Heating of Metal Particles in a Single-Mode Microwave Applicator

Abstract

Microwave (MW) heating behavior of various metal particles was investigated using a single-mode applicator. Considering the distributions of the electromagnetic fields in the wave guide, specimens were placed at four specific positions with respect to the electric and the magnetic fields of MW. They were heated at conditions of constant power input.It was demonstrated that iron particles were heated well in the magnetic field, and that ferro-magnetic metal particles having the higher Curie point was heated the better. It was possible to heat iron bulk particles ($3 mm) in a magnetic field without occurrence of electric discharge. In the range of nickel particle size between 45 and 150 mm, the particles with the smaller size were heated the better.Nickel oxide (NiO) was heated well only in the position of large electric field, which indicates that the heating was caused by the different (dielectric heating) mechanism from the metal particles.From these results, contribution of magnetic field to heating metal particles was discussed, considering the heating mechanisms of the magnetic loss and the eddy current loss. The dependence of the heating rate of metal particles on their size was discussed in terms of the heat transfer rate.

Microwave Sintering of Ni-Based Bulk Metallic Glass Matrix Composite in a Single-Mode Applicator

“…A mixture of Ni 52:5 Zr 15 Nb 10 Ti 15 Pt 7:5 glassy alloy powders and Sn powders failed to show noticeable response in E-field like other metals, 13,20) but could couple with MW and be heated up rapidly to appointed temperatures in H-field. As heating was performed by manipulating the three stubs manually, all heating curves are not smooth.…”

“…It has also been found that heating behavior of Ni particles above Curie point was dependent on the particle size and finer particles could be heated better in a range between 45 and 150 mm. 13,22) Although the detailed mechanism of the MW sintering metallic powders has not been interpreted clearly and differs with the materials, it might be believed that the mechanism of magnetic loss up to the Curie point and the eddy current loss are responsible for MW heating effect on Ni 52:5 Zr 15 Nb 10 Ti 15 Pt 7:5 metallic glassy powders with a particle size of no larger than 63 mm in Hfield. The retention of amorphous phase in the sintered specimens below 783 K may attribute mainly to the rapid heating and cooling, short hold time and low sintering temperature in MW sintering.…”

“…However, in E-field no noticeable response was seen, only in H-field these powders could be heated by MW energy absorption up to appointed temperatures (783, 813, 843 and 873 K) and held for about 600 s. The details of the experimental procedure as well as computer simulations indicating E and H field separation can be found in a recent work. 13) Temperature measurement of the MW-heating specimens was performed with an optical method (PhotoriX system, Luxtron, Santa Clara, CA, USA), using a sapphire rod for the light guide. In this method, it is not possible to measure the specimen temperature below 623 K. The adjustment of the temperature was done by controlling the three stubs to minimize the reflected power (P r ), while the input power (P f ) was kept constant.…”

“…8) Compared with conventional sintering, MW radiation can provide more efficient and rapid heating and sintering because it is a volumetric heating involving conversion of electromagnetic energy into thermal energy, which is instantaneous, rapid and efficient. 9,10) It has been shown recently that some metals in the form of powder can absorb MW at room temperature, be heated efficiently and rapidly, and be sintered at least as quick as or faster than upon conventional heating, [11][12][13][14] though bulk metals cannot be heated by MW since they are opaque to MW and are good reflectors. Recently microwave radiation was successfully applied to heat metallic glassy powders 15) due to it can provide some advantages over conventional heating such as direct volumetric heating, substantial energy savings, reduction in the processing time and lower environmental hazard.…”

Microwave Heating of Thin Au Film

“…1) On the other hand, recently there has been much interest in microwave heating and sintering of metal powder. [2][3][4][5][6][7] This is because metal powder has a large specific surface area compared to metal bulk. Thin metal film is similar to metal powder from a view point of specific surface area.…”