Ash Microspheres Research Articles

Effects of fly ash microspheres on sulfate erosion resistance and chlorion penetration resistance in concrete

Fly ash microsphere (FAM) is a superfine fly ash product consisting of perfectly spherical and smooth particles. In this study, FAM was added to concrete for use in saline soil areas. The replacement levels of cement by FAM were 10% and 20% with a water-to-binder (w/b) ratio of 0.42. The hydration heat, thermogravimetric (TG) analysis, rheological performance, and the flowability of pure cement (CF0) and FAM-doped cement (CF10 and CF20) were investigated. The second exothermic peak occurred earlier and was higher in the FAM-doped cement than the CF0. The results showed that the nucleation effect of the FAM accelerated the early hydration speed of the cement. The TG results indicated that the Ca(OH)2 consumption was higher at 28 days due the addition of the FAM, which improved the interfacial transition zone and blocked the connected porosity of the hardened cement paste. The ball-bearing effect of the FAM particles in the paste reduced the internal friction between the grains, thereby significantly improving the rheology and the flowability of the cement paste. In addition, the filler effect of the FAM particles significantly improved the pore structure, which increased the compressive strength and chlorion penetration of the concrete. It was also found that the FAM increased the workability while improving the resistance of the concrete to sulfate attack when exposed to multiple drying–wetting cycles.

Preparation and Properties of Zr-Bearing Sorption Materials Based on Coal Fly Ash Microspheres

The influence of hydrothermal conditions on synthesis of analcime and a composite material ZrO2- analcime as well as zirconomolybdate coverings with ion exchange properties was studied using narrow fractions of aluminosilicate microspheres with a high content of a glass phase (91-95 wt. %). The possibility to synthesize ZrO2-analcime composites of narrow particle size distributions with maximum of about 40 μm and 6 μm under hydrothermal treatment at 150 °С was demonstrated starting from microspheres with Si/Al=2.7 and applying different regimes of a reaction mixture agitation. A microsphere material of a “core-shell” type such as ZrMo2O7(OH)2(H2O)2@(SiO2-Al2O3)glass with the nanostructured covering was prepared. Sorption properties of the materials regarding Nd3+, Sr2+ and Cs+ were studied under equilibrium conditions by means of determination of sorption isotherms and their fitting by the Langmuir model. Sorption parameters were determined including distribution coefficients which reach the values of 104−105 mL/g

Microwave-Mediated Electroless Coating of Copper on Hollow Fly Ash Microspheres

Hollow fly ash microspheres (FAMs) were successfully coated with copper (Cu) deposits via microwave (MW) irradiation. Ascorbic acid was used to reduce Cu2+ ions from copper sulphate pentahydrate solution. Subsequently, metallic Cu wasdeposited on FAMs within 2 to 6 min of MW irradiation. Microstructural examinations revealed that the sizes of the Cu coating on FAMs increased as MW time increased. The average approximate sizes increased from 1.56 μm to 4.04 μm as the MW processing time increased from 2 min to 6 min. Therefore, coating size could be controlled by adjusting MW irradiation time. Furthermore, EDX and XRD results confirmed the presence of Cu coating on FAMs, which agreed with the findings from the microstructural characterization. The results presented here showed that MW irradiation could be used to provide rapid and uniform heating of reactants to deposit Cu on FAMs within a short time. These Cu-coated FAMs have potential use as electrical conducting fillers in composite materials.

Composition and Structure of Microspheres in Ash and Slag Wastes on the Far East of the Russian Federation (Case of the CHPP-2 plant, Vladivostok)

The results of laboratory studies of the composition and structure of microspheres of ash and slag wastes of Russian Far East energy enterprises (in particular, CHPP-2, Vladivostok) are presented in this scientific work. It has been established that the microspheres are concentrated in particles of technogenic wastes with a size of up to 500 μm, with the prevailing mass of valuable geomaterial (75-80 %) being in narrow granulometric classes from 71 to 100 μm and 100 to 200 μm. Part of the microspheres is represented by unusual techogenic metal alloys (for example, antimony with aluminium), has a density of more than 1g/cm3, and when wet enriched in water precipitates. From a practical point of view, the investigated microspheres cannot be considered a ready commercial product, since they contain a significant amount of carbon concentrate, which is unburned solid fuel particles. In this connection, it is required to develop effective technological solutions for the extraction and purification of microspheres from ash and slag wastes from the thermal power industry of the Far East of the Russian Federation.

Characteristics of the Narrow Fractions of Fly Ash Microspheres as the Basis of Light-Weight High-Strength Materials

The narrow fractions of microspheres with a size of −0.4 + 0.2 mm with a low bulk density in the range of 0.34–0.64 g/cm3 were separated from cenosphere concentrates of fly ashes and fly ash from local selection obtained from pulverized coal combustion. The main components of the chemical composition in obtained narrow fractions are SiO2 – 55–66 and Al2O3 – 21–40 wt. %. The part of amorphous glass phase are 63–93, the mullite phase are 1–34, the quartz phase are 2–8 and the calcite phase are 0–1 wt. %. It is found that microspheres, characterized by maximum values of bulk density 0.64 g/cm3 and apparent thickness of the shell 20 μm, has the best strength properties. The successive twofold compressive loading the particles by increased strength were selected, for which the values of bulk density and apparent shell thickness increased to 0.86 g/cm3 and 29 μm, respectively. It is shown that the spheres with the single-ring structure are primarily subjected to destruction; the particles with network and solid structure provide improved strength characteristics of narrow fractions of microspheres

Microstructural characterisation and corrosion behaviour of microwave-sintered magnesium alloy AZ61/fly ash microspheres syntactic foams

Magnesium alloy AZ61/fly ash microspheres (FAMs) syntactic composite foams were synthesised via powder metallurgy and microwave (MW) sintering techniques. MW sintering was rapidly completed in 20 min and minimized the formation of brittle interfacial products. Effect of FAMs on the density, microstructure, and corrosion resistance of the alloy were investigated. FAMs were intact and fairly distributed in the microstructure of the foams. Corrosion behaviour in 3 wt.% sodium chloride solution showed that Tafel polarization curves shifted to lower current densities as the volume fraction of FAMs increased. This indicated that FAMs generally enhanced the corrosion resistance of the foams due to minimal galvanic interaction and reduction in the surface area of the material exposed to the corrosion medium. These results are significant and outline the enhancement of corrosion resistance of magnesium alloy AZ61 foams by using FAMs.

Investigation on the poor fluidity of electrically conductive cement-graphite paste: Experiment and simulation

Electrically conductive cement-based material is a type of smart and multifunctional material, which can be prepared by adding graphite. However, the addition of graphite can dramatically decrease the fluidity of the paste. This phenomenon severely restricts its use in practical engineering. In this study, various testing methods and an expanded DLVO (Derjaguin-Landau-Verwey-Overbeek) theory were adopted to clarify the mechanism of the poor fluidity of graphite-cement composite paste. The results showed that the low hydrophilicity of graphite and the consequent great polar interaction energy resulted in extreme agglomeration of particles, which was the dominant factor that caused the poor fluidity. Conventional methods (e.g., changing particle size, adding fly ash microsphere and water-reducing agents), which were commonly used in cement-based materials to improve the workability, could not efficiently improve the fluidity of cement-graphite paste. Instead, the surfactants could improve the fluidity and decrease the yield stress of the composite paste due to their adsorption and the consequent modification on the surface of graphite.

Heat-insulating Finishing Composition of the Optimal Structure with Microspheres

As fillers in most heat-insulating finishing compounds, various highly porous materials with high open microporosity and moisture capacity are used - expanded vermiculite sand and expanded perlite sand. In composites based on such compositions in the pore structure, open pores predominate, which is why the performance properties deteriorate, the strength and water resistance of the resulting coatings decrease. Of great interest is the use as fillers of materials with closed microporosity - glass hollow microspheres and ash microspheres of aluminosilicate. The aim of the work is the development of a model for the heat-insulating composite of the optimal structure, which allows to minimize the consumption of the binding agent by achieving the maximally dense packing of the microspheres. On the basis of the developed model, the optimal content of hollow glass microspheres and ash microspheres of aluminosilicate, in the case of cement and lime as binding agent, was calculated in heat-insulating composites. The average density of composites of the optimal structure for each pair of “binder-filler” is predicted. It has been established that the composites of the optimal structure obtained with the use as binder of lime will have a lower density in comparison with composites obtained using binder cement. As a result of the conducted studies, the possibility of effective use of lime as a binder in heat-insulating composites obtained with the use of microspheres was identified. When it is used, it is possible to significantly reduce the density of the resulting thermal insulation coatings, thereby increasing their thermal insulation properties and vapour permeability.

Sorption Properties of Fly Ash Microspheres of Thermal Power Plants

The sorption characteristics of aluminosilicate microspheres of fly ash from thermal power plants with respect to heavy metal ions were studied with a view to their subsequent use for integrated treatment of household and industrial wastewater. The mechanism and kinetics of the sorption of total iron ions from aqueous solutions are studied, quantitative characteristics of the sorption capacity and adsorption equilibrium constants are obtained. It has been established that aluminosilicate microspheres of fly ash possess sorption properties with respect to common iron ions. The sorption isotherm of iron ions from water by the material under study is characteristic of microporous sorbents. The quantitative characteristics of the sorption process allow us to conclude about the possibility of using aluminosilicate fly ash microspheres without any additional treatment for the purification of waste water from heavy metal ions.

New composite fillers on the base of fly-ash cenospheres modified with titanium dioxide

The paper presents the results of a study of the surface modification of fly ash microspheres with titanium dioxide. To improve adhesion of titanium dioxide, the surface of microspheres was pretreated with concentrated alkali solutions followed by low-temperature sintering with mechanically activated mixture of titanium dioxide and alkali. After separation of microspheres, the mixture was hydrolyzed followed by high-temperature drying. The surface of fly ash microspheres were studied by Raman spectroscopy and Scanning electron microscopy (SEM) analysis. The studies have shown the formation of a uniform coating on the surface, consisting mainly of titanium dioxide in the rutile form. The simple instrumental design of the process, based on methods of mechanical activation and sintering, allows us to recommend this method for industrial application.

Effect of aluminium oxide and ash microspheres on nitriding of aluminium ferrosilicon in the combustion mode

A composite ceramic β-sialon-based material is obtained by the SHS method using aluminium ferrosilicon as an initial material. The effect of the addition of aluminium oxide (α-Al2O3) and ash microspheres on the synthesis of sialon is studied. The iron-containing sialon-based composite is shown to exhibit a high catalytic activity in the presence of H2O2, H2C2O4 during degradation of dyes and phenol under UV radiation.

On the Issue of an Ash Microsphere Application as a Framework Forming Filler in Composite Materials

Hollow aluminum and silica microsphere is a component of ash wastes from heat and power industry that today is widely used as a microaddition almost in all sectors of economy. It is used to improve properties of different materials and constructions or to produce advanced properties of these materials. Hollow aluminum and silica microsphere is non-reactive microaddition that determine its advantages in producing ecologically friendly materials and in providing materials with additional properties without changing the basic. In this paper research has been conducted on identifying the modulus of viscosity focused on the effect on the capacity to form structure links that are influence the properties of producing leak less framework. Modulus of viscosity is one of the main dynamic characteristics of fill finely divided materials that determine materials and constructions strength properties including the capability to form a rigid frame. The research was carried out to determine the correlation between the modulus of viscosity and the humidity of raw component in order to identify optimal conditions of material formation and producing an item with the highest level of durability and rigidity. Moreover, the paper revealed the connection between the modulus of viscosity and the size of non-reactive microaddition based on set humidity and the influence of the microaddition size on the trend in modulus of viscosity.

Photocatalytic degradation of methylene blue by TiO2: Fe3+ supported by fly ash

The supported TiO2:Fe3+ photocatalyst was prepared by a sol-gel method. Using the fly ash as the carrier, the Fe3+ doped TiO2 was loaded onto the surface of the fly ash microspheres. The photocatalyst was characterized by SEM and UV-Vis. The photocatalytic degradation of methylene blue was studied. With 15 mg/L of methylene blue and 0.15g of catalyst, when illuminated for 120 min, the degradation rate of methylene blue reached 96%.

High-Strength Concretes Based on Multicomponent Binding and Fractionated Aggregates from Waste from Processing of Subsurface Rocks

A review of the use of industrial wastes in our country and abroad was conducted, and prospects for using man-made raw materials at the Grozny CHP and wastes of subsurface rocks crushing were considered. The analysis of the results of the conducted research is carried out, which showed that secondary technogenic raw materials can successfully compete and replace exhaustible natural resources, since the chemical composition and qualitative parameters of the materials under study confirm its uniqueness and, moreover, there is can see a solution of environmental problems. The formulation of multicomponent binders and concretes based on fine-dispersed ash microspheres and enriched artificial aggregates promoted recycling of secondary raw materials and improvement of the ecological situation in the region.

Dynamic Rheological Behavior of Low Water-to-binder Ratio Mortars under Large Amplitude Oscillatory Shear (LAOS)

This work focuses on the dynamic rheological behavior of low water-to-binder ratio cement mortars blended with fly ash microspheres (FAM) or silica fume (SF). The initial slump flow of each group has been controlled at similar values by adjusting the superplasticizer dosages. With the help of a coaxial cylinder rheometer, the dynamic rheological behaviors of these mortars are investigated by frequency sweeping in the range of 0–2 Hz under large amplitude oscillatory shear (LAOS). Based on the systematical elaboration of dynamic rheological testing theory, the experimental data are processed according to Lissajous plot fitting to reveal the viscoelastic characteristics. The nonlinearity of response signals is further assessed with Fourier transform (FT) analysis. The parameters, storage modulus G', loss modulus G" and relative amplitude I3/I1 are proposed to clarify the influences of FAM and SF on the stability and energy consumption of local structures and nonlinearity of response torques. The hydration characteristics of various groups well confirmed the rheological phenomenon. This study is beneficial for the preparation and optimization of flow state concrete such as pumping concrete and self-compacting concrete.

Effect of fly ash microsphere on the rheology and microstructure of alkali-activated fly ash/slag pastes

The highly viscous property of alkali silicate-activated cements is one of the critical challenges that hinder their wide application. The present study focuses on ameliorating the rheological performance of sodium silicate-activated fly ash/slag pastes by using fly ash microsphere (FAM), which are highly spherical particles collected from fly ash with electrostatic adsorption classification technology. The FAM particles work as ‘ball-bearings’ in the pastes to reduce the internal friction between fly ash and slag grains, and meanwhile mitigate the agglomeration of flocs and fragmentation to release the locked water. The interrelationship between the FAM particle geometry and plastic viscosity of the paste is well described by the Krieger-Dougherty equation, which supports the proposed mechanisms of ‘ball-bearings’ effects. FAM can work as an inorganic dispersing agent to improve the workability of alkali-activated cement products for a variety of application aspects.

Microwave Absorbing Mortar Using Magnetic Hollow Fly Ash Microspheres/Fe3O4 Composite as Absorbent

AbstractA new type of microwave absorption cement-based material was prepared by using a magnetic hollow fly ash microspheres (HFAM)/Fe3O4 composite as the absorbent. Through the chemical precipita...

Influence of the reaction time on the crystal structure of Na-P1 zeolite obtained from coal fly ash microspheres

This paper presents a study of the influence of time on the mineral structure formation of GIS Na-P1 zeolite. Lightweight microspheres were used as a source of silica and aluminium. Material subjected to this study was synthesized on a quarter-technical scale using a prototype installation. Chemical, mineralogical, and textural properties of the material were determined by means of X-Ray diffraction (XRD), X-Ray fluorescence (XRF), scanning electron microscopy equipped with a system of chemical composition analysis based on energy dispersive X-ray (SEM–EDS), volumetric adsorption analyzer (ASAP 2020), Fourier transform infrared spectroscopy (FTIR) and particle size analyzer (PSA). Experimental calculations based on Miller indices show the interesting and indeed astonishing phenomenon of the lattice parameters ripening as a function of time. Both unit cell parameters (a, b, c and volume) and the amount of zeolite present increase with synthesis time. This process is clearly observed using the XRD and FTIR method. Structural, morphological and textural properties of the final product indicate that it could potentially be useful as an adsorbent for various types of environment pollution.

Reduced graphene oxide and titania nanosheet cowrapped coal fly ash microspheres alternately as a novel photocatalyst for water treatment

A novel photocatalyst with core@shell structure was prepared by alternately assembling titania nanosheets (TNS) and reduced graphene oxide (r-GO) on coal fly ash (CFA) microspheres via the layer-by-layer (LBL) assembly approach. The as-prepared samples CFA@(r-GO/TNS)n were characterized by SEM, HRTEM, XRD, FTIR, Raman, XPS, UV–vis, PL and their photocatalytic activities were evaluated by the photodegradation of methylene blue (MB) under UV irradiation. The results showed that TNS and r-GO wrapped on the surface of CFA alternately and tightly, which was very helpful not only to avoid the detachment of TNS and r-GO from the surface of CFA in the progress of using, but also to reduce the recombination of photogenerated electrons and holes due to excellent mobility of charge carriers on the surface of r-GO. The layer number of wrapped r-GO/TNS was found to be an important factor in the photocatalytic activity of composite. In our experimental conditions, CFA@(r-GO/TNS)8 presented the best photocatalytic activity, and the degradation efficiency of MB was improved to 55% from 32% of CFA@(r-GO/TNS)2. The improvement could be attributed to several advantageous factors by introduction of r-GO, such as the fast charge-carrier transfer, the reduction of the charge recombination rate, the improved light harvesting and the larger specific surface area.

Исследование химического состава «летучей» золы и ее влияние на прочность цементного камня

Статья посвящена проблемам, связанным со снижением негативного воздействия золошлаковых отходов ТЭЦ Казахстана на окружающую среду. Вырабатываемая в больших количествах летучая зола как продукт сгорания топлива на энергостанциях отрицательно влияет на внешнюю среду, загрязняя воздух, почвы, сточные воды и т.п. В статье приведены результаты химического состава золошлаковых отходов. Рассмотрены возможные пути использования золы. Также изучен фазовый состав цементного камня с добавлением летучей золы с помощью современных методов анализа: рентгенофазовый и рентгенофлуоресцентный. Было выявлено, что к основным макроэлементам золы относятся Si, Al, Fе, О, Ca, Ti, Mg, S, K, Na. Помимо изучения размеров и форм микросфер в работе ставились задачи определения видов термоактивных фаз, составляющих цементного камня при термообработке; изучение структурных изменений при термообработке. Рентгенофазовый анализ по исследованию зольных микросфер показал следующие фазы: муллита Al6Si2O13, кварца SiO2 и аморфной стеклофазы. Применение золы как источника оксидов алюминия и кремния не только позволит снизить использование невозобновляемых ресурсов, но и получить материалы с улучшенными теплофизическими характеристиками (прочность, термостойкость и теплопроводность). Выбор оптимального количества золы уноса взамен части цемента способствует образованию желательной структуры цементного камня.