Tetragonal ZrO2 Phase Research Articles

Characterization of magnesia-doped yttria-stabilized zirconia powders for dental technology applications.

This paper is focused on the works concerning preparation of zirconium oxide ceramic blocks recommended for CAD/CAM systems used in prosthetic dentistry for manufacturing fixed prosthetic restorations. Zirconium-yttrium-magnesium mixed ceramic oxides were prepared by sol-gel method via hydrolysis and condensation of zirconium alkoxide precursor (zirconium (IV) propoxide) with yttrium and magnesium nitrates diluted in 2-propanol. The aim of this work was to obtain 2% mol yttria-stabilized zirconia ceramic powders with magnesium as an additional tetragonal ZrO2 phase stabilizer in amount between 2÷6% mol (with 2% variable). Prepared gels were dried (24 h at 65 °C). Obtained powders were mixed with binder (carboxymethyl cellulose) and uniaxial pressed into specimens with a dimensions 38 × 22 × 6 mm. Afterwards green bodies were sintered in range of temperature between 1350-1550 °C. Powders and blocks were characterized by Scanning Electron Microscopy, Fourier Transform Infrared Spectroscopy, Specific Area Measurement. Highly homogeneous powders with a low open porosity were obtained. Prepared blocks after sintering showed numerous cracks. Nevertheless blocks were fine grained and showed quite reproducible chemical composition. A sol gel wet chemical route of powder synthesis allow us to obtain high homogenous ceramic materials with inconsiderable amount of pores with low variation in dimensions. In spite of a reproducible synthesis methods of a ceramic powders, applied to prepare green bodies procedure and sintering manner do not allowed to obtain zirconia cermic blocks free from cracks.

Fabrication of novel ZrO2(Y2O3)–Al2O3 ceramics having high strength and toughness utilising pulsed electric current pressure sintering (PECPS)

Pulsed electric current pressure sintering (PECPS) makes it possible to produce novel monolithic and composite materials with well controlled microstructure or nanostructure, which has not been realised before. ZrO2 based ceramics containing 25 mol.-%Al2O3 and 0·90–1·125 mol.-%Y2O3, i.e. ZrO2(1·2–1·5 mol.-%Y2O3)–25 mol.-%Al2O3, revealing high bending strength σb≧1 GPa and high fracture toughness KIC ≧15·5 MPa m1/2 simultaneously, have been fabricated by PECPS of cubic ZrO2 solid solution (ss) powders containing both Al2O3 and Y2O3 prepared via a sol–gel process. Tetragonal ZrO2 (t-ZrO2) phase composite ceramics sintered at 1573 to 1623 K (1300–1350°C) for 10 min under 60 MPa in Ar were composed of ∼φ200 nm grains with high relative density ≧97·5%. Transmission electron microscopy observation cleared that these mechanical properties might originate from homogeneous distribution of α-Al2O3 particles in the dense t-ZrO2 matrix; the precipitation of α-Al2O3 could be achieved by adopting the ss powders and PECPS.

Monoclinic to tetragonal phase transition in ZrO2 thin films under swift heavy ion irradiation: Structural and electronic structure study

ZrO2 thin films were deposited on Si (100) substrates using pulsed laser deposition. Swift heavy ion irradiation experiments, with different ion fluence, were performed using 200MeV Ag-ion beam. X-ray diffraction, Raman spectroscopy and O K – edge X-ray absorption spectroscopy measurements confirmed the dissolution of monoclinic phase and fruition of tetragonal phase of ZrO2 with the increase of ion fluence. The mechanism of such structural evolutions is briefly discussed in light of ion-irradiation induced local temperature rising, overlapping of latent tracks and energy loss processes.

Novel fabrication of high-quality zirconia ceramic thin films by polyglycol-assisted spreading deposition

A polyglycol-assisted spreading deposition (PASD) method has been used to prepare the high-quality ZrO2 thin film on single crystalline Si (111) substrate. The structure and composition of the films were studied by SEM, XRD and UV Raman techniques. Characterization results indicated that the ZrO2 films were composed of nano-sized small particles and have a crack-free, dense and homogeneous microstructure. After a heat treatment of 10min at 700–900°C, the films showed a mixture of monoclinic and tetragonal ZrO2 phases. And the grain sizes of monoclinic and tetragonal phases in the ZrO2 films were 5–16nm and 10–18nm, respectively. In addition, the thin films of Y2O3-stabilized ZrO2 (YSZ), La2Zr2O7, and the multilayer thin films of La2Zr2O7/YSZ were also fabricated by the PASD method.

Improving surface properties by laser-based drying, gelation, and densification of printed sol–gel coatings

In this article, an innovative laser-based inline-capable coating process for the production of highly wear resistant coatings is presented. A zirconia-based sol–gel material is applied onto hardened and tempered steel substrates by a PipeJet-based printing process and spin-coating. Green films with a thickness of 100–200 nm are produced. Drying, gelation, and transformation of the green films into mechanically resistant wear protection coatings is done by laser treatments. Due to the precise temporal and spatial controllability of the diode laser radiation it is possible to generate temperatures >1000°C, required for the crystallization of the films, as well as to minimize the thermal load of the substrate. The formation of a tetragonal ZrO2 phase within the films is achieved by the laser treatment. According to finite-element calculations the temperature penetration depth of temperatures >150°C (thermal stability of the substrate around 180°C) is reduced to 20–100 μm by using pulsed diode laser radiation. The evolution of the layer thickness as well as chemical and morphological coating properties is investigated by white light interferometry, Fourier transform infrared spectroscopy, and grazing-incidence XRD measurements.

Effect of the ZrO2 phase on the structure and behavior of supported Cu catalysts for ethanol conversion

The effect of amorphous (am-), monoclinic (m-), and tetragonal (t-) ZrO2 phase on the physicochemical and catalytic properties of supported Cu catalysts for ethanol conversion was studied. The electronic parameters of Cu/ZrO2 were determined by in situ XAS, and the surface properties of Cu/ZrO2 were defined by XPS and DRIFTS of CO-adsorbed. The results demonstrated that the kind of ZrO2 phase plays a key role in the determination of structure and catalytic properties of Cu/ZrO2 catalysts predetermined by the interface at Cu/ZrO2. The electron transfer between support and Cu surface, caused by the oxygen vacancies at m-ZrO2 and am-ZrO2, is responsible for the active sites for acetaldehyde and ethyl acetate formation. The highest selectivity to ethyl acetate for Cu/m-ZrO2 catalyst up to 513K was caused by the optimal ratio of Cu0/Cu+ species and the high density of basic sites (O2−) associated with the oxygen mobility from the bulk m-ZrO2.

Sol–gel synthesis of tetragonal ZrO2 nanoparticles stabilized by crystallite size and oxygen vacancies

In this letter, we present a facile route to produce metastable tetragonal zirconia (ZrO2) nanoparticles via pH-controlled precipitation of dilute zirconyl nitrate dihydrate [ZrO(NO3)2·2H2O] solution in liquid NH3 under ambient conditions and calcination at 500 °C for 2 h. The phase pure tetragonal ZrO2 nanoparticles are obtained at pH 9. The effect of pH on metastable phase stabilization in precipitated ZrO2 nanoparticles is demonstrated with the help of XRD, SEM/EDX, and X-ray photoelectron spectroscopy techniques. The stability of tetragonal ZrO2 phase is attributed to the smaller crystallite size and greater oxygen deficiency in phase-pure tetragonal ZrO2.

Interface Phenomena Responsible for Bonding between TRIP Steel and Partially Stabilised Zirconia as Revealed by TEM

In this study, we demonstrate results of the transmission electron microscopy investigations of phenomena at the interface between partially stabilized zirconia (PSZ) and TRIP steel (steel with the Transformation Induced Plasticity effect). The interface phenomena were studied in thin film samples, which were prepared as a model system by the deposition of PSZ on TRIP steel using magnetron sputtering, and in a bulk composite containing TRIP steel and PSZ powder. The bulk composite was produced by Spark Plasma Sintering. The phase composition and the orientation relationship of several crystallites of PSZ and TRIP steel in the vicinity of their mutual interface were analysed using high resolution transmission electron microscopy (HRTEM). The phase identification was facilitated by using energy dispersive X-ray spectroscopy and electron energy loss spectroscopy (EELS) in scanning transmission electron microscope. In particular, the analysis of the zirconium N2,3 edge in the electron energy loss spectra allowed the cubic, tetragonal and monoclinic ZrO2 phases to be distinguished from each other. Thus mainly EELS complemented the HRTEM analysis of the orientation relationships. The same experimental methods were utilized to follow the local phase transformations near the PSZ/TRIP steel interfaces after a mechanical deformation of the samples.

Interfacial layer reduction and high permittivity tetragonal ZrO2 on germanium reaching ultrathin 0.39 nm equivalent oxide thickness

The nearly free interfacial layer and the tetragonal phase ZrO2 with the high permittivity of 45 ± 3 on Ge (001) substrate lead to the equivalent oxide thickness as low as 0.39 nm and the low leakage current density of 2 × 10−3 A/cm−2. The ultrathin GeON layer formed by remote plasma treatment on GeO2/Ge can inhibit the interfacial layer regrowth by retarding the interdiffusion of Ge and O atoms. The initial ∼1 nm GeO2 layer is consumed during the remote plasma treatment, confirmed by x-ray photoelectron spectroscopy and further thinned down by post-deposition annealing to trigger the GeO desorption.

Surface Crystalline Phase and Basicity of MgO/ZrO<sub>2</sub>-La<sub>2</sub>O<sub>3</sub>-y Solid Base Catalyst

MgO/ZrO2-La2O3-y solid base catalyst was prepared by precipitation immersion process. Raman spectroscope and X-ray powder diffraction (XRD) were used to determinate the surface phase and bulk phase of solid base catalyst. Temperature programmed desorption of CO2 (CO2-TPD) was employed to study the surface basicity of the catalyst. The results reveal that Mg2+ ion plays a key role in the stabilization of tetragonal phase ZrO2 not only in the bulk but also on the surface of catalyst when the Mg/Zr molar ratio is 0.4. The doping of La2O3 has the role of improving the dispersion of the active component MgO on ZrO2 surface, consequently resulting in the improvement of the catalytic activity of the catalyst rather than stabilizing tetragonal phase ZrO2.

Effect of gadolinium doping on phase transformation and microstructure of Gd2O3-Y2O3-ZrO2 composite coatings prepared by electrophoretic deposition

4 mol.% Y2O3 stabilized ZrO2 (YSZ) doped with various quantities of Gd2O3 (G-YSZ) ceramic coatings were synthesized by electrophoretic deposition method, and followed by vacuum sintering and isothermally annealing at 1000 °C for different durations. X-ray diffraction (XRD) was used to investigate their phase composition. Scanning electron microscopy (SEM) was employed to examine their microstructure, while energy dispersive X-ray spectrometer (EDS) was used to assess composition of the composite coatings. The results indicated that YSZ coating was composed of tetragonal and monoclinic phase after vacuum sintering at 1000 °C for 2 h under vacuum (<10−3 Pa). G-YSZ composite coatings were composed of tetragonal, monoclinic phase and a small amount of Gd2Zr2O7 phase after vacuum sintering at 1000 °C for 2 h, whereas the content of monoclinic phase in G-YSZ composite coatings increased with increasing Gd2O3 concentration. It was found that G-YSZ composite coatings were composed of tetragonal ZrO2 phase, monoclinic ZrO2 phase and cubic phase, whereas Gd2Zr2O7 phase disappeared, after G-YSZ composite coatings were isothermally annealed at 1000 °C in air for 100 h. A detailed description of the results and their discussion was presented in the paper.

Effect of voltage on properties of microarc oxidation films prepared in phosphate electrolyte on Zr–1Nb alloy

A thin protective film on Zr–1Nb alloy was fabricated by AC microarc oxidation (MAO) in phosphate electrolyte. The morphology, microstructure and phase constituents of MAO films under different discharge voltages were examined by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy. Their surface roughness and microhardness were measured. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were used to evaluate corrosion behaviors of films. The equivalent circuits of EIS plots for bare Zr–1Nb alloy and MAO films were proposed. It was found that all of films at different discharge voltages consisted of the monoclinic ZrO2 and tetragonal ZrO2 phases, but the content of monoclinic ZrO2 was much higher than that of tetragonal ZrO2 phase. Microhardness of MAO films is over 570HV, which is higher than that of Zr–1Nb alloy substrate with 245HV. The film fabricated in higher voltage shows lower corrosion current density and higher impedance, which displays better corrosion resistance. The EIS results identify that the inner compact layer of MAO films plays a key role in improving the corrosion resistance of Zr–1Nb alloy.

Deposition and properties of zirconia coatings on a zirconium alloy produced by pulsed DC plasma electrolytic oxidation

In this study, zirconium oxide coatings were produced on Zr–2.5wt.% Nb alloy by a plasma electrolytic oxidation (PEO) process using a pulsed DC power source with various frequencies 1000, 2000 and 4000Hz. When a relatively low termination voltage (i.e. 400V) was set, the thickness of the coatings was in a range of 7–15μm and the treatment time to reach the preset voltage was less than 5min. The coatings' phase structure, tribological and corrosion properties were characterized by X-ray diffraction (XRD), pin-on-plate sliding wear test and potentiodynamic polarization corrosion test, respectively. The results indicate that the thickest coating of 15μm can be obtained by adopting the highest frequency pulsed DC, i.e., 4000Hz and the coating has almost the same surface roughness as other two coatings. In spite of the difference in thickness, all the coatings showed a similar phase structure with the main phase of monoclinic ZrO2 and less tetragonal ZrO2 phase. Furthermore, all the PEO coated samples can improve wear and corrosion protection of the Zr alloy, among which the coating produced by the highest frequency (4000Hz) achieved the highest corrosion polarization resistance, wear resistance and lowest friction coefficient under the testing conditions in this study.

Ceria supported on sulfated zirconia as a superacid catalyst for selective catalytic reduction of NO with NH3

In this paper, ceria supported on sulfated zirconia (CeSZ) as a superacid catalyst was synthesized and the resulted performances for selective catalytic reduction (SCR) of NO with NH3 were investigated. Experimental results revealed that the sulfation of zirconia supports could greatly improve the SCR activity of the catalysts. Among the tested samples, the CeSZ catalyst with Ce/Zr mole ratio at 0.095 possessed the highest NO conversion (i.e., 98.6% at ca. 420°C and 180,000h−1). The sulfation had led to a formation of pure tetragonal phase of ZrO2, a well dispersion of CeO2, abundant stable superacid sites, increasing surface area and enrichment of Ce3+ on the surface, all of which were responsible for its excellent performance in SCR of NO with NH3.

Synthesis of Alumina-Zirconia-Yttria Ceramics and Correlation of Mechanical Properties with Phase Formation and Microstructure

Phase formation dependence of microstructure and mechanical properties were studied in 0.65Al2O3–0.35ZrO2 with 2 to 8 wt.% Y2O3 addition (AZY). Phase composition of the samples were characterized by x-ray diffraction (XRD) technique. It was found that the major phase was the rhombohedral-Al2O3, while the minor phase consisted of the monoclinic (m)-ZrO2, tetragonal (t)-rO2, cubic (c)-ZrO2 and monoclinic (m)- Y2O3. It has been found that the optimal contents of Y2O3 prohibited growth of grain in ceramics and obtained highly dense ceramics. It was found that the smaller grains had high fracture toughness. The maximum fracture toughness of 4.204 MPa m1/2 was obtained from 8 wt% Y2O3. Refinement of lattice parameters using Rietveld analysis revealed that the quantitative phases of AZY ceramics. This shows that under Y2O3 addition conditions the proportion of tetragonal-ZrO2 phase play an important role for the mechanical properties of AZY ceramics.

Microstructure characterization and deposition mechanism studies of ZrO2 thin films deposited by LI-MOCVD

Zirconia (ZrO2) thin films were deposited by LI MOCVD technique using the precursor Zr(thd)4 over large ranges of deposition parameters. These films were studied by field emission gun scanning electron microscopy (FEG-SEM) for surface and cross-section morphologies. The crystalline structure and crystallographic texture evolution of obtained films were analyzed by X-ray diffraction. Based on those experimental results, two typical deposition mechanisms were discussed from the view of film morphologies and crystallographic texture evolutions. Besides, the influence of deposition conditions on the crystalline structures of ZrO2 films is studied, to bring information about the deposition of tetragonal phase ZrO2 films.

Characterization of Nano Ni/MgO-ZrO&lt;sub&gt;2&lt;/sub&gt; Catalysts

Catalysts of Ni/MgO-ZrO2 were synthesized by the impregnation method and co-precipitation. They were characterized by X-ray diffraction (XRD), Scanning electron microcopy (SEM). It was observed that the monoclinic ZrO2 turned to tetragonal ZrO2 with the Mg2+ mixed. The tetragonal phase ZrO2 is considered as the desired phase which exhibits both acidity and basicity, and active in many heterogeneous catalytic systems. The NiO-MgO solid solution is also discovered on the surface of catalysts. Since the formation of carbon deposit needs a certain size of metal Ni, so the solid solution inhibited the reduced state Ni agglomeration .

Annealing effects on nanostructure and mechanical properties of nanolaminated Ta–Zr coatings

This paper proposes Ta–Zr multilayer coatings fabricated by using magnetron co-sputtering, achieving high nanohardness and low roughness after annealing, as appropriate protective coatings for die materials. The as-deposited nanolaminated Ta–Zr coatings exhibited nanocrystalline or amorphous phases, depending on the chemical compositions. The Zr oxidized preferentially when annealed in oxygen-containing atmospheres. The nanohardness increased in relation to the oxygen content in the coating, which was attributed to the formation of a crystalline tetragonal ZrO2 phase. To serve as a protective coating when applied in high-temperature conditions with an appropriate nanohardness, such as coatings on glass molding dies, the coating must endure an annealing treatment in an oxygen-containing atmosphere at 600°C. In this study, the periods of nanolaminated coatings were controlled by the rotation speed of the substrate-holder. The annealing treatments were conducted at 600°C in atmospheres of 20-ppm and 50-ppm O2–N2. The variations in crystalline structure, nanohardness, and in-depth chemical composition profiles after various annealing durations were investigated. The feasibility of a protective Ta–Zr coating was improved by annealing the coating in a 1% O2–Ar environment for 30min at 600°C to achieve a nanohardness of 10GPa, which is higher than the hardnesses of molded glasses, and by being subsequently exposed to a 10-ppm O2–N2 atmosphere, which is a realistic glass molding atmosphere.

17O MAS NMR and first principles calculations of ZrO2 polymorphs

DFT has been used for the first time to calculate 17O NMR magnetic response of the monoclinic and tetragonal ZrO2 phases. The calculated values were compared with those obtained by solid state 17O NMR after in situ17O isotopic enrichment of the boehmite samples inside ZrO2 rotors. The theoretical and experimental results indicated that after drying (120°C) and calcination (500°C/3h) under ambient pressure, part of the ceramic structure of the ZrO2 rotor was exchanged, generating Zr17O2 species. A good correlation between DFT and experimental data for monoclinic and tetragonal ZrO2 polymorphs was achieved.

Fabrication of well-crystallized mesoporous ZrO2 thin films via Pluronic P123 templated sol–gel route

Abstract Mesoporous zirconia (ZrO2) thin films were prepared by dip-coating via Pluronic P123 templated sol–gel route. ZrOCl2·8 H2O was used as zirconium (Zr) precursors. Annealing of as-coated ZrO2 thin films is important in order to stiffen the respective films and to remove the Pluronic P123. The mesoporous structure and crystallite size of ZrO2 were characterized systematically by field-emission scanning electron microscope (FESEM), both low- and wide-angle X-ray diffraction, thermal analysis technique and Brunauer–Emmett–Teller method. At annealing temperature of 400 °C, amorphous ZrO2 was transformed into tetragonal phase of ZrO2 (t-ZrO2). At 450 °C, t-ZrO2 and monoclinic phase of ZrO2 (m-ZrO2) were obtained. By altering heating rate during annealing, volume fraction of t-ZrO2 and m-ZrO2 was changed. FESEM images showed that disordered mesostructures of ZrO2 were formed after annealing. The surface area of mesoporous ZrO2 obtained ranges from 54.33 to 93.39 m2/g.