Hollow Aluminosilicate Microspheres Research Articles

Spark plasma sintering of cenosphere-derived Cs/Sr-aluminosilicates for 137Cs and 90Sr immobilization in mineral-like ceramics

In this study, a promising method of spark plasma sintering (SPS) was investigated for the fabrication of ceramic matrices designed for the reliable immobilization of highly radioactive radionuclides 137Cs and 90Sr. The ceramic matrices were derived from a mixed composition of two aluminosilicate mineral-like phases – pollucite (Cs,Na)AlSi2O6 and gehlenite Sr2Al2SiO7. The originality of the developed approach lies in the utilization of hydrothermal synthesis for obtaining granulated precursor material. Hollow aluminosilicate microspheres (cenospheres) from coal fly ash served as the initial raw material, which were treated with alkaline solutions containing Cs+ and Sr2+ ions as simulants for the corresponding radionuclides. This method facilitated the achievement of high efficiency in cation removal from solutions exceeding 98%. For a comprehensive examination of the composition and morphology of cenosphere-derived precursor particles, and the influence of sintering temperature on phase and structure formation of ceramic matrices under non-equilibrium conditions of spark plasma heating, various analytical techniques were employed. These included thermogravimetry/differential thermal analysis (TG/DTA), powdered X-ray diffraction analysis (PXRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), as well as the method of low-temperature nitrogen adsorption for determining the specific surface area. The obtained ceramic samples exhibited high values of specific density (2.688–2.915g/cm³), compressive strength (666–808MPa), and Vickers microhardness (1.8–2.5GPa), attesting to their high quality and stability. The results of the hydrolytic stability assessment revealed that the leaching rates of Cs+ and Sr2+ ions from the ceramics are extremely low, within the range of 10-5–10-6g/cm²·day. These values fully satisfy the requirements of GOST R 50926-96 and the international standard ISO 6961:1982 for solidified forms of high-level waste.

Study of the effect of silicate fillers on the structural and rheological properties of acrylic dispersions

This work reports the rheological properties of an acrylic aqueous dispersion filled with hollow aluminosilicate microspheres and highly dispersed amorphous silicon dioxide studied by using rotational viscometry. It was established that an increase in the degree of filling with hollow microspheres leads to a significant increase in the viscosity of the aqueous dispersion, which results in technological difficulties when applying coatings to the surface. The introduction of a small amount of silicon dioxide additive leads to a decrease in the structural strength and effective viscosity of the aqueous dispersion of the acrylic copolymer, which allows significantly reducing the viscosity and regulating the rheological characteristics of highly filled systems, which is decisive in the technology of their application. The combination of such fillers as silicon dioxide and hollow aluminosilicate microspheres in an aqueous dispersion of an acrylic copolymer allows simultaneously reaching a number of positive phenomena: a reduction in the viscosity of the material during application (without dilution) due to the use of high shear rates and an increase in the rate of dispersion structuring after application, and also allows achieving sedimentation resistance during storage and transportation.

ПОЛУЧЕНИЕ ЛЮТЕЦИЙ/ИТТРИЙ-АЛЮМОСИЛИКАТНЫХ МИКРОСФЕР НА ОСНОВЕ ЦЕНОСФЕР В КАЧЕСТВЕ ПРЕКУРСОРОВ ИСТОЧНИКОВ РАДИАЦИОННОГО ИЗЛУЧЕНИЯ ДЛЯ БРАХИТЕРАПИИ

Coal fly ash hollow aluminosilicate microspheres (cenospheres) of stabilized composition (glass phase > 90 wt. %) were used to fabricate lutetium/yttrium-aluminosilicate microspheres as precursors of Lu-177 and Y-90 bearing β-irradiation sources applied for the selective radiation therapy of tumors. The zeolitized microspheres containing the zeolite phase NaP1 (GIS) were synthesized and their sorption properties with respect to Lu3+/Y3+ were studied. The fast heating–cooling cycle at 1200 oC in a moving bed resulted in amorphization of the zeolite component without the formation of the lutecium/yttrium crystal phase preserving the precursor spherical form.

Influence of Various Coal Energy Wastes and Foaming Agents on Foamed Geopolymer Materials' Synthesis.

The regularities of obtaining foamed alkali-activated geopolymer materials based on different wastes of coal power engineering (fly ash, fuel (boiler) slag, ash, and slag mixture) were considered. The phase composition of the studied waste showed the presence of a significant amount of the amorphous phase, as well as a crystalline phase. mostly in the form of high quartz. The microstructure of studied the waste showed that the fly ash consisted of monodisperse hollow aluminosilicate microspheres, the fuel slag was represented by polydisperse irregular particles, and the ash and slag mixture included both of these materials in different ratios. Blowing agents such as aluminum powder, hydrogen peroxide, and sodium hypochlorite were chosen to achieve the porous structure of the geopolymer materials. The calculations of the geopolymer precursor compositions were carried out. Samples were synthesized, and their physical and mechanical properties, such as density, strength, porosity, and thermal conductivity, were analyzed. The micro- and macrostructure of the samples, as well as the pore distribution of the obtained geopolymers were studied. Conclusions were made on the choice of the most-optimal foaming agent and the optimal coal combustion waste suitable for the synthesis of the geopolymer materials.

Cenosphere-Based Zeolite Precursors of Lutetium Encapsulated Aluminosilicate Microspheres for Application in Brachytherapy.

Coal fly ash hollow aluminosilicate microspheres (cenospheres) of stabilized composition (glass phase—95.4; (SiO2/Al2O3)glass—3.1; (Si/Al)at. = 2.6) were used to fabricate lutetium-176 encapsulated aluminosilicate microspheres as precursors of radiolabeled microspheres applied for selective irradiation of tumors. To incorporate Lu3+ ions into cenosphere’s aluminosilicate material, the following strategy was realized: (i) chemical modification of cenosphere globules by conversion of aluminosilicate glass into zeolites preserving a spherical form of cenospheres; (ii) loading of zeolitized microspheres with Lu3+ by means of ion exchange 3Na+ ↔ Lu3+; (iii) Lu3+ encapsulation in an aluminosilicate matrix by solid-phase transformation of the Lu3+ loaded microspheres under thermal treatment at 1273–1473 K. Two types of zeolitized products, such as NaX (FAU) and NaP1 (GIS) bearing microspheres having the specific surface area of 204 and 33 m2/g, accordingly, were prepared and their Lu3+ sorption abilities were studied. As revealed, the Lu3+ sorption capacities of the zeolitized products are about 130 and 70 mg/g Lu3+ for NaX and NaP1 microspheres, respectively. It was found that the long-time heating of the Lu3+-loaded zeolite precursors at 1273 K in a fixed bed resulted in the crystallization of monoclinic Lu2Si2O7 in both zeolite systems, which is a major component of crystalline constituents of the calcined microspheres. The fast heating–cooling cycle at 1473 K in a moving bed resulted in the amorphization of zeolite components in both precursors and softening glass crystalline matter of the NaX-bearing precursor with preserving its spherical form and partial elimination of surface open pores. The NaX-bearing microspheres, compared to NaP1-based precursor, are characterized by uneven Lu distribution over the zeolite-derived layer. The precursor based on gismondin-type zeolite provides a near-uniform Lu distribution and acceptable Lu content (up to 15 mol.% Lu2O3) in the solid phase.

Hollow aluminosilicate microspheres with increased surface hydroxyl groups by etching method for electrochemical detection of Hg(II)

Tuning the concentration of hydroxyl groups (–OH) to improve the adsorption ability of nanomaterials has attracted broad interest in the field of environmental contaminant analysis. In this work, we provide efficient directions for enhancing the detection performance of Hg(II) through controlling the etching time of SiO2 in NaAlO2 solution to modulate the concentration of surficial –OH. It is found that the hollow aluminosilicate microspheres (HAM) with an etching time of 28 min shows the best detection sensitivity of 795.33 μA μM−1 cm−2 for Hg(II), compared to that of SiO2 and yolk-shell microspheres (YSM). X-ray photoelectron spectroscopy (XPS) results confirm that the HAM exhibits the highest concentration of –OH, which can bond with Hg(II) to promote its adsorption on the electrode surface and then enhance the detection signal of Hg(II). In addition, the HAM modified electrode is used to realize the electrochemical analysis of Hg(II) in real water samples and achieved satisfactory results. This study facilitates understanding the adsorption mechanism between –OH and target HMIs during the detection process and designs the nanomaterials with highly –OH concentration for electrochemical detection of HMIs.

The effect of polymer-cement mortars with additives of aluminosilicate microspheres on the reservoir properties of exploration and production wells

The article shows that the use of lightweight grouting solution with hollow aluminosilicate microspheres can reduce the time and the cost of materials spent on securing exploration wells, ensure the rise of solution to the design height. Improved strength and fracturing of the stone ensures resistance to fracture during perforation, and a sufficiently strong bond can ensure tightness of the annulus in exploration and production wells.

Determination of rational parameters for heat treatment of concrete mixture based on a hollow aluminosilicate microsphere

The research on determining rational parameters of heat treatment of a concrete mixture based on hollow aluminosilicate microspheres has defined the features of the intensifying action on the structural concrete mixture by low-pressure steam with optimum heat and mass transfer. Optimum values of temperature, humidity and speed of the medium have been identified. The obtained heat treatment parameters are subject to general regularities of structures for the formation of hydraulic bindings and are in accordance with production conditions, thus providing possibilities for their adaptation into production. The mechanisms for determining the strength of concrete stone according to the structural and thermal effectiveness of the active medium have been defined. Thanks to the strength-building mechanisms obtained, it is possible to reduce the thermal destruction capacity of the system while reducing the process heat consumption. It is confirmed that the main direction in reducing the destructive capacity is determined by the mass flow of moisture, which has the greatest heat capacity and the least thermal conductivity at the initial stages. The invention relates to periods of temperature rise and isothermal heating without impairing the mechanical properties of concrete. It is shown that the real duration excludes high-temperature destruction processes, thereby increasing the mechanical strength of concrete and reducing the overall energy consumption. Thus, there is a reason to argue that it is possible to produce strong and light concrete products under accelerated structure formation and new technologies for heat treatment of concrete based on lightweight fillers with reduced heat consumption.

ТЕПЛОІЗОЛЯЦІЙНІ ПОКРИТТЯ НА ОСНОВІ СТИРОЛ-АКРИЛОВОЇ ДИСПЕРСІЇ ТА ПОРОЖНИСТИХ АЛЮМОСИЛІКАТНИХ МІКРОСФЕР

The article contains information about the areas of application of modern thin-layer polymer heat-insulating materials. Technological and operational indicators of the developed coating based on styrene-acrylic dispersion and hollow aluminosilicate microspheres are given. The developed thermal insulation coating has low water absorption, high thermal insulation performance, high adhesive strength to concrete.

The Study of the Dependence of Optimal Structure of Composite Materials Containing Hollow Aluminosilicate Microspheres on Humidity

Background: Experimental data on the conditions for the formation of gravel materials containing hollow aluminosilicate microspheres with a possibility to receive optimum structure and properties depending on humidity with the use of various binders are presented in this article. This article focuses on the scientific study of the possibility to optimize the physical and mechanical properties of composite materials. Objective: The main goal of this research is an exploration of energy-efficient building materials to be used to replace natural materials with industrial wastes and development of the theory and practice of how to obtain light and ultra-light gravel materials based on mineral binders and waste dump ash and slag mixtures of hydraulic removal. The objective of this research is to study the composite material containing hollow aluminosilicate microspheres. Method: The study is based on the application of the separation method for power and heat engineering functions. The method is based on the use of the structure optimality factor that takes the primary and secondary stress fields of the structural gravel material into account. It shows the possibility to obtain gravel material with the most uniform distribution of nano - and microparticles in the gravel material and to form stable matrices with minimization of stress concentrations. Experiments show that the thickness of the cement shell that performs power functions is directly related to the size of the raw granules. At the same time, the cement crust thickness regardless of the binder type has a higher formation rate for larger diameter granules when the moisture content increases. Results: The conditions of formation for gravel composite materials containing hollow aluminosilicate microspheres were studied. The optimal structure and properties of the gravel composite material were obtained. The dependence of the strength function on humidity and the binder type was investigated. The optimal size and shape of gravel material containing aluminosilicate hollow microspheres with a minimum thickness of a cement shell and a maximum strength function were obtained. Conclusion.: The obtained structure enables us to separate power and heat engineering functions in the material and to minimize the content of the aggressive environment centers.

Innovative Thermal Insulation Materials with Dual Properties

The paper presents the results of development and research of an innovative thin-layer thermal insulation material that protects the building from heat loss due to thermal radiation. The material is a dry mortar of cement binder and filler of hollow aluminosilicate microspheres. A thin-layer coating made from this optimally combines the functions of effective heat protection and external finishing warm plastering that is advantageous when reconstructing and restoring historical objects with a lavish decoration. The conducted studies have shown that aluminosilicate microspheres in the composite thermal insulation coating are also involved in the reflection of infrared radiation. The use of Class 2 admixtures made it possible to synthesize additional crystalline hydrates with the aluminate phase of clinker brick, which contributed to the strengthening of the cement composite at the micro- and submicrolevels. This was confirmed by electron microscopy. For the developed composition of the mineral thin-layer thermal insulation coating, the cost of the mixture is almost 3 times lower than for the known composition of the thermal insulation coating on the polymer binder. In addition, unlike polymer analogs, there are no restrictions in terms of temperature and service life. The thermal insulation coating may be applied both exteriorly and interiorly with no condensation being formed between the wall and the coating. Applying the developed thin-layer thermal insulation coating on a brick wall measuring 10 m by 10 m in the climatic conditions of Kharkiv allows reducing heat consumption by 0.188% per 1 m2 per year.

Effect of compressive stresses on permeability of coal with fracture filled with lightweight proppant

The paper presents laboratory testing results on effect of hydraulic fracturing on permeability of coal with and without wedging of created fractures by proppant. The tests were carried out with hollow aluminosilicate microspheres ASPM-500 without and with additional polymeric thermoreactive coating, specimens of dense long flame (grade D) coal with permeability of less than 3·10−3 μm2 and fractured fat coking coal (grade ZH) with permeability over 60·10−3 μm2. It is found that creation of fractures with and without propping considerably improves gas permeability of dense coal with weakly developed natural jointing. Created fractures are less effective in highly jointed highly permeable coal. It is experimentally proved that filling of created fractures with small opening of 0.4 mm with lightweight proppant under uniform compression of 1–5 MPa improves permeability of dense coal by 7–19.5 times. In jointed coal, application of lightweight proppant under the same conditions improves permeability less considerably—by 1.2–2.6 times. It is revealed that efficiency gas drainage in coal by hydraulic fractures without propping lowers as compressive stresses decrease. Reduction in permeability of coal with propped fracture under growing compression is probably connected with redistribution and compaction of proppant particles in the fracture. The obtained results show that application of lightweight propping materials is a promising way of advance in the technology of hydraulic fracturing for stimulation of coalbed methane drainage. The long-range research, in the authors’ opinion, should be focused on the development of lightweight proppants with improved strength characteristics.

Development of Technology for Preparing Composite Material Based on Aluminum Strengthened with Hollow Ceramic Microspheres

The possibility of preparing cast billets of aluminum alloy strengthened by adding hollow aluminosilicate microspheres is investigated. Results of microstructural analysis and a study of strength properties are provided. Experiments are conducted in order to increase molten metal adhesion to the surface of microspheres, both with classical microspheres, and with microspheres with surface modified by with a coating containing chromium and chromium carbide. The effect of adhesion on mechanical properties is demonstrated.

Elastomeric heat-shielding materials containing microspheres modified with a heteroorganic modifier*

The changes in the thermophysical and fire- and heat-shielding properties of compounds based on ethylene propylene rubber when hollow aluminosilicate microspheres (MSPs) are introduced were studied. The MSPs were treated with a heteroorganic modifier – phosphorus–boron–nitrogen-containing oligomer (PEDA), which is a combustion inhibitor. The physicomechanical characteristics of the vulcanisates and the magnitude of the Payne effect were determined. The vulcanisates contained 30 parts filler BS 120 and a sulphur vulcanising group, and also 1 part MSPs. The optimum MSP/PEDA ratio was 1:3. The ultra-high-frequency treatment of the mixture of MSPs and PEDA was especially effective. Using a Versa 3D electron microscope, the increase in the diameter of MSPs as a result of modification and the change in the atomic composition of the surface of MSPs were recorded. The modification of MSPs leads to a reduction in the Payne effect, to an increase in the interaction between rubber and filler, to a reduction in density, and to an increase in the cohesive strength. By comparison with a specimen without MSPs, the rate of linear combustion according to GOST 28157-89 decreases by 10%. The modification of MSPs leads to a decrease in this parameter by 5% by comparison with a specimen containing unmodified MSPs. The time of heating to 100°C of the unheated surface of a specimen heated on the other side to 2000°C increases by 50–60% and 11–19% respectively. The resistance to separation under conditions of erosion entrainment increases by 4–7%. The use of PEDA makes it possible to improve the adhesion of coating to substrate. A scheme of the interaction of MSPs and PEDA is put forward.

Rheological properties of aquaeous dispersion of styrene acrylate copolymer incorporating hollow microspheres and AEROSIL®

The rheological properties of aquaeous dispersion of styrene acrylate copolymer incorporating hollow aluminosilicate microspheres and AEROSIL® 300 fumed silica (a high-range water reducing admixture) have been investigated using rotational viscometer. It is established that an increase in the degree of filling with hollow microspheres results in a significant increase in the viscosity of aqueous dispersion leading to the technological difficulties when coating the protected surfaces. AEROSIL® 300 can be dosed in small amounts resulting in a decrease in the structural strength and optimal viscosity of aqueous dispersion of acrylate copolymer, which allows to significantly reduce the viscosity density, while maintaining relatively low water demand and characteristics of highly filled systems, which is crucial in the technology of their application. The combination of such fillers as AEROSIL® 300 and hollow aluminosilicate microspheres in the styrene acrylate copolymer aqueous dispersion allows the combination of a number of positive effects: a reduction in the viscosity of the material during application (without dilution) by applying high shear rate and increasing viscosity (structuring) after application, and also during their storage and transportation.

Thermal insulation coating based on water-based polymer dispersion

For Russia, due to its long winter period, improvement of thermal insulation properties of envelope structures by applying thermal insulation paint and varnish coating to its inner surface is considered perspective. Thermal insulation properties of such coatings are provided by adding aluminosilicate microspheres and aluminum pigment to their composition. This study was focused on defining the effect of hollow aluminosilicate microspheres and aluminum pigment on the paint thermal insulation coating based on water-based polymer dispersion and on its optimum filling ratio. The optimum filling ratio was determined using the method of critical pigment volume concentration (CPVC). The optimum filling ratio was found equal to 55%.

Thermal insulation coating based on water-based polymer dispersion

For Russia, due to its long winter period, improvement of thermal insulation properties of envelope structures by applying thermal insulation paint and varnish coating to its inner surface is considered perspective. Thermal insulation properties of such coatings are provided by adding aluminosilicate microspheres and aluminum pigment to their composition. This study was focused on defining the effect of hollow aluminosilicate microspheres and aluminum pigment on the paint thermal insulation coating based on water-based polymer dispersion and on its optimum filling ratio. The optimum filling ratio was determined using the method of critical pigment volume concentration (CPVC). The optimum filling ratio was found equal to 55%.

Elastomer Heat-Shielding Materials Containing Aluminosilicate Microspheres

The influence of hollow aluminosilicate microspheres on the efficiency of elastomeric thermoprotective materials based on ethylene—propylene rubber is considered. The introduction of hollow aluminosilicate microspheres, even in small quantities, decreases the density and heat conductivity of such materials, with no loss of physical and mechanical properties.

Physicomechanical, thermal, and flame-retardant properties of elastomer compounds based on ethylene–propylene–diene rubber and filled with hollow aluminosilicate microspheres

The effect of hollow aluminosilicate microspheres on the Payne effect and on physicomechanical, thermal, fire-retardant, and heat-protecting properties of elastomer compounds based on ethylene–propylene–diene rubber was studied. Based on the results obtained, the mechanism of the interaction of the elastomer matrix with the microspheres was suggested. Enhancement of the filler–matrix and filler–filler interaction favors additional three-dimensional cross-linking, which influences the set of the physicomechanical and thermal properties, and manifestation of the reinforcing effect in a coke layer under the conditions of erosion removal and detachment of the material with a high-velocity gas flow.

Vibration-Assisted Sputter Coating of Cenospheres: A New Approach for Realizing Cu-Based Metal Matrix Syntactic Foams

The coating of hollow alumino-silicate microspheres or cenospheres with thin layers of Cu by means of vibration-assisted magnetron sputtering yields a starting material with considerable potential for the production of new types of metal matrix syntactic foams as well as optimized variants of conventional materials of this kind. This study introduces the coating process and the production of macroscopic samples from the coated spheres via spark plasma sintering (SPS). The influence of processing parameters on the coating itself, and the syntactic foams are discussed in terms of the obtained density levels as a function of sintering temperature (which was varied between 850 and 1080 °C), time (0.5 to 4 min), and surface appearance before and after SPS treatment. Sintering temperatures of 900 °C and above were found to cause breaking-up of the homogeneous sputter coating into a net-like structure. This effect is attributed to wetting behavior of Cu on the alumino-silicate cenosphere shells. Cylindrical samples were subjected to conductivity measurements and mechanical tests, and the first performance characteristics are reported here. Compressive strengths for Cu-based materials in the density range of 0.90–1.50 g/cm3 were found to lie between 8.6 and 61.9 MPa, depending on sintering conditions and density. An approximate relationship between strength and density is suggested based on the well-known Gibson–Ashby law. Density-related strength of the new material is contrasted to similar findings for several types of established metal foams gathered from the literature. Besides discussing these first experimental results, this paper outlines the potential of coated microspheres as optimized filler particles in metal matrix syntactic foams, and suggests associated directions of future research.