Action Of Microwave Radiation Research Articles

Adsorption of 2,4-Dichlorophenoxyacetic Acid from an Aqueous Medium on Modified and Carbonized Carbon Material Formed from Lignin under the Action of Microwave Radiation

Adsorption of 2,4-Dichlorophenoxyacetic Acid from an Aqueous Medium on Modified and Carbonized Carbon Material Formed from Lignin under the Action of Microwave Radiation

Influence of the Polymer Matrix Composition on the Size Range of Silver Nanoparticles Formed in a Succinyl Chitosan Solution Under the Action of Microwave Radiation

Influence of the Polymer Matrix Composition on the Size Range of Silver Nanoparticles Formed in a Succinyl Chitosan Solution Under the Action of Microwave Radiation

MICROWAVE TECHNOLOGY OF LIQUID-GLASS HEAT-INSULATING MATERIALS BASED ON A GRANULAR PRODUCT

The paper investigates the properties of liquid glass thermal insulation products obtained on the basis of granular products under the influence of microwave radiation. Due to the volumetric heat release in the thickness of the liquid glass composition, it is possible to obtain homogeneously structured materials by applying the technology of simultaneous porosization with volumetric expansion of both granules and binder. Thanks to volumetric heating and the mechanism of "non-thermal" effect of microwave radiation on the processing objects, the duration and temperature of their heating is significantly reduced, as well as the operational properties of the products are improved. The properties of materials obtained by this technology are compared with the properties of materials obtained by binding pre-swollen granules. It was proved that the simultaneous swelling of granules with a binder made it possible to obtain materials of a monolithic, uniformly porous structure with high physical and mechanical parameters and an order of magnitude lower indicators of water absorption and sorption moisture due to the dense packing of the granules and the uniform distribution of the binder in the intergranular space. The developed technology for the production of composite materials in the form of heat-insulating products of various configurations by means of simultaneous porosization with volume expansion of granules and binding under the action of microwave radiation allows to obtain materials with a better set of operational characteristics than in the case of binding pre-swollen granules at lower energy costs for their production because it excludes the stage of separate swelling of the granules. The resulting composite thermal insulation materials do not deform and have a fairly high strength for their average density. They are practically incompressible, and this is a very important fact, since the compression of heat insulating materials over time leads to an increase in its thermal conductivity and a decrease in the heat-shielding properties of the structure.

Influence of Short-Pulse Microwave Radiation on Thermochemical Properties Aluminum Micropowder.

The thermochemical properties of Al micropowder after exposure to microwave irradiation were investigated. The Al micropowder was exposed to microwave irradiation in air with a frequency of 2.85 GHz, a power density of 8 W/cm2, and a pulse duration of 25 ns and 3 µs. The thermochemical parameters of the irradiated metal powders were determined by the method of thermal analysis at the heating in air. It was found that an increase in the duration of microwave pulses and irradiation time leads to the thermal annealing of the metal particles, and the thermal processes of melting and sintering begin to dominate over non-thermal processes. The specific thermal effect of irradiated Al micropowder oxidation increases from 7744 J/g to 10,154 J/g in comparison with the unirradiated powder. The modeling of thermal heating processes of aluminum (Al) micropowder under the action of pulsed microwave radiation has been performed. It is shown that with an increase in the duration of microwave pulses and irradiation time, a significant heating of the Al micropowder occurs, leading to its melting and sintering. The results of modeling on the action of microwave radiation on the Al micropowder were compared with experimental results.

The Study of Manufacturing Thermal Insulation Materials Based on Inorganic Polymers under Microwave Exposure.

The work is devoted to the creation of an energy-saving microwave technology of composite materials for thermal insulation based on an inorganic polymer—liquid glass—and the establishment of the formation patterns of their structure and properties, depending on the parameters of microwave radiation. Due to volumetric heating and the mechanism of "non-thermal" action of microwave radiation on processed objects, the duration of their heating is significantly reduced, and the performance properties of products are improved due to the modification of the structure of the liquid glass matrix under the influence of its irradiation with this type of energy. In the course of the research, the relationship between the processing conditions and the obtained properties of heat-insulating materials was established. The prospects of using the microwave electromagnetic field in the production of new building materials, expanding their range, and improving quality and competitiveness are shown, which is a priority for the modernization and innovative development of the construction industry.

Comparison of Physicochemical Properties and Catalytic Activity in the m-Xylene Isomerization of Catalysts Based on ZSM-12 Zeolites Prepared at Hydrothermal Conditions and under the Action of Microwave Radiation

Comparison of Physicochemical Properties and Catalytic Activity in the m-Xylene Isomerization of Catalysts Based on ZSM-12 Zeolites Prepared at Hydrothermal Conditions and under the Action of Microwave Radiation

Adsorption of petroleum products by modified and activated adsorbents

This research is aimed at investigating the adsorption of petroleum products from aqueous solutions by adsorbents modified with HCl and those activated by microwave radiation. The research objects were carbon adsorbents: activated coals, such as AD-05-2, IPI-T, KAD-iodine and zeolites of the TransBaikal deposit. The quantitative analysis of waters (standardised test solutions with an initial concentration of petroleum products not exceeding 10 mg/l) was carried out by the fluorimetric method using a Fluorat-02 liquid analyser. The adsorbents were activated in a microwave oven at a wave power of 800 W for 1 min. The modification was carried out according to the following procedure: 10 g of the adsorbents dried to a constant weight at a temperature of 120-150 °C were stirred for 24 h with 200 ml of a 12% HCl solution in water.Next, the suspension was filtered and washed with distilled water until neutral. It was found that the value of adsorption of petroleum products by adsorbents modified with HCl increases by 3.8 times for activated carbon KAD-iodine, 0.5 times for IPI-T, and equals 0.71 mg/g and 0.80 mg/g respectively. Among the studied sorbents, these sorbents have the largest grain size (3-5 mm) and micropore volume (0.28-0.29 cm3/g). It was established that the method of short-term (within 1 min) microwave activation makes it possible to increase the adsorption of petroleum products by: 4.2 times for activated carbon KAD-iodine and 0.6 times for IPI-T in comparison with the original adsorbents. The highest adsorption value of petroleum products corresponds to zeolites and equals 0.99 mg/g. The action of microwave radiation is associated with the dissociation and evaporation of the water bound in the adsorbents and flammable organic substances, which leads to an increase in the porosity of the adsorbent. The application of the microwave activation method is highly promising in comparison with the classic methods of chemical and steam-gas activation. This method simplifies the technological design and reduces the consumption of reagents for the production of effective adsorbents used to extract petroleum products from aqueous solutions, which acquires particular importance in the context of maintaining the environmental safety of water use.

RESEARCH OF PROCESSES OF FORMATION OF STRUCTURE OF COMPOSITE THERMAL INSULATION MATERIALS ON THE BASIS OF LIQUID GLASS BTAINED WITH THE USE OF ENVIRONMENTALLY SAFE MICROWAVE TECHNOLOGIES

Improving the efficiency of energy use is one of the main tasks in the chemical industry not only in Ukraine but also around the world, which is due to the steady rise in energy prices. In this regard, an effective way to save energy is the thermal modernization of buildings, industrial equipment and communications with thermal insulation materials. It should be noted that the share of domestic materials in the Ukrainian market is not more than 30 %. Therefore, the creation of new types of insulation materials is a very important task. This material is a heat–insulating material based on liquid glass, created with the involvement of microwave radiation as an alternative to traditional convective thermal heating. The technology of production of heat–insulating materials on the basis of liquid glass by hot foaming involves obtaining the material in the form of granules, not plates, due to the difficulty of uniform heating of the inner layers of large samples. The problem of large–scale production of high–quality thermal insulation materials based on liquid glass in plate form is not solved due to poor heating of the inner layers of the plate due to the low thermal conductivity of the swollen outer layers. That is why the production of composite thermal insulation materials based on granular filler and liquid glass binder is proposed to be carried out under the action of microwave radiation. Thermal insulation properties of expanded materials are directly determined by their macrostructure. Therefore, the purpose of this study is to determine changes in the structure of the material from the type and amount of ingredients used in the liquid glass composition. On the basis of the conducted researches it is shown that the materials with use as a filler of zinc oxide and as a gas–forming agent of hydrogen peroxide have the most ordered structure. It is established that their use in the amount of 9–10 wt.h. provides a rate of gas evolution and growth of pore centers, which is comparable to the process of curing composition, which allows to obtain materials with a homogeneous, fine and closed–porous structure, which provides high insulating properties with a thermal conductivity coefficient of 0.05–0.055 W / m · K, which meets the requirements for thermal insulation materials.

Application of Microwave Radiation to Produce Uranium Dioxide Powder from Its Trioxide

The possibility of producing UO2 powder from UO3 using microwave radiation (power 300 W) in the presence of organic compounds with amino groups: carbohydrazide (CH), acetohydroxamic (AHA), and aminoacetic (glycine) acids has been investigated. It was found that in these processes in an oxygen-free atmosphere, UO2 is produced from UO3, and in an air, U3O8. It was shown that under the action of microwave radiation in the presence of CH and AHA, powdered UO2 are synthesized from UO3. The physical properties of the powders obtained (bulk density with tapping 2.6–2.7 g/cm3, specific surface area up to 3.2 m2/g, moisture content less than 0.1 wt %) meet the requirements for ceramic-quality powders in the production of fuel pellets.

The Synthesis of Nanophosphors YPxV1–xO4 by Spray Pyrolysis and Microwave Methods

За счет редкоземельного допирования фосфаты и ванадаты являются ведущими материалами для синтеза люминофоров благодаря их термостойкости, низкой температуре спекания, химической стабильности. Особый интерес привлекают люминофоры в наноразмерном состоянии. Простой, быстрый и масштабируемый синтез нанолюминофоров высокой химической гомогенности является актуальной задачей. Целью работы являлся синтез порошков смешанных кристаллов ванадат-фосфата иттрия различного состава методами соосаждения под действием микроволнового излучения и спрей-пиролиза, а также сравнительный анализ характеристик полученных образцов.Методами соосаждения под действием микроволнового излучения и спрей-пиролиза в различных режимах синтезированы образцы YVхP1–хO4 разного состава. Данные рентгенофазового анализа в случае синтеза ванадат-фосфата иттрия YVхP1–хO4 методом спрей-пиролиза с последующим отжигом подтверждают образование однофазных нанопорошков. Методами просвечивающей электронной микроскопии и растровой электронной микроскопии выявлены морфологические характеристики образцов. В зависимости от режима отжига образцы представляют собой ограненные либо сферические частицы размером менее 100 нм. Состав образцов YVхP1–хO4, синтезированныхметодом соосаждения под действием микроволнового излучения, сильно зависит от рН раствора прекурсоров.Минимальное содержание примесных фаз достигается при рН, равном 9.Метод спрей-пиролиза позволяет синтезировать нанопорошки ванадат-фосфата иттрия YVхP1–хO4 высокой химической гомогенности с размером частиц менее 100 нм. При синтезе YVхP1–хO4 методом соосаждения под действием микроволнового излучения максимальной химической однородности порошков ванадат-фосфата иттрия удается достигнуть при рН = 9. Однако дисперсия частиц по размеру велика, лежит в интервале 2–60 мкм. ЛИТЕРАТУРА 1. Wu C., Wang Y., Jie W. 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Formation of Hydrogen Peroxide under the Action of Microwave Radiation in Aqueous Solutions of Vanadyl and Permanganate Ions

The amount of hydrogen peroxide formed in aqueous solutions directly in the course of microwave irradiation is considerably larger than the amounts detected previously in post-irradiated solutions. The degree of saturation of aqueous solutions with a gas is an important factor for the occurrence of microwave processes. The experiments were performed in aerated solutions and in solutions preliminarily saturated with Ar. The results obtained suggest that radical products of water decomposition are formed as a result of SHF breakdown of gas bubbles present in the solution.

Phase Transformations in Iron Oxide under the Action of Microwave Radiation

It has been shown that microwave radiation induces structural and, as a consequence, magnetic phase transformations in iron oxide α-Fe2O3 (hematite). After microwave irradiation of fine-dispersed partially amorphized Fe2O3 particles for 10 min in wet air, the percentage of crystalline hematite drops by 40% but the total amount of crystalline components increases owing to the formation of a new ferromagnetic modification, α-Fe2O3 maghemite. The initial antiferromagnetic and final ferromagnetic Fe2O3 samples are powders consisting of spherical particles with nearly equisized (40–60 nm) domains of X-ray coherent scattering.

Flocculation of Titanium Dioxide with Functionalized Citrus Pectin

Modified polysaccharides were prepared by the reaction of citrus pectin with a cationic monomer, (1,2-epoxypropyl)triethylammonium chloride, in alkaline medium and under the action of microwave radiation in the reactor system microwave–ultrasonic–UV-induced synthesis. Organic hybrids were prepared by mixing aqueous solutions of natural polysaccharides (pectin and modified pectin with chitosan) under ambient conditions in 1 : 1 ratio. The influence of the concentration of citrus pectin, its modified samples, chitosan, and their organic hybrids on the flocculating properties was studied for a model disperse system, a suspension of titanium dioxide in water and aqueous salt solutions, under the conditions of free (unrestricted) sedimentation. The influence of the ionic strength on the conformational state of polysaccharide macromolecules and on the aggregation of titanium dioxide particles was analyzed.

Investigation of heating of nanomodified polymers under the action of microwave radiation

The article presents the study of heating nanomodified polymers under the action of microwave radiation. Modification of polyethylene was carried out using CNTs synthesized on Co-Mo / Al2O3-MgO catalysts. The influence of CNTs concentration on the temperature regime of polymer heating is investigated. The study of interaction with microwave radiation was carried out at the emitter power of 800 W in 2 minute increments for 8 minutes

Microwave Stabilization of a Dynamic Membrane Layer

Dynamic membranes have been obtained by depositing a polystyrene (PS) layer onto a nylon substrate. The dynamic membrane layer of PS particles on the nylon substrate has been treated using 2450-MHz microwave radiation of a 350 W power in air. It has been found that as a result of the microwave irradiation of the membranes in atmospheric air, the membrane mass decreases to 0.69% of the initial value depending on the treatment time. Scanning electron microscopy examination has shown the formation of agglutinated polystyrene particles and melted and compacted regions on the membrane surface. According to the scanning electron microscopy data, the microwave treatment of the membrane has decreased the roughness of its surface layer by a factor of 8. According to IR data, the action of microwave radiation on the nylon–PS membrane leads to a decrease in the intensity of peaks in a range of absorption bands from 1500 to 3500 cm–1. An observed increase in the membrane flux by microwave irradiation for up to 10 min has been associated with the etching of membrane surfaces, whereas a decrease in the flux after irradiation for 20 min is explained by the compaction and melting of particles in the dynamic layer. The stability of the dynamic layer has been established by examining the flux of the membrane and changes in its mass after backwashing with a detergent solution. It has been found that the stability of the dynamic layer of the nylon–PS membrane is achieved with microwave irradiation for 5 min. An increase in the treatment time increases the degree of surface etching and leads to the formation of defective areas in the dynamic membrane layer. The microwave-irradiated dynamic nylon–PS membrane has been used to separate a water–oil emulsion. The degree of separation of the emulsion was 96.1% at a membrane flux of 19.1 dm3 m–2 h–1.

Simulation of the thermal state of the workpiece made of polymer-matrix composites using microwave radiation

The simulation results of the thermal state of a cylindrical workpiece made of composite material and exposed to the action of microwave radiation are presented. The mathematical model of a workpiece allows the analysis of the interconnected thermal and electromagnetic processes in the equipment operating area, and also takes into account the exothermic effect associated with the curing of the polymer matrix.

Microwave Synthesis of Co, Ni, Cu, Zn Ferrites

Solid-phase synthesis of cobalt, nickel, copper, and zinc ferrites with spinel structure was performed from oxides of these metals and natural magnetite under the action of microwave radiation. The optimal conditions in which the corresponding ferrites can be formed were determined by varying the irradiation parameters affecting the reaction (magnetron power and reaction duration). It was found that the solid-phase interaction of oxides of Ni, Zn, Cu, Co(II) metals gives in practically acceptable yields metal-substituted ferrospinels (NiFe2O4, CoFe2O4, ZnFe2O4, CuFe2O4) constituting the main phase of the samples. A high capacity of the precursors and target synthesis products for absorption of the microwave radiation energy at a frequency of 2.45 GHz and its transformation into heat was demonstrated. This gives reason to use these compounds when preparing catalysts for microwave-stimulated reactions.

Lignin conversion to hydrogen-containing gas under the action of microwave radiation

The paper describes the carbon dioxide reforming of lignin in the presence of Ni-, Fe, and Ni/Fe-containing active components formed directly on the surface under microwave irradiation. The deposition of 0.1 wt % iron acetylacetonate on the lignin surface results in a sharp increase in the microwave absorption capacity at a 0.5 kW power and induces lignin conversion to hydrogen-containing gas with a degree of hydrogen recovery reaching 90 %. The maximum lignin conversion (65%) is attained in 10 min under microwave irradiation. It was shown for the first time that deposition of metals (Fe and Ni) on lignin can provide for targeted change of the selectivity of reforming to synthesis gas and the process can thus be classified as a plasma catalytic one. Using the obtained results, it is possible to minimize the amount of catalyst and to propose an efficient route for hydrogen and synthesis gas production from lignin waste.

Carbon sorbent from carbonized peat

The physicochemical and adsorptive properties of a carbon sorbent obtained by the microwave carbonization of peat were studied. With the use of IR spectroscopy and elemental analysis, it was found that, under the action of microwave radiation, the concentration of functional groups in peat decreased and, as a result, the carbon content of peat increased. It was established that the adsorption activity of the carbon sorbent for iodine considerably increased as a result of carbonization, and that for methylene blue and methanyl yellow decreased. The carbon sorbents obtained by the microwave carbonization of peat had a total pore volume of 1.02 cm3/g and a specific surface area of no smaller than 1350 m2/g.

Interference of commensurate and microwave-induced oscillations of the magnetoresistance of a two-dimensional electron gas in a one-dimensional lateral superlattice

The influence of microwave radiation on the low-temperature magnetotransport of two-dimensional electrons in a one-dimensional lateral superlattice fabricated on the basis of a selectively doped GaAs/AlAs heterojunction has been investigated. It has been found that the resistance of the two-dimensional electron gas in this superlattice changes under the action of microwave radiation more substantially at the minima of commensurate oscillations than at the maxima. The experimental data demonstrate “interference” of classical commensurate magnetoresistance oscillations and quantum microwave-induced oscillations.