분무열분해법에 의한 나노크기의 BaTiO3 입자 제조에 관한 연구 = Preparation of nano-sized BaTiO3 particle by Spray Pyrolysis

다국어 초록 (Multilingual Abstract)

Nano-sized BaTiO3 particles for MLCC (Multilayer Ceramic Capacitor) were prepared by spray pyrolysis. Liquid to particle conversion (i.e., spray pyrolysis) has been used multicomponent functional particles and has several advantage including simple and low-cost process. Phase transformation and crystallite size of the calcined powders were investigated as the function of the calcination temperature and citric acid amount by X-ray diffraction methods, and particle morphology and size distribution were studied by scanning electron microscopy and particle size distribution analyzer. Also, BaTi ratio of BaTiO3 powder was investigated by X-ray fluorescence spectrometer, and specific surface area was studied by BET. High agglomerated particles of irregular shape were produced after the calcination when they were prepared from the nitrate solution without organic additive. After using citric acid, ethylene glycol and polyethylene glycol as organic additives, citric acid as organic additive was introduced in the precursor solution to form the easily crushable BaTiO3 particles. It was found that controlling the spray solution with organic additive made great differences in the structure and morphology of BaTiO3 particles during the calcination. High agglomerated particles of irregular shape were produced after the calcination at 1050 oC when they were prepared from the nitrate solution without organic additive. In contrary, coarse aggregates consisting of nano-sized BaTiO3 primary crystallites were obtained when used the nitrate solution containing organic additive (citric acid, CA). The coarse aggregates were successfully disintegrated to nano-sized BaTiO3 particles with narrow particle size distribution after a simple ball-milling process. The use of CA additive also affected the crystallographic behavior of BaTiO3 nanoparticles. The CA additive prevented from the phase separation of barium and produced phase-pure BaTiO3 particles at the as-prepared state and enhanced the phase transformability of metastable cubic phase to the tetragonal one by the calcination. As increasing the amount of citric acid, primary particle size and crystallite size of BaTiO3 particles were decreased. Also, tetragonality and surface area of BaTiO3 particles were improved. Consequently, the BaTiO3 nanoparticles of about 150 nm with good tetragonallity were successfully obtained by applying a simply ball-milling process to coarse aggregates which were prepared from the CA-assisted spray pyrolysis and calcined at 1050°C. Also, the CA-assisted spray pyrolysis can apply to synthesize other multicomponent functional nano particles.

국문 초록 (Abstract)

본 연구에서는 기상합성법의 하나인 분무열분해법을 이용하여 MLCC (Multilayer Ceramic Capacitor)의 유전체층에 사용되어지는 강유전체 물질인 나노크기의 BaTiO3 입자를 제조하였다. 제조된 BaTiO3 분말을 SEM, XRD, XRF, BET 및 PSA 분석을 통하여 해석하였다 유기첨가물이 없는 수용액으로부터 제조된 입자는 하소과정을 거친 후 불규칙적이며 응집이 심하였다. 본 연구에서는 나노입자를 합성하기 위하여 유기첨가제로 구연산, 에틸렌 글리콜, 폴리에틸렌 글리콜을 각각 첨가하였다. 이들 유기첨가물 중 BaTiO3 나노입자를 합성하는데 구연산이 가장 적합하였다. 유기첨가제인 구연산을 첨가하여 제조된 입자들은 하소과정에서 나노크기의 BaTiO3 일차입자들로 구성되어있는 응집체로 성장하는데, 이러한 응집체들이 간단한 밀링공정을 통하여 최종적으로 입도분포가 좁은 나노크기의 BaTiO3 입자들로 분리가능 하였다. 유기첨가제인 구연산은 BaTiO3 나노입자의 결정학적인 거동에 영향을 미쳤다. 유기첨가제인 구연산을 사용함으로서 바륨의 상분리를 억제하여 순수한 상의 BaTiO3 전구체 분말을 얻을 수 있었고 하소과정에서 입방정 구조에서 정방정 구조로 변화하는 상전이를 가속화시킴으로써 제조된 나노 BaTiO3의 tetragonality가 향상되었다. 구연산의 함양을 증가시킴으로서, BaTiO3의 일차입자와 결정자크기를 감소시키는 영향을 알 수 있었으며 또한 BaTiO3의 비표면적과 tetragonality를 향상시키는 영향도 알 수 있었다. 최종적으로, 유기첨가제인 구연산을 첨가하여 제조된 전구체 분말을 1050°C 온도에서 하소하고 밀링공정을 거친 나노 BaTiO3 분말은 우수한 tetragonality를 가지며 입자의 크기가 약 150nm 정도였다. 본 연구에서 시도된 나노분말 제조기술은 다른 다성분계 기능성 세라믹 분말합성에도 응용할 수 있을 것으로 기대된다.