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镁及镁合金是最轻的结构工程金属,符合当今减重、节能、环保等要求。镁合金还具有高阻尼能力、良好的铸造性和焊接性、较高的导热性和导电性以及可回收特性。对比目前应用广泛的铝合金,镁合金的使用在满足力学性能要求的同时可以达到减重的效果,并减小对环境的压力。镁合金应用前景广阔,但其对氧的高亲和力导致其在加工或使用过程中极易被氧化,且生成的氧化膜疏松多孔,不具有保护性,导致镁合金的加工与应用受到极大限制。因此,镁合金高温抗氧化性能研究是一个重要的研究方向。目前,国内外镁合金高温氧化研究主要集中在以下几个方面:(1)不同温度下镁合金的氧化行为研究;(2)合金化对镁合金高温氧化性能的影响;(3)不同状态(液态/固态)镁合金的氧化行为。虽然镁合金氧化性研究已经较为深入,但至今仍缺乏综述性的总结。因此,本文旨在综述并分析国内外镁合金高温氧化的研究现状,主要关注不同温度下镁合金的氧化行为、合金化对镁合金高温氧化性能的影响及其机理、镁合金氧化机理及保护性氧化膜失效的原因。 相似文献
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N 型和 K 型热电偶合金经1300℃,483h 高温氧化后,以电子探针 X 射线显微分析仪,X 射线衍射仪,金相显微镜分别对 K 型和 N 型热电偶合金高温氧化层的形态,合金元素分布,相组成,基体内氧化等情况进行对比分析。试验证明,N 型合金氧化层厚度较薄,其致密性及基体附着性均优于 K 型合金。此外,N 型合金氧化层中 Ni 含量低于基体含量,而 Cr,Si 的含量较高,在 NN 极合金中 Mg 明显地存在于氧化层中。N 型热电偶合金高温抗氧化性优于 K 型热电偶合金是由于 Cr_2O_3,SiO_2及 MgO 对高温氧化过程的扩散起阻碍作用。 相似文献
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镁合金微弧阳极氧化膜的特性 总被引:1,自引:0,他引:1
采用扫描电镜(SEM)、X射线衍射(XRD)等方法初步研究了镁合金微弧氧化膜的成分、相组成及其形貌特征.结果表明,在微弧氧化处理过程中,镁合金基体中的合金元素Al向表面扩散进入氧化膜层,微弧氧化处理液组分中的元素也进入了氧化膜层.氧化膜主要由MgO、Mg2SiO4、MgAl2O4和不定形相组成.在微孤氧化过程中,氧化膜中首先产生的物相为立方结构的MgO,随着氧化时间的延长,氧化膜中出现晶态的MgAl2O4及Mg2SiO4. 相似文献
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目的利用2,2,6,6-四甲基哌啶氧化物自由基(TEMPO)/NaClO/NaBr氧化体系改善废纸浆纤维成纸的性能。方法以废纸浆为原料,在碱性条件下采用TEMPO/NaClO/NaBr氧化体系对纤维进行选择性氧化,得到不同羧基含量的氧化废纸浆,通过纤维形态分析仪及化学分析法对纤维形态和羧基含量进行分析和测定;将氧化废纸浆、氧化废纸浆与原浆进行抄片和配抄,对手抄片的强度性能进行检测和分析;从经济效益出发,研究氧化体系中TEMPO及NaBr的循环使用次数对纸张强度性能的影响。结果随着NaClO用量的增加,废纸浆纤维的羧基含量增加;纤维长度、宽度和粗度有所降低;纸张抗张强度和环压强度增长较为明显;NaClO和NaBr循环使用2次后纸张的强度性能有所降低,但降低幅度不大。结论TEMPO氧化体系可用于废纸浆的氧化,改善废纸浆的性能。NaClO和NaBr的循环使用能够降低生产成本。 相似文献
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AbstractKey principles of alloy oxidation are discussed, with emphasis on Cr2O3 and Al2O3 formation on nickel-, cobalt, and iron-base alloys. The various special cases of alloy oxidation, which are quantifiable to varying degrees, are presented schematically. The important competition between surface scale development and internal oxidation is emphasized and extended to explain transient oxidation. The ability to measure and model the distribution of alloying elements in steady-state scale and substrate is described. The priority now is to understand further alloying element and defect segregation and transport in grain boundaries, and also other short-circuit paths including pores, in Cr2O3 and Al2O3 scales.Interaction between alloy depletion, void formation, and phase-boundary oxidant transport in single- and multi-phase alloy substrates requires further elucidation. Brief consideration of ternary and quaternary alloy oxidation illustrates the, ability partially to explain complex alloy behaviour. The role of reactive element additives and dispersoids is reviewed concisely in light of recent work. MST/442 相似文献
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通过叙述C/C和C/SiC两种复合材料的氧化特点分析了碳纤维增强陶瓷基复合材料(CFRCMCs)的氧化行为,分别从纤维、基体、界面层及外表面4个方面综述了碳纤维改性、基体抗氧化技术、界面层抗氧化技术和表面涂层技术4种CFRCMCs的抗氧化技术,分析了4类抗氧化技术的原理和特点。 相似文献
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The oxidation kinetics of polycrystalline aluminium nitride substrates in air at temperatures in the range 1150 to 1750°C have been studied by measuring the weight increase in the oxidized samples. At the lowest temperature, the oxide layer was not continuous on the AlN surface and the oxidation kinetics followed a linear rate law with an activation energy of 175 kJ mol–1. At all the higher temperatures, the growth kinetics followed a parabolic rate law with an activation energy of 395 kJ mol–1. Samples oxidized at these higher temperatures were covered with a dense oxide layer having a fine-grained microstructure. 相似文献
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Owing to their unique short- or medium-range ordered microstructures and excellent mechanical, physical, and chemical properties, amorphous alloys have attracted significant interest in recent years. For the application of amorphous alloys, clarifying their oxidation processes and mechanisms is necessary since many of the surface-related properties of amorphous alloys largely depend on the surface oxide layer. The aim of this paper is to review the recent research on the thermal oxidation behaviors of amorphous alloys under pure oxygen or air condition. The contents are divided into three categories according to the number of components the research considers, i.e., the oxidation of binary, ternary, and multi-component (>3) amorphous alloys. Each section discusses the thermal stability of the amorphous matrix, oxidation kinetics, and the oxide layer and amorphous substrate, which are strongly affected by internal factors (i.e., alloy elements and microstructure) and external factors (i.e., oxidation temperature, duration, and oxygen partial pressure, etc.). The general features of the oxidation of amorphous alloys – from simple binary to complex multi-component amorphous alloys – will be summarized. This overview of the current scientific understanding on the fundamentals of these materials may provide guidelines for the development of strongly corrosion-resistant amorphous alloys. 相似文献
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The physics and chemistry of the actinide elements form the scientific basis for rational handling of nuclear materials. In recent experiments, most unexpectedly, plutonium dioxide has been found to react with water to form higher oxides up to PuO(2.27), whereas PuO(2) had always been thought to be the highest stable oxide of plutonium. We perform a theoretical analysis of this complicated situation on the basis of total energies calculated within density functional theory combined with well-established thermodynamic data. The reactions of PuO(2) with either O(2) or H(2)O to form PuO(2+delta) are calculated to be endothermic: that is, in order to occur they require a supply of energy. However, our calculations show that PuO(2+delta) can be formed, as an intermediate product, by reactions with the products of radiolysis of water, such as H(2)O(2). 相似文献
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Y. A. Chang 《Journal of Materials Science》1969,4(7):641-643
The oxidation kinetics of molybdenum disilicide over the temperature interval, 1328 to 1765° K, has been studied using a thermal conductivity method. The rates of oxidation were found to follow a parabolic relationship once a protective coating was formed. From the temperature dependence of the parabolic rate constants, an activation energy of 20 kcal/mole was obtained. 相似文献