Pb Matrix Research Articles

Melting and possible amorphization of Sn and Pb in Ge/Sn and Ge/Pb mechanically milled powders

Mixtures of Ge–Sn and Ge–Pb powders were ball-milled to form a fine dispersion. After 32 h of milling the average diameter of the hard Ge particles embedded in the Sn (or Pb) matrix was about 10 nm. As the Ge concentration was increased in each system, the melting point,TM, and the enthalpy of fusion, ΔHM, of Sn (or Pb) decreased. Only small changes in ΔTMand ΔHMwere observed after heating cycles in the DSC to above the melting point. The melting endotherm measured by DSC disappeared for Ge-rich compositions (88 and 95 vol.% Ge for Ge–Sn; 93.5 vol.% Ge for Ge–Pb). It is suggested that atomic disorder/melting is nucleated at the Ge/Sn (or Ge/Pb) interfaces and the melting point and enthalpy of fusion decrease as the interfacial area increases. When the Ge volume reaches a value where essentially all the Sn (or Pb) atoms are adjacent to the Ge particle surfaces, the Sn is in a disordered–perhaps amorphous–state such that no melting transition is observed.

Effect of ion-lens tuning and flow injection on non-spectroscopic matrix interferences in inductively coupled plasma mass spectrometry

The effects of various matrix constituents, Co, Pb and synthetic ocean water, on analyte signal have been studied. Suppression of the 138Ba+ signal was observed in the presence of each matrix, with the Pb matrix having the greatest effect. These matrix-induced suppressions of analyte signal were compensated for in part by the use of In as an internal standard, and by initially tuning the ion lenses for maximum analyte signal in the presence of the matrix, rather than for a simple acidified standard solution. The severity of matrix-induced suppression was compared for flow injection and continuous sample introduction. No significant differences in suppression of analyte signal between the two methods were observed because of the relatively large sample volume used for flow injection. The experimental procedure adopted, continual reference of analyte signals with and without the matrix present, effectively eliminated any bias in the results due to nebuliser and cone blockage.

Fast solute diffusion in solid and supersaturated solid solutions

Abstract In this paper, we review the experimental data concerning fast diffusion of solute in Pb matrix and Pb (solute) solid solutions. Using both calorimetric and radiotracer techniques the temperature dependence of solute diffusion coefficients in Pb (solute) supersaturated solid solutions is determined. On the basis of experimental results it is shown that these coefficients can only be understood by assuming different defect states for solutes in solid and supersaturated solid solutions.

Physical characterization of blends of isotactic poly(butene-1) with ethylene-propylene copolymer

Melt-mixed blends of isotactic poly(butene-1) (PB) with an ethylene-propylene copolymer (EPM) containing 60 wt% PP were studied over the complete composition range. Phase-contrast polarizing microscopy and dynamic mechanical spectroscopy revealed that the blend is heterogeneous. DSC studies of quenched and annealed blends for both PB modifications indicate that total blend crystallinity decreases linearly with the EPM content. Pure PB crystallinity is enhanced to a small degree in the presence of EPM. Tensile behaviour of the blends was good up to moderate EPM levels. It was also demonstrated that blends containing EPM with increased PP content showed synergism in tensile behaviour not exhibited by blends with EPM of lower PP content. Appropriate mechanical models tested over the complete composition and temperature range suggest that the rubbery phase adheres strongly to the PB matrix. Overall, the experimental results support the contention that the system is mechanically compatible, possibly a result of component miscibility at elevated temperatures as predicted on thermodynamic grounds.

The Morphology and Structure of Polyacetylene-Polybutadiene Graft Copolymer Films

Abstract The morphology and the structure of a new PA copolymer has been investigated by means of TEM WAXS and ED techniques. Crystalline PA microdomains, less than 100 A in size, aggre gate preferentially into ca.2000 A long and ca.400 A wide worm like morphological units, in their turn embedded in a PA poor PB matrix.

Stress–strain behavior, hardness, and thermomechanical properties of butadiene–styrene block copolymers as a function of processing technique

AbstractStress–strain properties of star‐shaped butadiene–styrene block copolymers were carried out on extruded sheet and injection molded samples. A striking “plastic‐like” behavior was observed during the first extension, with a marked yield point, a drawing process, and an important hysteresis. These phenomena disappeared on the second elongation, but annealing below the polystyrene glass transition temperature gave again the initial behavior. A marked processing technique dependence was observed in the stress–strain experiments. An important variation in hardness was observed before and after stretching, and annealing experiments permitted the study of hardness recovery. A logarithmic relation between recovered hardness and the annealing time at constant temperature was deduced from the experimental data. Thermomechanical analysis curves show singular transitions between 20° and 85°C, which disappear on stretching. An important discrepancy occurs in TMA curves of extruded and injected samples. A comparison is made of thermomechanical behavior of linear and star‐shaped SBS block copolymers. A modified model is proposed for a reversibly deformable structure composed of polybutadiene and polystyrene linked ends at the diffuse interfacial region between the PS domains and the PB matrix.

The behaviour of lamellar second phases in a lead matrix under anodic action

Abstract Bimetallic test specimens consisting of lamellae of the metals Sb, Co, Cu, Ni, Ag and Sn embedded in a Pb matrix have been subjected to anodic testing. The paper studies the effect of thickness of these lamellae and nature of the metal which forms them on the penetration rate of anodic attack located preferentially on them. It is found that under a certain critical lamella thickness the attack rate tends to decrease as lamella thickness decreases. The dissolution mechanism is discussed as well as the effects of current density and time.