Взаимодействие цирконистографитового материала с расплавленым шлаком и воздушной средой

Zirconia graphite refractory is used in continuous casting of steel. Slag corrosion resistance influence on time of casting. With factorial experiment 25-1 influence mixture of refractory (content of graphite, silicon carbide, boron carbide) on oxidation resistance and interaction with mould powder (C/S = 1, F = 8 %) at 1400 °C. Boron carbide is better antioxidant than silicon carbide. Boron carbide 3 % mass decrease slag corrosion resistance of ZG-refractory. The thicknesses de-carbonized layer are within 1–7 mm Additives of boron carbide and silicon carbide reduce the thickness of the oxidized layer. It was established experimentally that the boron carbide has the best antioxidant properties than silicon carbide therefore, in the study circolatorio materials action SiC less effective than B4C.Цирконистографитовый материал применяется при непрерывной разливке стали. От устойчивости к шлаку зависит продолжительность разливки. Был использован дробный факторный эксперимент 25-1 для определения влияния состава огнеупора (содержание графита, карбида кремния, карбида бора) на окисляемость и взаимодействие с шлакообразующей смесью (C/S=1, F=8 %) при 1400 °С. Установлено, что карбид бора обладает лучшими антиокислительными свойствами по сравнению с карбидом кремния. Добавка карбида бора в количестве 3%(масс) снижает устойчивость цирконистографитового огнеупора к шлаку. Значения толщины обезуглероженного слоя находятся в пределах 1–7 мм. Добавки карбида бора и карбида кремния снижают толщину окисленного слоя. Экспериментально установлено, что карбид бора обладает лучшими антиокислительными свойствами, чем карбид кремния, поэтому в изучаемых цирконистографитовых материалах действие SiC менее эффективно, чем B4C

Studying the structure and adhesion strength of thermal barrier coating

The structure and adhesive strength of thermal barrier coatings produced by successive deposition of layers is studied. The coating is applied in three layers: I) a diffusion aluminosilicide coating that provides protection against high temperature oxidation and corrosion, with a thickness of 50μm; ii) a metal sublayer providing a smooth transition from a metal coating to a ceramic one, with a thickness of 100 to 120μm; iii) a ceramic layer decreasing the temperature of the blades during operation, with a thickness of 70 to 100μm. The total coating thickness ranges from 0.17 to 0.27mm. It is shown that the second and third layers deposited by plasma spraying are quite dense, the porosity being less than 5 vol%. During tensile tests carried out on an Instron testing machine, the failure of glued samples was always detected in the adhesive joint. The adhesive strength of the applied epoxy-based adhesive was 12MPa; it can be stated that the adhesive strength of the coating is higher than 12MPa. © 2019 Author(s)

Protective Coatings for the Graphite Facing in Calcium-Aluminothermal Processes

Results of pilot plant and full scale studies on the elaboration of high temperature protective coatings for graphite in the process of the reductive melting of niobium pentoxide and NbAl alloys production are presented. Graphite has found extensive application in high temperature processes due to its unique thermophysical properties. However, in these conditions it reacts very easily with air oxygen, liquid metals, oxides, and fluorides. As a result, porous graphite gets impregnated with liquid metal; besides, carbonization of melt and formation of a layer of metal carbides on graphite surface takes place. The layer of metal carbides has a low adhesion with graphite and a major part of them is transferred to the melt. The graphite facing of a furnace is quickly destructed. To avoid these harmful processes, special plasma sprayed protective coatings are used. In this work various coatings (Al2O3, Al2O3-CaO, ZrO2, NbC, Al2O3 + Nb, ZrO2 + Nb, NbC + Nb, Nb) were tested in pilot plant and industrial conditions. It was established that the best durability of the protective coating on graphite can be achieved in the case of its three-layer composition: Nb (0.07 mm) + NbC (0.4 mm) + Nb (0.3 mm). After industrial melting of 500-2000 kg ingots about 80% of this coating on the belt of the shaft furnace had preserved. Plasma sprayed protective coatings on the graphite facing extended its operation time, reduced the carbon content in the metal ingots to 0.02% (mass), and slag carbon content to 0.05-0.15% (mass).The financial support to V. G. from the Doctorate School of the Faculty of Chemical and Materials Technology of Tallinn University of Technology is gratefully acknowledged

STUDY OF HEATRESISTANCE OF ZIRCONIUMGRAPHITE MATERIALS

A study of the thermal stability of composite refractory materials based on zirconium dioxide stabilized with calcium oxide, with additives of graphite, silicon carbide and boron carbidewas made. The heat resistance of zirconistografite materials was estimated from the relative decrease in the bending strength of samples measuring 20x20x120 mm after thermal shock

Investigation of the effect of preliminary modification of solutions on the properties of precipitated hydrated zirconium oxides

In this study, hydrated zirconium oxides and yttrium stabilized zirconia powders were synthesized by precipitation. Influence of preliminary solution modification, namely preliminary heating of the solutions and the addition of sulfate ions was investigated. It is shown that the addition of sulfate ions leads to a decrease in the size of aggregates and an increase in the specific surface area of the particles. The greatest increase in the specific surface area was observed during precipitation of a preliminary heated solution with the addition of sulfate ions. © Published under licence by IOP Publishing Ltd.Ministry of Education and Science of the Russian Federation, Minobrnauka: 14.581.21.0028, RFMEFI58117X0028Research and DevelopmentThe work was supported by Act 211 Government of the Russian Federation, contract № 02.A03.21.0006.The study was financially supported by the Ministry of Education and Science of the Russian Federation within the framework of subsidizing agreement of October 23, 2017 (No. 14.581.21.0028, unique agreement identifier RFMEFI58117X0028) of the Federal Target Program “Research and development in priority directions of the progress of the scientific and technological complex of Russia for the years 2014–2020.” 5. References [1] Chandra N, Singh D K, Sharma M, Upadhyay R K, Amritphale S S and Sanghi S K 2010 Journal of Colloid and Interface Science 342 327–332 [2] Si-Jia Hao, Cheng Wang, Tong-Le Liu, Zhi-Ming Mao, Zong-Qiang Mao, Jian-Long Wang 201

THE INFLUENCE OF PRECIPITATION CONDITIONS ON ZrO2 – Y2O3 POWDERS PROPERTIES

The influence of the primary sol formation on zirconium oxide powders properties was investigated.Работа выполнена при финансовой поддержке Минобрнауки России, соглашение о предоставлении субсидии от 23.10.2017 г. № 14.581.21.0028 (уникальный идентификатор соглашения RFMEFI58117X0028), в рамках ФЦП “Исследования и разработки по приоритетным направлениям развития научно-технологического комплекса России на 2014–2020 годы”

THE INFLUENCE OF POWDERS BURNING TEMPERATURE ON DENSITY OF CERAMICS BASED ON ZIRCONIUM OXIDE

The influence of powders properties on the ceramic properties was investigated.Работа выполнена при финансовой поддержке Минобрнауки России, соглашение о предоставлении субсидии от 23.10.2017 г. № 14.581.21.0028 (уникальный идентификатор соглашения RFMEFI58117X0028), в рамках ФЦП “Исследования и разработки по приоритетным направлениям развития научно-технологического комплекса России на 2014–2020 годы”

PREPARATION OF MICROGRANULATED POWDERS OF THE ZRO2—Y2O3—CEO2 COMPOSITION BY THE METHOD OF FREEZING HYDROXIDE PERCIPITATES

In this work, studies have been carried out on the preparation of ZrO2–Y2O3–CeO2 powders with a controlled granulometric composition. It was found that a lower freezing temperature promotes the formation of finer dispersed powders. The optimal conditions for freezing hydroxide precipitates to obtain powders of the 10–100 μm fraction where determined: freezing temperature of –25 оС.В данной работе были проведены исследования по получению порошков ZrO2–Y2O3–CeO2 регулируемого гранулометрического состава. Установлено, что более низкая температура заморозки способствует образованию более мелкодисперсных порошков. Определены оптимальные условия замораживания гидроксидных осадков для получения порошков фракции 10–100 мкм: температура заморозки –25 оС.Работа выполнена при финансовой поддержке Минобрнауки России, соглашение о предоставлении субсидии № 14.581.21.0028 от 23 октября 2017 г. (уникальный идентификатор соглашения RFMEFI58117X0028), в рамках ФЦП «Исследования и разработки по приоритетным направлениям развития научно-технологического комплекса России на 2014–2020 годы»

STUDY OF THE PROPERTIES OF CERAMIC HEAT- PROTECTIVE COATINGS APPLIED ON METAL SUBSTANCES

The technology of hardening of heat-protective ceramic coatings ZrO2-Y2O3 is proposed. The method includes ceramic reinforcement of ceramic fibers and metal substrates using nichrome spirals