Zirconia Sol Research Articles

Catalytic coatings on steel for low-temperature propane prereforming to solid oxide fuel cell (SOFC) application

Catalyst layers (4–20 μm) of rhodium (1 wt%) supported on alumina, titania, and ceria–zirconia (Ce 0.5Zr 0.5O 2) were coated on stainless-steel corrugated sheets by dip-coating in very stable colloidal dispersions of nanoparticles in water. Catalytic performances were studied for low-temperature (⩽500 °C) steam reforming of propane at a steam to carbon ratio equal to 3 and low contact time (≈0.01 s). The best catalytic activity for propane steam reforming was observed for titania and ceria–zirconia supports for which propane conversion started at 250 °C and was more than three times better at 350 °C than conversion measured on alumina catalyst. For all catalysts a first-order kinetics was found with respect to propane at 500 °C. Addition of PEG 2000 in titania and ceria–zirconia sols eliminated the film cracking observed without additive with these supports. Besides, the PEG addition strongly expanded the porosity of the layers, so that full catalytic efficiency was maintained when the thickness of the ceria–zirconia and titania films was increased.

Production of meso- and giga-porous zirconia particles — An improved multi-step particle aggregation process

Macro- and giga-porous zirconia supports were prepared from a 20% colloidal sol of zirconia (ZrO 2) by a combination of a polymer-induced colloid aggregation (PICA) process and the oil emulsion (OE) method. The effect of the pH of the initial sol on the size of the PICA particles, and subsequently on the final product, made by oil-emulsion assisted aggregation of the PICA particles was thoroughly investigated. Both the PICA and the OE methods were further optimized for performance. Particle morphology and porosity of the resultant particles were characterized by scanning electron microscopy, mercury intrusion–extrusion porosimetry, and nitrogen adsorption–desorption sorptometry. The supports were comprised of stable aggregates of 50–250 μm in size. The pore and throat size distributions showed narrow bi-modal distributions over two distinct size scales: 10–100 nm and 600–3000 nm. In addition, different combinations of aggregation techniques and porous supports prepared in previous steps for use in a subsequent aggregation were evaluated. Optimal amounts of zirconia sol and 10–100 micron porous spherical particles produced by the OE method in an earlier step were combined in an additional OE process to yield stable giga-porous supports. Porous zirconia particles obtained after calcination and sintering had particle sizes of 0.15–3.5 mm and multimodal pore and throat distributions over a range of 50 nm–8 μm.

Lipase entrapment in a zirconia matrix: Sol–gel synthesis and catalytic properties

Zirconia-based sol–gels have been used for lipase entrapment, to avoid the biocatalyst inactivation associated to the use of basic or acid catalysts. The method developed allows a single-step entrapment of the enzyme in a zirconia sol–gel with mesopores of diameter in the range 2–4 nm, and a surface area of 219 m 2 g −1. The zirconia matrix is substantially unaffected by the presence of the lipase. The size of the pores, though smaller than that of the enzyme, seems large enough to minimise the effect of the internal diffusional limitations on the overall reaction kinetics, as demonstrated by the substantial equivalence between the activation energies measured with the free and with the immobilised lipase. The thermal inactivation of the zirconia-entrapped lipase, characterised by a mathematical model, is significantly reduced as compared to the inactivation of the free enzyme.

Preparation and characterization of sol–gel derived yttria doped zirconia coatings on AISI 316L

A stable 4 mol% yttria-stabilized zirconia (YSZ) sol has been synthesized for coating stainless steel AISI 316L for biomedical applications. The sol was prepared by controlled hydrolysis of zirconium n-butoxide using acetylacetone and nitric acid as chelating agent and catalyst, respectively. X-ray diffractograms of calcined YSZ xerogel indicated a tetragonal structure at temperature as low as 400 °C. Stainless steel was dip-coated in transparent yellow YSZ sol followed by heat treatment between 400 and 600 °C for 2 h in air. A homogeneous and crack-free YSZ film was, thus, obtained on the stainless steel surface. Adhesion strength, measured by scratch test in progressive loading sequence on coated AISI 316L, showed 27 ± 3 N critical load. Corrosion performance of the surface coating was evaluated through open-circuit potential (OCP) measurement, impedance, polarization and chronoamperometry in Ringer's solution at 37 °C. The coating enhanced the pitting potential of the substrate. The metal ions released from AISI 316L was effectively controlled by the coating.

Ultra-Low Shrinkage Hybrid Photosensitive Material for Two-Photon Polymerization Microfabrication

Investigations into the structuring by two-photon polymerization of a nonshrinking, photosensitive, zirconium sol-gel material are presented. This hybrid material can be photostructured even when it contains up to 30 mol % of zirconium propoxide (ZPO); by varying the material's inorganic content, it is possible to modify and tune its refractive index. The introduction of ZPO significantly increases the photosensitivity of the resulting photopolymer. The fabricated three-dimensional photonic crystal structures demonstrate high resolution and a clear band-stop in the near-IR region. In contrast to common practice, no additional effort is required to precompensate for shrinkage or to improve the structural stability of the fabricated photonic crystals; this, combined with the possibility of tuning this material's optical, mechanical, and chemical properties, makes it suitable for a variety of applications by two-photon polymerization manufacturing.

Sol–gel routes for microporous zirconia and titania membranes

Zirconia and titania nanoparticle sols were prepared, using either ligand-based precursor stabilization or acid stabilization routes. These sols were used to prepare microporous coatings on γ-alumina substrates. The acetylacetonate-based particles have very small hydrodynamic diameters (1–2 nm), which lead to sol intrusion into the supports. As a result no appropriate membrane layer was formed. A microemulsion-based zirconia sol leads to a membrane that was selective in pervaporation dehydration of a water/n-butanol mixture. An optimized membrane showed stable separation performance for 120 days with a high selectivity toward water. Permporometry and gas permeation results on a titania membrane based on an acid-stabilized sol not only show microporosity, but also a significant contribution from defect flow.

Effect of thermal treatment on yttria doped zirconia coated DIN 1˙4306

Thin films of 8 wt-% yttria doped zirconia (YZ) sol were deposited by a dip coating process on stainless steel (DIN 1˙4306) substrate for surface protection of this material widely used for corrosion resistance. The YZ sol coated specimens were heat treated in the temperature range of 500–1100°C for 30 min. The characterisation of the thin layer deposited was performed using thermal (TG-DTA) methods. The microstructure and phase identification analysis were carried out using scanning electron microscopy (SEM) having an energy dispersive system (EDS) as an attachment and X-ray diffraction (XRD). The coated surface specimen heat treated at 900°C showed fine grain surface without porosity, while specimens heat treated at 1100°C showed coarse grain structure with porosity. Three different phases, i.e. FeCr2O4, (Fe0˙6Cr0˙4)2O3 and ZrO2, were identified on the surface of coated specimens heat treated at 900 and 1100°C for 30 min. The YZ coated specimens show improved resistance in acidic environment. Tape adhesion testing has shown that YZ coatings on stainless steel are adherent. Good adhesion at the interface indicated that the sol–gel route is a feasible method for applying YZ coating on stainless steel substrates.

Nanostructured zirconia coatings processed by PROSOL deposition

The development of nanostructured coatings is a new field of interest in the world of thermal spraying. Novel techniques, such as HVOF or plasma spraying have been developed with respect to thermally activated processes, in order to reach the nanometric scale (10–20 nm). Frequently, the evolution consists in using agglomerated nanoparticles or suspension feedings. The CEA has patented a process called PROSOL [K. Wittmann-Ténèze, K. Vallé, L. Bianchi, F. Blein, P. Belleville, CEA Le Ripault, France, “Revêtement nanostructuré et procédé de revêtement”, Fr patent n°04 52390, (2004).], which is based on the injection of a sol–gel colloidal solution in a plasma source. Studies on the resulting coatings have principally shown that a nanostructured material could be prepared all the while preserving the intrinsic properties of the nanoparticle sol, the nanoparticle size and the crystalline phase distribution. The present investigation illustrates the PROSOL process through an example of spraying of a zirconia (ZrO 2) sol, prepared under hydrothermal conditions, in an atmospheric plasma jet. A time-stabilized sol of zirconia nanoparticles (10 nm) crystallized in both monoclinic and tetragonal phases was obtained. The injection of such a sol in the plasma plume was performed through a liquid injector that dispensed a sol jet under pressure without any pulverization gas. Because of the high temperature and the high velocity medium, the sol was fragmented into droplets and the liquid phase was vaporized. The resulting nanoparticle agglomerates embedded in droplets were accelerated and collected on a substrate without melting. By adjusting the plasma spraying parameters, more or less dense coatings could be obtained. Various characterization techniques were performed on the as-sprayed layers, including SEM, XRD and TEM. Results showed that the coatings were constituted of 10 nm-sized grains in the monoclinic and tetragonal phases. The flexibility of the process was also highlighted, i.e., the possibility to obtain coatings with thicknesses between one and several microns, produced without any physical change at a given deposition rate, on a variety of geometries and on a vast range of substrates.

Synthesis and Characterization of CaO Doped Alumina–Zirconia Fibers by Sol-Gel Process

Calcium oxide (CaO) doped Alumina–zirconia fibers were prepared by sol-gel process. The starting materials used for the preparation of alumina and zirconia sol were aluminium-tri-isopropoxide and zirconium oxychloride, respectively. Alumina sol and zirconia sol were mixed in definite proportions, so that the final composition contains 10 wt% ZrO2. CaO was introduced into the mixed sol in the form of calcium nitrate such that the final composition contains 1 and 2 wt%. Alumina–zirconia fibers were prepared from the mixed sol containing CaO, respectively. Sintered alumina–zirconia fiber has α -Al2O3, t-ZrO2, and m-ZrO2 phases. The phase transition to α -Al2O3 takes place at lower temperature in the presence of CaO. The addition of CaO increases the grain size.

Experimental research of laser-induced damage of the monolayer ZrO 2 PVD and sol–gel films

Monolayer zirconia physical vapor deposition (PVD) and sol–gel films on K9 glass substrates were prepared by electron beam evaporation and spin coating methods, respectively. The laser-induced damage threshold (LIDT) of each film was measured. Properties of the films were analyzed using Stanford photo-thermal solutions (SPTS), ellipsometry, atomic force microscopy (AFM) and optical microscopy to study the damage mechanism of films under laser irradiation. The experimental results showed that, compared with the monolayer zirconia sol–gel film, the monolayer zirconia PVD film had larger absorption and smaller porous ratio, and that it had smaller LIDT. The different damage morphologies of films were influenced by their different absorption and microstructure characteristics. The zirconia sol–gel film is more suitable for applications involving high-power lasers.

NANOSTRUCTURED ZrO2 POWDER SYNTHESIZED BY ULTRASONIC SPRAY PYROLYSIS

The synthesis of nanostructured zirconia particles from aqueous colloidal dispersion of zirconia (zirconia sol) was carried out by ultrasonic spray pyrolysis method. The morphology of these nanostructured particles was characterized by scanning electron microscopy and transmission electron microscopy. The synthesized particles are spherical in shape with the avarage size of 400 nm, consisting of smaller primary particles, with the mean crystallite size of 7 nm. The tetragonal phase was confirmed by both X-ray and electron diffraction measurements.

Comparative electrochemical study of myoglobin loaded in different types of layer-by-layer assembly films

Abstract Four different types of layer-by-layer films were assembled on solid surfaces and designated as PDDA/{ZrO 2 } n , {PDDA/ZrO 2 } n , {PDDA/NP-ZrO 2 } n , and {PDDA/PSS} n , where ZrO 2 stands for zirconia sol–gel formed by vapor-surface sol–gel deposition, NP-ZrO 2 represents ZrO 2 nanoparticles, PDDA is poly(diallyldimethylammonium), and PSS is poly(styrenesulfonate). When these films were immersed in myoglobin (Mb) solutions, Mb could be gradually “absorbed” or loaded into the films, and the Mb-loaded films at pyrolytic graphite (PG) electrodes demonstrated nearly reversible cyclic voltammetric (CV) responses for Mb Fe III /Fe II couple and good electrocatalytic property toward H 2 O 2 . The electrochemical and electrocatalytic activity of Mb in these films exhibited the sequence of PDDA/{ZrO 2 } n -Mb > {PDDA/ZrO 2 } n -Mb > {PDDA/NP-ZrO 2 } n -Mb > {PDDA/PSS} n -Mb. Among the four types of films, PDDA/{ZrO 2 } n films, formed by repeated vapor-surface sol–gel deposition of ZrO 2 on PDDA surface, demonstrated better porosity and permeability, and thus could load more amounts of Mb from its solutions. Also because of the better porosity of PDDA/{ZrO 2 } n -Mb films, the small counterions in buffer solution could get into and out of the films more easily, also resulting in the better CV responses of the films according to the mechanism of electron hopping. UV–vis and FTIR spectroscopic studies suggest that Mb in these films essentially retains its native structure. The protein-loaded multilayer films are a novel kind of protein layer-by-layer films, which provide a new route to immobilize proteins and may provide a foundation for fabricating the third generation biosensors based on the direct electrochemistry of enzymes.

Preparation of Crack-free 3Y-TZP/AI 2O 3 Composite Ceramic Fiber by Electrolysis-sol-gel Method

Polycrystalline 3Y-TZP/Al2O3 tetragonal zirconia fiber was obtained by the pyrolysis of gel fibers using zirconium oxychloride octahydrate (ZOC) as the raw material. The spinnable zirconia sol was prepared by electrolyzing the zirconium oxychloride octahydrate (ZOC) solution in the presence of acetic acid and sugar (sucrose, glucrose or fructose), in which the molar ratios of CH3COOH/ZOC and sugar/ZOC were 1. 0—4. 0 and 0. 2—0. 4, respectively. The prepared tetragonal zirconia fibers sintered at different temperatures showed smooth and crack-free surfaces with diameters of 5–10 μm. The addition of Al2O3 enhanced the sintering process and prevented the crystals from growing. Thermogravimetric analysis (TG), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscope (SEM) techniques were used to characterize the prepared fibers.

Zirconia Hollow Fiber: Preparation, Characterization, and Microextraction Application

A zirconia hollow fiber membrane in the macrorange was for the first time successfully synthesized via a template method coupled with a sol-gel process. A polypropylene hollow fiber was employed as the template. The preparation procedure includes repeated impregnation of the template in the proper zirconia sol precursor, and calcination to burn off the template, producing the zirconia hollow fiber. The resulting hollow fiber membrane is almost identical to its template in terms of morphology, exhibiting a hollow core structure. In addition to that, it has a bimodal porous substructure that is different from its template, narrowly distributed nanoskeleton pores, and uniform textural pores or throughpores. The wall thickness and substructures can be conveniently controlled by the synthetic conditions and postheat treatment. Moreover, the thus-prepared zirconia hollow fiber was applied for the microextraction and concentration of a nerve agent degradation product followed by liquid chromatography-mass spectrometric analysis. Since the zirconia fiber exists as an individual device and is directly usable for extracting, handling is more convenient than, for example, an adsorbent in powder form that needs to be coated on a rod for the extraction process. In addition, it is easily prepared and is superior to the monolithic material in this sense. Pinacolyl methylphosphonic acid, one degradation product of organophosphorus nerve agent (soman), was used as the model analyte. Zirconia hollow fiber was demonstrated to be a highly selective adsorbent for the phosphonic acid-containing compounds with high sensitivity. Limit of detection was as low as 0.07 ng/mL (0.39 nM).

Electrochemical Testing of Solid Oxide Fuel Cells with Sol Gel Impregnated Plasma Sprayed Electrolytes

Solid Oxide Fuel Cells (SOFCs) have been fabricated on tape cast anode substrates with plasma sprayed (PS) electrolytes and screen printed cathodes. To reduce the porosity in the PS electrolyte layers, spin coating was used to impregnate the as-sprayed electrolytes with yttria stabilized zirconia (YSZ) sols and YSZ composite sol powder suspensions. Fuel cells with electrolytes impregnated with different techniques were electrochemically tested and compared to fuel cells with no sol gel coatings to correlate the sol gel processing parameters with the resulting electrochemical performance changes. The sol gel impregnation significantly increased the open circuit voltage, slightly decreased the series resistance, and substantially decreased the polarization resistance compared to the cells with as-sprayed electrolytes. Impregnation of electrolytes offers the possibility of producing thinner electrolytes in simpler low-energy plasmas (100% nitrogen, no hydrogen) while lowering gas permeability through the electrolyte and improving fuel cell performance.

Preparation of Y-TZP ceramic fibers by electrolysis-sol-gel method

Polycrystalline yttria stabilized tetragonal Zirconia (T-ZrO2) fibers were obtained by pyrolysis of gel fibers using zirconium oxychloride octahydrate as raw material. The spinnable zirconia sol was prepared by electrolyzing the zirconium oxychloride octahydrate solution in the presence of acetic acid and sugar (sucrose, glucose or fructose), in which the molar ratio of CH3COOH/ZrOCl2 · 8H2O and sugar/ZrOCl2 · 8H2O was in the range of 1.0–4.0 and 0.2–0.4, respectively. The relation of spinnability to the shape of colloidal particle was discussed. The as-prepared zirconia fibers sintered at different temperatures show smooth and crack-free surface with the diameter of 5–10 μm. Slow heating rate below 600 °C and then sintering at 1,400 °C for 30 min were necessary to obtain the dense tetragonal zirconia ceramic fibers, the particles composed the fibers had the size of ∼150 nm.

Preparation of Zirconia Fibers via a Simple Aqueous Sol‐Gel Method

Polycrystalline tetragonal zirconia fiber was obtained by pyrolysis of precursor fibers from citrate‐acetate‐zirconium complex solution. The viscous zirconia sol with good spinnability was prepared by aging the starting solution of ZrOCl2 · 8H2O (ZOC) in the presence of acetic acid (HA) and citric acid (CA). The effects of molar ratio of zirconium cation to carboxylic acid and the aging time on the formation of spinnable sol were investigated. Thermogravimetric (TG) analysis, x‐ray diffraction (XRD), infrared (IR) spectra, and scanning electron microscope (SEM) techniques were used to characterize the sintered fibers. The results show that the fibers obtained at 1400°C are crack‐free with diameter of ca. 5–10 µm.

Process intensification by micro-channel reactor for steam reforming of methanol

Abstract Catalyst coating in micro-channel reactor for steam reforming of methanol (SRM) is advantageous compared to micro-packed reactor as one part of fuel processor in the application of fuel cell for portable application. In the present study, the performance and pressure drop of catalyst coated and catalyst packed in micro-channel reactor with commercial catalyst in both cases were compared for steam reforming of methanol. The different sols (alumina, zirconia and mixed sol of alumina and zirconia) as a binder for the catalyst have been used to compare the stability and performance. Though the initial performance exhibited by using different sols was same at 290 °C, the performance decay of 20% was observed after 6 days of continuous operation in the case of using zirconia as binder. This may be due to relatively unstable catalyst coating and nonuniform dispersion of catalyst particles on the ZrO 2 binder. Among the different sols, mixed sol of alumina and zirconia comparatively showed better stability and performance. Though the pressure drop in packed catalyst in micro-channel reactor was higher compared to that in catalyst coated micro-channel reactor, the almost complete conversion of methanol in SRM reaction was achieved with packed catalyst in micro-channel reactor at lower temperature.

Sintering Behavior of Sol–Gel-Derived Alumina and Alumina–Zirconia Minispheres

Alumina and alumina–zirconia minispheres were prepared by sol–gel process. The starting materials used for the preparation of alumina and zirconia sol were aluminium-tri-isopropoxide and zirconium oxychloride, respectively. Alumina sol and zirconia sol were mixed in definite proportions, so that the final composition contained 5, 10, 15, and 20 wt.% ZrO2. The sintering behavior of alumina and alumina–zirconia minispheres were studied by sintering at 1400, 1500, and 1600°C. X-ray diffraction analysis showed the presence of α -Al2O3 in alumina minispheres and α -Al2O3 and t-ZrO2 in minispheres containing 5 wt.% ZrO2 sintered at 1400°C. Monoclinic ZrO2 was also present in the minispheres containing higher amounts of ZrO2 and sintered at higher temperatures. Scanning electron microscopic observation revealed progressive densification with increasing sintering temperature and zirconia content. The density of the sintered spheres was found to be the highest for spheres containing 20 wt.% ZrO2 sintered at 1600°C.

Effects of rare-earth concentration and heat-treatment on the structural and luminescence properties of europium-doped zirconia sol–gel planar waveguides

Sol–gel zirconia films doped with Eu3+ concentrations ranging from 0.2% to 10%, were prepared by dip-coating a solution of the starting precursor, zirconium n-propoxide, ethanol, methanol, water, acetic acid and europium nitrate on glass and SiO2/Si wafer substrates. The ZrO2 sol thus synthesized remains stable for several months. Structural characterization of the zirconia films was performed using Waveguide Raman Spectroscopy. These films present an amorphous phase up to an annealing temperature of 400°C. Above 400°C the matrix evolves towards a metastable tetragonal phase. This transformation was found to depend on the concentration of Eu3+ ions. Indeed, while for samples doped with 0.2% Eu3+ this transformation occurs around 450°C, in the case of 10% of Eu3+ ions, the transition is pushed off to 500°C. The optical losses of these waveguides were found to be about 0.3dBcm−1 for samples annealed at 400°C. The surfaces of the films were characterized using Atomic Force Microscopy and the roughness was measured. The Eu-doped films were investigated using Waveguide Photoluminescence Spectroscopy. The dynamical behaviour of the Eu3+ emissions indicated that concentration quenching effect is not observed even when the matrix is doped up to 10%.