Composite films of poly(3-hexylthiophene) and single- as well as multi-walled carbon nanotubes are demonstrated to offer a competitive thermoelectric performance. The power factor significantly exceeds values obtained with either constituent alone provided that the conjugated polymer is sufficiently p-doped. The use of single-walled carbon nanotubes consistently results in a higher electrical conductivity with a maximum value above 103 S cm−1 and thus gives rise to a power factor of 25 ± 6 μW m−1 K−2 for a filler content of only 8 wt% and a maximum 95 ± 12 μW m−1 K−2 for 42–81 wt%. Moreover, a carbon nanotube content of 8–10 wt% does not compromise the low bulk thermal conductivity of the polymer matrix, which promises a high figure of merit of at least ZT > 10−2 at room-temperature. All samples are cast on plastic substrates, emphasising their suitability for large-area, flexible thermoelectric applications.

Thermoelectric composites of poly(3-hexylthiophene) and carbon nanotubes with a large power factor

New measurements of the thermal conductivity of stainless steel AISI 304L over the temperature range 300 to 550 K are reported. To perform the measurements, the transient hot-wire technique was employed, with a new wire sensor. The sensor makes use of a soft silicone paste material and of two thin polyimide films, between the hot wires of the apparatus and the stainless steel specimen. The transient temperature rise of the wire sensor is measured in response to an electrical heating step over a period of 40 μs to 2 s, allowing an absolute determination of the thermal conductivity of the solid, as well as of the polyimide film and the silicone paste. The method is based on a full theoretical model with equations solved by a two-dimensional finite-element method applied to the exact geometry. At the 95% confidence level, the standard deviation of the thermal conductivity measurements is 0.6%, while the standard uncertainty of the technique is less than 1.5%.

Measurement of the Thermal Conductivity of Stainless Steel AISI 304L Up to 550 K

Spectral collocation method for transient thermal analysis of coupled conductive, convective and radiative heat transfer in the moving plate with temperature dependent properties and heat generation

Abstract Nanosecond-pulsed, infrared (1064 nm) laser irradiation was used to create metal oxide coatings on the surface of polished stainless steel 304L austenite for application as color markings and unique tags/identifiers. By rastering a Gaussian-shaped, focused laser beam across a specimen in air, continuous metal oxide coatings were grown to thicknesses in the range of 20 to ~ 500 nm. Oxide coating thickness generally increased with laser fluence. However, for large accumulated fluences in excess of ~ 600–800 J/cm2, oxide growth was affected by evaporation and particle ejection resulting in a decreased coating thickness. Transmission electron microscopy and X-ray diffraction revealed that oxide coatings developed a polycrystalline, spinel structure having a lattice constant = 8.4 A (consistent with MnCr2O4 and Fe3O4). Pulsed laser irradiation and oxide growth modified the composition of stainless steel substrates by reducing the Cr and Mn concentration within the melt zone. The reflectance and chromaticity of laser-fabricated oxide coatings were characterized using spectrophotometry. These optical properties are described in the context of measured oxide thicknesses.

Nanosecond Pulsed Laser Irradiation of Stainless Steel 304L: Oxide Growth and Effects on Underlying Metal.

Nanosecond-pulsed, infrared (1064 nm) laser irradiation was used to create metal oxide coatings on the surface of polished stainless steel 304L austenite for application as color markings and unique tags/identifiers. By rastering a Gaussian-shaped, focused laser beam across a specimen in air, continuous metal oxide coatings were grown to thicknesses in the range of 20 to ~ 500 nm. Oxide coating thickness generally increased with laser fluence. However, for large accumulated fluences in excess of ~ 600–800 J/cm2, oxide growth was affected by evaporation and particle ejection resulting in a decreased coating thickness. Transmission electron microscopy and X-ray diffraction revealed that oxide coatings developed a polycrystalline, spinel structure having a lattice constant = 8.4 A (consistent with MnCr2O4 and Fe3O4). Pulsed laser irradiation and oxide growth modified the composition of stainless steel substrates by reducing the Cr and Mn concentration within the melt zone. The reflectance and chromaticity of laser-fabricated oxide coatings were characterized using spectrophotometry. These optical properties are described in the context of measured oxide thicknesses.

Nanosecond pulsed laser irradiation of stainless steel 304L: Oxide growth and effects on underlying metal

A compilation and critical analysis of the thermal conductivity (γ) of AISI 304 stainless steel (SS) between 100 and 1707 K has been given in the literature. The author represented his “recommended” values of λ by an inflection in the A versus temperature relationship between 300 and 500 K. Because a physical mechanism had not been identified that would produce such a temperature dependence in γ of 304 SS, interest was generated in the possible existence of an as yet undiscovered phenomenon that might cause such an inflection. Consequently, experimental verification of the inflection was sought. The present paper presents recent measurements of λ, the electrical resistivity, and the absolute Seebeck coefficient of 304L SS from 300 to 1000 K and of the thermal diffusivity (α) from 297 to 423 K. The λ values computed from the a measurements were within ± 1.6% of the directly measured λ An inflection was not observed in the temperature dependence of λ between 300 and 500 K. After careful evaluation and because a physical mechanism still has not been identified which would produce such an inflection, the authors conclude that the inflection in the λ vs T relationship reported in the literature was caused by the data analysis technique.

T. G. Kollie

Papers

The thermal conductivity of AISI 304L stainless steel