Design of core-shell structured particles via spray pyrolysis

Abstract

Core shell structure refers to a structure whose core substance is enveloped by other substance as a shell, in which the core is the major component with key properties and the shell improves performance of core substance, and/or inhibits undesired reaction of surface as protection layer, and/or brings new properties. The core-shell structured particles often exhibit superior physical, optical, electronic, chemical, and biomedi-cal properties as compared to single components counterpart. Accordingly, the core-shell structured particles are widely used in optics, magnetism, biomedicine, catalysis, energy conversion and storage. Several methods have been used to coat core particles, such as co-precipitation, heterogeneous precipitation, sol-gel process, homogeneous precipitation, hydrothermal process, emulsion evaporation and spray drying. However, most processes to prepare the core-shell structured particles are constructed with 2 stages; one is manufacture stage of core particles and another stage is to coat the surface of the core particles. This type of processes has disadvantages such as; it takes a longer time for process and requires high unit cost. Even it is more difficult to meet the additional requirements of the coated-particle properties such as aggregation-free morphology, high purity, homogeneous composition, narrow size distribution and small particle size. Thus, in this dissertation, studies were conducted on synthesis of particle with the core-shell structure by using the spray pyrolysis process. The one-step method for preparing the core-shell structured particles was proposed using spray pyrol-ysis in which one phase of substances is separated out from a core substance by difference of physical properties because the substance with high melting point tends to bond together due to strong bond energy between molecules so that it forms the core, while the substance with relatively lower melting point is being pushed outward and forms the coating...