High Temperature Thermal Process Research Articles

Flash Light Sintered Lanthanum Strontium Cobalt Ferrite(LSCF) Electrode for High Performance IT-SOFCs

The high temperature(900oC~) thermal sintering process is necessary to fabricate the Solid oxide fuel cells(SOFCs). However, the chemical reaction has occurred between solid oxide material components, electrode and electrolyte. In the case of lanthanum strontium cobalt ferrite (La0.6Sr0.4Co0.2Fe0.8O3-δ, LSCF) electrode, the SrZrO3(SZO) secondary phase is produced at the electrolyte interface even when using the gadolinium doped ceria(GDC) buffer layer for blocking the strontium and zirconium diffusion. The SZO layer hinders the oxygen ion transfer and deteriorates fuel cell performance. By using a novel flash light sintering(FLS) method, we have successfully solved the problem of secondary phase formation in the conventional high temperature thermal sintering process. The microstructure and thickness of the LSCF electrode are analyzed using a field emission scanning electron microscope(FE-SEM). The strontium diffusion and secondary phase are confirmed by X-ray diffraction (XRD), energy dispersive spectrometer method of SEM, TEM (SEM-, TEM-EDS). The NiO-YSZ anode supported LSCF cathode cells are adopted for electro chemical analysis which is measured at 750oC. The maximum power density of the thermal sintered LSCF cathode at 1050oC is 699.6mW/cm2, while that of the flash light sintered LSCF cathode is 711.6mW/cm2. This result proves that the electrode was successfully sintered without a secondary phase using flash light sintering.

Microscopic Reaction Mechanisms of Formic Acid Generated During Pyrolysis of Cellulosic Insulating Paper

Cellulosic insulating paper is the essential component of the insulation in power transformers. Under the thermal stress inside the transformer, the cellulosic insulating paper degrades and generates formic acid. Meanwhile, the presence of formic acid further accelerates the aging process of cellulosic insulating paper. This study takes the cellulose molecule composed of D-glucose as the research object. The ReaxFF reactive force field is applied to simulate the high-temperature thermal aging process of cellulosic insulating paper. During pyrolysis process, the number of formic acid molecules presents short-term fluctuations and continuous increases. Though simulation, the main reaction pathways of cellulose pyrolysis to generate formic acid are obtained. In addition, an accelerated thermal aging experiment of oil-paper insulation is designed. The formic acid in the experimental samples is detected by the silanization derivatization method. Through the combination of simulation and experimental results, the feasibility of formic acid as an aging indicator for cellulosic insulating paper is further demonstrated.

Characterization of GaON as a surface reinforcement layer of p-GaN in Schottky-type p-GaN gate HEMTs

The surface of the p-GaN layer in Schottky-type p-GaN gate high-electron-mobility transistors (HEMTs) can be reinforced with enhanced immunity to hot electron bombardment by reconstructing the surface region of p-GaN into GaON. The surface region of p-GaN is treated by remote oxygen plasma and subsequently annealed at 800 °C, thereby becoming a thin crystalline gallium oxynitride (GaON) layer that will be in direct contact with the Schottky metal. The GaON exhibits a lower valence band maximum energy than that of the p-GaN, which leads to a higher Schottky barrier at the metal/GaON interface to holes and, thus, greatly suppresses the forward gate leakage. More importantly, with higher thermodynamic stability and a larger bandgap of ∼4.1 eV, the GaON reinforces the susceptible metal/p-GaN interface against the hot electrons and, thus, substantially enhances the long-term gate reliability of p-GaN gate HEMTs under forward bias stress. The high-temperature thermal process is indispensable for the surface reconstruction, without which the plasma oxidation only reduces the gate leakage but fails to prolong the time-dependent gate breakdown lifetime.

A new gluten‐free product: Brown rice bulgur, and its physical and chemical properties

In this research, a new alternative food product, defined as brown rice bulgur (BRB), rich in functional components compared to white rice and cooked in a short time compared to brown rice was developed for society especially individuals with gluten intolerance and celiac disease. BRB was produced with two different methods as boiling (BRB-B) and steaming (BRB-S). The cooking time of raw brown rice decreased from 30 to 9 min in BRB samples. The phytic acid content of BRB samples decreased by about 15% and enzyme resistant starch content of BRB-B and BRB-S samples increased by about 9% and 21% compared to brown rice, respectively. The produced BRB samples were in the medium GI food group. In conclusion, it was evaluated that the newly developed BRB is superior than brown rice, white rice, and wheat bulgur in terms of short cooking time, lower GI, and being gluten-free, respectively. Practical applications In this study, brown rice bulgur has been produced from brown rice, unpreferable by consumers due to its long cooking time, hard texture, and dark color, with wheat bulgur production method. This new food product includes the advantages of wheat bulgur such as resistivity to insect and mold activity because of applied high-temperature thermal process and drying process, but do not include the disadvantages of brown rice such as long cooking time. Additionally, it could be attention to some consumers because of being a new gluten-free product. The obtained data can help diversify this product in the food industry.

Direct transfer of thermochromic tungsten-doped vanadium dioxide thin-films onto flexible polymeric substrates

In this study, we demonstrate the preparation of flexible thermochromic vanadium dioxide (VO2) thin films via the direct film transfer technique using adhesive polymer films. Phase-change VO2 films are prepared via solution-based deposition using sub-stoichiometric colloidal VOx nanoparticles (NPs) on mica substrates; subsequently, a high-temperature rapid thermal annealing process is employed to induce phase transformation to monoclinic VO2 (VO2(M)). Thereafter, the direct film transfer of VO2(M) on mica substrates is conducted using PET substrates coated with an acrylate adhesive to form flexible and transparent mica/VO2(M)/PET films. The reversible phase transition behaviors of the flexible VO2(M) films are observed, such as a high luminous transmittance (Tlum > 50%) and solar modulation ability (ΔTsol > 15%). In addition, doping with tungsten ions systematically decreases the phase transition temperature (Tc) such that it is approximately equal to the ambient temperature, depending on the doping concentration. We observed that VO2(M) doped with 1.3 at% of W exhibits a Tc of 29 °C with Tlum and ΔTsol values of 53% and 10%, respectively; these are the highest Tlum and ΔTsol values reported thus far for flexible VO2(M) thin films at a near-ambient Tc.

Study of Si–Ge Interdiffusion in Laser Recrystallization of Ge Epitaxial Film on Si Substrate

Direct epitaxial growth of germanium (Ge) film on silicon (Si) substrate (GOSS) holds great potential in micro-electronics and optoelectronics. However, due to the 4.2% lattice mismatch between Si and Ge, it is difficult to directly obtain high quality Ge by epitaxy on Si substrate. Laser recrystallization technology provides a simple, efficient and low-cost way to improve the crystal quality of epitaxial Ge film grown on Si substrate. This technology is essentially a process of thermally induced phase transformation. By controlling the laser process parameters, epitaxial film of a certain thickness is melted, so that lattice rearrangement and recrystallization are achieved, and high-quality thin Ge/Si can be prepared. Laser recrystallization is a high temperature thermal process, and Si–Ge interdiffusion may detrimentally occur. In this paper, the mechanism of Si–Ge interdiffusion is discussed. Based on Fick's law of diffusion, a numerical model for Si–Ge interdiffusion of GOSS is established. On this basis, the process simulation of thermal annealing and laser recrystallization Si–Ge interdiffusion is carried out by Sentaurus Process simulation. The results show that compared with the traditional thermal annealing, the Si–Ge interdiffusion of Ge on Si almost does not occur in the process of laser recrystallization. By reasonably controlling the process parameters of laser recrystallization, the thin Ge film near the Si–Ge interface does not melt, which can not only improve the crystal quality of Ge epitaxial layer, but also effectively avoid the Si–Ge interdiffusion in the process of laser recrystallization. Through this research, we have aimed at predicting and control the Si–Ge interdiffusion, providing an important technical reference for the preparation of high quality GOSS by laser recrystallization technology.

Experimental Use of Microwaves in the High Temperature Foaming Process of Glass Waste to Manufacture Heat Insulating Material in Building Construction


 
 
 
 Abstract 
 The aim of the paper was the experimental manufacture of cellular glass from glass waste and coal ash as raw material and silicon carbide as a foaming agent, using the unconventional microwave heating technique. This heating technique, although known since the last century and recognized worldwide as fast and economical, is not yet industrially applied in high temperature thermal processes. The cellular glass manufacturing process requires high temperatures and the use of microwaves in this process is the originality of the work. The experiments aimed at producing thermal insulating materials with high porosity and low thermal conductivity for building construction similar in terms of quality to those manufactured industrially by conventional techniques, but with lower energy consumption. The obtained samples had adequate characteristics (apparent density 0.22-0.32 g/cm3, porosity 85.5-90.0%, thermal conductivity 0.043-0.060 W/m·K, compressive strength 1.23-1.34 MPa), and the specific energy consumption was low (0.84-0.89 kWh/kg). Theoretically, given the use of microwave equipment on an industrial scale, this consumption comparable in value to that industrially achieved by conventional techniques could decrease by up to 25%.
 
 
 

Facile fabrication of nickel/porous g-C3N4 by using carbon dot as template for enhanced photocatalytic hydrogen production

Ni/porous g-C3N4 was prepared by high temperature thermal polymerization process using carbon dots as soft template and photodeposition. With nickel nanoparticles supported as co-catalyst, the hydrogen evolution reaction (HER) activity of the photocatalyst has been significantly enhanced under visible light, which is up to 1273.58 μmol g−1 h−1, superior to pristine g-C3N4 (4.12 μmol g−1 h−1). This is attributed to the inhibited recombination of photogenerated electron-hole pairs and the much better electron transport efficiency. The formed porous structure of carbon nitride could facilitate light utilization and together with nickel nanoparticles, better charge separation can be realized which are proved by the photoluminescence, time-resolved photoluminescence spectra, transient photocurrent measurements and electrochemical impendence spectroscopy. This work provides a useful route to obtain less expensive and efficient photocatalyst containing no noble metals for hydrogen production.

Conductive-radiative heat transfer within SiC-based cellular ceramics at high-temperatures: A discrete-scale finite element analysis

Cellular ceramic materials possess many favorable properties that allow to develop efficient modern-day high-temperature thermal energy conversion systems and processes. The energy conversion within these porous media is governed by tightly coupled conduction–radiation physics. To efficiently design and optimize these systems, a comprehensive understanding of the conduction–radiation behavior within these materials becomes important. In this study, by performing large-scale numerical experiments, we analyze the conduction–radiation coupling characteristics within different (with respect to topology and porosity) silicon carbide (SiC)-based open-cell cellular ceramics surrounded by fictitious vacuum up to temperatures of 1800 K. To induct minimal approximations, our finite element simulations are based on a discrete-scale approach within which realistic discrete (pore-level) representations of the cellular ceramics are used as numerical media. The results presented in this study provide means to better understand the role of radiation in the coupled conduction–radiation physics within the ceramic samples. A detailed comparison on effectiveness of energy conversion is established for SiC-based full-scale cubic-cell, Kelvin-cell, and pseudo-random-cell ceramic structures which are at 80% and 90% porosity each. In conclusion, among the different standalone and full-scale ceramic samples, the Kelvin-cell structures at 90% porosity have proven to benefit the most from radiation coupling.

Performance Comparison of Four-year-old Trees of Two Short-rotation Species Modified by High Temperature Thermal Process For Producing Furniture Artifacts

Four-year-old trees of two fast growing species, namely Corymbia citriodora (V1) and Eucalyptus hybrid (E. camaldulensis* E. urophylla) (V2) were subjected to high temperature thermal processing technique for improving certain wood quality parameters. Although, these species are generally grown for pulpwood production, value-added solid wood applications in furniture and other lifestyle artifacts can be produced after modifying the wood by eco-friendly thermal treatments. Small billets from bottom portion (2 meters) of the trees were converted into wooden planks which were subjected to heat treatment at 175±5°C for a fixed duration of 4 hours underpartial vacuum condition. Effect of he at treatment on physical and mechanical properties such as equilibrium moisture content (EMC), density, water absorption (WA), shrinkage, flexural strength (modulus of rupture-MOR) andstiffness (modulus ofelasticity-MOE), compressive strength parallel and perpendicular to grain and surface hardness was evaluated in both species and compared with respective controls. The moisture related wood properties such as EMC, WA and shrinkage were observed to be reduced significantly after thermal modification. Antishrinkage efficiency (ASE) increased by 43% in V1 compared to 31% in V2. MOE and maximum compressive strength values improved significantly in heat treated wood compared to respective controls. Reduction in MOR due to thermal processing was lower in V1 compared to V2.V1 samples showed greater enhancement in several desirable wood properties than V2. Basal portion of short rotation Corymbia citriodora (V1) trees can be thermally modified to improve aesthetic and techno-mechanical parameters for making value-added artifacts such as furniture, wall paneling etc. in nonstructural industry sectors, as an alternative to traditionally used species.

Nitrogen-doped carbon supported ZnO as highly stable heterogeneous catalysts for transesterification synthesis of ethyl methyl carbonate

Nitrogen-doped carbon material (NCM) supported ZnO catalysts were prepared by wet impregnation method, following a high-temperature thermal treatment process. The resultant ZnO/NCM catalysts calcined at different temperatures were characterized by X-ray diffraction (XRD), Raman spectroscopy, N2 adsorption–desorption, elemental analysis, X-ray photoelectron spectroscopy (XPS) to investigate their physicochemical properties and the interaction between ZnO and NCM support. Their catalytic properties were studied by liquid phase transesterification of dimethyl carbonate (DMC) with diethyl carbonate (DEC). Of these the catalyst calcined at 800 °C, named ZnO/NCM-800 exhibits the highest catalytic activity, as well as excellent stability and recyclability for the synthesis of ethyl methyl carbonate (EMC). The NCM support possesses abundant mesopores, rich surface oxygen-containing and nitrogen-containing functional groups, which are beneficial to build relatively strong interaction between ZnO nanoparticles and the NCM support, resulting in the generation of a highly active and stable acidic-basic bifunctional catalyst for the transesterification of DMC with DEC.

The transformation of phosphorus fractions in high-solid sludge by anaerobic digestion combined with the high temperature thermal hydrolysis process

Transforming inactive phosphorus (P) to active P to recover it from waste activated sludge is important. The transformation of P fractions from high-solid sludge by the anaerobic digestion (AD) and acidification phase of AD (AAD) combined with a high temperature thermal hydrolysis process (HTTHP) was investigated. The results showed that the sequence of P release effects by three processes was HTTHP + AAD > AD + HTTHP > HTTHP + AD. The PO43−-P release from high-solid sludge was directly affected by the temperature of HTTHP. At 140 °C, each process had more PO43−-P release than that at 160 °C. The total amount of PO43−-P release in AD + HTTHP was approximately 6 times that of HTTHP + AD. Based on the experimental results, a new process of mesophilic AD - post HTTHP was recommended, in which, enhancement of P release by sulfide ions was also proposed.

Effect of high-temperature thermal hydrolysis on rheological properties and dewaterability of sludge

ABSTRACT The disposal processes like dewatering and anaerobic digestion (AD) are commonly utilized to reduce the volume of sludge and recover energy. Thermal hydrolysis process is widely used as a pretreatment for sludge AD, which can change rheological properties and dehydration of sludge irreversibly. The experiment was designed to evaluate the effect of high-temperature thermal hydrolysis (120, 130, 145, 160 and 170°C) for 60 min on sludge rheological properties, as well as its dewaterability. Rheological tests were performed at (20 ± 0.1)°C with a HAAKE Viscotester 550 Rotary Viscometer. Both raw and thermal hydrolysis sludge has a considerable reduction on apparent viscosity and yield stress, but a somewhat increase in thixotropy. With the increase of temperature, the sludge flow behaviour index n increases linearly, while the consistency coefficient k follows the law of linear decline, showing that thermal hydrolysis can weaken the non-Newtonian fluid properties and then improve sludge fluidity. The dewaterability increases linearly with the temperature. Besides, the dewaterability of high-temperature thermal hydrolysis processes sludge was always significantly better than raw sludge as its mud cake has a much larger solid content. Notably, the increase in flow performance index n and the decrease of thixotropy kinetic coefficient K caused by thermal hydrolysis are all linear with the enhancement of dewaterability, which demonstrates that rheological indicators can be a new tool to evaluate the dewaterability of sludge.

Photocatalytic C–X borylation of aryl halides by hierarchical SiC nanowire-supported Pd nanoparticles

Hierarchical SiC nanowire-supported Pd nanoparticles showed high photocatalytic activity for the C-X (X = Br, I) borylation of aryl halides at 30 °C. The SiC/Pd Mott-Schottky contact enhances the rapid transfer of the photogenerated electrons from SiC to the Pd nanoparticles. As a result, the concentrated energetic electrons in the Pd nanoparticles can facilitate the cleavage of C-I or C-Br bonds, which normally requires high-temperature thermal processes. We show that the present Pd/SiC photocatalyst is capable of catalyzing the transformation of a large variety of aryl halides to their corresponding boronate esters under visible light irradiation, with excellent yields.

Synthesis of metallic copper modified g-C3N4 by molecular self-assembly structure and its combined catalytic performance with activated sludge

Copper modified carbon nitride (CuCN) was prepared by a hydrothermal self-assembly reaction and following high temperature thermal polymerization process. Finally, the sample exhibits uniform one-dimensional tubular structure. Interestingly, the separation efficiency of electron-hole pair is improved, and more catalytic active sites are exposed due to the special hollow structure. Meanwhile, the presence of copper element narrows its band gap, leading to the enhancement of photocatalytic degradation performance under simulated sunlight. In addition, the effect of CuCN on dehydrogenase activity of activated sludge was determined by TTC reduction method. After adding CuCN-2, the activity of activated sludge reached 0.134 μmol g−1 min−1, which indicated that the prepared CuCN-2 had good biocompatibility. It is suitable for both photocatalytic process and activated sludge treatment process. Therefore, the combination of photocatalytic technology and activated sludge process can further completely degrade organic pollutants. We found that CuCN could protect the survival and growth of microorganisms in activated sludge, so that the degradation efficiency of CuCN to nitrobenzene could reach 94.4 %. Therefore, CuCN has broad application prospects in photocatalytic-activated sludge combined treatment.

Superconductivity of Y5Rh6Sn18; Coexistence of the high temperature thermal lattice relaxation process and superconductivity

The heat capacity, magnetic, and electrical transport properties of skutterudite-related Y5Rh6Sn18 compound indicate intriguing coexistence of the high temperature thermal lattice relaxation process at temperatures higher than 350 K and superconductivity below the superconducting transition temperature Tc=3.08 K. Y5Rh6Sn18, having a cage-like structure crystallises in tetragonal structure with the space group I41/acd. The gap structure of this compound is found not to be characteristic of conventional BCS type superconductors. Anomalous behaviour observed in the electronic specific heat C(T)/T and the upper critical field Hc2(T) data may suggest the presence of two superconducting gaps in this compound. The ab initio band structure calculations showed a significant contribution of s and p Sn states as well as Rh and Y d-electron states to the total density of states near the Fermi level, which supports the multi-band superconductivity of this compound. Several electronic quantities and parameters characterising the superconducting and normal state of Y5Rh6Sn18 are calculated within the Ginzburg-Landau-Abrikosov-Gorkov theory. The data reveals dirty limit superconductivity in Y5Rh6Sn18 superconductor of type-II.

Effect of alkylamine chain length on high-temperature phase transformation and thermal decomposition process of kaolinite intercalation compounds

The structural changes and thermal decomposition of kaolinite (Kaol) intercalation compounds during heating process limit their application in polymers which need to be heated during the preparation process. In this study, homologous compounds, namely, hexylamine (HEA) and octadecylamine (OCA), were used to intercalate Kaol to explore the effect of molecular chain length on the structural stability and thermal decomposition of intercalated compounds. After the intercalation by HEA and OCA, the expansion only occurred along the C-axis, and the basal spacing increased to 28.7 and 57.3 Å, respectively. The morphology of Kaol changed remarkably, and all appeared curly. Compared with Kaol/HEA intercalation compounds, the Kaol/OCA intercalation compounds had better curling effect due to their different molecular chain length. The thermal decomposition process of Kaol/alkylamine intercalation compounds can be divided into two distinct stages. The molecules that adhered to the surface of the nanoscrolls and existed in the lumen of nanoscrolls began to deintercalate in the first step, and the other molecules that intercalated Kaol layers began to decompose in the second step. Thus, Kaol can be used as a potential carrier material, a carrier of sustained-release drug, or a carrier material for the catalyst. The reaction is regulated by controlling the temperature of the reaction.

High-temperature drying behavior and kinetics of lignite tested by the micro fluidization analytical method

To simulate the drying behavior of lignite in the high-temperature thermal conversion process, a micro fluidized bed reactor was adopted to measure the drying characteristics of moist char from 773 K to 1173 K and calculate the drying kinetics. Both temperature and the initial moisture strongly affected the drying behavior by changing the curve shape and drying time. The higher the initial moisture, the more obvious the influence of drying temperature. Compared to the conventional low-temperature lignite drying, the rate curve tested by MFBRA only had the growing-rate zone and falling-rate zone, but did not include the common constant-rate zone. Under the experimental condition, the Lewis drying model can describe the drying characteristics of wet char in MFBRA very well. The apparent diffusion coefficient and activation energy ranged from 1.765 E−10 to 4.756 E−10 m2/s, and 12.83–14.97 kJ/mol, respectively. The activation energy was much lower than those in literature.

Performance evaluation of thermochemical energy storage system based on lithium orthosilicate and zeolite

High-temperature thermal energy can be produced from renewable power sources such as high-temperature gas-cooled reactors and high-temperature thermal processes, without environmental pollution. Integration of thermochemical energy storage (TcES) systems within power generation systems provides flexible options for future power generation. This study evaluates the performance of a TcES system based on Li4SiO4/zeolite/CO2 for thermal energy storage at ∼700 °C. Isothermal experiments with Li4SiO4, accessed through a solid-state reaction method, revealed that carbonation and decarbonation were almost complete after 5 and 150 min, respectively. The maximum gravimetric mean thermal output and input rates were 7.2 and 1.9 kW kg−1 for Li4SiO4 (59% porosity), respectively. Moreover, zeolite F-9 was examined as a pressure conditioning material by investigating the CO2 desorption profile at various CO2 pressures, and ∼15 wt% CO2 could be controlled. The zeolite showed good cycling durability and temperature responsiveness for four repeated cycles. Hence, the TcES system based on Li4SiO4 and the zeolite could be used for thermal energy storage at about 700 °C, and only temperature control was required to switch between the output and input modes. The amount of zeolite required by the proposed TcES system was 2.4 times (by weight) greater than that of Li4SiO4.

Micron-Scale Annealing for Ohmic Contact Formation Applied in GaN HEMT Gate-First Technology

High-temperature thermal annealing process for ohmic contact hinders the development of monolithic integration of heterogeneous functional devices as well as gate-first approach for the GaN transistor. Other than reducing processing temperature, we developed a selective annealing method so that temperature-sensitive parts were not thermally affected. Here, we report a micron-scale annealing method by focused laser for ohmic contact in a GaN heterogeneous system/device. The micron-scale annealing method enabled the formation of a relatively thick TiN layer (35 nm) at the metal–semiconductor interface. As a result, a low contact resistance of 0.3 $\Omega \cdot \text {mm}$ was achieved. The miniaturized annealing method was applied to the gate-first approach for GaN high electron mobility transistor (HEMT). A better performance of larger current output, smaller gate leakage ( $1\times 10^{{6}}$ times smaller), and larger dynamic range of HEMT was hence obtained.