Bemerkungen über thermokraft und widerstand
Summary
Any perturbation introduced into a metal will give rise to an increased resistance and to a change in the thermoelectric power. Under certain circumstances a parallelism between these two changes may be expected. After a short review of the theoretical formulae (§ l), the following cases are considered as well from a theoretical as from an experimental point of view; solid solutions, ferromagnetic substances (§ 2), cold worked and liquid metals (§ 3).
References (3)
- H. Pélabon
Ann. de Phys.
(1920)
Cited by (79)
Revisiting Precipitation kinetics in Mg-Zn alloy – a multi-characterization and modeling study
2023, Acta MaterialiaThis work aims to provide new insights into understanding precipitation kinetics in Mg-Zn alloys. First, the evolution of Zn solute, precipitate size and volume fraction is characterized using a combination of thermoelectric power, X-ray diffraction, atom probe tomography and transmission-electron microscopy in an Mg-1.7at.%Zn alloy when aged at 150 °C and 200 °C. The experimental results are then supported by a precipitation model based on classical nucleation and growth theories for rod and plate-shaped precipitates. It is found that rod-shaped precipitates are prevalent in the early aging stage, while plate-shaped precipitates dominate the over-aging stage. The kinetics of both precipitates are depicted in detail to represent this competition. Finally, a time-temperature-transformation diagram for these two types of precipitates is proposed for this system.
Precipitation sequence in Al-Sc-Zr alloys revisited
2022, MaterialiaSc and Zr additions to Al provide significant strengthening through the formation of Al3(Sc,Zr) L12 dispersoids. Fe impurities are always present in commercial Al alloys and the effect of these impurities on precipitation mechanisms in Al-Sc-Zr alloys remain poorly understood. This is particularly relevant when considering recycled aluminium as recycling results in the build-up of impurities. We used a combination of resistivity and thermo-electric power (TEP) measurements to monitor the evolution of solid solution during ageing of an Al-Sc, Al-Zr and Al-Sc-Zr alloy. Sc first comes out of solution to form Al3Sc dispersoids, followed by Zr to form Al3Zr. A range of Al3Sc-core/Al3Zr-shell faceted morphologies were observed with high angular annular dark field scanning transmission electron microscopy (HAADF-STEM). The presence of a new class of Fe-rich plate-like precipitates in the {100}Al was revealed via HAADF-STEM. The ordered positions of the precipitate and matrix reflections in the selected area diffraction pattern and in high-resolution TEM images reveal that these precipitates display a multi-layered structure. The centre of the plates is pseudo-icosahedral with apparent five-fold symmetry, and is rich in Fe. The outside layer has a L12 structure and is rich in Sc and Zr. The layered structure allows complete coherency with the aluminium matrix. These precipitates are highly anisotropic with a thickness of 5-10 nm and a length up to ∼1000 nm. This is the first report of the formation of this type of coherent pseudo-icosahedral precipitates in isothermal conditions which is named the D-phase.
Thermopower measurements in magnetic nanowires
2020, Magnetic Nano- and Microwires: Design, Synthesis, Properties and ApplicationsFerromagnetic nanowires (NWs) are a unique material system for studying electrical transport in a well-defined direction. The electrochemical synthesis allows nanometer-thin films in a nanometer diameter pore of an alumina membrane. This nanostructuring is especially interesting in the context of predicted size effects of the thermopowers of such systems. In the last two decades, literature focused mostly on two distinguishable systems, namely, multilayered magnetic/nonmagnetic NWs, and magnetic alloy NWs. In the present work, models to describe the thermopower and electrical resistance behavior of both systems are presented. The literature on Ni NWs as a characteristic system is analyzed as function of temperature and compared to literature of bulk Ni samples in order to evaluate the influence of nanostructuring on the thermopower. The magnetic field dependence throughout literature is evaluated and the relation of thermopower and electrical resistance is analyzed. Overall, the importance of the use of absolute thermopowers and a strong agreement with the Mott formula is found.
Over-ageing of an Al-Mg-Si alloy with silicon excess
2018, Materials Science and Engineering: AThe over-ageing of an Al-Mg-Si alloy with Silicon excess was investigated using global thermoelectric power (TEP) and hardness measurements combined with local techniques (Transmission Electron Microscopy (TEM) and Atom Probe Tomography (APT)), in order to highlight how the peak-aged microstructure obtained by a T6 treatment evolves in use conditions at temperatures between 100 °C and 350 °C, leading to a progressive loss of mechanical strength. First, TEP was found to be relevant to study the over-ageing kinetics of the alloy due to its perfect correlation with hardness and its sensitivity to the microstructural changes occurring after peak hardness. Then, APT and TEM observations clearly showed that over-ageing is due to the progressive replacement of the β″ phase by a succession of different types of semi-coherent phases (firstly, of Type B and then of Type A and Type C) and by an extensive precipitation of pure silicon particles. At the highest temperature (T = 350 °C), it was highlighted that the influence of manganese cannot be neglected. From these studies, an experimental Isothermal Transformation Curve could be proposed in the investigated temperature range. Lastly, the decrease in mechanical strength taking place during isothermal and non-isothermal ageing from a T6 state was experimentally characterised and successfully analysed using the JMAK formalism.
Investigation of carbon segregation during low temperature tempering in a medium carbon steel
2016, Materials CharacterizationLow temperature tempering is important in improving the mechanical properties of steels. In this study, the thermoelectric power method was employed to investigate carbon segregation during low temperature tempering ranging from 110 °C to 170 °C of a medium carbon alloyed steel, combined with micro-hardness, transmission electron microscopy and atom probe tomography. Evolution of carbon dissolution from martensite and segregation to grain boundaries/interfaces and dislocations were investigated for different tempering conditions. Carbon concentration variation was quantified from 0.33 wt.% in quenching sample to 0.15 wt.% after long time tempering. The kinetic of carbon diffusion during tempering process was discussed through Johnson-Mehl-Avrami equation.
Evolution of carbon distribution and mechanical properties during the static strain ageing of heavily drawn pearlitic steel wires
2016, Materials Science and Engineering: AThe static strain ageing of heavily cold-drawn pearlitic steel wires was investigated using both global techniques and local techniques (Atom Probe Tomography (APT)), in order to highlight how the cold-drawn destabilized microstructure returns to a more stable state during post-drawing treatments between 20 °C and 150 °C. The global techniques (thermoelectric power, differential scanning calorimetry) clearly showed that ageing occurs in three successive ageing stages and is due to a redistribution of the carbon atoms coming from the strain-induced cementite dissolution. The first ageing stage was unambiguously attributed to the carbon segregation to the defects, while the second and third stages were interpreted as being due to the precipitation of intermediate carbides (2nd stage) and cementite (3rd stage). The true strain was not found to significantly affect the ageing kinetics and mechanisms but appeared to play a role in the amount of carbon atoms involved in the different ageing stages. APT analyses confirmed that ageing is governed by the carbon depletion of strain-induced supersaturated ferrite. The strengthening mechanisms associated with the different ageing stages were also discussed.