Electrophoretic deposition of Al2O3/ZrO2 layer with controllable thickness in ethanol medium

ZrO₂ toughened Al₂O₃ (Al₂O₃/ZrO₂) ceramic layers with required thickness were prepared by electrophoretic deposition (EPD) method using ethanol suspensions with stabilizing agent of polyethyleneimine (PEI) under constant-voltage mode in this paper. The deposition of Al₂O₃/ZrO₂ ceramic powders occurred on the titanium alloy cathode. A stable suspension with 1wt% PEI in ethanol at pH 5 was prepared in terms of the zeta potential and sedimentation of the suspension. The effects of the suspension concentration, applied voltage, deposition time and processing method of titanium alloy cathode on the coating thickness and morphology were investigated. The deposition layers on titanium alloys with smooth surfaces and thickness of 0.35?C1.2 mm could be obtained by adjusting the aforementioned parameters. In addition, after being sintered at 1500°C for 3 h in air atmosphere, ZrO₂ toughened Al₂O₃ ceramic layers became smooth and dense.     

Thermal Behaviour of a TiO2—ZrO2 Microcomposite Prepared by Chemical Coating

A microcomposite powder in the system TiO₂—ZrO₂ as a precursor of zirconium titanate (ZT) materials has been studied by thermal methods (DTA-TG) and X-ray diffraction (XRD). The microcomposite powder has been prepared by chemical processing of crystalline TiO₂ (rutile, 10 mass% anatase),as inner core, coated with in situ precipitated amorphous hydrated zirconia gel, asouter core. The morphology and chemical composition of the resultant powders has been examined by SEM-EDX (Scanning electron microscopy-energy dispersive X-ray spectroscopy). Thermal behaviour of the microcomposite powder was reported, showing the dehydration and dehydroxylation of the zirconia gel, the crystallization into metastable cubic/tetragonal zirconia at temperatures 400—470°C, and the feasibility of preparing ZT powder materials by progressive reaction of TiO₂ and ZrO₂ at higher temperatures (1400°C).This revised version was published online in November 2005 with corrections to the Cover Date.     

Sur l'Utilisation d'une electrode ponctuelle dans les cellules à oxyde electrolyte solide. II. Application a la détermination des tensions d'oxydoreduction des defauts ponctuels dans l'electrolyte

A method is described for direct measurement of oxidoreduction potential of point defects dissolved in solid electrolytes. Measurements were carried out with several solid oxide electrolytes based on zirconia ZrO₂ and hafnia HfO₂.Results allowed us to determine more accurately the electrolytic behaviour of these materials and the reactions involved in the electrochemical blackening of zirconia.     

Influence of the zirconia transformation on the thermal behavior of zircon–zirconia composites

During a heating?Ccooling cycle, zirconia (ZrO₂) undergoes a martensitic transformation from monoclinic to tetragonal structure phases, which presents special hysteresis loop in the dilatometry curve at temperatures between 800 and 1100?°C. Monoclinic zirconia (m-ZrO₂) particles reinforced ceramic matrix composites not always present this behavior. In order to elucidate this fact a series of zircon?Czirconia (ZrSiO₄?CZrO₂) ceramic composites have been obtained by slip casting and characterized. The final properties were also correlated with the zirconia content (0?C30?vol.%). The influence of the martensitic transformation (m?Ct) in well-dispersed zirconia grains ceramic composite on the thermal behavior was analyzed. Thermal behavior evaluation was carried out; the correlation between the thermal expansion coefficients with the zirconia content showed a deviation from the mixing rule applied. A hysteresis loop was observed in the reversible dilatometric curve of composites with enough zirconia grains (??10?vol.%). Over this threshold the zirconia content is correlated with the loop area. The transformation temperatures were evaluated and correlated with the zirconia addition. When detected the m?Ct temperature transformation is slightly influenced by the zirconia content (due to the previously evaluated decrease in the material stiffness) and similar to the temperature reported in literature. The reverse (cooling) transformation temperature is strongly decreased by the ceramic matrix. The DTA results are consistent with the dilatometric analysis, but this technique showed more reliable results. Particularly the endothermic m?Ct transformation temperature showed to be easily detected even when the only m-ZrO₂ present was the product of the slight thermal dissociation of the zircon during the processing of the pure zircon material.     

Metal/zirconia catalysts for the synthesis of methanol: characterization by vibrational spectroscopy

The activation of carbon dioxide by catalytic hydrogenation has been studied as a route for methanol synthesis. Metal/zirconia catalysts suitable for this reaction have been prepared by (i) activation of amorphous metal alloys [1] or (ii) coprecipitation of amorphous zirconia and metal oxides [2]. Vibrational spectroscopy has been used to obtain information on the catalytic reaction mechanism, by the in situ identification of adsorbed species and intermediates under reaction conditions.The reverse water-gas shift reaction, producing CO from CO₂ and hydrogen, plays a crucial role in the reaction mechanism. This reduction is shown to proceed via surface formate, adsorbed close to the metal/zirconia interface. Over Pd/ZrO₂ and Ni/ZrO₂, formate is reduced to methane without further observable intermediates. Pivotal intermediates on the route to methanol, as observed on Cu/ZrO₂ catalysts, are -bound formaldehyde and surface methylate. Addition of silver as a promoter can result in enhanced selectivities and productivities for methanol formation. The synergy between the two metals becomes evident from the spectroscopic measurements; the most prominent feature of the silver-promoted catalysts is a high concentration of surface formaldehyde, which is either preferentially formed or stabilized by the silver component.     

Sintering behavior and thermal expansion of zirconia–titanium composites

The dilatometric and thermogravimetric methods were used to investigate the sintering conditions of 3Y–ZrO₂ and 3Y–ZrO₂–Ti composites. For the materials preparation, the nanometric zirconia stabilized by 3 mol% Y₂O₃ powder and micrometric titanium powder (3 and 10 vol%) were used. The green body samples were formed by slip casting method. The morphology of samples microstructures was determined by SEM observations. The stereological analysis of zirconia and zirconia–titanium composites was carried out using computer program. The density was measured using the Archimedes method. The hardness of sinters was also investigated. Addition of Ti into ZrO₂ influenced the sintering behavior and thermal expansion of obtained composites. The analysis of the sintering process and characteristic temperatures confirmed the increase of onset and final temperature of shrinkage with the increase in Ti content. The changes of the thermal expansion curves for the pure zirconia and 3Y–ZrO₂–Ti composites were the result of the αTi → βTi transformation and the transition temperature of the zirconia m → t transformation. The zirconia and composite samples were characterized by relative density about 98%, close to theoretical density. The slight growth of zirconia grains was observed.     

Photocatalytic degradation of 2,4-dichlorophenoxiacetic acid and 2,4,6-trichlorophenol with ZrO2 and Mn/ZrO2 sol-gel materials

Because of its semiconductor properties, sol-gel zirconia can be used as a photocatalyst. When zirconia is doped with transition metals, its electronic properties are modified. In this work, sol-gel Mn/ZrO₂ and ZrO₂ materials were tested for photocatalytic degradation of 2,4-dichlorophenoxiacetic acid and 2,4,6-trichlorophenol. The powders were characterized by XRD, UV-Vis and Raman spectroscopy. The apparent rate constants were calculated assuming pseudo-first order kinetics. The results reveal that ZrO₂ is effective as a photocatalyst; moreover, its photocatalytic properties improve when it is doped with manganese.     

Au/ZrO2催化CO氧化反应中ZrO2纳米粒子的尺寸效应

从同一ZrO(OH)₂出发制备了三种不同尺寸的ZrO₂纳米颗粒(ZrO₂-CP: 40～200 nm, ZrO₂-AN: 18～25 nm, ZrO₂-AD: 10～15 nm), 采用沉积-沉淀方法制备了相应的Au/ZrO₂催化剂. 用XRD, XRF, TEM和低温N₂吸附对ZrO₂和Au/ZrO₂进行了表征. XRD和TEM分析表明Au/ZrO₂样品中Au粒子的平均尺寸为4～5 nm, 而ZrO₂的晶相和颗粒大小没有因为“负载”Au粒子而发生变化. CO催化氧化反应的结果表明, Au/ZrO₂催化活性随着ZrO₂纳米粒子尺寸的减小活性明显增加. TEM/HRTEM结果表明, Au/ZrO₂催化剂中Au粒子与ZrO₂颗粒接触界面随ZrO₂颗粒尺寸的减小而明显增加, 这很可能是含有更小尺寸ZrO₂纳米粒子的Au/ZrO₂催化剂具有更高催化活性的重要原因.     

Silica-Zirconia Coatings Produced by Dipping and EPD from Colloidal Sol–Gel Suspensions

SiO₂-ZrO₂ sols have been prepared via acid catalysis using a commercial colloidal suspension of zirconia and two silica alkoxides; tetraethoxysilane (TEOS) and methyltriethoxysilane (MTES). Suspensions with 10, 15 and 25-mol% of ZrO₂ were prepared. The stability of the suspensions was followed by rheological measurements showing that the amount of water incorporated with the colloidal suspension is the factor that limits the maximum ZrO₂ content. Coatings have been prepared by dipping using the suspensions up to 25-mol% ZrO₂ onto glass-slides at different withdrawal rates. EPD process has been used to prepare coatings onto stainless steel AISI 304 using the suspension with 25-mol% ZrO₂ at different pHs. The parameters associated with the EPD process (current density, electric field, potential and deposition time) have been evaluated. The critical thickness for a ZrO₂ addition of 25-mol% was 0.8 μm and it increased for diminishing ZrO₂ content.     

Strengthening of composite materials of the fluorohydroxyapatite–zirconia system by titanium nitride

Composite materials of the ZrO₂–fluorohydroxyapatite (FHA)–titanium nitride (TiN) system have been synthesized and studied. In the course of sintering even in a protective inert medium, the reaction between the components begins at 700°C to give calcium titanates, titanium oxides, and oxygen-deficient zirconia compounds. As a result of working through the procedure of synthesis of ultrafine powders and selecting sintering regimes, including the hot-pressing method, dense composite materials of the FHA–ZrO₂ system containing TiN were obtained with a bending strength of up to 273 MPa and a crack resistance of up to 3.3 MPa m^1/2.     

Yttria stabilized zirconia solid electrolyte surface modification with ZrO<Subscript>2</Subscript>, Y<Subscript>2</Subscript>O<Subscript>3</Subscript>, and ZrO<Subscript>2</Subscript> + 9 mol % Y<Subscript>2</Subscript>O<Subscript>3</Subscript> films

The surface of ceramic electrolyte ZrO₂ + 9 mol % Y₂O₃, hereinafter referred to as YSZ (abbreviated yttria stabilized zirconia), was modified with 0.1 to 0.2 μm oxide films of ZrO₂, Y₂O₃, and YSZ (same composition as substrate) by dip coating in alcohol solutions of the relevant salts and further annealing. The results of scanning electronic microscopy and X-ray diffraction evidence epitaxial film growth. By means of impedance spectroscopy at the temperatures of 500 to 600°C, the effect of YZS electrolyte surface modification with ZrO₂, Y₂O₃, and YSZ films to the polarization resistance of silver electrode was studied.     

Composite solid electrolyte based on (Ca2+, Al3+)-infiltrated ZrO2(MgO) for direct sulfur determination in the liquid iron

Magnesium-stabilized zirconia [ZrO₂(MgO)] with calcium aluminate (CaO–Al₂O₃) ceramic composite electrolyte based on (calcium ion [Ca²⁺], aluminum ion [Al³⁺])-infiltrated zirconia-magnesia [ZrO₂(MgO)] porous backbone was prepared for direct sulfur ([S]) determination in the liquid iron. Effect of amylum content on the phase composition, microstructures and mechanical properties of the composite electrolyte was detected and correlated to the electrochemical performance. The results indicated that the ZrO₂(MgO)-(CaO–Al₂O₃) composite electrolyte simultaneously inherited the mechanical and electrochemical properties of ZrO₂(MgO), and unique physical and chemical properties of CaO–Al₂O₃. The compressive strength of the composite electrolyte reached above 250 MPa and the conductivity reached up to 0.003 S/cm^-, meeting the requirements of the sensor for the electrolyte. The assembled sensor could respond to sulfur activity and showed fine response characteristics. Among the tested compositions, the composite electrolyte with 6.0 wt% of amylum added in ZrO₂(MgO) porous backbone exhibited the best properties and was more suitable for application in sulfur determination.     

Comparative studies on zirconia and graphene composites obtained by one-step and stepwise electrodeposition for deoxyribonucleic acid sensing

In this paper, the comparison of two kinds of electrochemically reduced graphene oxide (ERGNO) and zirconia composites, obtained by one-step (ZrO₂–ERGNO) and stepwise (ZrO₂/ERGNO) electrodeposition for DNA sensing, is systematically studied. The resulting composites were characterized by scanning electron microscopy, cyclic voltammetry, and differential pulse voltammetry. The results indicated that the ZrO₂–ERGNO presented fine globular nanostructure. However, ZrO₂/ERGNO presented agglomerate massive microstructure due to the absence of the oxygen-containing groups of graphene oxide, confirming the oxygen-containing groups provided a better affinity for the deposition of ZrO₂. Due to the strong binding of the phosphate groups of DNA with the zirconia film, DNA probes were attached on the ZrO₂-based composites. ZrO₂–ERGNO/Au owning fine nanostructure presented larger surface area than microstructured ZrO₂/ERGNO/Au. Moreover, compared with microstructured ZrO₂/ERGNO, the nanostructured ZrO₂–ERGNO provided more accessible space for immobilized DNA probe hybridization with target sequence, which consequently resulted in higher hybridization efficiency. Therefore, the ZrO₂–ERGNO was chosen for fabricating DNA sensor with a limit of detection 1.21 × 10⁻¹⁴ mol L⁻¹.     

Synthesis of zirconia‐incorporated titania layer by microarc oxidation for biomedical applications

The structural features, biocompatibility, and mechanical performance of a titania (TiO₂) layer with incorporated zirconia (ZrO₂) formed by microarc oxidation on commercially pure titanium have been examined in the present study. In comparison to the ZrO₂‐free TiO₂ layer, the ZrO₂‐incorporated oxide layer was dense and contained ZrTiO₄ as a new oxide as well as ZrO₂ particles. Associated changes in the microstructure enhanced the mechanical durability of TiO₂ layer. Owing to the incorporation of identical biocompatible compounds and almost similar surface roughness, no remarkable difference in bioactivities of the ZrO₂‐free and ZrO₂‐incorporated oxide layers was detected after simulated body fluid tests. Copyright © 2015 John Wiley & Sons, Ltd.     

(ZrO2)0.86(Sm2O3)0.14纳米粉体的水热法合成及其烧结体的电性能

以湿化学法制得Zr(OH)₄和Sm(OH)₃的共沉淀为前驱体, 在碱性介质中用水热法合成了(ZrO₂)_0.86(Sm₂O₃)_0.14及(ZrO₂)_0.88(Sm₂O₃)_0.12纳米粉体. 将纳米粉体在较低温度(1450 ℃)下烧结制得了致密的固体电解质陶瓷样品, 比通常高温固相反应法采用的烧结温度(＞1600 ℃)降低了150 ℃以上. XRD测定结果表明, (ZrO₂)_0.86(Sm₂O₃)_0.14纳米粉体及其烧结体均为立方相, 但(ZrO₂)_0.88(Sm₂O₃)_0.12纳米粉体为立方相, 它的烧结体为立方相和单斜相的混合相. 用交流阻抗谱法、氧浓差电池法及氧泵(氧的电化学透过)法研究了(ZrO₂)_0.86(Sm₂O₃)_0.14陶瓷样品在600～1000 ℃下的离子导电特性. 结果表明, 该陶瓷样品在600～1000 ℃下氧离子迁移数为1, 氧离子电导率的最大值为3.2×10^－2 S•cm^－1, 是一个优良的氧离子导体; 它的氧泵性能明显地优于YSZ.     

Atomic-Scale Structure of Water-Based Zirconia Xerogels by X-Ray Diffraction

The structural evolution of zirconia thin films and gel powders has been evaluated by X-ray diffraction. Maxima (r ₁ and r ₂) of the experimental radial distribution function RDF and the bond angles were determined and correlated with TGA (thermogravimetric analysis), DTA (differential thermal analysis) and MS (mass spectrometry). The results indicate that the topological short-range structure (<5 Å) of amorphous zirconia thin films, independent of drying temperature, resembles that of crystalline tetragonal ZrO₂. In contrast, amorphous zirconia powder gels dried at temperatures below 120°C show atomic arrangements similar to that of tetragonal ZrO₂. The structure of these gels annealed at temperatures between 165–340°C resembles a distorted tetragonal ZrO₂, monoclinic-like structure. Zirconia powders and films contain crystalline tetragonal ZrO₂ at 400°C.     

Sol–gel derived porous zirconium dioxide coated on 316L SS for orthopedic applications

The zirconia ceramics offers the required biocompatibility and corrosion resistance in the physiological medium, making it applicable for biomaterials. But, adequate utilization of porous zirconium dioxide (ZrO₂) thin film has not been assessed. Hence, in the present work an attempt has been made to utilize the corrosion resistance and biocompatibility property of porous ZrO₂. The ZrO₂ were prepared using the sol–gel process and coated on 316L SS substrate via dip-coating technique. The phase composition, morphology and the elemental distribution of the coatings were investigated using X-ray diffraction analysis, atomic force microscopy, Fourier transform infrared spectroscopy, scanning electron microscopy and energy dispersive X-ray analysis. The results revealed that the coated surface was porous, uniform and relatively well crystalline on the substrate. In vitro evaluation of the ZrO₂ coated 316L SS samples were carried out in simulated body fluid and the corrosion resistance of the ZrO₂ coated samples were examined using potentiodynamic cyclic polarisation and electrochemical impedance spectroscopy in simulated body fluid.     

Preparation and Evaluation of Octadecyl-Bonded ZrO2/SiO2

ZrO₂/SiO₂ particles, which were prepared by a layer-by-layer self-assemble technique and consist of micrometer-sized silica spheres as cores and nanometer-sized zirconia particles as surface coatings, have a higher surface area and pore volume than other zirconia supports have. Further more it is more stable than silica is. In this paper we made a reversed-phase support by bonding octadecyltrichlorosilane on ZrO₂/SiO₂ particles, it had a comparable high carbon amount of 9.62% and good chemical stability being stable up to pH 11. The chromatographic behavior showed that the support acted as a true reversed chromatographic stationary phase and had a hydrophobic selectivity. Basic and aromatic compounds are well separated and the peaks are symmetrical.     

Synthesis and properties of CaZrO<Subscript>3</Subscript> films on YSZ electrolyte surface

CaZrO₃ films are studied that were obtained on ceramic supports of solid electrolyte of ZrO₂ + 9 mol % Y₂O₃ (YSZ, yttria stabilized zirconia) from alcohol solutions of zirconium oxychloride and calcium nitrate using the method of dipping with the following drying and annealing. The thickness and morphology of films depend on the concentration of the film-forming solution. Vickers microhardness of the CaZrO₃ films was determined. The impedance spectroscopy method was used to study conductivity of films at the temperature of 400–600°C by comparison of impedance spectra of clean supports and supports with a film coating.     

Corallocarpus epigaeus mediated synthesis of ZnO/CuO integrated ZrO2 nanoparticles for enhanced in-vitro antibacterial,antifungal and antidiabetic activities

Zirconia based nanocomposites have attracted much research attention in recent years due to their exceptional biomedicinal activities. Rhizome extracts of Corallocarpus epigaeus based ZrO₂/CuO–ZnO nanocomposite were green synthesized in a facile synthesis strategy. The nanocomposites were examined with XRD technique for their structural information and FT-IR technique for surface functional group analysis. Electron microscopic images aided to elucidate the CuO and ZnO nanoparticles decorated ZrO₂ nanostructures. UV–vis absorption spectroscopic studies of the nanocomposite revealed the characteristic UV absorption of ZrO₂ and enhanced visible region absorption for the incorporated nanoparticles. Antibacterial and antifungal studies indicated enhanced activity of nanocomposites over the pristine zirconia nanoparticles. ZrO₂/CuO–ZnO nanocomposite had exhibited about 75% of α-amylase inhibition activity, whereas pristine ZrO₂ nanoparticles had exhibited only 57% suggesting the worthwhile application in the antidiabetic activity of the nanocomposite.