1,723,343 research outputs found
Microstructures and strengthening mechanisms of Cu/Ni/W nanolayered composites
No full textCu/Ni/W nanolayered composites with individual layer thickness ranging from 5nm to 300nm were prepared by a magnetron sputtering system. Microstructures and strength of the nanolayered composites were investigated by using the nanoindentation method combined with theoretical analysis. Microstructure characterization revealed that the Cu/Ni/W composite consists of a typical Cu/Ni coherent interface and Cu/W and Ni/W incoherent interfaces. Cu/Ni/W composites have an ultrahigh strength and a large strengthening ability compared with bi-constituent Cu–X(X¼Ni, W, Au, Ag, Cr, Nb, etc.) nanolayered composites. Summarizing the present results and those reported in the literature, we systematically analyze the origin of the ultrahigh strength and its length scale dependence by taking into account the constituent layer properties, layer scales and heterogeneous layer/layer interface characteristics, including lattice and modulus mismatch as well as interface structure
Estudio de compuestos sulfurados de Ni-W como catalizadores en reacciones de hidrogenación.
No full textSe analizaron por difracción de rayos X y microscopía electrónica catalizadores másicos, 3 grupos de muestras de sulfuro de níquel y un grupo. de sulfuros bimetálicos de Ni—W. Los especímenes de sulfuro de Ni fueron preparados por el método clásico de precipitación homogénea de sulfuros con 2 variantes. La primera consistió en la variación del tiempo de'homogenización, y la segunda en la temperatura de sulfuración. La presencia de otras fases, además de las reportadas previamente en la literatura, se puso en evidencia a partir de los resultados de caracterización. Las muestras de sulfuros bimetálicos se prepararon por descomposición de una tiosal impregnada con valores de r = 0.15, 0.3, 0.5, 0.6, 0.7 y 0.8, donde r E Ni / [Ni+W]. Los resultados de caracterización mostraron que la estructura del catalizador cambió a medida que se adicionó el metal promotor. La actividad catalítica de todas las muestras se probó en la reacción de hidrogenación de la ciclohexanona en un microrreactor de flujo contínuo a presión atmosférica. Se registró alta selectividad hacia ciclohexeno para todos los catalizadores. Asi mismo, no se observó relación alguna entre el área superficial y la actividad catalítica. Se encontró para el caso de los sulfuros mixtos, que el efecto sinergético se presenta en las muestras con r igual a 0.7.Unsupported catalysts, three groups of nickel sulfide and one group of N i-W sulfide, have been analyzed by X-ray diffraction and electron microscopy. The nickel sulfide samples were prepared by the homogeneous sulfide precipitation method following two variations. The first one was based on the change of the homogenization time, and the second one on the sulfiding temperature. The appearance of other phases, besides those reported by the literature, have been observed from the characterization results of these catalysts. The Ni-W sulfide samples were prepared by the impregnated thiosalt decomposition method with r = 0.15, 0.3, 0.5, 0.6, 0.7, and 0.8, where r 5 Ni / [Ni + W]. The characterization measurements showed that the catalyst structure changes as the amount of the metal precursor is increased. The catalytic activity of all samples, Ni sulfide and Ni-W sulfide, is tested by the hydrogenation of cyclohexanone using a dynamic atmospheric-pressure microreactor. A high selectivity of the catalysts toward cyclohexene was observed during the reactions. No relationship between surface area and catalytic actyvity was found. For the Ni-W sulfide catalysts, the synergetic effect was determined to be predominant for the r = 0.7 samples
Electrodeposition and structure of Ni-W-B amorphous alloy
No full textThe electrodeposition of Ni-W-B alloy and the composition, structure and microhardness of the deposits were studied by means of electrochemical techniques. XPS, DSC and XRD. The results showed that Ni-W-B alloy electrodeposit has a lower electrochemical activity compared with Ni-W alloy. Ni-W-B allow electrodeposition was accompanied by th electroless deposition of Ni and incorporation of Na2B4O7 in the deposit. The composition of Ni-W-B alloy deposit was not remarkably affected by changes of sodium tungstate concentration and the maximum electrodeposition current efficiency was 49.9% in the electrolyte solution with [W]/[W]+[Ni] mole ratio at 0.65. The Ni-W allow obtained was present in a nanocrystalline structure, Ni-W-B was amorphous. Treatment at 400 degreesC for 2 hours caused coarsening of grain size, phase evolution for the Ni-W-B alloy and increase of microhardnesses
Electrodepositing Process of Ni-W-P/Graphene Composite Coatings
No full textThe Ni-W-P/graphene composite coatings were prepared in the Ni-based electrodepositing solution and graphene oxide mixture, the effect of stirring modes (including no stirring, mechanical stirring or ultrasonic stirring) on the surface quality of the composite coatings was investigated and the optimum formula of the electrodepositing solution of the Ni-W-P/graphene composite coatings was obtained through the orthogonal experiments in 4 factors and 4 levels. It was determined that ultrasonic stirring was the optimum stirring mode during electrodeposition. The Raman spectrum and EDS have shown that there existed graphene, in addition to Ni, W and P in the Ni-W-P/graphene composite coatings. The surface of the Ni-W-P/graphene composite coatings was smooth and the structure was compact. The average microhardness of the Ni-W-P/graphene composite coatings was improved by 26.7% higher than that of the Ni-W-P coatings after the heat treatment of 600°C.</jats:p
Current Status of Research on Electrodeposited Ni-W Alloy Coating
No full textThis paper discusses the influence of pH value, temperature and current density on the crystalline and amorphous structure of Ni-W alloy coatings during the electroplating process. The relationship between the corrosion resistance of Ni-W alloy coating and its crystal structure is discussed. In addition, the most common types of ternary systems and composite coatings for electrodeposited Ni-W alloy coatings are introduced. The effects of element types and contents on the hardness, wear resistance, corrosion resistance and thermal stability of Ni-W alloy coatings are analyzed. Finally, the current problems and development directions of Ni-W alloy coatings are proposed
Effect of variations in Ni-W molar ratio on the microstructure, mechanical properties and tribology of electrodeposited Ni-W/diamond composite coatings
No full textAbstractIn this work, Ni-W/diamond composite alloy coatings were successfully fabricated on low carbon steel by using direct current (DC) electrodeposition. The Ni-W molar ratio was varied in the range of 0.22–2 in the plating bath. The effect of variation of Ni-W molar on the microstructure, mechanical properties and tribology of Ni-W/diamond composite coatings was analyzed. The obtained results show that the W content and deposition rate of the Ni-W alloy tends to decrease from 19.02 at. % to 2.1 at. % and 34.86 µm/h to 11.98 µm/h, respectively as the Ni-W molar ratio is increased from 0.22 to 2. The hardness results reveal that the highest microhardness of 1346 Hv was reported for the sample fabricated with 0.75 Ni-W molar ratio. Furthermore, the wear rate of the Ni-W/diamond coatings tends to show a significant reduction as the Ni-W molar ratio is increased from 0.22 to 0.75
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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