Effect of Surfactant Addition on Bi2Te3 Nanostructures Synthesized by Hydrothermal Method

In the present work, we have prepared Bi2Te3 nanostructures with different morphologies such as nano-spherical, nanoplates and nanoflakes obtained using various surfactant additions (EG, PVP, and EDTA) by a hydrothermal method. The shape of the nanoparticles can be controlled by addition of surfactants. The samples were characterized by x-ray diffraction (XRD) and scanning electron microscopy (SEM). It is found that the minority BiOCl phase disappears after maintained pH at 10 with EG as surfactant. SEM bulk microstructure reveals that the sample consists of fine and coarse grains. Temperature dependence of thermoelectric properties of the nanostructured bulk sample was investigated in the range of 300-450K. The presence of nanograins in the bulk sample exhibits a reduction of thermal conductivity and less effect on electrical conductivity. As a result, a figure of merit of the sintered bulk sample reached 0.2 at 400 K. A maximum micro Vickers hardness of 102 Hv was obtained for the nanostructured sample, which was higher than the other reported results

Investigation of the Microstructure and Thermoelectric Properties of P-Type BiSbTe Alloys by Usage of Different Revolutions Per Minute (RPM) During Mechanical Milling

In this work, p-type Bi0.5Sb1.5Te3 alloys were fabricated by high-energy ball milling (MA) and spark plasma sintering. Different revolutions per minute (RPM)s were used in the MA process, and their effect on microstructure, and thermoelectric properties of p-type Bi0.5Sb1.5Te3 were systematically investigated. The crystal structure of milled powders and sintered samples were characterized using X-ray diffraction. All the powders exhibited the same morphology albeit with slight differences find at 1100 RPM conditions. A slight grain size refinement was observed on the fracture surfaces from 500 to 1100 RPM specimens. The temperature dependence of Seebeck coefficient, electrical conductivity, and power factors were measured as a function of temperature with different RPM conditions. The power factor shows almost same (~3.5 W/mK2 at RT) for all samples due to unchanged Seebeck and electrical conductivity values. The peak ZT of 1.07 at 375K is obtained for 1100 RPM specimen due to low thermal conductivity

Reduction of Thermal Conductivity Through Complex Microstructure by Dispersion of Carbon Nanofiber in p-Type Bi0.5Sb1.5Te3 Alloys

The influence of nano dispersion on the thermoelectric properties of Bi2Te3 was actively investigating to wide-spread thermoelectric applications. Herein this report, we have systematically controlled the microstructure of Bi0.5Sb1.5Te3 (BST) alloys through the incorporation of carbon nanofiber (CNF), and studied their effect on thermoelectric properties, and mechanical properties. The BST/x-CNF (x-0, 0.05, 0.1, 0.2 wt.%) composites powder was fabricated using high energy ball milling, and subsequently consolidated the powder using spark plasma sintering. The identification of CNF in bulk composites was analyzed in Raman spectroscopy and corresponding CNF peaks were recognized. The BST matrix grain size was greatly reduced with CNF dispersion and consistently decreased along CNF percentage. The electrical conductivity was reduced and Seebeck coefficient varied in small-scale by embedding CNF. The thermal conductivity was progressively diminished, obtained lattice thermal conductivity was lowest compared to bare sample due to induced phonon scattering at interfaces of secondary phases as well as highly dense fine grain boundaries. The peak ZT of 0.95 achieved for 0.1 wt.% dispersed BST/CNF composites. The Vickers hardness value of 101.8 Hv was obtained for the BST/CNF composites

Effect of Milling Time Parameter on the Microstructure and the Thermoelectric Properties of n-Type Bi2Te2.7Se0.3 Alloys

Nanostructured thermoelectric materials receiving great attention for its high thermoelectric performance. In this research, nanostructured n-type Bi2 Te2.7 Se0.3 alloys have prepared using high energy ball milling and followed by spark plasma sintering. Also, we have varied ball milling time to investigate milling time parameter on the thermoelectric properties of n-type Bi2 Te2.7 Se0.3 powder. The powders were discrete at 10 min milling and later particles tend to agglomerate at higher milling time due to cold welding. The bulk fracture surface display multi-scale grains where small grains intersperse in between large grains. The maximum Seebeck coefficient value was obtained at 20-min milling time due to their lower carrier density. The κ values were decreased with increasing milling time due to the decreasing trend observed in their κL values. The highest ZT of 0.7 at 350 K was observed for 30-min milling time which was ascribed to its lower thermal conductivity. The Vickers hardness values also greatly improved due to their fine microstructure

Large scale production of high efficient and robust p-type Bi-Sb-Te based thermoelectric materials by powder metallurgy

International audienceDevelopment of large scale high performance thermoelectric materials is one of the challenges in thermoelectric energy conversion. We have successfully fabricated large scale production (3–5 kg/min) of bismuth antimony telluride (Bi-Sb-Te) alloys by gas atomization (GA) and achieved a high figure of merit (ZT) value over unity (1) at 350 K. To get more performance from thermoelectric materials, we controlled the grain size of GA powders via mechanical milling (GA + MA) and consolidated the resultant nano powder by spark plasma sintering. The ZT values of GA + MA samples were greatly improved (15%) over those of GA bulk due to shifting control of their grain size from micron order to submicron order. The improved ZT values are due to the suppression of lattice thermal conductivity, which was drastically decreased due high scattering of phonons at numerous grain boundaries and twin boundaries. The mechanical properties were greatly improved (GA + MA sample hardness improved > 61% over the GA sample), which would provide impressive benefits for device fabrication and practical applications for thermoelectric energy conversion. © 2016 Elsevier Lt

Large scale production of high efficient and robust p-type Bi-Sb-Te based thermoelectric materials by powder metallurgy

Development of large scale high performance thermoelectric materials is one of the challenges in thermoelectric energy conversion. We have successfully fabricated large scale production (3–5 kg/min) of bismuth antimony telluride (Bi-Sb-Te) alloys by gas atomization (GA) and achieved a high figure of merit (ZT) value over unity (1) at 350 K. To get more performance from thermoelectric materials, we controlled the grain size of GA powders via mechanical milling (GA + MA) and consolidated the resultant nano powder by spark plasma sintering. The ZT values of GA + MA samples were greatly improved (15%) over those of GA bulk due to shifting control of their grain size from micron order to submicron order. The improved ZT values are due to the suppression of lattice thermal conductivity, which was drastically decreased due high scattering of phonons at numerous grain boundaries and twin boundaries. The mechanical properties were greatly improved (GA + MA sample hardness improved > 61% over the GA sample), which would provide impressive benefits for device fabrication and practical applications for thermoelectric energy conversion. © 2016 Elsevier Lt

Effect Of Different Mechanical Milling Processes On Morphology And Microstructural Changes Of Nano And Micron Al-Powders

In this research, effect of the various mechanical milling process on morphology and microstructural changes of nano and micron Al-powders was studied. The milling of Al-powders was performed by both high energy and low energy ball milling process. The influence of milling (pulverizing) energy on the structural changes of Al-powders was studied. Al-nanoparticles were agglomerated during the MA and its size was increased with increasing milling while micron Al-powder gets flattened shape during high energy ball milling due to severe plastic deformation. Meanwhile, structural evolution during high energy ball milling of the nano powder occurred faster than that of the micron powder. A slight shift in the position of X-ray diffraction peaks was observed in nano Al-powders but it was un-altered in macro Al-powders. The variation in lattice parameters was observed only for nano Al powders during the high energy ball milling due to lattice distortion

Wpływ różnych procesów mielenia na morfologię i mikrostrukturę nanometrycznych i mikronowych proszków Al

In this research, effect of the various mechanical milling process on morphology and microstructural changes of nano and micron Al-powders was studied. The milling of Al-powders was performed by both high energy and low energy ball milling process. The influence of milling (pulverizing) energy on the structural changes of Al-powders was studied. Al-nanoparticles were agglomerated during the MA and its size was increased with increasing milling while micron Al-powder gets flattened shape during high energy ball milling due to severe plastic deformation. Meanwhile, structural evolution during high energy ball milling of the nano powder occurred faster than that of the micron powder. A slight shift in the position of X-ray diffraction peaks was observed in nano Al-powders but it was un-altered in macro Al-powders. The variation in lattice parameters was observed only for nano Al powders during the high energy ball milling due to lattice distortion