Stabilization Of Tetragonal ZrO2 Research Articles

The Influence of Silicon Dioxide on the Stability of the Phase Composition and Mechanical Properties of Alumina-Toughened Zirconia-Based Ceramics

The influence of SiO2 impurity (with a concentration varying from 0 to 10 mol %) on the stability of tetragonal ZrO2 (t-ZrO2) and on a set of micro- and macromechanical properties of calcia-stabilized (CCaO = 6.5 mol %) alumina-toughened ( $${{C}_{{{\text{A}}{{{\text{l}}}_{2}}{{{\text{O}}}_{3}}}}}$$ = 5.8 mol %) zirconia-based ceramics (ATZ ceramics) has been studied. It has been found that the introduction of SiO2 ( $${{C}_{{{\text{Si}}{{{\text{O}}}_{2}}}}}$$ = 5 mol %) raises fracture toughness Kc by nearly twofold (from 7.05 to 12.43 MPa m1/2), slightly decreases hardness H (from 12.75 to 10.9 GPa), and improves ultimate compression strength σS (from 2.44 to 2.73 GPa) and ductility (compression strain e grows from 5.3 to 7.3%) of ATZ ceramics. It has been shown that the above improvements were achieved by means of a reduction in t-ZrO2 stability.

Stabilization of tetragonal ZrO2 by oxygen plasma treatment of sputtered ZrCu and ZrAl thin films

The stabilization of tetragonal zirconium dioxide (zirconia) by doping at room temperature has already been carried out with dopant materials like Y or Mg. Also alternative dopants like Al and Cu have been investigated using reactive sputtering processes at elevated temperatures with oxygen as a reactive gas. In the present work we investigate if stabilization is possible by dopants like Al and Cu which are added by means of non-reactive sputtering in a dual cathode magnetron sputtering device. Because it is expected that the stabilization depends on the dopant concentration, the Zr coatings were produced with a dopant gradient. So it was possible to investigate many different compositions with only few samples. This dopant gradient could be produced with a modification of the substrate holder in the sputtering chamber where a small wall partially shadows the vapor beam of the dopant. After production of the metallic ZrAl and ZrCu samples, first their chemical composition was determined by energy dispersive X-ray spectroscopy in a scanning electron microscope. Then they were treated with oxygen plasma. Depth profiles were recorded by Auger electron spectroscopy to investigate the progress of the oxidation. For crystallographic analysis X-ray diffraction was used. The surface morphology was measured with an atomic force microscope.The results show that the stabilization worked successfully with Cu while for Al no formation of the tetragonal phase was observed and the films remained essentially amorphous. The results show that oxygen plasma treatment is a viable and fast way to transform doped metallic Zr films into tetragonal Zirconia.

Quantitative Analysis on the Influence of SiO2 Content on the Phase Behavior of ZrO2

The salient features of bioinert, chemical resistance, and high mechanical strength of synthetic ZrO2 and the bioactivity characteristics of SiO2 has been well‐known in biomedical applications. This study has been aimed at the synthesis and quantitative structural analysis of SiO2‐stabilized tetragonal ZrO2. The synthesis has been performed through sol–gel technique and the resultant characterization of the powders has been done through X‐ray diffraction (XRD) and X‐ray fluorescence (XRF) techniques. Quantitative analysis on the ZrO2–SiO2 binary oxide systems has been performed by Rietveld Refinement using GSAS‐EXPUGI software package. The results from this study have confirmed that SiO2 concentration has played a major role in the stabilization of tetragonal ZrO2. Lower SiO2 concentration has resulted in the formation of mixture of any two different phases comprising of monoclinic ZrO2 (P21/c symmetry) or cubic ZrO2 (Fm‐3 m symmetry) or tetragonal ZrO2 (P42/nmc symmetry), whereas higher SiO2 concentration has resulted in the stabilization of single phase tetragonal ZrO2 (P42/nmc symmetry).

Stabilization of tetragonal ZrO2 with Al2O3 in reactive magnetron sputtered thin films

Thin-film mixtures of zirconia and alumina 1–2 μm in thickness were produced by sputtering composite targets of zirconium and aluminum metals and reacting the metal vapor with oxygen. X-ray and selected area electron diffraction indicated that the films deposited at room temperature were amorphous. Rutherford backscattering measurements indicated that the films were stoichiometric. Annealing at 1000 °C for 48 h produced ordering of the zirconia phase, and the zirconia crystal structure was strongly dependent upon the relative amounts of zirconium and aluminum. Pure zirconia was monoclinic as was a mixture with a zirconium-to-aluminum atom ratio of 0.76:0.24. For the mixture with a zirconium-to-aluminum atom ratio of 0.52:0.48 the tetragonal phase of zirconia was observed with only a trace of the monoclinic phase. The alumina phase apparently orders much more slowly than zirconia, and no alumina diffraction peaks were observed in any of these mixtures with zirconium-to-aluminum atom ratios down to 0.52:0.48.

Influence of Y<sub>2</sub>O<sub>3</sub> Addition on the Transformation Behavior of ZrO<sub>2</sub> in Al<sub>2</sub>O<sub>3</sub>-ZrO<sub>2</sub> Composites

The effect of Y2O3 content on the stress-induced transformation of ZrO2 in sintered Al2O3-ZrO2 (Y2O2: 0-3mol%) composites was studied by using laser Raman spectroscopy and X-ray diffraction method, and their mechanical properties, such as Young's modulus, bending strength, Vickers hardness and fracture toughness, were measured. The tetragonal phase of ZrO2 was 54mol% in the Y2O3-free composite, and increased with increasing Y2O3 content. From SEM observation, the particle size of ZrO2 in the composites was from 0.9 to 1.2μm. The Raman measurement of ZrO2 phases on the fracture and tensile surfaces after bending test indicated that the stress-induced transformation proceeded more extensively in the composites with low Y2O3 contents and near the fracture surfaces. Consequently, fracture toughness increased with decreasing Y2O3 content, and this tendency was related to the stress-induced transformation and the presence of microcracking. On the other hand, bending strength, Vickers hardness and Young's modulus decreased with decreasing Y2O3 content due to microcracking in Al2O3-ZrO2 composites. The results obtained lead to the conclusion that the stress-induced transformation behavior is explained by the constraint of ZrO2 particles in the matrix of Al2O3, and is influenced by the stabilization of tetragonal ZrO2 by Y2O3.

Corrosion-Resistance for ZTA-Cr<sub>2</sub>O<sub>3</sub> Sintered Bodies in Molten Fluoride Salts

The stability of tetragonal ZrO2 in ZTA-Cr2O3 sintered bodies fabricated by an impregnation method was investigated in NaF, KF, Na2SiF6 and K2SiF6 at 900° and 1000°C. ZTA-Cr2O3 having relative density above 99%, flexural strength of about 450MPa and hardness of about 1600kg/mm2 at R. T. was used for the corrosion test. ZTA-Cr2O3 exhibited higher corrosion-resistance in carbonate and sulfate salts than in fluoride salts. The corrosion-resistance of ZTA-Cr2O3 in molten fluoride salts increased with an increase in the addition of ZrO2 to Al2O3. ZTA-Cr2O3 formed a reaction layer (on the sintered body) in molten fluoride salts. The reaction layer formed in KF consisted of K3AlF6 and Al2O3-Cr2O3 solid solution, and protected the t-ZrO2 phase beneath the reaction layer. The stability of t-ZrO2 phase was dependent on the thickness of the reaction layer. Three mol% Y2O3-ZTA-Cr2O3 was superior to the other ZTA with respect to the corrosion-resistance in molten fluoride salts.