Metals lower dimensional polymeric

Titanium oxide monolayer on y-AljOj is a potential support for noble metals [1-4]. Many studies have shown that two-dimensional transition metal oxide overlayers are formed when one metal oxide (Vj05, Nb205, MoOj, etc.) is deposited on an oxide support (AljOj, TiO, etc.) [5-7]. The influence of the molecular structures of surface metal oxide species on the catalytic properties of supported metal oxide catalyst has been examined [8-9]. It has been demonstrated that the formation and location of the surface metal oxide species are controlled by the surface hydroxyl chemistry. Moreover, thin-layer oxide catalysts have been synthesized on alumina by impregnation technique with alkoxide precursor [10]. It has been found for titanium oxide, by using Raman spectroscopy, that a monolayer structure is formed for titanium contents below 17% and that polymeric titanium oxide surface species only posses Ti-O-Ti bonds and not Ti=0 bonds. Titanium is typically ionic in its oxy-compounds, and while it can exist in lower oxidation states, the ionic form TF is generally observed in octahedral coordination [11-12]. However, there is no information available about the Ti coordination and structure of this oxide in a supported monolayer. In this work we have studied the structural evolution of the titanium oxy-hydroxide overlayer obtained from alkoxide precursor, during calcination. 

By the term particulate composites we are referring to composites reinforced with particles having dimensions of the same order of magnitude. Particulate composites are produced from a polymeric matrix, into which a suitable metal powder has been dispersed, and exhibit highly improved mechanical properties, better electrical and thermal conductivity than either phase, lower thermal expansivity, and improved dimensional stability and behaviour at elevated temperatures. 

Other alkylalumoxanes (e.g., ethylalumoxane or isobutylalumoxane) were also used as cocatalysts instead of MAO (67) but show a much lower polymerization activity. The combination of zirconocenes with MAO is evidently optimal. The three-dimensional structure plays a role (there is a rough similarity to enzymes)—changing either the metal or the alkyl groups leads to lower activity, as does changing the amino acids in enzymes. 

The loss of three-dimensionality in the higher temperature regime is not a consequence of internal sample geometry—the fibers are macroscopic. For example, the specific heat of the boron/aluminum composite contains the cubic term and conforms to the mixture principle for bulk metallic ingredients. Moreover, experiments performed previously and discussed elsewhere [ ] demonstrate the dominance of a quadratic term in the low-temperature specific heat of a fiberglass-cloth-reinforced resin. The tendency to lower-order dimensionality is presumably a property of the lattice dynamics of the polymeric chains and rings characteristic of the resin matrix. 

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