Formation of Ba_2Ti_9O_(20) ceramics from EDTA―gel-derived powders

摘要

Reactive powders have been prepared by the ethylenediaminetetraacetic acid―gel (EDTA) method. Single-phase Ba_2Ti_9O_(20) and ≈98% dense ceramic are readily obtained by sintering the fine powders at 1275 ℃ for 3 h. Powder derived from EDTA―gel precursor results in Ba_2Ti_9O_(20) and BaTi_4O_9 mixed phases when sintering was performed below 1200 ℃, and only become single Ba_2Ti_9O_(20) phase above 1250 ℃. However, single-phase Ba_2Ti_9O_(20) were obtained at 1150 ℃ if ball-milling process was applied to this powder. This is considered to be due to the deagglomeration and improved mixing effects of ball-milling. One batch, the EDTA―gel precursor with ethylene glycol, showing improved decomposition behavior, results in single Ba_2Ti_9O_(20) phase at 1200 ℃. It was observed that the surface areas of derived powders are in the order of precursors from EDTA-ball-milled (BM) > EDTA―ethylene glycol (EG) > EDTA. The formation of single Ba_2Ti_9O_(20) phase is enhanced by the high surface area. The microwave properties of Ba_2Ti_9O_(20) ceramics obtained from three EDTA-derived powders are discussed and compared.