Nickel-rich Particles Research Articles

Effects of aging heat treatment on microstructure and corrosion behavior of friction surfacing treated Al–Zn–Mg–Cu matrix composite

Effects of aging heat treatment on microstructure and corrosion behavior of friction surfacing treated Al–Zn–Mg–Cu matrix composite

Microwave absorption performance of porous carbon particles modified by nickel with different morphologies

• Porous carbon particles (PCPs) derived from flour were successfully prepared. • The nickels with different morphologies were successfully deposited on PCPs. • Only PCPs deposited chain-shaped nickels obtained better performance. • PCPs with chain-shaped nickels showed the best impedance matching. • PCPs with chain-shaped nickels exhibited the strongest loss ability. In this work, porous carbon particles were prepared from wheat flour by pyrolysis and activation. Through the subsequent coprecipitation and electroless plating, the surface and pores of carbon particles were modified by nickel-rich particles with different morphologies. Several loss mechanisms, including dielectric loss, magnetic loss, multiple reflection and scattering loss, were used to assess the attenuation ability to incident electromagnetic waves of these composite particles. The result shows that the chain-shaped morphology of nickel can provide the highest dielectric loss. Under the filler loading of 20 wt.%, the minimum reflection loss (RL min ) reached -38.42 dB at 13.2 GHz, and the maximum effective absorption bandwidth (EAB max ) was 5.2 GHz with a matching thickness of 2 mm. The excellent performance of the composite particles is attributed to the synergistic effect of outstanding impedance matching and superior electromagnetic loss ability caused by the chain structure. The result shows that the morphology of modifiers in carbon-based composites is important to improve microwave absorption performance, and this work provides inspiration for the design of high-performance porous carbon-based composites.

Electron microscopy study of the formation mechanism of catalytic nickel-rich particles and the role of carbonyl sulphide in the suppression of carbon deposition on 20Cr-25Ni steel

Abstract Austenitic stainless steel is used as fuel cladding in advanced gas-cooled nuclear reactors (AGR). At elevated temperatures, when the steel is exposed to CO2 based environments filamentary carbon deposits form on the surface of the steel. This filamentary carbon deposition is known to be catalysed by metallic nickel-rich particles. Adding trace amount of carbonyl sulphide (COS) into the gas mixtures suppresses the carbon deposition. In this current work, it has been shown that at 600 °C, the formation of filamentary carbon was suppressed by the addition of 215 ppb COS to a depositing gas mixture (containing approximately 1000 vppm C2H4/1% CO/bal. CO2) which was known to provide the environment suitable for carbon deposition. Samples exposed to the gas mixtures with and without 215 ppb COS were characterised using electron microscopy techniques to understand the formation mechanism of the nickel-rich particles and the inhibition mechanism due to the addition of COS. Electron diffraction study shows that the nickel-rich particles in the oxide layers assume the same crystallography as that of the austenitic metal underneath, regardless of the COS addition. The current observations also show that the metal-oxide interfaces was nickel-rich and a simple model has been proposed to explain the formation of nickel-rich particles within the subsurface oxide. Furthermore, it was found that when COS was added the surface of the nickel-rich particles in the oxide layer was found to be sulphur-rich by energy dispersive spectroscopy (EDS) on a scanning transmission electron microscope (STEM). It is believed that the surface sulphur adsorption onto the nickel-rich particles, rather than bulk sulphide formation, resulted in the inhibition of carbon deformation on the steel.

Co-precipitation of copper and nickel in crystalline silicon

Co-precipitation of copper and nickel in silicon bicrystals produced by wafer-bonding has been investigated. Transmission electron microscopy and energy-dispersive X-ray analysis show two types of precipitates: copper-rich silicide particles that contain a small partial mole fraction of 5% of nickel and nickel-rich particles containing a partial mole fraction between 15% and 25% of copper. Both types of precipitates are found inside large precipitate colonies typical for copper precipitation in silicon in the absence of nickel co-doping. Thermodynamically these precipitates can be assigned to the known binary metal silicide phases Cu3Si and NiSi2 and a solid solution of a second metal species therein.

Precipitate formation in recrystallized nickel plated non-sag tungsten wire

It is well established that some metals, such as palladium and nickel, can easily penetrate into tungsten by fast diffusion via crystal defects such as grain boundaries and dislocations. As a result of the fast penetration of these so called activators the recrystallization temperature of heavily drawn non-sag tungsten wire can be lower from about 2,000 C to about 1,000 C, thus the application of the tungsten wire, serving as reinforcement material in metal matrix composites used at high temperatures, is limited. An interesting question is in which form these activators exist in the recrystallized tungsten wire. It is generally believed that W-Ni intermediate compounds could form in the recrystallized material, presumably at grain boundaries. The free energy difference between the pure tungsten fibbers and the precipitating W(Ni) solid solution was suggested as the chemical driving force which governed the recrystallization process. The presence of nickel in small particles had also been observed in recrystallized grains of nickel plated tungsten wires using scanning electron microscopy (SEM) and secondary ion mass spectroscopy. These particles were considered to be nickel rich precipitates. However, a detailed investigation of the precipitation process has not been reported. In the present work an investigation of themore » structure, composition and distribution of nickel rich particles precipitated in recrystallized grains of nickel plated heavily drawn non-sage tungsten wires was carried out using analytical electron microscopy (AEM).« less