Magnetic binary nanofillers

Magnetic binary nanofillers containing multiwall carbon nanotubes (MWCNT) and hercynite were synthesized by Chemical Vapor Deposition (CVD) on Fe/AlOOH prepared by the sol–gel method. The catalyst precursor was fired at 450 °C, ground and sifted through different meshes. Two powders were obtained with different particle sizes: sample A (50–75 μm) and sample B (smaller than 50 μm). These powders are composed of iron oxide particles widely dispersed in the non-crystalline matrix of aluminum oxide and they are not ferromagnetic. After reduction process the powders are composed of α-Fe nanoparticles inside hercynite matrix. These nanofillers are composed of hercynite containing α-Fe nanoparticles and MWCNT. The binary magnetic nanofillers were slightly ferromagnetic. The saturation magnetization of the nanofillers depended on the powder particle size. The nanofiller obtained from powder particles in the range 50–75 μm showed a saturation magnetization 36% higher than the one formed from powder particles smaller than 50 μm. The phenomenon is explained in terms of changes in the magnetic environment of the particles as consequence of the presence of MWCNT.     

Thermal degradation of polyether-urethanes: Part 3—Polyether-urethanes prepared from methylene bis(4-phenylisocyanate) and low molecular weight poly(ethylene glycols)

Polyurethanes have been prepared by reaction of methylene bis(4-phenylisocyanate) with diethylene glycol and with poly(ethylene glycol) with a molecular weight of approximately 200. Degradation has been carried out at temperatures up to 500°C and volatile products and structural changes in the residual polymer analysed in detail. The primary degradation reaction is one of depolycondensation to form the two monomers but a large proportion of these undergo a further complex series of reactions while they diffuse from the hot reaction zone. A comprehensive mechanism for the overall process has been deduced and discussed.     

Determination of gold and silver in copper concentrates, using k0 based neutron activation analysis

Procedures for the determination of gold and silver in copper concentrates, using k ₀ based neutron activation analysis, were developed and tested. The effects of gamma-ray self attenuation, neutron self-shielding and spectral interference were considered; precision, accuracy, and detection limits were studied by repeated analysis of copper concentrate internal reference materials. The analytical results have shown good precision and satisfactory accuracy in concordance with the detection limit and range of concentration.     

Thermal degradation of polyether-urethanes: 5. Polyether-urethanes prepared from methylene bis(4-phenylisocyanate) and high molecular weight poly(ethylene glycols) and the effect of ammonium polyphosphate

Polyurethanes prepared by reaction of methylene bis(4-phenylisocyanate) with poly(ethylene glycols) with molecular weights of approximately 1000 and 1500 have been degraded thermally, alone and in the presence of ammonium polyphosphate (APP). Degradation has been carried out at temperatures up to 500°C and the volatile products and structural changes in the residue analysed in detail. From these data, comprehensive mechanisms have been deduced and discussed and the differences in absence and presence of APP emphasised.A brief general discussion of this and previous work on polyetherurethanes (PEU) is presented, which illustrates in particular the effect of the length of the polyether segment on the degradation reaction.     

Yang—Mills instantons over Riemann surfaces

Exact solutions to the self-dual Yang—Mills equations over Riemann surfaces of arbitrary genus are constructed. They are characterized by the conformal class of the Riemann surface. They correspond to U(1) instantonic solutions for an Abelian-Higgs system. A functional action of a genus g Riemann surface is constructed, with minimal points being the two-dimensional self-dual connections. The exact solutions may be interpreted as connecting initial and final nontrivial vacuum states of a conformal theory, in the sense of Segal, with a Feynman functor constructed from the functional integral of the action.