Th. Kyratsi

Design of Ball-Milling Experiments on Bi2Te3 Thermoelectric Material

In this work, factorial ball-milling experiments have been applied to Bi2Te3 material, for the first time, aiming to investigate the effect of the main process parameters on the structural features and thermoelectric properties of the ball-milled materials. The selected main parameters were the duration of milling, the speed, and the ball-to-material ratio. Analysis suggests a strong effect of the speed and duration of processing, whereas the ball-to-material ratio is of minor importance. This approach is advantageous for better understanding of the milling mechanism and the importance of the role of each independent parameter as well as their interaction. All experiments led to nanocrystalline Bi2Te3, whose structural features were studied. The nanocrystalline size was estimated based on x-ray diffraction analysis, while transmission electron microscopy (TEM) studies were also performed to confirm the presence of nanoscale crystals. A mathematical model was developed based on statistical analysis for prediction of the crystalline size and the Seebeck coefficient of the nanopowders. The thermoelectric properties were also investigated on selected, highly dense pellets fabricated via hot-pressing of the nanopowders.

Seebeck and thermal conductivity analysis in amorphous/crystalline β-K2Bi8Se13 nanocomposite materials

In this work, ball milling is applied on β-K2Bi8Se13 compounds in order to explore the potential of the process for the fabrication of nano-based material. Polycrystalline β-K2Bi8Se13, synthesized from melt, was ball milled under inert atmosphere. Powder x-ray diffraction showed a significantly increased disorder with ball milling time. TEM studies confirmed the presence of nanocrystalline material in an amorphous matrix, suggesting the development of crystalline/amorphous β-K2Bi8Se13 nanocomposite material via ball milling process. Seebeck coefficient and thermal conductivity were analyzed based on the effective medium theory and show a significant contribution of a nanocrystalline phase.

Understanding the mechanical and thermal property reinforcement of crosslinked polyethylene by nanodiamonds and carbon nanotubes

A comprehensive investigation of the mechanical and thermal property reinforcement of silane-crosslinked polyethylene nanocomposites, containing small amounts of multi-walled carbon nanotubes (MWCNTs) and nanodiamonds (NDs), is presented in this work. Lower filler concentrations allowed a satisfactory dispersion, enabling the successful reinforcement of the matrix in every aspect. As the nanofiller content increased, the formed aggregates enlarged and the performance of the composites became more brittle. The measured stiffness enhancement of all the composites was found to be mainly influenced by the crystalline characteristics of the matrix and filler–matrix adhesion. Moreover, it was concluded that filler dispersion and filler–matrix interactions govern the ultimate strength and toughness behavior of these composites, which were found to slightly increase in minimum filler concentrations. Fractography was employed to study the embrittleness of the composites with higher filler loadings, and the observations revealed that a ductile to brittle transition is caused by a micro-deformation mechanism change in these composites. Furthermore, the prepared composites had a significantly improved thermal conductivity, which was mainly related to their superior specific heat capacity, while a great thermal stability enhancement was also revealed.

Electronic Structure and Thermoelectric Properties of Pseudoquaternary \(\hbox{Mg}_{2}\hbox{Si}_{1-x-y}\hbox{Sn}_{x}\hbox{Ge}_{y}\) -Based Materials

A theoretical study is presented on complex pseudoternary Bi-doped Mg2Si1-x-ySnxGey\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}

Influence of processing conditions on the thermoelectric properties of La1-xSrxCoO3 (x=0, 0.05)

\hbox{Mg}_{2}\hbox{Si}_{1-x-y}\hbox{Sn}_{x}\hbox{Ge}_{y}

Macro and Micro-Scale Features of Thermoelectric PbTe (Br, Na) Systems: Micro-FTIR Spectroscopy, Micro-Seebeck Measurements, and SEM/EDX Observations

\end{document} materials, which have recently been revealed to reach high thermoelectric figures of merit (ZT) of ∼1.4. Morphological characterization by scanning electron microscopy and energy-dispersive x-ray spectroscopy indicated that the investigated samples were multiphase and that the alloy with nominal composition Mg2Si0.55Sn0.4Ge0.05\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}

On the Use of Thermoelectric (TE) Applications Based on Commercial Modules: The Case of TE Generator and TE Cooler

\hbox{Mg}_{2}\hbox{Si}_{0.55}\hbox{Sn}_{0.4}\hbox{Ge}_{0.05}