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    Modification of tetrahedrite Cu12Sb4S13 thermoelectric performance via the combined treatment of mechanochemistry and composite formation
    (Elsevier, 2024) Balaz, Peter; Burcak, Arda Baran; Aydemir, Umut; Mikula, Andrzej; Nieroda, Pawel; Balaz, Matej; Findorakova, Lenka
    Tetrahedrite Cu12Sb4S13 with its low thermal conductivity represents a flagship in sulphide thermoelectrics. However, to achieve a reasonable figure-of-merit ZT (measure of thermoelectric efficiency), adequate doping or special sample processing is needed. In this work, a different approach (without doping) is illustrated for the two tetrahedrite-containing systems. In the First approach binary composite tetrahedrite Cu12Sb4S13/chalcopyrite CuFeS2 was prepared by mechanochemical leaching with the aim to obtain partly decomposed tetrahedrite. In this approach, the alkaline leaching medium (Na2S + NaOH) was applied to extract Sb from tetrahedrite thus changing its composition. The obtained composite (formed from its own phases in an intrinsic mode) shows low values of ZT = 0.0022@673 K in comparison with the non-treated tetrahedrite where ZT was 0.0090@673 K. In this case the extremely high electric resistivity (6-20 m Omega cm-1) was documented. In the second approach binary composite tetrahedrite Cu12Sb4S13/muscovite KAl2(AlSi3O10)(OH)2 (formed from its own and foreign phases in an extrinsic mode) was prepared by two-step mechanical activation in which combined treatment of industrial vibratory milling and subsequent laboratory planetary milling was applied. The addition of a foreign phase, muscovite, did not give extraordinary thermoelectric performance results. However, the two-step milling process (without the addition of foreign phase) gives the value of ZT = 0.752@673 K which belongs to the highest in the tetrahedrite thermoelectric community. In this case, the two-times increase in specific surface area and the increased amount of tetrahedrite in comparison to famatinite are suspectable for this effect. Both applied nontraditional approaches to synthesize tetrahedrite composites form a platform for potential modification of its thermoelectric performance.
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    AN OVERVIEW OF SURFACE ANALYSIS TECHNIQUES FOR CHARACTERIZATION OF MECHANICALLY ACTIVATED MINERALS
    (Taylor & Francis Inc, 2012) Erdemoglu, Murat; Balaz, Peter
    Surface characteristics of particles; such as structure, morphology, and chemical composition of surface have a major effect on its response to metallurgical processing operations. In order to understand the characteristics and reactivity of the system, information on the physical topography, the chemical composition, the chemical structure, the atomic structure, the electronic state, and a detailed description of bonding of molecules at the surface are required. Most of the instrumental techniques used for identification of major/minor and bulk/surface characteristics of substances now can be easily utilized as well for the characterization of mechanically activated minerals. This article is concerned with several representative identification techniques which are currently used for characterization of the materials prepared by mechanochemical processes. Fundamental aspects of spectroscopic (Infrared, Raman, and X-ray photoelectron), electron microscopic (Scanning electron microscopy and Transmission electron microscopy), and probe microscopic (Scanning tunneling microscopy and Atomic force microscopy) techniques used for surface characterization of mechanically activated minerals are overviewed.