Coupling bimetallic Ni-La/MCM-41 catalyst enhanced by Radio frequency (RF) plasma for dry reforming

Controlling nickel particle size and inhibiting coke deposition on the supported catalyst was an enormous challenge. To solve this problem, La-doped nickel-based catalysts using MCM-41 as the support were prepared...

X-ray Fluorescence Spectroscopy Features of Micro- and Nanoscale Copper and Nickel Particle Compositions

The study is devoted to X-ray fluorescence spectroscopy (XRF) features of micro- and nanosized powder mixtures of copper and nickel. XRF is a high accuracy method that allows for both qualitative and quantitative analysis. However, the XRF measurement error due to the size of the studied particles is not usually taken into account, which limits the use of the method in some cases, such as analysis of Ni-Cu mixtures and coatings. In this paper, a method for obtaining copper and nickel nanoparticles was investigated, and the XRF of powder compositions was considered in detail. The initial micro- and nanoparticles of copper and nickel were studied in detail using SEM, TEM, XRD, and EDX. Based on experimental data, calibration curves for copper-nickel powder compositions of various sizes were developed. According to the results, it was experimentally established that the calibration curves constructed for nanoscale and microscale powders differ significantly. The presented approach can be expanded for other metals and particle sizes.

The Effect of Hydrodynamic Conditions on the Selective Flotation of Fully Liberated Low Grade Copper-Nickel Ore

Low grade sulfide ores are difficult to process due to their composite mineralogy and their fine grained dissemination with gangue minerals. Therefore, fine grinding of such ores becomes essential to liberate valuable minerals. In this research, selective flotation was carried out using two pitched blade turbine impellers with diameters of 6 cm and 7 cm to float copper and nickel. The main focus of this research was to generate optimum hydrodynamic conditions that can effectively separate nickel and copper from gangue minerals. In addition, we investigated the effects of superficial gas velocity, impeller speed, bubble size distribution, and bubble surface area flux on the flotation recovery and rate constant. The results demonstrated that a 7 cm impeller comparatively produced optimum hydrodynamic conditions that improved Cu-Ni recovery and the rate constant. The maximum copper and nickel recoveries in the 7 cm impeller tests were observed at 93.1% and 72.5%, respectively. However, a significant decrease in the flotation rate of nickel was observed, due to entrainment of nickel in copper concentrate and the slime coating of gangue minerals on the nickel particle surfaces.

Review and Evaluation of the Potential Health Effects of Oxidic Nickel Nanoparticles

The exceptional physical and chemical properties of nickel nanomaterials have been exploited in a range of applications such as electrical conductors, batteries, and biomaterials. However, it has been suggested that these unique properties may allow for increased bioavailability, bio-reactivity, and potential adverse health effects. Thus, the purpose of this review was to critically evaluate data regarding the toxicity of oxidic nickel nanoparticles (nickel oxide (NiO) and nickel hydroxide (Ni(OH)2) nanoparticles) with respect to: (1) physico-chemistry properties; (2) nanomaterial characterization in the defined delivery media; (3) appropriateness of model system and translation to potential human effects; (4) biodistribution, retention, and clearance; (5) routes and relevance of exposure; and (6) current research data gaps and likely directions of future research. Inhalation studies were prioritized for review as this represents a potential exposure route in humans. Oxidic nickel particle size ranged from 5 to 100 nm in the 60 studies that were identified. Inflammatory responses induced by exposure of oxidic nickel nanoparticles via inhalation in rodent studies was characterized as acute in nature and only displayed chronic effects after relatively large (high concentration and long duration) exposures. Furthermore, there is no evidence, thus far, to suggest that the effects induced by oxidic nickel nanoparticles are related to preneoplastic events. There are some data to suggest that nano- and micron-sized NiO particles follow a similar dose response when normalized to surface area. However, future experiments need to be conducted to better characterize the exposure–dose–response relationship according to specific surface area and reactivity as a dose metric, which drives particle dissolution and potential biological responses.

Influence of Nickel Powder Particle Size on the Microstructure and Densification of Spark Plasma Sintered Nickel-Based Superalloy

This study aims to investigate the effects of powder particle size on the densification and microhardness properties of spark plasma sintered superalloy. Three particles size ranges of nickel were used in this study, namely, (3-44, 45-106 and 106-150 μm), and this is the matrix in the IN738LC superalloy composition (powder), used in the study. The effects of the particle size were examined at a specific applied temperature and pressure. The transitioning stages during the sintering process of the green powders to the formation of the sintered alloy were analyzed and given as the particle rearrangement stage, the localized deformation stage and the neck formation/grain growth stage. There was the formation of γ, γ' and a solid solution within the microstructure of the sintered alloys. The effect of particle size was more pronounced on the grain sizes obtained, while the phases formed is the same for the three alloys. The results indicate that the nickel particle size (>60% of the total composition) has a significant influence on the densification, porosity, grain size and hardness properties of the IN738LC sintered alloy. Finer nickel particle size resulted in a sintered product with smaller grain size (9 µm), reduced percentage porosity (3.9%), increased relative density (96.1%) and increased hardness properties (371 Hv).

Electrically-activated Reaction Synthesis (EARS) of Ni-CNT/Al Hierarchical Composite Powders

The present study investigates the fabrication of Ni3Al-CNT nanocomposite using electrically-activated reaction synthesis (EARS) and its effects on the mechanical properties of the nanocomposite. The effect of initial nickel (Ni) particle size and mechanical milling time of Ni-CNT/Al hierarchical composite powder on reaction characteristics, product microstructure and properties was investigated for the first time. An increase in mechanical milling time was found to result in a decline in ignition temperature and time to ignition for the two investigated initial nickel particle sizes (4-8µm and 45-90µm). The smaller initial nickel particle size and longer milling times had a major influence on the homogeneity, decreasing porosity and increasing hardness of the reacted compacts.

Revealing the Effect of Nickel Particle Size on Carbon Formation Type in the Methane Decomposition Reaction

Carbon species deposition is recognized as the primary cause of catalyst deactivation for hydrocarbon cracking and reforming reactions. Exploring the formation mechanism and influencing factors for carbon deposits is crucial for the design of rational catalysts. In this work, a series of NixMgyAl-800 catalysts with nickel particles of varying mean sizes between 13.2 and 25.4 nm were obtained by co-precipitation method. These catalysts showed different deactivation behaviors in the catalytic decomposition of methane (CDM) reaction and the deactivation rate of catalysts increased with the decrease in nickel particle size. Employing TG-MS and TEM characterizations, we found that carbon nanotubes which could keep catalyst activity were more prone to form on large nickel particles, while encapsulated carbon species that led to deactivation were inclined to deposit on small particles. Supported by DFT calculations, we proposed the insufficient supply of carbon atoms and rapid nucleation of carbon precursors caused by the lesser terrace/step ratio on smaller nickel particles, compared with large particles, inhibit the formation of carbon nanotube, leading to the formation of encapsulated carbon species. The findings in this work may provide guidance for the rational design of nickel-based catalysts for CDM and other methane conversion reactions.

Potential of metal monoliths with grown carbon nanomaterials as catalyst support in intensified steam reformer: a perspective

A monolithic catalytic support is potentially a thermally effective system for application in an intensified steam reforming process. In contrast to ceramic analogues, metal monoliths exhibit better mechanical strength, thermal conductivity and a thermal expansion coefficient equivalent to that of the reformer tube. A layer of carbon nanomaterials grown on the metal monolith’s surface can act as a textural promoter offering sufficient surface area for hosting homogeneously dispersed catalytically active metal particles. Carbon nanomaterials possess good thermal conductivities and mechanical properties. The future potential of this system in steam reforming is envisaged based on hypothetical speculation supported by fundamental carbon studies from as early as the 1970s, and sufficient literature evidence from relatively recent research on the use of monoliths and carbon in catalysis. Thermodynamics and active interaction between metal particle surface and carbon-containing gas have resulted in coke deposition on the nickel-based catalysts in steam reforming. The coke is removable through gasification by increasing the steam-to-carbon ratio to above stoichiometric but risks a parallel gasification of the carbon nanomaterials textural promoter, leading to nickel particle sintering. We present our perspective based on literature in which, under the same coke gasification conditions, the highly crystallised carbon nanomaterials maintain high chemical and thermal stability.