Phase stability and thermal conductivity of ytterbia and yttria co-doped zirconia

Rare earth oxides doping has been extensively investigated as one of the effective methods to lower thermal conductivity of 4.55 mol% Y2O3stabilized ZrO2(YSZ) thermal barrier coatings(TBCs).In the present work,5–6 mol% Yb2O3and Y2O3co-doped ZrO2ceramics were synthesized by solid reaction sintering at 1600 1C.The phase stability of the samples after heat treatment at 1500 1C was investigated.Yb2O3and Y2O3co-doped zirconia,especially when Yb2O3/Y2O3≥1,contained less monoclinic phase than single Yb2O3or Y2O3phase doped zirconia,indicating that co-doped zirconia was more stable at high temperature than YSZ.The thermal conductivity of the 3 mol% Yb2O3+3 mol% Y2O3co-doped ZrO2was 1.8 W m 1K 1at 1000 1C,which was more than 20% lower than that of YSZ.     

Structure evolution of Y2O3 nanoparticle/Fe composite during mechanical milling and annealing

Fe-25 wt% Y2O3composite powders have been fabricated by mechanical milling(MM) Fe powders of 100 μm in diameter and Y2O3nanoparticles in an argon atmosphere for the milling periods of4,8,12,24,36,and 48 h,respectively.The features of these powders were characterized by using X-ray diffraction(XRD),scanning electron microscopy(SEM),electron probe micro analyzer(EPMA) and transmission electron microscopy(TEM).The experimental results showed that the mean particle size and crystalline size of MM powders decreased with the milling time increasing.All the elements distributed homogenously inside the powders after 48 h of MM.The lattice constant of the matrix α-Fe kept constant with the milling time,and no solid solution took place during MM process.After 8 h of MM,the α-Fe in each powder became nanocrystalline.After 48 h of MM,Y2O3changes from nanostructure into amorphous structure,and the crystalline size of α-Fe further decreased to 10 nm.The Y2O3in the powders mechanically milled for 48 h kept the amorphous structure after being annealed at 400 1C,and starts to crystallize when the powders are annealed at 600 1C.The amorphous Y2O3contains a small amount of Fe,and crystalline FeYO3appears at 800 1C.     

Microstructure, mechanical and thermo-physical properties of hot-pressed Al2O3-GdAlO3-ZrO2 ceramics with eutectic composition

A low cost chemical co-precipitation method was employed to fabricate nanoscale Al_2O_3-GdAlO_3-ZrO_2 powder with eutectic composition. A careful control of reaction conditions was required during the preparation. The synthesized nanopowders exhibited a particle size of 20-200 nm, and were highly dispersive and uniform. The results showed that calcination temperature had an important influence on the phase constituents of the nanopowders. With increasing the calcination temperature, a phase transformation from θ-Al_2O_3 to α-Al_2O_3 and a thermal decomposition from Gd_3 Al_5O_(12)(GdAG) to GdAlO_3 and α-Al_2O_3 occurred in sequence. A calcination temperature of 1300 ℃ was needed for the crystallization of α-Al_2 O_3. These nanosized powders were consolidated via hot pressing to produce a fully densified ceramic composite with eutectic composition. The Al_2O_3-GdAlO_3-ZrO_2 ceramic hot-pressed at 1500 ℃ exhibited a relative density of 99.4%, a flexural strength of 485 MPa and a fracture toughness of 6.5 MPa m~(1/2). The ceramic had a thermal conductivity of 1.9 W m K~(-1) at 1200 ℃ and a thermal expansion coefficient of 9.49 ×10~(-6) K~(-1) at 1100 ℃.     

Effect of B2O3 on the aqueous tape casting and microwave properties of Li2O–Nb2O5–TiO2 ceramics

The effect of B2O3 addition on the aqueous tape casting, sintering, microstructure and microwave dielectric properties of Li2O-Nb2O5-TiO2 ceramics has been investigated. The tape casting slurries exhibit a typical shear-thinning behavior without thixotropy, but the addition of B2O3 increases the viscosity of the slurries significantly. It was found that doping of B2O3 can decrease the tensile strength, strain to failure and density of the green tapes. The sintering temperature could be lowed down to 900℃ with the addition of 2 wt% B2O3 due to the liquid phase effect. No secondary phase is observed. The addition of B2O3 does not induce much degradation on the microwave dielectric properties. Optimum microwave dielectric properties of εr 67, Q×f 6560 GHz are obtained for Li2O-Nb2O5-TiO2 ceramics containing 2 wt% B2O3 sintered at 900 1C. It represents that the ceramics could be promising for multilayer low-temperature co-fired ceramics (LTCC) application.     

Microstructure and growth kinetics of Ce and Y jointly modified silicide coatings for Nb–Ti–Si based ultrahigh temperature alloy

In order to protect Nb-Ti-Si based ultrahigh temperature alloy from oxidation, pack cementation processes were utilized to prepare Ce and Y jointly modified silicide coatings. The Ce and Y jointly modified silicide coating has a double-layer structure: a relatively thick (Nb, X)Si2 (X represents Ti, Cr and Hf elements) outer layer and a thin (Ti, Nb)5Si4 transitional layer. The pack cementation experiments at 1150 ℃ for 8 h proved that the addition of certain amounts of CeO2 and Y2O3 powders in the packs distinctly influenced the coating thickness, the contents of Si, Ce and Y in the (Nb, X)Si2 outer layers, and the density of cavities in the coatings. In order to study the effects of Ce and Y joint modification in the silicide coatings, both only Ce and only Y modified silicide coatings were also prepared for comparison. The mechanisms of the beneficial effects of Ce and Y are discussed. A pack mixture containing 1.5CeO2-0.75Y2O3 (wt%) powders was employed to investigate the growth kinetics of the Ce and Y jointly modified silicide coating at 1050, 1150 and 1250 ℃. It has been found that the growth kinetics obeyed parabolic laws and the parabolic rate constants were 109.20 mm2/h at 1050 ℃, 366.75 mm2/h at 1150 ℃ and 569.78 mm2/h at 1250 ℃, and the activation energy for the growth of the Ce and Y jointly modified silicide coating was 197.53 kJ/mol.     

Preparation and catalytic effect of porous Co3O4 on the hydrogen storage properties of a Li-B-N-H system

A porous Co_3O_4 with a particle size of 1–3 μm was successfully prepared by heating Co-based metal organic frameworks MOF-74(Co) up to 500 °C in air atmospheric conditions. The as-prepared porous Co_3O_4 significantly reduced the dehydrogenation temperatures of the LiBH_4-2LiNH_2 system and improved the purity of the released hydrogen. The LiBH_4-2LiNH_2-0.05/3Co_3O_4 sample started to release hydrogen at 140 °C and released hydrogen levels of approximately 9.7 wt% at 225 °C. The end temperature for hydrogen release was lowered by 125 °C relative to that of the pristine sample. Structural analyses revealed that the as-prepared porous Co_3O_4 is in-situ reduced to metallic Co, which functions as an active catalyst, reducing the kinetic barriers and lowering the dehydrogenation temperatures of the LiBH_4-2LiNH_2 system. More importantly, the porous Co_3O_4-containing sample exhibited partially improved reversibility for hydrogen storage in the LiBH_4-2LiNH_2 system.     

La2O3–Al2O3 –SiO2 glass-infiltrated 3Y-TZP all-ceramic composite for the dental restora tive application

The 3 mol% yttria stabilized tetragonal zirconia polycrystals (3Y-TZP) powder had three particle size distributions, while the fine one was lower than 100 nm. The 3Y-TZP compact was prepared by dry-pressing under pressures ranged from 10 to 30 MPa and then presintered at 1250°C for 2 h. The matrix dry-pressed under the pressure of 20 MPa had a porosity of 16.7% and could be easily processed by computer aided design and computer aided manufacturing (CAD/CAM), and which had been infiltrated by the La2O3–Al2O3–SiO2 glass at 1200°C for 4 h. The flexural strength and fracture toughness of the composite were 710.7 MPa and 6.51 MPa m^1/2, respectively. The low shrinkage (0.3%) of the composite can satisfy the net-shape fabrication standard. XRD results illustrated that zirconia in the La2O3–Al2O3–SiO2 glass-infiltrated 3Y-TZP all-ceramic composite was mainly in the tetragonal phase. SEM and EDS results indicated that the pores of the matrix were almost filled by the La2O3–Al2O3 –SiO2 glass     

Effect of CuO addition on the sintering temperature and microwave dielectric properties of CaSiO3– Al2O3 ceramics

CuO-doped CaSiO3–1 wt% Al2O3 ceramics were synthesized via a traditional solid-state reaction method, and their sintering behavior,microstructure and microwave dielectric properties were investigated. The results showed that appropriate CuO addition could accelerate the sintering process and assist the densification of CaSiO3–1 wt% Al2O3 ceramics, which could effectively lower the densification temperature from1250 1C to 1050 1C. However, the addition of CuO undermined the microwave dielectric properties. The optimal amount of CuO addition was found to be 0.8 wt%, and the derived CaSiO3–Al2O3ceramic sintered at 1100 1C presented good microwave dielectric properties of εr?7.27,Q f?16,850 GHz and τf? 39.53 ppm/1C, which is much better than those of pure CaSiO3 ceramic sintered at 1340oC(Q f?13,109 GHz).The chemical compatibility of the above ceramic with 30 Pd/70 Ag during the cofiring process has also been investigated, and the result showed that there was no chemical reaction between palladium–silver alloys and ceramics.& 2014 Chinese Materials Research Society. Production and hosting by Elsevier B.V. All rights reserved.     

Effect of pickling processes on the microstructure and properties of electroless Ni–P coating on Mg–7.5Li–2Zn–1Y alloy

The electroless plating Ni–P is prepared on the surface of Mg–7.5Li–2Zn–1Y alloys with different pickling processes.The microstructure and properties of Ni–P coating are investigated.The results show that the Ni–P coatings deposited using the different pickling processes have a different high phosphorus content amorphous Ni–P solid solution structure,and the Ni–P coatings exhibit higher hardness.There is higher phosphorus content of Ni–P amorphous coating using 125 g/L Cr O3and 110 ml/L HNO3(w68%)than using 180 g/L Cr O3and 1 g/L KF during pre-treatment,and the coating structure is more compact,and the Ni–P coatings exhibit more excellent adhesion with substrate(Fcup to22 N).The corrosion potential of Ni–P coating is improved and exhibits good corrosion resistance.As a result,Mg-7.5Li-2Zn-1Y alloy is remarkably protected by the Ni–P coating.     

Preparation of electroless Ni–P composite coatings containing nano-scattered alumina in presence of polymeric surfactant

Ni–P electroless coating was applied on low carbon steel with the incorporation of different amounts of nano Al2O3 powder (ranging from 3 g/l to 30 g/l) in electroless bath. Corrosion properties and microstructures of the coating were studied. The dispersion stability of alumina colloidal particles stabilized by polymeric (non-ionic) surfactants in an electroless bath was also investigated. The surface morphology and the relevant structure were evaluated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Corrosion behavior of the coated steel was evaluated by electrochemical impedance spectroscopy (EIS) and polarization techniques. The results showed that increasing alumina concentration not only changed the surface morphology, but also promoted the corrosion resistance. Addition of surfactants has an indirect effect on the amount of the incorporated particles. Meanwhile, in the presence of surfactant, corrosion resistance of Ni–P coating containing even a small quantity of alumina was improved since a stabilized bath was obtained.     

A.C. conductivity and relaxation dynamics in zinc–borate glasses

The frequency-dependent dielectric dispersion of ZnO–Na2O–Al2O3–B2O3(in mol%) glass prepared by the melt quenching technique is investigated in the temperatur e ranges from room temperature to 420 K. Dielectric relaxation has been analyzed based on the behavior of electric modulus behavior. An analysis of the real and imaginary parts of dielectric is performed assuming the ideal Debye behavior as confirmed by Cole–Cole plot. The activation energy associated with the dielectric relaxation determined from the electric modulus spectra was found to be 1.863 eV, which is close to that the activation energy for d.c. conductivity (1.871 eV), indicating the similar nature of relaxation and conductivity.     

Effect of La0.8Sr0.2Co0.2Fe0.8O3-δ morphology on the performance of composite cathodes

In the present work,one dimensional La0.8Sr0.2Co0.2Fe0.8O3 δ(LSCF) nanofibers with the mean diameter of about 100 nm prepared by electrospinning were deposited on Gd0.2Ce0.8O1.9(GDC) electrolyte followed by sintering to form one dimensional LSCF nanofiber cathode. And LSCF/GDC composite cathodes were formed by introducing GDC phases into LSCF nanofiber scaffold using infiltration method. The polarization resistances for the composite cathode with an optimal LSCF/GDC mass ratio of 1/0.56 are 0.27,0.14 and 0.07 Ω cm2at 650,700 and750 1C,respectively,which are obviously smaller than 2.26,0.78 and 0.29 Ω cm2of pure LSCF nanofiber cathode. And the activation energy is1.194 eV,which is much lower than that of pure LSCF nanofiber cathode(1.684 eV). These results demonstrate that the infiltration of GDC into LSCF nanofiber scaffold is an effective approach to achieve high performance cathode for solid oxide fuel cells(SOFCs). In addition,the performance of composite cathode in this work was also compared with that of our previous nanorod structured LSCF/GDC composite cathode.     

Effect of Sr on microstructure and aging behavior of Mg–14Li alloys

The as-cast and as-extruded Mg–14 wt%Li–x Sr ( x=0.14, 0.19, 0.39 wt%) alloys were,respectively, prepared through a simple alloying process and hot extrusion. The effects of Sr addition on microstructure and aging behavior of the Mg–14 wt%Li–xSr alloys were studied. The results indicated that β(Li) and Mg2Sr were the two primary phases in the microstructures of both as-cast and as-extruded Mg–14 wt%Li–xSr alloys. Interestingly, with the increase of Sr content from 0.14 wt% to 0.39 wt%, the grain sizes of the as-cast and as-extruded Mg–14 wt%Li–xSr alloys markedly decreased from 5000mm and 38mm to 330 mm and 22mm respectively, while no obvious changes of the micro-hardness and microstructure of the as-extruded alloys were observed during the aging treatment.     

Integrated Bi2O3 nanostructure modified with Au nanoparticles for enhanced photocatalytic activity under visible light irradiation

An integrated Bi_2O_3(i-Bi_2O_3) nanostructure with a particle size 10 nm inducing agglomerated structure were synthesized by dissolving bismuth nitrate pentahydrate in diethylene glycol at 180 ℃ with post heat treatment.The prepared i-Bi_2O_3 nanostructures were employed for the construction of Au/i-Bi_2O_3 composite system and characterized by X-ray diffraction pattern,UV-visible diffuse reflectance spectroscopy(DRS),and transmission electron microscopy,X-ray photoemission spectroscopy(XPS) and Energy dispersive X-ray spectroscopy(EDS).The i-Bi_2O_3 nanostructure and Au/i-Bi_2O_3 composite system were found to exhibit high photocatalytic activity than commercial Bi_2O_3 in decomposing salicylic acid under visible light irradiation.The high catalytic activity of i-Bi_2O_3 nanostructure was deduced to be caused by charge separation facilitated by electron hopping between the particles within the integrated structure and space-charge separation between i-Bi_2O_3 and Au.The charge separation behavior in i-Bi_2O_3 nanostructure was further bolstered by comparing the measured.OH radical produced in the solution with i-Bi_2O_3 nanostructure,commercial Bi_2O_3 and Au/i-Bi_2O_3 composite which readily react with 1,4-terephthalic acid(TA) inducing 2-hydroxy terephthalic acid(TAOH) that shows unique fluorescence peak at 426 nm.The space-charge separation between i-Bi_2O_3 and An was confirmed by measuring the electron spin resonance(ESR) spectra.     

Addition of IrO2 to RuO2+TiO2 coated anodes and its effect on electrochemical performance of anodes in acid media

Ternary mixed metal oxide coatings with the nominal composition IrxRu(0.6-x)Ti0.4O2(x=0, 0.1, 0.2, 0.3) on the titanium substrate were prepared by thermal decomposition of a chloride precursor mixture. Surface morphology and microstructure of the coatings were investigated by Scanning electron microscopy(SEM), Field emission scanning electron microscopy(FE-SEM) and X-ray diffraction(XRD) analysis. Systematic study of electrochemical properties of these coatings was performed by cyclic voltammetry(CV) and polarization measurements. The corrosion behavior of the coatings was evaluated under accelerated conditions(j=2 A cm-2) in acidic electrolyte. The role of iridium oxide admixture in the change of electrocatalytic activity and stability of Ru0.6Ti0.4O2coating was discussed. Small addition of IrO2can improve the stability of the RuO2+TiO2mixed oxide, while the electrocatalytic activity for oxygen evolution reaction(OER) is decreased. The shift of redox potentials for Ru0.6Ti0.4O2electrode that is slightly activated with IrO2and improvement in the stability can be attributed to the synergetic effect of mixed oxide formation.     

The enhanced corrosion resistance of UMAO coatings on Mg by silane treatment

The surface silanization was carried out on ultrasonic micro-arc oxidation(UMAO) coatings on pure magnesium using KH550 as silane coupling agent(SCA). The surface morphology, chemical bonds and corrosion resistance of the silane films were investigated by scanning electron microscope(SEM), Fourier transform infrared spectroscopy(FTIR) and electrochemical workstation, respectively. The results showed that hybrid coatings were successfully prepared on pure magnesium by UMAO-Na OH(1 mol/L, 2 mol/L, 3 mol/L)-SCA processing. The organic films with Si–O–Mg bonds are helpful for the reduction of the pores in UMAO coatings. The pores decreased with increasing Na OH concentration. Compared with single UMAO treatment, the corrosion potentials(Ecorr) of magnesium plates with UMAO-Na OH(1 mol/L,2 mol/L, 3 mol/L)-SCA treatment increased by 29 m V, 53 m V and 75 m V, respectively, meanwhile the corrosion current density(Icorr) reduced one to two orders of magnitude. It indicated that the corrosion resistance of the coatings was improved by silane treatment.     

Sonochemical synthesis of nanostructured nickel hydroxide as an electrode material for improved electrochemical energy storage application

A facile and fast approach for the synthesis of a nanostructured nickel hydroxide(Ni(OH)_2) via sonochemical technique is reported in the present study. The X-ray diffraction results confirmed that the synthesized Ni(OH)_2 was oriented in β-phase of hexagonal brucite structure. The nanostructured Ni(OH)_2 electrode exhibited the maximum specific capacitance of 1256 F/g at a current density of 200 mA/g in 1 M KOH_((aq)). Ni(OH)_2 electrodes exhibited the pseudocapacitive behavior due to the presence of redox reaction. It also exhibited long-term cyclic stability of 85% after 2000 cycles, suggesting that the nanostructured Ni(OH)_2 electrode will play a promising role for high performance supercapacitor application.     

Effect of boehmite sol on the crystallization behavior and densification of mullite formed from a sol–gel precursor

Hybrid mullite sol was synthesized from an aqueous solution of aluminum nitrate (AN), aluminum isopropoxide (AIP) and tetraethylorthosilicate (TEOS), doped with boehmite sol with different ratios. Pressureless sintering of the xerogel was carried out at different temperatures in the presence of boehmite doping. The xerogel and sintered powder were characterized by FTIR, TG-DSC, XRD, SEM and bulk density. The addition of boehmite caused the formation of metaphase spinel (6Al2O3·SiO2) crystal before the appearance of mullite phase, which could lead to the formation of amorphous phase and suppress the premature formation of mullite. Both of these effects improve the densification of mullite. A maximum density about 98% of the theoretical density (TD, 3.01 g/cm3 ) of mullite could be obtained for 5 wt% boehmite addition at 1200 1C pressureless sintering.     

An in vitro evaluation of novel NHA/zircon plasma coating on 316L stainless steel dental implant

The surface characteristics of an implant that influence the speed and strength of osseointegration include crystal structure and bioactivity. The aim of this study was to evaluate the bioactivity of a novel natural hydroxyapatite/zircon(NHA/zircon) nanobiocomposite coating on 316L stainless steel(SS) dental implants soaking in simulated body fluid. A novel NHA/zircon nanobiocomposite was fabricated with 0(control),5, 10, and 15 wt% of zircon in NHA using ball mill for 1 h. The composite mixture was coated on SS implants using a plasma spray method.Scanning electron microscopy(SEM) was used to evaluate surface morphology, and X-ray diffraction(XRD) was used to analyze phase composition and crystallinity(Xc). Further, calcium ion release was measured to evaluate the coated nanobiocomposite samples. The prepared NHA/zircon coating had a nanoscale morphological structure with a mean crystallite size of 30–40 nm in diameter and a bone-like composition,which is similar to that of the biological apatite of a bone. For the prepared NHA powder, high bioactivity was observed owing to the formation of apatite crystals on its surface. Both minimum crystallinity(Xc=41.1%) and maximum bioactivity occurred in the sample containing 10 wt% of zircon because of minimum Xcand maximum biodegradation of the coating sample.     

Corrosion study of resorbable Ca60Mg15Zn25 bulk metallic glasses in physiological fluids

The corrosion activity of amorphous plates of Ca_(60)Mg_(15)Zn_(25)alloy was investigated.The biocompatible elements were selected for the alloy composition.The electrochemical corrosion and immersion tests were carried out in a multi-electrolyte fluid and Ringer's solution.Better corrosion behavior was observed for the samples tested in a multi-electrolyte fluid despite the active dissolution of Ca and Mg in Ringer's solution.The experimental results indicated that reducing concentration of NaCl from 8.6 g/dm~3for Ringer's solution to 5.75 g/dm~3caused the decrease of the corrosion rate.The volume of the hydrogen evolved after 480 min in Ringer's solution(40.1 ml/cm~2)was higher in comparison with that obtained in a multi-electrolyte fluid(24.4 ml/cm~2).The values of opencircuit potential(E_(OCP))for the Ca_(60)Mg_(15)Zn_(25)glass after 1 h incubation in Ringer's solution and a multielectrolyte fluid were determined to be-1553 and-1536 m V vs.a saturated calomel electrode(SCE).The electrochemical measurements indicated a shift of the corrosion current density(j_(corr))from 1062μA/cm~2for the sample tested in Ringer's solution to 788μA/cm~2for the specimen immersed in a multi-electrolyte fluid.The corrosion products analysis was conducted by using the X-ray photoelectron spectroscopy(XPS).The corrosion products were identified to be CaCO_3,Mg(OH)_2,CaO,MgO and Zn O.The mechanism of corrosion process was proposed and described based on the microscopic observations.The X-ray diffraction and Fourier transform infrared spectroscopy(FTIR)also indicated that Ca(OH)_2,CaCO_3,Zn(OH)_2and Ca(Zn(OH)_3)_2·2H_2O mainly formed on the surface of the studied alloy.