粉煤灰粒径分布对硅酸盐水泥水化性能的影响

为研究粉煤灰粒径对硅酸盐凝胶材料水化性能的影响,经球磨仪研磨得到3种不同粒径的粉煤灰,探讨其对硅酸盐水泥水化放热速率、水化放热总量、水化反应程度和粉煤灰自身水化反应程度的影响。结果表明:随粉煤灰粒径的减小,粉煤灰的水化活性明显增大,水化反应程度增大,养护龄期为7 d时,水化程度增加20.7%;粉煤灰粒径分布对硅酸盐水泥水化放热总量的影响较小,主要影响其水化放热速率、水化反应程度,养护龄期为28 d时,胶凝材料水化程度增加3%。     

粉煤灰漂珠粒径对粉煤灰漂珠/AZ91D镁合金复合材料阻尼性能的影响

通过搅拌铸造法向半固态AZ91D镁合金中添加粉煤灰漂珠（FAC）制备了FAC/AZ91D镁合金复合材料,研究了FAC粒径对该复合材料阻尼性能的影响。结果表明:FAC/AZ91D镁合金复合材料的阻尼性能明显优于基体材料,在FAC含量相同时,FAC的粒径越大,其阻尼性能越好。室温下FAC对提高FAC/AZ91D镁合金复合材料的阻尼性能起重要作用,FAC附近的基体产生了高密度的位错,形成了塑性区。室温下FAC粒径越大,在其附近产生的塑性区越大,阻尼性能越好。随温度的升高,FAC/AZ91D镁合金复合材料的阻尼性能迅速提高。位错、晶界以及FAC和基体之间的界面运动是提高阻尼性能的关键。      

Preparation of sintered foam glass with high fly ash content

Foam glasses with 50 wt.%, 60 wt.% and 70 wt.% fly ash are prepared using fly ash and flux agent sodium borate with sodium silicate as foaming agent at the temperature of 800 °C. Heat treatment at 800 °C for 1 h of pellets having different fly ash mass percentages results in well-sintered bodies of dark gray color featuring a vitreous aspect with smooth surface. The effect of amount of fly ash on the density, porosity, mechanical strength and microstructure is evaluated. The experimental results show that the foam glass with 70 wt.% fly ash exhibits the excellent comprehensive properties and the suitable sintered temperature is 800 °C.     

Waste glass and fly ash derived glass-ceramic

Crystallization behavior of a waste-based glass-ceramic was studied by means of X-ray diffraction analysis, and the surface morphological observations and chemical compositions were evaluated by field emission-scanning electron microscopy and energy dispersive X-ray spectrometry. Applying the mechanical milling method, the glass-ceramic was prepared by using fly ash from a thermal power plant mixed with waste glass cullet. Powder mixtures consisting of waste glass powder (70 wt%) and fly ash (30 wt%) were used to make glass-ceramic. Various heat treatment temperatures [900, 925, 950, 975, 1000 and 1025°C] were used to obtain a glass-ceramic of the optimum crystal phase, mechanical properties and chemical durability. The X-ray diffraction analysis showed that the crystalline phases in the glass-ceramic were diopside [Ca(Mg, Al)(Si, Al)₂O₆], augite [Ca(Mg, Fe)Si₂O₆] and wollastonite [CaSiO₃]. The crystallization of an acicular phase in the matrix was achieved in the heat treatment temperature range of 1000–1025°C, and the acicular type main crystal phase in the glass-ceramic was wollastonite [CaSiO₃]. The heat treatment temperature range [1000–1025°C] also showed much better mechanical properties.     

Dissolution and geopolymerization of synthetic fly ash glass

Journal of Materials Science - Two fly ash glasses were synthesized and dissolved in KOH at a water/solid ratio of?≤?0.3. We measured reaction kinetics, gel formation, and...     

Effect of particle size on kinetics crystallization of an iron-rich glass

The effect of glass particle size on the crystallization kinetics of an iron-rich glass from a nickel leaching waste has been investigated by means of differential thermal analysis (DTA). The results show that the crystallization of a pyroxene phase occurs by bulk nucleation from a constant number of nuclei. The crystallization mode and the dimensionality of crystals are strongly dependent on the glass particle size, 100 μm being the critical size. Glass fractions with particle size >100 μm show three-dimensional crystal growth controlled by diffusion, whereas a particle size <100 μm leads to an interface reaction mechanism with two-dimensional growth of crystals.     

Effect of fly ash fineness on compressive strength and pore size of blended cement paste

This paper presents an experimental investigation on the effect of fly ash fineness on compressive strength, porosity, and pore size distribution of hardened cement pastes. Class F fly ash with two fineness, an original fly ash and a classified fly ash, with median particle size of 19.1 and 6.4 μm respectively were used to partially replace portland cement at 0%, 20%, and 40% by weight. The water to binder ratio (w/b) of 0.35 was used for all the blended cement paste mixes.Test results indicated that the blended cement paste with classified fly ash produced paste with higher compressive strength than that with original fly ash. The porosity and pore size of blended cement paste was significantly affected by the replacement of fly ash and its fineness. The replacement of portland cement by original fly ash increased the porosity but decreased the average pore size of the paste. The measured gel porosity (5.7–10 nm) increased with an increase in the fly ash content. The incorporation of classified fly ash decreased the porosity and average pore size of the paste as compared to that with ordinary fly ash. The total porosity and capillary pores decreased while the gel pore increased as a result of the addition of finer fly ash at all replacement levels.     

Reaction kinetics of fly ash geopolymerization: Role of particle size controlled by using ball mill

Fly ash is milled for 0, 30 and 90?min and used to study the role of particle size on the kinetics of geopolymer formation. The increase in particle fineness is very prominent in the initial milling stage, and then slows down due to agglomeration effect of finer fraction. The fly ash geopolymerization kinetics and its mechanism is determined using heat of reaction data measured by isothermal conduction calorimeter. The improvement in reaction rate with milling is correlated with the median particle size of the fly ash. The apparent activation energy decreases with size reduction because finer fractions are more prone to alkali activation. Although the kinetics changes with particle fineness, but no alternation is detected in the reaction mechanism, governed by nucleation and growth. The apparent activation energy evaluated by rate method is showing three major steps of geopolymerization such as dissolution, gel formation and restructuring.     

Nucleation and crystal growth in a fly ash derived glass

The devitrification behaviour of a fly ash derived glass, examined by differential thermal analysis (DTA), X-ray diffraction and scanning electron microscopy (SEM), is reported and discussed. The crystallized phases were identified as mullite (3Al₂O₃·2SiO₂) and anorthite (CaO·Al₂O₃·2SiO₂). Kinetic parameters for nucleation and crystal growth were estimated from the DTA curves. The temperature of maximum nucleation rate was 790°C and the activation energy for crystal growth E=370 kJ mol^–1. The crystal morphology was investigated by SEM and the crystal shape found to be consistent with the morphological index n calculated by DTA. The glass-ceramic obtained from a previously nucleated glass showed a fine-grained texture.     

Thaumasite formation in concrete and mortars containing fly ash

Due to recent reports on deterioration of concrete structures, the thaumasite form of sulfate attack has become a subject of study and close investigation. This paper investigates the formation of thaumasite in concrete and mortars containing fly ash. The results show that thaumasite formation can occur within 84 days of exposure to sulfate solutions. High volumes of fly ash can limit or promote thaumasite formation depending on the type of cement used. Thaumasite and ettringite were found among the deterioration products. However, the thaumasite formation in the specimen prepared from sulfate resisting Portland cement was not accompanied by deterioration, except by 50% fly ash addition. The mixtures of Portland limestone cement with 40% fly ash exhibited a very limited thaumasite formation while the mixtures with 50% had no thaumasite at all. It is concluded that thaumasite can also be formed in mixtures incorporating fly ash.     

Structure formation of slag ash concrete on the basis of high-calcium fly ash and silica fume

Cementless slag ash concrete may be manufactured using high-calcium fly ash and silica fume as replacements for a binder and a microfiller, and incorporating slag sand from thermal power plants (TPP) as an aggregate. This concrete consists of waste products from TPP (fly ash and slag) and ferro-alloy plants (silica fume) and contains neither natural nor artificial aggregates for lightweight and heavy concretes. Silica fume (10–20% by weight of ash) and hot water together with subsequent heat treatment of concrete products or of castin situ structures binds the excess free calcium oxide present in the ash, and thus prevents deterioration of the concrete. The processes of concrete structure formation were investigated after 24 hours, 28 days, 3 and 6 months and the physico-mechanical, deformation and special properties (frost resistance, heat conductivity, protection of reinforcement from corrosion) were studied. This concrete conforms to the Russian Federation GOST requirement for use in single, two-storey buildings. The cost of the concrete is reduced by a factor of 3 compared with that of ordinary concrete.     

Variation of physical and rheological properties of fly ash slurries with particle size and its effect on hydraulic transportation at high concentrations

In thermal power plants, fly ash is collected at the bottom of electrostatic precipitator (ESP) hoppers and transported to common sump for further disposal to the ash pond by slurry pipelines. The fly ash from different fields of ESP hoppers vary widely in particle size as well as quantity. Depending on the sequence of evacuation, the overall particle size distribution (PSD) would vary with time which in turn would affect the head requirement in the high concentration slurry disposal (HCSD) system. Fly ash samples from different fields of ESP hoppers of a thermal power plant have been analyzed for their physical properties namely the PSD, specific gravity, settling characteristics, pH of the slurry, etc. and for rheological properties in the concentration range of 60–70% (by weight). The particle size (d_wm) of the fly ash samples decreases with the increase in ESP field, whereas the static settled concentration and specific density increase. The pH values of all samples are almost constant and nonreactive in nature. The rheological properties namely yield stress and Bingham viscosity of the fly ash slurries from different fields of ESP hoppers increase with increase in concentration. Further at any given concentration, these parameters exhibit a strong dependence on particle size. Using these properties and treating the distribution of particles across the pipe cross section as homogeneous in the concentration range of 60–70% (by weight), CFD computations are made to evaluate the head requirement in a HCSD pipeline. The head loss increases with increase in concentration for all fields of ESP hoppers. The present study also shows that head requirement varies significantly by mixing different proportion of fly ash from different ESP fields.     

Effect of copper content on glass formation and superconductivity in the Bi-Pb-Sr-Ca-Cu-O system

High-T _c superconducting ceramics of formula Bi_0.8Pb_0.2SrCaCu _x O _y (x=1.5, 1.8 and 2.0) were prepared by using the melt-quenching method, and the effect of copper content on glass formation and superconductivity was examined. It was found that the composition withx=1.5 had a tendency to form a glass and Bi₂(Sr, Ca)₂CuO_y crystals tended to precipitate easily during the rapid quenching of melts in the compositions withx=1.8 and 2.0. It was found from the temperature dependence of a.c. complex susceptibility that the intergrain coupling of superconducting crystals in the samples obtained was weak, but the weak coupling was improved by increasing the annealing time. The superconducting glass-ceramics Bi_0.8Pb_0.2SrCaCu_1.5O_y exhibited superconductivity with aT _c (zero) of 106 K and aJ _c of 250 Acm^–2.     

Al含量对漂珠/镁合金可溶复合材料组织与性能的影响

采用搅拌铸造法制备了不同Al含量下的漂珠（FAC）/镁合金可溶复合材料。采用金相显微镜、SEM及XRD观察分析了FAC/镁合金可溶复合材料的微观组织、溶解表面形貌及溶解产物的物相组成,采用力学性能试验机研究了复合材料的压缩性能,采用电化学工作站对复合材料进行电化学性能测试,在常温及水浴锅内进行复合材料在不同温度下的KCl溶液中的溶解试验。结果表明：该FAC/镁合金可溶复合材料主要由α-Mg基体相、β-Mg₁₇Al₁₂相、Mg₂Si相和MgO相组成。随着Al含量的增加,FAC/镁合金可溶复合材料的溶解速率先变快后减慢,在80℃的3wt% KCl溶液中,含15wt% Al的FAC/镁合金复合材料溶解速率最快,为56 mg/（h·cm²）。Al-FAC/镁合金可溶复合材料的抗压强度随Al含量的增加先提高后下降,四种合金的抗压强度均大于300 MPa,最高强度达到372 MPa。     

Effect of vibro-milling time on phase formation and particle size of nickel niobate nanopowders

A columbite-type phase of nickel niobate, NiNb₂O₆, nanopowder was synthesized by a solid-state reaction via a rapid vibro-milling technique. The effect of milling time on the phase formation and particle size of NiNb₂O₆ powder was investigated. Powder samples were characterized using DTA, XRD, SEM and laser diffraction techniques. It was found that the smallest particle size of 32 nm was achieved at 25 h of vibro-milling after which a higher degree of particle agglomeration was observed on continuation of milling to 35 h. In addition, by employing an appropriate choice of the milling time, a narrow particle size distribution curve was also observed.     

Effect of vibro-milling time on phase formation and particle size of lead zirconate nanopowders

A perovskite phase of lead zirconate, PbZrO₃, nanopowder was synthesized by a solid-state reaction via a rapid vibro-milling technique. The effect of milling time on the phase formation and particle size of PbZrO₃ powder was investigated. Powder samples were characterized using TG-DTA, XRD, SEM and laser diffraction techniques. It was found that an average particle size of 50 nm was achieved at 25 h of vibro-milling after which a higher degree of particle agglomeration was observed upon continuation of milling to 35 h. In addition, by employing an appropriate choice of milling time, a narrow particle size distribution curve was also observed.     

Controlling ettringite formation in FBC fly ash geopolymer concrete

Fluidized bed coal combstion (FBC) is extensively used in small self-generation power plants. The fly ash obtained from this FBC process contains high quantity of calcium and sulfate compounds which hinders its use in the construction industry. In addition, its reactivity is low and additional source material or additive is, therefore, needed to increase the reaction. This research studied the use of Al(OH)₃ and high concentrations of NaOH to control ettringite formation in the FBC fly ash geopolymer. Two replacement levels of 2.5 wt.% and 5.0 wt.% of Al(OH)₃ and three NaOH concentrations of 10, 12 and 15 M were used in the study. Results indicated that the NaOH concentration affected the ettringite formation and strength of the FBC geopolymer. No ettringite was formed at high NaOH concentration of 15 M which helped the dissolution of calcium sulfate and formed the additional calcium hydroxide. The subsequent pozzolanic reaction led to strength gain of the geopolymer. For 15 M NaOH, the addition of 2.5 wt.% Al(OH)₃ promoted the reaction and formed a dense matrix of alumino silicate compound. Relatively high 7-day compressive strength of 30 MPa was obtained.