수산화물 원료를 사용한 수열합성법에 의한 BaTiO3의 제조 및 물성

Abstract

High-purity ultrafine BaTiO3 powders are mainly applied in manufacturing electronic ceramics. Among them, the multi-layer ceramic capacitor(MLCC) and PTC thermistor have a close relation with our daily life and the latter has wide applications, such as starter for refrigerator, automatic magnetic eliminator for color TV, heater in the specified temperature range, dial telephone and energy saving lamp, etc.

The BaTiO3 is superior to the product made by the conventional solid-state reaction method due to its advantages such as high purity, homogeneous chemical composition, fine particle size and high sinterability of granules. These advantages contribute to the physical and electrical properties of the sintered ceramics.

According to the conventional hydrothermal process, the crystalline BaTiO3 powders can only be synthesized above pH 13 and the processes requires strong basic conditions using KOH or NaOH mineralizer. The hydrothermal process often needs relatively high temperature and takes long reaction time. The alkaline cations (K+ or Na+), which are known to be difficult to remove, deteriorate the sintering and electronic properties of the final ceramic products. For these reasons before, a modified hydrothermal process was studied with next objectives

8H2O) was used as both the Ba precursor and the mineralizer in the alkali-free system. Present process offers advantageous synthesis conditions at considerably lower temperature (≥80℃) with shorter reaction time (even without reaction time at 100℃) comparing to the conventional hydrothermal processes.

As the result, BaTiO3 powders were prepared by a modified hydrothermal synthesis from barium hydroxide and titanium-peroxo-hydroxide (TiO2O5(OH)2) precuresor. The advantageous features of the modified hydrothermal process are an alkali-free system, lower reaction temperature, and shorter reaction time comparing to the conventional hydrothermal process. The phase-pure BaTiO3 powders with a cubic perovskite structure were synthesized at temperature as low as 80℃. Synthesized powders were a ball shape having a particle diameter ranging from 0.5 to 1 ㎛. Well-developed crystalline (perovskite) BaTiO3 was obtained in the mild synthesis conditions (temperature <130℃, reaction time < 2 h, pH <13). The BaTiO3 ceramics sintered at a temperature as low as 1150℃ for 1 h had a density over 95 of theoretical.

to develope a modified hydrothermal synthesis in alkali-free system via a novel synthesis route from the titanium-peroxo-hydroxide precursor and to prepare BaTiO3 without alkaline mineralizer, KOH or NaOH, which influence the performance of the prepared powders and resulting sintered ceramics. Barium hydroxide octahydrate(Ba(OH)2 &#8228