Oxygen release behaviour of Ce(1−x)ZrxO2 powders and appearance of Ce(8−4y)Zr4yO(14−δ) solid solution in the ZrO2–CeO2–CeO1.5 system

To clarify the existence of metastable phases in the ZrO₂–CeO₂–CeO_1.5 system, evolved-oxygen gas analyses, (EGA), by heating a single phase of t′ and t″ (Ce_(1−x)Zr_xO₂) with various compositions, x, in a reducing gas and successive oxidation were carried out repeatedly. The oxygen release behaviour of the t′ and t″ phases was very complicated. The single κ phases, (Ce_(1−x)Zr_xO₂) with the composition, x=0.5 and 0.6, which were obtained by oxidizing the resulting pyrochlore as a precursor in O₂ gas at 873 K, exhibited a sharp oxygen release at the lowest temperature; the composition range of κ phase may be x=0.450.65. A new tetragonal phase t*, (Ce_(1−x)Zr_xO₂), which was attained by cyclic redox process together with annealing in O₂ gas at 1323 or 1423 K, exhibited a sharp oxygen release at the highest temperature; the composition range of t* phase may be as wide as x=0.200.65. A metastable solid solution expressed by a chemical formula of Ce_(8−4y)Zr_4yO_(14−δ) (y=01) possessing a CaF₂-related structure appeared on deoxidation of the t* phase. A ternary phase diagram containing the t* and Ce_(8−4y)Zr_4yO_(14−δ) solid solution was proposed.     

铸造Monel合金熔铸工艺

对铸造Ｍｏｎｅｌ合金进行了熔铸试验,其熔铸工艺的关键是除氢脱氧。试验运用了氧化驱氢,再充分脱氧的工艺,并通过含氧量和炉前试样剖面等测试和分析,表明该工艺是获得优良Ｍｏｎｅｌ合金铸件的简便有效的工艺方法。     

Al2O3/Cu复合材料的研究进展

概述了Ａｌ２Ｏ３／Ｃｕ复合材料的研究现状,并对其制备工艺以及影响性能的因素进行了介绍。     

Fe—Cr—Ni—N高温耐热钢的抗氧化性研究

用氧化增重法分析了Fe-Cr-Ni-N在1200℃和1250℃,的抗氧化性能,探讨了C,Si,N等元素对合金抗氧化性的影响,并用X－射线衍射法对氧化膜的结构进行了分析;结果表明,当合金的Cr/C在100左右时,0．26－0．30％的C对合金的抗氧化性是有利的;N量较低时能降低合金的氧化,但当量＞0．30％时,氧化加剧,分析表明,尖晶石结构不利于合金形成优异的保护性氧化膜,最佳的保护性氧化膜应是SiO2与Cr2O3构成的复合氧化膜。     

High-temperature oxidation of Fe3Al-based iron aluminides in oxygen

The isothermal high-temperature oxidation behavior of Fe₃Al-based iron aluminides in oxygen has been studied. Fe–25Al was oxidized at 1225, 1330, 1425 and 1530 K, while Fe–28Al, Fe–24Al–5Cr, Fe–24Al–5Ti, Fe–28Al–2Cr and Fe–30Al–4Cr (all compositions in atom percent) were oxidized at 1330 K. The weight gain data were analyzed and rate constants (k_p) determined by assuming a parabolic rate law. The variations of instantaneous parabolic rate constant with time reflected the complexity of the oxidation behavior. These have been attributed to the changes taking place in the nature and properties of the scale as a function of time. The values of k_p for oxidation of Fe₃Al were one to two orders of magnitude lower than those for Ti₃Al-based intermetallics. As revealed by X-ray diffraction, the scale formed on Fe–25Al was predominantly α-Al₂O₃ at higher temperatures, while θ-Al₂O₃ was observed after oxidation at lower temperatures. The observed kinetics matched with α-Al₂O₃-formation kinetics at higher temperatures and θ-Al₂O₃-formation kinetics at lower temperatures. For all the other intermetallics, only α-Al₂O₃ was identified at 1330 K. The whisker morphology of θ-Al₂O₃ and the ridged morphology of α-Al₂O₃ were confirmed by scanning electron microscopy. Alloying with Cr or Ti increased the oxidation rate of iron aluminides, especially during the initial stages. Addition of Ti changed the nature, color, and morphology of the scale, leading to improved adherence.     

钢材热浸镀铝抗高温氧化的动力学研究

通过静态高温氧化试验,研究了纯铝、铝－3％硅、铝－7％硅和铝－9％硅4种镀层高温氧化的动力学特性,推导了动力学方程式的算法,计算了4种镀层的氧化激活能（Q）及其与镀液中硅含量的关系。结果表明：Q＝1029－3226kJ/kg,4种镀层在700-900℃时的氧化规律为非线性递增,纯铝镀的最高使用温度为900℃,对于铝－硅镀层,当镀液中含硅低于3％时的最高使用温度为800℃,高于3％时的最高使用温度为700℃。     

光电式数字日照计安装不规范引起的测量误差分析

文章从光电式数字日照计测量日照时数的原理出发,分析了其安装不水平及未对准南北线、纬度所产生的太阳直接辐照度测量误差。日照时数是以直接辐照度≥120 W/m²作为有日照标准,因此,因安装不规范产生的测量误差仅在直接辐照度接近120 W/m²时会影响日照时数的计算。     

Oxidation and intergranular disintegration of the aluminides NiAl and NbAl3 and phases in the system Nb-Ni-Al

The oxidation behavior is very different for an aluminide with a wide homogeneity range such as -NiAl than for a line compound such as NbAl ₃.Oxidation of -NiAl at temperatures 1273 K leads to a slow-growing -alumina layer. The metal phase beneath the scale remains as -NiAl; however, cavity formation is observed. The cavity formation may be favored by sulphur surface segregation. Oxidation of NbAl ₃ at temperatures 1273 K initially leads to -Al ₂O₃,but the Al depletion causes the formation of Nb ₂ Al beneath the oxide layer. Cracking of the Al ₂O₃ layer opens Nb ₂ Al to the atmosphere, which oxidizes rapidly to Nb ₂O₅ and NbAlO₄.After consumption of the Nb ₂ Al, a layer of Al ₂O₃ formed again on the NbAl ₃ phase, but failure of the alumina and the fast growth of the other oxides occur as a repeated process. Thus, NbAl ₃ exhibited rapid linear oxidation kinetics. Multiphase alloys in the system Nb-Ni-Al generally behave better than NbAl ₃,and the low oxidation rates of -NiAl can be approached. In the temperature range below 1273 K, with a maximum at 1000 K, both NiAl and NbAl ₃ show the pest phenomenon, an intergranular disintegration. Preceding the disintegration, oxygen diffuses into the grain boundaries of the material and Al ₂O₃ is formed at the grain boundaries, beginning from the surface region. NiAl is susceptible only in a very limited range of oxygen pressures and temperatures, whereas NbAl ₃ is much more susceptible.     

Ozonation kinetics of winery wastewater in a pilot-scale bubble column reactor

The degradation of organic substances present in winery wastewater was studied in a pilot-scale, bubble column ozonation reactor. A steady reduction of chemical oxygen demand (COD) was observed under the action of ozone at the natural pH of the wastewater (pH 4). At alkaline and neutral pH the degradation rate was accelerated by the formation of radical species from the decomposition of ozone. Furthermore, the reaction of hydrogen peroxide (formed from natural organic matter in the wastewater) and ozone enhances the oxidation capacity of the ozonation process. The monitoring of pH, redox potential (ORP), UV absorbance (254 nm), polyphenol content and ozone consumption was correlated with the oxidation of the organic species in the water. The ozonation of winery wastewater in the bubble column was analysed in terms of a mole balance coupled with ozonation kinetics modeled by the two-film theory of mass transfer and chemical reaction. It was determined that the ozonation reaction can develop both in and across different kinetic regimes: fast, moderate and slow, depending on the experimental conditions. The dynamic change of the rate coefficient estimated by the model was correlated with changes in the water composition and oxidant species.     

Electrochemical oxidation of organics in water: Role of operative parameters in the absence and in the presence of NaCl

The electrochemical oxidation of organics in water was investigated theoretically and experimentally to determine the role of several operative parameters on the performances of the process in the presence and in the absence of sodium chloride. Theoretical considerations were used to design the experimental investigation and were confirmed by the results of the electrochemical oxidation of oxalic acid (OA) at boron doped diamond (BDD) or IrO₂-Ta₂O₅ (DSA-O₂) anodes in a continuous batch recirculation reaction system equipped with a parallel plate undivided electrochemical cell. Polarization curves and chronoamperometric measurements indicated that, in the presence of chlorides, the anodic oxidation of OA is partially replaced by an indirect oxidation process. This result was confirmed by electrolyses experiments that show that, in the presence of suitable amount of chlorides, oxidation of OA takes place mainly by a homogeneous process. Interestingly, a very different influence of the nature of the anodic material, the flow rate and the current density on the performances of the process arises in the absence and in the presence of chlorides so that optimization of the two processes requires very different operative conditions. In the absence of chlorides, high current efficiency (CE) is obtained at BDD when most part of the process is under charge transfer controlled kinetics, i.e. when low current densities and high flow rates are imposed. On the other hand, in the presence of NaCl, higher CE are generally obtained at DSA anode when high current densities and low flow rates are imposed, i.e. when a high concentration of chemical oxidants is obtained as a result of the chloride oxidation. The effect of other operative parameters such as the OA concentration and the pH were further investigated.