Adsorption of Hydroxypropyl Methyl Cellulose in an Aqueous System Containing Multicomponent Oxide Particles

The adsorption behavior of a hydroxypropyl methyl cellulose (HPMC) polymer in aqueous suspensions of alumina, silica, kaolin, and talc powders, two-component combinations, and one three-component combination was determined. Powders were well characterized by chemical analysis, XRD, DRIFT, SEM, particle size, surface area, and density analyses. The zeta-potential of each powder in aqueous suspension was determined over a range of pH to determine particle charging and the isoelectric point for each material. Alumina and silica powders having heavily hydroxylated surfaces were observed not to adsorb the HPMC polymer over a range of pH. The layer-type minerals talc, which was noticeably hydrophobic, and kaolin, which had differently hydrated basal planes, adsorbed the HPMC polymer but in different amounts per unit of surface area. In the two-component systems, HPMC polymer adsorption for systems of dispersed particles of like electrical charge (kaolin + silica, talc + silica or alumina, and kaolin + talc) was proportionate to the sum of the fraction x specific surface area x adsorption capacity for each particle type. In systems where particles had an opposite electrical charge (kaolin + alumina, kaolin + talc + alumina), the HPMC polymer adsorption was significantly lower than that calculated for a dispersed system. SEM analysis showed very fine, nonadsorbing alumina particles predominantly on the faces of the adsorbing kaolin particles that apparently masked polymer adsorption. Results suggested a hydrophobic mechanism for the HPMC polymer adsorption and adsorption on only one face of the kaolin particles.     

Reactive Multicomponent Powder Mixtures Prepared by Microencapsulation: Pb(Mg1/3Nb2/3)O3 Synthesis

Microencapsulation of ceramic powders using metalloorganic stearate soaps was investigated as an economical means to increase solid-state reactivity of multicomponent mixtures. The specific system investigated was lead magnesium niobate (PMN); however, the process may be applicable to a wide range of other compositions. The physical and chemical characteristics of the unfired powder mixtures and reactivity during subsequent calcination were studied as a function of batch composition and mixing method. Batch composition was varied by molar substitution of magnesium stearate for magnesium carbonate. Mixing method was investigated by comparing a dry-mixing technique developed for particle coating (mechanofusion) with conventional wet ball milling. Both mixing processes resulted in surface coating of the ceramic particles by the stearate soap. In addition, the mechanofusion process produced densely packed spherical granules of coated particles (multicored microcapsules) in the 50- to 200-μm range. Solid-state reactivity was measured in terms of perovskite phase yield, increased yields being indicative of a more reactive mixture. The highest perovskite yields (95 to 98 vol%) were achieved at 100 mol% substitution of magnesium stearate for magnesium carbonate, independent of mixing method. However, when magnesium stearate was only partially substituted for magnesium carbonate, the mechanofusion process produced consistently higher perovskite yields than did ball milling. Compared to conventional mixed-oxide processing, the increased reactivity of the microencapsulated mixtures can be attributed to higher chemical activity of the metallo-organic precursor, finer scale of mixing achieved by particle coating, and a further reduction in segregation scale due to the dense intragranule packing of multicore microcapsules.     

Studies of Cd, Pb and Cr distribution characteristics in bottom ash following agglomeration/defluidization in a fluidized bed boiler incinerating artificial waste

This study focused on the effects of agglomeration/defluidization on the Cd, Pb and Cr distribution in bottom ash particles of different sizes. In this study we have incinerated artificial waste, which was a mixture of sawdust, polypropylene, selected metal solutions, and polyethylene. The experimental parameters included Na concentration, addition of Ca and Mg and operating temperature. The results indicated that particle size decreased by attrition and thermal impact in the absence of added Na. When Na was added to the system, this metal reacted with silica sand to form eutectics, which increased particle size. Further addition of Ca and Mg was found to prolong the operating time, with greater amounts of liquid eutectic accumulating, leading to increase particle size.The heavy metal concentrations in coarse and fine particles were greater than those present in particles of intermediate sizes over a range of experimental conditions. As the particle size decreased below 0.59 mm or increased above 0.84 mm, the heavy metal concentrations increased. As Ca and Mg were added, the heavy metal concentrations in particles of all sizes increased relative to those present in identical particles when no metals or only Na were added. Additionally, the ratio of Cd sorption to silica sand decreased with increasing Na concentration, but Cr sorption had the opposite tendency. Therefore, while the addition of Na tended to increase agglomeration, it also increased the tendency for heavy metals to remain in the sand bed of fluidized bed incinerators. Addition of Ca and Mg not only inhibited the agglomeration/defluidization process, resulting in increased operating time, but also enhanced the removal of heavy metals by silica sand, decreasing the concentration of heavy metals in reactor exhaust.     

Powder metallurgy magnesium composite with magnesium silicide in using rice husk silica particles

By using the solid-state reaction of rice husk silica particles with magnesium powder, P/M magnesium based composites dispersed with the magnesium silicide (Mg₂Si) and magnesium oxide (MgO) were fabricated. High-purity silica particles were originated from rice husks, one of the major agricultural wastes, via the citric acid leaching treatment and combustion in air. The effects of the silica particle characteristics such as size, crystalline and porous structures, on the reactivity of silica and magnesium to synthesize Mg₂Si intermetallics were discussed. As the results by DTA and XRD analysis, finer silica particles were more effective for the solid-state reaction at low temperature due to the increase of their surface area contacted with magnesium powder. Amorphous silica was also more useful for this reaction than the crystalline one. The reactivity of rice husk silica was superior to that of the conventional mineral silica particles not only because of its amorphous structure but also the larger specific surface area due to their pore structures. In the case of the green compact of the elemental mixture of silica particles and Mg powder, the silica particle size was not effective on the reactivity because the coarse particles were fractured into fine ones by cold compaction. The distribution of Mg₂Si intermetallics of magnesium powder composites consolidated by SPS process was investigated by XRD and SEM-EDS analysis. When the sintering temperature was over the exothermic temperature of the mixture in the DTA profile, the synthesis of Mg₂Si completely occurred during sintering. The sinterability of the elemental mixture powder was improved when employing the amorphous rice husk silica particles. The density and hardness of their composites sintered over the ignition temperature of the DTA profile were remarkably high because of the good densification by the high reactivity and the distribution of Mg₂Si hard compounds.     

改性碳酸钙在聚氯乙烯中的应用研究

研究了一种改性碳酸钙在聚氯乙烯(PVC)中的应用情况。研究结果表明,这种经JL G0 1型改性剂(Modifier)改性的碳酸钙与普通碳酸钙相比,颗粒以原生粒子状态均匀分布,不团聚,其中部分以纳米粒子状态存在,因此填充于聚氯乙烯(PVC)硬质、软质制品中,不仅能改善体系的加工性能,而且赋予制品较好的物理机械性能,达到增韧补强的效果     

改性碳酸钙在聚氯乙烯（PVC）消防管中的应用研究

研究了一种改性碳酸钙在聚氯乙烯(PVC)消防管中的应用情况。研究结果表明,这种经JL-G01型改性剂(Modifier)改性的碳酸钙与普通碳酸钙相比,颗粒以原生粒子状态均匀分布,不团聚,其中部分以纳米粒子状态存在,因此填充于聚氯乙烯(PVC)消防管中,不仅能改善体系的加工性能,而且赋予制品较好的物理机械性能,达到增韧补强的效果。     

Three-dimensional numerical simulation of a circulating fluidized bed reactor for multi-pollutant control

Circulating fluidized bed adsorber (CFBA) technology is regarded as a potentially effective method for simultaneously controlling emissions of sulfur dioxide, fine particulate matter, and trace heavy metals, such as mercury vapor. In order to analyze CFBA systems in detail, a gas mixture/solids mixture model based on the three-dimensional Navier-Stokes equations is developed for particle flow, agglomeration, physical and chemical adsorption in a circulating fluidized bed. The solids mixture consists of two solids, one with components of CaO and CaSO₄, and the other being an activated carbon. The gas mixture is composed of fine particulate matter (PM), sulfur dioxide, mercury vapor, oxygen and inert gas. Source terms representing fine particulate matter agglomeration onto sorbent particles, sulfur dioxide removal through chemical adsorption onto calcined lime, and mercury vapor removal through physical adsorption onto activated carbon are formulated and included into the model. The governing equations are solved using high-resolution upwind-differencing methods, combined with a time-derivative preconditioning method for efficient time-integration. Numerical simulations of bench-scale operation of a prototype CFBA reactor for multi-pollutant control are described.     

Preparation of MEMO silane-coated SiO2 nanoparticles under high pressure of carbon dioxide and ethanol

The objective of this study is to investigate and compare methods of nanosilica coating with γ-methacryloxypropyltrimethoxy (MEMO) silane using supercritical carbon dioxide and carbon dioxide-ethanol mixture. Characterization of grafted silane coupling agent on the nanosilica surface was performed by the infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). The d₅₀ value and particle size distribution were determined by laser particle size analyzer (PSA). The operating parameters of silanization process at 40 °C, such as the silica/silane weight ratio, the presence of ethanol, and the pressure, were found to be important for the successful coating of silica particles with minimum agglomeration. The results indicate that presence of ethanol in high-pressure carbon dioxide plays an important role in achieving successful deagglomeration of coated nanoparticles. Dynamic mechanical analysis (DMA) and scanning electron microscopy (SEM) revealed that dispersion of the silica particles in the PMMA matrix and interfacial adhesion between silica particles and polymer matrix were enhanced, when silica nanoparticles treated with silane under high pressure of carbon dioxide and ethanol were used for the nanocomposite preparation.     

An AFM Study of the Genesis and Sintering in Hydrogen of a Realistic Cu/Amorphous Silica Planar Model Catalyst

The genesis and subsequent sintering in a hydrogen atmosphere of realistic Cu/amorphous silica planar model catalysts have been investigated by atomic force microscopy. Samples were prepared by standard wet chemical methods followed by calcination and reduction, mimicking as closely as possible the procedures used in the preparation of practical, dispersed Cu catalysts. Changes in size distribution and mean particle size are observed as the sequence of transformations, Cu nitrate → cupric oxide → Cu metal, proceeds and an interpretation is offered. Pronounced sintering in hydrogen is the result of migration, agglomeration and coalescence of entire Cu particles, as opposed to Ostwald ripening. A mechanism for this process is proposed on the basis of absorption/desorption of hydrogen at steady state.     

SiO2单分散溶胶微球制备的工艺条件研究

在乙醇介质中,以氨作为催化剂,正硅酸乙酯作为硅源,制备了单分散的二氧化硅溶胶微球。通过激光粒度分析仪及透射电镜测定溶胶粒子的大小。研究了不同工艺参数如催化剂和水的量、硅源的量以及溶剂的类型对二氧化硅粒子大小及形貌的影响,并考察了粒子的形成机理。结果显示:随着氨浓度的升高,溶液初始解离的[OH-]增大,二氧化硅粒子的粒径增大;随着硅源浓度的增加,溶液中水解的中间产物增加,二氧化硅微球的粒径显著增加;在r(水/正硅酸乙酯)值远大于4的情况下,随着初始加入水量的增加,二氧化硅微球的粒径有所增加,但当水量太多时,粒径反而下降;使用不同溶剂作为制备二氧化硅的介质,在丙醇和丁醇中二氧化硅严重团聚,没有得到单分散微球。     

高氯酸铵含量对高铝富燃料推进剂中重要组分高氯酸铵/铝 一次燃烧性能和铝粉团聚的影响

采用CO2激光点火装置联合高速摄影系统及扫描电子显微镜等凝聚相燃烧产物分析技术,研究了高氯酸铵(AP)含量对高Al富燃料推进剂中重要组分AP/Al一次燃烧过程中燃烧现象、引燃时间、燃烧扩散时间、燃尽时间、燃烧效率、颗粒团聚及凝聚相燃烧产物的表面形貌、粒径及其分布的影响。结果表明,各AP/Al混合粉体的燃烧过程均可分为表面引燃、燃烧扩散和火焰熄灭3个阶段,但各样品在不同燃烧阶段的燃烧现象存在明显差异。AP含量由10wt%增至30wt%,样品燃烧剧烈程度增强,燃烧过程中固相颗粒的溅射现象越加明显;在火焰熄灭阶段,各样品燃烧由以停留在样品燃面处的燃烧为主逐渐变为以溅射颗粒的燃烧为主,且随反应进行,燃面已燃固相颗粒最先熄灭,各样品表面引燃时间、燃烧扩散时间、燃烧持续时间均缩短,即燃烧反应速率逐渐加快。在AP/Al混合物中,铝粉的燃烧效率、凝聚相燃烧产物粒度及其团聚程度随AP含量增加而增加。     

Quantitative measurement of particle segregation mechanisms

Pharmaceutical, food, chemical, mining, and energy industries routinely handle and process materials with different particle sizes. Often the different size materials represent different chemical components. Pharmaceutical mixtures are typically mixtures of fine, active, with relatively coarse, incipient ingredients. Food industry mixtures combine particles with very different sizes and shapes. There is a great tendency for these dissimilar materials to separate during processing and handling. The cause of this separation depends on the size and shape of the particles in the mixture. If the fines are less than one-third the size of coarse particles and free flowing, they may percolate through the coarse matrix of particles resulting in sifting segregation. If the particle shapes are different, then the internal friction angles of individual components may be different, resulting in angle of repose segregation. Preventing segregation of a given material mixture depends on the cause of the segregation. If angle of repose segregation is the predominate mechanism, then segregation mitigation can be accomplished by limiting pile formation. However, if sifting segregation is the predominate mechanism, then limiting pile formation may not limit the segregation if the process equipment is subject to significant inter-particle motion or shear. This paper presents a method of measuring the magnitude of sifting segregation occurring in bulk material. It also includes data that relates bulk material strength to separation tendency. This relationship shows an inverse functionality between the yield strength of the material and the bulk segregation. Finally, the work presented in this paper compares segregation due to sifting and repose angle mechanisms to provide a means of differentiating between these mechanisms.     

二氧化硅溶胶的制备及其对硬盘基板NiP的抛光速率研究

离子交换法制备了不同粒径的纳米二氧化硅溶胶,采用TEM、DLS等手段对磨料进行了表征,并以二氧化硅溶胶作为磨料对存储器硬盘基板NiP进行化学机械抛光实验,考察了磨料粒径和数量等因素对存储器硬盘基板NiP的抛光去除速率的影响。     

Microstructure and reactivity evolution of colloidal silica binder in different systems at elevated temperatures

Colloidal silica as nanostructured binder for refractory castables has attracted many attentions in recent years. In the present study, phase composition, microstructure and reactivity evolution of silica gel at different heating conditions were investigated to find suitable system for colloidal silica application. The results showed that atmosphere and carbon slightly affected phase composition of the silica gel at elevated temperatures, and the crystalline phases were composed of major α-cristobalite and minor α-tridymite. The morphology and particle size of the silica gel were greatly affected by atmosphere and carbon during heating. The spherical nano-silica particles with sizes of 40–50 nm rapidly grew into macroscale rod-like particles with temperature increasing from 800-1000 °C to above 1200 °C in air, and sintering of silica particles was observed. However, the size and morphology of the spherical nano-silica particles retained at high temperature in a reducing atmosphere, and many well developed columnar mullite crystals and some SiC whiskers formed on heating silica gel, alumina fines and carbon at 1500 °C, which was due to carbon inclusions retarding the growth of nano-silica particles and the nano silica remained high reactivity at high temperature. Thus, colloidal silica was suitable for application in carbon-containing refractory castables.     

细颗粒物凝并技术机理的研究进展

凝并技术是提高烟气中细颗粒物(PM2.5)去除效率的关键技术之一。凝并机理的研究有利于加深对细颗粒物凝并过程的理解,最大限度地提高PM2.5的凝聚速度,使PM2.5在较短的时间内团聚成大颗粒。本工作对电凝并、化学凝并和声凝并3种凝并效果显著的凝并技术机理进行概述,分别介绍了电凝并机理的核心电凝并系数方程,不同化学添加剂对颗粒的作用机制,同向运动、流体力学和声致湍流作用下的声凝并机理的发展现状。阐述了现有研究的不足,并提出在后续凝并机理的研究中,可利用高速显微摄像技术实时观测颗粒的凝并过程,对已有凝并机理进行验证及修正。同时还需考虑实际烟气成分对颗粒凝并的影响,进一步完善颗粒的凝并机理。     

新型铝锆偶联剂在纳米CaCO3表面的吸附特性

利用新型铝锆偶联剂对纳米CaCO3进行表面改性,采用光谱学分析方法对铝锆偶联剂在纳米CaCO3表面的吸附特性进行探讨。通过透射电镜(TEM)、沉降体积、浊度测试等实验对纳米CaCO3的表面改性效果进行评价。红外光谱分析表明,铝锆偶联剂以化学键合的方式吸附在纳米CaCO3的表面。但X射线衍射分析证明,纳米CaCO3表面吸附层物质的引入并未对纳米CaCO3粉体的化学组成产生影响。经表面改性,纳米CaCO3的界面性质发生了很大变化,纳米CaCO3在水中的沉降体积减少,悬浮液浊度明显增大,说明纳米CaCO3在水中的分散性得到很大改善。     

Growth kinetics and mechanism of wet granulation in a laboratory-scale high shear mixer: Effect of initial polydispersity of particle size

The effect of initial polydispersity of particle size (unimodal versus bimodal distribution) and binder characteristics on the growth kinetics and mechanism of wet granulation was studied. Wet granulation of pharmaceutical powders with initial bimodal particle size distribution (PSD) presented growth kinetics consisting of two stages: fast growth followed by slow growth. The fast stage is controlled by the amount of binder and high probability of coalescence due to the collisions of small and large particles. The second stage is characterized by slow agglomeration of powder mixtures with water content 13.6% v/w, and slow breakage of powder mixtures with water content of 9.9% and 11.7% v/w. The wet granulation of powders with initial unimodal PSD exhibited slow growth kinetics consisting of one stage, since similar particle sizes do not promote agglomeration. The experimental results were better described by a population balance equation using a coalescence kernel that favors growth rate by collision between small and large particles. In general, the probability of a successful collision increased with higher size difference between particles, smaller particle size, and higher binder content.     

化学团聚促进电除尘脱除烟气中PM2.5和SO3

化学团聚技术是实现燃煤烟气超净排放的有效技术之一,采用燃煤热态实验系统,分析探讨化学团聚技术促进电除尘对PM_2.5和SO₃的脱除作用,考察了化学团聚剂添加前后细颗粒化学组分及粒径的变化,以及化学团聚室、电除尘出口PM_2.5和SO₃浓度变化,并分析促进PM_2.5和SO₃脱除的机理。结果表明：喷入化学团聚剂后,细颗粒粒径峰值由0.1 μm增大到3 μm左右,细颗粒化学组分基本保持不变;电除尘出口细颗粒物数量浓度由5.8×104 cm^-3降低到3.2×104 cm^-3,电除尘效率提高45%;烟气SO₃浓度由40 mg·m^-3提高到100 mg·m^-3时,单一化学团聚对SO₃的脱除效率由42%提高到68%,协同电除尘SO₃脱除效率由66%提高到86%。     

Complementary structure sensitive and insensitive catalytic relationships

The burgeoning field of nanoscience has stimulated an intense interest in properties that depend on particle size. For transition metal particles, one important property that depends on size is catalytic reactivity, in which bonds are broken or formed on the surface of the particles. Decreased particle size may increase, decrease, or have no effect on the reaction rates of a given catalytic system. This Account formulates a molecular theory of the structure sensitivity of catalytic reactions based on the computed activation energies of corresponding elementary reaction steps on transition metal surfaces. Recent progress in computational catalysis, surface science, and nanochemistry has significantly improved our theoretical understanding of particle-dependent reactivity changes in heterogeneous catalytic systems. Reactions that involve the cleavage or formation of molecular pi-bonds, as in CO or N(2), must be distinguished from reactions that involve the activation of sigma-bonds, such as CH bonds in methane. The activation of molecular pi-bonds requires a reaction center with a unique configuration of several metal atoms and step-edge sites, which can physically not be present on transition metal particles less than 2 nm. This is called class I surface sensitivity, and the rate of reaction will sharply decrease when particle size decreases below a critical size. The activation of sigma chemical bonds, in which the activation proceeds at a single metal atom, displays a markedly different size relationship. In this case, the dependence of reaction rate on coordinative unsaturation of reactive surface atoms is large in the forward direction of the reaction, but the activation energy of the reverse recombination reaction will not change. Dissociative adsorption with cleavage of a CH bond is strongly affected by the presence of surface atoms at the particle edges. This is class II surface sensitivity, and the rate will increase with decreasing particle size. Reverse reactions such as hydrogenation typically show particle-size-independent behavior. The rate-limiting step for these class III reactions is the recombination of an adsorbed hydrogen atom with the surface alkyl intermediate and the formation of a sigma-type bond. Herein is our molecular theory explaining the three classes of structure sensitivity. We describe how reactions with rates that are independent of particle size and reactions with a positive correlation between size and rate are in fact complementary phenomena. The elucidation of a complete theory explaining the size dependence of transition metal catalysts will assist in the rational design of new catalytic systems and accelerate the evolution of the field of nanotechnology.     

Distinguishing between aggregates and agglomerates of flame-made TiO2 by high-pressure dispersion

The potential of high-pressure dispersion (HPD) and dynamic light scattering (DLS) is explored for rapid and quantitative estimation of the extent of particle aggregation and agglomeration by analyzing the entire particle size distribution. Commercially available and tailor-made TiO₂ particles by flame spray pyrolysis (FSP) were characterized by X-ray diffraction, nitrogen adsorption and transmission electron microscopy (TEM). Volume distributions of these titania particles were obtained by DLS of their electrostatically stabilized (with Na₄P₂O₇) aqueous suspensions. Dispersing these suspensions through a nozzle at 200 to 1400 bar reduced the size of agglomerates (particles bonded by weak physical forces) resulting in bimodal size distributions composed of their constituent primary particles and aggregates (particles bonded by strong chemical or sinter forces). Sintering FSP-made particles from 200 to 800 °C for 4 h progressively increased the minimum primary particle size (by grain growth) and aggregate size (by neck growth and phase transformation).