Ni-Mo Layers Research Articles

Coupling of the redox history and enrichment of Ni-Mo in black shale during the early Cambrian: Constraints from S-Fe isotopes and trace elements of pyrite, South China

Black shales were widely distributed in the world during the early Cambrian. Ni and Mo are enriched in black shale and can be mined only in Guizhou and Hunan, South China. The enrichment and mineralization of Ni and Mo have always been considered. However, the genesis of the deposits still has many interpretations. The migration and precipitation of elements were controlled by redox. It is conducive to explore the genesis of Ni-Mo enrichment that clarifying the relationship between the marine redox structure and metal precipitation. Pyrite nodules were selected along the profile for Fe isotope analysis, and nodules, colloidal and granular pyrite were analyzed in situ for S isotope and trace elements in the Xiaozhuliushui (XZLS) Ni-Mo deposit, Guizhou. Results show that the Fe isotopes have a slight upward trend from the lower black shale profile to the Ni-Mo layer. The maximum values (δ56Femax = 0.63; δ57Femax = 0.94) are reached at the polymetallic layer and then decrease rapidly. The δ34S values of nodules and granular pyrite decrease first and then increase rapidly from the lower part of the black shale, through the polymetallic Ni-Mo layer to the upper part of the black shale. The Co/Ni values of nodules, granular and colloidal pyrite < 0.01, in totally. Ni, Mo, As and Se are abnormally enriched in the Ni-Mo layer. These results indicate that all pyrite were formed in sedimentary and that the formation of a polymetallic Ni-Mo layer involves hydrothermal fluid. A large volume of clastic particles and sulfate were supplied due to enhanced continental weathering. It gradually becomes relatively oxidized in the depths of the ocean, which allows the metal elements to easily migrate. Then with the addition of submarine hydrothermal fluid, which disturbs the redox balance of the system, metal precipitation and enrichment occur. Means, the enrichment of polymetallic Ni-Mo in black shale is due to the coupling of continental weathering, sedimentation and hydrothermal action.

Formation and hot corrosion behavior of MoSi2/NbSi2 composite coating on Nb-based alloys by combined electrodeposition and HAPC processes

MoSi2/NbSi2 composite coating was prepared on Nb-based alloys through electrodeposition and halide activated pack cementation (HAPC) process. Preferred electrodeposition process, the effect of electrolyte with different concentrations of MoO42- on the electrodeposition behavior and coating formation were investigated. Besides, the microstructures of the composite coatings, and the hot corrosion behavior of the MoSi2/NbSi2 composite coated Nb-based alloys in the mixture of Na2SO4/NaCl (3:1 wt%) salt at 900 ℃ were studied. The results had shown that the co-deposited Ni-Mo layer was low oxygen, crack-free, and denser. Correspondingly 55.87 at% O and many cracks were detected in the Mo layer. With the increase of MoO42− concentrations in the electrolyte, the Mo content of the Ni-Mo layer increased and the cellular structures also became prominent. The high Mo content of the Ni-Mo layer was silicified to form a composite coating with thick MoSi2 outer layer. During the hot corrosion process, the composite coating exhibited stronger resistance. A SiO2 scale formed in the MoSi2 outer layer blocked the diffusion of oxygen so it could isolate the NbSi2 layer from the corrosion salt. The SiO2 scale got denser as the Mo content increased, which further improved the corrosion resistance of the composite coating. After the MoSi2 layer was exhausted, the NbSi2 sub-layer turned into the source of silicon dioxide and the second protective layer of the substrate. The satisfactory hot corrosion resistance of the MoSi2/NbSi2 composite coatings was attributed to the compactness and liquidity of the SiO2 scale.

Stored energy in nanocrystalline Ni-Mo films processed by electrodeposition

The energy stored in the crystallographic defects in nanocrystalline Ni-Mo alloy films was determined experimentally by differential scanning calorimetry (DSC) and compared with the calculated values. Two Ni-Mo layers with low (∼0.4 at.%) and high (∼5.3 at.%) Mo contents were processed by electrodeposition. It was revealed that the majority of the heat released during DSC (∼77%) was related to the grain boundaries. It was also found that the increase of Mo content from 0.4 to 5.3 at.% yielded an enhancement of the stored energy with a factor of about two. The measured and the calculated stored energies were compared with the values obtained for ultrafine-grained Ni-Mo alloys with similar compositions but processed by severe plastic deformation (SPD). It was revealed that in the SPD-processed samples there was a considerable contribution of vacancies to stored energy while their effect in the electrodeposited layers was lower.

The influence of Mo addition on the microstructure and its thermal stability for electrodeposited Ni films

An investigation was conducted to study the effect of molybdenum (Mo) alloying on the grain size and lattice defect structure in nanocrystalline nickel (Ni) films processed by electrodeposition. Moreover, the influence of saccharin addition to the electrolyte bath on the microstructure of Ni-Mo layers with low and high Mo contents was studied. It was found that the higher Mo content resulted in a larger dislocation density and twin fault probability as well as a smaller grain size. The addition of saccharin to the bath resulted in a further increase in the density of both dislocations and twin faults. It was also revealed that Mo alloying improved the thermal stability of the nanostructure in Ni films while saccharin addition yielded a reduction of stability. The reasons for these opposite behaviors were discussed in detail. In addition, the defect structure and its stability in Ni-Mo layers were compared with that for fine-grained bulk samples with the same composition but processed by severe plastic deformation.

Cathodic Electrodeposition of Ni-Mo on Semiconducting NiFe2 O4 for Photoelectrochemical Hydrogen Evolution in Alkaline Media.

Photocathodes for hydrogen evolution from water were made by electrodeposition of Ni-Mo layers on NiFe2 O4 substrates, deposited by spin coating on F:SnO2 -glass. Analysis confirmed the formation of two separate layers, without significant reduction of NiFe2 O4 . Bare NiFe2 O4 was found to be unstable under alkaline conditions during (photo)electrochemistry. To improve the stability significantly, the deposition of a bifunctional Ni-Mo layer through a facile electrodeposition process was performed and the composite electrodes showed stable operation for at least 1 h. Moreover, photocurrents up to -2.1 mA cm-2 at -0.3 V vs. RHE were obtained for Ni-Mo/NiFe2 O4 under ambient conditions, showing that the new combination functions as both a stabilizing and catalytic layer for the photoelectrochemical evolution of hydrogen. The photoelectrochemical response of these composite electrodes decreased with increasing NiFe2 O4 layer thickness. Transient absorption spectroscopy showed that the lifetime of excited states is short and on the ns timescale. An increase in lifetime was observed for NiFe2 O4 of large layer thickness, likely explained by decreasing the defect density in the primary layer(s), as a result of repetitive annealing at elevated temperature. The photoelectrochemical and transient absorption spectroscopy results indicated that a short charge carrier lifetime limits the performance of Ni-Mo/NiFe2 O4 photocathodes.

Maximizing utilization of reactivated and left-over catalysts in heavy gas oil hydrotreater: A case study of ADNOC Refining

Recently, ADNOC Refining Research Center (ARRC) has studied the possibility to maximize the reutilization of left-overs and reactivated hydrodesulfurization catalysts for one of its hydrotreater producing Ultra Low Sulfur Diesel (ULSD) from Heavy Gas Oil (HGO). Based on the refinery inventory, several catalyst configurations composed of different amounts of reactivated and fresh CoMo catalyst, including a full reactivated configuration having a stacked CoMo/NiMo/CoMo combination (50/25/25), have been tested in a pilot-plant reactor under commercially-relevant conditions. Experimental results in terms of reactor bed temperature, H2 consumption, aromatics and diesel yields have been analyzed and compared to the current commercial hydrotreater load and catalyst supplier forecasts for the studied configurations. Results show excellent performances of reactivated catalysts and a strong effect of the NiMo layer in the case of the stacked configuration. In a pure CoMo configuration, up to 75% reactor volume of reactivated catalyst could be utilized without impacting the product quality and cycle length, compared to a full fresh CoMo catalyst load. The full reactivated stacked configuration performed even better than the full fresh CoMo catalyst, without impacting product quality and diesel yield. Potential effect of the reactivated catalysts on the reaction selectivity and the role of the NiMo layer in the stacked configuration are discussed. Pilot-plant experimental data were in strong accordance with catalyst supplier commercial forecasts, emphasizing the quality of the pilot-plant study. Implementation of one of the studied configuration by the refinery could lead to between 30% and 55% savings on the cost of catalyst for the next load.

Time-Dependent Surface Structure Evolution of NiMo Films Electrodeposited Under Super Gravity Field as Electrocatalyst for Hydrogen Evolution Reaction

The surface structures of the electrodeposited NiMo films from compact to porous structure are adjusted by the combination of gravity acceleration and electrodeposition time. The evolution mechanism of surface structure is discussed based on the protrusion growth theory. The dependence of catalytic activity of the NiMo films for hydrogen evolution reaction (HER) on surface structure evolution is studied. The results indicate that compact NiMo layer is first electrodeposited, and then protrusions are formed. Finally, the protrusions rapidly grow and form a porous structure. It is found that only the compact NiMo films are electrodeposited under normal gravity condition due to a long induced time for the protrusions formation. Under super gravity field, the induced time for the protrusions formation is only less than 5 min owing to the enhanced mass transfer by the gravity-induced convection and hydrogen bubble agitation convection. So, a porous structure is easily formed under high gravity acceleration and...

Prominent Lower Cambrian K-Bentonites In South China: Distribution, Mineralogy, and Geochemistry

Abstract The Lower Cambrian on the Yangtze Block in South China is valuable for understanding the early evolution of life, the global biogeochemical cycles, and the major changes of the ocean. However, both the placement of the Precambrian–Cambrian boundary in South China and the correlation of the Lower Cambrian across the Yangtze Block are still in controversy, which hinders the global correlation of the Lower Cambrian and understanding of environmental changes of the paleo-ocean. Discovery of K-bentonites in the Lower Cambrian in South China will facilitate clarifying the above-mentioned problems. In this study, systematic field investigations and mineralogical and geochemical studies were conducted on Lower Cambrian K-bentonites in South China. The field investigations have shown that the widespread K-bentonites occur in two important stratigraphic levels: the middle Zhujiaqing Formation and the basal Shiyantou Formation and their lateral equivalents. Biostratigraphically, the older K-bentonite bed is preserved in the Anabarites trisulcatus–Protohertzina anabarica Assemblage Zone and the younger K-bentonite in the poorly fossiliferous interzone. Geochemical studies reveal that the Lower Cambrian K-bentonite samples are plotted in the fields of trachyte, trachyandesite, rhyodacite (dacite), and rhyolite in a plot of Nb/Y against Zr/TiO2, suggesting that the K-bentonites are most probably derived from felsic magmas with sub-alkaline to alkaline nature. Compared with the K-bentonite in the basal Shiyantou Formation and its equivalent sequence, the K-bentonite in the middle Zhujiaqing Formation and its correlative succession is characterized by lower Zr and Nb concentrations. Volcanic eruptions recorded by the two K-bentonite beds may have taken place during an interval of tectonic transformation, and the source volcanoes were probably located in the east margin of the Ganze–Songpan Block. Correlation results of the two important Lower Cambrian K-bentonite beds indicate that a previous viewpoint considering the polymetallic Ni-Mo layer in the lowermost Niutitang Formation as the Precambrian–Cambrian boundary in South China is inappropriate. Combined with available geochronological data, the boundary should be placed in the sequence beneath the K-bentonite in the middle Zhujiaqing Formation and its correlative stratigraphic level.

Insights into the Early Growth of Homogeneous Single-Layer Graphene over Ni–Mo Binary Substrates

The employment of Ni–Mo films has recently been shown to yield strictly homogeneous single-layer graphene. In this study, we systematically investigate the different stages of nucleation and growth of graphene over Ni–Mo layers. The studies reveal that the Ni film breaks up and diffuses into the underlying Mo foil, forming a Ni–Mo intermetallic. Nucleation only occurs from Ni sites, and thus, the nucleation density can be controlled by the Ni film thickness. Both nucleation and growth of the graphene are shown to be susceptible to very efficient self-termination processes to the formation of molybdenum carbide, and this guarantees the formation of large area graphene that consists entirely of monolayer graphene.

SHRIMP zircon age for a K-bentonite in the top of the Laobao Formation at the Pingyin section, Guizhou, South China

The Lower Cambrian on the Yangtze Platform in South China (internationally equivalent to the Nerreneuvian and 2nd series of the Cambrian) is valuable for understanding the early evolution of life, the global biogeochemical circles, and the major changes of the ocean. In particular, a precise radiometric calibration of the Lower Cambrian of this region is a critical realm in its multidisciplinary studies. A SHRIMP U-Pb geochronology study of the K-bentonite in the topmost Laobao Formation at the Pingyin section, Guizhou, South China yielded an age of 536±5 Ma (MSWD = 0.75), suggesting that the K-bentonite here can be correlated with the intensely studied K-bentonite within the middle Zhongyicun Member (Bed 5) of the Zhujiaqing Formation at the Meishucun section in Yunnan. Such a regional correlation result reveals that the Bed 5 K-bentonite also extends into deeper-water environments rather than being deposited merely in the shallow platform interior of the Yangtze Platform. The age of the K-bentonite at the Pingyin section also implies that its overlying polymetallic Ni-Mo layer should be younger than 536±5 Ma. Hence the previous placement of the Precambrian/Cambrian boundary at this layer is inappropriate. Combined with the results of stratigraphic correlations, it is suggested that the K-bentonites in the middle Zhongyicun Member of the Zhujiaqing Formation (or the equivalents) and the base of the Shiyantou Formation (or its equivalents), together with the polymetallic Ni-Mo layer, serve as three important marker beds. Their self-consistent radiometric ages have established an improved geochronologic framework for the Lower Cambrian in South China.

Electroevolution of hydrogen on the polytiophene-modified Ni–Mo composite layers

The Ni–Mo + PTh layers were prepared by electrodeposition from a bath containing Ni 2+, MoO 4 2−, ClO 4 − ions and thiophene (Th). The process was conducted in galvanostatic conditions. Surface morphology was examined using scanning electron microscope. The steady-state polarization and electrochemical impedance spectroscopy (EIS) methods were used for characterization of electrochemical activity during hydrogen evolution. Based on the obtained results parameters of hydrogen evolution process have been determined. It was found that the process proceeds better on the coatings containing an embedded 4.6%PTh than on the Ni–Mo layers. Kinetic parameters of hydrogen evolution are better for the Ni–Mo + PTh layers for comparable Ni–Mo alloy.

Cini-Sawatzky's Model in Studies of Electrodeposited Ni-Mo Alloys with Polymers

Electronic structures of electrodeposited Ni-Mo layers with polyethylene, polytiophene and polypyrrole were studied by Auger electron spectroscopy using the Cini-Sawatzky's model. Comparison of the theoretical and experimental lines was carried out using the asymmetry parameter of the spectral lines. It is pointed out that the changes of the spectral main lines Ni and Mo are connected with the ways of polymerization. It has been also shown that the application of the Cini-Sawaztky model to the experimental spectral lines can be used to explain the distortion appearing in the materials. Model parameters, i.e., intra-atomic correlation and bandwidth were determined.

Hydrogen evolution on the polyethylene-modified Ni–Mo composite layers

The Ni–Mo + PE Ni layers were prepared by electrodeposition from a bath containing a suspension of polyethylene subjected to preliminary nickel plating (PE Ni). Surface morphology was examined using scanning electron microscope. The potentiodynamic and electrochemical impedance spectroscopy methods were used for characterisation of electrochemical activity during hydrogen evolution. Based on the obtained results parameters of hydrogen evolution process have been determined. It was found that the process proceeds better on the layers containing the embedded PE Ni than on the Ni–Mo layers. Kinetic parameters of hydrogen evolution are better for the Ni–Mo + PE layers than for comparable Ni–Mo alloy. It was concluded that embedding the polymer into the layer results in local shielding of the electrode surface and directing the electrochemical process to the free areas thus improving kinetics of hydrogen evolution process.

Electrolytical Obtaining of Ni-Mo Coatings with Polypyrrole

Electrolytic coatings Ni-Mo with PPy were obtained by electrodeposition and electropolymerization from a galvanic bath containing Ni2+, MoO4 2–, ClO4 – ions and pyrrole (Py). The cyclic chronovoltamperommetric curve was used to determine the potential and current density of electrodeposition process. As the electropolymerization is anodic process while the electrodeposition is cathodic one, the electrode was working alternately as anode and cathode. The process was conducted under alternating potentiostatic or galvanostatic conditions. Comparative tests were carried out for Ni-Mo alloy. The results of structural investigation of the obtained coatings by the X-ray diffraction method show, the Ni-Mo layers are nanocrystalline solid solution of molybdenum in nickel (α phase), whereas the Ni-Mo+PPy coatings are characterized by decreased peaks coming from Ni-Mo base. Surface morphology of obtained Ni-Mo+PPy and Ni-Mo coatings was investigated by scanning microscope. It was stated, that the coatings obtained by alternating potentiostatic method exhibit multilayer character, whereas the coatings obtained under alternating galvanostatic conditions are characterized by the presence of Ni-Mo nanoagglomerates plated on polymer surface.

Molybdenum alloy electrodeposits for magnetic actuation

This paper deals with the preparation and characterisation of alloys containing molybdenum applicable in MEMS. An electrodeposition process for achieving a homogeneous, low-stressed, soft-magnetic Co–Ni–Mo alloy is described. The electrochemical study allows setting bath composition and deposition conditions useful to perform the deposition process. Deposits with low nickel and molybdenum percentages (11–15 wt%) are virtually useful for magnetic actuation applications. Saccharine is an effective antistress agent and it also decreases grain size and surface roughness of the Co–Ni–Mo layers. The mechanical and magnetic properties of the ternary alloy have been compared with those shown by a binary Co–Mo alloy containing similar molybdenum percentages previously electrodeposited in our laboratory. Thin Co–Ni–Mo films exhibited higher microhardness values than Co–Mo films and better magnetic properties for magnetic actuation ( H c = 50 Oe, M r = 90 emu g −1 and μ r = 670). Furthermore, film appearance (such as brightness) and corrosion resistance improved due to nickel presence. Electrodeposition has been tested on silicon/seed-layer substrates and the process selectivity has been investigated on photolithographed silicon. Both alloys are compatible with fabrication techniques involved in MEMS technology. No damage was observed when silicon was removed over alloy films to get stand-alone layers. The response of a microsized valve (silicon + seed-layer + electrodeposited Co–Mo or Co–Ni–Mo film) under an external magnetic field has been explored with good results.

複合めっき法によるＴｉＯ２分散Ｎｉ‐Ｍｏ合金皮膜の作製とその評価

Composite electrodeposition of TiO2 particles in amorphous Ni-Mo alloy matrices was carried out using aqueous citrate solutions (pH5.0) where anatase- or brookite-TiO2 particles were suspended. A white and uniform composite coating was obtained from a solution containing 200g dm−3 of TiO2. The composition of the Ni-Mo alloy matrices remained unaltered with the inclusion of TiO2. Although the uptake of TiO2 did not exceed 0.1wt.%, the resulting Ni-Mo/TiO2 layer exhibited the ability to decompose gaseous NO in the air or Methylene Blue in water. It was suggested that the anti-corrosive ability of the Ni-Mo layer is improved by the inclusion of TiO2 in the layer.

Design of Acidic Ni-Mo Alloy Plating Baths Using a Set of Apparent Equilibrium Constants

The electrodeposition of Ni-Mo alloy using a series of aqueous acidic citrate plating baths (pH 5.0) were examined from the standpoint of the Ni(II)- and Mo(VI)-species present in the solutions. The distribution of the species was calculated using a set of the formation constants for polymolybdates and citrate complexes, optimized by a factor analysis of optical spectra. Through the design of the bath compositions such that the dominant Ni(II)- and Mo(VI)-species are both 1:1 complexes with citrate, lustrous and uniform Ni-Mo layers having almost constant Ni content were found to be plated over a wide range of Ni(II)/Mo(VI) analytical concentration ratios, although the current efficiency decreased with decreasing Ni(II) concentration. This indicates the validity and importance of the bath design using these constants. The deposition phenomena were briefly discussed in terms of the mechanisms hitherto reported. © 2004 The Electrochemical Society. All rights reserved.

Properties of electrodeposited Ni-Mo alloy coatings

The composition of Ni-Mo layers (metallic and non-metallic elements) electrodeposited at temperatures up to 160 °C and pressures up to 5 bars has been determined. The effect of molybdate concentration has been investigated. All the non-metallic elements (C, O, H, N and S) exhibit a maximum content for deposition temperatures between 60 and 80 °C. A correlation between deposit composition and properties is attempted. The deposit growth mode, crystallinity and the corrosion resistance markedly depend on the plating conditions.

Electron beam induced modification of nickel coated molybdenum surfaces

The paper presents the results of research carried out to produce Ni-Mo layers by melting with an oscillating electron beam a 40 μm thick galvanic nickel layer deposited onto a molybdenum surface. The power density of the beam, treated as a rectangular-Gaussian surface heat source, has been regulated in the range of 10 9–10 10 W m -2 and the exposure time was from 12.5 to 60 ms. The ranges for which continuous surface layers were obtained are presented. Within these ranges, the relations of thickness and structure of layers with the above-mentioned parameters are given. On the basis of structural testing (optical microscopy, scanning electron microscopy, electron probe microanalysis and X-ray diffraction) as well as microhardness measurements, the mechanism of formation of the layers is proposed.

Intermetallic phase formation and breakdown of Mo diffusion barriers in Ni-Mo-Cu layers

Ni-Mo-Cu reaction triads with varied thicknesses of Mo layers sandwiched by Ni and Cu disks were annealed in an inert atmosphere at 950 °C to 1050 °C for 5 to 300 hours. Parabolic growth of the intermetallic phase, NiMo, was observed at 1000 °C and 1050 °C. Both the Mo and the NiMo layers acted as barriers for interdiffusion in the Ni-Cu system. When the growing NiMo phase reached the Mo-Cu interface, the phase transformed into a Mo-rich solid solution and a Ni-Cu solid solution, whereupon the diffusion barrier was no longer effective. The kinetics of the NiMo phase growth and the breakdown of the barrier were modeled using finite difference methods.