| 1. |
- Hamawandi, Bejan, PhD, et al.
(författare)
-
A Comparative Study on the Thermoelectric Properties of Bismuth Chalcogenide Alloys Synthesized through Mechanochemical Alloying and Microwave-Assisted Solution Synthesis Routes
- 2020
-
Ingår i: Frontiers in Materials. - : Frontiers Media S.A.. - 2296-8016. ; 7
-
Tidskriftsartikel (refereegranskat)abstract
- The way a material is synthesized and processed has an immense effect on its microstructure, which in turn has a big impact on its transport properties. Here, we compare the thermoelectric (TE) properties of n- and p-type Bi2−xSbxTe3 (x: 0 and 1.5) materials synthesized through two different routes, specifically mechanochemical alloying (MA)—as a solid-state synthesis route—and microwave(MW)-assisted polyol synthesis—as a solution synthesis route. Reaction time is significantly reduced in the MW synthesis, leading to significantly lower energy consumption (i.e., higher energy efficiency) per batch than using the MA route. The resultant materials are compared for their crystallinity, phase purity, morphology, and microstructure. Spark plasma sintering was used to prepare pellets, and the resultant consolidates were evaluated for their transport properties. TE properties and microstructure of the specimens were investigated in relation to processing conditions and composition. MA samples formed fused structures (from 200 nm to several micrometers in size) composed of smaller particles. MW-synthesized materials exhibited hexagonal platelet morphology, high crystallinity, and phase purity. They also showed lower thermal conductivity, leading to a higher resultant TE figure-of-merit ZT. TE properties of Bi2−xSbxTe3 samples were studied on sintered cylindrical pellet samples, where the highest ZT values achieved were 1.04 (at 440 K) for MW-Bi2Te3 and 0.76 (at 523 K) for MW-Bi0.5Sb1.5Te3 samples, while MA-Bi2Te3 and MA-Bi0.5Sb1.5Te3 samples showed maximum ZT values of 0.74 (at 460 K) and 0.27 (at 300 K), respectively, as n- and p-type TE materials. The observed trend is much higher ZT values for MW samples, ascribed to their higher degree of texturing and nanostructured grains reducing the thermal conductivity, thus achieving a better overall performance, verifying the prospect to enhance ZT using MW-assisted solution synthesis approach.
|
|
| 2. |
- Hamawandi, Bejan, PhD, et al.
(författare)
-
Composition Tuning of Nanostructured Binary Copper Selenides through Rapid Chemical Synthesis and their Thermoelectric Property Evaluation
- 2020
-
Ingår i: Nanomaterials. - : MDPI. - 2079-4991. ; 10:5
-
Tidskriftsartikel (refereegranskat)abstract
- Reduced energy consumption and environmentally friendly, abundant constituents are gaining more attention for the synthesis of energy materials. A rapid, highly scalable, and process-temperature-sensitive solution synthesis route is demonstrated for the fabrication of thermoelectric Cu2−xSe. The process relies on readily available precursors and microwave-assisted thermolysis, which is sensitive to reaction conditions; yielding Cu1.8Se at 200 °C and Cu2Se at 250 °C within 6–8 min reaction time. Transmission electron microscopy (TEM) revealed crystalline nature of as-made particles with irregular truncated morphology, which exhibit a high phase purity as identified by X-ray powder diffraction (XRPD) analysis. Temperature-dependent transport properties were characterized via electrical conductivity, Seebeck coefficient, and thermal diffusivity measurements. Subsequent to spark plasma sintering, pure Cu1.8Se exhibited highly compacted and oriented grains that were similar in size in comparison to Cu2Se, which led to its high electrical and low thermal conductivity, reaching a very high power-factor (24 µW/K−2cm−1). Density-of-states (DOS) calculations confirm the observed trends in electronic properties of the material, where Cu-deficient phase exhibits metallic character. The TE figure of merit (ZT) was estimated for the materials, demonstrating an unprecedentedly high ZT at 875 K of 2.1 for Cu1.8Se sample, followed by 1.9 for Cu2Se. Synthetic and processing methods presented in this work enable large-scale production of TE materials and components for niche applications.
|
|
| 3. |
- Hamawandi, Bejan, PhD, et al.
(författare)
-
Facile Solution Synthesis, Processing and Characterization of n- and p-Type Binary and Ternary Bi-Sb Tellurides
- 2020
-
Ingår i: Applied Sciences. - : MDPI AG. - 2076-3417. ; 10:3
-
Tidskriftsartikel (refereegranskat)abstract
- The solution synthesis route as a scalable bottom-up synthetic method possesses significant advantages for synthesizing nanostructured bulk thermoelectric (TE) materials with improved performance. Tuning the composition of the materials directly in the solution, without needing any further processing, is important for adjusting the dominant carrier type. Here, we report a very rapid (2 min) and high yield (>8 g/batch) synthetic method using microwave-assisted heating, for the controlled growth of Bi2-xSbxTe3 (x: 0-2) nanoplatelets. Resultant materials exhibit a high crystallinity and phase purity, as characterized by XRD, and platelet morphology, as revealed by SEM. Surface chemistry of as-made materials showed a mixture of metallic and oxide phases, as evidenced by XPS. Zeta-potential analysis exhibited a systematic change of isoelectric point as a function of the material composition. As-made materials were directly sintered into pellets by using spark plasma sintering process. TE performance of Bi2-xSbxTe3 pellets were studied, where the highest ZT values of 1.04 (at 440 K) for Bi2Te3 and 1.37 (at 523 K) for Sb2Te3 were obtained, as n- and p-type TE materials. The presented microwave-assisted synthesis method is energy effective, a truly scalable and reproducible method, paving the way for large scale production and implementation of towards large-area TE applications.
|
|
| 4. |
- Lalegani, Z., et al.
(författare)
-
Modeling, design, and synthesis of gram-scale monodispersed silver nanoparticles using microwave-assisted polyol process for metamaterial applications
- 2020
-
Ingår i: Optical materials (Amsterdam). - : Elsevier BV. - 0925-3467 .- 1873-1252. ; 108
-
Tidskriftsartikel (refereegranskat)abstract
- High-yield monodispersed silver (Ag) nanospheres were modeled, designed, and synthesized by microwaveassisted (MW-assisted) polyol method from AgNO3, polyvinyl pyrrolidone (PVP), and ethylene glycol (EG), as precursors, at 145 degrees C within a short reaction time of 2 min, and the results were compared to those of conventional polyol method. Maintaining the PVP:AgNO3 molar ratio, the effect of increasing the amounts of AgNO3 and PVP at a constant amount of EG (40 mL) on the final product was evaluated. The synthesized nanoparticles (NPs) were characterized by SEM, UV-Vis spectroscopy, FTIR and DLS analysis. The results showed that with increasing the amount of AgNO3 to 0.5 and 1 g, monodispersed Ag nanoparticles (Ag NPs) with particle sizes of 54 and 61 nm were formed, as per the plasmon absorption peaks at 436 and 442 nm, respectively. Moreover, using 40 mL of the EG solution, we could obtain a high yield of the NPs (similar to 90%). The sub-gram yield was excellently high, offering great opportunities for commercializing the procedure. Also, the proposed study paves a new way for Ag NPs realization for different practical applications ranging from MW to optics.
|
|
| 5. |
- Rastan, Hamidreza, et al.
(författare)
-
Heat transfer study of enhanced additively manufactured minichannel heat exchangers
- 2020
-
Ingår i: International Journal of Heat and Mass Transfer. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0017-9310 .- 1879-2189. ; 161
-
Tidskriftsartikel (refereegranskat)abstract
- Three-dimensional (3D) printing, known as additive manufacturing, provides new opportunities for the design and fabrication of highly efficient industrial components. Given the widespread use of this technique by industries, 3D printing is no longer limited to building prototypes. Instead, small-to-medium scale production units focus on reducing the cost associated with each part. Among the various industrial components that can be developed with this manufacturing technology are heat transfer components such as heat exchangers. To this end, this study investigated the heat transfer characteristics of minichannel-based heat exchangers embedded with longitudinal vortex generators, both experimentally and numerically. Three enhanced prototypes with different vortex generator design parameters and a smooth channel as a reference case were printed with an aluminum alloy (AlSi10Mg) using direct metal laser sintering (DMLS). The rectangular minichannel had a hydraulic diameter of 2.86 mm. Distilled water was used as the test fluid, and the Reynolds number varied from 170 to 1380 (i.e., laminar flow). Prototypes were tested under two different constant heat fluxes of 15 kW m(-2) and 30 k m(-2). The experimental results were verified with a commercial simulation tool, Comsol Multiphysics (R), using the 3D conjugate heat transfer model. In the case of the smooth channel, the experimental results were also compared with well-known correlations in the field. The results showed that 95% and 79% of the experimental data were within 10% of the numerical simulation results and the values from the existing correlations, respectively. For the channel enhanced with the vortex generators, the numerical predictions agreed well with the experimental results. It was determined that the vortex generators can enhance the convective heat transfer up to three times with the designed parameter. The findings from this research underline the potential of additive manufacturing in the development of more sophisticated minichannel heat exchangers.
|
|
| 6. |
- Saladino, Giovanni, et al.
(författare)
-
Click chemical assembly and validation of bio-functionalized superparamagnetic hybrid microspheres
- 2020
-
Ingår i: Applied Nanoscience. - : Springer Nature. - 2190-5509 .- 2190-5517.
-
Tidskriftsartikel (refereegranskat)abstract
- Surface derivatized magnetic nanoparticles have been commonly used for magnetic separation. Facile mechanisms are needed to be developed for the design of bio-functionalized magnetic hybrid materials, where the surfaces can be re-generated for the re-use of the developed platforms. Superparamagnetic iron oxide nanoparticles with a diameter below 10 nm were synthesized via a novel microwave-assisted hydrothermal method in the presence of citrate ions, which allowed to obtain uniform and negatively charged nanoparticles. These were then coupled with Poly-l-lysine (PLL), forming micrometer-sized self-assembled spherical entities. Cross-linking the PLL within these microspheres with glutaraldehyde stabilized them chemically and mechanically. The active bio-functionality was introduced by a protein grafting methodology, using m-maleimidobenzoyl-N-hydroxysulfosuccinimide ester (SMBS). The Moringa oleifera Coagulant Protein (MOCP) from a seed extract was employed for its characteristic coagulation activity. The performance of the MOCP functionalized microspheres was evaluated as a function of turbidity removal of problematic colloidal clay from water via magnetic separation, resulting in over 80% of activity within 15 min. Surface of these hybrid materials can be re-generated by treatment with alcohol, allowing their easy magnetic separation and re-use. The rapid and strong response with tunable magnetic property makes these hybrid microspheres a powerful tool for many potential applications, due to the general applicability of the developed methodology.
|
|
