Papers by Keyword: Reoxidation

Abstract: At present, the performance enhancement for Si-based transistors can no longer be guaranteed due to intrinsic mobility issues. The considerably higher electron mobility of III-V compound semiconductors (e.g. InGaAs, InAs, InSb) has led to renewed interest and a following phase in the development of future transistors for the 7-5 nm technology node [1].

Abstract: The PTCR characteristics of (Ba_1-xSm_x)TiO₃ (BSMT) with different donor-doped concentration (x) sintered in a reducing atmosphere and reoxidized in air are investigated. The results reveal that the room temperature resistivity (ρ_RT) of the semiconducting BSMT ceramics first decreases and then increases with increasing of the x values, especially when x is 0.004, the semiconducting BSMT ceramics reoxidized at 850oC for 1 h after sintering at 1300 °C for 30 min in a reducing atmosphere achieve a lower room temperature resisitivity of 82.6 Ωcm. in addition, the doped 0.1 mol% Sm³⁺ BSMT samples fired at 1300 °C for 30 min in air exhibit remarkable PTCR effect with a resistance jumping ratio of 3.4 orders magnitude; moreover, a lower ρ_RT of the BSMT specimens sintered in a reducing atmosphere is obtained.

Abstract: Ceramic samples of (1 x)BaTiO_3–xNa_0.5Bi_0.5TiO₃ system were prepared by sintering in reducing atmosphere of N₂/H₂ and were subsequently reoxidized in air. The influence of reoxidation temperature firing on the PTCR effect of (1 x)BaTiO_3–xNa_0.5Bi_0.5TiO₃ ceramics was investigated. The effect of Na_0.5Bi_0.5TiO₃ concentration on resistivity and microstructure of the reoxidized samples was investigated by means of complex impedance spectroscopy and scanning electron microscopy. It has been found that the grain size decreases with the increase in Na_0.5Bi_0.5TiO₃ content. The values of minimum ρmin and maximum ρmax resistivities of the samples were observed to increase with the increase in reoxidation temperature in the 600 – 1000°C temperature range. It was shown that with increasing in reoxidation temperature of (1-x)BaTiO_3-xNa_0.5Bi_0.5TiO₃ solid solutions, potential barrier at grain boundaries increases.

Abstract: In present 92.8% of world steel production is casted on continuous casting machine. The key phase of continuous casting is tundish. Beside of refining effect of slag phase also steel flow in tundish is very important factor. The main causes for inclusion formation and contamination of the melt include reoxidation of the melt by air and carried over oxidizing ladle slag, entrainment of tundish and ladle slag, and emulsification of these slags into the melt. These causes are due to generation of turbulence in the melt. Although turbo stop lowers the turbulence in some extent. But it is not capable of totally decrease of turbulence specially during lowering of metal bath at the time of ladle exchange operation, cause contamination of the steel melt in tundish. So in the present work it has been focused to develop a novel shroud which have significant role to supply of steel from ladle to tundish at slow rate to avoid turbulence, emulsification and formation of slag eye in tundish to produce quality steel in a sustained manner.

Abstract: Physical modeling of argon shroud was carried out using a 2D 1:1 scaled model in order to gain the protection effect in steel casting. The speed field of protective gas around the steel steam was measured by PIV technique. The oxygen distribution was measured by an oxygen sensor. The main findings are following: (1)The distance between the ladle and the collar should be minimized to reduce the oxygen entrainment.(2)For single inlet, the oxygen contents were lower in the case of horizontal gas inlet than vertical gas inlet.(3)A dual gas inlet configuration would be more effective than a single inlet in ordinary operation conditions.

Abstract: The fabrication processes of SrTiO3-based varistors were investigated to obtain highly thermal-shock-resistant devices. It has been found that the reoxidation conditions are strongly related to the thermal cracking ratio (%) of the varistors. A large compressive stress was generated on the varistor surface by reoxidation, consequent upon the lattice parameter difference between its surface portion and its internal portion. This residual stress on the surface is thought to be the key factor of the achieved thermal-shock-resistance.

Abstract: The investigated nanometric magnetite powders were synthesized electrochemically, and examined by XRD and SEM techniques. Their reduction was conducted through the isothermal heating in hydrogen in the temperature range from 600 to 860 K. Kinetics of the hydrogen recovery process during oxidation of freshly formed Fe powders in a water vapor stream was also studied. It was assumed that the solid-gas reaction is diffusion controlled, and Jander’s model was applied to describe it. The experimental data suggest that the reoxidation process proceeds in two stages, at various activation energies. By changing the conditions of the electrochemical (EC) process we were able to produce the iron oxide powders with optimal particle size and activity, for pure hydrogen production through appropriate reduction/oxidation processes.