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1.
Pingping Jiang Guanzhong Lu Yun Guo Yanglong Guo Shunhai Zhang Xingyi Wang 《Surface & coatings technology》2005,190(2-3):314-320
Washcoat deposited on ceramic honeycomb was prepared using pseudoboehmite, the CeO2–ZrO2–La2O3 solid solution, pore enlarger and other additives. The microstructures and surface performances of washcoat/honeycomb were investigated by SEM, BET surface area, XRD, ultrasonic vibration and hot shock simulation. The results show that the performance and loading of washcoat are affected obviously by the properties of slurry gel, such as the apparent viscosity, solid content, particle size and its distribution. When the apparent viscosity of slurry is lower, the gel with a narrow particle size distribution and finer particles can be obtained, with which the coating having an excellent performance can be prepared. Adding a small quantity of the CeO2–ZrO2–La2O3 solid solution can promote the thermal stability of washcoat, such as, after calcined at 1000 °C for 5 h the sample exhibits mainly the γ-Al2O3 phases and the θ-Al2O3 -Al2O3 and κ-Al2O3 phases have not been detected in the XRD spectra. It is found also that the washcoat prepared has excellent properties of the vibration-resistant, heat-resistant and its BET surface area reaches 50 m2/g. 相似文献
2.
A. Larsson S. Ruppi 《International Journal of Refractory Metals and Hard Materials》2001,19(4-6):515-522
This work deals with the microstructures and wear properties of chemical vapour deposited γ-Al2O3. The γ-Al2O3 coatings were deposited at 800 °C on TiN and Ti(C,N) pre-coated cemented carbide substrates. The microstructures developed in the γ-Al2O3 coatings and the influence of the nucleation surface on the growth of γ-Al2O3 were characterised using transmission electron microscopy, electron energy-loss spectroscopy and X-ray diffraction. The γ-Al2O3 coatings were fine-grained with a high density of {1 1 1} growth twins and contained some residual sulphur. γ-Al2O3 was found to grow epitaxially on the investigated substrates. The mechanical properties were evaluated in metal cutting and were compared with those of κ-Al2O3 coated tools. As compared with the κ-Al2O3 coatings, the γ-Al2O3 coatings exhibited slightly worse adhesion and tendency for edge chipping. However, the γ-Al2O3 coatings showed better crater wear resistance on the rake face than κ-Al2O3 coatings. 相似文献
3.
Crystalline γ-AlO(OH) was synthesized by the precipitation of sodium aluminate and oxalic acids in aqueous solution. And then γ-AlO(OH) was successfully transferred to γ-Al2O3 after subsequent high temperature heat treatment. The effects of reaction conditions on formation of γ-AlO(OH) and γ-Al2O3 were further investigated in detail. The XRD analysis shows that the complete formation of crystalline γ-Al2O3 is at pH 8–9, reaction temperature of 93–96 °C and calcination temperature of higher than 400 °C. The product of γ-Al2O3 contains impurity, including iron, calcium and silicon ion with a low content of about 0.01% and has large specific surface area and high pore volume of 269.9 m2/g and 0.57 mL/g, which can be applied in catalysts and catalyst supports. 相似文献
4.
The dislocation structures of a low-angle tilt grain boundary in alumina bicrystal were investigated by transmission electron microscopy. The grain boundary was found to consist of two regions: an area with pairs of partial dislocations and an area with groups of odd numbered partial dislocations (multiple-partial-structure). Eight kinds of multiple-partial-structures were found in the fabricated grain boundary. The Burgers vectors of each partial dislocation in the grain boundary can be distinguished by dark-field imaging, and thus the arrangement of partial dislocations in the multiple-partial-structures are determined. It is concluded that a slight twist component of the boundary is the origin of the characteristic multiple-partial-structures. 相似文献
5.
The influence of nucleation on the microstructure and properties of CVD Al2O3 was investigated. The experimental α-Al2O3 layers were deposited (a) without nucleation control and (b) with nucleation steps resulting in pronounced , and growth textures. The experimental layers were characterised using X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Wear properties of the textured coatings were evaluated in turning. The chemistry of the nucleation surface appeared to be an important factor in pre-determining the phase content and growth textures of the Al2O3 layers. Optimised nucleation resulted in substantially improved wear properties and these kinds of α-Al2O3 layers were typically composed of relatively small, defect-free grains exhibiting no porosity. The textured α-Al2O3 layer showed the best wear resistance. 相似文献
6.
A. Larsson M. Halvarsson S. Vuorinen 《International Journal of Refractory Metals and Hard Materials》1998,16(4-6):369-376
In this work, the κ-Al2O3 to -Al2O3 phase transformation in CVD multilayer coatings has been investigated. Coatings with different degrees of transformation have been prepared by isothermal heat-treatments of as-deposited κ-Al2O3 multilayer coatings. These coatings have then been examined by means of transmission electron microscopy of cross-section specimens. The aim of this work was to examine the microstructural evolution during the κ-Al2O3 to -Al2O3 phase transformation and to describe how the transformation growth is affected by the κ-Al2O3 microstructure. The microstructure of the non-transformed κ-Al2O3 was not affected by the heat-treatments. During the phase transformation, a linkage of voids took place at the -Al2O3/TiC interfaces, resulting in large separated voids and continuous cracks. A large number of small faceted voids appeared within the -Al2O3 grains. It was found that during the transformation cκ → c, i.e. the close packed planes are preserved, but rotated slightly around the c-axis. Three modes for the κ-Al2O3 to -Al2O3 phase transformation were found: (i) a columnar transformation; (ii) a lateral transformation; and (iii) a mixed columnar-lateral transformation. The predominance of any of the transformation modes is attributed to the nucleation/growth ratio. A high ratio yields a columnar transformation, while a low ratio yields a lateral transformation. The nucleation sites in all transformation modes are suggested to be at voids at the κ-Al2O3/TiC interfaces. 相似文献
7.
Al films were grown epitaxially on single-crystal α-Al2O3 substrates by magnetron sputtering and molecular beam epitaxy, respectively. The microstructure and thermal stability of these films were analysed in detail using X-ray diffraction methods and electron microscopy techniques. The films consist of two twin-related growth variants, related by a 180° rotation around the <111> film normal resulting in a {111} Al || (0001) α-Al2O3, and ± <
> Al || <
> α-Al2O3 orientation relationship. The Al variants are separated by Σ3 {
} Al twin boundaries possessing a rigid body translation of the {111} Al planes across the boundary plane in order to reduce their energy. Motion of the twin boundaries was observed by annealing plan-view samples in situ in a transmission electron microscope. The twin boundaries advance in jerky motion at velocities of several μm/s at temperatures of ˜400 °C, resulting in grain coarsening. In all cases, heat treatments resulted in increased area fraction of one twin variant, which finally will result in single-crystal films upon further annealing. 相似文献
8.
Yibin Li Yue Sun Wenzhu Zhang Yujie Ding Xiaodong He 《Journal of Alloys and Compounds》2008,460(1-2):115-119
Nanocrystalline aluminum embedded in amorphous dielectric alumina matrix thin films (nc-Al/α-Al2O3) was synthesized via reactive magnetron sputtering. The nc-Al/α-Al2O3 films at different oxygen partial pressures were sputtered on p-type Si substrates from a pure Al target in the mixed ambient of Ar and O2. Both deposition rate and aluminum concentration increase as the oxygen partial pressure decreases. X-ray photoelectron spectroscopy and high-resolution transmission electron microscope studies give the confirmation of nanocrystalline Al embedded in amorphous Al2O3 matrix. This nanocomposite thin film exhibits memory effect as a result of charge trapping. The flat band voltage value depends on the Al nanocrystal concentration which is related to oxygen partial pressure. 相似文献
9.
相比汽油车而言,柴油车具有高效、低油耗的优势已得到广泛应用。本实验以ZrO2作为改性剂,探究了ZrO2与Al2O3的质量比对催化剂的影响。研究结果表明:随着ZrO2的加入,Pt粒子先减小后增大;Pt粒子与载体的交互作用先增大后减小。活性实验数据分析表明,ZrO2的最佳添加量为40 wt%,CO和C3H6完全氧化温度分别降低20 oC 、25 oC。贵金属在催化剂的分散度以及贵金属与载体的相互作用随着ZrO2与Al2O3质量比的变化而变化。Pt粒子越小,其与载体的交互作用越强,这表明催化剂性能越强。 相似文献
10.
C. Barbatti J. Garcia R. Pitonak A. Kostka M.H. Staia 《Surface & coatings technology》2009,203(24):3708-3717
Cemented carbides coated with CVD multilayers are commonly used in metal cutting turning and milling operations. For many applications, a micro-blasting finishing procedure based on an impact treatment of the surfaces is carried out in order to smooth the coated surface and reduce sharp cutting edges. In this work, micro-blasting with corundum in aqueous solution at pressures between 0.05 and 0.3 MPa was applied to CVD TiN/Ti(C,N)/κ-Al2O3 multilayer coatings deposited onto cemented carbides in order to investigate its influence on the micro-topography, microstructure and residual stresses. The results showed that the micro-blasting reduces the surface roughness and affects the coating thickness. TEM investigations revealed no significant changes on the microstructure of the κ-Al2O3 top layer. Synchrotron X-ray investigations showed that the residual stress state of the as-deposited κ-Al2O3 top layer is not affected by the micro-blasting treatment under the conditions investigated. 相似文献
11.
A.D. Pogrebnjak Yu.A. Kravchenko Sh.M. Ruzimov P. Misaelides 《Surface & coatings technology》2006,201(6):2621-2632
New experimental results are presented on the structure and the elemental and phase composition of hybrid coatings, which were deposited on a substrate of AISI 321 stainless steel using a combination of plasma-detonation, vacuum-arc and subsequent High-Current Electron Beam (HCEB) treatment. We found that an increase in energy density intensified mass transfer processes and resulted in changes in aluminum oxide phase composition (γ → α and β → α). Also we observed the formation of a nanocrystalline structure in Al2O3 coatings. Electron beam treatment of a hybrid coating surface induced higher adhesion, decreased the intensity of surface wear and increased corrosion resistance in a sulphuric acid solution. The corrosion resistance of the coatings was studied in several electrolytic solutions (0.5 M H2SO4, 1 M HCl, 0.75 M NaCl) using electrochemical techniques. In most cases the corrosion resistance was improved, except those in NaCl solutions. The nano-hardness of the protecting coating was 13 GPa before electron beam melting and 9 GPa after it (as a result of TiN and Al2O3 sub-layers mixing). 相似文献
12.
Hoon Sang Choi Geun-Sik Lim Jong Han Lee You Min Jang Dong Chul Yoo Jeong Yong Lee In-Hoon Choi 《Metals and Materials International》2003,9(3):293-298
Pt/SrBi2Nb2O9 (SBN)/Al2O3/Si (MFIS) ferroelectric gate oxide structures were prepared with the rf (radio frequency) magnetron sputtering method for
the application of non-destructive read-out ferroelectric RAM (NDRO-FRAM) devices. An Al2O3 intermediate layer between the perovskite SrBi2Nb2O9 film and Si substrate prevents the serious inter-diffusion of the SrBi2Nb2O9 (SBN) into the Si substrate. The coercive field that decisively affects the memory window was increased by inserting the
Al2O3 insulator between the SBN and Si, and thus the memory window also increased with the increase in the electric field to the
SBN. The memory windows of the metal-ferroelectric-insulator-semiconductors (MFIS) structures were in the range of 0.7–3.4
V when the gate voltage varied from 3 to 9 V. The memory windows of the MFIS structures were found to be dependent on the
thickness and stoichiometry of the buffer layer. We obtained the maximum memory window in an MFIS with an insulator of 11.4
nm in thickness deposited in the deposition condition of a 15∶5 flow ratio (Ar:O2) during sputtering. 相似文献
13.
R.K. Sadangi V. Shukla B.H. Kear 《International Journal of Refractory Metals and Hard Materials》2005,23(4-6):363-368
Nanocomposites of yttria-stabilized zirconia (YSZ), containing 20 and 40 wt% alumina, were prepared by a two-step process: (1) fine-particle aggregates of the constituent phases were melted and homogenized in a high enthalpy plasma, prior to rapid quenching in water to obtain metastable starting powders, and (2) the metastable powders were consolidated by hot isostatic pressing (HIP), under conditions designed to ensure the formation of nanocomposites by controlling the metastable-to-stable phase transformation during sintering. In both cases, the resulting nanocomposites had completely uniform structures, comprising 27 and 50 vol% of -Al2O3 in a tetragonal YSZ matrix phase. Measurements of hardness and indentation toughness were correlated with observed structures. 相似文献
14.
Michael Hoch 《Journal of Alloys and Compounds》2001,320(2):267-275
We calculated the binary phase diagrams B2O3–Ga2O3, B2O3–In2O3 and B2O3–Al2O3, and the Gibbs energy of formation of the binary compounds, using experimental liquidus data. The B2O3–Ga2O3 system is of industrial importance, because liquid B2O3, in which Ga2O3 is not very soluble, is used to protect GaAs during growth of single crystals of GaAs. During recovery of noble metals B2O3 is added to slags containing Al2O3 to lower the melting point and the viscosity. The B2O3–In2O3 system is of much less importance to industry. In all three systems we have a liquid miscibility gap, and also solid binary compounds, none of which melt congruently. The miscibility gaps are not surprising, because even in the B2O3–Bi2O3 system where four congruently melting compounds are present, a liquid miscibility gap exists close to B2O3. 相似文献
15.
Magnetic BaxFe3−xO4 (x 0.23) with spinel structure was fabricated by ball milling of mixture of BaCO3 and nonmagnetic α-Fe2O3 powders, and the molar ratio of BaCO3 and α-Fe2O3 is 1:6. In the milling process, a mechanochemical reaction took place between BaCO3 and α-Fe2O3, and Ba cation incorporated into α-Fe2O3 with rhombohedral structure to form a α-(Fe,Ba)2O3 solid solution. The Ba content in the α-(Fe,Ba)2O3 increased with increasing milling time, when the Ba content exceeded a limited solubility, the α-(Fe,Ba)2O3 transformed into a phase of BaxFe3−xO4 with spinel structure, where the Ba cation occupied an octahedral site or tetrahedral site. The product obtained in the balling process was different from that prepared in the annealing process at atmospheric pressure, which was BaFe2O4 with orthorhombic structure. Accompanying the crystal structure transition from α-(Fe,Ba)2O3 to BaxFe3−xO4, the magnetic properties also changed from nonmagnetism into ferromagnetism. The saturation magnetization was 53.3 emu/g and coercivity was 113.7 Oe. The mechanism of transitions of the crystal structure was discussed in the present work. 相似文献
16.
本文采用原子层沉积(ALD)的方法,选择三甲基铝(TMA)和H2O2作为反应前驱体,在高定向热解石墨(HOPG)基体上沉积Al2O3。系统研究了反应温度和生长周次对Al2O3生长行为的影响。研究表明:受HOPG表面饱和成键的影响,Al2O3在衬底表面处形核困难,在生长初期主要表现为台阶处择优生长,其形态为线状结构。当沉积100周次Al2O3时,其中在沉积温度为50 °C、150 °C和200 °C时呈现为纳米线状结构,而在100 °C时呈现为非连续薄膜。随着生长周次的增加,不同温度下沉积态Al2O3都趋于形成连续薄膜,表明其生长行为发生了由三维岛状生长模式向二维平面生长模式的转变。分析认为,生长模式的转变是由纳米线状结构横向生长造成的;横向生长速率主要受生长温度影响。拉曼结果表明:沉积后的石墨烯层结构未受影响,可保留其原有的优越性能。 相似文献
17.
Yadong Zhang Dragos SegheteAziz Abdulagatov Zachary GibbsAndrew Cavanagh Ronggui YangSteven George Yung-Cheng Lee 《Surface & coatings technology》2011,205(10):3334-3339
The film perfection in terms of pinhole defect densities of ultra-thin Al2O3 grown by atomic layer deposition (ALD) has been quantitatively characterized. A significant defect density reduction from ~ 1.2 × 105/cm2 to ~ 90/cm2 was demonstrated for 2 nm-thick Al2O3 by using an ALD tungsten (W) buffer layer on the nickel (Ni) substrate. The reason for the defect reduction was attributed to efficient nucleation of ALD Al2O3 on ALD W. The effect of the buffer layer becomes less essential as the Al2O3 thickness increases, where the substrate surface physical conditions such as particle contamination become the main cause for defects. 相似文献
18.
通过对Ni-Cr2O3复合镀层620 ℃部分渗铝制备了δ-Ni2Al3-Cr2O3/Ni-Cr2O3涂层体系。Cr2O3颗粒在渗铝的过程中和Al反应生成更为稳定的Al2O3。1000 ℃恒温氧化20 h后发现,铝化物涂层和复合镀层内掺杂的Cr2O3颗粒完全转化为Al2O3,并在铝化物涂层/Ni镀层界面自发形成了一层Al2O3富集层,该富集层起扩散障作用,阻碍铝化物涂层因互扩散所致的退化。 相似文献
19.
The adhesion of sputtered copper thin films was measured with a quantitative indentation technique utilizing refractory superlayers to trigger and promote delamination. Adhesion energies of the indentation-induced delaminations were analyzed in terms of the critical strain energy release rate. Two groups of films were investigated. Group I ranged in thickness from 225 to 1000 nm in both the as-deposited and annealed condition. Adhesion energies ranged from 2 to 15 J/m2, with higher adhesion for the annealed condition. Group II films had nominal thicknesses of 430 and 1100 nm, some with 7–10 nm interlayers of either titanium or chromium. Adhesion energies of these films ranged from 4 to 30 J/m2, increasing by a factor from 1.3 to 7.5, as a function of the interlayer presence and type, with the increase in energy due to a chromium interlayer exceeding that of titanium. Adhesion energies increased with film thickness for all films, with interlayers and annealing producing a larger increase. These quantitative results were compared to previous semi-quantitative and quantitative results, and shown to have comparable magnitudes and trends. 相似文献
20.
D Gavrila A Georgakab V Loukopoulosb G Karaiskakisb B E Nieuwenhuysa 《Gold bulletin》2006,39(4):192-199
New findings give further information on the mechanism of carbon monoxide selective oxidation over γ-alumina supported nanoparticle
sized gold catalysts. a) CO2 formation, increasing with rising temperature, is observed in the absence of hydrogen and oxygen pointing to a model of active
sites consisting of an ensemble of metallic Au atoms and a cationic Au with a hydroxyl group, b) At high temperatures (>200
°C) in excess of H2, reversed water gas shift (RWGS) reaction results in CO2 consumption towards CO and H2O formation. c) Hydrogen strongly influences the interaction of CO on Auγ-Al2O3, by weakening the CO adsorption. The presence of hydrogen plays an important role both decreasing the strength of CO bonding
and in the prevention of deactivation and regeneration. 相似文献