Peculiarities of phase formation in Al2O3-CeO2 nanopowders

The results of the investigations on the influence of CeO₂ adding on the transformation of the metastable Al₂O₃ forms obtained by thermal treatment of xerogels are presented. It is established that in the presence of CeO₂ the process of the formation of a stable phase of α-Al₂O₃ (corundum) takes place in a wider temperature range and is accomplished at a higher temperature (1300°C). It is suggested that the revealed mismatches on the diffractograms between the intensity values of the main analytical peaks of the corundum and its content in the samples are associated with the effect of screening caused by the differences in the mass coefficients of absorption of (μ) CeO₂ and Al₂O₃.     

Effect of Preparation Conditions on the Phase Composition of ZrO2–Al2O3–CeO2 Powders

Data are presented on the phase composition of ZrO₂–Al₂O₃–CeO₂ powders containing 10, 30, and 70 mol %, prepared via coprecipitation and successive precipitation. The precipitation procedure is shown to have a strong effect on the phase composition of the heat-treated powders and the state (inter- or intracrystalline) of the T-ZrO₂ phase, thereby changing its stability. At an Al₂O₃ content of 30 mol %, the M-ZrO₂ content is independent of the precipitation procedure.     

The Probe Length Effect on the Cantilever of an Atomic Force Microscope in Measuring the Mechanical Properties of Living Neurons

Living sensory neurons were studied by atomic force microscopy in the PeakForce QNM mode under near-physiological conditions. The dependence of the measured apparent Young modulus of cells on the ratio of the probe height to the beam length on a used cantilever was revealed. A qualitative explanation based on the analysis of beam strains in two limit cases, in which the probe slides over a studied object and the probe sticks to the latter, was given to the obtained result. It was proposed to classify native cells by the character of their interaction with the probe (sliding or sticking).     

Effect of the precipitation sequence on phase formation in the ZrO<Subscript>2</Subscript>-CeO<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> system

We have studied phase formation processes during heat treatment of precipitates in the ZrO₂-Al₂O₃ and ZrO₂-CeO₂-Al₂O₃ systems. During heat treatment of powders prepared by coprecipitation of precursors to ZrO₂, CeO₂, and Al₂O₃, α-Al₂O₃ is formed at higher temperatures, which is due to the formation and decomposition of T-ZrO₂ and metastable Al₂O₃ phases. The precipitation sequence in the ZrO₂-CeO₂-Al₂O₃ system influences the lattice parameters of the forming T-ZrO₂-based solid solutions because of the different degrees of Ce⁴⁺ and Al³⁺ substitutions for Zr⁴⁺.     

An atomic-force-microscopy study of the structure of surface layers of intact fibroblasts

Intact embryonic fibroblasts on a collagen-treated substrate have been studied by atomic-force microscopy (AFM) using probes of two types: (i) standard probes with tip curvature radii of 2–10 nm and (ii) special probes with a calibrated 325-nm SiO₂ ball radius at the tip apex. It is established that, irrespective of probe type, the average maximum fibroblast height is on a level of ~1.7 μm and the average stiffness of the probe–cell contact amounts to ~16.5 mN/m. The obtained AFM data reveal a peculiarity of the fibroblast structure, whereby its external layers move as a rigid shell relative to the interior and can be pressed inside to a depth dependent on the load only.     

Phase Formation in Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–ZrO<Subscript>2</Subscript>–CeO<Subscript>2</Subscript> Nanopowders Modified with Calcium Cations

We have studied phase formation in calcium-modified Al₂O₃–ZrO₂–CeO₂ nanopowders during sol–gel synthesis. The results demonstrate that heat treatment of the nanopowders first leads to the formation of a zirconium dioxide-based solid solution stabilized with cerium cations. Raising the heat treatment temperature helps the crystallization of corundum, a stable phase of aluminum oxide, to reach completion. In the temperature range 1400–1550°C, we observe the formation of a second aluminum-containing phase: calcium cerium hexaaluminate consisting of long prismatic grains.     

Phase formation of zirconia-based solid solutions synthesized from peroxides

A finely crystalline powder of the tetragonal solid solution based on zirconia with a crystal size of less than 40 nm is synthesized from zirconium and cerium peroxides. The amorphous phase formed as an intermediate product upon decomposition of the peroxides is characterized by structural disordering and involves chemical defects (OH^-, H₂O). Crystallization of (Zr_{1 - x}Ce_x)O₂ solid solutions (x = 0–0.2) and the sequence of phase and structural transformations of precursors upon heating are investigated. It is found that, during heat treatment at temperatures in the range 500–1200°C, recrystallization and growth of grains occur very slowly (from 5 to 60 nm). This makes it possible to obtain nanomaterials for different applications.Original Russian Text Copyright © 2004 by Fizika i Khimiya Stekla, Glushkova, Lapshin, Vershinin, Podzorova, Polikanova.     

Electrtic transport properties and the size effect in ZrO2-based ceramic materials

Amorphous nanomaterials in the ZrO₂-CeO₂ system are synthesized. The aging and crystallization processes in a complex zirconium-cerium hydrogel are investigated. Powders with a crystal size of 45–100 nm are prepared. Samples having a porosity of less than 2.2% are produced from the powders. It is demonstrated that tetragonal zirconia-based solid solutions Zr_1?x Ce_xO_2?δ sintered at a temperature of 1500°C possess ionic conductivity in air and in noble gasses. The assumptions are made regarding the mechanisms of ionic (surface anionic) and electronic (hopping) conduction in samples of the 88ZrO₂ · 12CeO₂ (mol %) composition. The solid solutions prepared can be used at a temperature of 720°C as high-strength inexpensive solid electrolytes.     

Surface micromorphology of dental composites [CE‐TZP]‐[Al2O3] with Ca+2 modifier

The objective of this study was to characterize the three‐dimensional (3D) surface micromorphology of the ceramics produced from nanoparticles of alumina and tetragonal zirconia (t‐ZrO₂) with addition of Ca⁺² for sintering improvement. The 3D surface roughness of samples was studied by atomic force microscopy (AFM), fractal analysis of the 3D AFM‐images, and statistical analysis of surface roughness parameters. Cube counting method, based on the linear interpolation type, applied for AFM data was used for fractal analysis. The morphology of non‐modified ceramic sample was characterized by the rather big (1–2 μm) grains of α‐Al₂O₃ phase with a habit close to hexagonal drowned in solid solution of t‐ZrO₂ with smooth surface. The pattern surfaces of modified composite content a little amount of elongated prismatic grains with composition close to the phase of СаСеAl₃О₇ as well as hexahedral α‐Al₂O₃‐grains. Fractal dimension, D, as well as height values distribution have been determined for the surfaces of the samples with and without modifying. It can be concluded that the smoothest surface is of the modified samples with Ca⁺² modifier but the most regular one is of the non‐modified samples. A connection was observed between the surface morphology and the physical properties as assessed in previous works. Microsc. Res. Tech. 78:840–846, 2015. © 2015 Wiley Periodicals, Inc.