Particle features, oxidation behaviors and magnetic properties of ultrafine particles of Ni–Co alloy prepared by hydrogen plasma metal reaction

Abstract

Ni–Co ultrafine particles (UFPs) were prepared by hydrogen plasma metal reaction. Particle characteristics, oxidation, and magnetic properties were investigated and compared. fcc structured Ni–Co UFPs with a sphere shape were prepared over the whole composition range. The particles distribute from 5 to 100 nm in size with an average particle size of about 35 nm. They are thermally stable in air below 433 K, but oxidize quickly at the higher temperatures. The saturation magnetization of the UFPs is lower than that of the corresponding bulk alloy, especially in the Co rich side. Formation of oxide layer on the particle’s surface is an important reason for this reduction. Ni–Co UFPs possess large residual magnetization and coercive force above 60% Co. The composition dependence of the saturation magnetization and the coercive force changes remarkably around 60% Co, which implies a large variation in magnetic status around this composition.

In-situ reaction synthesis of pure bulk gadolinium dihydride materials

“…The gadolinium hydrides nanoparticles were prepared by hydrogen plasma metal reaction, the experimental apparatus for arc discharge was similar to those previously reported [12], which mainly consists of a stainless steel vacuum chamber, a moveable tungsten cathode and a copper anode, a gas flow system, a particle filter, a cooling-water system, a DC power supply, and a pump. The pure bulk gadolinium metal to be evaporated was laid on the watercooled copper anode, the vacuum chamber was pumped to 10 À4 Pa and then was backfilled with argon and hydrogen mixed gas to the desired pressure.…”

“…The Hydrogen Plasma Metal Reaction (HPAM) technology is very suitable to fabricate metallic nanoparticles, due to its low cost and high production [11][12][13]. Spark plasma sintering (SPS) method as a novel technology has been introduced into the field of fabricating powders into the bulk materials, due to the energy saving, highspeed, high pressure, and low temperature sintering with shorter holding time than conventional sintering techniques [14][15][16][17][18][19].…”

Synthesis and characteristics of Ti–Fe nanoparticles by hydrogen plasma–metal reaction

“…It was found that pure metal UFPs can be produced from less reactive metals including Ag, Co, Cr, Cu, Fe, Mn and Ni, while metal hydride UFPs are made from some of the reactive metals such as Sc, Ta and V. In the past decade, considerable efforts have been directed to the formation and characteristics of UFPs of less reactive metals and their alloys by HPMR [10][11][12][13][14][15][16][17]. Uda and Ohno studied the preparations and particle features of Fe-Ni and FeCu binary alloys [10], and Li and co-workers systematically investigated synthesis and magnetism of Fe, Co and Ni binary and ternary alloys [13][14][15][16][17]. It was concluded that substitutional solid solutions always form in these alloy nanoparticles.…”

Synthesis and Characterization of Metallic Nanoparticles Stabilized with Polyvinylpirrolidone

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The study of ultra-fine particles has been extensive in the last years for its unique properties and potential technological applications in different areas [1][2][3]. Magnetic ultra-fine metallic particles have been broadly investigated by its great coercive force and residual magnetization [2].

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“…The nanoparticles of Fe, Co and Ni and the FeCo were obtained by the reduction of the metal acetylacetonate: Ni(acac) 2 , Co(acac) 3 and Fe(acac) 3 with sodium boron hydride (NaBH 4 ) in ethanol and they were stabilized with polyvinylpyrrolidone (PVP = 40.000) to 25 ºC. The synthesis was carried out in inert atmosphere placing in a ball the precursor, the stabilizer, the reducing agent and the solvent under continuous agitation for 24 hours until the solution turns brown or black.…”