Gharagozlou Mehrnaz
Department of Nanotechnology and Nanomaterials, Institute for Color Science and Technology, P,O, Box 16765-654 Tehran, Iran.
Chem Cent J. 2011 Apr 13;5(1):19. doi: 10.1186/1752-153X-5-19.
Effects of calcination temperatures varying from 400 to 1000°C on structural and magnetic properties of nanocomposites formed by Co-ferrite dispersed in the sol-gel silica matrix using tetrakis(2-hydroxyethyl) orthosilicate (THEOS) as water-soluble silica precursor have been investigated. Studies carried out using XRD, FT-IR, TEM, STA (TG-DTG-DTA) and VSM techniques. Results indicated that magnetic properties of samples such as superparamagnetism and ferromagnetism showed great dependence on the variation of the crystallinity and particle size caused by the calcination temperature. The crystallization, saturation magnetization Ms and remenant magnetization Mr increased as the calcination temperature increased. But the variation of coercivity Hc was not in accordance with that of Ms and Mr, indicating that Hc is not determined only by the crystallinity and size of CoFe2O4 nanoparticles. TEM images showed spherical nanoparticles dispersed in the silica network with sizes of 10-30 nm. Results showed that the well-established silica network provided nucleation locations for CoFe2O4 nanoparticles to confinement the coarsening and aggregation of nanoparticles. THEOS as silica matrix network provides an ideal nucleation environment to disperse CoFe2O4 nanoparticles and thus to confine them to aggregate and coarsen. By using THEOS as water-soluble silica precursor over the currently used TEOS and TMOS, the organic solvents are not needed owing to the complete solubility of THEOS in water. Synthesized nanocomposites with adjustable particle sizes and controllable magnetic properties make the applicability of Co-ferrite even more versatile.
研究了煅烧温度在400至1000°C之间变化时，对以原硅酸四（2-羟乙基）酯（THEOS）作为水溶性二氧化硅前驱体，分散在溶胶-凝胶二氧化硅基质中的钴铁氧体形成的纳米复合材料的结构和磁性的影响。使用X射线衍射（XRD）、傅里叶变换红外光谱（FT-IR）、透射电子显微镜（TEM）、热重-差示扫描量热联用仪（STA，包括TG-DTG-DTA）和振动样品磁强计（VSM）技术进行了研究。结果表明，样品的磁性如超顺磁性和铁磁性对煅烧温度引起的结晶度和粒径变化有很大依赖性。随着煅烧温度升高，结晶度、饱和磁化强度Ms和剩余磁化强度Mr增加。但矫顽力Hc的变化与Ms和Mr的变化不一致，表明Hc并非仅由CoFe2O4纳米颗粒的结晶度和尺寸决定。TEM图像显示球形纳米颗粒分散在二氧化硅网络中，尺寸为10 - 30 nm。结果表明，完善的二氧化硅网络为CoFe2O4纳米颗粒提供了成核位置，以限制纳米颗粒的粗化和聚集。THEOS作为二氧化硅基质网络提供了理想的成核环境，以分散CoFe2O4纳米颗粒，从而限制它们聚集和粗化。通过使用THEOS作为水溶性二氧化硅前驱体，相比于目前使用的正硅酸乙酯（TEOS）和四甲氧基硅烷（TMOS），由于THEOS在水中完全可溶，因此不需要有机溶剂。合成的具有可调粒径和可控磁性的纳米复合材料使钴铁氧体的适用性更加广泛。
