Titanate Ceramics from Wet-Chemically Prepared Powders
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INTRODUCTION Titanate ceramics find extensive application in electronic components. Titanate powders are conventionally produced by solid-state sintering method. This procedure is not only tedious because crushing and grinding are required after presintering, but also not uniform both in chemical composition and particle size. Several studies have bee undertaken to find a better method to produce titanate powders. Sol-gel method" 13, although a good method, still requires presintering and expensive organometallic compounds. Hydrothermal method 23 is also a good method, but expensive equipment is required. Titanium tetrachloride and barium hydroxide are most frequently used to produce barium titanate. Titanium hydroxide, which is inexpensive, was used to produce titanate powders by the present authorst2 3 by the wet-chemical method. A further study is made in this article regarding the production of manufacturing titanate ceramics from titanium hydroxide by wet-chemical method. Titanium hydroxide (Ti02-xH20) used in this study was obtained from China Metal & Chemical Co., which produces Ti0 2 from ilmenite by sulfuric method, i.e., Ti02-xH20 is obtained by reacting ilmenite and sulfuric and, subsequently, hydrolysing the reaction product TiOSO4 . A substantial aging may have occurred in Ti02-xH20 during several months of storage before it was used in this study. EXPERIMENTAL The molarity of Ti02-xH2 0 and the composition of products were analyzed by ICP.
Ti02-
xH20 was reacted with Ba(OH)2 and/or Sr(OH)2 in water. After the reaction, the powders were 0
washed and dried. The powders were compacted and sintered between 1200 and 1300 C for 4 hrs, and cooled in a furnace. XID, SEI, TD4, particle size analyzer and impedance analyzer were used to analyze the structures, particle sizes, shapes of the powders end the structures, grain sizes, electrical properties of the ceramics.
RESULTS AND DISCUSSIONS During the reaction between barium ion and TiD2 -xH20, the Ba/Ti ratio of the reaction product increases with time. Figure 1 shows that at 680 C among three Ba/Ti ratios of the react231 Mat. Res. Soc. Symp. Proc. Vol. 346. 01994 Materials Research Society
ants, 2, 1.6, and 1.2, a higher reaction rate occurs between barium ion &nd T102 -xH2O with s
higher the Ba/Ti ratio of the reactants. At a reactant ratio of Be/Ti=2, the product B8TiO3 forms within 1 how. A longer reaction time forms a product which has a Be/Ti ratio higher than 1. For a reactant rtio of Ba/Ti=1.6, it took 10 hours to form BaTiO3 so as to-obtain For Be/Ti=l.2, it never rewched the exact the exact Ba/Ti stoichiometry ratio of BeTiGO. Ba/Ti stoichiometry ratio. High alkali promotes the formoation of barium titanate. Figure 2 shows that high temperature speeds up the reaction and strontium ion is more reactive than barium ion, set the initial Be/Ti or Sr/Ti ratio=1.2, react at 98°C for4 hrs. The product has a Be/Ti ratio of 0.9, while the other product has Sr/Ti ratio 1.12. The particle size of barium titanate Indicated in Figure 3 slightly increases w
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