Conventional High-temperature Process Research Articles

Linear topology in amorphous metal oxide electrochromic networks obtained via low-temperature solution processing

Amorphous transition metal oxides are recognized as leading candidates for electrochromic window coatings that can dynamically modulate solar irradiation and improve building energy efficiency. However, their thin films are normally prepared by energy-intensive sputtering techniques or high-temperature solution methods, which increase manufacturing cost and complexity. Here, we report on a room-temperature solution process to fabricate electrochromic films of niobium oxide glass (NbOx) and 'nanocrystal-in-glass' composites (that is, tin-doped indium oxide (ITO) nanocrystals embedded in NbOx glass) via acid-catalysed condensation of polyniobate clusters. A combination of X-ray scattering and spectroscopic characterization with complementary simulations reveals that this strategy leads to a unique one-dimensional chain-like NbOx structure, which significantly enhances the electrochromic performance, compared to a typical three-dimensional NbOx network obtained from conventional high-temperature thermal processing. In addition, we show how self-assembled ITO-in-NbOx composite films can be successfully integrated into high-performance flexible electrochromic devices.

Anode-supported Type SOFCs based on Novel Low Temperature Ceramic Coating Process

To prevent an interfacial reaction between the anode and the electrolyte layer during the conventional high-temperature co-firing process, an anode-supported type cell with a thin-film electrolyte was fabricated by low-temperature ceramic thick film coating process. Ni-GDC cermet composite was used as the anode material and YSZ was used as the electrolyte material. Open circuit voltage and maximum power density were found to strongly depend on the surface uniformity of the anode functional layer. By optimizing the microstructure of the anode functional layer, the open circuit voltage and maximum powder density of the cell increased to 1.11 V and 1.35 W/㎠, respectively, at 750℃. When a GDC barrier layer was applied between the YSZ electrolyte and the LSCF cathode, the cell showed good stability, with almost no degradation up to 100 h. Anode-supported type SOFCs with high performance and good stability were fabricated using a coating process.

III–V compound semiconductor multi-junction solar cells fabricated by room-temperature wafer-bonding technique

We have developed III–V compound semiconductor multi-junction solar cells by a room-temperature wafer-bonding technique to avoid the formation of dislocations and voids due to lattice mismatch and thermal damage during a conventional high-temperature wafer-bonding process. First, we separately grew an (Al)GaAs top cell on a GaAs substrate and an InGaAs bottom cell on an InP substrate by metal solid source molecular beam epitaxy. Thereafter, we successfully bonded these sub-cells by the room-temperature wafer-bonding technique and fabricated (Al)GaAs ∥ InGaAs wafer-bonded solar cells. To the best of our knowledge, the obtained GaAs ∥ InGaAs and AlGaAs ∥ InGaAs wafer-bonded solar cells exhibited the lowest electrical and optical losses ever reported. The AlGaAs ∥ InGaAs solar cells reached the maximum efficiency of 27.7% at 120 suns. These results suggest that the room-temperature wafer-bonding technique has high potential for achieving higher conversion efficiencies.

Cold spray as an emerging technology for biocompatible and antibacterial coatings: state of art

The use of coatings in biomaterials has been fundamental on the applicability of many medical devices and has helped improve mechanical properties such as wear and fatigue and biological properties such as biocompatibility and bioactivity of implant prosthesis, thus, in essence, ameliorating human quality life. The aim of the present paper is to give a review on cold spray (CS) coating systems that are emerging in orthopedics industry (internal fixation systems and prosthesis) as well as those for antibacterial purposes (in body and touch external surfaces). These studies are very new, the oldest dating from the half of last decade and most deal with the improvement of biocompatibility and bioactivity of hard tissue replacement; therefore, research on biocoatings is in constant development with the aim to produce implant surfaces that provide a balance between cell adhesion and low cytotoxicity, mechanical properties, and functionalization. CS offers many advantages over conventional high-temperature processes and seems to be able to become competitive in front of the low-temperature techniques. It is mainly cost effective, appropriate for oxygen-sensitive materials, and environmentally green. It basically involves the use of feedstock material in powder form, which is supersonically sprayed onto the appropriate substrate but without any melting as it occurs in conventional thermal spray processes. Biocompatible metallic materials and polymers have been successfully deposited by this method because it is based on the plasticity of the coating material; pure ceramic deposits, for example of hydroxyapatite, are still a challenge.

Viscosity reduction of cassava for very high gravity ethanol fermentation using cell wall degrading enzymes from Aspergillus aculeatus

Cassava is an important feedstock for bioethanol production; however, its use in very high gravity (VHG) fermentation is limited by the high viscosity of mash due to the presence of plant cell wall derived polysaccharides. In this study, viscosity reduction of cassava root mash, chips, and pulp was achieved using a mixture of cell wall degrading enzymes prepared from solid state fermentation of Aspergillus aculeatus BCC17849. Proteomic analysis showed the mixture contained endo- and exo-acting cellulases, hemicellulases, and pectinases from various glycosyl hydrolase families. Enzymatic pretreatment of cassava substrates with the enzyme mixture containing endoglucanase, FPase, xylanase, polygalacturonase, β-glucanase, and mannanase activities at 45°C, pH 5.0 for 2h reduced viscosity to the operating level of <500mPas, equivalent to the final viscosity of 3.0–51.3% of the initial levels. Simultaneous saccharification and fermentation of the pretreated root mash (32% initial solid) by Saccharomyces cerevisiae with a conventional high-temperature liquefaction process and an uncooked process using a raw starch degrading amylase at 32°C for 96h led to a final ethanol concentration of 19.65 and 17.54% (v/v), respectively. The results demonstrated potential of the enzyme for improving process efficiency and economics in VHG bioethanol production.

Microwave assisted processing of silver thick films for microelectronic applications

This paper aims to focus on the microwave processing of thick films which is a fast, cheap technique and could be the alternative to the currently used conventional high temperature processing technique. Microwave processing has gained worldwide acceptance as a novel method for heating and sintering a variety of materials, as it offers specific advantages in terms of speed, energy efficiency, process simplicity, finer microstructures and lower environmental hazards. Silver conducting thick films were prepared and processed in the household microwave oven. The films sintered at different time period by keeping the other parameter such as microwave power, film thickness etc constant. The microstructure analysis revealed that the surface morphology of the microwave processed films become compact with respect to the processing time. The sheet resistance for microwave sintered silver films is in the range of 0.003 to 1.207 Ω /  where as the films fired at 750 and 850 o C showed the resistance of 0.009 and 0.003 Ω/ which can be comparable. The results revealed that the microstructure of the microwave sintered films has more uniform and compact surface than that of the conventionally fired films. The paper reports upon the preparation of silver thick film by screen printing technique and processing the same by microwave which also compared with the conventionally processed thick films.

Fully Plastic Dye Solar Cell Devices by Low‐Temperature UV‐Irradiation of both the Mesoporous TiO2 Photo‐ and Platinized Counter‐Electrodes

AbstractThe application of UV irradiation processes are successfully proposed for the first time in the fabrication of both of the two plastic electrodes in flexible dye solar cells (DSCs) and modules. For the realization of the photo‐electrode, a customized TiO2 paste formulation and UV processing method was developed which yields 134% (48%) performance enhancement with respect to the same (binder‐free) paste treated at 120 °C. UV treatment induces both complete removal of organic media and more efficient charge collection. Significantly, highly catalytic platinized flexible counter‐electrodes are also obtained via UV photo‐induced reduction of screen‐printed platinum precursor pastes based on hexachloroplatinic acid. Using both UV‐processed electrodes, a fully plastic DSC is fabricated with a conversion efficiency of 4.3% under 1 Sun (semitransparent) and 5.3% under 0.2 Sun (opaque). Performance is within 10% of the efficiency of a glass‐based DSC prepared with the same materials but with conventional high temperature processes. The material formulations and processes are simple, and easily up‐scaled over large areas, even directly and simultaneously applicable to the preparation of both the photo‐and counter‐electrode on the same substrate which enabled us to demonstrate the first module on plastic realized with a W series interconnection.

Nano-ZnO incorporated titania composite coating for orthodontic applications

In the present study, a novel nano-ZnO incorporated nanotitania coating was developed for orthodontic applications with special reference to anticorrosive and antibacterial applications. High corrosion resistance and antibacterial activity of the titania coating were achieved due to the incorporation of nano-ZnO. Nano-ZnO was characterised using sophisticated techniques, including TEM, before the present study. The coating methodology adopted in the present work was distinct from other conventional high temperature processes. The content of nano-ZnO was optimised to be 30 wt-%, which caused high surface uniformity and homogeneity significantly even after dissolution in aggressive environments. The improvement in the layer-wise coating structure favoured other coating characteristics. In the present study, many of the tests and assessment were designed with special reference to electrochemical characterisation.

No-Cook Process for Ethanol Production Using Indian Broken Rice and Pearl Millet

No-cook process using granular starch hydrolyzing enzyme (GSHE) was evaluated for Indian broken rice and pearl millet. One-factor-at-a-time optimization method was used in ethanol production to identify optimum concentration of GSHE, under yeast fermentation conditions using broken rice and pearl millet as fermentation feedstocks. An acid fungal protease at a concentration of 0.2 kg per metric ton of grain was used along with various dosages of GSHE under yeast fermentation conditions to degrade the grain proteins into free amino nitrogen for yeast growth. To measure the efficacy of GSHE to hydrolyze no-cook broken rice and pearl millet, the chemical composition, fermentation efficiency, and ethanol recovery were determined. In both feedstocks, fermentation efficiency and ethanol recovery obtained through single-step no-cook process were higher than conventional multistep high-temperature process, currently considered the ideal industrial process. Furthermore, the no-cook process can directly impact energy consumption through steam saving and reducing the water cooling capacity needs, compared to conventional high-temperature process.

Integrated chemical process for exothermic wave synthesis of high luminance YAG:Ce phosphors

In this paper, high-luminance yellow-emitting Y 3Al 5O 12:Ce 3+ phosphor (YAG:Ce) microparticles were prepared in a solid flame using a 1.425Y 2O 3+2.5Al 2O 3+0.15CeO 2+ k(KClO 3+urea)+ mNH 4F precursor mixture (here k is the number of moles of the KClO 3+urea red-ox mixture, and m is the number of moles of NH 4F). The self-sustaining combustion process for the entire reaction sample was provided by the heat generated from the KClO 3+urea mixture. Parametric studies demonstrated that the maximum temperature in the combustion wave varied from 885 to 1200 °C for k=2.0–3.0 mole and m=0–1.5 mole. X-ray analysis results showed that the product obtained in the solid flame consisted of Y 3Al 5O 12:Ce 3+ and KCl phases. Therefore, after dissolving potassium chloride in distillated water, pure-phase YAG:Ce phosphor powder was obtained. The as-prepared YAG:Ce phosphor particles had diameters of 10–25 μm and good dispersity and exhibited luminescence properties comparable to those of YAG:Ce phosphor powders prepared by conventional high-temperature processing.

Mechanochemical synthesis of double vanadate in Cu–Fe–V–O system and its physicochemical and catalytic properties

Mechanochemical synthesis has been successfully employed to prepare a Cu 3Fe 4(VO 4) 6 powder. The formation of designed compound (in α-polymorphic form) is due to the reactions of copper, iron and vanadium oxide precursors which were activated by high-energy ball milling ( Activator 2S, Novosibirsk, Russia) for 8 h instead of heat energy required in the conventional multi-stage high-temperature process during 80 h forming β-polymorphic form. Catalytic properties of Cu 3Fe 4(VO 4) 6 compound, which has been prepared by two different mentioned above techniques, tested in the methanol steam reforming reaction are satisfactory and closely the same. However, α-, as well as, β-polymorphic forms of Cu 3Fe 4(VO 4) 6 are structural unstable during steam reforming of methanol and form a metallic copper beside V 2O 3 and iron oxides, which probably catalyze simultaneously undesired methanation reaction. The real chemical mechanism is still not clear.

Carbon Recycling for Reduction of Carbon Dioxide Emission from Iron-making Process

A new energy transformation concept based on carbon recycling, called the Active Carbon Recycling Energy System, ACRES, is discussed. In this system, hydrocarbons are regenerated from carbon dioxide by using a heat source that does not emit carbon dioxide, allowing the hydrocarbons to be re-used cyclically as energy carrier media. The thermodynamic feasibility of ACRES is compared with that of a hydrogen energy system. Carbon monoxide has a higher energy density than hydrogen and is highly compatible with conventional chemical, steel, and high-temperature manufacturing processes. Thus, it is a suitable carbon medium for ACRES. A high-temperature gas type nuclear reactor is a good power source for ACRES. The combination of the nuclear reactor and ACRES with carbon monoxide is expected to form the basis of a new iron-making process that has low carbon dioxide emissions.

Spray-deposited CuInSe2 nanocrystal photovoltaics

Photovoltaic devices (PVs) were fabricated by spray-coating an ink of copper indium diselenide (CIS) nanocrystals as the light-absorbing layer. Without high-temperature post-deposition annealing, PVs were made on glass and plastic substrates with power conversion efficiencies of up to 1.9% and 1.1%, respectively, under AM1.5 illumination. The mild processing conditions also enabled fabrication of alternative device structures that are not compatible with conventional high-temperature PV processing, including substrate and superstrate designs, and devices with transparent back contacts of conducting indium tin oxide (ITO) and plastic substrates. Device performance is observed to be limited by poor charge extraction from the nanocrystal films, with the highest efficiencies being obtained from PVs with relatively thin absorber layers. To improve light absorption without sacrificing internal quantum efficiency, stacked PVs were fabricated, which exhibited improved short-circuit current and power conversion efficiency compared to stand-alone single junction devices.

Transparent conducting aluminum-doped zinc oxide thin film prepared by sol–gel process followed by laser irradiation treatment

Aluminum-doped zinc oxide (AZO) films were fabricated at a low substrate temperature (300 °C) in air by KrF excimer laser irradiation of sol–gel spin-coated films. Structural, electrical and optical properties of the laser-irradiated films at different laser energies were studied and compared with those prepared by conventional high-temperature processing. The 200 nm laser-irradiated AZO film shows a resistivity of 44 × 10 − 3 Ω-cm and about 90% optical transmittance in the visible range upon laser irradiation. The films were oriented preferentially along (002) direction.

Thermally Processed High-Mobility MOS Thin-Film Transistors on Transferable Single-Crystal Elastically Strain-Sharing Si/SiGe/Si Nanomembranes

Demonstration of high-performance MOS thin-film transistors (TFTs) on elastically strain-sharing single-crystal Si/SiGe/Si nanomembranes (SiNMs) that are transferred to foreign substrates is reported. The transferable SiNMs are realized by first growing pseudomorphic SiGe and Si layers on silicon-on-insulator (SOI) substrates, and then, selectively removing the buried oxide (BOX) layer from the SOI. Before the release, only the SiGe layer is compressively strained. Upon release, part of the compressive strain in the SiGe layer is transferred to the thin Si layers, and the Si layers, thus, become tensile strained. Both the initial compressive strain state in the SiGe layer and the final strain sharing state between the SiGe and the Si layers are verified with X-ray diffraction measurements. The TFTs are fabricated employing the conventional high-temperature MOS process on the strain-shared SiNMs that are transferred to an oxidized Si substrate. The transferred strained-sharing SiNMs show outstanding thermal stability and can withstand the high-temperature TFT process on the new host substrate. The strained-channel TFTs fabricated on the new host substrate show high current drive capability and an average electron effective mobility of 270 cm2/V ldr s. The results suggest that transferable and thermally stable single-crystal elastically strain- sharing SiNMs can serve as excellent active material for high-speed device application with a simple and scalable transfer method. The demonstration of MOS TFTs on the transferable nanomembranes may create the opportunity for future high-speed Si CMOS heterogeneous integration on any substrate.

Structural characteristics of nanocrystalline ZrO2 powder sol–gel derived to luminescent applications

Interest in nanocrystalline ceramics is increasing nowadays. Sol–gel is a low temperature method, which uses chemical precursors to produce ceramics and glasses with better purity and homogeneity than the conventional high-temperature processes. This new preparation method of nanophosphors has been recently strongly developed for producing high-efficiency luminescent devices. When producing ZrO2 it is important to retain a high degree of crystallization of ZrO2 and its possible correlation with the concentration of defects. The X-ray diffraction patterns of ZrO2 showed that the calcined material has a strongly monoclinic structure. The thermoluminescent glow curve of ZrO2 exhibited two peaks. Photoluminescence spectra of ZrO2 also were obtained.

Optical Properties of Dy 3+ Doped in Boroaluminasilicate Glass

Dy 3+ doped boroaluminasilicate glasses were synthesized in air atmosphere with conventional high temperature process. Optical absorption, emission and excitation spectra of the glasses were measured. Effect of concentration quenching on the lifetime and fluorescence yield was discussed. The pilot study on the changes in emission spectra of Dy 3+/Tb 3+, Dy 3+/Pr 3+ co-doped glasses was carried out. 451 nm was found to be the ideal wavelength among five excitation wavelength in the UV-Vis region from excitation spectra. The fluorescence spectrum of the sample had three major emission bands at 482, 575 and 662 nm, respectively. The strongest emission band peak was at 575 nm. With an increase in Dy 3+ concentration beyond a particular value (1%), the concentration quenching phenomenon occurred. The lifetime of 4F 9/2 level reduced from 0.9 ms to 0.5 ms when Dy 3+ concentration increased from 0.2% to 4%. The energy transfer from Dy 3+ to Tb 3+ and from Pr 3+ to Dy 3+ were detected in the co-doped glasses.

Engineered Nanocomposites for Solid Oxide Fuel Cells By Colloidal Crystal Templating

ABSTRACTColloidal crystal templating has been used to prepare three-dimensionally ordered macroporous (3DOM) films of La1-xSrxMnO3-d (LSM), yttria stabilized zirconia (YSZ) and porous composites of LSM and YSZ. These materials have direct applications as cathodes in solid oxide fuel cells (SOFCs). The 3DOM materials have been prepared by low temperature processing, which is a major step towards overcoming electrode sintering, interdiffusion and deleterious phase formation associated with conventional high temperature processing. The preparation of porous composites and the elimination of high temperature densification presents an opportunity to create SOFCs with a large number of triple phase boundaries which should be accompanied by an corresponding improvement in device performance. The microstructure of the 3DOM films was assessed using scanning electron microscopy and the crystal structure and phase purity assessed by x-ray diffraction.

Luminescent properties of BaO-La2O3-B2O3 glasses with dopant

The luminescent properties of glasses synthesized in air atmosphere by conventional high temperature process were studied. The emissions spectra of Eu2+ and Eu3+ were observed in BaO-La2O3-B2O3-Eu2O3 glasses. The results show that the broad emission peaks at 430 nm correspond to 5d→4f emission transition of Eu2+, the sharp emission peaks at 592, 616, 650 and 750 nm correspond to 5D0→7F j (j=1–4) emission transition of Eu3+, respectively, which indicates that the BaO-La2O3-B2O3-Eu2O3 glass can convert ultraviolet and green components of sunlight into blue and red light so as to increase the intensity of blue and red light, respectively. The luminescent intensity of Eu2+ increases with increasing the molar ratio of Tb3+ in BaO-La2O3-B2O3-Eu2O3-Tb4O7 glasses, whereas the luminescent intensity of Eu3+ decreases. So the luminescent intensity of Eu(III, II) is influenced by Tb3+. These phenomena can be explained by electron transfer mechanism: Eu3+ (4f6) + Tb3+ (4f8) → Eu2+ (4f7) + Tb4+ (4f7). Taking advantage of the luminescent properties of BaO-La2O3-B2O3-Eu2O3 glasses, light-conversion glass for agriculture can be produced.

Deposition of ceramic materials from aqueous solution induced by organic templates

Besides conventional high-temperature sintering processes for the preparation of ceramics, synthesis routes like chemical and physical vapor phase deposition or molecular beam epitaxy as well as sol-gel and polymer thermolysis carried out at decreased temperatures gain in significance. Such a trend is especially pronounced in the case of the deposition of oxide-based solids from aqueous solutions induced by organic templates. This approach is inspired by biomineralization that in general involves the formation of well-structured and complex-shaped organic/inorganic composites by the deposition of an inorganic solid on an organic matrix that consists of biomolecules like proteins. It occurs at ambient conditions with respect to temperature, pressure and atmosphere. The imitation of these processes by technical means is the deposition of thin oxide films from aqueous solutions in the presence of organic self-assembled monolayers. Besides general features of this technique like low synthesis temperatures, processing costs and equipment expenditure as well as the line-of-sight deposition suitable for coating complex shaped and/or temperature-sensitive substrates the characteristics of the films and their mechanisms of formation are discussed by way of the oxide systems TiO 2 , ZrO 2 and ZnO.