My research interests includes Thermoelectric(TE) materials (Direct conversion of waste heat in to useful electric energy), specially, synthesis of nanocomposites and characterization of novel thermoelctric materials for enhancing TE performance. Currently, I am working on the fabrication of hierarchical -nanostructured p-type BiSbTe based thermoelectric materials and their transport properties at ambient temperature.
The dispersion of nanoparticles in the host matrix is a novel approach to enhance the thermoelect... more The dispersion of nanoparticles in the host matrix is a novel approach to enhance the thermoelectric performance. In this work, we incorporate the TiC (x = 0, 1 and 2 wt.%) nanoparticles into a p-type Bi0.5Sb1.5Te3 matrix, and their effects on microstructure and thermoelectric properties were systematically investigated. The existence of TiC contents in a base matrix was confirmed by energy dispersive X-ray spectroscopy analysis. The grain size decreases with increasing the addition of TiC content due to grain boundary hardening where the dispersed nanoparticles acted as pinning points in the entire matrix. The electrical conductivity significantly decreased and the Seebeck coefficient was slightly enhanced, which attributes to the decrease in carrier concentration by the addition of TiC content. Meanwhile, the lowest thermal conductivity of 0.97 W/mK for the 2 wt.% TiC nanocomposite sample, which is ~16% lower than 0 wt.% TiC sample. The maximum figure of merit of 0.90 was obtained...
Journal of Materials Science: Materials in Electronics, 2021
Thermoelectric devices are environmentally friendly renewable energy sources that use waste heat ... more Thermoelectric devices are environmentally friendly renewable energy sources that use waste heat to generate electricity. So far, p-type Bi–Sb–Te-based alloys with high thermoelectric properties were fabricated using low-dimensional and single growth methods as small-scale, laboratory-grown samples. However, large-scale fabrication processes are required for commercial applications of thermoelectric devices. In this work, large amounts (2–3 kg) of p-type 20%Bi2Te3–80%Sb2Te3 alloy powders were fabricated using the gas atomization (GA) process under an inert gas atmosphere. Subsequently, a large-scale sample, 64 mm thick and 25 mm in diameter, was consolidated from the as-fabricated GA powders using spark plasma sintering at 673 K. The homogeneity of the microstructure, density, thermoelectric properties, and mechanical properties of the high-thickness sintered bulk were systematically investigated at various positions. The EBSD texture analysis revealed that an almost similar microstructure existed in all positions of the bulk sample, which was comprised of a mixture of coarse grains and fine grains randomly distributed throughout the matrix. The peak electrical conductivity of 1100 Ω−1 cm−1 was obtained from the top position of the thick sample, which had a relatively higher carrier mobility. The maximum power factor of 3.96 mW/mK2 was achieved by the top part of the specimen, because of its higher electrical conductivity. The lowest thermal conductivity of 0.964 W/mK at 350 K was obtained from the bottom part of the specimen. As a result, the maximum figure of merit, ZT of 1.25 was achieved in the bottom position of the high-thickness sample. Homogeneous (within 5% of variation) thermoelectric transport properties were observed throughout the fabricated high-thickness sintered sample, regardless of position.
Abstract In this study, equiatomic CoCrFeMnNi high entropy alloy (HEA) was fabricated by inductio... more Abstract In this study, equiatomic CoCrFeMnNi high entropy alloy (HEA) was fabricated by induction melting and subsequent thermomechanical treatments were carried out to achieve single FCC phase with equiaxed grains. The friction and wear behavior of HEA was investigated using ball-on-disc configuration in dry and ambient conditions under different sliding time, normal load and velocity. The detailed microscopic characterizations were invested to examine the worn surface and subsurface deformation mechanisms to identify the kinds of wear involved during dry sliding process. Results revealed the hardness of deformed layer showed 63% higher than matrix owing to grain refinement induced by sliding friction. The friction coefficient stabilized at longer sliding time due to oxidized wear debris acting as as lubricant behavior during sliding. While wear rate significantly decreased with increasing sliding time due to oxidation of wear debris on worn surface and formation of deformed layer with grain refinement resists the plastic deformation by strengthening the subsurface layers. On the other hand, wear rate stabilized for 6 and 8 N due to worn surface oxidation and subsurface hardening. Moreover, wear rate stabilized at higher sliding velocity owing to balance between subsurface hardening and delamination behavior.
In this work, Nd–Fe–B alloy powders are fabricated via high energy ball milling and their fractur... more In this work, Nd–Fe–B alloy powders are fabricated via high energy ball milling and their fracture behavior and magnetic properties are investigated at different milling times. The powder characteristics (particle shape, size, size distribution, and microstructure) and magnetic properties of the Nd–Fe–B alloys are systematically analyzed. The initial spherical Nd–Fe–B powder is cracked/crushed even after a short period of milling (30 s) due to the high impact energy generated during high energy ball milling. These randomly cracked polygonal-shaped powders are fragmented after 5 min of milling and converted to fine powders. Interestingly, the fine particles after milling for 5 min are conducive to agglomeration at longer milling times (20–60 min) and formed spherically-shaped agglomerated powder. Additionally, the sphericity of the powder increased to 92% by re-pulverization and agglomeration at 60 min. The milled powder shows the Nd2Fe14B phase, and the x-ray diffraction patterns ex...
Abstract For economic viability of thermoelectric modules, issues of scalability and sturdiness t... more Abstract For economic viability of thermoelectric modules, issues of scalability and sturdiness to drive down production and manufacturing cost must be adequately addressed. In this study, we report a large-scale production of 3 Kg/batch of 75%Sb2Te3-25%Bi2Te3 powder by gas atomization. The as-produced large-scale atomized powder was subsequently sintered by hot isostatic pressing (HIP) at two different temperatures. The microstructure of the HIPed fracture surface reveals a transgranular mode of fracture in the basal plane of the grains perpendicular to the contact surface. The texture analysis showed that grains were randomly distributed and indicating no preferred alignment in any direction. The sample HIPed at 450 °C shows the highest electrical conductivity of 1350 Ω−1 cm−1 at room temperature due to their high carrier mobility. The highest ZT of 1.15 at 375 K was observed for the sample HIPed at 450 °C owing to their high electrical conductivity, and reasonable low thermal conductivity.
Journal of Korean Powder Metallurgy Institute, 2017
In this study, Bi-Sb-Te thermoelectric materials are produced by mechanical alloying (MA) and spa... more In this study, Bi-Sb-Te thermoelectric materials are produced by mechanical alloying (MA) and spark plasma sintering (SPS). To examine the influence of the milling atmosphere on the microstructure and thermo-electric (TE) properties, a p-type Bi-Sb-Te composite powder is mechanically alloyed in the presence of argon and air atmospheres. The oxygen content increases to 55% when the powder is milled in the air atmosphere, compared with argon. All grains are similar in size and uniformly, distributed in both atmospheric sintered samples. The Seebeck coefficient is higher, while the electrical conductivity is lower in the MA (Air) sample due to a low carrier concentration compared to the MA (Ar) sintered sample. The maximum figure of merit (ZT) is 0.91 and 0.82 at 350 K for the MA (Ar) and MA (Air) sintered samples, respectively. The slight enhancement in the ZT value is due to the decrease in the oxygen content during the MA (Ar) process. Moreover, the combination of mechanical alloying and SPS process shows a higher hardness and density values for the sintered samples.
In this research, p-type BiSbTe/ZrO2 nanocomposite powders were fabricated by high-energy ball mi... more In this research, p-type BiSbTe/ZrO2 nanocomposite powders were fabricated by high-energy ball milling. Different weight percentages of ZrO2 (2, 4, and 6 wt. %) nanoparticles were incorporated into the bulk (BiSbTe) matrix by consolidation of as-synthesized nanocomposites (NCs) powder by spark plasma sintering at 673 K. The phase and existence of ZrO2 nano-inclusions was confirmed by X-ray diffraction and transmission electron microscopy-selected area electron diffraction analysis. The Seebeck coefficient of the BiSbTe/ZrO2 NCs was significantly improved (∼36% for 4 wt. % added NCs) by a decrease in the carrier concentration and energy filtering effect, whereas the thermal conductivity was much reduced via strong scattering of carriers/phonons. The peak thermoelectric figure-of-merit (1.34 ± 0.06) was obtained for BiSbTe into which 2 wt. % ZrO2 was dispersed, which was approximately 20% greater than that of the undispersed sample. The hardness of the nanocomposites was significantly...
Abstract (GeTe)x(AgSbTe2)100−x: TAGS thermoelectrics are an attractive class of materials due to ... more Abstract (GeTe)x(AgSbTe2)100−x: TAGS thermoelectrics are an attractive class of materials due to their combination of non-toxicity and good conversion efficiency at mid-temperature ranges. In the present work, we have utilized energy and time efficient high-pressure gas atomization and spark-plasma sintering techniques for large-scale preparation of samples with varying composition (i.e., (GeTe)x(AgSbTe2)100−x where x = 75, 80, 85, and 90). High-temperature x-ray diffraction was used to understand the phase transformation mechanism of the as-atomized powders. Detailed high-resolution transmission electron microscopy of the sintered samples revealed the presence of nanoscale precipitates, antiphase, and twin boundaries. The nanoscale twins and antiphase boundaries serve as phonon scattering centers, leading to the reduction of total thermal conductivity in TAGS-80 and 90 samples. The maximum ZT obtained was 1.56 at 623 K for TAGS-90, which was ∼94% improvement compared to values previously reported. The presence of the twin boundaries also resulted in a high fracture toughness (KIC) of the TAGS-90 sample due to inhibition of dislocation movement at the twin boundary.
The dispersion of nanoparticles in the host matrix is a novel approach to enhance the thermoelect... more The dispersion of nanoparticles in the host matrix is a novel approach to enhance the thermoelectric performance. In this work, we incorporate the TiC (x = 0, 1 and 2 wt.%) nanoparticles into a p-type Bi0.5Sb1.5Te3 matrix, and their effects on microstructure and thermoelectric properties were systematically investigated. The existence of TiC contents in a base matrix was confirmed by energy dispersive X-ray spectroscopy analysis. The grain size decreases with increasing the addition of TiC content due to grain boundary hardening where the dispersed nanoparticles acted as pinning points in the entire matrix. The electrical conductivity significantly decreased and the Seebeck coefficient was slightly enhanced, which attributes to the decrease in carrier concentration by the addition of TiC content. Meanwhile, the lowest thermal conductivity of 0.97 W/mK for the 2 wt.% TiC nanocomposite sample, which is ~16% lower than 0 wt.% TiC sample. The maximum figure of merit of 0.90 was obtained...
Journal of Materials Science: Materials in Electronics, 2021
Thermoelectric devices are environmentally friendly renewable energy sources that use waste heat ... more Thermoelectric devices are environmentally friendly renewable energy sources that use waste heat to generate electricity. So far, p-type Bi–Sb–Te-based alloys with high thermoelectric properties were fabricated using low-dimensional and single growth methods as small-scale, laboratory-grown samples. However, large-scale fabrication processes are required for commercial applications of thermoelectric devices. In this work, large amounts (2–3 kg) of p-type 20%Bi2Te3–80%Sb2Te3 alloy powders were fabricated using the gas atomization (GA) process under an inert gas atmosphere. Subsequently, a large-scale sample, 64 mm thick and 25 mm in diameter, was consolidated from the as-fabricated GA powders using spark plasma sintering at 673 K. The homogeneity of the microstructure, density, thermoelectric properties, and mechanical properties of the high-thickness sintered bulk were systematically investigated at various positions. The EBSD texture analysis revealed that an almost similar microstructure existed in all positions of the bulk sample, which was comprised of a mixture of coarse grains and fine grains randomly distributed throughout the matrix. The peak electrical conductivity of 1100 Ω−1 cm−1 was obtained from the top position of the thick sample, which had a relatively higher carrier mobility. The maximum power factor of 3.96 mW/mK2 was achieved by the top part of the specimen, because of its higher electrical conductivity. The lowest thermal conductivity of 0.964 W/mK at 350 K was obtained from the bottom part of the specimen. As a result, the maximum figure of merit, ZT of 1.25 was achieved in the bottom position of the high-thickness sample. Homogeneous (within 5% of variation) thermoelectric transport properties were observed throughout the fabricated high-thickness sintered sample, regardless of position.
Abstract In this study, equiatomic CoCrFeMnNi high entropy alloy (HEA) was fabricated by inductio... more Abstract In this study, equiatomic CoCrFeMnNi high entropy alloy (HEA) was fabricated by induction melting and subsequent thermomechanical treatments were carried out to achieve single FCC phase with equiaxed grains. The friction and wear behavior of HEA was investigated using ball-on-disc configuration in dry and ambient conditions under different sliding time, normal load and velocity. The detailed microscopic characterizations were invested to examine the worn surface and subsurface deformation mechanisms to identify the kinds of wear involved during dry sliding process. Results revealed the hardness of deformed layer showed 63% higher than matrix owing to grain refinement induced by sliding friction. The friction coefficient stabilized at longer sliding time due to oxidized wear debris acting as as lubricant behavior during sliding. While wear rate significantly decreased with increasing sliding time due to oxidation of wear debris on worn surface and formation of deformed layer with grain refinement resists the plastic deformation by strengthening the subsurface layers. On the other hand, wear rate stabilized for 6 and 8 N due to worn surface oxidation and subsurface hardening. Moreover, wear rate stabilized at higher sliding velocity owing to balance between subsurface hardening and delamination behavior.
In this work, Nd–Fe–B alloy powders are fabricated via high energy ball milling and their fractur... more In this work, Nd–Fe–B alloy powders are fabricated via high energy ball milling and their fracture behavior and magnetic properties are investigated at different milling times. The powder characteristics (particle shape, size, size distribution, and microstructure) and magnetic properties of the Nd–Fe–B alloys are systematically analyzed. The initial spherical Nd–Fe–B powder is cracked/crushed even after a short period of milling (30 s) due to the high impact energy generated during high energy ball milling. These randomly cracked polygonal-shaped powders are fragmented after 5 min of milling and converted to fine powders. Interestingly, the fine particles after milling for 5 min are conducive to agglomeration at longer milling times (20–60 min) and formed spherically-shaped agglomerated powder. Additionally, the sphericity of the powder increased to 92% by re-pulverization and agglomeration at 60 min. The milled powder shows the Nd2Fe14B phase, and the x-ray diffraction patterns ex...
Abstract For economic viability of thermoelectric modules, issues of scalability and sturdiness t... more Abstract For economic viability of thermoelectric modules, issues of scalability and sturdiness to drive down production and manufacturing cost must be adequately addressed. In this study, we report a large-scale production of 3 Kg/batch of 75%Sb2Te3-25%Bi2Te3 powder by gas atomization. The as-produced large-scale atomized powder was subsequently sintered by hot isostatic pressing (HIP) at two different temperatures. The microstructure of the HIPed fracture surface reveals a transgranular mode of fracture in the basal plane of the grains perpendicular to the contact surface. The texture analysis showed that grains were randomly distributed and indicating no preferred alignment in any direction. The sample HIPed at 450 °C shows the highest electrical conductivity of 1350 Ω−1 cm−1 at room temperature due to their high carrier mobility. The highest ZT of 1.15 at 375 K was observed for the sample HIPed at 450 °C owing to their high electrical conductivity, and reasonable low thermal conductivity.
Journal of Korean Powder Metallurgy Institute, 2017
In this study, Bi-Sb-Te thermoelectric materials are produced by mechanical alloying (MA) and spa... more In this study, Bi-Sb-Te thermoelectric materials are produced by mechanical alloying (MA) and spark plasma sintering (SPS). To examine the influence of the milling atmosphere on the microstructure and thermo-electric (TE) properties, a p-type Bi-Sb-Te composite powder is mechanically alloyed in the presence of argon and air atmospheres. The oxygen content increases to 55% when the powder is milled in the air atmosphere, compared with argon. All grains are similar in size and uniformly, distributed in both atmospheric sintered samples. The Seebeck coefficient is higher, while the electrical conductivity is lower in the MA (Air) sample due to a low carrier concentration compared to the MA (Ar) sintered sample. The maximum figure of merit (ZT) is 0.91 and 0.82 at 350 K for the MA (Ar) and MA (Air) sintered samples, respectively. The slight enhancement in the ZT value is due to the decrease in the oxygen content during the MA (Ar) process. Moreover, the combination of mechanical alloying and SPS process shows a higher hardness and density values for the sintered samples.
In this research, p-type BiSbTe/ZrO2 nanocomposite powders were fabricated by high-energy ball mi... more In this research, p-type BiSbTe/ZrO2 nanocomposite powders were fabricated by high-energy ball milling. Different weight percentages of ZrO2 (2, 4, and 6 wt. %) nanoparticles were incorporated into the bulk (BiSbTe) matrix by consolidation of as-synthesized nanocomposites (NCs) powder by spark plasma sintering at 673 K. The phase and existence of ZrO2 nano-inclusions was confirmed by X-ray diffraction and transmission electron microscopy-selected area electron diffraction analysis. The Seebeck coefficient of the BiSbTe/ZrO2 NCs was significantly improved (∼36% for 4 wt. % added NCs) by a decrease in the carrier concentration and energy filtering effect, whereas the thermal conductivity was much reduced via strong scattering of carriers/phonons. The peak thermoelectric figure-of-merit (1.34 ± 0.06) was obtained for BiSbTe into which 2 wt. % ZrO2 was dispersed, which was approximately 20% greater than that of the undispersed sample. The hardness of the nanocomposites was significantly...
Abstract (GeTe)x(AgSbTe2)100−x: TAGS thermoelectrics are an attractive class of materials due to ... more Abstract (GeTe)x(AgSbTe2)100−x: TAGS thermoelectrics are an attractive class of materials due to their combination of non-toxicity and good conversion efficiency at mid-temperature ranges. In the present work, we have utilized energy and time efficient high-pressure gas atomization and spark-plasma sintering techniques for large-scale preparation of samples with varying composition (i.e., (GeTe)x(AgSbTe2)100−x where x = 75, 80, 85, and 90). High-temperature x-ray diffraction was used to understand the phase transformation mechanism of the as-atomized powders. Detailed high-resolution transmission electron microscopy of the sintered samples revealed the presence of nanoscale precipitates, antiphase, and twin boundaries. The nanoscale twins and antiphase boundaries serve as phonon scattering centers, leading to the reduction of total thermal conductivity in TAGS-80 and 90 samples. The maximum ZT obtained was 1.56 at 623 K for TAGS-90, which was ∼94% improvement compared to values previously reported. The presence of the twin boundaries also resulted in a high fracture toughness (KIC) of the TAGS-90 sample due to inhibition of dislocation movement at the twin boundary.
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