Preparation of Ultrafine Magnetic Particles Using Microemulsions and Vesicles

近年来，人们对制备均匀尺寸的超细磁性氧化物的需求越来越大，这些氧化物主要用于计算机数据存储、音频和视频记录、磁性液体和某些微波器件的制造。提出的研究计划的主要目标是利用微乳液处理和泡内沉淀合成磁性氧化物纳米颗粒。这些都是独特的方法，可以用来制备粒度分布窄的超细、微均一的颗粒，这是固相反应、本体沉淀、溶胶-凝胶法和喷雾干燥等传统方法无法实现的。微乳液处理包括在油包水微乳液的水核(通常尺寸为10-50 nm)内沉淀前驱体氢氧化物或磁性氧化物的碳酸盐。然后，这些纳米级的前体将被进一步加工和焙烧，以产生磁性氧化物。囊内沉淀包括水相沉淀或在由囊泡定义的有机约束微域内的还原。每个小泡都变成了一个尺寸在几百埃量级的亚微型反应器。捕获在囊泡内空间中的阳离子将与从囊泡外区域渗透到囊泡壁上的阴离子反应，或者被光解/化学还原而形成产物。囊内共沉淀以及对被包裹的种子颗粒的沉淀将被用于创建纳米复合材料，从而打开了通过在近分子尺度上操纵产品的形态和组成来定制产品功能的可能性。研究结果将说明这两个过程(微乳处理和囊内沉淀)在涉及的机制和其中形成的产品方面的相似和不同之处。

In recent years there has an increasing demand for the preparation of ultrafine magnetic oxides of uniform size which are mainly used in computer data storage, audio and video recording, magnetic fluids and fabrication of certain microwave devices. The primary objective of the proposed research program is to synthesize nanoparticles of magnetic oxides using microemulsion processing and intravesicular precipitation. These are unique methods which can be used to produce ultrafine, microhomogeneous particles with a narrow size distribution, which cannot be achieved by conventional methods such as solid-state reaction, bulk precipitation, sol- gel processing and spray drying. Microemulsion processing consists of the precipitation of precursor hydroxides or carbonates of magnetic oxides within the aqueous cores (typically 10 - 50 nm in size) of water-in- oil microemulsions. These nanosize precursors would then be further processed and calcined to produce the magnetic oxides. Intravesicular precipitation consists of aqueous phase precipitation or reduction inside organically constrained microdomains defined by vesicles. Each vesicle becomes a submicroreactor of dimensions of the order of a few hundreds of angstroms. Cations trapped in the intravesicular spaces will react with anions permeating through the vesicle wall from the extravesicular region or be photolytically/chemically reduced to form the product. Intravesicular coprecipitation as well as precipitation upon encapsulated seed particles will be used to create nanocomposites, opening up the possibility of tailoring the functionality of products by manipulating both their morphology and composition at a near molecular scale. The results of the research would delineate the similarities as well as differences between the two processes (microemulsion processing and intravesicular precipitation) in relation to the mechanisms involved and the products formed in them.