On the anomalies in density,Young's modulus and glass temperature of PdSi glasses

The densities, Young's moduli and glass transition temperatures have been measured for binary PdSi glassy alloys. These glassy alloys exhibit a negative deviation from Vegard's law an enhancement in Young's modulus and a tendency to lower the glass transition temperature in the region of the eutectic composition. The observed nonlinearity in these physical properties is shown to be better agreement with an alloy mixing effect rather than the structural ordering model.     

Sub-Tg mechanical relaxation of a La55Al25Ni20 amorphous alloy

Dynamic mechanical properties of an amorphous La₅₅Al₂₅Ni₂₀ alloy were measured by a forced oscillation method in the temperature range from room temperature to 453 K, just below the glass transition temperature (T_g = 481 K). The internal friction at a constant frequency 62.8 rad/s of this alloy showed a peak at about 400 K and the peak position shifts with frequency. Structural relaxation reduces the magnitude of the relaxation peak but has little affect on the peak position. Using the time-temperature superposition process, master curves for storage E′ (ln ω) and loss E″ (ln ω) moduli are constructed. Activation energy of the relaxation obtained from shift factors is low, 100 kJ/mol, which is close to that for diffusion of the Al in Al and Ni in Al. The relaxation spectra are very broad with a half width of 2 3 decades.     

The structural relaxation and glass transition of La---Al---Ni and Zr---Al---Cu amorphous alloys with a significant supercooled liquid region

An amorphous phase with a wide supercooled liquid region, > 50 K, was found to form over wide composition ranges in the La---Al---Ni and Zr---Al---Cu systems. The largest values for the temperature span between the crystallization temperature, T_x, and the glass transition temperature, T_g, ΔT_x(-T_x−T_g), are 69 K for La₅₅ Al₂₅Ni₂₀ and 88 K for Zr₆₅Al_7.5Cu_27.5. The structural relaxation behavior on annealing was examined for the two amorphous alloys with the largest ΔT_x values. The magnitude of the structural relaxation increases gradually with increasing annealing temperature, T_a, and then rapidly in the T_a range slightly below T_g and decreases significantly on annealing T_g. The rapid increase in the magnitude of the structural relaxation on annealing near T_g is due to the glass transition. The single-stage structural relaxation indicates that there is no distinct difference in relaxation times (atomic bonding forces) between the constituent atoms in the two metal-metal-type amorphous alloys. The existence of an optimum bonding state is thought to cause the wide supercooled liquid region for the two amorphous alloys.     

Synthesis and Electrochemistry of Tetraphenylporphyrins Containing an Antimony-Carbon sigma-Bond

The following five antimony(V) tetraphenylporphyrins with sigma-bonded antimony-carbon bonds were synthesized: [(TPP)Sb(CH(3))(2)](+)PF(6)(-), [(TPP)Sb(OCH(3))(OH)](+)PF(6)(-), [(TPP)Sb(CH(3))(OH)](+)ClO(4)(-), [(TPP)Sb(CH(3))(OCH(3))](+)ClO(4)(-), and [(TPP)Sb(CH(3))(F)](+)PF(6)(-). Each compound is stable toward air and moisture and has a high melting point (>250 degrees C). The electrochemistry and spectroelectrochemistry of these sigma-bonded porphyrins were examined in benzonitrile or dichloromethane containing 0.1 M tetrabutylammonium perchlorate as supporting electrolyte and the data compared to those for three previously synthesized OEP derivatives containing similar sigma-bonded and/or anionic axial ligands. Each porphyrin shows two reversible reductions and up to a maximun of one oxidation within the potential window of the solvent. Spectroelectrochemical data indicate formation of a porphyrin pi anion radical upon the first reduction as do ESR spectra of the singly reduced species. However, a small amount of the Sb(III) porphyrin products may be generated via a chemical reaction following electron tranfer. An X-ray crystallographic analysis of [(TPP)Sb(CH(3))(F)](+)PF(6)(-) is also presented: monoclinic, space group C2/c, Z = 8, a = 24.068(5) ?, b = 19.456(4) ?, c = 18.745(3) ?, beta = 94.69(2) degrees, R = 0.056.