Yurii Ivakin

• PhD
• Senior Researcher at Lomonosov Moscow State University

20.06.2014 The formation of fine-crystalline corundum from hydrargillite at 400 C in supercritical water fluid (SCWF) at a pressure of 26.8 MPa in the presence of corundum particles is investigated. It was found that the addition of fused corundum particles into the reaction medium accelerates the formation of fine-crystalline corundum by the incre...

In the report the results of investigations of the mechanism and kinetics of the formation of cobalt doped corundum in water vapor medium are represented. Moreover, it is given the study result of changing of lattice position of cobalt ions and their state during synthesis. Aluminium hydroxide was using as raw material. Doping agent was cobalt nitr...

Gahnite with various particles size was synthesized from boehmite of different particles sizes via interaction with zinc oxide or zinc acetate. It was found that the decrease of the size of gahnite particles is accompanied by decrease of the crystallite size, change of the state of oxygen vacancies and optical properties. The UV light absorption de...

The kinetics and mechanism of corundum formation from hydrargillite in an water medium under sub- and supercritical conditions in the presence of manganese ions was studied. The conclusion was drawn that corundum structure formation with the insertion and uniform distribution of manganese ions occurred thanks to solid-state mobility, which appeared...

In the present paper the formation mechanism of zinc aluminate (gahnite, ZnAl2O4) under hydrothermal and thermovaporous conditions has been investigated. The gahnite was obtained by treatment in water medium of a mixture of zinc oxide and oxide or hydroxide of aluminum at 180–400°C and under pressure of water vapor 1–26 MPa. It was found that forma...

Thermovapour treatment (TVT) of SnO 2 and CaO oxides in an autoclave at 673 K leads to the formation of isometric CaSnO 3 perovskite-type crystals. TVT at 623 K leads to a previously unknown CaSn 2 O 4 (OH) 2 phase with lamellar crystals. The structure of the new compound CaSn 2 O 4 (OH) 2 was determined using powder X-ray diffraction and character...

Objectives . To obtain porous corundum ceramics using an innovative cold sintering process starting from different phase modifications of aluminum oxohydroxide — boehmite γ-AlOOH and diaspore α-AlOOH; to study the phase and structural properties of the resulting materials; and to assess their permeability to water. Results. Cold sintering enables t...

Porous α-Al2O3 ceramics are a highly sought-after material with a multitude of applications; for example, they are used as filters, substrates, biomedicine materials, etc. Despite the availability of raw materials, a challenge associated with this technology is the high energy budget caused by sintering above 1500 °C. For the cold sintering process...

Porous α-Al2O3 ceramics is a highly demanded material for multitude applications such as filters, substrates, biomedicine materials, etc. Despite the availability of the raw materials, a challenge of their technology is in a high energy budget caused by the sintering above 1500 °C. For a cold sintering processing (CSP) of ceramics, the lowering of...

A facile and environmentally benign method for single-phase barium titanate synthesis in a water vapor medium was studied to reveal the mechanism of phase transformation of the initial simple oxide mixture and estimate the capability of the product to be used as a raw material for low-frequency dielectric ceramics. The composition and structure of...

A facile and environmentally benign method for a single-phase barium titanate synthesis in water vapor medium was studied to reveal the mechanism of phase transformation of the initial simple oxides mixture and estimate the capability of the product to be used as a raw material for low-frequency dielectric ceramics. The composition and structure of...

This paper describes a method for the synthesis of nanosized oxide powders exemplified by Al2O3, MgO, and SiO2, which includes combustion of a saturated aqueous solution of salts and carbohydrates with multi-stage thermal treatment. A new approach to the synthesis of dispersed oxides with controlled properties has been developed. Particular attenti...

A developing energy-saving approach of cold sintering in a pure aqueous medium was applied to the preparation of α-Al2O3 ceramics and performed on spark plasma sintering equipment. The initial γ-Al(OH)3 and γ-AlOOH powders and the cold-sintered ceramics were studied by X-ray diffraction analysis, infrared spectroscopy, thermal analysis, and scannin...

A developing energy-saving approach of cold sintering in a pure aqueous medium was applied to the preparation of α-Al2O3 ceramics and performed on spark plasma sintering equipment. The initial γ-Al(OH)3 and γ-AlOOH powders and the cold-sintered ceramics were studied by X-ray diffraction analysis, infrared spectroscopy, thermal analysis, and scannin...

The influence of the method of applying the activating additive ammonium chloride and its concentration on the density and microstructure of zinc oxide ceramic obtained by cold sintering at 244 °C was investigated. The activating agent was applied by two methods: impregnation and subsequent autoclave treatment. When the powder was activated by the...

Objectives . To obtain experimental data on the effect of activating additive type on the cold sintering process of (MnFeCoNiCu) 3 O 4 high-entropy ceramic. The following substances were used as activating additives: ammonium acetate (CH 3 COONH 4 ), acetic acid (CH 3 COOH), ammonium chloride (NH 4 Cl), potassium fluoride dihydrate (КF·2H 2 O), lit...

Although the activating effect of an acetate medium in the cold sintering process of zinc oxide ceramics is well known, some problems need to be solved on the effect of process conditions and the initial powder’s preparation methods on the ceramic’s density and microstructure. This article describes an effect of the zinc acetate introduction method...

The formation and subsequent recrystallization of nanoboehmite under hydrothermal treatment of γ-Al2O3 nanopowder at a temperature of 150 °C in a 1.5% HCl solution have been studied. It has been found that boehmite nanowhiskers up to 2–3 μm in length and no more than 50 nm in diameter are formed from the crystals with a size of 10–20 nm, when kept...

The great prospects for introducing the cold sintering process (CSP) into industry determine the importance of finding approaches to reduce the processing time and mechanical pressure required to obtain dense ceramics using CSP. The introducing zinc acetate into the initial ZnO powder of methods, such as impregnation, thermovapor autoclave treatmen...

The effect of triple doping with chromium, lanthanum and barium on the mechanical, degassing and gas diffusion properties of fine-crystalline corundum synthesized in a supercritical water fluid was studied. The influence of chromium monodoping on the mechanical and optical properties of fine-crystalline corundum was also investigated. It was found...

The paper presents the preliminary study results of the influence of the electric current (direct or alternating), the values of voltage and current, the presence or absence of activating additives, and external heating of the mold on the process of cold sintering of ZnO and BaTiO 3 powders. The microstructures of the obtained samples are analyzed....

This paper reports the synthesis of highly dispersed zinc oxide via combustion of a mixture of zinc nitrate or acetate and glucose or cellulose at 800°C. Heat treatment of such a reaction mixture has been shown to lead to the formation of highly dispersed zinc oxide with various particle sizes and shapes, depending on the carbohydrates used.

Методом анализа изображений, полученных с использованием сканирующего электронного микроскопа, исследовано влияние механического давления на изменение распределения кристаллов по размерам при обработке оксида цинка в водной среде в присутствии активирующей добавки ацетата цинка или хлорида аммония. Сравниваются результаты обработки ZnO при температ...

Thermodynamic characteristics and water evaporation mechanism from silica structure in temperature range 100–1000°С have been studied by thermogravimetry, mass spectrometry, ¹Н and ²⁹Si NMR. It has been shown that liquid, surface-bound, and molecular-dispersed water is present on the surface and in the bulk of silica particles. The role of differen...

The release and content of water and gases in fine-crystalline lanthanum aluminate doped with europium (LaAlO3:Eu³⁺) was quantitatively studied for the first time using the method of kinetic thermodesorption mass spectrometry. LaAlO3:Eu⁺³ with an average size of 0.28 μm was synthesized in a two-stage regime: in a sub- and then in a supercritical wa...

The mechanism of synthesis of fine-crystalline yttrium aluminum garnet Y3Al5O12 (YAG) in sub- and supercritical conditions of water medium was studied. It was found that, under subcritical conditions, the initial oxides are hydroxylated to form yttrium hydroxide, boehmite, and agglomerates of nanoscale YAG crystals and, under supercritical conditio...

Analysis of scanning electron microscopy images was used to study the changes in the crystal size distribution of ZnO, which occurred during its processing in an aqueous medium at 220–255 °C and an equilibrium vapor pressure in an autoclave. The results were compared with those of ZnO placed in a die for treatment under similar conditions supplemen...

Strontium and barium titanates deposited on a porous support (α-Al2O3) are synthesized by the treatment of previously deposited precursors (titanium oxide, strontium nitrate, or barium nitrite) in a water fluid medium at 400°C. The obtained samples are characterized by X-ray powder diffraction (XRD) analysis and scanning electron microscopy (SEM) w...

The regularities of the formation of the phase composition of crystalline silica during the processing of amorphous precursors in the aqueous fluid media below and above the critical point of water aimed at the formation of optimal support for the methane oxidative coupling (OCM) catalyst were studied. It was shown that the phase composition of SiO...

The conversion of gibbsite to boehmite via hydrothermal treatment at 200°С in 1.5 wt % HCl is studied by X-ray powder diffraction, IR spectroscopy, Brunauer–Emmett–Teller analysis, scanning (SEM) and transmission (TEM) electron microscopy. The steps of the process are identified. Gibbsite is split in an acidic medium, with its specific surface area...

Методом электронной микроскопии исследовано формирование дисперсного состава мелкокристаллического порошка в ходе рекристаллизации оксида цинка в водной среде при 100-400 °С. Установлено, что в конденсированной воде процесс рекристаллизации затруднен, но протекает в среде воды в состоянии пара или сверхкритического флюида в присутствии активатора (...

Исследованы структура и морфология мелкокристаллического титаната бария, синтезированного в докритическом водном флюиде при температуре 230 °С и давлении 2,9 МПа с использованием различные исходныгх реагентов: оксида бария BaO., октагидрата гидроксида бария Ba(OH) • 8HO и двух модификаций оксида титана (рутил и анатаз). Установлена связь между сост...

Рассмотрен механизм синтеза мелкокристаллического корунда из гидроксидаалюминия в условиях индуцированного зародышеобразования в среде сверхкритического водного флюида при температуре 400 °С, начальном давлении 26,4 МПаи последующей продолжительной выдержке в среде синтеза. Распределение поразмерам кристаллов строилось на основе анализа электронно-...

Fine-crystalline barium titanate was synthesized from a mixture of barium hydroxide monohydrate and titanium dioxide in water vapor medium at 200 °C and 1.55 MPa and subsequently treated in subcritical vapor and supercritical water at 200−400 °C and 1.55-26.3 MPa. Recrystallization of synthesized powder led to an increase in average crystal size an...

Bi2O3 was investigated in the role of a modifier for BaTiO3 powder synthesized in a water vapor atmosphere at 200 °C and 1.55 MPa. Modification was aimed at increasing the sinterability of the powder as well as improving the structural and dielectric properties of the obtained ceramics. The morphology and phase contents of the synthesized BaTiO3 po...

Electron microscopy was used to study the formation of a dispersed composition of a fine-crystal�line powder during the recrystallization of zinc oxide in a water medium at 100–400°C. It was shown that recrystallization in condensed water is difficult but proceeds in a water medium in a vapor or supercritical state in the presence of an activator (...

The effect of doping corundum with lanthanum on the content of water and other gas impurities, on the diffusion characteristics, on the unit cell size and static strength of fine-crystalline corundum synthesized under thermovapours conditions in a supercritical water fluid was studied. Content, release and diffusion coefficients of water and other...

A study of the compaction of zinc oxide powder under conditions reproducing the cold sintering process, described in 2017 by C. Randall’s research group in the USA, is presented. The obtained results show that a dense ceramic can be obtained from zinc oxide by pressing (pressing pressure p = 77 MPa) in a water medium at temperatures 220 – 250°C. It...

A new method for the synthesis of high-purity fine-crystalline aluminum-magnesium spinel MgAl2O4 was been proposed. The procedure includes treatment of mixture finely dispersed MgO and hydroxide Al(OH)3 or aluminum oxyhydroxide AlOOH by water fluid under supercritical conditions (T = 380-400 °С, PH2O = 22,8-23,0 MPa). It was been shown that the pro...

A new method for synthesis of high-purity fine crystalline magnesium aluminate spinel (MgAl2O4) has been proposed by treating a mixture of finely divided MgO and aluminum hydroxide (Al(OH)3) or oxyhydroxide (AlOOH) with aqueous fluid under supercritical conditions (T = 380–400°С, Р\(_{{{{{\text{H}}}_{{\text{2}}}}{\text{O}}}}\) = 22.8–23.0 MPa). It...

BaTiO3 powders synthesized by two different methods based on the solid-state mechanism of formation were studied as raw materials for ferroelectric ceramics production. Fine-crystalline BaTiO3 obtained by reaction between BaO and TiO2 in supercritical water at 400 °C and 26 MPa had superior properties to the powder obtained by conventional high-tem...

The structure and morphology of fine-crystalline barium titanate synthesized in a subcritical water fluid at 230°C and 2.9 MPa were studied. Barium oxide, barium hydroxide octahydrate (Ba(OH) 2 · 8H 2 O), and two modifications of titanium oxide (rutile and anatase) were used as starting reactants. Relationships between the composition and propertie...

The paper is aimed to perform and compare the capabilities of the solid state technology and a new method of synthesis in supercritical water for the production of barium titanate powder. This material is of interest for applications such as dense piezoceramics. The new method of synthesis in an aqueous medium allowed obtaining barium titanate of h...

Content, evolution and diffusion characteristics of water and gases in fine-crystalline spinel MgAl2O4 were studied by kinetic thermodesoption mass spectrometry. Water is the main volatile component by quantity in the spinel structure. From the spinel crystals with an average size of 0.52 μm, water is released in vacuum in three temperature ranges:...

A mechanism of the fine crystalline corundum synthesis from aluminum hydroxide in the conditions of induced nucleation in the supercritical water fluid at 400oC, an initial pressure of 26.4 MPa, and subsequent exposure in a synthesis medium is considered. The size distribution of the crystals was based on the analysis of electron microscopic images...

Fine-crystalline barium titanate was synthesized by a new method using supercritical water and examined as a raw material for dielectric ceramics preparation by semidry pressing and further high-temperature sintering. The nature of temporary technological binder utilized at the stage of pressing significantly affected the structural, mechanical and...

Barium titanate has been known for its ferroelectric properties for more than 70 years and remains of high importance for dielectric ceramics. Nowadays the most dynamical development of BaTiO3 based materials is related to the production of multilayer ceramic capacitors. A widely utilized method of BaTiO3 powder synthesis at the laboratory and ind...

Palladium supported on carbon (Pd/C) catalysts (0.55–0.65 wt.% of Pd) were synthesized by pyrolysis of birch sawdust under inert atmosphere proceeded by prolonged impregnation of sawdust in aqueous solution of palladium nitrate. In some cases, hydrothermal treatment (HT) of the pristine sawdust was conducted to modify the specific surface area of t...

The promoting effect of water in different states of aggregation on the transformation processes in oxide mixture was studied in case of BaTiO3 formation. The reaction between barium and titanium oxide was carried out in liquid, in gaseous and in supercritical water. The state of aggregation of the reaction medium had an influence on the degree of...

The formation of fine�crystalline corundum (α�Al2O3) from hydrargillite in supercritical water fluid (SCWF) at 400°C and 26.8 MPa in the presence of corundum particles was studied. It was found that the α-�Al2O3 particles added to the reaction medium accelerated the formation of fine�-crystalline corundum due to an increase in the rate of nucleatio...

Barium titanate is known and widely applied in microelectronics due to its outstanding ferroelectric properties. Ceramics based on BaTiO3 serve as component of MLCCs, PTCRs, piezoelectric transducers, pyroelectric sensors and electrooptic devices. Align with solid state reaction and co-precipitation, hydrothermal synthesis is one of the most used m...

Submicron crystals of BaTiO3 were synthesized in mild conditions of low-density water fluid media at T = 230 ◦C, PH2O = 2.94 MPa during 20 h. The crystals showed narrow size distribution with the average sizes of 165 and 168 nm. As-synthesized samples of BaTiO3 were annealed in air at 500 ◦C and washed in acid. It was found that this procedure cont...

Anastasia Kholodkova received the Diploma of specialist in physical chemistry from Chemistry Department of Lomonosov Moscow State University in 2011. Since 2011 she has been working as Ph.D. student in physical chemistry at Chemistry Department of Lomonosov MSU under supervision of Dr. M.N. Danchevskaya and Dr. Yu.D. Ivakin. Her research interests...

Изучена кинетика и механизм образования корунда в водной среде в до – и надкритических условиях в присутствии ионов марганца. Сделан вывод о том, что формирование структуры корунда с внедрением и равномерным распределением ионов марганца происходит благодаря твёрдофазной подвижности, которая возникает в условиях обратимого дегидроксилирования при в...

Barium titanate was synthesized in mild conditions of low-density water fluid media (230°C, 2,94 MPa, 20 h.). The product consisted of uniform crystals with average size 165-170 nm. Post-synthetic treatment of BaTiO 3 samples included washing in acid and water and heating in air at 500°C for 1 h. It was found that the sequence of the treatment has...

Fine crystalline spinel MgAl2O4 was synthesized from mixture of AlOOH or Al(OH)3 and MgO with addition of activator, using stepwise heating of mixture precursors in water fluid: at 230oC, PH2O=2,3 MPa, and then at 400oC, PH2O=26 MPa. The spinel formation is realized through a stage of deep hydration of reagents and with the advent of intermediate p...

The formation of fine-crystalline corundum from hydrargillite at 400 C in supercritical water fluid (SCWF) at a pressure of 26.8 MPa in the presence of -Al2O3 particles is investigated. It was found that the addition of fused -Al2O3 particles into the reaction medium accelerates the formation of fine-crystalline corundum by the increase of the n...

The formation of fine-crystalline corundum from hydrargillite at 400 C in supercritical water fluid (SCWF) at a pressure of 26.8 MPa in the presence of -Al 2 O 3 particles is investigated. It was found that the addition of fused -Al 2 O 3 particles into the reaction medium accelerates the formation of fine-crystalline corundum by the increase of th...

A new mineral barioferrite—a natural analogue of synthetic barium ferrite Ba Fe 123+O19—has been identified in the central part of a metamorphosed barite nodule in the rock of the Haturim Formation (Mottled Zone) on the southern slope of Mount Ye’elim in Israel. The mineral is associated with barite, calcite, magnetite, and maghemite and occurs as...

In this paper the continuous stepwise method of a production of fine crystalline yttrium aluminum garnet doped with cerium (YAG: Ce3+) in supercritical water fluid (SCWF) are represented. The synthesis was carried out in water medium in two stages: first in subcritical conditions and then in an atmosphere of supercritical water fluid. The stoichiom...

The properties of fine crystalline corundum doped with cerium (α-Al2O3: Ce3+) during synthesis in a supercritical fluid have been studied. The synthesis of corundum has been carried out by the thermal treatment of hydrargillite, Al(OH)3, at T = 415°C and {ie290-1} MPa in reaction media that contained from 0.001 to 0.25 wt % of cerium. Cerium ions a...

В работе исследованы свойства мелкокристаллического корунда, легированного церием (a-Al2O3:Ce3+) в процессе синтеза в сверхкритическом водном флюиде. Синтез корунда проводился путем термообработки гидраргиллита Al(OH)3 при T = 415°C и PH2O=21–31 МПа с содержанием церия в реакционной среде в интервале 0,001–0,25 мас.%. При превращении гидраргиллита...

The kinetics and formation mechanism of doped corundum (α-Al2O3) from hydrargillite (γ-Al(OH)3) in supercritical water fluid (SCWF) in the presence of manganese ions are studied. It was ascertained that due to the reversible dehydroxylation in an aqueous medium, solid-phase transformation of hydrargillite into boehmite (γ-AlOOH) and then into corun...

Doping of fine crystalline corundum has performed during synthesis in water fluid at T=415°C and P=21.6-31.6 MPa with concentration of cerium in interval 0.001 – 0.25 % in reaction medium. Kinetics and mechanism of corundum (-Al2O3) formation from Al(OH)3 (hydrargillite) in supercritical water fluid (SCWF) in presence of cerium ions were investiga...

The opportunity of the using of synthetic fine-crystalline corundum as raw material for a growth of monocrystals of leucosapphire is investigated. The growth of a monocrystal of leucosapphire was carried out by method horizontal directed melt crystallization with use of fine-crystalline corundum as raw material. The fine-crystalline corundum was sy...

This technology is based on the use of water fluid as a reaction medium for synthesis of fine-crystalline oxides. The production of fine-crystalline oxides in a pilot plant using the industrial autoclaves has demonstrated the economical expediency and environmental safety of manufacturing of various fine-crystalline oxides by this method. The synth...

In this report the results of investigations of formation of various fine crystalline modifications of silicon dioxide under the action of supercritical water fluid containing the additives of activators are represented. Synthesis of solid oxides was carried out in laboratory autoclaves (18 mL). As raw material was used amorphous silicon dioxide (p...

In this article, a brief exposition of results of the investigations, which have been carried out by the authors in the past twenty-year period, of solid-phase synthesis in sub- and supercritical water fluid, and also of the of the peculiarity of properties of synthesized materials are presented.

In paper the brief exposition of results of the investigations, which have been carried out by the authors in twenty-year period, of solid-phase synthesis in sub- and supercritical water fluid, and also of the peculiarity of properties of synthesized materials are represented.

This paper reports on investigations of the kinetics and mechanism of the synthesis of simple fine-crystalline oxides from solid-phase precursors in sub- and supercritical water fluid (SCWF). The rate of the processes strongly depends on the water vapor pressure. X-ray analysis, mass-spectrometry and IR-spectrometry of products obtained during synt...

The effect of ammonia contained in water fluid on the synthesis and properties of gahnite (ZnAl2O4) doped with (0.4–4mol%) europium was investigated. Gahnite synthesized in water–ammoniac fluid has a smaller crystal size than does the one synthesized in water fluid, and bound nitrogen is detected in its structure. However, europium ions more effect...

In this paper the results of investigations of the mechanism and kinetics of reactions of formation of fine crystalline complicated oxides in thermovaporous and solvothermal conditions are presented. The processes of formation of complicated oxides, magnesian spinel (MgAl2O4), aluminate of lanthanum (LaAlO3), gahnite (ZnAl2O4), barium hexaferrite (...

In the present work it was shown that a diminution of a molar ratio -water in fluid/Al 2 O 3 -slows down the process of the formation of boehmite and corundum from hydrargillite. In case values of this molar ratio less than 2, the tohdite (5Al 2 O 3 ·H 2 O) in products of alumina or of hydrargillite transformation in SCWF appears. In case values of...

This paper describes a solid phase transformation of aluminium hydroxide into oxyhydroxide (boehmite), and then into well formed fine crystals of corundum (α-Al 2 O 3) in the medium of a supercritical water fluid at a temperature of 450 • C and a pressure of 30 MPa. Using electron microscopy the development and processing of corundum crystal format...

The present paper is devoted to studying the influence of water vapour pressure on the α-Al2O3 phase nucleation process and on the size distribution and doping level of the synthesized fine crystalline corundum. The effect of preliminary compaction of precursors and pressure variation on the corundum synthesis process in water vapour was also inves...

In present paper the investigation of influence doping by chrome, manganese or europium on optical and mechanical characteristics of corundum are represented. The doping carried out during process synthesis of corundum in supercritical water fluid in the laboratory autoclaves at 400°C and under water pressure 26 – 30 MPa. The optimal concentrations...

In this report the results of studies of processes, taking place in fluids of primary alcohols, and in solid phase, aluminum hydroxide, in autoclave were represented. The processes were carried out at contact of alcohol to aluminum hydroxide in supercritical conditions (T=400°C, P=20 MPa). The products of alcohols transformation in supercritical co...

The mechanical and optical properties of fine-crystalline corundum doped by chrome in a supercritical water fluid at 400 - 410°C (PH 2O= 26-29 MPa) are investigated. It was established, that the introduction of chrome in structure of corundum during its synthesis changes the size, habitus and properties of crystals. At the content of chrome in coru...

Authors have investigated the mechanism and the kinetics of fine-crystalline quartz and corundum synthesis in supercritical water. The thermovaporous treatment of raw materials has been carried out in laboratory (v = 20 ml) and technical (v = 2 m(3) and v = 4 m(3)) autoclaves at temperatures between 390 and 410degreesC and vapor pressures of water...

Lithium-manganese oxide spinel LiMn2O4 was synthesized in hydrothermal conditions (400°C, 20 MPa) in the course of thermovaporous treatment mixtures of MnO2 and LiOH/or Li2CO3. The conditions of synthesis of the spinel as monophase product were determined. The obtained product has been characterized by means of various physical and chemical methods...