Nickel-alumina Composites Research Articles

Application of Ni(II)-alumina composites for electrocatalytic reduction of 4-nitrophenol

Nickel-alumina composites with various content of nickel were synthetized by sol-gel method. The characterization of samples was performed by diffuse reflectance spectroscopy and electrochemical impedance spectroscopy using the Mott-Schottky analysis. Glassy carbon electrode modified by synthesized composites was investigated for reduction of 4-nitrophenol. Modification of glassy carbon electrode with composite sample led to the strong apparent electrocatalysis. Principal component analysis was used to establish correlation between structural, textural and electrochemical data of investigated composites.

Synthesis and Characterization of Nickel-Alumina Composites from Recycled Nickel Powder

The recycling of metallic waste to create more valuable materials and their valorization into upgraded metal-based composites constitutes an important field of study. The composite industry nowadays considers environmental improvements as important as other properties of the materials. In the present paper, nickel powder was recycled from ferrous scrap, a low-cost and largely available material, by an effective hydrometallurgical recovery process. Then, this recycled powder was successfully used along with particulateα-alumina to prepare oblong nickel-based composite specimens with ceramic reinforcement loadings ranging from 0 to 30 wt.% by applying powder processing manufacturing techniques including cold isostatic pressing (CIP) and sintering. The microstructures obtained were characterized, the specimens were subjected to three-point bend tests, and their fracture behaviour was evaluated. By increasing the % ceramic reinforcement content, density clearly decreases while strengthening is achieved, thus leading to development of lightweight and enhanced oblong nickel-alumina composites. The composite microstructure, and particularly the metal-ceramic interface bonding, has a strong impact on fracture behaviour upon external loading.

Nanocrystalline alumina dispersed in nanocrystalline nickel: enhanced mechanical properties

Nickel–alumina nano-composites have been electrochemically deposited by pulse plating from a suspension of nano-Al2O3 in a Watts-type electrolyte. The influence of duty cycle and amount of suspended Al2O3 on the content of Al2O3 in the deposit was studied. With an optimized set of plating parameters, the influences of additives on wear resistance, hardness and the deformation behaviour (quasistatic and dynamic compression tests) of these nickel–alumina nano-composites in comparison to pure nano-nickel were investigated. The addition of Al2O3 tripled the yield stress and improved the hardness up to twice the value of pure nickel. Due to its high hardness and stiffness, the nickel–alumina composites deposited with the additive naphthalene-1,3,6-trisulfonic acid trisodium salt in the electrolyte are appropriate to wear resistant coating. Nickel–alumina nano-composites deposited without any additives are hard and at the same time ductile and so considered as ideal structural materials.

Influence of ethanol on the electrocodeposition of Ni/Al 2O 3 nanocomposite films

The effect of ethanol on the electrocodeposition of nickel alumina nanocomposites was investigated using an acidic nickel sulfamate electrolyte. The surface charge and sedimentation behaviour of the 13 nm alumina particles in the nickel plating bath were characterized as a function of the ethanol concentration and the pH of the electrolyte. High ethanol contents cause a decrease in the surface charge and dispersion stability of the alumina particles in the plating electrolyte. The effects of the deposition conditions, i.e. ethanol content, current density, and particle content of the electrolyte on the codeposition of nickel alumina composites were investigated systematically. Low values of current density and high amounts of ethanol in the plating bath were found to be beneficial for the particle entrapment. The structure as well as the microhardness of the nickel films were investigated as a function of the electrolyte composition and the particle incorporation. A textural modification combined with a distinct grain refinement was found with increasing ethanol content of the electrolyte and due to the alumina incorporation. The microhardness of the layers increased with decreasing ethanol content of the electrolyte and increasing nanoparticle incorporation.

Effect of TiO2 Nanopowder on the Sintering Behavior of Nickel–Alumina Composites for Functionally Graded Materials

The use of TiO2 nanopowder as a sintering aid in a pressureless sintering process has been investigated to improve the compatibility of the shrinkage rate in graded nickel–alumina composites. The results indicate that a 3 wt% TiO2 nanopowder ball mixed into Al2O3 powder substantially reduces sintered porosity in nickel–alumina composite specimens, improving the compatibility of shrinkage rates while increasing Vickers microhardness. Previously developed porosity reduction and sintering models were used to quantify improvement in shrinkage rates. However, the porosity reduction model had to be modified to account for sintering of agglomerated reinforcing particles in alumina‐rich composites. A power law sensitivity of Vickers microhardness to relative density was determined from homogeneous specimens. Vickers microhardness profiles of graded composites were then used to provide an insight into the effects of hydrostatic internal stresses that develop due to differential shrinkage, indicating that substantial hydrostatic stress retards shrinkage, which reduces microhardness at the interface of the nickel‐ and alumina‐rich regions and leads to crack formation without a nanopowder sintering aid.

Gradient Nickel – Alumina Composite Coatings

Particle reinforced metal matrix composite (MMC) coatings have been developed due to property combinations such as increased hardness, high creep/fatigue resistance as well as superior wear and oxidation resistance. MMC coatings can be produced by various techniques, which include powder metallurgy (plasma spray and HVOF processes), liquid metal processes and electrodeposition. This paper presents the development of the electrodeposition process to obtain nickel-alumina composites. The process conditions were optimized and based on these gradient nickel-alumina composites were prepared. Microstructural characterization and hardness determinations were carried out. The effect of process parameters on the amount and distribution of alumina particles as well as morphology of the deposits with and without alumina gradients are presented and discussed.

Fabrication of Graded Nickel-Alumina Composites with a Thermal-Behavior-Matching Process

Composites of nickel and Al2O3 with compositionally graded microstructures were fabricated from powders through an empirically determined thermal-behavior-matching process that was designed to minimize processing-induced stresses. Compositions ranged from pure Al2O3 to pure nickel. Specimen geometries included round disks 25 mm in diameter and 5–25 mm thick, as well as rectangular bars 25 mm × 25 mm in cross section and 75 mm long. Several different gradients were produced, including samples with single interlayers. Compacts were formed by cold uniaxial pressing in a die, followed by consolidation through sintering at 1 atm or hot isostatic pressing. Several different particle sizes of nickel and Al2O3 comprised the composite interlayers. The compaction behavior, sintering start temperature, sintering rate, and total linear shrinkage of each composition were evaluated. Careful data analysis, coupled with sintering theory, led to a layer configuration with matched green density and sintering behavior. Thermomechanically matched layers allowed large, crack-free, graded composites to be produced.

Effect of stress and microstructural changes on magnetic properties of nickel-alumina composites

In this work the effect of inclusions such as alumina on the structure-sensitive magnetic properties of nickel under prolonged exposure to stress and high temperature was studied. Samples containing varying amounts of alumina inclusions were prepared by powder metallurgical techniques. The tests were conducted under a stress range of 0–20 MPa at a temperature of 650°C, and the magnetic properties were measured at predetermined time intervals. Results from the study indicate that the product of coercivity and remanence is a good indicator of the evolution of the microstructure.

Micro-infiltrated micro-laminated nickel-alumina composites: A. Bose et al (Southwest Research Inst, USA)

Micro-infiltrated micro-laminated nickel-alumina composites: A. Bose et al (Southwest Research Inst, USA)

Ｎｉ‐Ａｌ２Ｏ３複合体の電析に及ぼす分散粒子の粒度分布の影響

The alumina content of nickel-alumina composites electrodeposited on a rotating cylindrical cathode in an alumina dispersed Watts solution decreased With increasing revolution rate of the cathode. The maximum size of alumina particles deposited also decreased with increasing revolution rate. These new findings on the behaviours of the deposits have been studied in detail with measurements of the size distribution both of particles in the plating solution and of the particles in the composites. The increase in the revolution rate of the cathode displaced the cumulative size distribution curve of the particles embedded in the deposit to smaller size range. The particle size on the distribution urve, which corresponds to the efficiency of transfer of dispersed alumina is inversely proportional to the revolution rate. This observation can be explained in terms of an estimated value of the Hamaker constant of 2.5×10-19[J] for the heterocoagulation between alumina and nickel.

A THERMAL-ETCHING STUDY OF THE NICKEL/ALUMINA INTERFACE

Nickel-alumina compacts have been thermally etched. Sections taken through the surface revealed that characteristic dihedral angles tended to develop at the lines of intersection between the alumina particles and the nickel surface. The angles seen in the section were measured and from these the dihedral angles and hence the surface and interfacial energies in the system were estimated. It is suggested that the results of Humenik and Kingery (J. Amer. Ceram. Soc., 1954, 37, 18) on the equilibrium of a liquid-nickel drop on alumina are probably not accurate, and in view of this the agreement between the two sets of results is satisfactory. It is concluded that solid nickel does not “wet” alumina, and that this is why it is difficult to sinter nickel-alumina composites to theoretical density. The addition of 5% aluminium to the nickel results in no significant improvement.