Synthesis of Barium-Ferrite Ultrafine Particles by a Hydrothermal Method

以硝酸铁、针铁矿和氢氧化钡为原料，采用水热法制备了超细钛酸钡铁氧体。研究了碱浓度、高压釜内搅拌速度、水热温度和时间对颗粒形状和大小的影响，并推测了颗粒的形成机理。确定了合成尺寸小于0.1微米的六方片状粒子的反应条件。在含有硝酸铁和氢氧化钡的水热合成体系中，粒子的生长和成核同时发生在反应的早期阶段。约过1h后，由于Ostwald成熟而导致的颗粒生长成为主导。随着高压灭菌器中温度和压力的升高，颗粒的生长速度加快，颗粒长大到大…。更多的e尺码。颗粒尺寸随(OH^-]/[NO^-]摩尔比(R)和搅拌速度(N)的增大而减小。当R&lt；大于或等于-gt；6且n&lt；在300ﾟC时大于或等于-gt；30orpm时，可以得到尺寸小于0.1um、厚度小于0.02um的六方片状Ba铁氧体颗粒。在300ﾟC下，经过短暂的水热处理后，形成了Ba型铁氧体。随着处理的进行，颗粒尺寸减小。这可能是由于处理提高了结晶度的事实。随着温度的升高、搅拌速度和碱浓度的增加，针铁矿颗粒的粒度减小，针铁矿颗粒粒度分布的不确定性容易导致所制备的Ba型铁氧体颗粒的粒度分布较宽。为此，探索了生产出粒度分布较窄的超细针铁矿的操作条件。通过以较低的转化率将进料流经导流管送入鼓泡塔的氧气浓度降至较低的水平，制备的颗粒的粒度分布变窄(几何标准偏差小于1.18)。较少

Barium-ferrite ultrafine particles were synthesized from two kinds of starting materials; either ferric nitrate or goethite and barium hydroxide, by means of a hydrothermal method. The effects of alkali (NaOH) concentration, stirring speed in the autoclave, hydrothermal temperature and time on the particle shape and size were studied, and the mechanism of particle formation was deduced. The reaction conditions were clarified for which hexagonal plate-like particles of less than 0.1mum in size, suitable for coated perpendicular magnetic recording media, are synthesized.In the hydrothermal synthesis from an aqueous suspension containing ferric nitrate and barium hydroxide, the nucleation and the particle growth occur simultaneously in the early stage of the reaction. After about lh has passed, the particle growth due to Ostwald ripening becomes dominating. As the temperature and hence the pressure in the autoclave rises, the rate of particle growth increases and particles grow up to larg … More e sizes. The particle size decreases with increasing molar ratio (R) defined by (OH^-]/[NO^-_] and increasing stirring speed (n). When R <greater than or equal> 6 and n <greater than or equal> 3OOrpm at 300ﾟC, hexagonal plate-like Ba-ferrite parti- cles of less than 0.1mum in size and 0.02mum in thickness can be producedHexagonal plate-like Ba-ferrite particles of submicron size are also prepared when goethite is employed as a reactant. At 300ﾟC, Ba-ferrite was formed after a short hydrothermal treatment. As the treatment proceeded, the particle size decreased. This may be due to the fact that the crystallinity is enhanced by the treatment. The particle size decreases with rising temperature and increasing stirring speed and alkali concentration.The uncertainty of size distribution of goethite particles is apt to cause a wide size distribution of prepared Ba-ferrite particles. Therefore, the operating conditions in which extremely fine goethite particles of a narrow size distribution are produced, were searched for. By shirting the oxygen concentration in the feed stream fed to the bubble column with a draft tube to a lower level at a low conversion, the size distribution of the prepared particles becomes narrow (geometric standard deviation less than 1.18). Less