Multiscale structure of (Al2O3)CoAlO/CoAl porous ceramometal composites
A multiscale structure of two CoxAlyOz ceramometals (cermets) with aims to get a high porosity or the mechanical strength was examined by a combination of XRD, SEM with EDX techniques, NMR (59Co and 27Al), and the textural measurements. The strong CoAlO/CoAl monolith cermet prepared by Co and Al powders mechanical alloying followed by the hydrothermal treatment and a calcination under the air was revealed to be composed of two parts. The first metallic cores were presented by Co metal and Co-Al alloy, and the second oxide matrix contained the mixture of spinel CoxAl3-xO4 structures and cobalt oxides. The interface between these two cermet parts was represented by alumina shell protecting the metallic core against further oxidation. On the other hand, the ceramometal Al2O3/CoAlO/CoAl prepared by mixing the Co-Al mechanical alloying product and a pure aluminum hydroxide with subsequent hydrothermal treatment and the calcination under the air was found to consist of three main parts. The first showed the cobalt-free large porous alumina globules surrounded by the second oxide part represented by spinel CoxAl3-xO4 oxides. The third one was the oxygen-free metallic part consisting of cobalt-based metal particles covered by Co-Al oxide. An enhanced microwaves adsorption caused by a random distribution of metallic particles distributed through oxides and the high porosity provided the catalyst activity prepared from porous cermet in the reaction of the hexane dehydrogenation.