Gnanaprakash G, Philip John, Jayakumar T, Raj Baldev
Metallurgy and Materials Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102, Tamilnadu, India.
J Phys Chem B. 2007 Jul 19;111(28):7978-86. doi: 10.1021/jp071299b. Epub 2007 Jun 20.
We investigate the effect of digestion time and alkali addition rate on the size and magnetic properties of precipitated magnetite nanoparticles. It is observed that the time required to complete the growth process for magnetite nanocrystals is very short (approximately 300 s), compared to long digestion times (20-190 min) required for MnO and CdSe nanocrystals. The rapid growth of magnetite nanoparticles suggests that Oswald ripening is insignificant during the precipitation stage, due to the low solubility of the oxides and the domination of a solid-state reaction where high electron mobility between Fe2+ and Fe3+ ions drives a local cubic close-packed ordering. During the growth stage (0-300 s), the increase in the particle size is nominal (6.7-8.2 nm). The effect of alkali addition rate on particle size reveals that the nanocrystal size decreases with increasing alkali addition rate. The particle size decreases from 11 to 6.8 nm as the alkali addition rate is increased from 1 to 80 mL/s. During the size decrease, the lattice parameter decreases from 0.838 to 0.835 nm, which is attributed to an increase in the amount of Fe3+ atoms at the surface due to oxidation. As the alkali addition rate increases, the solution reaches supersaturation state rapidly leading to the formation of large number of initial nuclei at the nucleation stage, resulting in large number of particles with smaller size. When alkali addition rate is increased from 1 to 80 mL/s, the saturation magnetization of the particles decreases from 60 to 46 emu/g due to the reduced particle size.
我们研究了消化时间和碱添加速率对沉淀法制备的磁铁矿纳米颗粒尺寸和磁性的影响。据观察，与MnO和CdSe纳米晶体所需的较长消化时间（20 - 190分钟）相比，磁铁矿纳米晶体完成生长过程所需的时间非常短（约300秒）。磁铁矿纳米颗粒的快速生长表明，在沉淀阶段奥斯特瓦尔德熟化并不显著，这是由于氧化物的低溶解度以及固态反应占主导地位，其中Fe2 +和Fe3 +离子之间的高电子迁移率驱动了局部立方密堆积有序化。在生长阶段（0 - 300秒），颗粒尺寸的增加微不足道（6.7 - 8.2纳米）。碱添加速率对颗粒尺寸的影响表明，纳米晶体尺寸随碱添加速率的增加而减小。当碱添加速率从1 mL/s增加到80 mL/s时，颗粒尺寸从11纳米减小到6.8纳米。在尺寸减小过程中，晶格参数从0.838纳米减小到0.835纳米，这归因于表面Fe3 +原子因氧化而增加。随着碱添加速率的增加，溶液迅速达到过饱和状态，导致在成核阶段形成大量初始核，从而产生大量尺寸较小的颗粒。当碱添加速率从1 mL/s增加到8 mL/s时，由于颗粒尺寸减小，颗粒的饱和磁化强度从60 emu/g降低到46 emu/g。
