Shear properties of C/C-SiC sandwich structures

Carbon fiber reinforced carbon-silicon carbide (C/C-SiC) sandwich structures have been developed using the Liquid Silicon Infiltration process and the in situ joining method. They offer high mass-specific stiffness, low thermal expansion, and high environmental stability. Potential application areas are highly precise satellite structures, like optical benches. In this study, sandwich samples were manufactured using prepregs based on 2D carbon fibre fabrics and a phenolic resin precursor. Carbon fibre reinforced polymer preforms for folded and grid-cores, as well as for the skin panels were manufactured using autoclave technique. In the second step, the sandwich components were pyrolyzed, leading to C/C preforms. For the build-up of the sandwich samples, two skin panels were joined to a core structure and subsequently, the resulting C/C sandwich preform was siliconized. C/C-SiC sandwich samples were tested under shear load. Shear strength, modulus, and fracture strain were determined and compared to the results obtained by analytical calculation. The shear properties were dependent on the fiber orientation in the core structure as well as on the core type and orientation. The sandwich shear stiffness obtained in the tests was close to the expected theoretical values, calculated on the basis of the material properties and the core geometry.     

Damp-heat durability comparison of Al-doped ZnO transparent electrodes deposited at low temperatures on glass and PI-tape/PC substrates

Durability performances are compared for Al-doped ZnO (AZO) transparent electrodes deposited on hard slide-glass and flexible polyimide-tape attached to polycarbonate (PI-tape/PC) substrates. To identify the appropriate sputtering configuration, the AZO thin films are first deposited on the glass substrates via reactive RF-magnetron sputtering under 90 sccm of argon gas and 3 sccm of oxygen gas at room temperature (RT) with 83 to 90 W of RF power for 30 min. When deposited, only the sputtering configuration with 85 W of RF power could produce the AZO films with acceptable optoelectrical properties for transparent electrodes: 80% average visual transparency and 10 Ω/□ at the thickness of 1.1 μm. The temperature at the surface of the substrates rises from RT to 88 °C due to the sputtering with 85W of RF power for 30 min, and this configuration is successfully conducted for AZO film depositions on both the glass and PI-tape/PC substrates. After exposure to a damp-heat (DH) test at 85 °C and 85% relative humidity (RH) for 25 days, the conductivity of the AZO films on the PI-tape/PC substrates is significantly degraded: many cracks are visible on the films, significantly decreasing the Hall mobility. Conversely, the films deposited on the glass substrates exhibit durable high conductivity, no cracks, and excellent stability of the Hall mobility. Despite this significant difference in Hall mobility evolution, the films on both substrates show similar patterns of a slight decrease in carrier concentrations, suggesting that chemical characteristics, extensively reported as the key for the DH degradation of AZO films, are less involved in this durability study featuring AZO films prepared via a low oxygen-to-argon gas ratio of reactive sputtering at low temperatures.     

Nanopore diameter-dependent properties of thin three-dimensional ZnO layers deposited onto nanoporous silicon substrates

In this paper, nanoporous silicon (NPSi) substrates with various pore diameters-ranging from 50 nm to 100 nm-were prepared by inductively coupled plasma (ICP) etching using anodic aluminum oxide (AAO) masks. Thin three-dimensional (3D) ZnO layers were deposited onto as-obtained NPSi substrates using atomic layer deposition (ALD). The results show that the silicon nanopore diameter has a large influence on the morphology, structure, and optical properties of thin 3D ZnO layers deposited onto NPSi substrate. A thin ZnO layer with optimal 3D morphology, crystallinity and luminescence performance is obtained when the silicon nanopore diameter is 90 nm. The results also reveal that a silicon nanopore diameter increase greatly benefits thin 3D ZnO layer growth given that the NPSi substrate morphology is not destroyed. These investigations bring important guiding role for attaining AAO-assisted 3D semiconductor materials with nanoscale structure and high luminescence performance.     

ZnO/Al_2O_3催化剂乙醇水蒸气重整反应失活研究

采用浸渍法制备了一系列ZnO/Al2O3催化剂,考察了该催化剂在水醇摩尔比为3、常压、450℃工作条件下乙醇水蒸气重整(SRE)制氢反应活性及稳定性。结果表明,ZnO负载量达到10wt%时,C2H5OH转化率最高,但催化剂在160 min内出现明显失活。利用BET等表征手段考察了反应前后催化剂的物理化学性质,并通过失活模型模拟,提出了ZnO/Al2O3催化剂上SRE制氢反应的失活原因。     

活性形貌对CuO/ZnO/Al2O3催化加氢反应的影响

以硝酸铜、硝酸锌等为原料,采用沉淀-沉积法制备了载体是介孔Al_2O_3的CuO/ZnO/Al_2O_3催化剂,通过改变焙烧时间可得到不同活性组分形貌(团簇球状和棒状)的催化剂,并用于CO/CO_2加氢反应。通过XRD、BET、N_2吸附-脱附、TEM、H_2-TPR、CO_2-TPD、NH_3-TPD和FTIR对催化剂进行了表征与测试。结果表明,活性组分(CuO/ZnO)形貌的改变影响了催化剂的Cu O晶粒尺寸、比表面积、孔径及其还原性能,且对催化剂的酸性位点和碱性位点的相对数量影响较大。团簇球状催化剂中活性组分的分散度高、易还原、碱性位多、酸性位少,有利于甲醇的生成;而棒状催化剂中孔道不均匀、碱性位少、酸性位多,更有利于二甲醚(DME)的生成。活性测试结果表明,团簇球状催化剂表现出高甲醇选择性(95.05%)和低DME选择性(4.18%);棒状催化剂的产物选择性与团簇球状相反,表现出高DME选择性(75.41%)和低甲醇选择性(12.81%)。     

Dynamical Changes in Cu/ZnO/Al2O3 Catalysts

A combination of various transient and steady-state kinetic experiments was used to provide evidence for dynamical changes in a Cu/ZnO/Al₂O₃ catalyst of industrial interest. From these it can be deduced that the reversible structural alterations strongly depend on the reaction conditions as well as on the pretreatment. The pretreatment was found to induce changes in the morphology of the metallic Cu particles to some extent, and surface alloying under more severe reducing conditions.     

Formation mechanism of Al2O3-YAG amorphous ceramic coating deposited via atmospheric plasma spraying

Al₂O₃-YAG (Al₅Y₃O₁₂) amorphous ceramic coatings exhibit excellent crack propagation resistance under harsh wear services due to the amorphous phase contributing to the plastic deformation performance of the coating. However, the formation mechanism of the amorphous phase is ambiguous. This study mainly investigated the formation mechanism of Al₂O₃-YAG amorphous coating prepared by atmospheric plasma spraying from the perspective of crystallization chemistry. Nano and microsized powders with low eutectic point ratio were selected as feedstock for comparison. X-ray diffraction, scanning electron microscope, and electron backscattered diffraction were used to analyze the phase composition, morphologies, phase distribution, and structure of the coating. It is concluded that the significant thermodynamically stable structure of polycompound with high coordination numbers of cations prioritized crystallizing in the Al₂O₃-YAG melt, but it needed more time to crystallize and hardly crystallized in the limited time during plasma spraying. Therefore, the selection of as-sprayable powder should also be considered the critical factor for preparing amorphous coatings. The nanoscale or submicro scale powder distributed uniformly with low eutectic point ratio was chosen as the feedstock to ensure the powder droplets diffuse sufficiently during deposition.     

Experimental and numerical investigation on the ablation mechanism of Al2O3/Al2O3-CMCs under continuous-wave laser irradiation

In this study, the ablation mechanism of Al₂O₃/Al₂O₃-CMCs under laser irradiation and the influence of laser parameters on the ablation efficiency were examined. The experimental results show that the diameters of the ablation centre and transition area are both positively correlated to the irradiation energy, and the irradiation power has a more prominent effect on the diameter of the ablation centre. The molten Al₂O₃ changes the reflection and transmission properties of laser beam, which results in an elliptical ablation pit. A macro-meso two-scale finite element (FE) model was established to simulate the laser ablation process progressively. The FE results show that the difference in thermal conductivity between the Al₂O₃ fibre and matrix induces a discrepancy in ablation at the mesoscale. The radius and depth of the ablation pit increase rapidly at the initial stage, then slowly increase with time. A good correlation between the experimental and numerical results was achieved.     

Erosion mechanism of the postmortem Al2O3-Ti2O3-Al sliding gate containing novel Al2O3-Ti2O3 raw materials

Al₂O₃-Ti₂O₃-Al sliding gates were prepared from Al₂O₃-Ti₂O₃ raw materials, sintered corundum and aluminum, and used in trials at steel works. The sliding gate with 30 wt% Al₂O₃-Ti₂O₃ added was used on an 80 t ladle for 4 cycles without macrocracks. The postmortem sliding gate can be divided into the permeation layer (0–0.1 mm), transition I layer (0.1–10 mm), transition II layer (10–20 mm) and unchanged layer from the hole working face outward. XRD, SEM and industrial CT were used to analyze the postmortem sliding gate. The results show that, in the Al₂O₃-Ti₂O₃-Al sliding gate, both Al and Ti₂O₃ are involved in reactions, Ti₂O₃ transforms into Ti₂O and TiO in the transition I layer, and part of the Ti₂O₃ in the transition II layer transforms into Ti₈O₁₅. Titanium compounds with different densities are dispersed in the matrix and form microcracks to improve the thermal shock resistance of the sliding gate, which improved the performance.     

CO2对CuO/ZnO/Al2O3催化剂前体老化及催化性能的影响

采用并流共沉淀法制备CuO/ZnO/Al2O3甲醇合成催化剂前体,在通入CO2条件下老化,采用XRD、FT-IR、DTG、H2-TPR、XPS等表征手段对制备的前体及焙烧后的催化剂进行表征,研究不同CO2通入量对前体晶相转变、微观结构及其焙烧后催化性能的影响。研究结果表明,老化阶段通入CO2后,沉淀母液的pH值趋于7,产生CO32?离子,进而影响Zn2+的沉淀,促进Cu2+进入Zn5(CO3)2(OH)6晶格中取代Zn2+形成绿铜锌矿(Zn,Cu)5(CO3)2(OH)6物相,有助于增强焙烧后催化剂的Cu-Zn之间协同作用,增加活性组分Cu分散度。CO2通入量为40 mL/min时,制备的催化剂在浆态床合成甲醇过程中表现出良好的催化活性和稳定性,甲醇时空收率（STY）达到301.78 g/(kg?h),失活率仅为0.15%/d,与未通入CO2辅助老化制备的催化剂相比,时空收率提高了9.72%,平均失活率降低了33.33%。     

用于二乙醇胺脱氢的Cu/ZnO/Al2O3/ZrO2催化剂的制备与表征

以氢氧化钠为沉淀剂,硝酸铜、硝酸锌、硝酸铝和硝酸氧锆为原料,采用共沉淀法制备出了用于二乙醇胺脱氢制亚氨基二乙酸的Cu/ZnO/Al2O3/ZrO2催化剂,并用物理吸附(BET)和X射线衍射(XRD)对不同种类的铜基催化剂进行了表征,探讨了ZnO和Al2O3的不同比例对催化剂性能的影响。结果表明,同时加入ZnO和Al2O3的Cu/ZnO/Al2O3/ZrO2催化剂具有大的比表面积,Cu/ZnO/Al2O3/ZrO2催化剂具有非晶态结构。该催化剂适宜的反应条件为:w(NaOH)=30%、反应温度160℃、压力1.0 MPa,二乙醇胺转化率可达100%,亚氨基二乙酸收率可达95.61%。     

Strong Eu2+ light emission in Eu silicate through Eu3+ reduction in Eu2O3/Si multilayer deposited on Si substrates

Eu₂O₃/Si multilayer nanostructured films are deposited on Si substrates by magnetron sputtering. Transmission electron microscopy and X-ray diffraction measurements demonstrate that multicrystalline Eu silicate is homogeneously distributed in the film after high-temperature treatment in N₂. The Eu²⁺ silicate is formed by the reaction of Eu₂O₃ and Si layers, showing an intense and broad room-temperature photoluminescence peak centered at 610 nm. It is found that the Si layer thickness in nanostructures has great influence on Eu ion optical behavior by forming different Eu silicate crystalline phases. These findings open a promising way to prepare efficient Eu²⁺ materials for photonic application.     

Preparation of Cu/ZnO/M2O3 (M = Al, Cr) Catalyst to Stabilize Cu/ZnO Catalyst in Methanol Dehydrogenation

ZnO reducibility in three component catalysts was monitored in a methanol stream by a microbalance. The ZnO in the Cu/ZnO is reduced in the methanol stream from ca 500 K, but the addition of a third component to Cu/ZnO can suppress the reduction of ZnO. The Cu/ZnO/Cr₂O₃ prepared from a hydrotalcite-like precursor shows high stability in methanol dehydrogenation. The high stability of Cu/ZnO/Cr₂O₃ is due to the stabilization of ZnO by formation of ZnCr₂O₄ even in the reduced condition.     

Compressive strength and impact resistance of Al2O3/Al composite structures fabricated by digital light processing

The combination of multi-materials is an alternative way to meet the diverse requirements for various applications. However, the processing difficulty especially in ceramic forming limited the structural innovations. In this paper, a combined methods of ceramic digital light processing (DLP) and metal infiltration is proposed to fabricate the Al₂O₃/Al composite structures with controllable ceramic skeletons. The interfacial, compressive and impact resistance properties were studied. The results showed that the Al₂O₃ grains were closely bonded, and no destructive defects occurred at the interface between Al₂O₃ and Al. The energy dispersive spectrometer (EDS) and X-ray diffraction (XRD) results showed that the formation of protective phases contributed to the improvement of bonding strength. The compressive tests showed that the composite structures had better capabilities to absorb and resist the applied loads compared with Al structures. Finally, the impact resistance of the structures was discussed, the finite element analysis and the experimental results showed that the composite structures had advantages in dissipating the energy of incident objects and reducing the penetration depth. Based on these results, the damage model of Al₂O₃/Al structures was established, and the roles of different materials were revealed.     

Activity and stability of Cu/ZnO/Al2O3 catalyst promoted with B2O3 for methanol synthesis

The addition of B₂O₃ to a Cu/ZnO/Al₂O₃ catalyst increased the activity of the catalyst for methanol synthesis after an induction period during the reaction. The stability of the B₂O₃-containing Cu/ZnO/Al₂O₃ catalyst was greatly improved by the addition of a small amount of colloidal silica to the catalyst. This revised version was published online in July 2006 with corrections to the Cover Date.     

发泡镍负载CuO/ZnO/Al2O3对甲醇水蒸汽重整的催化作用

以三维网状多孔发泡镍为载体，制备了负载CuO/ZnO/Al₂O₃的催化剂，研究了催化剂对甲醇水蒸汽重整制氢气的催化作用，考察了催化剂的制备方法、重整反应温度、催化反应器液体空速对催化反应以及催化剂稳定性的影响。结果表明，通过预先在发泡镍上包覆一层Al₂O₃，能够提高催化剂负载的均匀性，所制备的催化剂具有很好的低温初活性和选择性。在反应温度为220 ℃，液体空速为7.2 h^-1的条件下，甲醇初始转化率为98.36%，CO₂选择性为98.4%，产品气中CO摩尔分数为0.41%。通过40 h的连续实验，甲醇转化率始终维持在80%以上，产品气中CO摩尔分数保持在0.5%，CO2的选择性维持在98%。     

Effect of Metallic Zn Powder on Oxidation Resistance of Al2O3 -C Refractories

1 IntroductionCharacterized by excellent thermal shock resist-ance, slag erosion resistance, Al2O3-C refractory hasalready been widely used as some functional parts forcontinuous casting system, such as slide plate, nozzleand so on. However, during the ap…     

Cu–ZnO and Cu–ZnO/Al2O3 Catalysts for the Reverse Water-Gas Shift Reaction. The Effect of the Cu/Zn Ratio on Precursor Characteristics and on the Activity of the Derived Catalysts

Comparison is made between Cu–ZnO and alumina-supported Cu–ZnO as catalysts for the reverse water-gas shift (RWGS) reaction. For both types of catalyst the Cu/Zn ratio has been varied between Cu-rich and Zn-rich compositions. By applying X-ray diffractometry, X-ray line broadening, optical reflectance spectroscopy and other techniques the effects on the structural and physical properties of the hydroxycarbonate precursors, the calcined products and the ultimately derived catalysts are determined. The presence of alumina decreases the crystallite size of the CuO and ZnO particles produced on calcination and at high Cu/Zn ratios increases the dispersion of copper in the final catalyst. The activities of the catalysts for the RWGS reaction at 513K are compared and the most active are shown to be those which are Cu rich (Cu/Zn > 3) and contain alumina as support. The activities of all the catalysts can be rationalized by referring the activity to unit surface area of copper metal.     

机械研磨燃烧法制备Cu/ZnO/Al2O3甲醇合成催化剂

引言Cu/ZnO/Al2O3催化剂近年来广泛应用于低压甲醇合成、二甲醚合成和水煤气变换等领域[1-2],该催化体系具有活性高、使用寿命长、反应温度及     

Hydrogenolysis of Dimethyl Maleate on Cu/ZnO/Al2O3 Catalysts

The gas‐phase hydrogenolysis of dimethyl maleate at 10 bar and 513 K was investigated over a series of co‐precipitated Cu/ZnO/Al₂O₃ catalysts. High copper surface areas were obtained with a molar Al content of 5 % in the catalysts. Upon variation of composition at fixed alumina content, copper surface areas increased until the molar ratio exceeded Cu/Zn = 2:1. At the given reaction conditions, dimethyl maleate was completely converted to dimethyl succinate, which further reacted to methanol, γ‐butyrolactone, tetrahydrofuran, and water over all catalysts. Initial deactivation of catalysts was mainly caused by a loss of copper surface area. The catalyst with a molar Cu/Zn ratio of 1:2 was found to be most active and stable under reaction conditions.