Formation of Metal-Oxide Nanocomposites with Highly Dispersed Co Particles from a Co-Zr Powder Blend by Mechanical Alloying and Hydrogen Treatment

Abstract

The use of metal powders produced by mechanical treatment in various fields, such as catalysis or gas absorption, is often limited by the low specific surface area of the resulting particles. One of the possible solutions for increasing the particle fineness is hydrogen treatment; however, its effect on the structure of mechanically treated powders remains unexplored. In this work, for the first time, a metal-oxide nanocomposite powder was produced by mechanical alloying (MA) in a high-energy planetary ball mill from commercial powders of Zr and Co in the atomic ratio Co:Zr = 53:47 in an inert atmosphere, followed by high-pressure hydrogenation at room temperature. The initial powders and products of alloying and hydrogenation were studied by XRD, 59Co Internal Field NMR, SEM, and HRTEM microscopy with EDX mapping, as well as Raman spectroscopy. MA resulted in significant amorphization of the powders, as well as extensive oxidation of zirconium by water according to the so-called “Fukushima effect”. Moreover, an increase in hcp Co sites was observed. 59Cо IF NMR spectra revealed the formation of magnetically single-domain cobalt particles after hydrogenation. The crystallite sizes remained unchanged, which was not observed earlier. The pulverization of Co and an increase in hcp Co sites made this nanocomposite suitable for the synthesis of promising Fischer–Tropsch catalysts.

CoZr nanocomposites in a ceramic–metal AlOx(OH)y/Al matrix with a different Co/Zr ratio and its potential for syngas processing

“…30,31 According to the literature, the particles of metallic cobalt with a size of less than 70 nm are considered single-domain (in the magnetic sense). Thus, each of the nanocomposites contained fairly small particles, the origin of which was most likely associated with the treatment with hydrogen under high pressure (the starting Co metal was shown to contain almost exclusively multi-domain particles in our previous work 22 ). The relative content of single-domain cobalt particles (Table 2) nonlinearly depended on the n Co /n Zr ratio in the samples, and the maximum content of such particles was observed for a sample with n Co /n Zr = 1 : 1.…”

“…In the subsequent hydrogen treatment under pressure, zirconium 22 -Co fcc single domain). 25 Afterwards, the hydrothermal treatment of mechanical mixtures of CoZr n H alloys and metallic aluminum powder is carried out to obtain ceramic-metal samples.…”

“…When synthesizing powder Co-Zr nanocomposites in this work, we used metallic cobalt powder, which consists of a mixture of Co hcp and Co fcc crystallites. 22 It is likely that during the synthesis of this cobalt powder, the resulting small Co fcc crystallites randomly intergrew with each other. In this case, the compensation of surface energy turned out to be better than the process of phase transition in Co hcp .…”

“…The CoZr nanocomposites were obtained by mechanochemical activation in a high-energy mill under an argon atmosphere, followed by treatment with hydrogen at high pressure and room temperature. 22 The treatment with gaseous hydrogen at high pressure is one of the possible approaches (or rather a group of approaches) used for particle dispersion (hydrogen pulverization). [23][24][25]…”

Phase textures of metal–oxide nanocomposites self-orchestrated by atomic diffusions through precursor alloys

“…[1][2][3] MONs are usually materialized by assembling nano-scale building blocks of metal and oxides through bottom-up approaches including mechanical mixing, sol-gel processes, or coprecipitation methods. [4][5][6][7][8][9][10] Indeed, nano-scale particles of nickel (Ni) and yttria-stabilized zirconia (YSZ) materials are mixed with high-speed ball mills, pelletized, or spread over electrolyte membranes, and finally calcined at high temperatures to yield anodes for solid-oxide fuel cells (SOFCs). 11 The MON materials obtained in such bottom-up approaches, however, often suffer from poor transport performances that lead to increased power loss of the fuel cells and/or batteries.…”