Ashis Kumar Mandal

An overview on microwave processing of material: A special emphasis on glass melting

ABSTRACT Material processing adopting microwave heating has emerged as an alternative tool owing to faster processing, a cleaner environment, and several other advantages. This review provides a summary of recent reports of microwave synthesis of materials. This study reviews the use of microwave energy for application in several material processing technologies apart from food processing. A special emphasis has been made in the processing of glass adopting microwave energy. Melting of glass comprising SiO2, P2O5, B2O3 as the main building block has been discussed. It has been revealed that silica, a microwave transparent material as reported earlier, can be heated under microwave heating directly. Microwave absorption of raw materials and different glass system has been discussed. Dielectric properties, particularly loss tangent or loss factor, are presented for some glass composition. Less evaporation of ingredient and low contamination from the crucible wall are noticed during glass melting using microwave heating. Enhanced iron redox ratio (Fe+2/∑Fe) in microwave processing may be considered an advantage in the preparation of heat absorbing filter glass. Small-scale glass melting using the microwave heating has a significant impact on energy and time saving. However, the challenges associated with the upscaling glass melting with microwave heating and future scope have been talked about.

Energy Efficient Melting of Glass for Nuclear Waste Immobilization Using Microwave Radiation

A base glass suitable for immobilization of nuclear waste was prepared by melt quenching technique using microwave radiation as a heating source. Microwave absorption behavior of major raw materials was studied and presented. The glass was also prepared in a conventional resistance heating furnace using the same batch composition. X-ray diffraction analysis of the sample prepared in microwave furnace has confirmed glass formation, which is in a similar agreement with that of glass prepared in the conventional resistance heating furnace. Comparative property analysis indicated identical glass prepared in both the routes. In microwave furnace, total power consumption was found to be ˜5 kWh with the maximum power demand of 1.5 kW. Electrical power consumption in resistance heating furnace was studied in three different capacities of furnaces and compared with that of microwave furnace. Energy saving in the range ˜60% was recorded in microwave heating compared to resistance heating furnace. Further, the time needed to melt the glass in a microwave furnace was recorded less than 2 hr compared to 6–7 hr needed in resistance heating furnace. Thus, microwave heating yields identical glass consuming substantially less electrical power and time, signifying possibility of drastic reduction of cost in glass melting.

Microwave Preparation of SiO2-B2O3-Na2O-K2O-CaO-Fe2O3-TiO2 Glass System

This study reports preparation of glass composition (54.50 wt.%) SiO2, (10.80 wt.%) B2O3, (14.20 wt.%) Na2O, (1.20 wt.%) K2O, (6.00 wt.%) CaO, (4.00 wt.%) Fe2O3 and (9.30 wt.%) TiO2 by melt quenching method using direct microwave heating and conventional resistive heating. Study of dielectric loss factor of the glass as function of temperature illustrated increasing loss factor above 370 o C, 550 o C, 650 o C and 900 o C, indicating enhanced microwave absorption by the glass at above these temperatures. Chemical analysis results of both the glasses depicted more volatilization loss of volatile ingredients in conventional heating. The study of chemical durability was performed from leachate analysis describing less leaching of Na2O, K2O and other constituents from glass melted in microwave furnace. Glass transition temperatures (Tg) were found to be 576.3 o C and 569.5 o C for glass melted in conventional and microwave heating route, respectively. Laboratory experiment of glass melting utilizing microwave energy as an alternate heating source demonstrated 70%-75% electrical power saving.

Microwave-assisted brazing of alumina ceramics for electron tube applications

Alumina was joined with alumina using microwave-assisted and conventional brazing methods at 960∘C for 15 min using TiCuSil (68.8Ag–26.7Cu–4.5Ti in wt.%) as the brazing alloy. The brazed joints were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, Vickers microhardness evaluation, brazing strength measurement and helium leak test. X-ray diffraction analysis confirmed the formation of Ti-based compounds at the substrate-filler alloy interfaces of the microwave and conventionally brazed joints. The elemental compositions at the joint cross-section were determined by energy dispersive X-ray analysis. Vickers microhardness measurement indicated reliable joint performance for the microwave-assisted brazed joints during actual application in an electron tube. Brazing strength measurement and helium leak test provided the evidence for good alumina-alumina joint formation.

A Comparative Spectrophotometric Study Using Ferrozine and 1,10-Ortho-phenanthroline to Evaluate the Iron Redox Ratio (Fe(2+)/ΣFe) in Glass Prepared by Microwave Heating.

In the present study, Fe-doped barium borosilicate glass has been melted at 1250°C under microwave heating. The iron redox ratio (Fe(2+)/total Fe) in the glass is investigated by two spectrophotometric methods. A novel decomposition technique has been optimized to measure the ferrous oxidation state in glass. Ferrozine was chosen as a specific complexing reagent; it forms a deep violet color complex with Fe(2+) and has a broad absorbance peak centered at ∼562 nm. 1,10-ortho-phenanthroline develops an orange color complex with Fe(2+) (having an absorbance peak centered at ∼510 nm) and has been used to determine ferrous ion in glass. Both the methods are compared and the estimated redox ratio was found to be higher in the ferrozine method. The error limit of measurement has been determined as 0.012 and 0.023 for the ferrozine and 1,10-ortho-phenanthroline methods, respectively.

Toxic Metal Removal Using Biosorption Process and Inertization of Generated Hazardous Metal-Laden Biosorbent

The tannery industry waste was used in this study as a low-cost biosorbent. The presence of large number of functional groups in the tannery waste resulting from both live and dead microbial fractions positively favours for higher and faster sequestration rate of metal ions. The batch mode of biosorption process were performed with dried activated tannery sludge for removal of Ni(II), Co(II), Zn(II) and Cd(II) ions in multi-metal system. Zn(II) and Cd(II) ions showed 99% removal efficiency within 10 min of contact time, while Ni(II) and Co(II) attained 98% removal at 20–24 h. The influence of various experimental variables like pH, contact time, biosorbent dosage and initial metal concentrations was studied. The biosorbent was characterized using FESEM-EDX and XPS analysis.