Strain determination in thermally-grown alumina scales using fluorescence spectroscopy

By exploiting the strain dependence of the ruby luminescence line, we have measured room-temperature residual strains in thermally-grown alumina scales. Measurements were made on two alloys Fe-5Cr-28Al and Fe-18Cr 10Al (at.% bal. Fe), oxidized between 300–1300°C. Significantly different levels of strain buildup were observed in scales on these alloys. Results on similar alloys containing a dilute reactive element (RE) are also presented. Scales formed on RE-containing alloys (Zr or Hf) could support significantly higher strains at T 1000°C. Strain relief associated with spallation thresholds is readily observed. In early-stage oxidation, the evolution of transition phases is monitored using Raman and fluorescence spectroscopies. The fluorescence technique also provides a sensitive probe of early-stage formation of -Al₂O₃. It appears that, in the presence of Cr₂O₃ or Fe₂O₃, the -phase of Al₂O₃ can form at anomalously low temperatures.     

导热绝缘硅胶材料用氧化铝性能研究

本文论述了氧化铝粉体在导热绝缘硅胶材料中的导热机理,并分别论述了氧化铝形貌、粒径分布、杂质含量等对导热绝缘硅胶性能的影响,并提出提高导热绝缘硅胶导热率及柔韧性的措施:提高氧化铝球形度可以提高硅胶的柔韧性,提高氧化铝α-相转化率和晶体的致密度、合理的粒度分布可以提高硅胶的导热率。严格控制杂质含量不但提高硅胶的绝缘性能且能提高导热率。     

Protective behavior of alumina scales in sulfidizing atmospheres

Fe-17Cr steel was aluminized (three different pack-cementation treatments were used) and then oxidized before exposure to a sulfidizing (H ₂/10%H₂S) atmosphere. When the oxidation time is sufficiently high (30 min), the corrosion remains nil for a period termed the immunity time. The corrosion initiates by sulfur diffusion through the alumina scale, which had been formed previously. A diffusion model was established: the sulfur diffusion coefficient in the oxide depends on the oxidation duration and on the aliminizing treatment. Its activation energy was calculated to be 353 kJ and was constant regardless of the prior cementation treatment.     

多壁碳纳米管对氧化铝陶瓷电学和力学性能的影响

利用放电等离子烧结技术(Spark Plasma Sintering,简称SPS)制备得到了不同配比的氧化铝/多壁碳纳米管(Multi-Walled Carbon Nanotubes,简称MWNTs)复合材料,研究了其直流电导率和力学性能.结果表明,当MWNTs含量为5%(体积分数)时,复合材料的电导率比单纯Al2O3提高了近12个数量级,而断裂韧性也提高了大约39%,从3.2 MPa提高到4.44 MPa.因此,通过掺杂少量MWNTs的方法可同时提高氧化铝陶瓷的电学和力学性能而基本不改变其其他性能.     

多壁碳纳米管对氧化铝陶瓷电学和力学性能的影响

利用放电等离子烧结技术（Spark Plasma Sintering，简称SPS）制备得到了不同配比的氧化铝／多壁碳纳米管（Multi—Walled Carbon Nanotubes，简称MWNTs）复合材料，研究了其直流电导率和力学性能。结果表明，当MWNTs含量为5％（体积分数）时，复合材料的电导率比单纯Al2O3提高了近12个数量级，而断裂韧性也提高了大约39％，从3．2MPa提高到4．44MPa。因此，通过掺杂少量MWNTs的方法可同时提高氧化铝陶瓷的电学和力学性能而基本不改变其其他性能。     

氧化铝原料对合成SrAl2O4(Eu,Dy)材料余辉发光性能的影响

通研究不同氧化铝原材料的组成和形貌,分析它们对合成稀土铝酸盐长余辉发光材料性能的影响,发现原晶结构和晶粒类型是影响合成产物长余辉发光性能的重要因素;而通常氧化铝原料的纯度基本上可以满足合成原料的纯度要求。     

Mechanical properties of oxide scales

At high temperatures most alloys rely on the protective effect of oxide scales formed by the reaction between oxygen from the environment and components of the alloy. The protective effect of these scales may, however, be impaired if stresses lead to cracking or spalling. Therefore, the mechanical properties of the scales play a vital part in protection, in particular under service conditions of the materials where the presence of stresses cannot be excluded. The paper provides a survey of the existing models that describe the mechanical properties of scales (the emphasis being on mechanical scale failure), the measuring techniques and the data. It will be demonstrated that, in the case of tensile conditions, the situation is relatively well understood and that a fair amount of data exists. With regard to compressive conditions scale failure consists of a combination of different failure steps, which can each be described by a quantitative model, but there is still clearly a need for experimental verification. While the measuring techniques for the properties under tensile stresses are fairly well developed, those for the behavior under compressive stresses, in particular those characterizing scale adhesion, are still under discussion and relatively few experimentally determined data are available in this case. Nevertheless, existing knowledge can be put to good use in assessing scale behavior under the effect of stresses, based on the models and data given in the paper.     

Microstructural characterization and adherence of α-Al2O3 oxide scales on Fe-Cr-Al and Fe-Cr-Al-Y alloys

Several features of the microstructure and the adherence of alumina scales formed on Fe–Cr–Al and Fe–Cr–Al–Y single- and polycrystalline alloys after oxidation at 1000°C were examined. The convolutions of the scale and especially of the scale/alloy interface are thought to be the major reason of poor spallation resistance of scales on the yttrium-free alloy. The flat oxide scale on the even interface of the yttrium-doped alloy, on the contrary, exhibits excellent adherence upon cooling. Interfacial cavities observed on the Fe–Cr–Al alloy result from the scale undulation under compressive growth stresses. The shape and the number of cavities depend on the initial surface orientation and most probably reflect a balance between the interfacial energy of convoluted substrate in contact with the oxide layer and the energy of separated surfaces.     

氧化铝生产过程中结疤的生成及防治技术的探索

探讨了碱法生产氧化铝过程中结疤的生成机理和危害以及传统处理方法的弊端,结合中国铝业山东分公司第二氧化铝厂生产物料的结疤状况,对预脱硅工艺预防管道化溶出器结疤进行试验和研究,得出了技术控制条件;将新型化学阻垢剂应用在管式降膜蒸发器,减少了蒸发器结疤速度,延长了蒸发器酸洗周期;将永磁防垢装置应用在精液管道上,减少精液结疤,延长精液降温板式换热器的清洗周期,同时预期解决结疤影响流量计计量准确问题;通过对几种防治结疤的技术在预防氧化铝生产结疤生成方面的实际应用效果展开综合论述,总结并提出了几种切实可行的防治或减缓结疤的途径。     

Mechanical behaviors of alumina ceramics doped with rare-earth oxides

The effects of three types of additives Y₂O₃, La₂O₃, and Sm₂O₃ on the sintering and mechanical behaviors of alumina ceramics were investigated. The bending strengths of alumina ceramics with Sm₂O₃ and Y₂O₃ additions were 455 and 439 MPa, respectively, higher than that with La₂O₃ addition. The fracture toughness of the ceramics with Sm₂O₃ and Y₂O₃ were also higher than that with La₂O₃ addition. The fracture mode of rare earth oxides doped alumina ceramics exhibited obvious transgranular fractures as well as intergranular fracture. The results of research show that the improvement of bending strength and fracture toughness of alumina ceramics with rare earth oxides was achieved by refining the grain size and strengthening the grain boundary.     

氧化铝增强化学镀镍基合金涂层的性能

研究了氧化铝微粒增强化学镀镍 (铜 ,磷 )合金涂层的性能。在Al2 O3和Ni(Cu ,P)合金共沉积过程中 ,Al2 O3在溶液中的加入量增多 ,Al2 O3在镀层中的复合量逐渐提高 ;Al2 O3的复合 ,显著改变了Ni(Cu ,P)合金沉积层的组织与性能 ,使Ni(Cu ,P) Al2 O3复合材料具有更高的硬度、耐磨性和抗氧化性。     

Metallic yttrium additions to high temperature alloys: Influence on Al2O3 scale properties

In the present study, the effect of adding yttrium to alloys is investigated. The microstructure of the cast Fe-25Cr-4Al-0.5Y alloy used in the study shows that the vttrium is present in different shapes and sizes as the intermetallic phase, (Fe, Cr)₄(Al, Y), previously unreported in the literature. Upon oxidation in dry oxygen in the 1100–1200 °C temperature range, a columnar, fine-grained (0.5–1 m) -Al₂O₃ scale is formed which grows predominantly by inward oxygen grain-boundary transport. The intermetallic phase, during incorporation into the oxide scale, is converted into Y₃Al₅O₁₂, the chromium and iron from the intermetallic diffusing back into the metal matrix. The Y₃Al₅O₁₂ phase saturates the oxide scale with yttrium, which segregates to oxide grain boundaries. The microstructural features of the oxide scale resemble those of the scale formed on the yttria-dispersed alloy we investigated earlier. The improved adherence of the oxide scale is a consequence of yttrium doping, which facilitates the formation of a fine-grained scale in which oxide growth stresses can be relieved by diffusional plastic flow. Further, yttrium suppresses Al transport in the oxide scale and prevents Al₂O₃ nucleation within the scale, a process which can generate compressive stresses in the scale. The yttrium doping in the oxide scale is somewhat more efficient when it is present as a dispersoid in the metal.     

Al_2O_3陶瓷基片电子封装材料研究进展

总结微电子封装技术对封装基片材料性能的要求,介绍Al2O3的多晶转变和典型性能,讨论超细Al2O3粉体的3种制备方法:固相法、气相法和液相法;分析Al2O3陶瓷常用烧结助剂的基本作用和Al2O3陶瓷常用的6种烧结方法:常压烧结法、热压烧结法、热等静压烧结法、微波加热烧结法、微波等离子烧结法和放电等离子烧结法;指出Al2O3陶瓷基片的发展方向。     

Transport processes in the oxidation of Ni studied using tracers in growing NiO scales

Experimental techniques have been developed for determining Ni⁶³ and O¹⁸ tracer distributions in NiO scales ranging in thickness from 0.1 to 100 . These have been used to investigate Ni and O transport in scales on {100} Ni crystals and polycrystalline Ni in the temperature range 500–1300° C. NiO grown on {100} Ni crystals at 1000°C was uniform and compact and grew by the bulk diffusion of Ni in NiO by a vacancy mechanism. At temperatures below 800°C the principal transport mechanism was short-circuit diffusion of Ni in NiO. At all temperatures short-circuit diffusion of oxygen contributed to scale growth on polycrystalline Ni and was responsible for growth of the inner layer of duplex scales. The oxygen diffusion paths are believed to be micro-cracks induced by growth stresses.     

CuxAlO2(0.92≤x≤1.0)陶瓷电输运性能

使用高温固相烧结法制备不同化学剂量比的CuAlO2陶瓷,研究CuxAlO2(0.92≤x≤1.0)中Cu、Al摩尔比的相对变化对其结构和导电性能的影响.结果表明:CuxAlO2(0.92≤x≤1.0)陶瓷片的结构和密度随着x值的增大,样品的结晶性逐渐变好,密度也逐渐增大,在x为0.98时,得到密度最大(5.02 g/cm3)且结晶良好的纯相CuAlO2;样品的光学带隙均约为3.44 eV;随着x值的增加,室温电导率先增大然后减小,在x为0.98时得到最大电导率为8.03×10-3 S/cm;电导率随温度的升高而显著增大,且曲线在100～300 K之间很好地符合Arrhenius关系,x为0.98时激活能最低,仅为0.085 eV;在所研究的成分范围内,CuAlO2陶瓷的导电能力主要取决于陶瓷片的致密度.     

Influence of annealing treatment on properties and microstructures of alumina dispersion strengthened copper alloy

Alumina dispersion strengthened copper(ADSC) alloy was produced by internal oxidation. The hardness, ultimate tensile strength and electrical conductivity measurements and microstructure observation on the produced 0.12?SC (0.24% Al2O3, mass fraction) and 0.25% ADSC (0.50% Al2O3) subjected to different annealing treatments were conducted. The results show that the microstructure of the produced ADSC is characterized by an uniform distribution of nano-Al2O3 particles in Cu-matrix; the particles range in size from 20 to 50 nm with an interparticle spacing of 30 - 100 nm. The produced 0.12% ADSC can maintain more than 87% hardness retention after 900℃, 1 h annealing treatment; the recrystallization can be largely retarded and is not fully completed even after annealing at 1 000℃ for 1 h, followed by cold deformation of 84% ; local grain growth can be observed after 1 050℃ ,1 h annealing treatment. The results also show that increasing either the alumina content or cold deformation degree increases the hardness of the produced ADSC.     

粉煤灰精细利用--提取氧化铝研究进展

阐述了电厂废弃物粉煤灰精细利用的重要意义，介绍了粉煤灰的物理化学性质以及从粉煤灰中提取氧化铝的研究现状。在此基础上指出了粉煤灰精细利用的不足和研究方向。     

Intensifying digestion of diaspore and separation of alumina and silica

1　INTRODUCTIONDespitetheabundantdepositofbauxitesinChi na ,ofthosepredominantisthediasporictypewithhighalumina ,highsilicaandlowferricoxides .Thebauxitedeposit,withthemassratioofaluminatosil ica(A/S)between 4and 8,accountsfor 80 %ofallthebauxitedeposit.Thenatureofhighsilicacontentdeterminesthatthemainlyadoptedtechniquetopro ducealuminainChinashouldbeBayer sinteringcom binationprocessorevenpuresinteringprocess .Althoughadramaticadvancementinaluminaproductionhasbeenachievedandthetechnolo…     

Laser dressing of alumina grinding wheels

High-power lasers are being explored as a non-contact-type dressing tool for alumina grinding wheels. The alumina grinding wheel surface underwent melting and/or vaporization on the surface when laser-dressed, forming a modified layer on the surface. Refinement of the grain size took place. The individual particles that formed on the surface had well-defined faceted structures. Microcutting edges were generated on the individual grains and particles, which can act as cutting edges for efficient grinding. The results of x-ray diffraction and pole figure analysis suggested that the formation of these faceted structures was due to the preferential orientation of the grains after dressing. This paper was presented at the fourth International Surface Engineering Congress and Exposition held August 1–3, 2005 in St. Paul, MN.     

AlCl3-BMIC离子液体的电导率

研究AlCl3-BMIC(氯化-1-甲基-3-丁基咪唑)离子液体电导率与温度、组分之间的关系。结果表明:当离子液体中AlCl3的摩尔分数x(AlCl3)<0.667时,离子液体的电导率随着x(AlCl3)的增加而增大;但在0.6670.5的路易斯酸性区域,x(AlCl3)对温度系数α、β的影响均不明显。