Preparation of nanocrystalline yttria-stabilized zirconia
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Nanocrystalline powder with an average crystallite size of 8-12 nm, which was produced by a combustion synthesis process, was used to prepare dense, nanocrystalline articles. Green compacts of high green density were prepared by dry pressing and densified by a fast-firing process. During fast-firing, the dwell temperature significantly affected the final grain size and final density. On the other hand, the ranges of heating rates and dwell times that were used had a much less significant effect on the final density and final grain size. It was determined, however, that a high final density (>99% pth) and a very fine final average grain size (2,5 BaTiC>3,6 and A12O3.7-8 Fast-firing is a relatively nonconventional approach that is used to densify ceramic powder compacts in which the green compacts are subjected to rapid heating rates (>100 °C/min) and brief sintering times (typically, several minutes). Fast-firing minimizes the opportunity for grain growth to occur during the sintering of ceramic articles, thus establishing its advantage over conventional sintering. This may be understood in terms of the difference of the activation enthalpies for the densification and grain growth mechanisms.7 If the activation enthalpy that is associated with the lattice/boundary diffusion (which is known to be responsible for densification) is higher than that associated with the surface diffusion (which is known to be responsible for grain growth), then the unwanted grain growth can be suppressed if the furnace temperature is increased quickly to a temperature at which densification can progress more rapidly than grain growth. 1995 Materials Research Society
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K. R. Venkatachari et al.: Preparation of nanocrystalline yttria-stabilized zirconia
The aim of the present investigation was to study the fast-firing of yttria-stabilized zirconia to identify the conditions under which samples of high density and fine grain size can be obtained simultaneously. Heating rates from 250 °C/min to 750 °C/min, dwell times from 1 min to 5 min, and dwell temperatures from 700 °C to 1500 °C were employed to study the effect of fast-firing conditions on the outcome of the process. In particular, the effect of these variables on the final density and the final average grain size was determined in our study. II. EXPERIMENTAL PROCEDURE A. Sample preparation
Salts of zirconyl nitrate and yttrium nitrate (Aldrich Chemical Co., Inc., Milwaukee, WI), corresponding to a final composition of 4 mol % yttria-stabilized zirconia, were dissolved in de-ionized water to give a total salt concentration of 0.1 mol/L. An appropriate organic fuel, in an amount that correspond to the desired ratio on a dry-weight basis of salt to fuel, was added to the above solution and stirred until a clear solution formed. The solution was spray dried using a laboratory spray dryer (The Virtis Company, Gardiner, NY). Subsequently, the dried precursor mixture particles were ignited by pouring them into a beaker that was heated by a hot plate maintained at
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