Recent Researches on Microwave Processing for Materials and Environmental Technology in Our Group

Microwave processing has been taken into consideration for various purposes,not only for cooking,drying and enhancement of solution reaction kinetics but also various high temperature processes.In the presentation,selected research projects conducted in our group will be reported.The first topic is the microwave processing for recycling valuable metals from by-products originated in the iron and steel industries.We studied microwave application to handling of the pickling sludge,which occurs in stainless steel rolling process.Microwave use for dehydration and carbo-thermic reduction processes was attempted.Next,because Pb elution from the wasted funnel glass used for the cathod-ray tube is one of the serious environmental problems,microwave application to leaching process of Pb from a Pb-conatining glass was performed.The kinetic study of the acid dissolution was performed.Last topic is fabrication of filter material for burning particulate matter(PM)from diesel engine(Diesel Particulate Filter:DPF).Microwave rapid heating characteristics are applied to the cold start(ignition)condition of engine for prevention of PM emission.

Fabrication of Porous SiO_2·RO/SUS Composite Body for DPF (Diesel Particulate Filter) and Microwave Heating Behavior

Glass/stainless steel porous composite body were prepared by the polyurethane sponge replica method using slurries containing mixture of SiO_2-RO/30 vol%SUS.Sintered porous samples were obtained which consists of well-distributed stainless steel particles within the glass matrix.Such a microstructure is desired for the purpose as a soot particulate filters(DPF)utilizing microwave rapid heating in cold start phase.Heating ability of the fabricated porous composite body was carried out placing the specimen in the maximum H-field of a 2.45 GHz single mode applicator. Heating behavior of the samples was mainly influenced by the volume fraction of stainless steel.Higher heating rate was observed for samples with higher stainless steel fraction.Due to the different microwave absorbability of the materials, stainless steel particle in the porous matrix structure was firstly heated up by microwave and transferred the heat energy throughout the whole sample.Increasing of the fraction of the stainless steel particle in the matrix structure led the better heating;however the strength of the samples decreased.

Combustion Synthesized Porous Body of Fe_3O_4/Al System by Controlled Microwave Heating and Heating Behavior of the Products

Microwave-induced substitutional combustion reaction was utilized to fabricate porous ceramic composite from Fe_3O_4/Al powder mixtures.The porous composite body was obtained by controlling the combustion reaction progress in a 2.45 GHz single mode applicator.Prior to the fabrication of the porous body,heating behavior of the powder mixtures were studied in the separated electric(E)and magnetic(H)fields.In addition,heating ability of the microwave fabricated porous product was also investigated.Fe_3O_4 powder can be heated up easily in both maximum H and E field, but a better heating was observed in the maximum H field.Regardless of the mixtures ratio(mixing compositions), maximum H field shows better heating characteristics.In E-field heating,temperature of the Fe_3O_4 samples decreased sharply when Al powder was added.However,the same phenomenon was not observed in the maximum H field heating. Thus,fabrication of the porous composite body was carrying out in maximum H field.Through an adequate control of the reaction progress,products with a porous structure consisting of well-distributed metal particles in the alumina and/or hercynite matrix were obtained.Consequently,heating of the fabricated porous composite body was also been successfully carried out in the maximum H field.Product phases and microstructure were the main factors influencing the heating ability of the porous composite body.