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Supercritical Fluid Technology
Published in Shintaro Furusaki, John Garside, L.S. Fan, The Expanding World of Chemical Engineering, 2019
The method to produce metal (hydro)oxides by using these reactions is the hydrothermal crystallization method. Ordinary, this method is operated at around 100–200°C. Adschiri et al. (1992a, 1992b, 1998) have developed a new processes for the hydrothermal crystallization of metal oxide fine particles in supercritical water. By using the experimental apparatus shown in Figure 7.9, an aqueous metal salt solution was fed by a HPLC pump and mixed with supercritical water at a mixing point. By this method, the metal salt solution rapidly heats up to the supercritical state and hydrothermal synthesis initiates. Results are summarized in Table 7.3. Synthesis of fine metal oxide particles with specific morphologies with this method has been demonstrated for nitrates, chlorides, and sulfates for various metals. Some specific features of the supercritical hydrothermal synthesis method that have been elucidated are: 1) nano size particles are produced due to the fast hydrolysis rate and the lower solubility in supercritical water. 2) morphology of the particles can be controlled due to the drastic change of properties of water around the critical point, as shown in Figure 7.10 (Adschiri, 1992b). 3) oxidizing or reducing atmosphere can be controlled by introducing oxygen, CO or hydrogen gases as a homogeneous reaction atmosphere can be formed. This method has been applied to produce a magnetic material (barrium hexaferrite), phosphor (YAG:Tb), and a Li ion battery material (LiCoO2) (Hakuta et al. 1995, 1998, Adschiri, 1999).
Introduction to Fault Detection and Diagnosis
Published in Janos J. Gertler, Fault Detection and Diagnosis in Engineering Systems, 2017
The function of the catalytic converter is to remove the three pollutants from the exhaust gas. On most cars, a single-bed catalyst is employed. While the removal of carbon monoxide and hydrocarbons requires an oxidizing atmosphere (excess oxygen), nitrous oxides can be removed in a reducing atmosphere (no excess oxygen). Reasonable performance for all three pollutants can be achieved if the air-to-fuel ratio is kept close to the stoichiometric value of 14.7 (Fig. 1.3). To maintain this stoichiometric ratio is the main objective of the engine’s fuel control system, which is implemented as a function of the on-board computer.
Amorphous In-Ga-Zn-O Thin Film Transistors: Fabrication and Properties
Published in Zhe Chuan Feng, Handbook of Zinc Oxide and Related Materials, 2012
This fact in turn indicates that electron doping is possible just by forming oxygen deficiencies, which is the same model of residual free electrons in TCOs. This is done by reducing oxygen partial pressure during film deposition (PO2) or post-deposition thermal annealing in a reducing atmosphere. Alternatively, ion implantation such as H+/H2+/Li+is also an effective way to change the charge neutrality [6,129]. Thus substitution doping is not a valid concept to understand doping in AOSs, and counting formal changes of constituent ions [6] is a simple and effective way.
Control of a pulse combustion reactor with thermoacoustic phenomena
Published in Instrumentation Science & Technology, 2018
Gregor Križan, Janez Križan, Ivan Bajsić, Miran Gaberšček
There are two ways to maintain the slightly reducing atmosphere: by introducing a reductive gas into a heated reactor or by the non-stoichiometric burning of carbonaceous fuels. The most commonly used reductive gases are hydrogen and carbon monoxide; the latter is also a reductive species when burning carbonaceous fuels. It is also possible to completely combust stoichiometric mixtures[12] or have a stable combustion of fuel-rich mixtures. This makes it possible for the combustor to operate in a reductive environment, albeit with reduced thermal efficiency. To take advantage of the efficiency of combustion and to enhance the reductive character of the atmosphere inside the reactor, it is possible to add reductive gases in the neck of the combustor, similar to staged combustion. In this manner, the reductive gas does not burn and is used exclusively for reduction inside the reactor. The position of the reductive gas inlet is marked in Figure 1.
Trap creation, trap conversion and thermoluminescence process in barite – effect of flux
Published in Radiation Effects and Defects in Solids, 2020
J. Nandha Gopal, Bhaskar Sanyal, Arunachalam Lakshmanan
Typical TL glow curves of Undoped BaSO4(A), Na2SO4 doped BaSO4 (B) and NaCl doped BaSO4 (C) as a function of 60Co γ-dose obtained after various sintering treatments are shown in Figures 7–9, respectively. Table 4 compares the TL sensitivities (total area of glow curve) of these samples after various sintering treatments. The TL sensitivities of all three phosphors increased with sintering temperature in the range 500–1000°C as a result of increased production/stabilization of defect centers giving rise to TL. In all three samples, on 500°C, 1h air annealing, peak I is the major TL peak while peak II is weak in intensity. On 600°C, 1h air annealing, peak II occurring at 250°C is dominant. On 700°C, 1 h air annealing the peak II to peak I TL peak ratio increased further. On 1000°C, 1 h air annealing the peak II is quite dominant as compared to peak I. At 1000°C sintering temperature, the TL sensitivity of undoped BaSO4 (A1000) is only 25% of the one made with NaCl flux (C1000). This shows that NaCl flux improves the creation of defects causing peak II. In Table 4, in the sintering temperature range 500–700°C, no significant change in TL sensitivity is seen between the undoped, Na2SO4 and NaCl doped BaSO4. Only at 1000°C sintering temperature which is above the melting points of NaCl (801°C) and Na2SO4 (884°C), the TL sensitivities show a drastic change. NaCl enhances the TL sensitivity by a factor of 3.94 while Na2SO decreases the TL sensitivity by a factor of 1.75. The BaSO4 made by precipitation method and sintered at 850°C for 1h in reducing atmosphere (A850) showed a higher TL sensitivity which is comparable to that of sample (C1000) sintered in air at 1000°C. It is known that during co-precipitation involving BaCl2 and Na2SO4, precipitation products such as NaCl can get into the BaSO4 lattice (23) leading to the high TL sensitivity comparable to the NaCl mixed BaSO4 sintered at 1000°C (C1000). The nano sample (A180) shows the least TL sensitivity. At 180°C sintering temperature only peak I is produced. High-temperature peak near 250°C (peak II) requires thermal activation energy which occur when the BaSO4 sample is sintered at temperatures > 500°C in air. A850 is made by co-precipitation technique usually adopted for the preparation of BaSO4:Eu2+ (22, 23) while the other materials are commercial grade undoped BaSO4. The purpose of reducing atmosphere has relevance to reducing Eu3+ to Eu2+. But in this work, no Eu doping was done. Reducing atmosphere in general prevents oxygen incorporation. The fact that even air firing results in higher TL sensitivity indicates that oxidation is not an issue in the TL of undoped BaSO4.