Fabrication of a transversal multilayer thermoelectric generator with substituted calcium manganite

The sintering behavior and thermoelectric performance of Ca_0.99Gd_0.01Mn_0.99W_0.01O₃ was studied, and a multilayer thermoelectric generator was fabricated. The addition of CuO as sintering additive was found to be effective for the reduction in the sintering temperature from 1300°C to about 1000°C‐1050°C. Dense samples were obtained after firing at 1050°C, whereas some porosity remained after firing at 1000°C. Samples sintered at reduced temperature exhibit lower electrical conductivity, whereas the Seebeck coefficient S = ?150 μV/K at 100°C is not affected by lowering the sintering temperature. The figure of merit is ZT = 0.12 at 700°C for samples sintered at 1300°C; ZT = 0.08 and 0.03 were obtained for multilayer laminates sintered at 1050°C and 1000°C, respectively. A transversal multilayer thermoelectric generator (TMLTEG) was built by stacking layers of substituted CaMnO₃ green tapes, and printing AgPd conductor stripes onto the thermoelectric layers at an angle of 30° relative to the direction of the heat flow. The multilayer stack was co‐fired at 1000°C. The TMLTEG has a power output of 2.5 mW at ?T= 200 K in the temperature interval of 25°C‐300°C. A meander‐like generator with larger power output comprising six TMTEGs is also presented.     

Quality evaluation of pineapple fruit during drying process

Pineapple (Anana comosus) slices were dried by hot-air convective drying technique at fixed temperature (45, 60 and 75 °C) and constant air velocity of 1.5 m/s. The effect of drying conditions (drying time and air temperature) on the pineapple quality was evaluated. The quality of dehydrated pineapple was analyzed by color and texture changes, l-ascorbic acid loss and the ability of water uptake during rehydration procedure. Water uptake during rehydration was described by Page model. Statistical analysis of data revealed not significant difference (p > 0.05) among color and mechanical characteristics of pineapple samples dried at different drying temperatures to preset moisture content. Pineapple samples dried at 45 °C had better rehydration ability and more l-ascorbic acid retention than those obtained by air drying 75 °C. Hence, 45 °C drying temperature was best condition for pineapple quality preservation.     

Usage of solar-assisted spouted bed drier in drying of pea

The main objective of this study is to evaluate the effects of solar-assisted spouted bed and open sun drying on the drying rate and quality parameters of pea. Color, shrinkage, bulk and apparent densities, internal and bulk porosities, rehydration capacity and microstructure were the quality parameters investigated in dried product.Drying rate for solar-assisted spouted bed was about 3.5 times of drying rate for open sun drying. Air temperature changed between 20 °C and 27.4 °C during open sun drying while temperature of air at the inlet of solar-assisted spouted bed dryer varied between 35.3 °C and 65.5 °C during the experiments. Effective diffusivities were found to be 0.64 × 10^?10 and 3.27 × 10^?10 m²/s for open sun and solar-assisted spouted bed drying of pea, respectively. In color analysis, it was observed that a* value increased while b* value decreased for both drying methods. Bulk density and apparent density of peas dried under open sun was higher than that in solar-assisted spouted bed drier. In both drying methods, internal and bulk porosities decreased. Shrinkage was more for open sun dried samples. Rehydration capacity for solar-assisted spouted bed dried sample was higher than the one for open sun dried.     

Hydrothermal synthesis of V2O5 nanospheres as catalyst for hydrogen sulfide removal from sour water

Vanadium pentoxide (V₂O₅) nanospheres were synthesized hydrothermally for the first time with high specific surface area. The effect of different parameters including pH level, H₂O₂/H₂O volume ratio and reaction temperature on the precipitate yield was investigated, and the highest yield was attained at the pH level of 3, H₂O₂/H₂O volume ratio of 0.01 and the reaction temperature of 160 °C. Freeze drying, oven drying and vacuum drying methods along with auxiliary processes were employed to improve the drying process and minimize the aggregation of the synthesized nanoparticles (NPs). Two auxiliary processes were used prior to drying in the oven to improve the performance of drying. Firstly, precipitates were immersed in ethanol to get replaced in place of water molecules in a week. The precipitates were then dried at room temperature for a week to evaporate their moisture. In vacuum drying method, only the second auxiliary process was employed. In freeze drying technique, the segregate and uniform nanospheres of V₂O₅ were produced with an average diameter of 37 nm. Generally, the employed additional treatments cause the drying techniques to enhance and the extent of particles aggregation to reduce. Finally, the application of the synthesized NPs as catalyst was investigated for the elimination of H₂S from sour water with the initial concentration of 1300 ppm. The sour water was provided from Shiraz Oil Refinery Company. Results revealed that the synthesized NPs enable to completely eliminate hydrogen sulfide from sour water with 20% greater conversion at early contact seconds as compared to commercial V₂O₅ powder.     

Phase evolution and thermochromism of vanadium oxide thin films grown at low substrate temperatures during magnetron sputtering

Vanadium oxides (VO_x) have been studied extensively for applications in thermochromic materials, electrochomics, and infrared detectors due to their unique phase transition characteristics. However, various vanadium oxide phases usually occur under different deposition conditions due to their particularly complex vanadium-oxygen system. In this research, V₃O₇, VO₂(B), VO₂(M), and V₂O₅ thin films were obtained as pure or mixed phases by controlling the substrate temperatures between 250 °C and 400 °C during magnetron sputtering. The microstructure and phase composition of vanadium oxide thin films were characterized and analyzed using X-ray diffraction and Raman spectroscopy. The phase evolution was dependent on the substrate temperature and could be clarified. Metastable V₃O₇ and VO₂(B) phases were obtained at substrate temperatures of 250–300 °C, while stable VO₂ and V₂O₅ phases were obtained at 350–400 °C. The surface morphology and optical properties of vanadium oxide thin films with different substrate temperatures were investigated in detail. Our results provide methods for transforming vanadium oxide phases under well controlled substrate temperatures.     

Enhanced thermoelectric properties of 2H–MoS2 thin film by tuning post sulfurization temperature

Two-dimensional transition metal dichalcogenide semiconductors (TMDCs) like MoS₂ are becoming more popular as thermoelectric materials because they are abundant, nontoxic, and have good performance. In the study, the MoS₂ thin films have prepared by the sputtering and post-sulfurization process at various temperatures 450 °C, 550 °C, 650 °C, and 750 °C. The XRD data exhibits the formation of the 2H phase of MoS₂ thin film with (002), (004), and (006) planes. The Raman spectroscopy has confirmed the 2H–MoS₂ thin films with 2LA (M), A_1g, E_2g, and E_g vibrational modes. The SEM images have shown the thin MoS₂ flakes. The Seebeck and electrical conductivity data indicated an enhancement in Seebeck coefficient and electrical conductivity from 20 to 31 μV/^°C and 26–53 S/m, respectively, as the post sulfurization temperature increased from 450 °C to 750 °C. The enhancement of the Seebeck coefficient and electrical conductivity have been linked to the perfection of the 2H phase of MoS₂ film. The improved crystal structure has increased carrier mobility, leading to a high power factor of the 5.09 μWm^?1C^?2.     

Development and characterisation of a Y2Ti2O7-based glass-ceramic as a potential oxidation protective coating for titanium suboxide (TiOx)

A silica-based glass-ceramic, with Y₂Ti₂O₇ as the major crystalline phase, is designed, characterised and tested as an oxidation-protective coating for a titanium suboxide (TiO_x) thermoelectric material at temperatures of up to 600 °C. The optimised sinter-crystallisation treatment temperatures are found to be 1300 °C and 855 °C for a duration of 30 min, and this treatment leads to a glass-ceramic with cubic Y₂Ti₂O₇ and CaAl₂Si₂O₈ as crystalline phases. An increase of ~270 °C in the dilatometric softening temperature is observed after devitrification of the parent glass, thus further extending its working temperature range.Excellent adhesion of the glass-ceramic coating to the thermoelectric material is maintained after exposure to a temperature of 600 °C for 120 h under oxidising conditions, thus confirming the effectiveness of the T1 glass-ceramic in protecting the TiO_x material.     

Physical evaluation of pure zein films by atomic force microscopy and thermal mechanical analysis

Biodegradable edible films can be made from corn protein, α-zein. Pure zein films are cast from an organic solution of α-zein. This report outlines the surface conditions of such pure zein films. First, the transition temperature, T _t′ of the pure zein film was measured with a thermomechanical analyzer. T _t was between 167.0 and 172.7°C. The thermal elongation of the films depended on the drying conditions used during film preparation. Second, the surface microstructure of pure zein films, produced under several different drying conditions, was observed by atomic force microscopy. The surface had a morphology that showed depressions either with acutely (90–120°) or obtusely (121–180°) angled features depending upon the drying conditions. On the other hand, the surface microstructure after thermal elongation analysis appeared to have a pattern of projections that was repeated every 25 nm. Third, we measured the contact angle of the pure zein films. We found a correlation between surface microstructure and contact angle. Pure zein films with projections smaller than 200 nm in base diameter on the surface had a high contact angle (>70°).     

Energy requirements and production cost of the spray drying process of cheese whey

The influence of spray drying conditions on the energy required, production cost, and physicochemical characteristics of cheese whey was researched. The factors investigated were the inlet air temperature (180–220°C), outlet air temperature (80–100°C), and silica and maltodextrin (DE-10) as additives at 2 and 5% (w/w), respectively. Analysis of variance revealed that the inlet and outlet air temperatures, and the addition of additives had significant effects (p?T_inlet of 180°C, T_outlet of 80°C, and the addition of 5% additive material. Under these conditions, 0.2165?kg/h of dried product was obtained, with a moisture content of 2.08% and water activity of 0.125, and the product cost was $17.06?kg with an energy consumption of 2.0490?kW?·?h/kg of dry product.     

A micro sensor based on TiO2 nanorod arrays for the detection of oxygen at room temperature

A new micro gas sensor based on the TiO₂ nanorod arrays (NRAs) was developed and its response properties to oxygen (O₂) at room temperature were investigated. The micro sensor combined a pair of micro interdigitated electrodes realized by the MEMS process and sensing materials based on the TiO₂ NRAs. The TiO₂ NRAs were selectively grown on the patterned straps of Ti/Pd films through the acid vapor oxidation (AVO) process. Relationship between the morphology of the TiO₂ NRAs and reaction temperatures was analyzed with the scanning electronic microscopy (SEM) and X-ray diffraction (XRD). The results indicate that the diameters of the TiO₂ NRs enlarged as the reaction temperature increased from 140 °C to 180 °C. The TiO₂ NRAs sensors showed a good response to O₂ at room temperature (25 °C) due to the large specific surface areas of the TiO₂ NRs and the TiO₂ NR/NR junctions. The TiO₂ NRAs sensors prepared at 140 °C for 3 h exhibited better response properties to O₂ at room temperature with a fast response and recovery time. The research indicates that the TiO₂ NRAs prepared by the simple AVO process is a good choice for detecting O₂ at room temperature.     

Formation and destruction of physical crosslinks by mild treatments in chemically crosslinked poly(vinyl alcohol) gels

We report the formation, destruction, and re-formation of the microcrystallites in a chemical PVA gel, crosslinked slightly by glutaraldehyde. The dried gel, in which the microcrystallites were formed, was immersed in a poor solvent of a mixture of DMSO and water at 8 °C, where the gel stayed in its collapsed state. The gels swelled on heating to 50 °C, but did not return to the initial state on cooling to 8 °C. After washing the gel completely in water, a drying process caused the microcrystallites to be re-formed and the gel could return to the initial dried state at 8 °C. By using XRD and FT-IR measurements, it was concluded that the formation and destruction of microcrystallites in chemically crosslinked PVA gels could be controlled by the mild treatments of initial drying, temperature change, and washing and drying.     

Effect of drying temperatures on starch-related functional and thermal properties of chestnut flours

The use of starchy flours in food systems greatly depends on the related functional properties of starch. The effect of drying temperatures on starch-related functional properties of flours obtained from fruits of the two most common Portuguese Castanea sativa varieties (Martainha and Longal) was evaluated. Flours were analysed for amylose and resistant starch contents, swelling ability, pasting properties and thermal characteristics. Drying temperature is positively correlated with amylose content, resistant starch and viscoamylographic properties, mainly the temperatures higher than 40 °C. Amylograms of fruits dried at 60 °C displayed higher peak viscosity (1370 B.U. and 2260 B.U. respectively for Longal and Martainha) when compared to the other temperatures tested (40 °C, 50 °C and 70 °C). Decreases in transition temperatures and in enthalpy evaluated by thermal analysis were observed with increasing drying temperatures, suggesting modifications in starch structure during the drying process. The effects of drying temperatures were more evident in Longal variety. The flours from the two chestnut varieties and from fruits dried at low temperatures and fruits dried at high temperature showed significant differences between the evaluated properties.     

Fast Response NO2 Gas Sensor Based on In2O3 Nanoparticles

In this research, hydrothermal‐calcination route was applied to synthesize In₂O₃ nanoparticles for gas sensor application. Hydrothermal synthesis with duration of 5 h at 180°C resulted in In(OH)₃ nanorods. Then, in the calcination step, considering controlled rate of heating and temperature, In₂O₃ nanoparticles with rough surfaces were obtained. In the next step, these nanoparticles were deposited by low frequency AC electrophoretic deposition between the interdigitated electrodes to fabricate gas sensor. Deposition in the frequency of 10 kHz resulted in the chained nanoparticles in the interelectrode space. At the end, gas sensitivity measurements were conducted at 150°C–300°C and revealed that fabricated sensor had fast response and recovery times to NO₂ gas.     

Activity and sulfidation behavior of the CoMo/Al2O3 hydrotreating catalyst: The effect of drying conditions

The influence of drying condition of the CoMo/Al₂O₃ catalyst prepared using citric acid as a chelating agent on the sulfidation behavior and on the catalytic activity to hydrodesulfurization of straight-run gas oil (SRGO) was investigated. The catalysts dried at 110, 220, 300 and 400 °C were studied using Raman, IRS and DTG techniques. The sulfidation behavior with straight-run gas oil spiked with dimethyldisulfide (DMDS) was investigated using gas chromatography (GC) with a thermal conductivity detector and GC with an atomic-emission detector for analysis of gas and the liquid phases, respectively. It was shown that the sulfidation behavior of the catalysts prepared using the chelating agents depends on the drying condition: the lower drying temperature, the later DMDS conversion and oxide precursor sulfidation starts. A higher activity in SRGO desulfurization was obtained with catalysts dried at 110 and 220 °C. This phenomenon was accounted for by the stabilization effect of chelating agent that retards precursor sulfiding but provides favorably the formation of active CoMoS phase and achieving the highest activity.     

Sol–Gel Synthesis and Characterization of Na0.5Bi0.5TiO3–NaTaO3Thin Films

Thin films with the composition 70 mol% Na_0.5Bi_0.5TiO₃ + 30 mol% NaTaO₃ were prepared by sol–gel synthesis and spin coating. The influence of the annealing temperature on the microstructural development and its further influence on the dielectric properties in the low‐ (kHz–MHz) and microwave‐frequency (15 GHz) ranges were investigated. In the low‐frequency range we observed that with an increasing annealing temperature from 550°C to 650°C the average grain size increased from 90 to 170 nm, which led to an increase in the dielectric permittivity from 130 to 240. The temperature‐stable dielectric properties were measured for thin films annealed at 650°C in the temperature range between ?25°C and 150°C. The thin films deposited on corundum substrates had a lower average grain size than those on Si/SiO₂/TiO₂/Pt substrates. The highest average grain size of 130 nm was obtained for a thin film annealed at 600°C, which displayed a dielectric permittivity of 130, measured at 15 GHz.     

Storage stability of vacuum-dried probiotic bacterium Lactobacillus paracasei F19

There is still lack of the insight into the storage stability of dry probiotics produced by vacuum drying. Therefore, in this study we assessed the stability of a vacuum-dried Lactobacillus paracasei F19 under varying storage conditions. L. paracasei F19 was vacuum-dried with and without sorbitol and trehalose. The dried cells were stored at 4, 20 and 37 °C, and at a_w = 0.07, 0.22 and 0.33. The survival was determined by viable counts on MRS agar plates. The inactivation rate constants were determined for each storage condition. The survival after drying of cells dried without and with trehalose and sorbitol was 29, 70 and 54%, respectively. All vacuum-dried cells were very stable at 4 °C. However, high stability at non-refrigerated temperatures was obtained only in the presence of sorbitol. In contrast to sorbitol, the supplementation of trehalose did not stabilize cells during storage. This is supposedly due to the rapid crystallization of trehalose during storage. While glass transition temperatures of dry cell-sorbitol increased from ?32 °C to 12 °C during storage at 37 °C and a_w = 0.07, T_g of dry cell-trehalose (?15 °C after drying) could not be determined after storage for only 24 h. In conclusion, we showed that high stability of probiotic cells at non-refrigerated temperatures could be obtained by vacuum drying process with appropriate protectant.     

Thermoelectricity and antivibration properties of screen-printed nanodoped In1.35ZnO2.11/In2O3 thin-film thermocouples on alumina substrates

Owing to the low flow field disturbances and fast response, thin-film thermocouples (TFTCs) are used to measure the service temperature of aero-engines. Indium tin oxide (ITO) and In₂O₃ are widely used in high–temperature measurements. However, ITO undergoes phase transition and consequent thermoelectric failure at above 1300 °C. In this study, In_1.35ZnO_2.11/In₂O₃ TFTCs were prepared on alumina substrates via screen printing method through introduction of ZnO nanopowder followed by annealing treatment. Results show that prepared TFTCs exhibited good thermoelectric properties at 1500 °C. The morphology, structure, and electrical coefficients of TFTCs were investigated. The average Seebeck coefficient was 39.8 μV/°C at 1500 °C with a drift rate (DT) of 0.84 °C/h, which was significantly improved with respect to that of ITO/In₂O₃, corresponding to 44.5 μV/°C at 1270 °C with a DT of 5.44 °C/h and failed at higher temperature. The result of lumped capacity method test show that the response time was 4.8 ms at 100 °C. Preliminary engine gas temperature measurements with a heat load of 1000 °C at 1 Mach show that these TFTCs are promising candidates for engineering applications. Finally, the structural reliability under high-magnitude vibration and impact tests (10–2000 Hz/20 g and 100 g/11 ms) was also investigated. As a result of the excellent bonding strengths of 47.36 and 59.83 N between the film and the substrate for both In_1.35ZnO_2.11 and In₂O₃, respectively, destructive cracking and peeling of the film were not observed, and no change in the Seebeck coefficient of the sample occurred after impact and vibration tests. These results provide an important basis for the potential application of In_1.35ZnO_2.11/In₂O₃ TFTCs in aero-engine high-temperature measurements of flow channel components.     

Influence of Drying Conditions on Physical Properties of Alginate Films

The effect of drying conditions of the film-forming solution on thickness, moisture content, water vapor permeability, and tensile properties of alginate films were investigated. A long period of constant rate was observed in all conditions and the model proposed by Wang and Singh was able to adjust the drying data. As expected, there was a clear effect of temperature on drying kinetics; that is, increasing the drying temperature decreased the drying time. Considerable glycerol losses were observed when alginate gel was oven dried at temperatures above 40°C. Compared to other drying conditions, films oven dried at 60°C were thinner, had lower moisture content, and were less flexible.     

Effect of long-chain monoacrylate on the residual monomer content, swelling and thermomechanical properties of SAP hydrogels

Residual monomer is an important factor, particularly in hygienic materials such as superabsorbent polymer (SAP) hydrogels. Recently, we reported different approaches to minimizing residual monomer content in SAPs. In this paper, the effect of a long-chain monomer, poly(ethylene glycol) methylether methacrylate (PEG.MEMA), on the residual monomer content of SAP networks of partially neutralized acrylic acid–PEG.MEMA is investigated. The aim of using PEG.MEMA in SAP synthesis was to reduce the glass transition temperature (T _g) of SAP. As the temperature that is conventionally used to dry SAP (70–110 °C) is lower than the T _g of ordinary SAPs, the polymer is in the glassy state during the heating stage. It was assumed that converting SAP from the glassy state to the rubbery state during drying would facilitate the removal of acrylic acid monomer (AA) from the gel, thus reducing the residual monomer content. The results showed that the use of PEG.MEMA led to a reduction in residual AA when the drying temperature was 100 °C. The residual AA was decreased from 169 to 95 ppm when the drying time was increased from 3 to 15 hours at 100 °C. This positive effect of PEG.MEMA on the level of unwanted residual AA became insignificant at a higher drying temperature (140 °C). The effects of PEG.MEMA content on the thermal and mechanical properties (in the dried state) and the rheological properties (in the water-swollen state) of the SAP hydrogels were also investigated. The swelling capacity and rate was studied in relation to the PEG.MEMA content. It was found that a high level of PEG.MEMA restricted both the absorption capacity and the rate of water absorption.     

High-entropy alloy: An alternative approach for high temperature microwave-infrared compatible stealth

To achieve microwave-infrared compatible stealth in high temperature conditions, high-entropy alloys (HEAs) thin films were deposited on Al₂O₃ matrix by magnetron sputtering technology. Films were annealed to investigate thermal stability at 500 °C, 600 °C and 700 °C, respectively. Results from X-ray diffract meter (XRD), atomic force microscope (AFM), scanning electron microscope (SEM), and Fourier transform infrared spectrometer (FTIR) suggested that high-entropy alloy (HEA) film was seriously oxidized when the annealed temperature reached 700 °C for 6 h, causing a significant decrease of infrared reflectivity. Conversely, HEA films showed low infrared emissivity of 0.09 at 600 °C. Additionally, the films possessed excellent thermal stability at 500 °C for 20 h with low infrared emissivity of 0.11. Finally, a simple metamaterial design utilizing HEA films was proposed for infrared-microwave compatible stealth. With the ability of incorporating excellent thermal stability and durable high temperature stealth performance, the study shows great potential of introducing HEAs in the field of high temperature compatible stealth.