Fine Ni Particles Research Articles

Sonochemical decomposition effects of nickelocene aiming for low-temperature and dispersant-free synthesis of nickel fine particle

Sonochemical decomposition effects of nickelocene, which sublimates easily were investigated to synthesize dispersant-free nickel fine particles at low temperature. In a hydrazine monohydrate and 2-propanol mixed solvent, the reduction of nickelocene was promoted by ultrasound irradiation, and nickel fine particles were synthesized while precluding the sublimation of nickelocene. Unlike the common hydrazine reduction of nickel salts, which requires multiple-step reactions, nickelocene was reduced directly without forming intermediates. The effect of the water-bath temperature (20–60 °C) was investigated, where larger fine particles were synthesized using a higher water-bath temperature (60 °C). When irradiated at 20 °C, the reduction rate of nickelocene was low, leading to the formation of nickel fine particles and organic nanoparticles via the reduction and decomposition of nickelocene. The ultrasound frequency was also investigated, where fine nickel particles were synthesized using low-frequency ultrasound irradiation. The formation of high-temperature hotspots led to the diffusion and growth of nickel on the surface of the nickel fine particles; therefore, raspberry-like nickel fine particles were synthesized. In this study, the difficult-to-handle nature of nickelocene, owing to its sublimation properties, was easily overcome by ultrasound irradiation. Instantaneous and localized reactions at hotspots contributed to inhibiting particle growth. Furthermore, Ni fine particles were synthesized via a direct reduction pathway, which differs from previous reactions. This method represents a new, dispersant-free, low-temperature process for synthesizing Ni fine particles.

Metallic Honeycomb Catalysts for Methane Steam Reforming: Effect of the Bimetallic Surface Coating on Catalytic Properties

Metallic honeycomb catalysts are promising candidates for fuel cell and small-scale onsite hydrogen production applications. In this study, high-cell-density Ni honeycomb catalysts coated with a series of bimetallic surface layers were synthesized. Their catalytic performance for CH4 steam reforming was investigated under a low steam-to-carbon ratio of 1.36 and a gas hourly space velocity of 6400 h-1 in the temperature range of 400–700°C. The catalysts coated with Ni-Mg and Ni-Zr showed excellent catalytic performance, reaching a high CH4 conversion and CO selectivity close to the equilibrium values within the test temperature range. The enhanced catalytic performance of the Ni-Mg and Ni-Zr coatings was attributed to the formation of oxide-supported fine Ni particles. In contrast, the catalysts coated with Ni-Fe and Ni-Sn exhibited an extremely low activity, which was lower than that of the catalyst coated with only Ni. The low activity of the Ni-Fe and Ni-Sn coatings is supposed to be due to the formation of aggregated Ni3Fe, Ni3Sn, and Ni3Sn2 phases.

The construction of nanotubular Ni-Mg phyllosilicate solid solution catalyst for boosting CO2 catalytic conversion: Identifying the species variations and interactions

Addressing the problems of easy collapse, Ni sintering and low catalytic activity over the nanotubular nickel phyllosilicate catalyst, the Mg species was doped via a simple hydrothermal method to construct the nanotubular Ni-Mg bimetallic phyllosilicate solid solution. The high thermal stability, nonreducible property and strong basicity of magnesium species led to the enhancement of anti-collapse, Ni-sintering resistance and basicity. As a result, the fine Ni particles and enhanced H2 and CO2 chemisorption and activation properties resulted in boosting the catalytic activity of both CO2 methanation and CH4-CO2 reforming reactions. The Ni/Mg ratios and the reduction temperatures were detailed optimized, and the 600oC-reduced Ni8Mg2-NT catalyst with the Ni/Mg ratio of 8:2 was the optimal, which also exhibited high long-term stability. In short, the formed Ni-Mg-phyllosilicate solid solution structure and the special interactions of different species brought about high catalytic performance of the nanotubular Ni-Mg phyllosilicate catalyst.

Effects of Sulfur and Phosphorus on Binder Decomposition Behavior of Nickel Powder

Fine Ni particles are utilized as internal electrode materials for multilayer ceramic capacitors. Despite extensive research, the effects of the surface properties (additional elements) remain unclear. To the best of our knowledge, the present study is the first to demonstrate the effects of the addition of sulfur (S) and phosphorus (P) on surface modification and binder decomposition during the production of fine Ni particles. Scanning electron microscopy, X-ray diffractometry, thermogravimetry-differential thermal analysis, hydrogen temperature-programmed reduction, temperature-programmed decomposition, and X-ray photoelectron spectroscopy were performed to analyze non-doped Ni, S-doped Ni and P-doped Ni powder. S existed as S–O or Ni–S on the particle surface in the S-doped Ni powder, whereas P existed solely as P–O on the particle surface in the P-doped Ni powder. When formed into a paste with these powders, the decomposition temperature of the binder is lower than that of the binder alone owing to the catalytic effect of the unmodified surface of Ni in non-doped Ni. However, the catalyst poisoning effect of S in S-doped Ni and the coating effect of P–O in P-doped Ni suppressed the lowering of the binder decomposition temperature due to the catalysis of the Ni surface. The results of the present study are expected to inspire future research on the optimization of the manufacturing process of multilayer ceramic capacitors.

Fe-promoted Ni catalyst with extremely high loading and oxygen vacancy for lipid deoxygenation into green diesel

The catalytic performance of Ni catalyst in lipid deoxygenation into green diesel is commonly limited by the quantity of accessible active sites, the specific surface area, and the acidity of the catalyst. To cope with these problems, the Fe-promoted Ni catalyst on ZrO2 with 60 wt% Ni loading (60%Ni–Fe/ZrO2) is synthesized by the co-precipitation method. The deoxygenation of oleic acid over 60%Ni–Fe/ZrO2 catalyst attained 98.7% conversion and 91.8% alkane yield, much higher than that of 20%Ni–Fe/ZrO2-2 prepared with the impregnation method (42.8% conversion and 16.2% alkane yield). The kinetics of octadecanol hydrotreatment revealed that the activation energy over 60%Ni–Fe/ZrO2 was much lower than Ni–Fe/ZrO2-2 (78.48 kJ/mol vs.191.90 kJ/mol). From the catalyst characterizations, the excellent performance of 60%Ni–Fe/ZrO2 was ascribed to its fine Ni particles, abundant Ni sites, high surface area, and coordinated acidity. Moreover, the mechanism of lipid deoxygenation over 60%Ni–Fe/ZrO2 was proposed.

Effects of modifier (Gd, Sc, La) addition on the stability of low Ni content catalyst for dry reforming of model biogas

Biogas consists of a larger part of methane and a smaller part of carbon dioxide. Reforming biogas is highly desirable due to the direct conversion of the two components, yet not possible due to the current state of catalyst development. For such dry reforming of methane-rich gases (CH4/CO2 = 2) we now present catalysts with low Ni loading (2.5 wt%) modified with Gd, Sc, or La. The best catalyst reaches 49% CH4 conversion and 95% CO2 conversion at 750 °C. The La-modification only shows limited influence on coking and protection against catalyst deactivation although this catalyst exposed highest basicity. On the other side, Sc- and especially Gd-modified catalysts exposed stronger metal-support interaction and thus enhanced stabilization of fine Ni particles during the reaction, which is critical to preserve high performance in CH4-rich DRM. This suppressed carbon deposition and the growth of structured carbon as evidenced by STEM images and TPO of spent catalysts. In this way, exceptionally high specific H2 productivity (94 l/(gcat·h)) compared to literature was obtained on Gd-modified catalyst, and, most noteworthy, after extending the time on stream from 8 to 100 h the amount of deposited coke increased only from 3 to 4 wt%.

Green synthesis of MCM-41 derived from renewable biomass and construction of VOx-Modified nickel phyllosilicate catalyst for CO2 methanation

In order to achieve green synthesis of MCM-41 and address the sintering problem of Ni-based catalyst supported on silica material, MCM-41 with regular spherical morphology was prepared using sodium silicate extracted from renewable equisetum fluviatile as silicon source, and then a group of nickel phyllosilicates were synthesized via the reaction of MCM-41 sphere and nickel nitrate under hydrothermal condition. Much denser nanosheets corresponding to lamellar nickel phyllosilicate were formed on the surface of MCM-41 sphere with the raise of hydrothermal temperature in the range of 180–220 °C, resulting in the nickel content varying from 17.2 to 41.8 wt%. Fine Ni particles with size smaller than 6 nm could be obtained on the 750oC-reduced catalyst owing to the strong nickel-silica interaction derived from Ni-phyllosilicate. After the addition of V2O5 promoter, Ni particle size was further reduced to around 4.5 nm at high Ni loading above 30 wt%. Vanadium species was in the mixed valence state of V(III), V(IV) and V(V) after reduction, which increased the electron cloud density of Ni0, resulting in high catalytic activity of the VOx-modified Ni-phyllosilicate catalyst for CO2 methanation. In a 100 h-400oC-lifetime test and 600 °C-steam hydrothermal treatment, the VOx-modified Ni-phyllosilicate catalyst also showed high long-term stability, excellent sintering resistance of metallic nickel particles and high hydrothermal stability due to the strong surface confinement effect of nickel phyllosilicate and promotion of VOx species. In all, this work provided a green synthesis of MCM-41 as well as an efficient Ni/SiO2 catalyst derived from nickel phyllosilicate for CO2 methanation.

Influence of nickel addition on the microstructure and mechanical properties of Al2O3-5vol%ZrO2 ceramic composites prepared via precipitation method

The aim of this work was to investigate the microstructure and mechanical properties of 1 vol%-Ni-added yttria-stabilized zirconia (YSZ) toughened alumina composites. First, Ni powders were heterogeneously precipitated in an alumina-zirconia powder mixture suspended in water; the prepared specimens were then pressureless sintered at 1550°C/2 h in a 90vol%Ar/10vol% H2 atmosphere. The structure of phases and microstructure of the composites were characterized by X-ray diffraction and scanning electron microscopy, respectively. Mechanical characterization of the specimens was carried out through Vickers hardness, Vickers indentation toughness, and three-point flexural bending tests. The fine Ni particles were homogeneously dispersed throughout the alumina matrix because of the employed processing method. Furthermore, hardness and toughness values were found to increase by 8% and 50%, respectively, with Ni addition, whereas the relative densities and flexural strength values were found to remain unchanged.

Effect of steam and hydrogen treatments on the catalytic activity of pure Ni honeycomb for methane steam reforming

The effect of steam and hydrogen treatments on the catalytic properties of a high-cell-density pure Ni honeycomb catalyst for methane steam reforming was investigated. A pretreatment consisting of steam treatment and subsequent hydrogen reduction at 1173 K significantly enhanced the catalytic activity of the Ni honeycomb catalyst at low temperatures below 1073 K. In situ X-ray absorption fine structure spectroscopy analysis showed that during the steam treatment, the surface Ni atoms were oxidized, and then these oxides were completely reduced to metallic Ni during the subsequent hydrogen reduction. The evolution analysis in surface morphology during pretreatment showed that many fine Ni particles formed on the surface. This surface structure was considered to be catalytically active for the methane steam reforming which is known to be structure sensitive.

A Transient Liquid Phase Sintering Bonding Process Using Nickel-Tin Mixed Powder for the New Generation of High-Temperature Power Devices

A transient liquid phase sintering (TLPS) bonding process, Ni-Sn TLPS bonding was developed for the new generation of power semiconductor packaging. A model Ni/Ni-Sn/Ni sandwiched structure was assembled by using 30Ni-70Sn mixed powder as the reactive system. The results show that the bonding layer is composed of Ni3Sn4 and residual fine Ni particles with a small amount of Ni3Sn2 at 340°C for 240 min, which has a heat-resistant temperature higher than 790°C. The microstructural evolution and thermal characteristic of the bonding layer for various times at 300°C and 340°C were also studied, respectively. This reveals that, after isothermally holding for 240 min at 300°C and for 180 min at 340°C, Sn has been completely transformed into Ni-Sn intermetallic compounds (IMCs) and the bonding layer is mainly composed of Ni3Sn4 and residual Ni particles. The analysis result for the mechanical properties of the joint shows that the hardness of the bonding layer at 340°C for 240 min is uniform and that the average value reaches 3.66 GPa, which is close to that of the Ni3Sn4 block material. The shear test shows that, as the holding time increases from 60 min to 180 min at 340°C, because of the existence of Sn, the disparity of shear strength between room temperature and 350°C is large. But when the holding time is 180 min or longer, Sn has been completely transformed into Ni-Sn IMCs. Their performances are very similar whether at room temperature or 350°C.

SiO2 nanoparticles surface modified with polyethyleneimine-oleic acid complex as stabilizers of Ni fine particles in dense nonaqueous suspensions

SiO2 nanoparticles (NPs) surface modified with polyethyleneimine-oleic acid complex (PEI-OA) has successfully prepared in a simple manner as a stabilizer of metal (Ni) fine particles (FPs) as well as a component of Ni/SiO2 composite particles. Starting from SiO2 NPs which were collected through centrifugation of commercial SiO2 colloids, it was found that PEI-OA can effectively adsorbed on collected SiO2 NPs surface during their redispersion process in toluene with the assistance of ultrasonication. The aggregated particle size (Z-average size) in toluene could be successfully reduced to c.a. 100nm under saturated adsorption of PEI-OA. It was also found that PEI-OA-modified SiO2 NPs can effectively attach to the Ni FPs by a simple mixing process in toluene. The FE-SEM observation confirmed the adsorption of the PEI-OA-modified SiO2 NPs on the Ni FPs without forming severe NP aggregates. Owing to the attachment of the PEI-OA-modified SiO2 NPs with surfaces that are compatible to toluene and α-terpineol, the suspension stability of the Ni/SiO2 composite particles in these solvents drastically improved. The result was confirmed by the effective reduction of the sedimentation velocity of diluted suspensions as well as by the reduction of the viscosity of dense suspensions.

Optical effect on the growth of Ni-filled carbon nanotubes using gas/solid interfacial discharge pyrolysis

We report on a growth technique of carbon nanotubes (CNTs) whose core and interlayer spaces were filled with Ni fine particles using discharge pyrolysis at gas/solid interface with optical-parametric-oscillation (OPO) laser beam assist. Transmission electron microscope observation reveals that CNTs were grown at around a cathode spot and, in most cases, Ni fine particles had 3–4 nm diameters. With decreasing the wavelength of OPO laser, G/D ratios obtained from Raman spectrum analysis increased gradually and, in fact, the structures of CNTs were improved from amorphous-like structures to the long and straight CNTs. For longer wavelengths (593 nm, 650 nm) of OPO laser, diameters of CNTs became thicker (typically 10 ~ 100 nm) and therefore, Ni nanowires were formed in the core spaces of CNTs. However, for shorter wavelength (456 nm, 507 nm), diameters of CNTs were significantly reduced and Ni fine particles were embedded in between CNT layers. It was found that the structures of CNTs strongly depend on both...

Effects of ball milling and particle size on microstructure and properties 5083 Al–Ni composites fabricated by friction stir processing

Ni particles were incorporated in a 5083 Al alloy matrix by friction stir processing (FSP) to fabricate metal particle reinforced composite. During the optimization of the process parameters for uniform particle distribution, it was found that ball-milled finer particles (10μm) were dispersed more uniformly in the matrix compared to as-received coarse particles (70μm). Hence, the particles were ball-milled before incorporating into 5083 Al matrix. The finer ball-milled particles were dispersed uniformly, however a thin intermetallic layer was formed at the particle-matrix interface. The layer was found to be Al–Ni intermetallic. When as-received fine particles of similar size (10μm) were incorporated using the same FSP parameters no such layer was observed in the processed composite. Hence, ball milling of particles influenced the microstructure of the composite. The high-energy state of the ball-milled particles can be attributed to the formation of the interfacial layer. The strength of both the composite was higher compared to the unreinforced 5083 Al alloy. FSP also refined the grain size of the aluminum matrix from 25µm to 3.5µm and this also contributed to the strength enhancement of the composites. The strength and ductility of the ball-milled composite were lower as expected compared to the composite with as-received fine Ni particles due to the presence of the interfacial reaction layer.

Performance of SOFC Power Unit Assisted by Paper-Structured Catalyst

This study aims at the performance enhancement of direct internal reforming (DIR)-SOFC. Paper-structured catalyst (PSC) is a flexible catalyst material composed of inorganic fiber network loaded with metal catalyst which can be applied into cell stack to assist hydrocarbon reforming. Catalytic performance of PSC was considerably improved by the dispersion of Mg/Al hydrotalcite (HDT) in the inorganic fiber network to have higher tolerance to fuel impurity (sulfur) poisoning because of the formation of fine Ni particles and suppression of Ni loading on the inorganic fiber (SiO2-Al2O3) to cause coking. High temperature SOFCs can convert chemical energy of a fuel directly to electricity even in the feed of low calorie gas. The use of engine-exhaust, which is most accessible lean gas, as a fuel for SOFC is promising idea. Recently, a compact SOFC unit operated by the direct feed of engine-exhaust was developed by Atsumitec Co., Ltd. However, performance of the DIR-SOFC unit can easily deteriorate, unless fuel is homogeneously supplied into the unit in which several numbers of stacks were arrayed. This study demonstrated that insertion of the HDT-dispersed PSC into the real SOFC stack between the cells led to 36 % increase in the performance because PSCs can boost up the output power of stacks placed at the positions where fuel is not well supplied.

Performance of SOFC Power Unit Assisted by Paper-Structured Catalyst

Paper-structured catalyst (PSC) is a flexible catalyst material composed of inorganic fiber network loaded with metal catalyst which can be applied into cell stack to assist hydrocarbon reforming. Catalytic performance of PSC was considerably improved by the dispersion of Mg-Al hydrotalcite (HT) in the inorganic fiber network because of the formation of fine Ni particles and suppression of Ni loading on the inorganic fiber (SiO2-Al2O3) to cause coking. High temperature SOFCs can convert chemical energy of a fuel directly to electricity even in the feed of low calorie gas. The use of engine-exhaust, which contains unburned hydrocarbons, H2 and CO, as a fuel for SOFC is promising idea. Recently, a compact SOFC unit operated by the direct feed of engine-exhaust was developed by Atsumitec Co., Ltd. However, performance of the unit can easily deteriorate, unless the fuel is homogeneously supplied into the unit in which several numbers of stacks were arrayed. This study demonstrated that insertion of the HT-dispersed PSC into the real SOFC stack led to large increase in the unit performance because PSCs can boost up the output power of stacks placed at the positions where fuel is not well supplied.

Fabrication of Friction Stir Processed Al-Ni Particulate Composite and Its Impression Creep Behaviour

Nickel powders were troweled on roughened Al base plate using a friction tool made from tool steel. Friction stir processing (FSP) was carried out using a load of 8 kN and with a tool rotation speed of 800 rpm and thus a surface composite was processed. Processed samples were characterized for revealing the microstructural features. SEM and XRD analysis revealed the presence of fine Ni particles in the stir zone which lead to a significant increase in hardness. Using the “refined energy model,” the maximum temperature developed within the processed zone was estimated and found to be around 275°C. Impression creep behaviour was assessed on both the base metal and processed zone at the temperature of 30, 100, and 200°C. Creep curves were generated and steady state creep rate (SSCR) values were found out to determine the activation energy. It is observed that friction stirred regions record higher creep rate values compared to the base metal. Estimated activation energy is in the range of 6 to 16 kJ/mol. Activation energy is marginally lower in the base metal compared to friction stir processed region.

Liquid Phase Hydrogenation of Maleic Anhydride over Ni Catalysts: Effect of Support on the Catalytic Performance

Ni catalysts supported on CeO2 and HZSM-5 supports were prepared and tested as catalysts in the liquid hydrogenation of maleic anhydride. Particularly Ni/HZSM-5 was active and selective in the hydrogenation of maleic anhydride to ڃ-butyrolactone. The characterization results of X-ray diffraction (XRD), N2 adsorption and CO temperature programmed reduction (CO-TPR) evidenced that the higher C=O hydrogenation ability of Ni/HZSM-5 catalyst was related to strong interaction between Ni particles and HZSM-5, and the high dispersion of fine Ni particles on the surface of support. Further, the acidic HZSM-5 support benefits the dehydration performance during the C=O bond hydrogenation process, which favored the production of ڃ-butyrolactone. The dual-functional Ni/HZSM-5 catalyst possesses both hydrogenation and dehydration activity.

Enhanced electrochemical performance and carbon deposition resistance of Ni–YSZ anode of solid oxide fuel cells by in situ formed Ni–MnO layer for CH4on-cell reforming

Two types of anode were prepared for a comparative study of their electrochemical performance and carbon deposition resistance. The first one was the Ni–YSZ cermet anode; and the other, designated as the Ni–MnO/Ni–YSZ, was the Ni–YSZ anode plus an on-cell reforming layer of Ni–MnO in situ reduced from MnNi2O4 with a microstructure of fine Ni particles embedded in MnO matrix. With the Ni–MnO layer on the top surface, open circuit polarization resistance of the Ni–YSZ anode decreased approximately by 1/2 in H2-3 mol% H2O and by more than 1/3 in CH4-3 mol% H2O at temperatures ranging from 650 to 800 °C. Carbon fibers were observed in the Ni–YSZ anode, rather than in the Ni–MnO/Ni–YSZ anode, after initial impedance measurements in CH4-3 mol% H2O for 1 h. The polarization resistance of both anodes at 800 °C increased with time up to 6 h in CH4-3 mol% H2O due to carbon deposition; however, the carbon formed in the Ni–MnO/Ni–YSZ anode had a lower degree of graphitization. In the atmosphere of CH4-20 mol% H2O, carbon deposition was completely depressed in the Ni–MnO/Ni–YSZ anode at 800 °C and 200 mA cm−2, which ensured a higher and more stable electrochemical performance than that of the Ni–YSZ anode.

Improved microstructure and performance of Ni-based anode for intermediate temperature solid oxide fuel cells

Three kinds of anodes prepared by NiO impregnation, (Ni, Mg)O impregnation and conventional sintering methods are investigated under the conditions of anodic current polarization and redox cycling. The optimized NiO loading in the NiO-impregnated anode is 40 wt%; and the minimum polarization resistance is 1.40, 0.71 and 0.60 Ω cm2 at 700, 750 and 800 °C, respectively, due to the increased triple phase boundary and conductivity that promote the charge-transfer process of H2 oxidation reaction. The conventional Ni–YSZ cermet anode is less sensitive to the current polarization at 200 mA cm−2; however, its polarization resistance is much higher than those of the impregnated anodes. (Ni, Mg)O impregnation improves the performance durability and redox-ability at 800 °C, with a low polarization resistance of 0.93 Ω cm2 after 48 h of current polarization and of 0.71 Ω cm2 after 10 redox cycles. The addition of Mg lowers the reducibility of (Ni, Mg)O particles; and its improved electrochemical performance and redox cycling resistance are attributed to its stabilized microstructure consisting of nano-scale Ni particles distributed on the surface of the pre-sintered YSZ scaffold. The agglomeration of fine Ni particles is suppressed by the unreduced (Ni, Mg)O in the anode.

Preparation and Characterization of Spherical Fine Nickel Particles by Ultrasonic Spray Pyrolysis

Spherical fine Ni particles were prepared by ultrasonic spray pyrolysis, and the effects of starting materials, carrier gas, and pyrolysis temperature on the crystal phase of the fine particles were investigated. When the mist of starting solution was pyrolyzed at 850 °C in a N2 atmosphere, the crystal phase of fine particles obtained from Ni (CH3COO)2·4H2O was in good agreement with that of Ni. Furthermore, the other phases were not observed. The average particle size of the spherical Ni fine particles was 0.45 μm.