MoS2 coated with Al2O3 for Ni-MoS2/Al2O3 composite coatings by pulse electrodeposition

The MoS₂ powders were coated with Al₂O₃ (5 wt.%) through controlling hydrolysis of Al (NO₃)₃·9H₂O. MoS₂ powder coated with Al₂O₃ was written as MoS₂/Al₂O₃ hereinafter. MoS₂/Al₂O₃ powders were put into Ni plating electrolyte bath. Cetyltrimethylammonium bromide (CTAB) — the surfactant was also put into the bath. The experiment proves that MoS₂/Al₂O₃ particles were absorbed onto the Ni plate. The amount of MoS₂/Al₂O₃ deposited on Ni plate rises with the increasing concentration of MoS₂/Al₂O₃ in the bath. The microhardness, micro-surface, phase and the tribological property of the MoS₂/Al₂O₃ multi-plating coating were measured and analyzed. The performances of microhardness and wear resistance of the Ni-MoS₂/Al₂O₃ composite are better than those of Ni-MoS₂ composite.     

High tunability of pulsed laser deposited Ba0.7Sr0.3TiO3 thin films on perovskite oxide electrode

Ferroelectric thin films such as BST, PZT and PLZT are extensively being studied for the fabrication of DRAMS since they have high dielectric constant. The large and reversible remnant polarization of these materials makes it attractive for nonvolatile ferroelectric RAM application. In this paper we report the characterization of Ba_0.7Sr_0.3TiO₃ (BST) thin films grown by pulsed laser ablation on oxide electrodes. The structural and electrical properties of the fabricated devices were studied. Growth of crystalline BST films was observed on La_0.5Sr_0.5CoO₃ (LSCO) thin film electrodes at relatively low substrate temperature compared to BST grown on PtSi substrates. Electrical characterization was carried out by fabricating PtSi/LSCO/BST/LSCO heterostructures. The leakage current of the heterostructure is studied and a band structure is modeled based on the transport properties of the heterostructure. The dielectric constant of the BST film is found to be 630 at 100 kHz with a loss tangent of 0.04. The capacitance voltage characteristics show high tunability for BST thin films.     

Microwave ECR plasma CVD of cubic Y2O3 coatings and their characterization

Yttrium oxide (Y₂O₃) thin films are deposited by microwave electron cyclotron resonance (ECR) plasma assisted metal organic chemical vapour deposition (MOCVD) process at a substrate temperature of 350 °C using indigenously developed metal organic precursors (2,2,6,6-tetra methyl-3,5-heptane dionate) yttrium, commonly known as Y(thd)₃ synthesized by ultrasound method. The deposited coatings are characterized by X-ray photoelectron spectroscopy, glancing angle X-ray diffraction, scanning electron microscopy, EDS and infrared spectroscopy. The characterization results indicate that it is possible to deposit non-porous coatings with excellent uniformity of a single phase cubic Y₂O₃ on various substrates by this process at reasonably low substrate temperature that is desirable in various manufacturing processes.     

Application of the induction plasma to the synthesis of two dimensional steam methane reforming Ni/Al2O3 catalyst

The purpose of the study is to develop a new protocol for preparing supported two dimensional catalysts with high external and low internal surface by combining thermal plasma spraying and thermal plasma chemical vapour deposition (TPCVD) processes. The method was tested for the production of an Al₂O₃ supported Ni catalysts used for methane steam reforming. The deposition of catalytic materials is made in 2 successive steps. The first step deals with alumina powder sprayed by induction plasma spraying (IPS) on a molybdenum substrate. The experimental conditions have been turned towards γ-Al₂O_3. The second stage deals with the deposition of nickel at the nanometric scale on the alumina layer using the thermal plasma chemical vapour deposition method. This last step was focused on the study of the influence of the nozzle type employed for the nickel solution spraying, the reactor internal pressure, the concentration and the flow rate of nickel salts solution, Ni(NO₃)₂·6H₂O, on the catalyst response. The formulations were tested as methane steam reforming catalysts.The results demonstrate that the catalyst morphology depends on plasma projection conditions and show the effectiveness of combining IPS and TPCVD processes for producing catalysts in methane steam reforming.     

Preparation and characterization of Y3Al5O12:Ce and Y2O3:Eu phosphors powders by combustion process

A nickel hydroxide, Ni(OH)₂, was prepared by microwave-assisted heating technique from nickel nitrate aqueous solution and sodium hydroxide (assigned as PM). Then, the as-prepared PM was oxidized by liquid oxidation with sodium hypochlorite (assigned as PMO). Further, pure nanocrystalline nickel oxide (NiO) particles were obtained from the as-prepared PMO by calcination at 300, 400, 500, 600, 650 and 700 °C (labeled as C300, C400, C500, C600, C650 and C700, respectively). The as-prepared powders (PM and PMO) and the NiO nanoparticles were characterized by X-ray diffraction (XRD), infrared spectroscopy (IR), temperature-programmed reduction (TPR) and scanning electron microscope (SEM). The results indicated that the particle size of nickel oxide was controlled by the calcined temperature. The average crystal size of the NiO nanoparticles ranges from about 5 to 35 nm at 300–700 °C. Mechanism of nickel oxide nanocrystallite growth during thermal treatment was investigated.     

Corrosion protection of AZ31 magnesium alloy by a TiO2 coating prepared by LPD method

TiO₂ layer was prepared as a protective coating for AZ31 magnesium alloy by the liquid phase deposition (LPD) method followed by an annealing treatment. The structural evolution and crystallization of coating brought by annealing were investigated by field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD), respectively. The corrosion protection performance was evaluated in a three-electrode electrochemical examination system. The anatase TiO₂ layer shows evident corrosion resistance. With the increase of the annealing temperature and prolongation of annealing time, the anticorrosion property was improved. The improvements of the anticorrosion properties were related with the structural evolution of the coating brought by the annealing treatment.     

Processing and properties of ZrO2(3Y2O3)–Al2O3 nanocomposites

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.     

Electronic structures and Eu photoluminescence behaviors in Y2Si2O7 and La2Si2O7

The electronic structures and linear optical properties of Y₂Si₂O₇ (YSO) and La₂Si₂O₇ (LSO) are calculated by LDA method based on the theory of DFT. Both YSO and LSO are direct-gap materials with the direct band gap of 5.89 and 6.06 eV, respectively. The calculated total and partial density of states indicate that in both YSO and LSO the valence band (VB) is mainly constructed from O 2p and the conduction band (CB) is mostly formed from Y 4d or La 5d. Both the calculated VB and CB of YSO exhibit relatively wider dispersion than that of LSO. In addition, the CB of YSO presents more electronic states. Meanwhile, the VB of LSO shows narrower energy distribution with higher electronic states density. The theoretical absorption of YSO shows larger bandwidth and higher intensity than that of LSO. The results are compared with the experimental host excitations and impurity photoluminescence in Eu³⁺-doped YSO and LSO.     

Thermal cycle behavior of plasma sprayed La2O3, Y2O3 stabilized ZrO2 coatings

The effects of La₂O₃ addition on thermal conductivity, phase stability and thermal cycle life of Y₂O₃ stabilized ZrO₂ plasma sprayed coatings were investigated. Although low thermal conductivity as well as high resistance to sintering was achieved by La₂O₃ addition, it tended to also result in lower phase stability and thermal cycle life of the coatings. Optimization of the composition and structure of the coatings improved these properties, and the optimized coatings showed prolonged thermal cycle life.     

Influence of ZnO content and annealing temperature on the dielectric properties of ZnO/Al2O3 composite coatings

ZnO/Al₂O₃ coatings were prepared by atmospheric plasma spraying (APS) using ZnO powders and Al₂O₃ powders as starting materials. The dielectric properties of these coatings were discussed. Both the real part of permittivity and the energy loss increase greatly with increasing ZnO content over the frequency range 8.2-12.4 GHz, which can be ascribed to orientation polarization and relaxation polarization due to a higher ZnO content. The frequency-dependent maximum of the loss tangent is found to obey Debye theory. In addition, annealing temperature which leads to the change of ZnO content also plays an important role in the dielectric performance.     

Studies on Y2O3:Eu phosphor with different particle size prepared by wet chemical method

Europium activated yttrium oxide phosphors were prepared by reagent simultaneous addition technique, using oxalic acid as precipitating reagent. The aim of the paper is to establish the flux influence and thermal regime on photoluminescence and morpho-structural characteristics of phosphor powders. In this respect different mineralising agents such as sodium/lithium carbonate, sodium tetraborate ans sodium pyrophosphate were used during the thermal synthesis stage. Thermal analysis, X-ray diffraction, scanning electron microscopy, infrared spectroscopy and photoluminescence measurements were used to investigate precursor and phosphor powders. The correlation between the phosphor properties and precursor quality enabled us to select the optimal synthesis conditions.     

Ultraviolet and violet upconversion luminescence in Ho-doped Y2O3 ceramic induced by 532-nm CW laser

Ultraviolet and violet upconversion luminescence spectra of holmium-doped Y₂O₃ were produced under the excitation of a compact continues-wave 532 nm solid-state laser. Emissions around 306, 362, 412, 390 and 428 nm can be assigned to the transitions of ³D₃ → ⁵I_J (J = 8, 7, 6), ⁵G₄ → ⁵I₈ and ⁵G₅ → ⁵I₈, respectively. Power dependence and upconversion dynamics analysis demonstrated that both the energy transfer upconversion (ETU) and the excited state absorption (ESA) processes were involved in the population of ³D₃ state via the coupled intermediate states ⁵S₂/⁵F₄. Fluorescence spectra in the visible and infrared ranges showed that ⁵G₄ and ⁵G₅ states were populated by the ESA process from ⁵I₆ and ⁵I₇ states, respectively, while the ⁵I₆ and ⁵I₇ states were radiatively populated from the excited ⁵S₂/⁵F₄ states. Upconversion mechanisms have been evaluated based on a rate equation model.     

Cu/Y2O3掺杂MgB2的组织控制及动力学分析

观察并研究了不同Y2O3含量的Cu/Y2O3共掺杂MgB2的体系,样品通过传统的固相烧结法制备。结合扫描电镜和X射线衍射技术的分析发现,只有在5%Y2O3掺杂的样品中获得了层状组织。选择5%Y2O3含量的体系结合热分析曲线对固相反应阶段进行了动力学分析,得出最概然机理函数为Avrami-Erofeev,n=2,表达式为2[-ln(1-α)]1/2。其意义是随机形核和随后的瞬时生长。最后对动力学参数进行了计算,结果表明反应的活化能和指前因子均先趋于稳定后减小。     

Y2O3-BaO-SiO2-B2O3-Al2O3 glass sealant for solid oxide fuel cells

A glass based on Y₂O₃-BaO-SiO₂-B₂O₃-Al₂O₃ (named YBA) has been investigated as sealant for planar solid oxide fuel cells (SOFCs). The YBA glass has been systematically characterized by differential thermal analysis, dilatometer, scanning electron microscopy, impedance analysis, and open circuit voltage to examine their suitability as sealant. The coefficient of thermal expansion of YBA is 11.64 × 10⁻⁶ K⁻¹ between 323 and 873 K. The resistivity is 9.1 × 10⁴ Ω cm at 800 °C. The glass sealant is found to be well adhered with other cell components, such as electrolytes and stainless steels, at an optimum sealing temperature of 800 °C. All measured results showed that the YBA glass appears to be a promising sealant for SOFCs.     

CVD deposition and characterization of coloured Al2O3/ZrO2 multilayers

Coloured Al₂O₃/ZrO₂ multilayers have been deposited onto WC-Co based inserts by a CVD process. Through physical as well as optical analysis of such multilayers, colour is believed to originate from interference. The coatings are obtained with good process reproducibility. It was found that the ZrO₂ process used in the multilayer, with ZrCl₄ as the only metal chloride precursor, results in a mixture of tetragonal and monoclinic ZrO₂ phases. However by adding a relatively small amount of AlCl₃ during such a process results in ZrO₂ layers being composed of predominantly tetragonal ZrO₂ phase. Corresponding multilayers seem to have a more fine grained and smoother morphology whereas multilayers containing monoclinic ZrO₂ phase seem to be less perfect with existence of larger grains of ZrO₂ which are believed to scatter light and alter the reflectance of such a multilayer. In addition to this, such multilayers were found to be free of or with greatly reduced amount of thermal cracks, normally present in pure CVD grown Al₂O₃ layers.It is believed that, in the studied Al₂O₃/ZrO₂ multilayers, the observed tetragonal ZrO₂ phase is the result of a size effect, where small enough ZrO₂ crystallites energetically favor the tetragonal phase. However as the ZrO₂ crystallite size distribution is shifted to larger sizes it is believed that a mixture of crystallites with both stable and metastable tetragonal phases as well as a stable monoclinic phase is obtained. The proposed metastable tetragonal ZrO₂ phase may in fact explain the absence of thermal cracks in such multilayers through a transformation toughening mechanism, well known in ZrO₂ based ceramics.     

烧结助剂Y2O3和Pr6O11对Al2O3陶瓷相对密度和热导率的影响

采用高分子网络法制备混合纳米粉体,研究稀土氧化物Y2O3和Pr6O11加入量对Al2O3陶瓷相对密度和热导率的影响。采用阿基米德方法测定样品的体积密度,利用激光脉冲法测量试样的热扩散率并计算得出热导率。结果表明:两种添加剂都可以降低Al2O3陶瓷的烧结温度,提高Al2O3陶瓷的热导率,其中Y2O3的促进作用较强;当保温时间相同、烧结温度为1 500~1 650℃时,Al2O3陶瓷的相对密度和热导率都随烧结温度的升高而增大;当烧结温度相同、保温时间为30~120 min时,Al2O3陶瓷的相对密度和热导率也随保温时间的延长而增大。     

Corrosion behaviour of Y2O3-ZrO2 coatings on IN713LC in a LiCl-Li2O molten salt

Hot corrosion studies were performed on superalloy specimens. The IN713LC superalloy were sprayed with an aluminized NiCrAlY-bond coat and then with an yttria-zirconia top coat. The bare superalloy reveals an obvious weight loss due to spalling of the scales by the rapid scale growth and thermal stress. The top coatings showed a much better hot corrosion resistance in the presence of LiCl-3 wt.% Li₂O molten salt when compared with those of the bare superalloy and the aluminized bond coatings. These coatings have been found to be beneficial for increasing hot corrosion resistance of structural materials for lithium molten salts.     

Development of moderate temperature CVD Al2O3 coatings

Chemically vapor deposited Al₂O₃ coatings, due to their high hardness and chemical inertness, are currently the state of art in the cutting tool industry. The conventional high deposition temperature of about 1050 °C for Al₂O₃ coatings, based on the water–gas shift process, has to a great extend restricted the development of several hybrid coatings, such as TiC/TiN/TiCN/Al₂O₃. To overcome this limitation, alternate systems to deposit Al₂O₃ at moderate temperatures have been investigated. Systems using NO–H₂, H₂O₂, NO₂–H₂ and HCOOH were identified and thermodynamic calculations were performed to evaluate them as potential sources of oxygen donors to form Al₂O₃ in the moderate temperature range of 700–950 °C. Preliminary results have clearly demonstrated that it is possible to grow moderate temperature alumina (using such alternate sources) on the TiC/TiN coated cemented carbide substrates.     

Synthesis and characterization of Y3Al5O12 and ZrO2-Y2O3 thermal barrier coatings by combustion spray pyrolysis

Y₃Al₅O₁₂ and ZrO₂-Y₂O₃ (8 mol% YSZ) coatings for potential application as thermal barrier coatings were prepared by combustion spray pyrolysis. Thermal cycling of as deposited coatings on stainless steel and FeCrAlY bond coat substrates was carried out at 1000 °C and 1200 °C to determine the thermal fatigue response. Structural and morphological studies on Y₃Al₅O₁₂ and 8 mol% YSZ coatings before and after thermal cycling have been carried out. It has been noted that the coatings on FeCrAlY substrates remain intact after 50 cycles between room temperature and 1200 °C, whereas the coatings on stainless steel show some minor damage such as peeling off near the periphery after 50 cycles at 1000 °C. Thermal diffusivity values of Y₃Al₅O₁₂ and 8 mol% YSZ films were measured by using photo thermal deflection spectroscopy and the values are lower than those of coatings produced by conventional techniques such as EBPVD and APS.     

Y2O3—AlO3对SiC纤维烧结特性的影响

研究了纳米Y2O3－Al2O3在烧结时形成液相YAG9yttrium-aluminum garnet)对SiC纤维烧结特性的影响。实验结果表明,液相YAG的形成可以有效地提高SiC纤维的密度,在较低的烧结温度下达到完全致密,同时使纤维的强度由168MPa提高到844MPa。当烧结温度高于1800℃时,纤维中各组份间发生化学反应,产生的气体逸出后,在纤维组织中留下孔隙,使纤维强度降低。