"Lithium fluoride (LiF) is used to enhance the sinterability of perovskites, as it results in the formation of a liquid phase. In this study, the mechanism and kinetics of sintering for LiF-fluxed strontium titanate (SrTiO3) were investigated. The Sr/Ti ratio was varied between 0.98 and 1.03, and the LiF content in the green compact ranged from 0.5 to 2.0 weight percent. Sintering was conducted at temperatures between 695° and 925°C for isothermal dilatometric shrinkage measurements for time intervals of 6000 seconds or less. Weight loss, shrinkage, density and porosity measurements were conducted on samples isothermally sintered between 690° and 910°C. The isothermal weight loss measurements were taken at exponential time intervals up to a total of 250 hours of sintering; whereas measurements to determine shrinkage by micrometer, percent theoretical density of SrTiO3 achieved and percent open porosity remaining were made at the end of the 250 hour sintering period. Chemical analysis, density, porosity and shrinkage measurements, as well as scanning electron microscopy for both fractured and polished surfaces were carried out at different sintering stages for samples fluxed with 2.0 w % LiF and fired at 910°C in most cases. Unfluxed SrTiO3 powder, as well as LiF-fluxed SrTiO3 powder, both before and after heating at elevated temperatures, were subjected to x-rays. The vapor condensate of the fluxed strontium titanate was also subjected to x-ray diffraction. DTA/TGA were also carried out on both unfluxed and fluxed SrTiO3 in order to determine the temperature range in which the LiF-SrTiO3 mixture interacts.
In this system, densifications of up to 96% T.D. of SrTiO3 can be achieved using high LiF and Sr contents with open porosities as low as 0.3%. It is observed that the rate and percentage of both shrinkage and weight loss increase as Sr/Ti ratio, initial LiF content and sintering temperature increase. It is also observed that the grain size is dependent on cation stoichiometry, but not much on sintering temperature and time. Also observed is that the weight which the material loses upon sintering is always greater than the weight of LiF originally in the green compact. This suggests volatile compound formation, as can be deduced also from the TGA of the mixture and the observed high percentages of weight loss far below the melting point of LiF (846°C)"--Abstract, pages iii-iv.
Anderson, H. U. (Harlan U.)
Moore, Robert E., 1930-2003
James, William Joseph
Materials Science and Engineering
M.S. in Ceramic Engineering
University of Missouri--Rolla
xii, 125 pages
© 1983 Marie-Christine P. Proudian, All rights reserved.
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Proudian, Marie-Christine P., "Sintering of LiF-fluxed SrTiO₃" (1983). Masters Theses. 4066.
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