Synthesis Of Aluminate Spinels Via Ultrasonic Assisted Electroless Plating

Aluminate spinel has been one kind of potential functional material due to its structural speciality and draws great attentions in magnetic materials,dielectric ceramics,semiconductors and catalysts in recent years.The conventional methods of preparing aluminate spinels include such as sol-gel,solid state reaction and hydrothermal synthesis etc.There are many defects in these conventional methods like that the reaction temperature is too high,the particle scales are overly coarse and can't be controlled efficiently.A new synthesis of aluminate spinels-electroless plating has been tried as following steps:Me/Al₂O₃→MeO/Al₂O₃,first,the Me/Al₂O₃ composite powder is prepared via electroless plating and then transforms to MeO/Al₂O₃ composite powder which is just the aluminate spinel by special heat-treatment process.The CoAl₂O₄ spinel was prepared as an example via ultrasonic assisted electroless plating.The Co/Al₂O₃ composite powder was prepared by electroless plating and transformed to CoAl₂O₄ spinels by heat-treatment.Another kind of CoAl₂O₄ spinel was prepared by sol-gel method in order to study the structure and properties of CoAl₂O₄ spinel prepared via electroless plating.The morphology, composition and crystalline structure were characterized by SEM,TEM and XRD.The spinel transition temperature of the Co/Al₂O₃ composite powder was characterized by DTA.Compared to the powder prepared by sol-gel process,the morphology, composition and structure of these two kinds of powder were tested in the same methods.The result shows that:the pretreatment of Al₂O₃ powder evidently affects the later plating process.Microstructures as dents and ledges form at the surface of powder particles after coarsening which make the powder surface coarse.Sn₂₊ions are adsorbed by the powder surface after sensitization and palladium forms at the particle surface via powder activation which is just the nucleation centre with autocatalytic properties in electroless plating.Co/Al₂O₃ composite powder was prepared via ultrasonic assisted electroless plating.The Al₂O₃ particles distribute closely and single particle is horned with clear edge before plating,but after plating the particles become bigger and disperse well due to the loose coating.The composition elements of the composite powder are Al,O,Co and composition phases are Al₂O₃ and Co which have a special structure that a large amount of Co particles enwrap the Al₂O₃ cores.Co/Al₂O₃ composite powder transform to CoAl₂O₄ spinels by heat-treatment and the transition temperature is 890℃.The powder after transition is one kind of CoAl₂O₄/Al₂O₃ composite powder with CoAl₂O₄ and Al₂O₃ composition phases and the structure is still as before that CoAl₂O₃ particles enwrap the Al₂O₃ cores.Another kind of CoAl₂O₄ spinel was prepared by sol-gel method as a comparison with the powder prepared via electroless plating.The results shows as follows:The powder prepared by these two methods gain spinel structure at the same temperature.The powder prepared by sol-gel meets to the stoichiometric proportion of cobalt aluminate.,but the element of Al is excessive in the powder prepared by electroless plating.Compared to sol-gel process, preparation of cobalt aluminate by electroless plating can not only gain smaller particle size and larger specific area but also control the particle size of the product. and reduce the cost since Al₂O₃ substitutes for part of CoAl-2O₄ and CoAl₂O₄ is more expensive.So,electroless plating is one effective method of preparing cobalt aluminate.