粉煤灰与水泥浆体间界面的形貌特征

用ＳＥＭ和ＥＤＳ研究了粉煤灰掺入水泥后与水泥浆体间所形成界面的形貌特征，结果表明，在水泥水化初期，粉煤灰表面呈三种状态：（１）被ＣＳＨ单层膜包裹；（２）被ＣＨ－ＣＳＨ双层膜包裹；（３）嵌入块状ＣＨ晶体内，在水泥水化后期，粉煤灰颗粒表面层已完全与水泥水化产物发生反应，且形成若干层反应物，呈致密的粒状或环状凝胶体。     

添加秸秆类生物质对长平煤灰熔融特性的影响

借助高温热台显微镜、扫描电子显微镜-能谱仪、灰熔点仪和X射线衍射仪考察了添加稻草和棉秆两种秸秆对长平煤灰熔融特性的影响.研究结果表明添加两种秸秆都能有效地降低长平煤灰的熔融温度.在高温弱还原性气氛下,长平煤灰主要矿物组成为耐熔性石英和莫来石,而添加秸秆后产生了白榴石、尖晶橄榄石、钙长石等低温共熔化合物,使长平煤灰熔点降低.不同灰的高温熔融图像表明,煤灰在熔融过程中由于受热而使固相持续软化,形成了不利于难熔物分解的高黏度熔体.而煤和稻草的混合灰在熔融时形成了易发生流动的低黏度熔体,能够促进矿物质发生反应而更易熔融.     

Investigation of high-density polyethylene film surface treated with chromic acid mixture by use of 2,4-dinitrophenylhydrazine. II. Film surfaces treated at 70°C

High-density polyethylene films were treated with chromic acid mixture at 70°C. The treated films were then reacted with 2,4-Dinitrophenylhydrazine. The changes in the amounts of carbonyl groups and 2,4-dinitrophenylhydrazones formed in the films were estimated by comparing their absorptions in the infrared and ultraviolet spectra, respectively. Scanning electron micrographs of the treated film surfaces were taken. Oxidation of the film surface zone, etching of the film surface zone, and oxidation of surface zone bared from the film inner zone seem to have occured with increase in treatment time. High-density polyethylene film surfaces were oxidized to a greater extent than low-density polyethylene film surfaces; however, the rate of etching of the low-density polyethylene film surface zone was larger than that of the high-density polyethylene film surface zone.     

The contact zone between portland cement paste and glass “aggregate” surfaces

The morphology of the contact zone developed between Portland cement paste and glass slide “aggregates” has been explored using SEM and other techniques. A duplex film of about 1 μm total thickness is rapidly deposited on the glass surface. This is a continuous film of Ca(OH)₂ overlain by a parallel array of rod-shaped CSH gel particles projecting normal to the interface. The nearby cement paste exhibits high porosity, but after a few days becomes partly filled with a secondary deposit of stacked platelets of relatively pure Ca(OH)₂. Cement particles near the interface hydrate in a peculiar manner. A hydration product shell is quickly formed, but the encapsulated cement particles dissolve away to leave partly or completely empty shells. This behavior occurs with various Portland cement types and presumably occurs near aggregate surfaces in concrete.     

Nanostructured mullite steam oxidation resistant coatings for silicon carbide deposited via atomic layer deposition

Oxidation resistant, thin, pinhole‐free, crystalline mullite coatings were deposited on zirconia and silicon carbide particles using atomic layer deposition (ALD). The composition of the films was confirmed with inductively coupled plasma optical emission spectroscopy (ICP OES), and the conformality and elemental dispersion of the films were characterized with transmission electron microscopy (TEM) and energy dispersive X‐ray spectroscopy (EDS), respectively. The films are deposited on the particle surface with a deposition rate of ~1 Å/cycle. The elemental concentration of aluminum relative to silicon in the film was determined to be 2.68:1 which agrees closely with the ratio of stable 3:2 mullite (2.88:1). A high‐temperature anneal for 5 hours at 1500°C was used to crystallize the films into the mullite phase. This work represents the first deposition of mullite films by ALD. The mullite and alumina‐coated particles were exposed to high‐temperature steam for 20 hours at 1000°C to assess the oxidation resistance of the films, which reduced the oxidation of silicon carbide by up to 62% relative to uncoated particles under these conditions. The activation energy of oxygen diffusion in the films was determined with density functional theory, and the computational results aligned well with the experimental outcomes.     

Studies of sintering of coal ash relevant to pulverised coal utility boilers: 2. Preliminary studies of compressive strengths of fly ash sinters

The development of strength of pellets of fly ash with sintering temperature was investigated. Pellets heated below the shrinkage or electrical (Raask) sinter point did not develop strength over several hours. Hot crushing of pellets above the sinter point gave plastic deformation, presumably due to liquid on the particle surfaces. Cooling below the sinter point before crushing gave the same strength as crushing at room temperature, showing strength was due to solidification. Strength as a function of heat treatment temperature (1 h duration) above the sinter point went through a maximum, indicating that liquid is removed at higher temperature. SEM analysis of the cold pellets showed glassy sintering at conditions of maximum strength, and crystallization of mullite as strength decreased with higher heat treatment temperatures. Results suggest that iron silicate compositions increased the maximum sinter strength more than sodium silicate compositions. Water washing of fly ash reduced maximum strength. Addition of Na₂0 or surface films of sodium carbonate to a synthetic mineral mixture reduced the sinter point and led to strength development at lower temperatures: however, too high additions reduced the maximum strength.     

锆刚玉莫来石-碳化硅复合材料的显微结构

采用OM、SEM、TEM及EDAX等手段研究了锆刚玉莫来石-碳化硅复合材料的显微结构。结果表明,ZrO_2及SiC均匀地分散于刚玉/莫来石构成的基质中。刚玉-刚玉(或莫来石)及莫来石-莫来石的晶间表面多数存在非晶质薄膜,但也有刚玉-莫来石两相直接结合的相界因扩散而形成固溶层。ZrO_2-刚玉(或莫来石)及SiC-刚玉(或莫来石)的相表面因相间扩散形成固溶层或扩散层而皆属直接结合。在刚玉和莫来石晶体里观察到有晶内ZrO_2存在,其形成原因可能是在烧结过程中,刚玉或莫来石晶体再结晶长大而包裹ZrO_2微粒所致。     

不同炉型潞安煤灰理化及酸/碱溶解特性

对潞安煤经循环流化床、煤粉炉和气化炉处理后得到的煤灰进行了化学组成、矿物组成、特征基团、粒径分布、比表面积及微观形貌等理化性质的对比研究,并考察了其在酸浸和碱浸过程中Al^3+,Si^4+,Fe^3+,Ca^2+,K^+和Ti^4+等离子的溶解特性。结果表明:不同炉型潞安煤灰中铝、钙、硫等元素的含量有明显的差异;矿物组成包括晶相的鳞石英、方石英、莫来石、硬石膏及非晶相的偏高岭石、假莫来石、无定型二氧化硅等;相比较而言,气化炉灰中铝硅酸盐矿物结构更加不稳定。循环流化床灰颗粒呈具有一定孔洞结构的不规则状,而煤粉炉灰和气化炉灰均为光滑球形颗粒,循环流化床灰的粒径>煤粉炉灰的粒径>气化炉灰的粒径,循环流化床灰的比表面积>气化炉灰的比表面积>煤粉炉灰的比表面积。在HCl溶液中,Al^3+,Fe^3+,Ca^2+,K^+,Ti^4+的溶出率均较高;在NaOH溶液中,仅Si^4+和K^+的溶出率较高。不同炉型潞安煤灰中各元素的溶出率具有较大差异,主要与其矿物组成、结构稳定性、粒径和比表面积等相关。     

Investigation of high-density polyethylene film surface treated with chromic acid mixture by use of 2,4-dinitrophenylhydrazine

High-density polyethylene films were treated with chromic acid mixture. 2,4-Dinitrophenylhydrazine was reacted on the treated films. The changes in amounts of 2,4-dinitrophenylhydrazones formed in the films were inferred by comparing the absorptions in the ultraviolet spectra. The changes in the film surfaces by chromic acid mixture treatment were investigated by comparing the changes in the amount of the hydrazones with changes in water wettability of the treated films. Scanning electron micrographs of the treated film surfaces were taken. Oxidation of the film surface zone, partial breakdown of polymer in the film surface zone, and oxidation of surface zone bared from the film inner zone seem to have occurred with increase in treatment time. When the treatment temperature was raised, the increase in carbonyl groups in the surface of the high-density polyethylene film with rise in treatment temperature seems to have been prevented by an increase in partial breakdown of polymer in the film surface.     

Thin polymer films from fluidized electrode bed reactors

The formation and deposition of a polymer as a thin, uniform solid film on a metal particle substrate is investigated in detail in a fluidized electrode bed reactor. Experiments were carried out in different designs of fluidized bed electrode cell reactor, using various metal particles and monomers. It was observed that diacetone acrylamide (DAA) monomer in 0.1N H₂SO₄ with aluminum particles (3530 μm) as cathode, in a concentric dual compartment cell, appeared to yield the best films. Infrared and elemental analyses were used to characterize the polymer film on the metal particles. Scanning electron microscopy (SEM) was employed to examine the surface and cross-sectional profiles of the films. The potential profiles in both particulate and solution phases were measured and the importance of particulate electrical conductivity in the polymerization is thus explained. It was observed that the optimum particulate conductivity and hence the maximum yield occurs in the range of 10–20% bed expansion. The experimental product yields for various liquid superficial velocities (i.e., bed expansion) at different feeder current densities were compared to explain the possible controlling mechanism in packed and fluidized bed cells, noting that both chemical reaction and mass transfer control in the low bed expansion region while chemical reaction controls in the high bed expansion region. The current effciency decreases in the high current region due to side reactions at the fluidized bed electrode and due to pore diffusion in the polymer film.     

Analysis of evaporating thick liquid films on solids

The diffusion-controlled evaporation of small circular volatile liquid films from solid surfaces was monitored by employing video microscopy from a plan view and then applying digital image analysis techniques. The decrease of the liquid-solid contact area of these films during the last stages of the evaporation was found to be linear with time. This paper presents experimental results of four organic liquid films (n-nonane, n-octane, toluene, n-butanol) on three substrates poly(methyl methacrylate), poly(ethylene terephthalate) (Mylar), and glass. The linear decreases of the surface areas of hanging drops from a polypropylene fiber for the same liquids were also monitored using both plan and side view video cameras for comparison. Analyses of optically recorded liquid film and drop shapes were carried out and a diffusion model depending on the presence or absence of the substrate was developed. By combining the experimental area decrease of a spherical drop due to the diffusion-controlled evaporation with that of a small spherical cap shaped liquid film resting on a solid surface, it is possible to calculate the small contact angles (less than 10°) of the wetting thick liquid films on solids. The relationship between film evaporation rate and the solid-liquid interfacial interactions is also discussed.     

Formation of hydrophilic starch coatings on polyethylene films

Thin starch coatings were deposited onto polyethylene (PE) film surfaces when PE films were immersed in 1% jet cooked starch solutions and the hot solutions were allowed to cool. Normal cornstarch, waxy cornstarch, high amylose cornstarch, and solvent‐extracted normal cornstarch (to remove native lipid) were used in these experiments. Amounts of adsorbed starch varied from about 0.03–0.05 mg per cm² of PE, and these starch coatings imparted hydrophilic properties to film surfaces, as evidenced by contact angle measurements. Although starch could be removed by gently rubbing water‐wet PE surfaces, air‐dried coatings were more firmly attached, and did not separate from the PE surface when films were bent or flexed. SEM images of starch‐coated film surfaces showed that starch was deposited as particles less than 1 μm in diameter, and also as aggregates of these submicron particles. Despite the fact that some starch samples contained only very small amounts of amylose and native lipid, surface‐deposited starch in all experiments contained 90–100% amylose; and exhibited the same V_h X‐ray diffraction pattern, indicative of helical inclusion complex formation. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1781–1788, 2002; DOI 10.1002/app.10589     

Microhardness of Sputter-Deposited Zirconia Films on Silicon Wafers

Calcia-stabilized zirconia films were deposited on the surface of silicon 111 wafers using radio frequency (rf) magnetron sputter deposition. Deposition was conducted at substrate temperatures that varied in the range of 80°–900°C. X-ray diffractometry results showed that all the films consisted of cubic zirconia. The fracture surface morphology and etched surfaces of the films were studied using scanning electron microscopy (SEM). Depending on the deposition temperature, the structure of the film was either columnar or equiaxed. The transition temperature from the columnar structure to the equiaxed structure was at a ratio of deposition temperature to melting temperature of } 0.42. The microhardness of the films was evaluated using a developed model that is based on the plastic zone analysis below a diamond (Vickers) indentor. From this model, the microhardness was found to increase as the deposition temperature increased, which was probably because the hardness of ceramic materials decreases as the defect concentration increases.     

Fundamentals of bitumen coking processes analogous to granulations: A critical review

A number of coking processes use hot particles to heat liquid bitumen or petroleum residue to cause cracking reactions. These particles may be mineral or coke solids. Interactions of these particles, in fluid beds, moving beds and other types of contactors, are governed by the liquid films on the particle surfaces. This paper explores the analogy between granulation and coking, and suggests that the key relationships that will govern the behavior of wet particles in coking processes are the Stokes number of the particles, the thickness or the liquid films, and the diameter and surface roughness of the particles. The implications for distribution of liquid feed in the reactor, fouling, and defluidization or bogging are discussed. This analysis suggests experiments that can be performed under non‐reactive conditions with scaled variables in order to study phenomena that cannot be observed in situ in high‐temperature cracking processes.     

Evaluation of the wettability of spherical cement particle surfaces using penetration rate method

The wettability of cement particles is related to the fluidity of cement paste. This paper describes the mechanism of the higher fluidity imparted by the spherical cement particles in light of their wettability. In addition, the effects of gypsum on the wettability were also studied. This study has shown the following: (1) The weight of water and water-reducing agent solution penetrating the spherical cement powder bed is 24-150% higher than that for the ordinary Portland cement powder bed. This results in the improvement of the wettability of the particle surfaces of spherical cement. The high wettability of spherical cement contributes to its high fluidity. (2) The presence of many fine gypsum particles on the spherical cement particle surface reduces the wettability. (3) To prepare spherical cement, the optimum amount of gypsum added is determined by the acceleration of the formation of spherical particles and the wettability of particle surfaces.     

Characterisation of the glass fraction of a selection of European coal fly ashes

Fly ash largely consists of the inorganic content of coal that remains after combustion. The crystalline phases present in fly ash may form upon cooling of a molten alumino‐silicate glass. This view is supported by the spherical shape of many fly ash particles, inferring that they have gone through a viscous fluid state. The amorphous content in fly ash is believed to dominate reactivity behaviour, under both alkaline and acid conditions, because glasses have a higher potential energy than the equivalent crystal structure and the variation of bond angles and distances in a glass makes the bond breakage easier. It is the degradation behaviour under alkaline conditions, and the subsequent release of silica from the glass phase, that is important in the use of fly ash for conversion to zeolites and for pozzolanic applications in cement. This research comprehensively studies the composition, quantity and stability of the glass phase in a series of nine fly ashes sourced from Spanish and Italian power plants. The quantitative elemental composition of the glass phase in each fly ash was determined. Samples of the ashes then underwent a series of tests to determine the internal structure of the ash particles. Heat treatment of most of the ashes results in mullite crystallising from the glass phase; this is the crystalline phase that is predicated to form by both the relevant phase diagrams and also by NMR spectroscopy. In the ashes, mullite is present as a spherical shell, tracing the outline of the particle but in some specific cases the mullite skeleton is made up of coarse crystals reach also the internal parts of the particles. The morphology and density of the mullite crystals in these shells varies greatly. This work has supported the view that some crystalline phases present in fly ashes, such as mullite, form upon cooling of the amorphous glass melt as opposed to direct conversion from existing mineral phases in the coal during the combustion process. Copyright © 2004 Society of Chemical Industry     

Mass transfer characterization for hydrocarbon liquid–particle collision based on sensitive tracing of fluorescent probe

The heat and mass transfer characteristics during the collision process of hydrocarbon droplets and polyethylene particles in a liquid-containing gas–solid polyethylene fluidized bed reactor significantly affect the product quality. In this work, the mass transfer process of single-component hydrocarbon and bi-component hydrocarbon liquid films on the polyethylene particle surface were quantitatively characterized by a newly developed experimental approach, based on a novel synthesized hydrocarbon liquid soluble fluorescent probe for sensitive tracing of hydrocarbon liquid diffusion. It was found that the boiling point and surface tension of the liquid as well as the surface temperature of the particle are the key factors affecting the mass transfer properties of the liquid film. Marangoni convection was observed and characterized on the particle surface. The critical time for the onset of Marangoni flow is between 4 and 8 s.     

Dewetting and photochemical crosslinking of adhesive pads onto lithographically patterned surfaces

The design of structured adhesive interfaces can be realized by dewetting of a liquid adhesive onto substrates with hydrophilic and hydrophobic domains followed by photochemical crosslinking. The latter allows the creation of well-defined arrays of confined adhesive pads with a controlled geometry. In a first step, the surfaces are covered by a hydrophobic film and lithographically patterned through a mask with an array of spots with diameter of 2 mm. The adhesive can consequently be locally deposited by a dosing syringe and remains confined within the hydrophilic spots. By defining the volume of the adhesive droplets, the contact angle and height of the adhesive pads are controlled through pinning at the hydrophilic/hydrophobic interface, which prevents further spreading. Alternatively, the dip coating and spontaneous dewetting of liquid adhesive over the patterned surface provide a continuous fabrication method for adhesive pad arrays. In a second step, the geometry of the deposited adhesive pads is stabilized by partial crosslinking during different times under UV light. Finally, an adhesive joint is created by applying the counterface followed by full cross-linking. The adhesive strength and mechanical performance are further optimized by considering different crosslinking times and pattern designs. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47321.     

A scanning electron microscope study on agglomeration in petroleum coke-fired FBC boilers

Ten samples originating from different boiler FBC systems burning petroleum coke and one laboratory sample were chosen to perform a study on the development, structure, and composition of deposits formed by agglomeration in various locations. The work focused on examination by scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis. The possibility of a contribution of liquid phases in the adherence to solid surfaces and in agglomeration was discussed and checks by SEM, EDX, and analysis by neutron activation were performed; no evidence could be found either for liquid phases or for any role of vanadium or alkaline element compounds. The agglomerations result from the continued sintering of CaSO₄ particles until they build up a strong framework that is indefinitely extended, into which particles of different and complex compositions are bound, without contributing to the cohesion. Chemical sintering occurring by the sulphation of CaO into CaSO₄ appears to be an important contribution while CaO is still available, but sintering also occurs by mass transfer mechanisms and continues after the depletion of CaO. Deposits formed in regions only reached by fly ash (convection section), and also in in-bed deposits, grow from particles <50 μm, mostly in the range of 10 μm or less. In regions collecting bed ash (e.g., J-valves), the deposit grows from the sintering together of particles on the order of 100–300 μm (originally bed ash particles), which themselves appear as conglomerates of extensively sintered smaller particles.     

AGGLOMERATION BEHAVIOR IN A BUBBLING FLUIDIZED BED AT HIGH TEMPERATURE

Minimum fluidization velocity and agglomeration behavior were investigated at high temperature in an 80?×?30?mm two-dimensional quartz fluidized bed and in an 82?mm i.d. circular fluidized bed. Bed materials tested were two sizes of glass beads as well as three sizes of fluidized bed combustor (FBC) ash. The minimum fluidization velocity decreased with increasing bed temperature, whereas the minimum sintering fluidization velocity increased with the bed temperature. The sintering of glass beads belongs to visco plastic sintering, the first type. FBC ash agglomerate has higher amounts of SiO₂, Al₂O₃, Na₂O, K₂O, and SiO₂ than in the original ash, indicating that low melting eutectics were formed and that the liquid phase in a silicate system was formed. The agglomeration of FBC ash belongs to the second type, an excessive quantity of liquid being formed by melting or chemical reaction.