Ni Wt Research Articles

Catalytic Influence of Bimetallic Bifunctional Ni-Pd/H-β and H-Mordenite Nanoporous Catalysts for Hydroisomerisation of n-Octane

Zeolite-β and mordenite were impregnated with 0.1 wt% Pd and varying the amount (0.1–0.5 wt%) of Ni. The prepared nanoporous catalyst were characterized by various physico-chemical techniques such as XRD, nitrogen adsorption–desorption isotherm (BET), NH3-TPD and TPR, XPS and TEM. Hydroisomerisation of n-octane was carried out in the temperature range from 200 to 450 °C in the presence of flowing H2 gas under 1 atm. Finally we found that Ni addition up to 0.3 and 0.2 wt% over 0.1 wt% Pd/H-β and H-mordenite enhances the n-octane conversion and isomerisation selectivity. As the Ni amount exceeds the threshold values, the conversion decreases with increase in cracked products, and also, the selectivity of mono and dibranched isomers were improved suggestion operation of PCP intermediate mechanism. The bimetallic catalysts were more selective to the formation of dibranched isomers with higher octane number, when compared with monometallic catalysts. Ni-Pd loaded zeolite-β supports always show higher activity and selectivity than mordenite supports. Moreover, we achieved higher conversion (74.9 %) and isomerisation selectivity (92.5 %) at low Ni loading (0.3 Ni wt% over 0.1 Pd wt%/Hβ) for the first time.

Quenching and Partitioning of Ultrahigh Carbon (1.69 Mass% C) Steel

Quenching and partitioning (Q&P) or quenching and tempering (Q&T) process of modified ultrahigh carbon steel (UHCS, Fe–1.69C–1.38Si–1.84Mn–2.20Cr–0.54Mo–0.43Ni wt%) was investigated by means of scanning electronic microscopy (SEM) equipped with energy-dispersive spectrometry (EDS) and x-ray diffraction (XRD). Mechanical properties, including hardness and impact toughness, and wear resistance were also measured. After Q&P, high impact toughness (10.5 J/cm2) and wear resistance at 100 N load in dry sliding were achieved on tested samples. We attributed the optimum mechanical properties and high wear resistance to better microstructure consisting of carbon-depleted martensite, uniformly distributed fine carbides, and high volume fraction of retained austenite.

High temperature oxidation behavior of a novel Ni−Cr binary alloy coating prepared by cathode plasma electrolytic deposition

Abstract A Ni-20 wt.% Cr binary alloy coating was prepared by cathode plasma electrolytic deposition from nickel-trivalent chromium sulfate electrolyte directly. Microstructure and high temperature oxidation behavior of the coating were investigated by SEM, EDS, TEM, XRD and cyclic oxidation test. It is found that the deposited coating is well-alloyed, dense and uniform with a typically molten morphology, and possesses nanocrystalline structure with the grain size of 30–50 nm. This finer-grained structure contributes to the selective oxidation of chromium and the formation of a thin, compact and protective Cr 2 O 3 scale, which exhibits good properties of oxidation and spallation resistance.

Influencia de la adición de estaño en el proceso de precipitación en una aleación de Cu-Ni-Zn

The influence of 1.1 wt% tin additions on the precipitation hardening of Cu-11 wt% Ni-20 wt% Zn alloy was studied by Differential Scanning Calorimetry (DSC), microhardeness measurements and High Resolution Transmission Electron Microscopy (HRTEM). The calorimetric curves, in the range of temperatures analyzed, show the presence of two exothermic reactions in the ternary alloy, associated to the short-range-order development assisted by migration of excess vacancies. On the other hand, one exothermic and one endothermic reaction are observed in the quaternary alloy, associated to the formation and dissolution of Cu 2 NiZn precipitates, respectively. It has been show that an addition of 1.1% tin plays an important role in the formation of Cu 2 NiZn precipitates, responsible for the precipitation hardening of the ternary alloy.

Characterization of Ni-Al Solar Absorber Prepared by Flame Spray Technique

In this research, a Ni-Al solar absorber was successfully prepared by the flame spray technique with Ni-5 wt.%Al particles as a starting material. The Ni-5 wt.%Al particles were melted and sprayed onto the outer surface of a stainless steel 316L tube in order to form a Ni-Al composite coating. The phase, morphology and reflectance (R) spectrum of the Ni-Al solar absorber were characterized by X-ray Diffraction (XRD), a Scanning electron microscope (SEM) equipped with an energy dispersive X-ray (EDX) analyzer and an Ultraviolet-visible-near infrared spectrophotometer at the wavelength 300-2500 nm. The results revealed that the surface of the Ni-Al solar absorber was rough, and its cross section was overlapped layer by layer. The Ni-Al solar absorber was composed of Nickel (Ni) and aluminum (Al) phases. NiO and Al2O3 phases were also found on the surface. The chemical composition of the Ni-Al solar absorber was Ni (72.94 wt.%), Al (11.76 wt.%) and O (15.29 wt.%). The solar absorptance (α)of this solar absorber was 0.77. This demonstrates that a Ni-Al composite coating can be applied as a solar absorber material for solar collector at high operating temperatures.

Three-dimensional reconstruction of anomalous eutectic in laser remelted Ni-30 wt.% Sn alloy

Laser remelting has been performed on Ni-30 wt.% Sn hypoeutectic alloy. An anomalous eutectic formed at the bottom of the molten pool when the sample was remelted thoroughly. 3D morphologies of the α-Ni and Ni3Sn phases in the anomalous eutectic region were obtained and investigated using serial sectioning reconstruction technology. It is found that the Ni3Sn phase has a continuous interconnected network structure and the α-Ni phase is distributed as separate particles in the anomalous eutectic, which is consistent with the electron backscatter diffraction pattern examinations. The α-Ni particles in the anomalous eutectic are supersaturated with Sn element as compared with the equilibrium phase diagram. Meanwhile, small wavy lamella eutectics coexist with anomalous eutectics. The Trivedi–Magnin–Kurz model was used to estimate undercooling with lamellar spacing. The results suggest that the critical undercooling found in undercooling solidification is not a sufficient condition for anomalous eutectic formation. Besides, α-Ni particles in the anomalous eutectic do not exhibit a completely random misorientation and some neighboring α-Ni particles have the same orientation. It is shown that both the coupled and decoupled growth of the eutectic two phases can generate the α-Ni + Ni3Sn anomalous eutectic structure.

Interdiffusion in fcc Ni–X (X = Rh, Ta, W, Re and Ir) alloys

The interdiffusion coefficients in binary face-centered cubic (fcc) Ni–X (X = Rh, Ta, W, Re and Ir) alloys at 1473, 1523, 1573 and 1623 K were measured by using semi-infinite diffusion couples together with the Sauer–Freise method. A scientific method was employed to evaluate the errors of the determined interdiffusivities by considering the error propagation. The measured interdiffusion coefficients agree in general with the literature data. In order to find out the possible substitutional element for Re in Ni-based superalloys, a comprehensive comparison among the interdiffusion coefficients in fcc Ni–X (X = Nb, Mo, Ru, Rh, Pd, Ta, W, Re, Os, Ir and Pt) alloys with 6 wt% X at 1473–1623 K was conducted. The comparison results indicate that fcc Ni-6 wt% Os alloys exhibit the lowest diffusion coefficient, followed by Ni-6 wt% Re and Ni-6 wt% Ir alloys. The further analysis on the variation of interdiffusion coefficient with its influence factors including alloying concentration, temperature, atomic number, activation energy, atomic radius and compressibility was also performed.

Effect of Substrates Temperatures on the Spreading Behavior of Plasma-Sprayed Ni and Ni-20 wt.% Cr Splats

In the formation of plasma-sprayed splats, the spreading behavior of molten droplets is essential for forming desirable lamella with good adhesion to the substrate. To understand the effect of the active element chromium on droplet spreading, pure Ni and Ni-20 wt.% (Ni20Cr) alloyed powders were plasma sprayed on mirror-polished 304 stainless steel substrates heated to different temperatures (below 200 °C). The substrate heating resulted in very little change in the surface roughness. However, there was a measureable change in the surface chemistry of the outermost few nanometers, which became increasingly enriched in Fe at higher temperatures. The splat morphologies were characterized and the transition temperatures were estimated. The results show that the transition from splashed to disk splats was not solely dependent on the temperature of the substrate. In some cases, some splashing still occurred to a measureable extent even at relatively high substrate temperatures, even above temperatures at which adsorbates (moisture) were totally removed from the surface. The splashing behavior could be correlated to a combination of the change in the surface chemistry of the substrate and the presence of active elements in the coating materials.

Size effects and temperature dependence on strain-hardening mechanisms in some face centered cubic materials

The mechanical behavior of face centered cubic metals is deeply affected when specimen dimensions decrease from a few millimeters to a few micrometers. At room temperature, a critical thickness (t) to grain size (d) ratio (t/d)c was previously highlighted, under which the softening of mechanical properties became very pronounced both in terms of Hall–Petch relation and work hardening mechanisms. In this work, new experimental results are provided concerning the influence of temperature on this size effect for copper, nickel and Ni–20wt.%Cr, representative of a wide range of deformation mechanisms (i.e. dislocation slip character). It is shown that multicrystalline samples (t/d<(t/d)c) are not deeply affected by an increase in temperature, independently of the planar or wavy character of dislocation glide. For pronounced wavy slip character metals, surface effects in polycrystals (t/d>(t/d)c) are not significant enough to reduce the gap between polycrystal and multicrystal mechanical behavior when the temperature increases. However, a transition from wavy slip to planar glide mechanisms induces a modification of the polycrystalline behavior which tends toward multicrystalline one with a moderate increase in temperature. This work demonstrates that surface effects and grain size influence can be successfully disassociated for the three studied materials using an analysis supported by the Kocks–Mecking formalism. All these results are supported by microscopic investigations of dislocation substructures and compared to numerical simulations using a strain gradient plasticity model.

Enhancing the Oxidation Properties of Gamma Prime + Gamma Platinum Bond Coat by Rhenium and Yttrium Additions for Improved Adhesion of Thermal Barrier Coatings on Nickel-Base Superalloys

A Re- and Y-modified γ′ + γ Pt bond coat was synthesized by diffusing 25 μm layer of Ni-6 wt%Re–0.5 wt%Y alloy and 5 μm layer of Pt into a Ni-based superalloy. It was observed that the modified bond coat can extend the useful life of thermal barrier coating systems with yttria-stabilized zirconia as top coat by more than double relative to the conventional bond coat synthesized by diffusing 8 μm layer of Pt into the same superalloy. The superior performance of the modified bond coat is explained in terms of the combined beneficial effects of Re and Y on the oxidation properties as determined from thermal exposure tests at 1150 °C and detailed microstructural characterization using various electron-optical techniques.

Applicability of Scheil–Gulliver solidification model in real alloy: a case study with Cu-9wt%Ni-6wt%Sn alloy

The present work explores the possibilities of the application of Scheil–Gulliver equation in modelling the solidification of a real alloy. For this study, Cu-9 wt%Ni-6 wt%Sn alloy was chosen which exhibits profuse micro-segregation during solidification, and hence easy to quantify experimentally. Also, this alloy is spinodally strengthened high strength copper alloy and has industrial importance. In this study, thermodynamic assessment using Scheil–Gulliver solidification model was carried out. Subsequently, the assessed result was compared with the experimentally obtained results from energy-dispersive X-ray spectroscopy analysis, and a good agreement was observed between these results. Therefore, it could be concluded that the solidification of this particular alloy system can be modelled using Scheil–Gulliver equation.

Fast Prepared Ni-Al2O3 Nanocomposite Through Solution Combustion Synthesis

Solution combustion synthesis (SCS) is a well-known method for fabrication of different materials such as oxides and composite materials in an extensive range. In this investigation, solution combustion synthesis is used for fabrication of Ni-10 wt% Al2O3 nanocomposite. Nickel and aluminum nitrates, urea, and distilled water are used as oxidizer, fuel, and solvent, respectively. The results show that if the fuel to oxidizer ratio exceeds the stoichiometric ratio, the combustion temperature increases. However, introduction of graphite to the solution could conduce to the reduction of the combustion temperature. With the addition of an auxiliary material, graphite, so a nickel oxidation is postponed, Ni-Al2O3 nanocomposite is produced only in one step.

Development and High Temperature Property Evaluation of Ni-Co-Cr-Al Composite Electroforms

Ni-Co-Cr-Al composite electroforms were developed with cobalt content of 10 and 40 wt.%. Cr and Al nano-particles were suspended in sulphamate electrolyte and co-deposited in the Ni-Co matrices. The surface morphology was investigated using field emission scanning electron microscope and the composition analyzed by energy-dispersive x-ray analysis. The oxidation resistance of the electroforms was studied from 600 to 1000 °C. The weight gain of Ni-10 wt.%Co-Cr-Al was less (better oxidation resistance) compared to Ni-Cr-Al and Ni-40 wt.%Co-Cr-Al. The x-ray diffraction studies revealed that the oxidation product formed on the surface of Ni-Cr-Al and Ni-10 wt.%Co-Cr-Al consisted of NiO and Al2O3, while Ni-40 wt.%Co-Cr-Al comprised oxides such as NiCo2O4, CrO3, CoO, NiO, and Al2O3. The hot corrosion behavior was investigated in 75%Na2SO4 + 25%NaCl environment at 800 °C. It was found that the hot corrosion resistance of the composite coating improved with increase in cobalt content. The probable composition suitable for high-temperature applications was found to be Ni-10 wt.%Co-Cr-Al.

Microstructure Evolution During Al, Ti, and Mo Surface Deposition and Volume Diffusion in Ni-20Cr Wires and Woven Structures

Ni-20 wt pct Cr wires, as individual wires or within 3D woven structures, are alloyed with Mo, Al, and Ti by gas-phase surface deposition and volume interdiffusion. Mo deposition creates Mo-rich coating and Kirkendall pores. Al + Ti co-deposition creates uniform triple-layered coating. The resulting homogenized and aged Ni-(17.4-19.6)Cr-(1.6-1.8)Al-(2.5-3.6)Ti-(1.5-4.5)Mo(wt pct) wires exhibit γ + γ′ superalloy microstructure. This demonstrates the feasibility of fabricating 3D woven Ni-base structures via gas-phase alloying and heat treatments, into multi-element superalloys with solid-state bonding at wire contacts.

Oxidation Behavior of Selected Bond Coats Based on the γ′ + γ Structure and Their Performance in Thermal Barrier Coatings Deposited on a Nickel-Based Superalloy

Three bond coats based on the γ′-Ni3Al + γ-Ni microstructure were developed by diffusing pairs of Pt layers and metallic layers with selected compositions into a Ni-based superalloy. Thermal exposure tests at 1,150 °C with 24-h cycling period to room temperature were used to evaluate the thermal stability and oxidation behavior of the bond coats as well as their performance in thermal barrier coating systems utilizing zirconia-7 wt% yttria as the top coat. It is shown that a bond coat developed by a Pt layer and a layer of Ni-6 wt% Re-0.5 wt% Y alloy outperforms the conventional γ′ + γ Pt bond coats by more than two folds. Most evidence points out that the proper concentrations of Re and Y in the presence of balanced concentrations of other elements, particularly Al, Ti, Cr and Co can significantly enhance the thermal stability and oxidation resistance of γ′ + γ Pt bond coats.

Steam Reforming of Glycerol Over Nano Size Ni-Ce/LaAlO3 Catalysts.

In this work, hydrogen production from glycerol by Steam Reforming (SR) was studied by Ni-Ce catalysts supported on LaAlO3 perovskite in order to effect of the cerium loading amount and the reaction conditions. Nano size Ni-Ce/LaAlO3 catalysts were prepared by precipitation method. The structure of the catalysts was characterized by XRD analysis. The morphology, dispersion and the reduction properties of catalysts was examined by SEM, TEM, H2-chemisorption and TPR, respectively. It was found that 15 wt% Ni-5 wt% Ce/LaAlO3 catalyst showed the highest glycerol conversion and hydrogen selectivity. In addition, the catalyst also showed the high carbon dioxide selectivity and the lowest methane selectivity. The results indicate that the catalyst promotes methane reforming reaction. The highest activity in the 15 wt% Ni-5 wt% Ce/LaAlO3 was attributed to the proper cerium loading amount. Moreover, the lowest metal crystal size and rise in active site were found to have an effect on catalytic activity and hydrogen selectivity. The 15 wt% Ni-5 wt% Ce/LaAlO3 catalyst exhibited excellent performance with respect to hydrogen production at reaction temperature of 450 degrees C, at atmospheric pressure, 20 wt% glycerol solution and GHSV = 6,000 mL/g-cat x hr.

Growth mechanisms of dendrites and eutectics within undercooled liquid Al-Ni alloys

Al-4 wt.%Ni (hypoeutectic), Al-5.69 wt.%Ni (eutectic) and Al-8 wt.%Ni (hypereutectic) liquid alloys are highly undercooled and rapidly solidified under free fall condition. Theoretical calculations indicate that the coupled zone of (Al+Al3 Ni) fibrous eutectic is an unclosed region in the composition range from 4.8 to 15 wt.% Ni, which is strongly skewed towards the Al3 Ni phase side. It is found that the cooling rate and undercooling of liquid alloys would increase as the droplet size decreases. Then the microstructural evolution of Al-Ni alloys will be induced by the competitive growth of (Al) dendrite, Al3 Ni dendrite, and (Al+Al3 Ni) eutectic. During the rapid solidification of Al-4 wt.%Ni hypoeutectic alloy, complete solute trapping effect occurs and then causes the formation of metastable segregationless (Al) solid solution phase. When the droplet undercooling exceeds 58 K, the structural morphology of Al-5.69 wt.%Ni eutectic alloy shows a transition from (Al+Al3 Ni) fibrous eutectic to primary phase (Al)-dominated hypoeutectic structure. As the undercooling increases further, the fibrous eutectic becomes the unique microstructure of Al-8 wt.%Ni hypereutectic alloy, and finally evolves into a kind of granular eutectic.

Highly loaded well dispersed stable Ni species in NiXMg2AlOY nanocomposites: Application to hydrogen production from bioethanol

Inexpensive NiXMg2AlOY nanocomposites with high Ni content (Ni wt% >40%) are developed as efficient catalysts for the sustainable hydrogen production from a mixture of ethanol and water at low temperature. The NiXMg2AlOY nanocomposites are composed of small and uniform nanoparticles (4–6nm) of NiO, Ni–Mg–(Al)–O and/or MgO. The strong interactions existing between Ni2+ cations and Mg2+ and/or Al3+ cations either in the Ni–Mg–(Al)–O solid solution and/or at the interface of nanoparticles of NiO and/or Ni–Mg–(Al)−O make the catalyst highly active and stable. The behavior of the solids is analyzed in the presence of low and high concentrations of ethanol while maintaining a H2O/EtOH molar ratio of 3. The NiXMg2AlOY catalysts are shown to be efficient toward H2 production between 250 and 650°C. In the presence of low concentration of ethanol, on the highly loaded Ni compound (Ni12Mg2AlOY), total conversion of ethanol is obtained at 250°C without formation of CO and carbon, and at 300°C a H2 yield of 3molmolEtOH−1 is obtained without the formation of CO, exhibiting a remarkable stability with the time on stream even if some carbon is formed. In high concentration of ethanol, total conversion of ethanol is obtained at 450°C on the highly loaded Ni compound (Ni12Mg2AlOY). In such conditions, a stable co-generation of carbon nanofibrous materials which amount increases with Ni content is also obtained. The catalytic stability is related to the type and morphology of the carbon species formed. The correlations among the catalyst properties, the catalytic performances and the characterizations are thoroughly discussed.

Pack Aluminization Synthesis of Superalloy 3D Woven and 3D Braided Structures

Micro-architectured, precipitation-strengthened structures were created in a new process combining weaving, gas-phase alloying, diffusion, and precipitation. First, high-ductility Ni-20 wt pct Cr wires with 202 μm diameter were braided, or non-crimp orthogonal woven, into three-dimensional structures. Second, these structures were vapor-phase alloyed with Al at 1273 K (1000 °C) by pack cementation, creating uniform NiAl coatings on the wires when using a retort. Also, solid-state bonding was achieved at wire intersections, where two wires were sufficiently close to each other, as determined via optical and X-ray tomographic microscopy. Third, the NiAl-coated wires were fully homogenized and aged to form γ′ precipitates distributed in a γ matrix phase, the same microstructure providing strength in nickel-based superalloys. The resulting structures—consisting of wires (i) woven in a controlled three-dimensional architecture, (ii) bonded at contact points and (iii) strengthened by γ′ precipitates—are expected to show high strength at ambient and elevated temperatures, low density, and high permeability which is useful for active cooling.

Hydrogenation Kinetics and Physical Characteristics of Ni, Ti, and Fe2O3-Added Mg by Reactive Mechanical Grinding

Abstract: Samples with the compositions of 80 wt% Mg-14 wt% Ni-6 wt% Fe2O3, 80 wt% Mg-14 wt% Ni- 6 wt% Ti and 80 wt% Mg-14 wt% Ni-3 wt% Fe2O3-3 wt% Ti (called Mg-14Ni-6Fe2O3, Mg-14Ni-6Ti and Mg-14Ni-3Fe2O3-3Ti, respectively) were prepared by reactive mechanical grinding. Their hydriding and dehydriding rates were then measured at the first cycle, and the specific BET surface areas, grain sizes, and strains of the samples were analyzed. The quantities of hydrogen absorbed and desorbed for x min are indicated as Ha (x min) and Hd (x min), respectively. The values of Ha (10 min) and Hd (30 min) for Mg-14Ni-6Ti were the largest, followed in order by Mg-14Ni-3Fe2O3-3Ti and Mg-14Ni-6Fe2O3. The particles on the surface of the Mg-14Ni-6Ti were the finest, followed in order by Mg-14Ni-3Fe2O3-3Ti and Mg-14Ni-6Fe2O3. Mg-14Ni-6Ti had the smallest grain size, followed in order by Mg-14Ni-3Fe2O3-3Ti and Mg-14Ni-6Fe2O3. The inverse dependence of the values of Ha (10 min) and Hd (30 min) on the grain size indicates that the values of Ha (10 min) and Hd (30 min) increase as the grain size decreases and thus the grain boundary area increases.