Polymer magnetic microactuators fabricated with hot embossing and layer-by-layer nano self-assembly

Polymer-based magnetic microactuators have been fabricated with hot embossing technique and layer-by-layer (LbL) nano self-assembly. Silicon molds are fabricated with conventional UV lithography and wet etching techniques. Hot embossing is used to transfer the patterns from silicon molds to polymethylmethacrylate (PMMA) sheets. The overall processing time for the pattern transfer is less than 20 min. Low-cost devices with massive and rapid replication can be fabricated. Six layers of magnetic iron oxide (Fe2O3) nanoparticles are LbL self-assembled on the PMMA surface as the magnetically sensitive material. Positive photoresist PR1813 is used as the sacrificial layer to protect the gold electrode on the back side of the membrane. LbL nano self-assembly technique provides a simple method to obtain the magnetic film with low cost, short processing time, simple fabrication steps at room temperature. The volume of the magnetic material can be precisely controlled by the number of nano-assembled iron oxide layers. The mechanical, electrical, and magnetic properties of the microactuator are characterized by a laser interferometer. The natural frequency of the actuator is approximately 151 Hz; and the maximum deflection amplitude is about 34 nm. At all frequencies, the increase of the magnetic field increases the deflection amplitude which is in agreement with the theoretical equation.     

热处理温度对510L热轧带钢原始氧化皮结构及其腐蚀行为的影响

利用不同温度的热处理工艺改善510L热轧带钢表面原始氧化皮结构,通过X射线衍射(XRD)、扫描电子显微镜(SEM)、EDS、电化学测试方法对不同结构氧化皮的热轧带钢在NaHSO<,3>溶液中的腐蚀行为进行了研究.结果表明:当温度低于570℃时,随氧化温度的增加,氧化皮上分布的白色弥散状组织减少,氧化皮的微观形貌由带毛刺...     

Effect of Oxide Assisted Metal Nanoparticles on Microstructure and Morphology of Gallium oxide Nanowires

Several researches have been reported about the characteristic of β-Ga2O3 nanowires which was synthesized on nickel oxide particle. But indeed, recent researches about synthesis of β-Ga2O3 nanowires on oxide-assisted transition metal are limited to nickel or cobalt oxide catalyst. In this work, Gallium oxide (β-Ga2O3 ) nanowires were synthesized by a simple thermal evaporation method from gallium powder in the range of 700 - 1000℃ using the iron, nickel, copper, cobalt and zinc oxide as a catalyst, respectively. The β-Ga2O3 nanowires with single crystalline without defects were successfully synthesized at the reaction temperature of 850, 900 and 950℃ in all the catalysts. But optimum experimental condition in synthesis of nanowires varied with the kind of catalyst. As increasing synthesis temperature,the morphology of gallium oxide nanowires changed from nanowires to nanorods, and its diameter increased. From these results, we could be proposed that the growth mechanism of β-Ga2O3 nanowires was changed with synthesis temperature of nanowires. Microstructure and morphology of Synthesized nanowire was characterized by HR-TEM, FE-SEM, EDX and XRD.     

Growth and process conditions of aligned and patternable films of iron(III) oxide nanowires by thermal oxidation of iron

A simple, catalyst-free growth method for vertically aligned, highly crystalline iron oxide (α-Fe(2)O(3)) wires and needles is reported. Wires are grown by the thermal oxidation of iron foils. Growth properties are studied as a function of temperature, growth time and oxygen partial pressure. The size, morphology and density of the nanostructures can be controlled by varying growth temperature and time. Oxygen partial pressure shows no effect on the morphology of resulting nanostructures, although the oxide thickness increases with oxygen partial pressure. Additionally, by using sputtered iron films, the possibility of growth and patterning on a range of different substrates is demonstrated. Growth conditions can be adapted to less tolerant substrates by using lower temperatures and longer growth time. The results provide some insight into the mechanism of growth.     

制备金属氧化物纳米粉的液雾燃烧工艺研究

将金属熔融并过热到一定的温度，然后由高压纯氧将其雾化并立即于燃烧塔内进行直接氧化燃烧，可快速制得金属氧化物纳米粉体。应用该工艺不仅制备出了Ｂｉ２Ｏ３、ＳｎＯ２、Ｉｎ２Ｏ３粉末，同时对Ｓｎ－Ｉｎ合金熔体进行液雾燃烧时，获得了复合的ＳｎＯ２／Ｉｎ２Ｏ３金属氧化物纳米粉体，粉末的最大粒径为２５ｎｍ。金属雾滴燃烧时的强烈挥发、高速飞行过程中的再雾化以及表面氧化膜的快速剥离是使得燃烧产物达到纳米级粉体的基本原因。     

Improvement on the Oxidation Resistance of a Ti3Al Based Alloy by Cr1-xAlxN (0≤x≤0.47) Coatings

Cr1-xAlxN coatings have been deposited on a Ti3Al based alloy by reactive sputtering method. The results of the isothermal oxidation test at 800-900 ℃ showed that Cr1-xAlxN coatings could remarkably reduce the oxidation rate of the alloy owing to the formation of Al2O3 Cr2O3 mixture oxide scale on the surface of the coatings. No spallation of the coatings or oxide scales took place during the cyclic oxidation at 800℃. Ti was observed to diffuse into the coatings, the diffusion distance of which was very short, and the diffusion ability of it was proportional to the Al content in the coatings. Compared to Ti, Nb can diffuse much more easily through the whole coatings and oxide scales.     

Improvement on the Oxidation Resistance of a Ti3Al Based Alloy by Cr1-xAlxN （0≤x≤0.47） Coatings

Cr1-xAlxN coatings have been deposited on a Ti3Al based alloy by reactive sputtering method. The results of the isothermal oxidation test at 800-900℃ showed that Cr1-xAlxN coatings could remarkably reduce the oxidation rate of the alloy owing to the formation of Al2O3＋Cr2O3 mixture oxide scale on the surface of the coatings. No spallation of the coatings or oxide scales took place during the cyclic oxidation at 800℃. Ti was observed to diffuse into the coatings, the diffusion distance of which was very short, and the diffusion ability of it was proportional to the AI content in the coatings. Compared to Ti, Nb can diffuse much more easily through the whole coatings and oxide scales.     

扫描电镜在热轧板表面氧化铁皮分析中的应用

用扫描电镜(SEM)及能谱分析(EDS)、X射线衍射(XRD)等方法对精轧前采用及未采用除鳞系统(FSB)的两种工艺下的热轧板表面的氧化铁皮作了对比分析。结果表明，两种工艺下的热轧板表面氧化铁皮结构均由三种铁的氧化物FeO、Fe3O4和Fe2O3构成；在靠近基板到表层的氧化铁皮中三种铁的氧化物按FeO，Fe3O4和Fe2O3顺序逐渐增多，且内层的结构成分以氧化亚铁为主。FeO含量较少的氧化铁皮层与钢板基体结合比较疏松，容易去除。精轧前采用FSB除鳞系统工艺并不能显著缓解热轧板表面的氧化铁皮缺陷问题，通过对热轧生产工艺的优化调整可解决热轧氧化铁皮去除难的问题。     

Scale formation mechanisms of martensitic steels in high CO2/H2O-containing gases simulating oxyfuel environments

Abstract

In oxyfuel power plants, metallic components will be exposed to service environments containing high amounts of CO₂ and water vapour. Therefore, the oxidation behaviour of a number of martensitic 9–12%Cr steels in a model gas mixture containing 70% CO₂–30% H₂O was studied in the temperature range 550–700°C. The results were compared with the behaviour in air, Ar–CO₂ and Ar–H₂O. It was found that in the CO₂- and/or H₂O-rich gases, the mentioned steels tended to form iron-rich oxide scales with significantly higher growth rates than the Cr-rich surface scales formed during air exposure. The iron-rich scales were formed as a result of a decreased flux of chromium in the bulk alloy toward the surface because of enhanced internal oxidation of chromium in the H₂O-containing gases and carbide formation in the CO₂-rich gases. Additionally, the presence of water vapour in the exposure atmosphere led to buckling of the outer haematite layer, apparently as a result of compressive oxide growth stresses. The Fe-base oxide scales formed in CO₂(–H₂O)-rich gases appeared to be permeable to CO₂ molecules resulting in substantial carburization of the steel.     

Influence of TiC additions on the oxidation behaviour of Si3N4-based ceramics

The oxidation behaviour in air of Si3N4 ceramics containing Y2O3 and Al2O3 as sintering aids, with and without a dispersion of TiC particles, has been studied between 1200 and 1400 °C. The influence of TiC additions on the oxidation kinetics is discussed in comparison with the results obtained for the Si3N4–Y2O3–Al2O3 reference material. However, in all cases and within the experimental temperature range, the oxidation kinetics were observed to be of a parabolic type. The microstructure of the oxide scales formed, which has been characterized by scanning and transmission electron microscopy, was observed to depend on the oxidation temperature and the initial composition of the material. © 1998 Chapman & Hall     

靶向药物载体-纳米级磁性氧化铁的合成与性能

研究了纳米级磁性氧化铁的合成工艺和生成产物粒径之间的关系 ,探究了各种因素对Fe3O4 粒径及其分布的影响。结果表明 ,反应体系的 pH值、二价和三价铁离子的摩尔比以及反应温度等均对产物的粒径有不同程度的影响。粒子分散性的研究显示 ,由纯粹反应成分组成的体系中生成的Fe3O4 粒子会相互聚集 ,形成大的具有次级结构的宏观粒子 ,而加入表面活性剂后 ,可有效的防止这种现象的发生 ,粒子的分散性明显变好。     

Thin cuprous oxide films prepared by thermal oxidation of copper foils with water vapor

We present an improved preparation method for the growth of high quality crystals of cuprous oxide films grown by thermal oxidation of cupper foils with water vapor. This method proved to be good for preparing cuprous oxide films with high purity and large grain size. X-ray diffraction studies revealed the formation of Cu₂O films with preferred (111) orientation. The cuprous oxide diodes fabricated by the above technique have been studied using current-voltage method.     

Controlled Growth of One-Dimensional Oxide Nanomaterials

This article reviews the recent developments in the controlled growth of one-dimensional （1D） oxide nanomaterials, including ZnO, SnO2, In203, Ga203, SiOx, MgO, and Al203. The growth of 2D oxide nanomaterials was carried out in a simple chemical vapor transport and condensation system. This article will begin with a survey of nanotechnology and 1D nanomaterials achieved by many researchers, and then mainly discuss on the controlled growth of ID oxide nanomaterials with their morphologies, sizes, compositions, and microstructures controlled by altering experimental parameters, such as the temperature at the source material and the substrate, temperature gradient in the tube furnace, the total reaction time, the heating rate of the furnace, the gas flow rate, and the starting material. Their roles in the formation of various morphologies are analyzed and discussed. Finally, this review will be concluded with personal perspectives on the future research directions of this area.     

Effect of Colouring Process on Pitting Susceptibility of Austenitic Stainless Steel

Colouring of the austenitic stainless steel alloy （20.45% Cr, 8.57% Ni） was carried out in NaNO3-KNO3 eutectic melt without and with additions of Na2O2, NaCl and their mixtures at different temperatures ranging from 400-600℃, under open-circuit and galvanostatic anodic polarization conditions. The produced colours greatly depend on the thickness of oxide films, which in turn depends on the composition of the molten bath and its temperature. The more attractive, bright, adherent and uniform coloured oxide films can be obtained at 400, 450 and 500℃ in molten nitrate bath containing NaCl and Na2O2 mixtures. The pitting corrosion susceptibility of the coloured oxide films was tested in FeCl3 and NaCl as corrosive media. The obtained results indicate that the pitting corrosion susceptibility of the coloured oxide films greatly depends on the previous operating conditions of the colouring process of the stainless steel specimens such as the composition of molten bath, temperature and technique of colouring process.     

Preparation of Manganese Oxide Nanobelts

Oriented nanobelts of manganese oxide have been firstly and successfully prepared by a microemulsion technique under controlled circumstances. The samples were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM). Influences of sodium chloride and annealed temperature on the synthesis of Mn3O4 nanobelts were investigated. It was found that NaCl is the key factor to synthesize oriented Mn3O4 nanobelts and 827 K is optimum temperature to produce fine nanobelts. Oriented growth mechanism of Mn3O4 nanobelts was discussed.     

Effect of water vapour on growth and adherence of chromia scales formed on Cr in high and low pO2-environments at 1000 and 1050°C

Abstract

The oxidation behaviour of pure Cr at 1000 and 1050°C was studied in Ar–O₂ and Ar–H₂–H₂O mixtures. It was found that in the low-pO₂ gases the oxide scales exhibited higher growth rates than in the high-pO₂ gases. The scales formed in the low-pO₂ gases showed substantially better adherence during cooling, than scales formed in the high-pO₂ gases. These differences in growth rate and adherence can be correlated with differences in size and location of the in-scale voids formed during the isothermal exposure. Exposures in Ar-O₂-H₂O mixtures revealed that the differences in scale growth rates as well as in scale void formation and growth are not primarily related to differences in the oxygen partial pressure of the atmosphere but to the presence of water vapour in the test gas. At sufficiently high H₂O/O₂-ratios, water vapour promotes oxide formation at the scale/metal interface thereby suppressing excessive growth of existing voids, and also as a consequence improved scale adherence. Whether the enhancement of inward scale growth is related to transport of H₂O- or H₂-molecules or due to OH^? ions, cannot be derived with certainty from the present results.     

Light-emitting nanocasts formed from bio-templates: FESEM and cathodoluminescent imaging studies of butterfly scale replicas

Nanocasts comprising of red-light-emitting cubic Y(2)O(3):Eu phosphors were made from butterfly wing scale bio-templates. We report herein the first cathodoluminescent images made from such nanocasts and show that valuable insights into the nature of the internal structure of the casts can be gained by the use of this technique. The casts faithfully reproduced the fine sub-micrometre size detail of the scales, as was made evident by both FESEM and cathodoluminescent images that were collected from the same sample areas using a hyphenated FESEM-CL instrument. There was excellent agreement between the FESEM and cathodoluminescent images, the image quality of the latter indicating that the Eu(3+) activator ions were evenly dispersed in the Y(2)O(3):Eu phosphor on a sub-micrometre scale. The casts were made by infilling the natural moulds with a Y(2)O(3):Eu precursor solution that was subsequently dried and fired to convert it into the phosphor material. This method provides a simple, low cost route for fabricating nanostructures having feature dimensions as small as 20?nm in size, and it has the potential to be applied to other metal oxide systems for producing nano-and micro-components for electronic, magnetic or photonic integrated systems.     

Tensile stress and creep in thermally grown oxide

Structural components that operate at high temperatures (for example, turbine blades) rely on thermally grown oxide (TGO), commonly alumina, for corrosion protection. Strains that develop in TGOs during operation can reduce the protectiveness of the TGO. However, the occurrence of growth strains in TGOs, and mechanisms that cause them, are poorly understood. It is accepted that compressive strains can develop as oxygen and metal atoms meet to form new growth within constrained oxide. More controversial is the experimental finding that large tensile stresses, close to 1 GPa, develop during isothermal growth conditions in alumina TGO formed on a FeCrAlY alloy. Using a novel technique based on synchrotron radiation, we have confirmed these previous results, and show that the tensile strain develops as the early oxide, (Fe,Cr,Al)(2)O(3), converts to alpha-Al2O3 during the growth process. This allows us to model the strain behaviour by including creep and this diffusion-controlled phase change.     

Formation of chromium rich oxide scales for protection against metal dusting

Abstract

Metal dusting is a disintegration of metals and alloys into graphite and metal particles, caused by strongly carburizing gas mixtures mainly in the temperature range 400–700°C. Protection of steels against metal dusting is possible through the formation of dense chromium rich oxide scales but it is not guaranteed that such scales are formed at low temperatures, even on high Cr-steels.

Surface analytical studies have been conducted on the formation and composition of the oxide scales on 9–20%Cr steels. The growth of oxide films was followed by AES for 3 hours at 10^–7 mbar O₂ great differences were observed in dependence on surface finish. On ground samples, Mn and Si appeared early and Cr-rich oxide was formed, whereas on chemically etched samples Fe-rich oxides grew.

After long term exposures (240 h) under metal dusting conditions, i.e. in CO–H₂–H₂O mixtures at 600°C, thin Cr-rich scales were observed on ground steels which were impermeable to carbon whereas on chemically etched steels thick Fe-rich scales had grown and carbon penetration was detectable. Accordingly, the oxide formation on Cr-steels at relatively low temperatures strongly depends on the surface treatment. Any surface working such as grinding and sand-blasting etc. introduces dislocations and causes a fine-grained microstructure near the surface, and the dislocations and grain boundaries act as rapid diffusion paths for supply of Cr to the surface in the first minutes of exposure, which leads to the formation of a protective oxide scale.     

原位Al2O3片晶/Ce-TZP和SrO·6Al2O3棒晶/Ce-TZP复合材料的制备与显微结构

通过在Ce-TZP基体中加入AlOOH及矿化剂TiO₂或反应剂SrCO₃制备了原位Al₂O₃片晶/Ce-TZP复合材料和原位SrO·6Al₂O₃棒晶/Ce-TZP复合材料。在烧结过程中TiO₂促进Al₂O₃晶粒发生显著的各向异性生长原位生成的片晶、Al₂O₃与SrCO₃发生反应,原位生成的高度各向异性的棒晶,它们在基体中分布均匀,具有较大的纵横比。烧结温度对片晶/棒晶的大小和含量有明显影响。通过在基体中原位形成片晶或棒晶,材料的力学性能有明显的改善。