Obtaining the fine-grained silicon carbide, used in the synthesis of construction ceramics

Silicon carbide is used in the production of construction and temperature-resistant goods, capable of withstanding high mechanical and thermal loads. During recent times, silicon carbide has been frequently used in the electronics industry. Since sintered silicon carbide has increasingly been used as a replacement for metal components of various devices, the process of obtaining compact goods from silicon powder has become the defining factor in the technology used for its synthesis. The selection of conditions in which the sintering is conducted depends on granulometric structure, the form and the surface condition of the initial powder. The work consists of the synthesis of silicon carbide powder using the purified form of metallurgical silicon powder and soot. The qualities of testing samples were studied, where silicon carbide was obtained using established technology, from mechanically activated elementary, fine-grained silicon and soot, by pyrolytic synthesis. It was demonstrated that synthesis produces highly pure silicon carbide powder, (α- and β-phases) with a granulometric composition that allowed subsequent sintering to produce high quality compact goods. It was established that the content of silica in synthesized silicon carbide powder does not exceed 1-2% of the total mass

Coal layer under microwave heating: analytical study under mixed boundary conditions I and II of the genus

The relevance of the work is due to the prospect of the use of microwave radiation in the energy technologies of fuel use at the stages of preparation of solid fuels for coal-fired incineration, including drying and heat treatment. A few well-known results of laboratory experiments indicate structural effects, resulting in increased reactivity and reduction of unburnt fuel. Objective: to obtain an analytical expression for the temperature field in the coal array required for parametric analysis of technological conditions of microwave exposure. Methods: construction of analytically rigorous heat transfer problems, the solution of which is usually possible only in conditions of significant simplifications. If adopted by the constancy of the electrical and technological properties of coal physical picture of the process is determined by the incident on the coal layer of a plane electromagnetic wave that generates internal heat source of Buger law. The energy equation in the form of Fourier is solved independently of Maxwell equations. In this formulation the solution of allocated tasks is carried out by the method of integral transformation of Laplace. Results. The derived analytical solutions of temperature fields are received with mixed boundary conditions with fairly arbitrary changes in time and temperature of a surface flux density of fire on the border. For some special cases on this basis can be obtained an extensive series of simplified solutions available for parametric analysis of the rationale of optimal control parameters of the technology demanded by the engineering practice in project development and operation of microwave systems for processing of solid fuels in the energy sector

Coal layer under microwave heating: analytical study under mixed boundary conditions I and II of the genus

The relevance of the work is due to the prospect of the use of microwave radiation in the energy technologies of fuel use at the stages of preparation of solid fuels for coal-fired incineration, including drying and heat treatment. A few well-known results of laboratory experiments indicate structural effects, resulting in increased reactivity and reduction of unburnt fuel. Objective: to obtain an analytical expression for the temperature field in the coal array required for parametric analysis of technological conditions of microwave exposure. Methods: construction of analytically rigorous heat transfer problems, the solution of which is usually possible only in conditions of significant simplifications. If adopted by the constancy of the electrical and technological properties of coal physical picture of the process is determined by the incident on the coal layer of a plane electromagnetic wave that generates internal heat source of Buger law. The energy equation in the form of Fourier is solved independently of Maxwell equations. In this formulation the solution of allocated tasks is carried out by the method of integral transformation of Laplace. Results. The derived analytical solutions of temperature fields are received with mixed boundary conditions with fairly arbitrary changes in time and temperature of a surface flux density of fire on the border. For some special cases on this basis can be obtained an extensive series of simplified solutions available for parametric analysis of the rationale of optimal control parameters of the technology demanded by the engineering practice in project development and operation of microwave systems for processing of solid fuels in the energy sector

Heat treatment of the coal layer by microwave energy: an analytical study in conditions of heat removal of II and III order

Relevance of the research is related to the necessity of scientific study of microwave exposure technology parameters for coal, especially when drying, at thermal treatment, burning intensification and others. Experiments show that use of microwave radiation help reduce harmful emissions from coal burning, increase energy efficiency, reduce process time, etc. For optimal conditions of microwave treatment it is very popular to search for theoretical approaches, in particular, the engineering practice requires analytical solutions for heat treatment of coal array, which was done in the study. The aim of the research is to develop strict analytic solutions of the problems of coal layer heating by microwave radiation under the heat removal of the II and III order, which allow carrying out the parametric analysis of microwave exposure and searching for the most advantageous modes of heating coal layer. Methods. The tasks of coal bed heating by microwave radiation with boundary conditions of the II and III order were set with a number of simplifications, such as persistence of thermal and electrical properties of the material, they are isotropy, one-dimensionality. This physical process itself is plane electromagnetic wave energy absorption and formation of heat sources in coal array, modeled on the Bouguer law. The energy equation in the form of Fourier in this case is considered independently of the Maxwell equations of electrodynamics. A new dependent variable was determined. It modifies the boundary conditions into homogeneous, and simplifies the search of solutions. As a result, the basic system of equations is divided into two subsystems, and the final solution was found making a superposition of these two sub-tasks. Results. The authors have found analytically strong dependences of temperature distribution over the cross section and time for carbon bed heated by microwave radiation, under heat removal of II and III order of boundary surfaces. These solutions are the basis for optimum parameters of microwave heating technology, a tool to reduce the spread of temperature field on the desired temperature distribution within the layer. They help determine quickly: maximum temperature inside a coal array, coordinates of its location, thermos-destructive voltage, limits of discharged heat fluxes and other

Coal layer under microwave heating: analytical study under mixed boundary conditions I and II of the genus

Актуальность работы обусловлена перспективностью применения СВЧ-излучения в технологиях энергетического топливоиспользования на стадиях подготовки твердого топлива к пылеугольному сжиганию, включая подсушку и предгорелочную термическую обработку. Немногочисленные известные результаты лабораторных экспериментов свидетельствуют о наличии структурных эффектов, приводящих к повышению реакционной способности и уменьшению недожога топлива, а также к сокращению генерации токсинов. Цель работы. Получение аналитического выражения для температурного поля в угольном массиве, необходимого для параметрического анализа технологических условий микроволнового воздействия. Методы исследования. Построение аналитически строгих задач теплопереноса, решение которых, как правило, возможно только в условиях существенных упрощений. При принятом постоянстве электрофизических и технологических свойств угля физическая картина процесса определяется падающей на угольный слой плоской электромагнитной волной, которая формирует внутренний источник тепла по закону Бугера. Уравнение энергии в форме Фурье в этом случае рассматривается независимо от уравнений электродинамики Максвелла. В данной постановке решение выделенных задач проведено с помощью метода интегрального преобразования Лапласа. Результаты. Выведенные аналитические решения по температурным полям получены при смешанных граничных условиях с достаточно произвольными изменениями во времени температуры одной поверхности и плотности потока на противоположной границе. Для ряда частных случаев на этой основе может быть получен обширной ряд упрощенных решений, доступных для параметрического анализа, с обоснованием оптимальных управляющих параметров технологии, востребованных инженерной практикой при проектной разработке и эксплуатации СВЧ-систем обработки твердого топлива в энергетике, а также в углехимии.The relevance of the work is due to the prospect of the use of microwave radiation in the energy technologies of fuel use at the stages of preparation of solid fuels for coal-fired incineration, including drying and heat treatment. A few well-known results of laboratory experiments indicate structural effects, resulting in increased reactivity and reduction of unburnt fuel. Objective: to obtain an analytical expression for the temperature field in the coal array required for parametric analysis of technological conditions of microwave exposure. Methods: construction of analytically rigorous heat transfer problems, the solution of which is usually possible only in conditions of significant simplifications. If adopted by the constancy of the electrical and technological properties of coal physical picture of the process is determined by the incident on the coal layer of a plane electromagnetic wave that generates internal heat source of Buger law. The energy equation in the form of Fourier is solved independently of Maxwell equations. In this formulation the solution of allocated tasks is carried out by the method of integral transformation of Laplace. Results. The derived analytical solutions of temperature fields are received with mixed boundary conditions with fairly arbitrary changes in time and temperature of a surface flux density of fire on the border. For some special cases on this basis can be obtained an extensive series of simplified solutions available for parametric analysis of the rationale of optimal control parameters of the technology demanded by the engineering practice in project development and operation of microwave systems for processing of solid fuels in the energy sector

Processes of electrostatic separation and flotation in the beneficiation of ilmenite ores from Vietnam and chemical processing of the obtained concentrates

Актуальность исследования определяется созданием принципиально нового способа синтеза титановых порошков высокой степени чистоты из ильменитовых руд месторождений Вьетнама, содержащих в тяжелой фракции смесь ильменита с рутилом. Это одно из приоритетных направлений комплексного развития месторождений редких и редкоземельных элементов во Вьетнаме. Цель: выбор условий, методов и последовательности проведения технологических операций по обогащению вьетнамских ильменитовых руд и последующей их химической переработки с получением высокочистого титана. Объекты: ильменитовая руда месторождения Ха Тинь (Вьетнам) с высоким содержанием оксидов титана, железа, циркония и низким содержанием кремния, алюминия, редкоземельных элементов, ванадия, а также ильменитовый концентрат, полученный в результате обогащения исходной ильменитовой руды. Методы: в процессе обогащения - электростатическая сепарация, флотация, использование коллекторов, активаторов и депрессоров, добавляемых к флотореагентам; при электролитическом синтезе титана - применение расплава в виде смеси фторидов лития, натрия и калия, обладающих минимальной температурой плавления, с добавкой тетрафторида титана; выбор условий запуска электролизера, катодной плотности тока, силы тока и напряжения для осаждения титана на катоде; исследование оптимальных условий выделения титанового порошка при низких температурах с использованием безводного фтороводорода. Результаты. Показана перспективность использования методов электростатической сепарации и флотации при обогащении вьетнамских ильменитовых руд месторождения Ха Тинь. Получен ильменитовый концентрат с содержанием диоксида титана более 50 %. Обоснованы преимущества использования метода прямого фторирования ильменитового концентрата элементным фтором, позволяющего обеспечить полноту его вскрытия и отделить летучие фториды титана, ниобия, ванадия и кремния от нелетучих - фторидов железа, циркония, гафния и церия. Это позволяет оптимизировать число стадий при дальнейшем применении TiF4 в качестве материала для получения титанового порошка. При электролитическом получении титана обоснована необходимость применения расплава фторидных солей лития, натрия и калия, имеющих состав: LiF (0,465 М)-NaF (0,115 М)-KF (0,42 М), обладающего минимальной температурой плавления (454 °С) и пределами изменения концентрации K2TiF6 (25-30 %). При этом величины плотности тока и выхода по току приближаются к максимальным значениям - 3,5-4,0 А/см2 и 60-65 % соответственно. Содержание примесей в титановом порошке не превышает 0,135 %, что удовлетворяет требованиям для изготовления изделий из компактного титана.The relevance of the study is determined by the creation of a fundamentally new method for the synthesis of titanium powders of high purity from ilmenite ores of Vietnam deposits, containing a mixture of ilmenite with rutile in the heavy fraction. This is one of the priority areas for the integrated development of deposits of rare and rare earth elements in Vietnam. The main aim: selection of conditions, methods and sequence of technological operations for the beneficiation of Vietnamese ilmenite ores and their subsequent chemical processing to obtain high-purity titanium. Objects: ilmenite ore of the Ha Tinh deposit (Vietnam) with a high content of oxides of titanium, iron, zirconium and a low content of silicon, aluminum, rare earth elements, vanadium, as well as ilmenite concentrate obtained as a result of enrichment of the original ilmenite ore. Methods: in the beneficiation process - electrostatic separation, flotation, the use of collectors, activators and depressants added to flotation reagents; in the electrolytic synthesis of titanium - the use of a low-melting eutectic of fluoride salts of alkali metals with the addition of titanium tetrafluoride; selection of the conditions for starting the electrolyzer, cathode current density, current and voltage for the deposition of titanium on the cathode; investigation of the optimal conditions for the release of titanium powder at low temperatures using anhydrous hydrogen fluoride. Results. The prospects of using the methods of electrostatic separation and flotation in the dressing of Vietnamese ilmenite ores of the Ha Tinh deposit are shown. An ilmenite concentrate with a titanium dioxide content of more than 50 % was obtained. The advantages of using the method of direct fluorination of an ilmenite concentrate with gaseous fluorine are substantiated, which makes it possible to ensure both the completeness of the decomposition of the solid phase and to separate the fluorides of titanium, niobium, vanadium and silicon that pass into the gas phase from those remaining in the condensed state - fluorides of iron, zirconium, hafnium and cerium. This allows you to optimize the number of stages in the subsequent processing of titanium tetrafluoride and the synthesis of metallic titanium. In titanium electrolysis, the authors have substantiated the use of composition of the eutectic of fluoride salts of alkali metals LiF (0,465 M)-NaF (0,115 M)- KF (0,42 M), which has a minimum melting point (454 °C) and the range of changes in the concentration of K2TiF6 (25-30 %). In this case, the values of current density and current efficiency approach the maximum values of 3,5-4,0 A/cm2 and 60-65 %, respectively. The content of impurities in titanium powder does not exceed 0,135 %, which meets the requirements for the manufacture of products from compact titanium