1,725,662 research outputs found
Корозійні властивості гальванічних Fe–Mo(W), Fe–Mo–W покриттів
No full textThe methods of analysis of polarization dependences, the electrode impedance spectroscopy and gravimetry were used for the investigation of the corrosion properties of galvanic binary Fe–Mo(W) and ternary Fe–Mo–W coatings in the media of a different acidity. It was shown that the corrosion rate of Fe–Mo–W and Fe–Mo(W) alloys is decreased with an increase in the pH of the solutions and with the enrichment of the alloys by doping refractory components. The dependence of the control of corrosion process on the composition of electrolytic alloys has been specified. It was established that the corrosion resistance of binary alloys is 1.1 to 1.5 orders of magnitude higher in comparison with the parameters of substrate materials, in particular the mild steel. The corrosion resistance indices for the coatings applied using the ternary Fe–Mo–W alloys substantially prevail over those for mild steel, individual metals and binary Fe–Mo and Fe–W coatings. The corrosion resistance of Fe–Mo–W system is equal to 8300 Ohm·cm² and it is conditioned by the formation of the two-component layer film consisting of molybdenum oxides and tungsten oxides. Using the data of gravimetric investigations we constructed the diagrams "the corrosion depth index kh, mm/year – the composition" for the Fe–Mo–W system that allow us to define the metal content ratio for Fe–Mo(W), Fe–Mo–W alloys in order to provide an appropriate corrosion resistance depending on service conditions.Методами аналізу поляризаційних залежностей, спектроскопії електродного імпедансу та гравіметрії досліджені корозійні властивості гальванічних бінарних Fe-Mo (або W) і тернарного Fe–Mo–W покриттів у середовищах різної кислотності. Показано, що швидкість корозії Fe–Mo–W і Fe–Mo (або W) сплавів зменшується у напрямку зростання pH розчинів, а також зі збагаченням сплавів легуючими тугоплавкими компонентами. Визначено залежність контролю корозійного процесу від складу електролітичних сплавів. Встановлено, що корозійна стійкість бінарних сплавів на 1,1-1,5 порядки величини вища за параметри матеріалу підкладки і низьковуглецевої сталі. За показниками корозійної стійкості покриття сплавами Fe–Mo–W суттєво переважають низьковуглецеву сталь, індивідуальні метали та бінарні Fe–Mo і Fe–W покриття. Опір корозії сплаву Fe–Mo–W становить 8300 Ом, що обумовлено формуванням на поверхні покриття шарів плівки оксидів молібдену та вольфраму. За результатами гравіметрічних досліджень побудовано діаграми "склад – глибинний показник корозії kh, мм/рік" для системи Fe–Mo–W, які дозволяють визначити співвідношення вмісту металів у Fe–Mo(W), Fe–Mo–W сплавах для реалізації необхідної корозійної стійкості залежно від умов експлуатації
Study on palm oil hydrogenation for clean fuel over Ni-Mo-W/gamma-Al2O3-ZSM-5 catalyst
No full textBiodiesel, derived from vegetable oil via hydrotreating, is becoming a promising alternative energy. Novel Ni-Mo-W/gamma-Al2O3-ZSM-5 catalysts were developed and firstly applied in palm oil hydrogenation process. The catalysts were prepared by extrusion method and characterized by XRD, SEM, TEM, BET, NH3-TPD, and H-2-TPR The influences of acidity on the activity, selectivity, and stability of catalysts were systematically studied. The mechanisms of deoxygenation and isomerization were discussed. The catalyst Ni-Mo-W (5 wt.%-5 wt.%-15 wt.%)/gamma-Al2O3-ZSM-5 (85 wt.% 15 wt.%) was confirmed as the optimum one. Finally, the key reaction parameters such as reaction temperature, pressure, liquid hourly space velocity and H-2/oil volume ratio were optimized. The hydrogenation reaction path of palm oil was also proposed. (C) 2015 Elsevier B.V. All rights reserved
Synthesis and structure of [M(CO)4{(PPh2)2CHAu(PPh3)}] (M = Cr, Mo, W)
Get PDFThe reaction of diethyl ether solutions of Li[M(CO)4{(PPh2)2CH}] with [AuCl(PPh3)] gives [M(CO)4{(PPh2)2CHAu(PPh3)}] (M = Cr, Mo, W). The structure of the derivative with M = Mo was determined by single-crystal X-ray diffraction at 173 K. Crystals are monoclinic, space group P22, a = 13.552(3), b = 17.390(4), c = 17.390(4) A ̊, β = 90.94(2)°, Z = 4 and R(F) = 0.031. The two independent molecules are very similar. The molybdenum and the gold atoms display octahedral and linear geometries, respectively; the shortest intramolecular molybdenum-gold interaction is 4.52 Å. © 1995
Untersuchung und Verständnis von ungeträgerten Ni-Mo-W Sulfiden fürs Hydrotreating
No full textUnsupported Ni-Mo, Ni-W and Ni-Mo-W catalysts consist of stacks of Mo(W)S2 slabs decorated by Ni at the edges and NiSx crystals. In NiMoW materials, intralayer Mo-W sulfide slabs are present. All materials were active in the removal of N and S from model compounds. The composition does not affect the reaction pathway but the degree of Mo-W alloying, direct interaction with Ni, and morphology determined the activity.Ungeträgerte Ni-Mo, Ni-W und Ni-Mo-W Katalysatoren bestehen aus NiSx Kristallen und Mo(W)S2. In kleineren Konzentrationen wird Ni an den Rändern der Mo(W)S2 Schichten eingebaut. Mo und W können gemeinsam in einer Schicht der Sulfide vorliegen. Bei der hydrierenden Eliminierung von N und S aus Modellverbindungen waren alle Katalysatoren aktiv. Die Aktivität wurde durch die Synergie zwischen Ni, Mo und W beeinflusst, die sowohl Morphologie als auch die Oberflächenzusammensetzung bestimmte
Electron Microscopy Investigation of the Microstructure of Unsupported Ni-Mo-W Sulfide
No full textAn exploration was made on structure and active sites of the unsupported Ni-Mo-W sulfide hydrodesulphurization catalyst prepared by a thiosalt decomposition method. More insights into the nanocomposite structure were provided by introducing the concept of average curvature of Mo(W)S2 and establishing a new structure model. The defects of cross and mixed stacks, steps along c-axis, expansion of (002) interplanar spacing and mixing structure of Mo(W)/Ni sulfides were investigated using advanced electron microscopy. All these defects in Mo(W) sulfides are closely correlated with increasing active sites of unsupported Ni-Mo-W sulfide catalyst
Multiferroic Properties of Cu3(Mo,W)2O9
No full textAbstractWe report the substitution effects of W6+ ions on multiferroic material Cu3Mo2O9 having a dis- torted tetrahedral quasi-one-dimensional spin structure. In Cu3Mo2O9, the weak ferromagnetic component of the spin moments and the ferroelectricity coexist below TN = 7.9K. In case of Cu3(Mo,W)2O9, the nonmagnetic Mo6+ ions are replaced with the nonmagnetic W6+ ions. We study the specific heat, magnetization, and dielectric constants, and show the magnetic-field- temperature phase diagrams in the single crystals with various W concentrations. We compare the phase diagram of Cu3(Mo,W)2O9 to that of (Cu,Zn)3Mo2O9 and discuss the similarity and the difference between the direct and the indirect substitution effects. The efficiency of the W substitution is much weaker than that of the Zn substitution
Synthesis and kinetic study of (Mo,W)Si ²-WSi ² nanocomposite by mechanical alloying
Get PDFIn this study, nanocomposite of (Mo,W)Si2–WSi2 was synthesized via mechanical alloying (MA) and heat treatment. The phase transformation of the powders after various milling durations and annealing was investigated by X-ray diffraction (XRD) and differential thermal analysis (DTA). Microstructural evolutions were characterized by scanning electron microscopy and transmission electron microscopy (TEM). Increasing the milling time to 80 h caused the formation of (Mo, W, Si) solid solution, t-(Mo,W)Si2, h-WSi2 phase, and a trace amount of unreacted raw material. However the post-annealing at 1000 °C caused the complete formation of (Mo,W)Si2–WSi2 nanocomposite. The values of the grain growth exponent of t-(Mo,W)Si2 phase for the powders milled for 40 and 80 h were 0.3 and 0.8, respectively, at 1000 °C. The grain growth activation energy of t-(Mo,W)Si2 phase for the 80 h milled powders (97.19 KJ/mol) was lower than that for the 40 h sample (120.83 KJ/mol). The crystallite size of t-(Mo,W)Si2 decreased to 32 nm (40 h) and 24 nm (80 h) with increasing milling time. However, the crystallite size of the milled samples increased to 60 and 87 nm after annealing at 1000 °C for 90 min. The DTA results of the as-milled specimens showed two exothermic peaks at around 600 and 900 °C relating to the formation of t-(Mo,W)Si2 and h-WSi2, respectively. The formation activation energy of t-(Mo,W)Si2 was higher (144.58 KJ/mol) for the 80 h milled sample compared to the 40 h milled sample (131.61 KJ/mol). The microhardness of (Mo,W)Si2–WSi2 nanocomposite increased with increasing milling time to 1020 Hv but decreased with escalating annealing temperature to 726 Hv
Towards Understanding Structure-Activity Relationships of Ni-Mo-W Sulfide Hydrotreating Catalysts
No full textThe relation between activity and selectivity of a series of unsupported Ni–Mo, Ni–W, and Ni–Mo–W sulfides and the physicochemical properties of the sulfides and oxide precursors were explored. Bimetallic oxide precursors were a crystalline molybdate with layered structure ((NH)HNi(OH)(MoO)) or a wolframite-type nickel tungstate (NiWO). Trimetallic precursors were mixed Mo–W–Ni phases appearing amorphous in XRD analysis, in which metal cations had environments similar to those in the bimetallic precursors. The XRD-amorphous layered structure (obtained for a Ni–Mo–W precursor) led to the fastest sulfidation of Ni cations. The proximity of metal cations in precursors was retained after sulfidation, which lead to intralayer mixed MoWS (in trimetallic materials) and varying concentrations of Ni at the perimeter of the Mo(W)S slabs. At MoS and WS edges, Ni has a square-pyramidal coordination, which is significantly distorted at the Mo–W mixed edges. The catalyst with the lowest Mo/W–Ni coordination had the lowest rates for hydrodenitrogenation of o-propylaniline and hydrodesulfurization of dibenzothiophene. Among the materials with significant Ni–Mo(W) coordinations, the most active sulfide catalyst at low temperatures was Ni–W with highly defective slabs, at high temperatures the Ni–Mo–W sulfide with the highest Ni concentration at the perimeter was the most active catalyst
Электрохимическое формирование покрытий сплавом Fe-Mo-W из цитратного электролита
Get PDFPeculiarities of the electrochemical deposition of Fe–Mo–W coatings from citrate electrolyte containing iron (III) on the substrates of mild steel and gray cast iron are investigated. The effect of the salt concentration of alloying components and electrolysis modes on the quality, composition, and properties of the alloys is determined. It is shown that the alloys formed via nonstationary electrolysis exhibit a more uniform surface and lower content of impurities. The improved physical and mechanical properties as well as corrosion resistance of Fe–Mo–W coatings in comparison with the base metal can be considered as promising technologies for surface hardening and repair of worn items.Исследованы особенности электрохимического формирования покрытий Fe-Mo-W из цитратного электролита на основе железа (III) на подложках из малоуглеродистой стали и серого чугуна. Установлено влияние концентрации солей сплавообразующих компонентов и режимов электролиза на качество, состав и свойства полученных сплавов. Показано, что сплавы, сформированные в условиях нестационарного электролиза, имеют более равномерную поверхность и характеризуются меньшим содержанием примесей. Повышенные физико-механические и антикоррозионные свойства покрытий Fe-Mo-W в сравнении с основным металлом позволяют рассматривать их как перспективные в технологиях упрочнения поверхностей и ремонта изношенных изделий
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