Impact of pulsed plasma beam on the thermal erosion and the surface structure of graphite

Among materials prospective as plasmaface materials for first wall of fusion reactor a priority is given to the materials with low atomic number, high threshold for physical sputtering, high thermal conductivity, low chemical activity to hydrogen, high thermal resistance and melting point. According to modern point of view, preferred plasma-face materials for tokamaks and future Generation IV reactors should be based on the carbon, beryllium and tungsten. Tungsten is one of the most promising materials for protection of tokamaks diverter plates

Impact of pulsed plasma beam on the thermal erosion and the surface structure of graphite

Among materials prospective as plasmaface materials for first wall of fusion reactor a priority is given to the materials with low atomic number, high threshold for physical sputtering, high thermal conductivity, low chemical activity to hydrogen, high thermal resistance and melting point. According to modern point of view, preferred plasma-face materials for tokamaks and future Generation IV reactors should be based on the carbon, beryllium and tungsten. Tungsten is one of the most promising materials for protection of tokamaks diverter plates

Research on the improvement of mixed titania and Co(Mn) oxide nano-composite coatings

The structure and the properties of the oxide films formed on titanium in the diphosphate based electrolytes by means of plasma electrolytic oxidizing at direct current density of 2-2.5 A·dm⁻² have been studied. Oxide layers of different composition and content of alloying elements were obtained by modification of electrolytes and variation in current density. The interelectrode voltage during PEO, chemical and phase composition, topography and microstructure of the formed layers depend on the electrolyte composition and applied current density. The spark-discharge regime was shown to be reached at inter-electrode voltage 100 to 130 V depending on the composition of electrolyte. The effect of chemical composition and surface morphology formed mixed oxide films on the corrosion resistance and catalytic activity has been discussed

Mixed alumina and cobalt containing plasma electrolytic oxide coatings

Principles of plasma electrolytic oxidation of the AL25 aluminum alloy in diphosphate alkali solutions containing cobalt(2+) cations are discussed. It has been established that a variation in the concentration of the electrolyte components provides the formation of mixed-oxide coatings consisting of the basic matrix materials and the cobalt oxides of different content. An increase in the cobalt oxide content in the coating is achieved by the variation in electrolysis current density as well as the treatment time due to both the electrochemical and thermo-chemical reactions at substrate surface and in spark region. Current density intervals that provide micro-globular surface formation and uniform cobalt distribution in the coating are determined. The composition and morphology of the surface causes high catalytic properties of synthesized materials, which confirmed the results of testing in model reaction CO and benzene oxidation as well as fuel combustion for various modes of engine operation

Composition and Corrosion Behavior of Iron-Cobalt-Tungsten

Principles of three component Iron-Cobalt-Tungsten alloys electrodeposition from complex Fe (III) based citrate electrolytes are discussed. It is shown, that deposition of ternary alloys proceeds through competitive reduction of cobalt and tungsten with iron. With increasing ligand concentration coatings are enriched with a refractory component; however, increasing current density favors a reverse trend. The effect of both current density and pulse on/off time on the quality, content of alloying metals and surface topography of electrolytic coatings were determined. The application of pulsed electrolysis provides increasing tungsten content up to 13 at.%, at current efficiency of 70–75%. Globular relief of Fe-Co-W coatings is caused by refractory metals incorporation, and crystalline and amorphous parts of structure are visualized by X-ray spectroscopy, including inter-metallic phases Co7W6, Fe7W6 along with α-Fe and Fe3C. The crystallite size of the amorphous part is near 7–8 nm. Corrosion resistance of the coatings is 1.3–2.0 orders of magnitude higher than the substrate parameters as follows from data of polarization resistance method and electrode impedance spectroscopy

Surface analysis of Fe-Co-Mo electrolytic coatings

Coatings Fe-Co-Mo with a composition of 47 at.% iron, 28 at.% Cobalt and 25 at.% Molybdenum were deposited from citrate electrolyte using pulse electrolysis mode. Scanning electron and atomic force microscopy have established the surface morphology and topography. It was identified the parts with a globular structure which have an average size of 0.2-0.5μm and singly located sharp grains. Within the same scan area sites with developed surface were detected the topography of which is identical to the crystal structure of cobalt with the crystallites size of 0.2–1.75μm. The parameters Ra and Rq for parts with different morphology as well as average characteristics of coatings demonstrated the low roughness of the surface. It is found that the coercive force of Fe-Co-Mo films is 7-10 Oe, which allow us to classify the Fe-Co-Mo coatings as soft magnetic materials

Physicochemical Investigations of Scheelite Concentrate Decomposition

In the article results of kinetic studies of autoclave-carbonate decomposition of scheelite concentrates are presented. Studies are carried out in temperature range of 368–523 K, at mixing with a speed of 100–400 revolutions per minute. Solutions of sodium carbonate, mol/ dm3: 0.5, 0.75, 1.0, 1.25, 1.5, 2.0 was used to determine the dependence of the degree of tungsten leaching from scheelite on concentration. It was established, that with increase of concentration of sodium carbonate leaching degree increases and at the concentration of 1.5–2.0 mol/dm3 it is reached rapid, within 45–60 min, 80−90% of leaching, and the almost complete leaching of tungsten (95.2–99.3%) achieved in 2 h. For interaction of WO3 with Na2CO3 solution it was obtained the kinetic mode. In this case there is practically no concentration gradient of sodium carbonate at an oxide surface. It is obvious, that increase of the hydrolysis takes place due to the fact that to oxides reaction with a reagent-solvent precedes hydration of their surface. In the adsorbed water molecules due to their interaction with the oxide surface intramolecular bonds are weakened, thereby hydrolysis of oxide ions coming to the hydrated surface flows more fully

Бинарные и тройные сплавы железа с молибденом и вольфрамом

Electrodeposition of Fe-Mo-W and Fe-Mo layers from a citrate solution containing iron(III) on steel and iron substrates is compared. The utilization of iron(III) compounds significantly improved the electrolyte stability eliminating side anodic redox reactions. The influence of concentration ratios and electrodeposition mode on quality, chemical composition, and functional properties of the alloys is determined. It has been found that alloys deposited in pulse mode have more uniform surface morphology and chemical composition and contain less impurities. Improvement in physical and mechanical properties as well as corrosion resistance of Fe-Mo and Fe-Mo-W deposits when compared with main alloy forming metals is driven by alloying components chemical passivity as well as by alloys amorphous structure. Indicated deposits can be considered promising materials in surface hardening technologies and repair of worn out items.Покрытия сплавами Fe-Mo-W и Fe-Mo получены из цитратных электролитов на основе железа (III) на подложках из стали и чугуна. Использование солей железа(III) существенно повышает стабильность электролита за счет элиминирования побочных анодных реакций. Установлено влияние соотношения концентраций и режимов электроосаждения на качество, химический состав и функциональные свойства сплавов. Показано, что полученные в импульсном режиме сплавы характеризуются более равномерной поверхностью, распределением компонентов и содержат меньше примесей. Повышение физико-механических свойств и коррозионной стойкости покрытий Fe-Mo и Fe-Mo-W по сравнению со сплавообразующими металлами и подложкой обусловлено химической инертностью компонентов и аморфной структурой сплава. Полученные покрытия можно рассматривать как перспективные материалы для упрочнения поверхности и восстановления деталей

Peculiarities of corrosion inhibition by mixture of phosphate and calcium containing pigments

Several possible alternatives to toxic chromate pigments have been considered for a variety of inhibitive applications. One of the more promising pigment combinations involves mixtures of phosphate and calcium ion-exchange pigments for inhibition of corrosion on organic coated galvanized steel. This paper presents recent work on a detailed study of the mechanisms of action of this mixture which has been established as effective in cut edge and zinc inhibition, but as less effective for inhibition of steel. The use of the blend of inhibitors is shown to result in the development of an adsorbed phosphate film on the metal which plays an important role in the development of anodic and cathodic inhibitive control. Zinc ions also appear to have an important synergistic effect on the film composition and structure increasing its coherence and decreasing its porosity. Traditional and localised electrochemical methods (EIS and SVET) were used in this study of corrosion of coated galvanized steel in artificial acid rain solution. The data confirms the anticorrosion efficiency of the pigment blend dispersed in organic coating on galvanized steel and reveals the peculiarities of their inhibiting action at coating defects