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Alumina-toughened zirconia composites are attractive materials for biomedical and demanding mechanical engineering applications as the added alumina increases hardness and strength while the fracture toughness of zirconia is preserved. In the present study an unstabilized pyrogenic zirconia nanopowder was coated with 1 mol% ytterbia and 2 mol% neodymia via the nitrate route, the powder was blended with 20 vol% submicron size alumina. Samples were hot-pressed at 1250 – 1450 °C for 1 h at 60 MPa axial pressure. Microstructure, phase composition and mechanical properties were investigated. The co …
Surface Strengthening of Extrusion-Formed Polymer/Filler-Derived Ceramic Composites
L. Schlier, N. Travitzky, J. Gegner, P. Greil
Pages 181-188 · DOI: 10.4416/JCST2012-00018
Surface nitridation of extrusion-formed Fe-Si-Cr-filler-loaded polysiloxane polymer filaments was investigated. After the filaments were exposed to a nitrogen atmosphere at temperatures above 1000 °C, a gas-solid reaction caused the formation of a nitridation reaction layer covering the filament surface. Thermo-chemical calculations of equilibrium phase compositions at different nitrogen activity suggest the formation of Si2N2O and Si3N4 near the filament surface (high nitrogen content) whereas SiC and unreacted CrSi2 and FeSi dominate in the core region (low nitrogen content), which was confi …
Electrochemically Induced Degradation of Screen-Printed Gold Thick Films
T.J. Rabbow, N. Junker, C. Kretzschmar, M. Schneider, A. Michaelis
Pages 199-210 · DOI: 10.4416/JCST2012-00023
Gold thick films have been characterized by means of cyclic voltammetry in nitric acid and are compared with a pure gold electrode. Surface reconstruction and roughening is found for all electrodes, whereby the pure gold reference sample rapidly exhibits stationary behavior. In contrast, the screen-printed electrodes show a permanent linear increase of the gold surface area as measured by the charge densities for gold oxidation, which is connected with the dissolution of glass-ceramic compounds. Oxides of bismuth and copper and their aluminates are regularly used to adjust the morphology of th …
Mechanical Characterization of PZT Ceramics for Multilayer Piezoelectric Actuators
R. Bermejo, M. Deluca
Pages 159-168 · DOI: 10.4416/JCST2012-00025
Multilayer piezoelectric actuators (MPA) are commonly used to control injection valves in modern combustion engines operating in a temperature range from -40 °C up to 125 °C. They consist of a stack of very thin piezoceramic layers, mostly based on Lead Zirconate Titanate (PZT) material with interdigitated metallic electrodes in between. In this work the mechanical properties of both pure piezoceramic material and the multilayer structure are investigated in terms of strength and crack growth resistance. The results of strength tests are interpreted in the mainframe of Weibull theory, and frac …
Phase Evaluation of YSZ upon Doping with Ta5+, Ti4+ and Ca2+ with Combined Raman and XRD Analysis
A. Bhattacharya, T. Wermelinger, V. Shklover
Pages 211-214 · DOI: 10.4416/JCST2012-00028
To improve the phase stability of 7YSZ (7 wt%-Y2O3-doped ZrO2), it has been doped with larger (Ca2+) and smaller (Ti4+ or Ta5+) ions. Complementary Raman and XRD studies of these stabilized systems have been performed. The tetragonal symmetry of the Ta5+-ion-doped YSZ sample and the Ti4+-doped YSZ sample, and the cubic symmetry of Ca2+-doped YSZ have been confirmed both by means of XRD and Raman analyses. Raman scattering measurements show shifts of characteristic peaks when the YSZ is doped with Ta5+, Ti4+ and Ca2+ cations. The peak shift increased with increasing dopant concentration in the …
Growth of 2M-Wollastonite Polycrystals by a Partial Melting and Recrystallization Process for the Preparation of High-Aspect-Ratio Particles
L. Zhu, H.Y. Sohn
Pages 169-180 · DOI: 10.4416/JCST2012-00032
A polytype of wollastonite, 2M-wollastonite, that breaks into acicular particles under external forces was synthesized in a partial melting and recrystallization process using relatively pure component materials. In the first step, samples containing SiO2 and CaO and small amounts of various additives were pressed into discs and sintered at 1270 °C. These temperatures are lower than the melting points of the major components but higher than the melting points of most of the additives so as to partially melt the samples. The samples were then cooled to below 550 °C at an average rate of 2 – 3 K …
