Stabilized ZrO2 Powders Research Articles

Erratum to: Methods of Electron Microdiffraction and X-Ray Analysis in Structure Study of Nanodisperse Partially Stabilized ZrO2 Powders

The name of the fourth author should read D. V. Bocharov.

Phase stability, thermal conductivity and crystal growth behavior of RE2O3 (RE = La,Yb,Ce,Gd) co-doped Y2O3 stabilized ZrO2 powder

The RE2O3 (RE = La, Yb, Ce, Gd) co-doped Y2O3 stabilized ZrO2 (RE-YSZ) powders were prepared by a sol–gel method. To study the effect of RE2O3 addition on phase and structure formations, crystal growth and thermal conductivity, the investigations proposed in this paper cover X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and laser thermal conductivity meter. The results indicate that RE2O3 (RE = La, Yb, Ce, Gd) co-doped Y2O3 stabilized ZrO2 powder could improve phase stability and reduce thermal conductivity. In addition, crystal growth occurs due to different growth mechanisms at low and high temperature; the activation energy at low temperature is obviously lower than that at high temperature. Considering the comprehensive performance, it can be concluded that Yb-yttrium oxide-stabilized zirconia powder is a good thermal barrier coating.

Phase transformation and crystal growth behavior of 8mol% (SmO1.5, GdO1.5, and YO1.5) stabilized ZrO2 powders

Nanocrystalline powders of ZrO2–8mol%SmO1.5 (8SmSZ), ZrO2–8mol%GdO1.5 (8GdSZ), and ZrO2–8mol%YO1.5 (8YSZ) were prepared by a simple reverse-coprecipitation technique. Differential thermal analysis/thermogravimetry (DTA/TG), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Raman spectroscopy, and high-resolution transmission electron microscopy (HRTEM) were used to study the phase transformation and crystal growth behavior. The DTA results showed that the ZrO2 freeze-dried precipitates crystallized at 529, 465, and 467°C in the case of 8SmSZ, 8GdSZ, and 8YSZ, respectively. The XRD and Raman results confirmed the presence of tetragonal ZrO2 when the dried precipitates were calcined in the temperature range from 600 to 1000°C for 2 h. The crystallite size increased with increasing calcination temperature. The activation energies were calculated as 12.39, 12.45, and 16.59 kJ/mol for 8SmSZ, 8GdSZ, and 8YSZ respectively.

Materials Diffusion Stability at Interface Between Stabilized ZrO2 Electrolyte and CeOx Interlayer in Model SOFC Cell

We observed the solid state reaction at the interface between ZrO2 electrolyte and CeOx interlayer in a model SOFC. At that interface, ZrOx and CeOx diffuse each other and the Zr-CeO solid solution lowers the cell performance. In this report, diffusion coefficient which enables to predict how much the reaction occurs is derived by using the ZrO2 / CeOx diffusion couples, simulating the long time operation. Stabilized ZrO2 powder and Gd-added CeO2 powder were laminated into two layers and pressed. To measure more practical interface, we chose the material powders used for cell production. Then the pressed powder was sintered at tempertures of 1350 to 1600 oC for 24 hours. The sintered blocks were cut into 3mm thick samples and polished. The ZrOx / CeOx interface were observed by scanning electron microscope (SEM) and analyzed about composition and their amount by Energy-dispersive X-ray spectroscopy (EDS).

Thermal Insulation Property of Nanostructured Alumina Coated Zirconia Thermal Barrier Coating

nanostructured Al2O3 coated ZrO2-Y2O3 thermal barrier coatings were prepared by plasma spraying method using nanostructured alumina coated 8mol%Y2O3 stabilized ZrO2 powder as starting material and the thermal insulation property was investigated as a function of the thickness of the coating. The results indicate that the structure and property of thermal barrier coating using nanoAl2O3 coated ZrO2-Y2O3 powder was superior to that of using single zirconia powder. The thermal insulation property of the thermal barrier coating increased with thickness of the coating increasing, and the advantage is more obvious with temperature increasing.

Effects of RE3+ Ionic Radius on Monoclinic Phase Content of 8 mol% REO1.5 Partially Stabilized ZrO2 (RE = Yb, Y, Gd, and Nd) Powder Compacts after Annealing at High Temperature

Powders of zirconia doped with 8 mol% REO1.5 (RE = Yb, Y, Gd, and Nd) were synthesized by using the sol–spray pyrolysis method. The effects of RE3+ ionic radius on monoclinic (m) phase content of powders were investigated. The XRD results showed that the metastable tetragonal (t′) phase underwent a complete phase change to form m and cubic (c) phases after a heat treatment of 50–100 h at 1450°C. A cation size‐dependent reduction in the m phase content of the REO1.5 partially stabilized ZrO2 powders was observed. The SEM–EDS analysis of the powders revealed that the RE3+ concentrations in the c phases decreased with decreasing the RE3+ ionic radius. These results indicate that the stabilizer concentration of the c phase can be attributed to RE3+ ionic radii, resulting in different m phase contents. Compared to the REO1.5 single doped ZrO2, the m phase contents of 8 mol% (RE0.5Yb0.5)–ZrO2 (RE = Y, Gd, and Nd) powders were significantly reduced. The results prove that the stabilizer with a lower RE3+ size is effective in reducing the m phase content of partially stabilized ZrO2 after annealing at high temperatures.

Preparation and Performance of β-Sialon Bonded ZrO<sub>2</sub> Composites

β-Sialon bonded ZrO2 composites were prepared by reaction sintering process using β-Sialon and CaO stabilized ZrO2 powders as raw materials.The effect of β-Sialon powder additions on the properties of the composites was investigated. The results show that the samples with 10 wt% of β-Sialon addition had the lowest apparent porosity (29.80%) and the highest of flexural strength (68.70MPa). The thermal shock resistance in carbon addition of the composites could be improved by addtion of 5wt% β-Sialon. It may be relative with that the sample had the lowest thermal expansion coefficient in vacuum.

Methods of electron microdiffraction and X-ray analysis in structure study of nanodisperse partially stabilized ZrO2 powders

Analytical electron microscopy (AEM) has been used to study both structure and morphology of partially yttria-stabilized zirconia dioxide nanopowders (YSZ) obtained by wet-chemical methods (glycine and azeotropic distillation) and ceramics produced from them. Both morphological and structural inhomogeneity of nanopowders obtained by glycine (glc) method has been estimated. Besides the tetragonal ZrO2 phase (results of X-ray analyses) the cubic phase of ZrO2 with different degree of crystallinity has been estimated by Electron Microdiffraction (EMD) methods. In powders obtained by azeotropic distillation (dest) method besides the amorphous phase (identified in X-ray investigations) the high disperse cubic zirconia phase has been identified using high local EMD method. It has been detected the yttrium influence on the degree of crystallinity in nanopowders obtained by azeotropic distillation method without yttria (dest-0YSZ) and with 5 wt % Y2O3 (dest-5YSZ). It has been determined the difference in ceramic morphology produced from these powders. Ceramics mode of nanopowders containing yttria (glc-5YSZ and dest-5YSZ) have a homogeneous surface which consists of different size globules (0.1–0.6 μm) and contains some little pores (∼370 nm). Ceramics mode of nanopowders without yttria have inhomogeneous surface with numerous cracks. Separate parts of the latter ceramics consist of globules, their sizes are of 0.2–0.5 μm.

Agglomerate formation during drying

The evolution of agglomerate structure during drying of particles from suspension has been studied for a nanocrystalline Y2O3 (8% mol fraction)-stabilized ZrO2 powder. Agglomerates in drying and dried suspensions were examined at the smallest size scales (1 nm to 1 μm) using ultra-small angle x-ray scattering (USAXS) and at the largest size scales (100 nm to 10 μm) using scanning electron microscopy. The results were correlated with the degree of particle dissolution in each suspension (measured by flame absorption spectroscopy of the suspension filtrate) and the zeta potential of the particles in suspension prior to drying. Results show that large agglomerates readily form across a pH range from 2 to 9. The fact that Y+3 ion dissolution varies by over four orders of magnitude in this range leads to the conclusion that there is little direct correlation between the degree of Y dissolution and agglomeration in this system (Zr ion dissolution was below the detection limit at all pH values studied). The observation of large agglomerates well before the introduction of air-water interfaces into the drying mass likewise leads to the conclusion that capillary forces are not essential to agglomerate formation. Instead, agglomerates appear to form as a direct consequence of increasing suspension concentration. Zeta potential also plays a role. Specifically, there was a notable change in agglomerate morphology as the isoelectric point was approached, at approximately pH 8. Here USAXS shows the particles in suspension to have a layered interior structure, with small primary particles aggregated in sheets to form each blocky particle. This is in contrast to the more rounded agglomerates formed away from the isoelectric point, which appear to be composed of the same primary particles arranged in chainlike structures. USAXS of powders from the dried suspensions confirms that the structures seen after drying are the same as those present in suspension. The two structural morphologies are attributed to diffusion-limited (sheets) versus reaction-limited (chains) aggregation, respectively.

A novel polymer matrix method for synthesizing ZrO2 nanocrystals at moderate temperature

A novel polymer matrix method for synthesizing ZrO2 nanocrystals at moderate temperature

THE THERMAL SHOCK ENDURANCE OF A PLASMA SPRAYED ZrO2COATING ON STEEL

Abstract By addition of a Ni-Cr undercoating to a steel substrate, a ZrO2; coating with high thermal shock endurance was produced. This coating resists to an initial quenching temperature gradient of 1000 K. The plasma spray coating material is 7wt%-CaO stabilized ZrO2 powder. The chemical composition and the thermal expansion coefficient of the base steel, and also the Ni-Cr undercoating were evaluated for thermal shock endurance. The thermal shock endurance of the ZrO2 coatings is enhanced by the (Cr+Co) contents in the steels and by applying a Ni-Cr undercoating. The thermal expansivities of the steels have little influence on the thermal shock endurance. The carbon in the steels deteriorates the bonding of the Ni-Cr undercoating, but does not influence the ZrO2 coatings themselves.

Processing and Sintering of Ultrafine MgO‐ZrO2 and (MgO, Y2O3)‐ZrO2 Powders

Chemical coprecipitation was used to produce ultrafine and easily sinterable MgO‐stabilized and (MgO, Y2O3) stabilized ZrO2 powders. The sintering behavior is very sensitive to post‐precipitation washing because “hard” agglomerates form when the precipitated gels are washed with water, whereas “soft” agglomerates form when they are washed with ethanol. The soft agglomerates pack uniformly, resulting in homogeneous shrinkage of powder compacts to near‐theoretical density. The hard agglomerates result in compacts which have regions of localized densification and a signifiint fraction of residual porosity.

Mortars for zirconia refractories

The composition was developed for a mortar based on zirconium dioxide and orthophosphoric acid intended for laying zirconia refractories. The filler should be stabilized ZrO2 powder of a particle size below 0.5 mm with 10% monoclinic fine-grain ZrO2 mixed with orthophosphoric acid added in the proportion of 2–4% in terms of P2O5.