Thermoelectric inks and power factor tunability in hybrid films through all solution process

Thermoelectric (TE) materials can have a strong benefit to harvest thermal energy if they can be applied to large areas without losing their performance over time. One way of achieving large-area films is through hybrid materials, where a blend of TE materials with polymers can be applied as coating. Here, we present the development of all solution-processed TE ink and hybrid films with varying contents of TE Sb2Te3 and Bi2Te3 nanomaterials, along with their characterization. Using (1-methoxy-2-propyl) acetate (MPA) as the solvent and poly (methyl methacrylate) as the durable polymer, large-area homogeneous hybrid TE films have been fabricated. The conductivity and TE power factor improve with nanoparticle volume fraction, peaking around 60–70% solid material fill factor. For larger fill factors, the conductivity drops, possibly because of an increase in the interface resistance through interface defects and reduced connectivity between the platelets in the medium. The use of dodecanethiol (DDT) as an additive in the ink formulation enabled an improvement in the electrical conductivity through modification of interfaces and the compactness of the resultant films, leading to a 4–5 times increase in the power factor for both p- and n-type hybrid TE films, respectively. The observed trends were captured by combining percolation theory with analytical resistive theory, with the above assumption of increasing interface resistance and connectivity with polymer volume reduction. The results obtained on these hybrid films open a new low-cost route to produce and implement TE coatings on a large scale, which can be ideal for driving flexible, large-area energy scavenging technologies such as personal medical devices and the IoT

Design, Synthesis and Characterization of Nanostructured Thermoelectric Materials

The demand for energy is rapidly increasing, triggering more carbon emission and global warming. Alternative green energy sources are essential to secure the future generation from the effect of pollution and global warming. During the last few decades, thermoelectric (TE) materials gained interest, due to their capability of directly interconverting between heat and power, which can be used to convert waste heat to electricity.  One of the strategic TE adaptation approaches is to develop high efficiency TE materials from earth-abundant and non-toxic components. Not only the TE materials’ composition, but also the synthesis method, has to be environment friendly in order to create a green transition, with minimum adverse environmental impacts. Bottom-up microwave (MW) assisted synthesis routes, using water and polyalcohol as green solvents were demonstrated feasible to generate binary and ternary compositions of Bi2-xSbxTe3, which were effective in room temperature. A more earth abundant and environment friendly material composition, copper selenide (Cu2-XSe), effective at intermediate temperature regime (200-600 °C), was synthesized by MW-assisted thermolysis. The synthesized materials were characterized in terms of structure, microstructure, surface chemistry and TE transport properties, and showed significant improvement of TE performance compared to materials synthesized using conventional methods - mainly attributed to the preservation of nanostructure. Significant results have been achieved with improved material characteristics, while the time and the energy investment were substantially reduced. The developed processes with reduced time and carbon footprint offer excellent sustainable synthesis routes for large-scale synthesis of high-performance nanostructured TE materials as strategic energy materials. Efterfrågan på energi ökar snabbt, vilket leder till mer koldioxidutsläpp och global uppvärmning. Alternativa gröna energikällor är nödvändigt för att skydda kommande generationer från effekterna av miljöföroreningar och global uppvärmning. Under de senaste decennierna har intresset för termoelektriska (TE) material ökat på grund av deras förmåga att direkt omvandla spillvärme till elektricitet. En av strategierna för TE-anpassning är att utveckla effektiva TE-material från i jordskorpan vanligt förekommande och ogiftig föreningar. Inte bara TE-materialens sammansättning, utan också hur de syntetiseras, bör vara miljövänligt för att skapa en grön övergång med minimal negativ miljöpåverkan. Grön mikrovågsassisterad botten upp syntes med vatten och sockeralkohol som lösningsmedel visades vara en möjlig metod för att generera binära och ternära föreningar av Bi2-xSbxTe3, vilka är effektiva vid rumstemperatur. Den i jordskorpan vanligt förekommande och miljövänliga kemiska föreningen kopparselenid (Cu2-XSe), vilken är effektivt vid mellantemperaturer (200-600°C), har syntetiseras genom MW-assisterad termolys. De syntetiserade materialen karakteriserades av deras struktur, mikrostruktur, ytkemi och termoelektriska transportegenskaper och visade betydande förbättringar av TE-prestanda jämfört med material syntetiserade med konventionella metoder, vilket primärt kan tillskrivas bevarandet av nanostrukturer. Betydande resultat har uppnåtts med överlägsna materialegenskaper, samtidigt som tid och energiåtgång reducerats avsevärt. Den utvecklade processen, med minskad tidsåtgång och koldioxidavtryck, erbjuder hållbara syntesvägar för storskalig syntes av effektiva TE-material med nanostrukturer för strategiska energimaterial

Formation of NiGeSn Material for Thermoelectric Applications

Group IV-based nanowires are excellent designed thermoelectric materials for high temperature applications. Ni silicide (germanide) has been widely used to reduce the contact resistance for group IV nanowires. In this work, the interaction of Ni with relaxed, compressive and tensile strained GeSn was investigated. The layers were epitaxially grown by chemical vapor deposition in temperature range 290-350 °C and the phase transformation of germanides was studied for three different rapid thermal annealing (RTA) temperatures of 350, 450, and 550 °C. The germanide layers were characterized using scanning electron microscopy, high resolution X-ray diffraction, and four point resistivity measurements. The results showed that NiGeSn phase with lowest resistivity is formed at 450 °C annealing and was stable up to 550 °C. The thermal stability of NiGeSn is dependent on the type, amount of the strain and the Sn content. The thickness of germanide layer for a certain RTA treatment was dependent on strain

The Effect of Adding V and Nb Microalloy Elements on the Bake Hardening Properties of ULC Steel before and after Annealing

Bake hardening (BH) is a vital part of special steel production. Studies in this field have focused on steels under homogeneous yielding, but until now, none have been conducted on the phenomena that occur for steels under heterogeneous yielding. In the current study, the effect of adding Nb and V alloying elements on the strength of ultra-low carbon (ULC) steel after bake hardening was investigated. The effects of pre-strain, grain size, and recrystallization annealing temperature were analyzed, as well as the effect of Nb and V on the yield stress caused by the bake hardening process. For this purpose, five types of alloys with different V and Nb contents were melted, cast in an induction furnace, and subjected to hot hammering and hot rolling. Then, cold rolling was applied to the samples by ~80%. To eliminate the effects of cold working, tensile samples were subjected to recrystallization annealing at 750 and 800 °C for 30 min, and the samples were quickly quenched in a mixture of a NaCl solution and ice. The annealed samples were subjected to a pre-tensile strain in the range of 2–12% and then aged in a silicone oil bath at 180 °C for 30 min. Then they were subjected to a tensile test. The obtained results showed that with the increase of the pre-strain and the annealing temperature, the values of baking hardness increased. The presence of V in the composition of steel reduced the annealing temperature

Anisotropic Magnetoresistance Evaluation of Electrodeposited Ni80Fe20 Thin Film on Silicon

In this study, a simple growth of permalloy NiFe (Py) thin films on a semiconductive Si substrate using the electrochemical deposition method is presented. The electrodeposition was performed by applying a direct current of 2 mA/cm2 during different times of 120 and 150 s and thin films with different thicknesses of 56 and 70 nm were obtained, respectively. The effect of Py thickness on the magnetic properties of thin films was investigated. Field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), atomic force microscopy (AFM), ferromagnetic resonance (FMR), anisotropic magnetoresistance (AMR), and magneto-optic Kerr effect (MOKE) analyses were performed to characterize the Py thin films. It was observed that the coercivity of the Py thin film increases by increasing the thickness of the layer. Microscopic images of the layers indicated granular growth of the Py thin films with different roughness values leading to different magnetic properties. The magnetic resonance of the Py thin films was measured to fully describe the magnetic properties of the layers. The magnetoresistance ratios of deposited Py thin films at times of 120 and 150 s were obtained as 0.226% and 0.235%, respectively. Additionally, the damping constant for the deposited sample for 120 s was estimated as 1.36 × 10−2, which is comparable to expensive sputtered layers’ characteristics

The Effect of Eco-Friendly Inhibitors on the Corrosion Properties of Concrete Reinforcement in Harsh Environments

In the present research, the synergistic effect of Arabic and guar gum inhibitors on the corrosion efficiency of concrete reinforcement was investigated. Thus, eight types of Arabic and guar gum combinations with 100, 250, 500, 750, and 1000 ppm were added to the steel reinforcement for 1, 7, 28, 48, and 72 days. The corrosion behavior of the samples was investigated by the electrochemical impedance (EIS) test. Water transmissibility, electrical resistivity, and compressive strength of concrete were also studied. The results showed that adding inhibitors generally increased the compressive strength of concrete. It was also found that water transmissibility was reduced by the addition of inhibitors. The electrical resistivity of the samples increased slightly with increasing time up to 72 days. EIS and Tafel results have demonstrated that Arabic and guar gums are effective inhibitors for reinforced concrete structures. Furthermore, scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) utilized to analyze the samples indicated that inhibitor grain size was enhanced by enhancing the concentration of the inhibitor combination, showing that the guar and Arabic inhibitor combinations were properly absorbed on the reinforcement surface. Results showed that a sample with 250 ppm Arabic gum and 250 ppm guar gum having a properly distributed inhibitor combination on the reinforcement surface creates a desirable cathode current

Microstructural Evolution during Accelerated Tensile Creep Test of ZK60/SiC_p Composite after KoBo Extrusion

In the current study, the creep properties of magnesium alloy reinforced with SiC particles were investigated. For this purpose, ZK60/SiCp composite was produced by the stir casting method following the KoBo extrusion and precipitation hardening processes. The creep tests were performed at 150 °C under 10–110 MPa. The results showed that the stress exponent (n) and the average true activation energy (Q) was changed at high stresses, was found with increasing stress, the creep mechanism changing from grain boundary sliding to dislocation climb. The results of microstructure characterization after the creep test showed that at low stresses, the dynamic recrystallization resulting from twinning induced the GBS mechanism. However, at high stresses, with increasing diffusion rates, conditions are provided for dynamic precipitation and the dislocation climb of the dominant creep mechanism. Examination of the fracture surfaces and the surrounding areas showed that the cavity nucleation in the ternary boundary and surrounding precipitation was the main cause of damage. The evaluation of the samples texture after creep showed that the unreinforced alloy showed a moderately strong fiber texture along the angle of ϕ1 = 0–90°, which was tilted about Φ = 10°. A new strong texture component was observed at (90°, 5°, 0°) for the composite sample, which crept due to minor splitting of the basal pole by ~5° toward RD

Characterization of the Nano-Rod Arrays of Pyrite Thin Films Prepared by Aqueous Chemical Growth and a Subsequent Sulfurization

Pyrite is an earth-abundant and low-cost material with a specific collection of properties including a low band gap and high absorption coefficient of solar light. These properties make pyrite a good choice in a wide variety of applications such as catalysts, batteries, and photovoltaic devices. A thin film composed of vertically aligned pyrite nano-rods was processed via a hydration-condensation method followed by subsequent aging and sulfurization. In this process, no ionic salt was used which resulted in a lower cost process with a lower level of impurities. Field emission scanning electron microscopy, X-ray diffraction, and Raman spectroscopy analyses were used to characterize the thin films in different steps of the process. The major impurity of the final thin films was the marcasite phase according to the Raman analysis which could be minimized by lowering sulfurizing time to about 60 min. In addition, after structural, electrical, and optical characterization of thin films, these layers’ performances in a photovoltaic device were also examined. After deposition of a thin aluminum layer, Schottky-type solar cells of pyrite formed which were then illuminated to measure their current-voltage characteristics. The results show that a combination of low-cost materials and a low-cost preparation method is applicable for building future solar cells

Investigation of Microstructure and Magnetic Properties of CH₄ Heat Treated Sr-Hexaferrite Powders during Re-Calcination Process

The microstructure and magnetic properties of methane (CH4) heat-treated Sr-hexaferrite powders during the re-calcination process were investigated and compared with the magnetic properties of conventionally synthesized Sr-hexaferrite powder. Gradual changes in the magnetic behavior of the produced powder in each re-calcination stage were investigated using magnetization curves obtained from the vibration sample magnetometry (VSM) technique. First, the initial Sr-hexaferrite powder was prepared by the conventional route. Then the powder was heat treated in a dynamic CH4 atmosphere in previously optimized conditions (temperature: 950 °C, gas flow rate:15 cc min−1 and time: 30 min), and finally, re-calcined in various temperatures from 200 to 1200 °C. By investigating the hysteresis loops, we found the transition temperature of soft to hard magnetic behavior to be 700 °C. The maximum ratio Mr/Ms was obtained at temperatures of 800–1100 °C. At 1100 °C, and despite the Sr-hexaferrite single phase, the magnetic behavior showed a multiphase behavior that was demonstrated by a kink in the hysteresis loop. Uniform magnetic behavior was observed only at 900 °C and 1000 °C. Although the ratio Mr/Ms was almost the same at these temperatures, the values of Mr and Ms at 1000 °C were almost double of 900 °C. At 1000 °C, the second quadrant of hysteresis curve had the maximum area. Therefore, 1000 °C was the optimum temperature for re-calcination after CH4 gas heat treatment in the optimized conditions. Due to the presence of a small amount of hematite soft phase at 1000 °C, the most probable reason for the exclusive properties of the optimized product may be the exchange coupling phenomenon between the hard Sr-hexaferrite phase and the impurity of the soft hematite phase

Microstructure, Mechanical and Thermal Properties of Al/Cu/SiC Laminated Composites, Fabricated by the ARB and CARB Processes

The aim of the current work is to investigate the effect of SiC particle weight percent and rolling passes on Al/Cu/SiC laminated composites, fabricated by accumulative roll-bonding (ARB) and cross-accumulative roll-bonding (CARB) processes. The optical microscopy (OM) images of composites revealed that despite the good bonding of the layers, they underwent plastic instabilities as a consequence of strain hardening of the layers. However, these instabilities occurred more in ARBed composites than in composites fabricated by the CARB process. This is because in the latter process, the composites are rolled in two directions, which leads to better strain distribution. Furthermore, with an increase in passes, SiC particles were well distributed in the matrix and interfaces. The mechanical findings showed that, by increasing passes, there was a growth in the values of strengths and elongation. This behavior is believed to be related to increased work-hardening of layers, better distribution of reinforcing particles, and an enhanced bonding of interfaces at higher rolling passes. In addition, the results of thermal conductivities showed a downward trend with an increase in passes; in fact, the increased number of Al/Cu interfaces declined the heat conduction of composites