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.     

Pyrolysis and gasification characterization of sewage sludge for high quality gas and char production

A study on pyrolysis, steam gasification, and carbonization-activation was conducted to produce energy and resource from waste sewage sludge. Carbonization-activation is a sequential process of pyrolysis and steam gasification. The experiment was conducted with a batch-type fixed bed reactor. A comparative analysis on the formation characteristics of products, such as gas, tar, and char, was conducted to evaluate the three cases. For sludge char, carbonization-activation showed the largest amount of porosity in the char, and its specific surface area was 80.28 m²/g with an average pore diameter of 6.229 nm. The best adsorption ability of benzene, a light tar, was 175 mg/g. For the producer gas, steam gasification obtained the largest amount of 20.1 L. Similarly, carbonization-activation showed a large value of 16.6 L. Hydrogen and carbon monoxide concentrations were higher in the producer gas due to steam reforming compared with carbonization-activation. Energy yields were 209 kJ and 226 kJ for steam gasification and carbonization-activation, respectively. The amount of tar formation did not show a significant difference, but the largest one was found in steam gasification. The gravimetric tar amount for steam gasification was 23.5 g/Nm³. However, the selected light tar displayed the lowest concentration for the carbonization-activation. Such concentrations were 2.79 g/Nm³, 0.75 g/Nm³, 0.14 g/Nm³, and 0.14 g/Nm³ for benzene, naphthalene, anthracene, and pyrene, respectively. Therefore, carbonization-activation was found to be the most effective process for producing high quality sludge char and producer gas for utilizing waste sludge into renewable energy and resources.     

Removal of Boron from Silicon-Tin Solvent by Slag Treatment

To eliminate B effectively from Si for its use in a solar cell, a novel process involving the slag refining of molten Si with Sn addition was investigated. The partition ratio of B between CaO-SiO₂-24 mol pct CaF₂ slag and Si-Sn alloy at 1673 K (1400 °C) was determined by the chemical equilibrium technique. It was found that the partition ratio of B was remarkably increased with the increase in Sn content of alloy, which attributes to the increase in activity coefficient of B as well as the oxygen partial pressure. The partition function was accounted as much as 200 when the alloy composition was Si-82.4 mol pct Sn, which was much higher than the reported values in the range of 1 to 3. The required amounts of slag used for B removal from Si-30, 50, and 70 mol pct Sn melts were only 15.6 pct, 6.5 pct, and 1.2 pct of that used for the removal of B directly from MG-Si without Sn addition in a single slag treatment.     

Deformation Behavior Estimation of Aluminum Foam by X-ray CT Image-based Finite Element Analysis

Aluminum foam is a lightweight material owing to the existence of a large number of internal pores. The compressive properties and deformation behavior of aluminum foam are considered to be directly affected by the shape and distribution of these pores. In this study, we performed image-based finite element (FE) analyses of aluminum foam using X-ray computed tomography (CT) images and investigated the possibility of predicting its deformation behavior by comparing the results of FE analyses with those of actual compressive tests. We found that it was possible to create an analytic model reflecting the three-dimensional (3D) pore structure using image-based modeling based on X-ray CT images. The stress distribution obtained from image-based FE analysis correctly indicates the layer where deformation first occurs as observed in actual compressive tests. Also, by calculating the mean stress of each plane perpendicular to the direction of compression based on the stress distribution obtained from image-based FE analysis, it was found that deformation begins in the layer containing the plane with maximum stress. It was thus possible to estimate the layer where deformation begins during the compression of aluminum foam.