Mid-temperature Range Research Articles

Mechanical properties, nano-tribological behavior and deformation mechanism of FeCrNi MEA with the addition of Co/Cu: Molecular dynamics simulation

During manufacturing processes, alloys face increasingly demanding requirements for their mechanical and tribological properties, underscoring the importance of revealing their deformation mechanisms. This study employed molecular dynamics simulation to construct models of FeCrNi (C1), FeCoCrNi (C2), FeCrNiCu (C3), and FeCoCrNiCu (C4), investigating the tribological properties of C1 alloy under various conditions and the mechanical properties across a wide temperature range (223–1073 K). The results indicate that the elastic modulus of the alloys follows the order C2 > C4 > C3 > C1 across the temperature range of 223 K to 1073 K. The elastic modulus increases with rising temperatures and decreases before rising once again as temperatures decrease. The phase transitions become more pronounced below 300 K. The addition of Co elements to the FeCrNi alloy contributes to fine-grain strengthening, uniform distribution of internal stress and strain, reduction in local stress concentration, and improvement of the alloy ductility and tensile strength. Compared to sliding friction, rolling friction reduces the number of worn atoms; however, the tensile and shear effects cause an increase in the stress gradient, leading to more severe subsurface damage and shear deformation. Temperature significantly affects the tribological properties of the alloys: phase transitions at high temperatures promote dislocation slip and plastic deformation, while at low temperatures, higher hardness and strength are observed. The roughness of stacking faults is greatly influenced by temperature, with an increase at the low-temperature range (223–273 K), a decrease in the mid-temperature range (273–673 K), and a smoother surface at the high-temperature range (673–1073 K). The research aims to provide a deeper understanding of the excellent mechanical and tribological properties of FeCrNi alloy at the micro/nano scales, thereby advancing their application and development in manufacturing processes.

Multiple defect states engineering towards high thermoelectric performance in GeTe-based materials

GeTe is a promising material for thermoelectric (TE) applications. However, its low Seebeck coefficient and high thermal conductivity in the mid-temperature range of 298–550 K have hindered its widespread use in TE devices. In this work, we show that a combination of band engineering, Fermi level tuning, and miscibility gap exploration can significantly improve the energy conversion performance of GeTe. Bi provides the optimized carrier concentration and induces band convergence, while Ga possibly forms a resonant state. The synergistic effects of Bi and Ga significantly improve the Seebeck coefficient from 38 µVK−1 for undoped GeTe to over 120 µVK−1 for Bi and Ga-containing materials at 298 K and provide a high power factor over a wide temperature range. Phonon scattering is strengthened by optimizing the microstructure through Pb-induced spinodal decomposition and enhanced point defect scattering due to increased dopant solubility, resulting in a very low lattice thermal conductivity of about 0.5 Wm-1K−1 at 600 K for the triple-doped samples. The maximum thermoelectric figure of merit ZT was significantly increased to 2.1 at 600 K for the Ge0.87Pb0.05Bi0.06Ga0.02Te sample due to the improved power factor and reduced lattice thermal conductivity. Additionally, the average figure of merit ZTave for this sample achieved a very high value of 1.4 for Ge0.87Pb0.05Bi0.06Ga0.02Te at a temperature gradient of 475 K (Tc = 298 K). The developed material shows great potential for use in energy conversion devices, with an estimated energy conversion efficiency exceeding 17 %.

Enhancement in power factor through rare-earth samarium doping in Cu2SnSe3 system

Cu2SnSe3 has drawn enough attention as a potential thermoelectric material due to its unique electronic and thermal properties. We present the impact of Sm doping on the Cu2SnSe3 system’s Sn site. The polycrystalline samples of Cu2Sn1-x Sm x Se3 (0 ≤ x ≤ 0.08) were prepared using the solid-state reaction technique followed by conventional sintering. The crystal structure was characterized using XRD and the results reveal that the samples have a diamond cubic structure with a space group of F4̄3m. Scanning Electron Microscopy (SEM) analysis indicates a uniform surface homogeneity within the sample. Furthermore, the introduction of Sm causes a reduction in porosity. The electrical transport characteristics were studied in the mid temperature range of 300–650 K. The Seebeck coefficient of all the samples were found to be positive within the temperature range under study, suggesting that holes constitute the majority charge carriers. This is also confirmed by the Hall measurements as the carrier concentration was positive for all the samples. The inclusion of Sm has led to a reduction of electrical resistivity and Seebeck coefficient and hence power factor of ~539 μW mK−2 for x = 0.08 at 630 K which is ten times greater as compared to x = 0 whose power factor is ~56 μW mK−2 at 630 K is achieved which makes it suitable for thermoelectric applications.

Comprehensive study of photoluminescence and device properties in Cu2Zn(Sn1−xGex)S4 monograins and monograin layer solar cells

Ge-alloying of Cu2ZnSnS4 is a promising strategy for producing wide-bandgap absorber materials suitable for use in tandem structures or indoor solar cell applications. Incorporating Ge can suppress Sn-related defects while maintaining the kesterite structure and p-type conductivity throughout the entire range of composition. In this study, Cu2Zn(Sn1−xGex)S4 monograins were synthesized in molten salt by the synthesis-growth method, where value x was varied from 0 to 1, with a step of 0.2. The inclusion of Ge into the crystals was confirmed by energy-dispersive X-ray spectroscopy, Raman spectroscopy, and X-ray diffraction analysis. The bandgaps of Cu2Zn(Sn1−xGex)S4 solid solutions were determined as Eg = 1.50–2.25 eV by external quantum efficiency measurement. A detailed study of temperature and laser power-dependent photoluminescence (PL) for powder crystals with x = 0, x = 0.2 and x = 0.4 revealed that the dominant recombination mechanisms originate from defect clusters involving a shallow acceptor and deep donor defect. Ge-alloying helped to suppress the harmful SnZn donor defects, but at the same time shifted the defects' energy levels deeper into the bandgap. The obtained activation energies indicate that the acceptor defect becomes shallower with the inclusion of Ge. At the mid-temperature range (T = 60–200 K), the presence of two different recombinations was revealed in the system, originating from very closely located PL emission bands.

Lattice Softening and Band Convergence in GeTe-Based Alloys for High Thermoelectric Performance.

GeTe-based alloys have been studied as promising TE materials in the midtemperature range as a lead-free alternate to PbTe due to their nontoxicity. Our previous study on GeTe1-xIx revealed that I-doping increases lattice anharmonicity and decreases the structural phase transition temperature, consequently enhancing the thermoelectric performance. Our current work elucidates the synergistic interplay between band convergence and lattice softening, resulting in an enhanced thermoelectric performance for Ge1-ySbyTe0.9I0.1 (y = 0.10, 0.12, 0.14, and 0.16). Sb doping in GeTe0.9I0.1 serves a double role: first, it leads to lattice softening, thereby reducing lattice thermal conductivity; second, it promotes a band convergence, thus a higher valley degeneracy. The presence of lattice softening is corroborated by an increase in the internal strain ratio observed in X-ray diffraction patterns. Doping also introduces phonon scattering centers, further diminishing lattice thermal conductivity. Additionally, variations in the electronic band structure are indicated by an increase in density of state effective mass and a decrease in carrier mobility with Sb concentration. Besides, Sb doping optimizes the carrier concentration efficiently. Through a two-band modeling and electronic band structure calculations, the valence band convergence due to Sb doping can be confirmed. Specifically, the energy difference between valence bands progressively narrows upon Sb doping in Ge1-ySbyTe0.9I0.1 (y = 0, 0.02, 0.05, 0.10, 0.12, 0.14, and 0.16). As a culmination of these effects, we have achieved a significant enhancement in zT for Ge1-ySbyTe0.9I0.1 (y = 0.10, 0.12, 0.14, and 0.16) across the entire range of measured temperatures. Notably, the sample with y = 0.12 exhibits the highest zT value of 1.70 at 723 K.

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Pure titanium due to its high corrosion resistance, low stiffness and good mechanical properties is commonly used in medicine for orthopaedic applications. However, its material properties (especially in the case of α\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\upalpha }$$\\end{document}-titanium) require a further enhancement to fulfil its role. The thermoplastic deformation in mid-temperature is proposed as a method for microstructure improvement. Titanium samples were compressed in different temperatures and strain rates to determine the best conditions for grain fragmentation—the main factor responsible for strength and hardness increase. The thermoplastic stress–strain curves were registered. Then microstructure observations and electron backscatter analysis were performed on the chosen samples. Finally, mechanical response of the previously deformed material was obtained in room temperature compression tests. A significant grain fragmentation was recorded for the material deformed in 400 ∘C\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{\\circ }\\hbox {C}$$\\end{document}, at 0.1/s and 1/s strain rates. Desirable results were also noticed for the deformation performed at 500–600 ∘C\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{\\circ }\\hbox {C}$$\\end{document}. However, high temperatures (700–800 ∘C\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{\\circ }\\hbox {C}$$\\end{document}) and strain rates (10/s) resulted in dynamic recrystallization, causing undesirable grain growth. An increase in hardness was observed in all cases, with higher values recorded in lower deformation temperatures. Room temperature compression tests revealed slight increase of ductility.

Artificial neural network aided unstable combustion state prediction and dominant chemical kinetic analysis

An ANN model was designed to predict unstable states in MILD combustion systems out of six kinds of input factors. The effectiveness of the established ANN model was validated, demonstrating accurate predictions for the imbalanced classification problem in systems described by both GRI3.0 and POLIMI2003 mechanisms. The predictions in high-dimensional parameter spaces revealed that unstable states are more likely to occur under stoichiometric conditions or in the presence of a reactive bath gas, such as CO2 or H2O. Additionally, these states could manifest in narrow parameter spaces, such as within a very confined mid-temperature range in a fuel-rich system with a low dilution level. Interestingly, the analysis of dominant reactions and feedback loops unveiled similarities in thermodynamic feedback mechanisms across a spectrum of parameter combinations. Meanwhile, feedback loops construct shortcut pathways on the level of oxidation extent and can facilitate the switching between high and low temperature chemistry.

Evolution of thermoelectric transport properties of Sb2Te3–Sb2Se3 solid-solution alloys depending on phase formation behavior

Sb2Te3-based alloys exhibit decent thermoelectric transport properties in the mid-temperature range above 550 K. However, the study on Sb2Te3 alloys has been limited in simple doping approach. Herein, evolution in the thermoelectric transport properties associated with the phase formation of solid solution alloys of Sb2(Te1−xSex)3 (x = 0, 0.25, 0.33, 0.5, 0.75, and 1.0) compositions is investigated to widen the strategy to solid solution alloying. A single phase of the Sb2Te3 rhombohedral structure formed from x = 0 to 0.5, whereas mixed phases with an orthorhombic structure of Sb2Se3 was observed at x = 0.75. The electrical conductivity weighted mobility were gradually decreased as Se content increases to x = 0.75. Consequently, the power factor was decreased gradually and significantly to 0.076 mW/mK2 for x = 0.75 (Sb2(Te0·25Se0.75)3) compared with 2.6 mW/mK2 of the pristine sample. The total thermal conductivity of 2.0 W/mK for the Sb2Te3 was significantly reduced gradually to 0.64 W/mK for x = 0.75 owing to simultaneous decrease in electrical and lattice thermal conductivities. The reduction in lattice thermal conductivity is mainly owing to the addition point defect scattering caused by the Se addition. Nevertheless, thermoelectric figure of merit zT of Sb2Te3 is gradually decreased from 0.64 to 0.11 for x = 0.75 at 650 K due to the degradation in electrical transport properties. Furthermore, the theoretical zT was estimated for all samples with varying carrier concentration based on single parabolic band model.

Incorporation of Ni in Cu2SnSe3: An insight into the reduction in electrical resistivity

In the present study, Cu2SnSe3/x% Ni (x = 0, 1, 2 and 3 wt%) composite thermoelectric were synthesized using solid-state reaction followed by sintering in the mid-temperature range 300–570 K. XRD studies revealed that the samples have a diamond cubic structure with the F4¯3m space group. Scanning Electron Microscopy indicates that the synthesized samples possess homogeneous surfaces with fewer pores. The sample with 3% Ni exhibits an approximately eight-fold increase in electrical conductivity than the pure sample at 307 K. However, the addition of Ni decreased the Seebeck coefficient, resulting in a lower overall power factor (PF) for the composites. The highest PF of ∼420 μW/mK2, was observed in the pristine sample at 570 K. Although Ni addition improves electrical properties, it negatively impacts the overall thermoelectric performance due to the significant reduction in Seebeck coefficient, thereby lowering the overall power factor.

Heavy elemental compound addition enhancing thermoelectric performance of Chromium Silicide synthesized by Spark plasma sintering

Silicide-based materials drive great potential in developing mid-temperature range thermoelectric generators (TEGs) applications. However, realizing the efficient and stable silicide materials is still a constraint for its real potential device applications. Chromium silicide will likely become p-type thermoelectric materials in this direction for thermoelectric power generation applications. However, high thermal conductivity values impede the figure-of-merit (zT). The present work adopts the chromium silicide, adding different weight percentages of well-known ZrCoSbSn compounds employing the compaction spark plasma sintering (SPS) technique. By adopting these combinations, the thermal conductivity is significantly reduced by enhanced scattering of heat-carrying phonons by multiple interfaces. Also, the maximum power factor value of ≃ 2.1 × 10−3 W/mK2 is achieved by employing a CrSi2 -ZrCoSbSn compound addition. The enhanced figure-of-merit value (zT) ≃ 0.26 is realized in the temperature at 623 K for the CrSi2-5wt% ZrCoSbSn compound material.

Mid-temperature CO2 Adsorption over Different Alkaline Sorbents Dispersed over Mesoporous Al2O3.

CO2 adsorbents comprising various alkaline sorption active phases supported on mesoporous Al2O3 were prepared. The materials were tested regarding their CO2 adsorption behavior in the mid-temperature range, i.e., around 300 °C, as well as characterized via XRD, N2 physisorption, CO2-TPD and TEM. It was found that the Na2O sorption active phase supported on Al2O3 (originated following NaNO3 impregnation) led to the highest CO2 adsorption capacity due to the presence of CO2-philic interfacial Al-O--Na+ sites, and the optimum active phase load was shown to be 12 wt % (0.22 Na/Al molar ratio). Additional adsorbents were prepared by dispersing Na2O over different metal oxide supports (ZrO2, TiO2, CeO2 and SiO2), showing an inferior performance than that of Na2O/Al2O3. The kinetics and thermodynamics of CO2 adsorption were also investigated at various temperatures, showing that CO2 adsorption over the best-performing Na2O/Al2O3 material is exothermic and follows the Avrami model, while tests under varying CO2 partial pressures revealed that the Langmuir isotherm best fits the adsorption data. Lastly, Na2O/Al2O3 was tested under multiple CO2 adsorption-desorption cycles at 300 and 500 °C, respectively. The material was found to maintain its CO2 adsorption capacity with no detrimental effects on its nanostructure, porosity and surface basic sites, thereby rendering it suitable as a reversible CO2 chemisorbent or as a support for the preparation of dual-function materials.

Melting and Solidification Characteristic of Mixture of Two Types of Latent Heat Storage Material in Direct Contact Heat Exchanger

ABSTRACT The aim of this study is to develop a latent heat storage system designed to utilize waste heat from industrial processes in the mid-temperature range of 100–200°C. Mannitol and a mixture of mannitol and erythritol, both classified as sugar alcohols, were utilized as phase change materials in this study. The present study investigated the melting and solidification characteristics of the mixture of C M = 70mass% (with a composition of 70% mannitol and 30% erythritol by mass) for latent heat storage at approximately 150°C. Additionally, the study aims to experimentally establish the thermal performance of the mixture of C M = 70mass% in a direct contact heat exchanger during melting and solidification. Comparative analysis with mannitol was conducted to determine the melting and solidification behavior of the mixture of C M = 70mass%. Moreover, the heat transfer characteristics, including heat storage and heat release speed, were investigated. Finally, the heat transfer mechanism of each phase change material (PCM) was considered through the overall heat transfer rate. keyword : Phase change material(PCM), Direct contact heat exchanger, Mixture of C M =70mass%, melting & soidification behaviors, Overall coefficient of heat transfer.

Multiscale Length Structural Investigation and Thermoelectric Performance of Double-Filled Sr0.2Yb0.2Co4Sb12: An Exceptional Thermal Conductivity Reduction by Filler Segregation to the Grain Boundaries.

Among thermoelectric materials, skutterudites are the most prominent candidates in the mid-temperature range applications. In the multiple-filled Sr0.2Yb0.2Co4Sb12 skutterudite, with Sr and Yb as fillers, we have enhanced the thermoelectric performance of CoSb3 through the reduction of lattice thermal conductivity and the optimization of carrier concentration and electrical conductivity. The high-pressure synthesis of the double-filled derivative promotes filling fraction fluctuation. This is observed by high angular resolution synchrotron X-ray diffraction, showing a phase segregation that corresponds to an inhomogeneous distribution of the filler atoms, located at the 2a positions of the cubic space group Im3̅. In addition, scanning transmission electron microscopy (STEM) combined with EELS spectroscopy clearly shows a segregation of Sr atoms from the surface of the grains, which is compatible with the synchrotron X-ray powder diffraction results. Mean square displacement parameters analysis results in Einstein temperatures of ∼94 and ∼67 K for Sr and Yb, respectively, and a Debye temperature of ∼250 K. The strong effect on resonant and disorder scattering yields a significantly lower lattice thermal conductivity of 2.5 W m-1 K-1 at 773 K. Still, good weighed-mobility values were obtained, with high filling fraction of the Yb and Sr elements. This drives a reduced electrical resistivity of 2.1 × 10-5 Ω m, which leads to a peak zT of 0.26 at 773 K. The analysis and results performed for the synthesized (Sr,Yb)-double filled CoSb3, shed light on skutterudites for potential waste-heat recovery applications.

A comprehensive review of entropy engineered GeTe: an antidote to phase transformation

Driven by the burgeoning demand for high performance eco-friendly thermoelectric materials in the mid-temperature range (573–773 K), we herein focus on GeTe based alloys exhibiting high ZT of >2.0 owing to their promising band structure.

Functionally separated electronic band engineering via multi-element doping plus high-density defects advances board-temperature-range thermoelectric performance in GeTe

GeTe has attracted widespread attention as an ideal mid-temperature thermoelectric (TE) material, but its peak performance within a narrow mid-temperature range limits the conversion efficiency improvement of future TE devices. Here, to achieve the overall enhancement of GeTe over a broad temperature range, especially near room temperature, we demonstrate the functionally separated electronic band engineering strategy (resonance energy levels and band convergence) coupling the construction of high-density defects by designing multi-element SnSe-In-Sb co-doping. Fundamentally, to distinguish the functions of selected elements, it was found that SnSe alloying mainly promotes the band convergence of GeTe in elevated temperatures, In doping can create the resonance energy level for enhancing the TE performance near room temperature, and Sb can optimize symmetry and the overall carrier concentration, thereby jointly improving the effective mass and Seebeck coefficient. Moreover, the construction of various phonon scattering centers including high-density Ge micro/nano-precipitates, van der Waals gaps, dislocations, and strong stress fields, strongly inhibits phonon transport. Benefiting from these synergistic effects, a peak ZT of ∼ 2.0 at 653 K, ZTave of ∼ 1.2 in the range from 303 to 803 K, and Vickers microhardness of ∼ 234 Hv are obtained in (Ge0.91In0.01Sb0.08Te)0.98(SnSe)0.02 sample. This study demonstrates a promising strategy to optimize thermoelectric performance by selectively co-doping functionally separated elements for developing high-performance TE materials.

Control of the tribological temperature dependence of hydrogenated amorphous carbon films by doping with W

While numerous strategies have been developed to enhance the high-temperature performance of amorphous carbon films, challenges persist regarding high coefficients of friction and wear rates within the mid-temperature range (200–300 °C). In this study, we developed a series of a-C:H(W) films with varying tungsten concentrations and systematically investigated their wear and friction characteristics using Al2O3 ceramic balls at different temperatures. The results reveal that the a-C:H(W) film (W3) with a WC target current of 0.3 A exhibits friction coefficients of 0.10 and 0.06 at 300 °C and 500 °C, respectively. The addition of hydrogen to the film enables stable lubrication in the intermediate temperature range. The presence of carbide facilitates the formation of a continuous protective layer during friction at 500 °C. Additionally, the inclusion of tungsten trioxide effectively reduces friction during high-temperature lubrication. Overall, this a-C:H(W) film shows promise in addressing the challenges of high-temperature wear in mechanical engineering applications under harsh operating conditions.

Examination of NCSL (near-coincidence site lattice) structures formed during β2 (Ni3-xTe2) precipitation in diffusion-bonded PbTe-Ni interfaces – A TEM study

Establishing dependable interconnects within thermoelectric (TE) modules is of utmost significance in ensuring the longevity and functionality of these solid-state devices. PbTe-based devices are used in mid-temperature range applications, with Ni being the most preferred interconnect. The available literature has focused primarily on optimizing the joining parameters. However, fine microstructural features have not been reported that can affect the local semiconducting and mechanical properties. This research paper presents novel findings regarding the formation of previously undiscovered fine (Ni3-xTe2) β2 precipitates resembling Widmanstätten morphology within the PbTe matrix during joining processes. PbTe and Ni discs are diffusion bonded at 600 °C for various holding times. The precipitation is studied through advanced analytical TEM/STEM techniques. The current study leads to two noteworthy observations: 1) specific orientation relationships were discovered between the two phases: [001] PbTe ‖ [001] β2, (020) PbTe ‖ (210) β2 and growth directions were along 〈100〉 in PbTe matrix phase. 2) Formation of near-coincidence site lattice (NCSL) structures occurring periodically at the growing fronts of these precipitates. Atomic scale lattice strain mapping indicates a cyclic state of compression and tension at these interfaces. These findings shed light on local composition changes and strain fields within the PbTe matrix during fine β2 precipitation, which has the potential to impact interface reliability.

Thermoelectric performance of lead-free manganese telluride via alkaline Mg doping for mid-temperature application

Manganese telluride (MnTe) is a potential p- type semiconducting thermoelectric material in the mid temperature range. Herein, magnesium (Mg) is incorporated with Manganese telluride (MnTe) in the stoichiometric ratio of Mn1.12−xMgxTe (x = 0, 0.025, 0.05, 0.075, 0.1) via vacuum sealing and hot press densification methods. The interstitial Mn atoms and Mg atoms create point defects and mass fluctuation, simultaneously. Stacking faults, twin boundaries and lattice dislocations are distinguished from HRTEM (High resolution transmission electron microscope). These defects are acting as a phonon scattering centers results in reduced total thermal conductivity of 0.827 W/mK at 653 K for Mn1.02Mg0.1Te. The excess Mn atoms in MnTe matrix and the substituted Mg atoms firmly contribute to improve the electrical conductivity by producing more acceptor levels, which significantly enhance the power factor of 439 µW/mK2 at 753 K for Mn1.07Mg0.05Te. Consequently, the maximum zT of 0.33 is achieved at 803 K for Mn1.07Mg0.05Te due to the synergistic effects of increased electrical property and reduced thermal conductivity.

Microwave-assisted acidic hydrolysis of phytate from rye bran – Experimental procedure and model prediction

Phytate is an abundant phosphorus (P) compound in plant material, which cannot be taken up by monogastric animals but is to a significant part released into the environment with excreta. In order to make use of cereals' phytate content, phytate hydrolysis by microwave-assisted thermal treatment of an acidic rye bran extract into inorganic phosphate was investigated experimentally and by modelling for process application. A phytate conversion of 98.5% could be achieved at 200 °C and 15 min reaction time and showed to be highly dependent on the temperature by a sigmoidal correlation. Treatment time showed its main influence in the mid temperature range (between 150 and 180 °C), thus didn't play a role anymore at beginning hydrolysis and towards full conversion. A mathematical quartic model represented phytate conversion with an optimum at harshest examined conditions and allows for predictions of the hydrolysis within the parameter range investigated. A kinetic model gives parameters of reaction order 0.68 and an activation energy of 118.7 kJ/mol with the option to predict phytate hydrolysis beyond the investigated parameter range and for varying input concentration. Equal liberation of all six phosphate groups from phytate is mechanistically suggested. Both model approaches show comparable results.

Improved thermoelectric power factor of multilayered poly(3,4-ethylenedioxythiophene) polystyrene sulfonate and Cu2Se thin films

Cu2Se is a promising thermoelectric material due to its superionic behavior with superior transport properties. Here we report a facile method of spin coating for the fabrication of multilayers of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) and Cu2Se thermoelectric materials for mid-temperature range applications. The synthesis of multilayered thin films with a unique organic-inorganic hybrid framework could be used in flexible thermoelectric devices. The detailed investigation of PEDOT:PSS and Cu2Se multilayered thin films reveals interaction between organic and inorganic material as inferred by AFM and FTIR. The electronic transport properties were investigated for all specimens, with the highest PF of 20.1 µW/m. K2 at 450 K was achieved from the bilayer stacking of Cu2Se and PEDOT:PSS, which is about 82 % higher as compared to that of pure PEDOT:PSS at the same temperature. These improved transport properties are the combined effect of energy filtering and interface effects. The proposed strategy opens up an avenue for research on chalcogenide based composite materials with an organic framework for flexible thermoelectric device applications.