of cation and anion. The sign and relative magnitude of precipitation potentials have also been explained on the basis of ion—water interaction.     

Role of interfaces in damage process of irradiated lithium aluminate nanocrystals

Molecular dynamics simulations were performed to understand the differences in the response of single crystal and nanocrystalline γ-LiAlO₂ to energy deposition by 10 keV Li recoils. The simulations are performed at 573 K and focus on the damage production in the absence of thermal annealing. The grain boundaries in the nanocrystals are found to be amorphous. Analyses of the fate of the beam ions show that the amorphous grain boundaries and differently oriented nanograins increase the number of backscattered ions and decrease the number of transmitted ions. Damaged regions protruding from the grain boundaries provide a direct evidence of the role of the grain boundaries as scattering centers in collision cascades. The simulations show that the defect density produced in the nanocrystals is about twice that in the single crystals. In both samples, Li defects account for 70% of the defects, demonstrating that LiO₄ tetrahedra are much more susceptible to damage than AlO₄ tetrahedra. Furthermore, Li defects occur preferentially near grain boundaries. Diffusion simulations confirm the limited thermal diffusion of defects at 573 K, effectively separating the damage production from thermal annealing in the irradiation simulations. Nevertheless, the mean square displacements of grain-boundary defects are found to be larger than lattice defects and surface defects.