Microwave-driven asbestos treatment and its scale-up for use after natural disasters.

Asbestos-containing debris generated by the tsunami after the Great East Japan Earthquake of March 11, 2011, was processed by microwave heating. The analysis of the treated samples employing thermo gravimetry, differential thermal analysis, X-ray diffractometry, scanning electron microscopy, and phase-contrast microscopy revealed the rapid detoxification of the waste by conversion of the asbestos fibers to a nonfibrous glassy material. The detoxification by the microwave method occurred at a significantly lower processing temperature than the thermal methods actually established for the treatment of asbestos-containing waste. The lower treatment temperature is considered to be a consequence of the microwave penetration depth into the waste material and the increased intensity of the microwave electric field in the gaps between the asbestos fibers resulting in a rapid heating of the fibers inside the debris. A continuous treatment plant having a capacity of 2000 kg day(-1) of asbestos-containing waste was built in the area affected by the earthquake disaster. This treatment plant consists of a rotary kiln to burn the combustible waste (wood) and a microwave rotary kiln to treat asbestos-containing inorganic materials. The hot flue gas produced by the combustion of wood is introduced into the connected microwave rotary kiln to increase the energy efficiency of the combined process. Successful operation of this combined device with regard to asbestos decomposition is demonstrated.

Microstructure analysis of Fe3O4 heated by microwaves in a TE10 mode cavity: surface and volume characterization.

Detailed observations of the single mode H-field heated magnetite was conducted. The heated magnetite contains a shiny area, which exists in the width of 5 mm and thickness in 1 mm. The observation of the area reveals wavy surface patterns. The microstructures of the shiny area consists of an undefined phase and a magnetite phase which fills the space among the undefined phases. The XRD pattern from the shiny area is different from that of the random magnetite crystals, which is caused by the magnetite grains having almost same orientation in large area. There are banded areas surrounding the undefined phase of several microns in thickness, in which the existence of nano-sized crystals is indicated by means of EBSD and TEM.

Fundamentals and applications of microwave heating of metals.

As the fundamentals of microwave (MW) interaction with metals, boundary conditions of electromagnetic (EM) field on metal surface are discussed, which consider the EM field in the metal surface layer in terms of surface impedance. Experimental report on heating behavior of separated electric (E-) and magnetic (H-) fields of metal particles and films are shown. Temperature peak formation at the first heating curves was observed in both cases, which are discussed considering the microstructural alteration by MW heating. In the last half section, various reports on MW heating of metal are reviewed. They were classified into the major application for sintering and materials fabrication. And also, its usage as a heating aid of glasses and soils, topics on metal hydride and catalytic metal particles are included.

Numerical simulation of temperature distribution in multi-phase materials as a result of selective heating by microwave energy.

In order to discuss the temperature distributions due to microwave (MW) selective heating of multi-phase solids, numerical analysis was conducted. The simulation was performed assuming the dielectric heating mechanism in a dual phase solid in which one phase has much larger permittivity (loss factor) than the other In addition, an electric (E-) field inside the solid was assumed to be homogeneous, the value of which was estimated by a macroscopic electromagnetic (EM) simulation of the solid body placed in a TE10 cavity. In this EM simulation, a single phase solid body having an averaged permittivity value of the dual-phase is assumed. Next, heat transfer calculations were performed in order to obtain the temperature distribution in the dual phase solid, assigning different permittivity values to the phases giving rise different heat source terms in the thermal conduction equation. The boundary conditions were either adiabatic or considering the thermal energy dissipation by radiation to obtain the realistic temperature in the model solid. It was shown that a larger temperature difference resulted in larger particle size. The model considering the temperature dependence of the permittivity predicted a largest temperature difference during several ten milli-seconds.

Microwave heating characteristic of multilayered structures in a single-mode cavity.

In this study, nonconductor (PZT), semiconductor (Si) and conductor (Pt/Ti) whose permittivity and permeability are distinctive are prepared into various multilayered structures for exploring the heating behavior of microwave (2.45 Hz) in a single-mode cavity. The heating efficiency of the semiconductor and conductor was much higher at the maximum of H field than that of E field. At the H maximum, the Si layer was useful to generate high temperature and the Pt/Ti accelerated the heating rate. At the E maximum, the Si layer was also in favor of obtaining high temperature, but the Pt/Ti layer partially suppressed the microwave heating. The effect of PZT on the heating processing was not obviously observed at the maximum of both H and E fields.

Fabrication of Ni-Nb-Sn metallic glassy alloy powder and its microwave-induced sintering behavior.

In the present study, we prepared Ni59.35Nb34.45Sn6.2 metallic glassy alloy powder by an argon gas atomization process. Microwave (MW)-induced heating and sintering was carried out by a single-mode 2.45 GHz MW applicator in the separated magnetic field or electric field using the obtained glassy powders. The structure and thermal stability of the sintered glassy alloy specimens were investigated.

Prophylactic effect of Lactobacillus oral vaccine expressing a Japanese cedar pollen allergen.

Lactic acid bacteria (LAB) represent an attractive delivery vehicle for oral allergy vaccine because of their safety as a food microorganism as well as their potent adjuvant activity triggering anti-allergic immune response. Here, we report the generation of recombinant LAB expressing a major Japanese cedar pollen allergen Cry j 1 (Cry j 1-LAB), and their prophylactic effect in vivo. To facilitate heterologous expression, the codon usage in the Cry j 1 gene was optimized for the host LAB strain Lactobacillus plantarum by the recursive PCR-based exhaustive site-directed mutagenesis. Use of the codon-optimized Cry j 1 cDNA and a lactate dehydrogenase gene fusion system led to a successful production of recombinant Cry j 1 in L. plantarum NCL21. We also found that oral vaccination with the Cry j 1-LAB suppressed allergen-specific IgE response and nasal symptoms in a murine model of cedar pollinosis.