Materials Chemistry最新文献

The conductivity, Seebeck effect and magnetic susceptibility of the oxides La_2−xA_1+xCu₂O_6−x/2+σ (A = Ca, Sr) have been investigated. These compounds which contain variable amounts of trivalent copper are characterized by a hole conduction. A progressive evolution of the electron transport properties from a semi-conductor to a semi-metal is observed according to the amount of Cu³⁺. These properties are interpreted in terms of a Mott band model. The influence of the oxygen pressure during the electrical measurements is also considered.

A study of thermal degradation of Poly(vinyl chloride) commercial samples is made by means of extrusion capillary rheometer.

Samples are degradated under different conditions of temperature and shear stress. The influence of variables as molecular weight, particle size, stabilizer and shear rate is studied, obtaining results in agreement with general data in literature.

Other techniques as intrinsic viscosity measurements and infrared spectroscopy are also employed.

It is seen that the higher the melt viscosity of the sample, the more stable it is.

Experimental evidence is presented for the existence of quinone, aromatic ether, carboxylic acid and phenol groups on the surface of a graphitized carbon black (GCB), that is P-33 (2700°C). This evidence has been achieved by using polarographic analysis of a slurry of GCB particles.

Polarographic analysis has been also performed for ungraphitized P-33.

By comparison, it appears that the heating at 2700°C does not remarkably change the nature and the amount of chemical groups chemically bound to the surface of the carbon black.

The E.S.R. and optical spectra of glasses of basic composition 30% Li₂ O-30% ZnO-40% P₂ O₅ doped with vanadium have been studied.

The partial substitution of ZnO with Al₂O₃ and PbO has a great effect on the chemical durability of the glasses but does not affect their magnetic and optical properties.

The E.S.R. and optical data suggest that the dxy orbital of the umpaired spin of the V(IV) specie is not bonded with the π orbitals of the in plane ligands while there is a strong σ bonding with the same ligands. The bonding between the vanadium and the vanadyl oxygen is only slightly covalent. The E.S.R. spectra show a large reduction of the line-width when the concentration of the V₂O₅ goes from 1% to 0.1% showing that the dipolar broadening gives the larger contribution to the E.S.R. line-width.

The catalytic oxidation of methanol on copper, silver and copper - silver alloys has been studied in a large range of temperature changes, alloy compositions, reaction gas mixture compositions and flow rates. A reaction mechanism is proposed and the reaction conditions providing for highest catalytic activity and selectivity are outlined. It is possible using the scheme, to explain why copper is not so suitable as a catalyst as silver. A correlation has been established between the phase diagram of the bimetallic copper-silver system and its catalytic activity. Some copper-silver alloys prove suitable to be used as industrial catalysts for the oxidation of methanol to formaldehyde.

The specific constants of the phenol nitrosation reaction were determined over a temperature range of 0°C to 40°C in the following solvents: water, ethanol, dimethylsulfoxide, acetonitrile, chloroform, benzene and cyclohexane. The influence of several strong electrolytes on the nitrosation rate in aqueous media was studied in the presence of a strong acid, 0.1 N, HCl, and without it. The magnitude of the primary isotopic effect which is produced in protic and aprotic solvents was also investigated. On the basis of an analysis of the yields and from the reaction kinetics found in this work we propose a nitrosation reaction mechanism in aprotic solvents. The nitrosonium ion plays no role in the mechanism.