Preparation and characterisation of metallic glassy/amorphous materials

This thesis studied the plastic deformation behaviour of bulk metallic glasses by conducting indentations on various thermal histories using bonded interface technique. Another effort was to probe the route to fabricate bulk amorphous alloy via consolidating amorphous powder.

Effect of crystallization on corrosion resistance of Cu52.5Ti30Zr11.5Ni6 bulk amorphous alloy

The effects of crystallization on the corrosion resistance of a  Cu52.5Ti30Zr11.5Ni6 bulk amorphous alloy in 1 mol/L HCl, and 6 mol/L NaOH solutions were studied. The amorphous alloy was identified by  differential thermal analysis(DSC) and by X-ray diffraction(XRD). The partially and fully crystallized alloys were prepared by controlling the annealing  temperatures at 738 and 873 K for 1 and 12 min, respectively, and the corrosion resistances of those annealed alloys were compared with that of the amorphous alloy by immersion test and potentiodynamic measurements in 1 mol/L HCl and 6 mol/L NaOH solutions. The results show that the  partially crystallized alloy exhibits high corrosion resistance, whereas full crystallization results in deteriorated corrosion resistance compared with that of the as-cast amorphous alloy.

Plastic deformation in a partially crystallized Zr-based BMG under Vickers indenter

Vickers indentations were carried out on an anneal-introduced partially crystallized Zr₄₁Ti₁₄Cu_12.5 Ni₁₀Be_22.5 bulk metallic glass (BMG), and the evolution of the shear bands in this samplewas investigated and compared to the as-cast, aswell as the structurally relaxed counterparts. The results indicate that the plastic deformation in the partially crystallized BMG was accommodated by the semi-circular (primary) and radial (secondary) shear bands. A full crack or flake that was produced due to the spring back during the load removal was observed. The shear band density in the annealed alloy which was dispersed with crystalliteswas significantly lower than that of the as-cast alloy. The difference of the shear band features among the three kinds of alloy status, i.e., partially crystallized, structurally relaxed and as-cast alloys was discussed in terms of the free volume in the BMGs and the characteristics of nano-composites. It has been demonstrated that the plasticity for the three statuses of alloys queues in the descending order as the as-cast, annealed with partial crystallization, and annealed without crystallization.

Conductivity in amorphous polyether nanocomposite materials

Using a completely amorphous polyether we have investigated the effect of the inclusion of a nano-particulate filler on a polymer electrolyte. Nano-sized TiO₂ is shown not to significantly affect the conductivity of composite electrolytes containing 1.0 or 1.25 mol/kg LiClO₄ or 1.5 or 2.0 mol/kg LiTFSI. At 1.5 mol/kg LiClO₄ a significant increase in conductivity is observed. Raman spectroscopy experiments have been used to investigate the effect of filler on ion-aggregation. Only one new vibrational mode can be assigned to the composite which is not due to the polymer electrolyte or the filler. From this work, we believe the increased conductivity observed by previous researchers as a result of filler addition may be largely attributed to the effect on the degree of crystallinity along with some disruption of ion-aggregation by the fillers in PEO based electrolytes.

Ion conductivity in amorphous polymer/salt mixtures

Amorphous polymer/salt mixtures based on polyvinyl alcohol and poly(hydroxyethylacrylate) and poly(hydroxyethylmethacrylate) are described. The polyvinylalcohol materials have been prepared by a solvent free hot pressing technique as well as the traditional solvent casting method. The hot pressing technique allows the production of samples which are genuinely free of solvents and thereby has allowed an assessment in this work of the effect of residual solvent on conductivity. The acrylate materials were prepared by direct polymerization of monomer/salt mixtures, thus avoiding the need for solvents. These materials have glass transitions around or well above room temperature, but nonetheless have conductivities as high as 10⁻⁷ S/cm at room temperature. The temperature and composition dependence of conductivity are also presented.

Xe NMR spectroscopy of adsorbed xenon: Possibilites for exploration of microporous carbon materials

Despite the extensive use of 129Xe NMR for characterization of high surface-to-volume porous solids, particularly zeolites, this method has not been widely used to explore the properties of microporous carbon materials. In this study, commercial amorphous carbons of different origin (produced from different precursors) and a series of activated carbons obtained by successive cyclic air oxidation/pyrolysis treatments of a single precursor were examined. Models of 129Xe chemical shift as a function of local Xe density, mean pore size, and temperature are discussed. The virial coefficient arising from binary xenon collisions, σXe-Xe, varied linearly with the mean pore size given by N2 adsorption analysis; σ Xe-Xe appeared to be a better probe of the mean pore size than the chemical shift extrapolated to zero pressure, σS. © 2008 MAIK Nauka.