W. P. Leung

Thermal conductivity of amorphous alloys above room temperature

The thermal conductivity of ten amorphous alloys has been measured between 280 and 500 K. The thermal conductivity, K, can be separated into the electronic (Ke) and phonon (Kph) contributions. The electronic thermal conductivity, deduced from the Wiedemann–Franz law, varies almost linearly with temperature, whereas the phonon thermal conductivity shows a slower increase. At 300 K, Kph accounts for 34–49% of K. The phonon mean free path l is 12.5 A for the binary alloy Fe80B20, but l decreases as the number of chemical components increases, reaching 7 A for the five‐component alloys Fe32Ni36Cr14P12B6 and Co66Fe4Mo2B12Si16. The metal‐metal glasses, Cu70Zr30 and Cu45Zr55, have l values slightly larger than 11 A, indicating that they have short‐range order similar to that of Fe80B20.

Specific heat and thermal diffusivity of strontium barium niobate (Sr1−xBaxNb2O6) single crystals

The specific heat and thermal diffusivity of Sr1−xBaxNb2O6 (x=0.33 and 0.48) single crystals have been measured between 130 and 500 K, and the sound velocity has been measured at 295 K. At x=0.33 the specific heat shows a broad peak at 335 K, indicating the onset of a ferroelectric phase transition. The peak sharpens and shifts to about 383 K at x=0.48. A jump in the thermal diffusivity D is observed at the transition. Away from the transition, however, D is roughly independent of temperature. There is very little anisotropy in D, with the value along the a axis marginally higher than that along the c axis. Outside the transition region the phonon mean free path l is approximately constant, and has values of 5.1 and 5.6 A, respectively, below and above the transition. The low values of D and l are due to the disorder arising from the random distribution of five Sr/Ba ions over six possible sites in a unit cell.

Thermal conductivity of metallic glasses

The thermal diffusivity D of three metallic glasses Fe80B20, Fe40Ni40P14B6, and Fe32Ni36Cr14P12B6 has been measured from 160 to 500 K by the laser‐flash radiometry method and the thermal conductivity K has been calculated from these data. The accuracy of D and K is 6% and 8%, respectively. The electronic contribution (Ke) to the thermal conductivity, evaluated by using the Wiedemann–Franz law, increases almost linearly with increasing temperature. The phonon thermal conductivity Kph follows the temperature dependence exhibited by all amorphous dielectrics, i.e., Kph is roughly proportional to the phonon specific heat, thus giving an approximately constant phonon mean free path. When the metalloid atom B is replaced by P or the number of chemical components in the alloy is increased, both Ke and Kph decrease, but the drop in Kph is much more significant. The phonon mean free paths for Fe80B20 and Fe40Ni40P14B6 are 14 and 12 A, respectively, which are substantially higher than the values (5–8 A) for amorpho...

Elastic Moduli of Injection-Molded Short-Fiber-Reinforced Poly(ether-ether-ketone)

The nine independent elastic constants of injection-molded bars of poly(ether-ether-ketone) reinforced with 30% by weight of carbon fibers and 20% and 30 % by weight of glass fibers have been determined by ultrasonic techniques. The tensile and shear moduli increase with increasing fiber volume fraction, with the tensile modulus along the longitudinal (mold flow) direction showing the greatest change. The longitudinal tensile modulus of 30 weight % carbon- and glass-fiber-reinforced composites exceeds the tensile modulus of the matrix by factors of 6 and 3, respectively. By regarding the injection-molded bar as a multidirectional laminate comprising a large number of uni directional plies, the elastic moduli have been calculated and found to agree closely with the experimental data.