Preparation and wear resistance of pulse electrodeposited Ni-W/Al2O3 composite coatings

The aim of this work is to obtain the electroplating parameters for preparation of Ni-W/Al₂O₃ composite coating with high tungsten content, high micro-hardness and excellent wear resistance by pulse plating procedure. Our results showed that the duty cycle is a dominant parameter for the tungsten content in the coating and the tungsten content increases significantly with increasing duty cycle. The further analysis showed the great influence of tungsten content on micro-hardness of the coating. A maximum micro-hardness of about 859 Hv was obtained in pulse electrodeposited Ni-W/Al₂O₃ composite with tungsten content of 40 wt.% at a peak current density of 20 A/dm², a duty cycle of 80%, a pulse frequency of 1000 Hz and a particle loading of 10 g/L alumina in the plating bath. Although the hardness of Ni-W/Al₂O₃ composite coating was only slightly affected by the alumina content of the deposits prepared in present investigation, the alumina content effect on the tribological characteristic of Ni-W/Al₂O₃ composite coatings is significant. The friction coefficient was lowered to 0.25 and the wear loss was reduced to 1.05 mg by setting the control factors according to the values mentioned above for obtaining the coating with the highest micro-hardness.     

EPR studies of Gd3+-doped Ce2(SO4)3.8H2O and La2(SO4)3.9H2O single crystals

EPR spectra of Gd³⁺-doped Ce₂(SO₄)₃.8H₂O and La₂(SO₄)₃.9H₂O single crystals have been measured with an X-band spectrometer at room and low temperatures. The absolute signs of spin Hamiltonian parameters have been determined for the La₂(SO₄)₃.9H₂O host from intensities of lines at liquid helium temperature; for the Ce₂(SO₄).8H₂O host the lines broaden considerably below 60 K, not permitting the determination of absolute signs of spin Hamiltonian parameters. The data are analysed using a rigourous least-squares procedure, fitting simultaneously all lines obtained for several orientations of the external magnetic field. The zero-field splittings have been computed for both the hosts. The characteristics of EPR spectra of Gd³⁺ in these hosts are compared with those obtained in other rare-earth trisulphate octahydrate hosts.     

Double-ceramic-layer thermal barrier coatings based on La2(Zr0.7Ce0.3)2O7/La2Ce2O7 deposited by electron beam-physical vapor deposition

Double-ceramic-layer (DCL) thermal barrier coatings (TBCs) of La₂(Zr_0.7Ce_0.3)₂O₇ (LZ7C3) and La₂Ce₂O₇ (LC) were deposited by electron beam-physical vapor deposition (EB-PVD). The composition, interdiffusion, surface and cross-sectional morphologies, cyclic oxidation behavior of DCL coating were studied. Energy dispersive spectroscopy and X-ray diffraction analyses indicate that both LZ7C3 and LC coatings are effectively fabricated by a single LZ7C3 ingot with properly controlling the deposition energy. The chemical compatibility of LC coating and thermally grown oxide (TGO) layer is unstable. LaAlO₃ is formed due to the chemical reaction between LC and Al₂O₃ which is the main composition of TGO layer. Additionally, the thermal cycling behavior of DCL coating is influenced by the interdiffusion of Zr and Ce between LZ7C3 and LC coatings. The failure of DCL coating is a result of the sintering of LZ7C3 coating surface, the chemical incompatibility of LC coating and TGO layer and the abnormal oxidation of bond coat. Since no single material that has been studied so far satisfies all the requirements for high temperature applications, DCL coating is an important development direction of TBCs.     

Correlation between Al2O3 particles and interface of Al-Al2O3 coatings by cold spray

Al-Al₂O₃ composite coatings with different Al₂O₃ particle shapes were prepared on Si and Al substrate by cold spray. The powder compositions of metal (Al) and ceramic (Al₂O₃) having different sizes and agglomerations were varied into ratios of 10:1 wt% and 1:1 wt%. Al₂O₃ particles were successfully incorporated into the soft metal matrix of Al. It was found that crater formation between the coatings and substrate, which is typical characteristic signature of cold spray could be affected by initial starting Al₂O₃ particles. In addition, when the large hard particles of fused Al₂O₃ were employed, the deep and big craters were generated at the interface between coatings and hard substrates. In the case of pure soft metal coating such as Al on hard substrate, it is very hard to get proper adhesion due to lack of crater formation. Therefore, the composite coating would have certain advantages.     

Atmospheric reactive plasma sprayed Fe-Al2O3-FeAl2O4 composite coating and its property evaluation

In the present study, Fe-Al₂O₃-FeAl₂O₄ composite coatings were successfully deposited by reactive plasma sprayed Al/Fe₂O₃ agglomerated powder. Phase composition and microstructure of the coatings were determined by XRD and SEM. The results indicated that the composite coatings were principally composed of three different phases, i.e. FeAl₂O₄ phase as main framework, dispersed ball-like Fe-rich phase, and small splats of Al₂O₃ phase, and it was thought that the in situ synthesized metal phase was helpful to toughen the coating matrix. According to the results of the indentation and frictional wear tests, the composite coating exhibited excellent toughness and anti-friction properties in comparison with conventional Al₂O₃ monophase coating, though its microhardness value was a little lower than that of Al₂O₃ coating. The formation mechanism and the toughening mechanism of the composite coating were clarified in detail.     

In situ formation of Al2O3-SiO2-SnO2 composite ceramic coating by microarc oxidation on Al-20%Sn alloy

In situ formation of Al₂O₃-SiO₂-SnO₂ composite ceramic coating on Al-20%Sn alloy was successfully fabricated in aqueous Na₂SiO₃ electrolyte by microarc oxidation technology. The compositions, structure, mechanical and tribological properties of the composite coating were detailed studied by scanning electron microscope, energy dispersive spectroscopy, X-ray diffraction, hardness tester and ball-on-disc friction tester. It is found that the species originating from the Al-20%Sn alloy substrate and the electrolyte solution both participate in reaction and contribute to the composition of the coating, which results in the generated coating firmly adherent to the substrate. The composite ceramic coating can greatly improve the microhardness and tribological property of Al-20%Sn alloy.     

Influence of Al2O3 additions on crystallization mechanism and conductivity of Li2O-Ge2O-P2O5 glass-ceramics

The crystallization mechanism and conductivity of lithium aluminum germanium phosphate [LAGP] glass-ceramics fabricated from Li_1+xAl_xGe_2−x(PO₄)₃ (x=0.0-0.7) glass system were investigated as a function of Al₂O₃ additions. A non-isothermal analysis was performed to study the crystallization behavior of LAGP glass-ceramics at various heating rates (5-25K min⁻¹) by the Kissinger equation and the Augis-Bennett equation, illustrating volume crystallization for the glass-ceramics. The crystal identification and microstructure in glass-ceramics containing various Al₂O₃ contents were analyzed by means of XRD and FESEM. The main phase of the glass-ceramics was found to be LiGe₂(PO₄)₃, with AlPO₄ as the impurity phase. Additionally the highest total ionic conductivity (5.8×10⁻⁴ S/cm) at room temperature was obtained when x=0.5 for Li_1+xAl_xGe_2−x(PO₄)₃ (x=0.0-0.7) glass-ceramics, suggesting that it was a promising electrolyte for practical application in all-solid-state lithium batteries.     

Preparation and properties of composite ceramic coating containing Al2O3–ZrO2–Y2O3 on AZ91D magnesium alloy by plasma electrolytic oxidation

A composite ceramic coating containing Al₂O₃–ZrO₂–Y₂O₃ was successfully prepared on AZ91D magnesium alloy by plasma electrolytic oxidation (PEO) technique in an alkaline aluminate electrolyte. The morphology, elemental and phase composition, corrosion behavior and thermal stability of the uncoated and coated samples were studied by environmental scanning electron microscopy (ESEM), energy dispersive X-ray spectrometer (EDS), X-ray diffractometer (XRD), electrochemical corrosion test, high temperature oxidation test and thermal shock test. The results showed that the composite ceramic coating was composed of Al₂O₃, c-ZrO₂, t-ZrO₂, Y₂O₃ and some magnesium compounds, such as MgO, MgF₂ and MgAl₂O₄. After PEO treatment, the corrosion potential of AZ91D alloy was increased and the corrosion current density was significantly reduced. Besides, the coated magnesium alloys also showed excellent high temperature oxidation resistance and thermal shock resistance at 500 °C environment.     

Preparation and characterization of the electrodeposited Cr-Al2O3/SiC composite coating

To increase the SiC content in Cr-based coatings, Cr-Al₂O₃/SiC composite coatings were plated in Cr(VI) baths which contained Al₂O₃-coated SiC powders. The Al₂O₃-coated SiC composite particles were synthesized by calcining the precursor prepared by heterogeneous deposition method. The transmission electron microscopy analysis of the particles showed that the nano-SiC particle was packaged by alumina. The zeta potential of the particles collected from the bath was up to +23 mV, a favorable condition for the co-deposition of the particles and chromium. Pulse current was used during the electrodeposition. Scanning Electron Microscopy (SEM) indicated that the coating was compact and combined well with the substrate. Energy dispersive X-ray analysis of Cr-Al₂O₃/SiC coatings demonstrated that the concentration of SiC in the coating reached about 2.5 wt.%. The corrosion behavior of the composite coating was studied by potentiodynamic polarization and electrochemical impedance spectroscopy techniques. The data obtained suggested that the Al₂O₃/SiC particles significantly enhanced the corrosion resistance of the composite coating in 0.05 M HCl solution.     

Preparation and characterization of visible light responsive Fe2O3-TiO2 composites

In this study we present the effects of iron oxide (Fe₂O₃) on titanium dioxide (TiO₂) in synthesising visible-light reactive photocatalysts. A Fe₂O₃-TiO₂ composite photocatalyst was synthesized from Fe₂(SO₄)₃ and Ti(SO₄)₂ by a ethanol-assisted hydrothermal method. The preparation conditions were optimized through the investigation of the effects of hydrothermal temperature and time as well as molar ratio of Ti to Fe on the photocatalytic activity. The visual, physical and chemical properties of the Fe₂O₃-TiO₂ composites were investigated. The results showed that α-Fe₂O₃ and anatase TiO₂ were present in the composites. The Fe₂O₃-TiO₂ synthesized under optimum condition consisted of mesoporous structure with an average pore size of 4 nm and a surface area of 43 m²/g. Under visible and solar light irradiation, the photocatalytic activity of optimized sample was significantly higher than that of pure TiO₂. This sample led to a photodegradation efficiency of 90% and 40% of auramine under visible light and solar light, respectively.     

Microstructure and properties of Ni-Co/nano-Al2O3 composite coatings by pulse reversal current electrodeposition

Ni-Co/nano-Al₂O₃ (Ni-Co/Al₂O₃) composite coatings were prepared under pulse reversal current (PRC) and direct current (dc) methods respectively. The microstructure of coatings was characterized by means of XRD, SEM and TEM. Both the Ni-Co alloy and composite coatings exhibit single phase of Ni matrix with face-centered cubic (fcc) crystal structure, and the crystal orientation of the Ni-Co/Al₂O₃ composite coating was transformed from crystal face (2 0 0) to (1 1 1) compared with alloy coatings. The hardness, anti-wear property and macro-residual stress were also investigated. The results showed that the microstructure and performance of the coatings were greatly affected by Al₂O₃ content and the electrodeposition methods. With the increasing of Al₂O₃ content, the hardness and wear resistance of the composite coatings enhanced. The PRC composite coatings exhibited compact surface, high hardness, better wear resistance and lower macro-residual stress compared with that of the dc composite coatings.     

Orange emission enhancement by energy transfer in Sr3Al2O5Cl2:Ce, Eu phosphor for solid-state lighting

Orange-emissive Ce³⁺/Eu²⁺ co-doped Sr₃Al₂O₅Cl₂ phosphors were synthesized by a solid-state reaction. The large overlap between the emission spectrum of blue Sr₃Al₂O₅Cl₂:Ce³⁺ and the excitation spectrum of orange Sr₃Al₂O₅Cl₂:Eu²⁺, and the shortening trend in lifetime of Ce³⁺ donors with increasing Eu²⁺ concentration in Sr₃Al₂O₅Cl₂:Ce³⁺, Eu²⁺ provide the strong evidence of energy transfer from Ce³⁺ to Eu²⁺ ions. It supports that the orange emission intensity of the optimal co-doped phosphor is 1.5 times stronger than that of single Eu²⁺-doped one. The Sr₃Al₂O₅Cl₂:Ce³⁺, Eu²⁺ phosphor is a promising orange-emitting phosphor for warm-white-light-emitting diode because of its effective excitation in the near ultraviolet range.     

SHS等离子喷涂制备FeAl2O4-Al2O3-Fe纳米复合涂层的研究

利用SHS等离子喷涂技术，将经过机械团聚法制备的Fe₂O₃-Al复合粉体送入等离子焰流，沉积出厚度约为400 μm的复合涂层.利用XRD，SEM 和TEM等检测手段对涂层的成分和组织进行了分析，测定了涂层的显微硬度、断裂韧性以及耐磨性.结果表明涂层为具有纳米结构的FeAl₂O₄-Al₂O₃-Fe纳米复合组织；涂层的显微硬度为HV_100g870；断裂韧性是普通Al₂O₃涂层的2倍；无润滑磨损的耐磨性是普通Al₂O₃涂层的2.5倍. 关键词： SHS等离子喷涂 纳米涂层 断裂韧性     

Effects of Al2O3 nanofiller and EC plasticizer on the ionic conductivity enhancement of solid PEO-LiCF3SO3 solid polymer electrolyte

A solid polymer electrolyte (SPE) is synthesized by solution casting technique. The SPE uses poly(ethylene oxide) PEO as a host matrix doped with lithium triflate (LiCF₃SO₃), ethylene carbonate (EC) as plasticizer and nano alumina (Al₂O₃) as filler. The polymer electrolytes are characterized by Impedance Spectroscopy (IS) to determine the composition of the additive which gives the highest conductivity for each system. At room temperature, the highest conductivity is obtained for the composition PEO-LiCF₃SO₃-EC-15%Al₂O₃ with a value of 5.07 10^− 4 S/cm. The ionic conductivity of the polymer electrolytes increases with temperature and obeys the Arrhenius law. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) studies indicate that the conductivity increase is due to an increase in amorphous content which enhances the segmental flexibility of polymeric chains and the disordered structure of the electrolyte. Fourier transform infrared spectroscopy (FTIR) spectra show the occurrence of complexation and interaction among the components. Scanning electron microscopy (SEM) images show the changes morphology of solid polymer electrolyte.     

Effect of NaAlO2 concentrations on microstructure and corrosion resistance of Al2O3/ZrO2 coatings formed on zirconium by micro-arc oxidation

In this study, Al₂O₃/ZrO₂ composite coatings were prepared on Zr substrates by micro-arc oxidation (MAO) in the NaAlO₂-containing electrolytes, and the effect of NaAlO₂ concentration on the microstructure, bond strength, microhardness and corrosion resistance of coatings was systematically investigated. The study reveals that the adequate NaAlO₂ in the electrolyte (>0.2 M) is essential to the formation of needle-like α-Al₂O₃ in the coatings, and the amount of α-Al₂O₃ rises with the increase of the NaAlO₂ concentration. m-ZrO₂ and t-ZrO₂ are present in all of the coatings, but their relative amount largely depends on the amount of Al₂O₃. It is also found that as the NaAlO₂ concentration increases from 0.2 to 0.3 M, the coating becomes denser and thicker, and its bond strength, maximum microhardness and corrosion resistance increases as well. The coating formed at 0.3 M NaAlO₂ demonstrates the highest bond strength of 52 MPa, the maximum microhardness of 1600 Hv_0.2N and the superior corrosion resistance. However, the overhigh concentration of NaAlO₂ (0.35 M) is found harmful to the coating's microstructure and properties.     

Interfacial reactions and oxidation behavior of Al2O3 and Al2O3/Al coatings on an orthorhombic Ti2AlNb alloy

The uniform and dense Al₂O₃ and Al₂O₃/Al coatings were deposited on an orthorhombic Ti₂AlNb alloy by filtered arc ion plating. The interfacial reactions of the Al₂O₃/Ti₂AlNb and Al₂O₃/Al/Ti₂AlNb specimens after vacuum annealing at 750 °C were studied. In the Al₂O₃/Ti₂AlNb specimens, the Al₂O₃ coating decomposed significantly due to reaction between the Al₂O₃ coating and the O-Ti₂AlNb substrate. In the Al₂O₃/Al/Ti₂AlNb specimens, a γ-TiAl layer and an Nb-rich zone came into being by interdiffusion between the Al layer and the O-Ti₂AlNb substrate. The γ-TiAl layer is chemically compatible with Al₂O₃, with no decomposition of Al₂O₃ being detected. No internal oxidation or oxygen and nitrogen dissolution zone was observed in the O-Ti₂AlNb alloy. The Al₂O₃/Al/Ti₂AlNb specimens exhibited excellent oxidation resistance at 750 °C.     

Synthesis and characterization of monodisperse spherical core-shell structured SiO2@Y3Al5O12:Ce3+/Tb3+ phosphors for field emission displays

Nanocrystalline Y₃Al₅O₁₂: Ce³⁺/Tb³⁺ (average crystalline size 30 nm) phosphor layers were coated on non-aggregated, monodisperse and spherical SiO₂ particles by the sol-gel method, resulting in the formation of core-shell structured SiO₂@Y₃Al₅O₁₂:Ce³⁺/Tb³⁺ particles. X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, photoluminescence, cathodoluminescence spectra, as well as lifetimes were utilized to characterize the core-shell structured SiO₂@Y₃Al₅O₁₂:Ce³⁺/Tb³⁺ phosphor particles. The obtained core-shell structured phosphors consist of well-dispersed submicron spherical particles with a narrow size distribution. The thickness of the Y₃Al₅O₁₂:Ce³⁺/Tb³⁺ shells on the SiO₂ cores (average size about 500 nm, crystalline size about 30 nm) could be easily tailored by varying the number of deposition cycles (100 nm for four deposition cycles). Under the excitation of ultraviolet and low-voltage electron beams (1–3 kV), the core-shell SiO₂@Y₃Al₅O₁₂:Ce³⁺/Tb³⁺ particles show strong yellow-green and green emission corresponding to the 5d–4f emission of Ce³⁺ and ⁵D₄–⁷F _J (J = 6, 5, 4, 3) emission of Tb³⁺, respectively. These phosphors may have potential application in field emission displays.     

Zero field splittings of Gd3+IN Nd2(SO4)3 · 8H2O and Sm2(SO4)3 · 8H2O crystals at 273 K

The electron paramagnetic resonance (EPR) of Nd₂(SO₄)₃ · 8H₂O and Sm₂(SO₄)₃ · 8H₂O doped with Gd³⁺ has been carried out at 273 K and the spin-Hamiltonian parameters are deduced. The zero field splittings have been computed and compared with those observed directly by Bogle and Symmons. It is found that the discrepancy in the zero field splittings. between computed and directly observed values falls within the range of linewidths of directly observed values.     

Deposition and characterization of binary Al2O3/SiO2 coating layers on the surfaces of rutile TiO2 and the pigmentary properties

Binary Al₂O₃/SiO₂-coated rutile TiO₂ composites were prepared by a liquid-phase deposition method starting from Na₂SiO₃·9H₂O and NaAlO₂. The chemical structure and morphology of binary Al₂O₃/SiO₂ coating layers were investigated by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, TG-DSC, Zeta potential, powder X-ray diffraction, and transmission electron microscopy techniques. Binary Al₂O₃/SiO₂ coating layers both in amorphous phase were formed at TiO₂ surfaces. The silica coating layers were anchored at TiO₂ surfaces via Si-O-Ti bonds and the alumina coating layers were probably anchored at the SiO₂-coated TiO₂ surfaces via Al-O-Si bonds. The formation of continuous and dense binary Al₂O₃/SiO₂ coating layers depended on the pH value of reaction solution and the alumina loading. The binary Al₂O₃/SiO₂-coated TiO₂ composites had a high dispersibility in water. The whiteness and brightness of the binary Al₂O₃/SiO₂-coated TiO₂ composites were higher than those of the naked rutile TiO₂ and the SiO₂-coated TiO₂ samples. The relative light scattering index was found to depend on the composition of coating layers.     

Y2O3·Cr2O3复合氧化物热力学性质的研究

在1182—1386K温度范围内,用固体电解质氧浓差电池:Mo|Cr,Y₂O₃,Y₂O₃·Cr₂O₃|ZrO₂(+MgO)|Cr,Cr₂O₃|Mo测定了复合氧化物Y₂O₃·Cr₂O₃的热力学性质。对于反应Y_{2关键词：}