Prospects of microwave processing: An overview

Abstract

Microwave processing has been emerging as an innovative sintering method for many traditional ceramics, advanced ceramics, specialty ceramics and ceramic composites as well as polymer and polymer composites. Development of functionally gradient materials: joining; melting; fibre drawing; reaction synthesis of ceramics; synthesis of ceramic powder, phosphor materials, whiskers, microtubes and nanotubes; sintering of zinc oxide varistors; glazing of coating surface and coating development have been performed using microwave heating. In addition, microwave energy is being explored for the sintering of metal powders also. Ceramic and metal nanopowders have been sintered in microwave. Furthermore, initiatives have been taken to process the amorphous materials (e.g. glass) by microwave heating. Besides this, attempt has been made to study the heating behaviour of materials in the electric and magnetic fields at microwave frequencies. The research is now focused on the use of microwave processing for industrial applications.

Impact of Surface Chemistry on Microwave-Induced Degradation of Atrazine in Mineral Micropores

“…The microwave heating, particularly formation of microscale "hot spots" within the micropores, was expected to cause gradual removal of nonstructural water from the zeolite (SI Figure S3), leaving behind the relatively microwave-transparent mineral phase. 2,3 As the zeolite got increasingly dry, it became more permeable for the microwave. Overall, the essentially micro- a The microwave complex permittivities of the dealuminated Y zeolites were calculated from the effective complex permittivities (ε eff ) measured for the composites of zeolite and polyethylene wax based on the volumetric mixing law: ε eff = V Z ε Z + V P ε P , where V Z and V P are the volume fractions and ε Z and ε P are the permittivities of zeolite and polyethylene wax, respectively.…”

“…1,2 Interactions of materials with microwave occur at the molecular level, with the external electromagnetic field inducing reorganization of the electrical charges, including migration of free or bound charges and rotation of electric dipole. 3 Complex permittivity (ε*), which contains a real part (ε′) and an imaginary part (ε″), is used to characterize the response of a given material to alternating electric fields. The relative dielectric constant, ε′, describes the ability of a dielectric material to store energy under the influence of an external electric field, whereas the loss factor, ε″, represents the dissipation of the absorbed energy as heat.…”

“…5 Microwave radiation is often used as an alternative to conventional thermal heating because of the faster heating rate, selective heating, better process control, and no direct contact of heated materials. 1,3,6 In addition, microwave radiation can also have "microwave specific effect" by accelerating reaction rates, improving yields, and selectively activating or suppressing reaction pathways compared to the use of conventional heating. 4,6−10 Microwave radiation has found uses in the environmental field as well: it has been applied in decontamination of soils, sludge, and wastewater, and regeneration of activated carbon, with the significant benefit of drastic reduction in the processing time.…”

Fabrication of Reliable Joints of Alumina Ceramics by Microwave-Assisted Reactive Brazing Technique

“…To solve this type of non-uniformity, microwave hybrid heating (MHH) 8) has been proposed by the researchers. In this method some susceptors that are good absorbers of microwave energy at a specific temperature range, used to provide extra heat flux to the sample by conduction and radiation of heat energy.…”

The Application of Response Surface Methodology in Hydrotropic Microwave Assisted Extraction of Andrographolide

“…It is due to evaporation of the internal moisture content which result in the subsequent rupture of the plant tissue and the release of the active compounds into the organic solvent. Therefore, MAE is an interesting alternative to conventional extraction methods, especially in the case of extractions of thermolabile compounds [13,16].…”