燃煤飞灰中铁质微珠的显微结构及其组成研究

选用我国三个典型燃煤煤种的电厂飞灰中铁质微珠,进行显微结构与物相组成等方面的研究。揭示出铁质微珠中存在空心微珠、子母珠和实心微珠三种显微颗粒类型,在这些显微颗粒表面可识别出以微粒状和八面体自形晶两种方式存在的赤铁矿和磁铁矿析晶;元素分析表明,燃烧褐煤电厂铁质微珠主要由Fe、Ca、Al、和Si元素组成,燃烧烟煤和无烟煤的电厂铁质微珠主要由Fe、Al和Si元素组成;物相分析发现,Fe在铁质微珠中以四种存在形式：Fe3O4、α-Fe2O3、γ-Fe2O3和Fe3+-玻璃相。这些物相在三个电厂飞灰中呈现出不同的分布特征,反映出不同的燃煤煤种在锅炉中燃烧温度的差异。随着温度的升高,Fe3O4先氧化为γ-Fe2O3,或γ-Fe2O3与Fe3O4的固熔体,然后再转变为α-Fe2O3,当温度超过 1 400 ℃时,Fe2O3又转化为Fe3O4。     

An empirical constitutive law for concentrated colloidal suspensions in the approach of the glass transition

Concentrated, non-crystallizing colloidal suspensions in their approach of the glass state exhibit distinct dynamics patterns. These patterns suggest a powerlaw rheological constitutive model for near-glass viscoelasticity, as presented here. The rheological parameters used for this model originate in the mode-coupling theory. The proposed constitutive model provides explicit expressions for the steady shear viscosity, the steady normal stress coefficient, the modulus-compliance relation, and the α peak of G″. The relaxation pattern distinctly differs from gelation.     

虚拟边界法研究正交双圆柱及串列双圆球绕流

把Goldstein等人提出的虚拟边界法推广到三维情况,研究了 Re=150时不同间距下正交双圆柱绕流,和Re=250时不同间距下串列双 圆球绕流流场. 对于正交双圆柱绕流,当间距比大于3,下游圆柱对上游圆柱尾流的影响只 限定在下游圆柱的尾流所扫过的范围之内;当间距比小于等于3,下游圆柱对上游圆柱尾流 的影响扩大,下游圆柱尾流扫过区上下出现两排三维流向二次涡结构. 对于串列圆球绕流, 研究发现,在小间距比(L/D≈ 1.5)的情况下,由于上下游圆球尾流区的相互抑 制消除了压力不稳定性,整个流场呈现稳 态轴对称特征;间距比为2.0时,周向压力梯度诱发出流体的周向输运,流场呈现稳态非对 称性,但流场中存在特定的对称面;间距比增大到2.5后,绕流场开始周期振荡,原有的对 称面依旧存在;在间距比3.5时下游圆球下表面的涡结构强度有所减弱,导致占优频率发生 交替;间距比增至7.0时,整个流场恢复稳态特征,两圆球尾部同时出现双线涡,这时流场 对称面的位置发生了变动.     

Effect of Charge,Size and Temperature on Stability of Charged Colloidal Nano Particles

Molecular simulation of charged colloidal suspension is performed in NVT canonical ensemble using Monte Carlo method and primitive model. The well-known Derjaguin-Landau-Verwey-Overbeek theory is applied to account for effective interactions between particles. Effect of temperature, valance of micro-ions and the size of colloidal particles on the phase stability of the solution is investigated. The results indicate that the suspension is more stable at higher temperatures. On the other hand, for a more stable suspension to exist, lower micro-ion valance is favorable. For micro-ions of higher charge the number of aggregates and the number of particle in each of aggregate on average is higher. However for the best of our results larger colloidal particle are less stable. Comparing the results with theoretical formula considering the influence of surface curvature shows qualitative consistency.     

低温催化法制备石墨化碳空心球

石墨化碳空心球因具有密度小、稳定性好和可填充中空结构等特点,受到了研究者的广泛关注。本文结合国内外的研究进展,综述了近年来发展起来的采用过渡金属如铁、钴、镍等为催化剂,低温(<1 000℃)催化法合成石墨化碳空心球的最新研究进展。介绍了低温催化法提高碳空心球石墨化程度的机理,说明了石墨化碳空心球的表征方法,展望了石墨化碳空心球的应用前景。最后指出了相关研究中有待解决的问题。     

Drop-on-demand drop formation of colloidal suspensions

The drop formation dynamics in the drop-on-demand (DOD) inkjet process is studied for model inks including a Newtonian liquid and colloidal dispersions. The ink shear viscosity is a parameter often adjusted in tuning the DOD drop formation process. Apparent shear viscosity measured at low shear rates is currently used to characterize inkjet inks throughout both the inkjet industry and academia. However, during the ejection process in inkjet printing, very high shear rates (above 1 × 10⁵ s⁻¹) are involved. In this paper, the drop formation characteristics at 10 kHz drop formation rate in a DOD mode of a simple Newtonian liquid are compared with those of a colloidal suspension system which has the same low-shear-rate viscosity as the simple Newtonian liquid, but significantly different high-shear-rate viscosity. Under conditions of good jetting, the drop formation dynamics of the colloidal suspension is similar to that of the simple Newtonian liquid of similar low-shear viscosity, with only slight systematic differences observed. Good jetting is, however, difficult to obtain in the colloidal particle inks, with non-straight trajectories and non-axisymmetric ligaments commonly observed. These observations suggest that evaporation, nonuniform wetting, and particle-related changes in properties play a role when poor jetting behavior is observed for colloidal inks.     

Online Determination of Colloidal Properties of Tannin Solutions under Microwave Irradiation using a Modified Zetasizer

A rapid and exact method for the determination of the colloidal properties of tannin solutions following microwave irradiation was developed and validated using a modified zetasizer. The accuracy and feasibility online detection compared with the conventional method were characterized by the particle size and zeta potential of the tannin solutions treated with microwave irradiation using the optimized conditions, including the tannin concentration, microwave radiation time, and temperature. The results showed that the values determined by the online method presented a linear relationship at a tannin concentration of 4?g/L, microwave times of 30–90?min, and temperatures from 25 to 40?°C. These values were essentially unchanged using conventional detection. In addition, the online method is feasible for both hydrolyzable and condensed tannins. Ten parallel measurements had relatively small standard deviations, showing that the precision was within acceptable limits. Therefore, the online method is appropriate for the characterization of tannin colloidal properties treated with microwave radiation which may have practical applications.     

Activated carbon spheres (ACS)@SnO2@NiO with a 3D nanospherical structure and its synergistic effect with AHP on improving the flame retardancy of epoxy resin

A novel activated carbon spheres (ACS)@SnO₂@NiO hierarchical hybrid architecture was first synthesized and applied for enhancing the flame retardancy of epoxy (EP) resin via a cooperative effect. Herein, using activated carbon microspheres as the template, SnO₂ and NiO nanospheres were successively anchored to it by a sedimentation‐calcination strategy. The well‐designed ACS@SnO₂@NiO significantly enhanced the flame retardancy for consistency of EP composites, as demonstrated by thermogravimetric and cone calorimeter experiments. For instance, the incorporation of 2 wt% ACS@SnO2@NiO decreased by 15.5% maximum in the total smoke production, accompanying the higher graphitized char layer. In addition, the synergetic mechanism of flame retardancy between ACS@SnO₂@NiO and aluminum hypophosphite (AHP) was investigated. The obtained sample satisfied the UL‐94 V‐0 rating with a 5.0 wt% addition of AHP and ACS@SnO₂@NiO (the ratio of the mass fraction of AHP to ACS@SnO₂@NiO is 4.5:0.5). Notably, the incorporation of AHP and ACS@SnO₂@NiO resulted in a significant decrease in the fire hazard properties of EP resin; for instance, 4.5AHP‐0.5ACS@SnO₂@NiO/EP resulted in a maximum decrease of 32.4% in the total smoke production as compared with that of pure EP resin. It should be noted that the improved flame‐retardant performance for the EP composites is primarily attributed to the synergistic effect of ACS@SnO₂@NiO and AHP in promoting the formation of residual char in the condensed phase.     

Experimental synthesis and characterization of rough particles for colloidal and granular rheology

We review the experimental synthesis of smooth and rough particles, characterization of surface roughness, quantification of the pairwise and bulk friction coefficients, and their effect on the rheology of wet particulate flows. Even in the absence of interparticle attraction or cohesion, such types of flows are broadly ubiquitous, spanning enormous length scales ranging from consumer and food products to earth movements. The increasing availability of model frictional particles is useful to advancing new understanding of particulate rheology. Although hard-sphere particles remain the most widely studied system due to their simplicity, their rigid and frictionless nature cannot predict many of the complex flow phenomena in colloidal and granular suspensions. Besides a myriad of interparticle forces, the presence of tangential interparticle friction arising from either hydrodynamics or solid contacts of asperities is now thought to be responsible for commonalities in shear thickening and jamming phenomena at high volume fractions and shear stresses. The overall richness of the suspension mechanics landscape points to the reunification of colloidal and granular physics in the near future: one in which it may become possible to apply a universal set of physical frameworks to understand the flows of model rough particles across multiple spatiotemporal scales. This can only be accomplished by properly distinguishing between microscopic and bulk friction and by decoupling hydrodynamics and contact contributions within the context of experimental observations.     

Thermoelectric effect on charged colloids in the Hückel limit

We study the thermophoretic coefficient D_T of a charged colloid. The non-uniform electrolyte is characterized in terms of densities and diffusion currents of mobile ions. The hydrodynamic treatment in the vicinity of a solute particle relies on the Hückel approximation, which is valid for particles smaller than the Debye length, a ≪ . To leading order in the parameter a/ , we find that the coefficient D_T consists of two contributions, a dielectrophoretic term proportional to the permittivity derivative d/dT , and a Seebeck term, i.e., the macroscopic electric field induced by the thermal gradient in the electrolyte solution. Depending on the particle valency, these terms may take opposite signs, and their temperature dependence may result in a change of sign of thermophoresis, as observed in several recent experiments.