Papers by Keyword: Oxygen Content

Abstract: When zirconium alloy is corroded, an oxide film is formed on the surface, which hinders the ion transfer during the corrosion process. Therefore, the analysis of the oxide film is an important part of the research on the corrosion resistance of zirconium alloys. In this paper, two kinds of Zr-Sn-Nb alloys were corroded in 400 °C/10.3 MPa pure steam and 500 °C/10.3 MPa pure steam in autoclave to obtain samples with oxide thickness of 14 um and 18 um respectively. Then they were annealed at 800 °C at a pressure of 10^-4 Pa for 18 h. XRD and WDS studies were used to analyze the structure and oxygen content of the oxide film after annealing. The results indicate that the oxide films of alloys change from zirconium dioxide to zirconium after annealing. The oxygen diffuses into the substrate and its content decreases continuously with increasing diffusion distance. Combined with the SEM analysis of cross-section samples, it is found that the annealed samples are composed of several layers. An oxygen-saturated zirconium layer, a transitional layer with micro-cracks, an oxygen-dissolved α-Zr layer and a β-Zr layer are identified. Based on these results, the mechanism of the ion transfer in the oxide film during annealing is analyzed deeply. It is proposed that space charges in the oxide film have a major impact on deoxidation kinetics. This study provides a new research method for the corrosion mechanism of zirconium alloys.

Abstract: Ti-6Al-4V alloy is widely used in Aerospace applications owing to its high specific strength, low coefficient of thermal expansion and good corrosion resistance. Presence of interstitial elements in the alloy has some significant effects on its properties. However the poor notch toughness and cryogenic ductility restricts the usage of Ti-6Al-4V for temperatures lower than 77 K (-196 °C). The Extra Lower Interstitial grade alloy was developed in order to improve the notch toughness and cryogenic ductility of the Ti-6Al-4V alloy. In this refined grade, the interstitials, Oxygen and Carbon are controlled to a maximum limit of 0.12% and 0.08% respectively as compared to a maximum of 0.2% and 0.1% of standard Ti-6Al-4V alloy. In this study, the ELI grade of Ti-6Al-4V rods from three different manufacturing sources were subjected to tensile test at liquid hydrogen temperature at 20 K (-253 oC). The tensile properties obtained are compared and analyzed. The obtained ductility at 20 K is observed to have close relation with the chemical composition and interstitial content and compared with the Ti5Al2.5Sn-ELI which is ideally suitable for low temperatures upto 20 K, owing to its single phase HCP structure. A correlation has been made between the ductile properties and microstructure. By close control of chemical composition and mechanical working, Ti6Al4V-ELI can be used for temperatures lower than 77 K (-196 oC), which is otherwise is forbidden. This paper details the test data obtained from three different compositions of Ti6Al4V-ELI at 20 K, which enables the usage of this material for temperatures lower than 77 K (-196 °C) upto 20 K.

Abstract: In this research, heat treatment is the final finishing process applied on nanocrystalline CoNiFe to improve microstructure for good hardness property. Nanocrystalline CoNiFe has been synthesized using the electrodeposition method. This study investigated the effect of heat treatment at 500°C, 600°C, 700°C and 800°C on electrodeposited nanocrystalline CoNiFe. The heat treatment process was performed in the tube furnace with flowing Argon gas. By changing the heat treatment temperature, physical properties such as phase and crystallographic structure, surface morphology, grain size and hardness of nanocrystalline CoNiFe was studied. The nanocrystalline CoNiFe phase revealed the Face Centered Cubic (FCC) and Body Centered Cubic (BCC) crystal structure. FESEM micrographs showed that the grain sizes of the coatings were in the range of 78.76 nm to 132 nm. Dendrite shape was found in the microstructure of nanocrystalline CoNiFe. The nanocrystalline CoNiFe prepared in heat treatment temperature of 700°C, achieved the highest hardness of 449 HVN. The surface roughness of nanocrystalline CoNiFe heated at 700°C was found to be smaller than other temperatures.

Abstract: The Hesigewula lignite was studied by heat treatment in a fixed bed and moisture absorption experiment. The temperature of heat treatment was considered as a factor to investigate its influence on product yield. Under the gas carrier (N₂) flow rate of 200 SCCM, 0.5 MPa and holding for 20 min, the yield of tar firstly increased and reached the maximum of 5.67 wt% at 500 °C, then came to a decrease with the increasing temperature. The proximate and ultimate analyses of the solid products had been measured. As to the moisture adsorption experiment, the equilibrium moisture content of the solid products at different humidity (30 °C) had been calculated. It was shown that the char of 600 °C adsorbed the least moisture with the minimum content of oxygen. It indicated that heat treatment can remove the oxygen-containing functional group and to some extent upgraded the coal rank.

Abstract: WC-FeAl composites were fabricated by vacuum sintering technique from mixture of WC and FeAl powders containing various oxygen content. Mechanical properties such as hardness, fracture toughness and transverse rupture strength were influenced by the oxygen content in the powders. Control of the oxygen content was succeeded by changing the powder preparation process. Contrary to expectations, the reduction of oxygen content led to degrade the fracture toughness and transverse rupture strength of the composites. This result was attributed to the microstructural change in the sintered composite. The sintered composite of lower oxygen content exhibited WC grain growth or inhomogeneous microstructure, which can be the cause of degradation of those mechanical properties. It was concluded that the oxygen content was one of the key factors to influence the microstructure or mechanical properties of WC-FeAl composites.

Abstract: The measurement of oxygen content in liquid iron and steel has been a challenge for decades and there have been many attempts to develop oxygen sensor to adjustment the smelting process on the basis of the probe for monitoring oxygen dissolved in molten liquid. However, there was still not a common standards of zirconium tubes about domestic product, which limited their application and improvement This work selected several domestic enterprises oxygen measuring half-cell system to study the relationship between the physical properties and microstructure at room temperature. Furthermore, we also analyzed about the typical performance of the domestic Oxygen content products, which would be beneficial to test and improve the quality of domestic products. Keywords: zirconia tubes, oxygen content, oxygen sensor

Abstract: It is known that Cu valence of cuprate superconductors govern transition temperature (T_c). For La_2-xSr_xCuO_y, when x = 0.15, that is, Cu valence is 2.15, the highest T_c around 40K is achieved. The Cu valence is determined both by strontium and oxygen content. So far, coulometry and iodometry have been used for determining oxygen content. However, these chemical analyses usually require experience. The purpose of this research is to develop a novel measuring method of oxygen content in cuprate superconductors with a developed dissolved oxygen sensor. Signal received from the sensor is sent to PC automatically without any external power supply. Oxygen content obtained with the sensor was newly compared with iodometry. It was found that this method is reliable enough to determine oxygen content in La_2-xSr_xCuO_y, and is called dissolved oxygen method.

Abstract: The YBa₂Cu₃O_7-δ(Y123) compounds were synthesized by solid state reaction method. The home-made four-probes apparatus was used for the resistivity measurement. The highest T_c is 91.95 K in sample C and sample A has lowest T_c onset at 89.85 K. The crystal structure properties and oxygen content were characterized by powder X-ray diffraction using CuK_α radiation (λ=1.5406 Å). The Pmmm and Pnma space group corresponding on the superconducting phase and the non-superconducting phase. The atomic position of samples were consisted of various element atom. The longer time of oxygen-doping, the increase the critical temperature , superconducting phase and c lattice parameters.

Abstract: In this article the research methods and theoretical models of moisture transfer in the porous medium material are reviewed and summarized. The optimal theoretical model of moisture transfer in the underground tunnel is found out. Through the comparison among different calculating methods of surface moisture content, the limestone material moisture equilibrium curve and the variation curve of time-dependent moisture transmission coefficient and the amount of moisture transfer are calculated. Based on all the statistics above, using the state equation of ideal gas, the variation trend of time-dependent oxygen content under the condition that the moisture transfer amount increased in the underground tunnel is gained, making ways and offering reference for further related research.

Abstract: As the main substrate materials for solar cell, Czochralskisilicon (CZ-Si) has more crystal defects, higher impurities content and so on, which limit the further improvement of conversion efficiency (h). Floating zone melting silicon (FZ-Si) has excellent performance but the feed rod cost is much higher, so it is hardly used for solar cell widely. To solve this problem, we developed CFZ silicon monocrystal (CFZ-Si). First the poly was made into poly rod withΦ110~Φ130mm by CZ process and then made into CFZ-Si by FZ method. During FZ process, the resistivity is controlled by gas doping and the process is adjustable. CFZ-Si combines advantages of CZ-Si with FZ-Si. It has less crystal defects, lower impurities content especially oxygen content (<0.2 ppm) and excellent consistency of axial resistivity. Meanwhile, poly rod used has lower price and easier fabrication, so CFZ-Si cost is much lower and the further cost reduction is easy. Therefore, CFZ-Si has significant comprehensive advantages and broader prospect in the future photovoltaic field.