所報 104

19/38

－　　－17Published PaperRapid and Continuous Production of Ferrite Nanoparticles by Hydrothermal Synthesis at 673 K and 30 MPaToshiyuki SATO, Kiwamu SUE, Wataru SUZUKI, Muneyuki SUZUKI, Keitaro MATSUI, Yukiya HAKUTA, Hiromichi HAYASHI, Kunio ARAI, Shin-Ichiro KAWASAKI, Akiko Kawai-NAKAMURA, and Toshihiko HIAKIMeFe2O4 (Me = Ni, Cu, Zn) nanoparticles synthesis from Fe (NO3)3 and Me (NO3)2 aqueous solution was carried out at 673 K and 30 MPa using a flow apparatus. A T-type micro-mixer with inner diameter of 0.33 mm was used for super-rapid heating of the starting solution to supercritical water condition. The Me/Fe molar ratio in starting solution changed less than 0.50. Residence time ranged from 0.002 to 4.000 s. Conversion, average particle size, crystal phase, lattice parameters and Me/Fe molar ratios were characterized by ICP, TEM, XRD and XRF, respectively.For the solid-solution nanoparticles of MeFe2O4 and γ-Fe2O3 with a cubic spinel structure, the average particle size of under 10 nm was obtained. The particle size decreased and the conversion increased with decreasing solubility of the metal oxides in the order ZnO > CuO > NiO > Fe2O3 on the basis of classical nucleation theory. The results of the experiments lead to the conclusion that MeFe2O4 particles were formed by secondary nucleation of mixed oxide of Me and Fe on the primary particles, low-crystallinity γ-Fe2O3, through both dissolution-recrystalliation and also Ostwald ripening.Keywords: hydrothermal synthesis, nanoparticles, supercritical water, micro-mixer, ferrite超臨界水熱法におけるフェライトナノ粒子の連続合成　本研究は，T型マイクロミキサを組み込んだ流通式反応装置を用いて，Fe(NO3)3およびMe(NO3)2 (Me = Ni, Cu, Zn)を原料としてMeFe2O4ナノ粒子の合成を，反応温度673 K，反応圧力30 MPa，滞在時間0.002から4.000で行った．T型マイクロミキサには，流路内径0.33 mmを用いて原料金属塩水溶液を高温高圧水との混合時に急速昇温させるために使用した．各種金属イオンの転化率，粒径，相同定，格子定数の算出および生成物中のMe/Feモル比の分析には，ICP，TEM，XRDおよびXRFをそれぞれ用いた．　生成物は，MeFe2O4(またはγ-Fe2O3)の単一相であり平均粒径は10 nm以下であった．また，滞在時間の増加にともない各金属イオンの転化率は，原料由来の金属酸化物の溶解度差に準じて上昇することに起因して，得られるMeFe2O4ナノ粒子の粒径も増加する傾向を示した．実験結果より，MeFe2O4粒子は，まず一次粒子である低結晶性のγ-Fe2O3が生成後，溶解再析出とオストワルド熟成の両方により，Me2+イオンを取り込み二次核生成によって形成される生成機構を明らかにした．キーワード：水熱合成，ナノ粒子，超臨界水，マイクロミキサ，フェライトJournal（掲載誌）Industrial and Engineering Chemistry Research, Volume 47, No.6, 1855-1860, 2008.