16th International Conference
on Microwave and High Frequency Heating

18-21 September 2017, Delft, The Netherlands
09:45   Materials processing (1)
Chair: Balasubramaniam Vaidhyanathan
15 mins
Lorena Gil, María Dolores Salvador-Moya, Felipe Penaranda-Foix, José M. Catalá-Civera, Antoni J. Canós, Amparo Borrell
Abstract: Ceramic materials are commonly used as biomaterials in prostheses because they have superb mechanical properties and do not produce allergic reactions or rejection. The most popular ceramic materials in this field are zirconia-based materials. Therefore, the purpose of the present study is to sinter zirconia doped with ceria and toughened with alumina by non-conventional method; microwave sintering technology. This bioceramic has already been sintered by a conventional method at high temperature (1450 ºC) with good results. Nevertheless, this process requires a lot of time (>9h) and high energy consumption and, consequently, it has an important environmental impact in ceramic powder processing. However, using microwave technology it is possible to reduce both, time and production costs in the sintering process. For this reason, the aim of this investigation is to sinter zirconia-alumina composites doped with Ce by microwave and evaluate the Ce effect in microwave radiation, as well as assess the mechanical properties, final density and microstructure of the samples obtained. Furthermore, the studied material is compared with zirconia-based bioceramics that have already been sintered by microwave by the authors [1]. All obtained properties of the composites with Ce sintered by microwave were better than obtained by conventional method.
15 mins
Gabriel Llorens-Vallés, Pedro Plaza-González, Antoni J. Canós
Abstract: Dielectric properties of materials describe their ability to interact with microwaves. Thermal variations in the materials alter such properties. Considering that microwave heating is progressively becoming one of the most used methods for material processing the dynamic monitoring of dielectric properties of materials with temperature emerge as a major issue at this respect [1]. Single-mode resonators have been previously used to obtain dielectric properties over temperature. Such kind of resonators relies on mechanical tuning which reduces its operating range [2]. The dual-mode resonator used for the present work allows the simultaneous measuring and heating of the sample with a variable solid state amplifier. Thus, the geometry of the applicator is not modified. The use of polymers is common, as target materials or as materials for transport, fixing /protecting elements, etc., due to the fact that metal parts cause arching problems when microwave fields are applied. Depending on the use, the requirements on the polymers’ dielectric properties are different. Thus, the dielectric characterization with temperature of such materials is demanded for the design of microwave devices [3]. In this work, the dielectric properties with temperature under microwave heating of several polymers like Rexolite, PTFE, PSU1000 and others are presented.
15 mins
Amir Shelef, Yuri Nerovni, Mihael Fugenfirov, Eli Jerby
Abstract: The recently proposed implementation of localized microwave-heating (LMH) for 3D-printing and additive-manufacturing (AM) [1, 2] is further studied and developed here. A solid-state (LDMOS) amplifier with a positive-feedback loop [3] is employed here (instead of a magnetron) as the microwave generator for the LMH-AM process. The feasibility of metal-powder solidification and incremental consolidation of ~10 mm3 powder batches is demonstrated here at lower power levels, in the order of ~100 W. The stepwise LMH solidification quality in metal powders is improved at various gaseous environments (e.g. of CO2 or argon). The powder-batch fixation prior to their LMH is performed either by ceramic holders or by a contact-less magnetic-confinement technique [4]. Mechanical tests and micro-structure observations enable us to compare the quality of the LMH-AM products with respect to other AM techniques. Theoretical analyses of (a) the metal-powder magnetic fixation effect, and (b) the magnetically-based LMH mechanism, are presented. Various causes are identified for the temperature dependence of the metal-powder magnetic permeability (real and imaginary components). The expected feasibility and limitations of the proposed LMH-AM technology, as well as its pros and cons, are discussed. References 1. Jerby, E., Y. Meir, A. Salzberg, E. Aharoni, A. Levy, X. Planta Torralba, B. Cavallini, Additive Manufact., 2015, 6, 53-66. 2. E. Jerby, X. Planta, R. Rubio, A. Salzberg, B. Cavallini, Y. Meir, Prov. Pat. App. US-61/449,674. 3. Meir, Y., E. Jerby, IEEE Trans. Microwave Theory Tech., 2012, 60, 2665-2672. 4. Fugenfirov, M., Y. Meir, E. Jerby, Submitted to Int’l Jour. Comp. Math. Elect. Electron. Eng. (COMPEL).