Decomposition Of Metal Carbonyls Research Articles

Morphology study of metal oxide nanoparticles and aerogels produced via thermal decomposition of metal carbonyls in supercritical carbon dioxide

In this work, a process of thermal decomposition of metal carbonyls in oxygen-enriched supercritical carbon dioxide was studied. Manganese, iron, cobalt, and tungsten carbonyls were found to be soluble in supercritical CO2 at relatively mild conditions. For each metal carbonyl studied in this work, the thermal decomposition led to the formation of branched agglomerated structures throughout the high-pressure vessel. More specifically, for manganese and iron carbonyls, the procedure yielded partially monolithic aerogel-like structures, while for cobalt and tungsten carbonyls, the formation of branched aggregates was observed. The morphology of all the obtained metal oxides was studied by means of TEM. The study revealed that all materials consisted of individual nanoparticles with sizes between 2 and 40 nm. Pore structure was investigated by analyzing N2 adsorption/desorption curves. The specific surface area varied greatly depending on the type of oxide from 10 m2/g for CoOx to 130 m2/g for MnOx.

Formation of uncapped nanometre-sized metal particles by decomposition of metal carbonyls in carbon nanotubes

Carbonyl complexes of transition metals (Mx(CO)y, where x = 1, 2, or 3 and y = 6, 10, or 12 for M = W, Re, or Os, respectively) inserted into single walled carbon nanotubes (SWNT, diameter 1.5 nm) transform into metallic nanoparticles (MNPs) under heat treatment or electron beam irradiation. The host-nanotube acts as an efficient template, controlling the growth of MNPs to ∼1 nm in diameter. The only co-product of nanoparticle formation, carbon monoxide (CO) gas, creates pockets of high pressure between nanoparticles, thus preventing their collision and coalescence into larger structures. As a result, the MNPs stay largely spheroidal in shape and are uniformly distributed throughout the entire length of the SWNT. Despite their extremely small size (on average each MNP contains 30–90 atoms) and no protection of their surface by a capping layer of molecules, the metallic nanoparticles encapsulated in nanotubes are very stable under ambient conditions and even at elevated temperatures. Aberration-corrected high-resolution transmission electron microscopy reveals the crystalline nature of the MNPs, probes their interactions with the nanotube interior and illustrates the complex dynamics of confined MNPs in real-time and direct-space.

An alternative model for the formation of iron meteorites

The formation of iron meteorites is, at present, considered to have been a high temperature process. It seems generally accepted that these bodies are derived from molten cores of small planets with some 10 z km in diameter. They are thought to have been broken up later. This hypothesis implies a heating up of the rather small bodies and a subsequent separation of liquid metal from a silicate phase. For this hypothesis it is necessary that in the beginning short-living radioactive nuclides acted as a heat source. The separation mechanism of metals and silicates, however, is difficult to imagine because the gravitational forces in such small bodies appear to be insufficient. Even the moon has been found to have no or only a small metal core. Moreover, the disruption of a body of asteroidal size up to its core presents severe difficulties. Problems also arise regarding the structure of certain iron meteorites. Many features are incompatible with a fused metallic phase at the time of enveloping materials such as crystals of Laurencite (FeC12) and broken silicates with sharp corners. Neither of them could have survived temperatures near the melting point of the iron phase in which they have been found (P. Ramdohr [1] ). All this suggests that the existing models of iron meteorite formation are not quite satisfactory. As an alternative method for iron meteorite formation, a mechanism working primarily at low temperatures could have great advantages. We propose as a mechanism the thermal decomposit ion of metal carbonyls (Mex(CO)y). It is well known that comets contain carbon monoxide, iron and nickel, among other constituents and therefore a reaction leading to carbonyls is not at all unlikely. The formation of Fe(CO)s and Ni(CO)4 is now performed industrially (Mond [2] ). This type of reaction is exothermic (50 kcal/mole). It can be performed at atmospheric pressure and below 100°C, although the BASF uses several hundred atmospheres in order to gain time (Zimmermann [3] ), and iron sulfide as a catalyst. If ironand nickel-carbonyls are heated to about IO0°C, decomposit ion takes place and the free metals are formed together with carbon monoxide. 100°C Me (CO)x ~ Me + xCO