16th International Conference
on Microwave and High Frequency Heating

18-21 September 2017, Delft, The Netherlands
11:00   Materials processing (2)
Chair: Georgios Dimitrakis
11:00
15 mins
SYNTHESIS AND SINTERING OF LEAD-FREE PIEZOELECTRICS BY ONE-SINGLE STEP BY MICROWAVE TECHNOLOGY
Ánggel Lagunas-Chavarría, María G. Navarro-Rojero, María Dolores Salvador-Moya, Amparo Borrell, Felipe Penaranda-Foix, José M. Catalá-Civera
Abstract: The (Ti,Zr)PbO3 based piezoelectric ceramics are widely used in actuators, sensors, and transducers by their remarkable piezoelectric properties [1]. However, for a sustainable future, its necessary to find alternative compounds to substitute the use of the toxic lead. The (K,Na)NbO3 (KNN) based systems are a promissory alternative due to their relatively strong piezoelectricity and good Curie temperature, however, some difficulties during synthesis are caused by the volatility of alkali elements at high temperatures and the moisture absorption of precursors. The common processing (mixed oxide route) of KNN involve two heating steps; (i) calcination (~850 ºC for ~5 h), and (ii) sintering (~1125 ºC for ~4 h) [2]. In this work, a monomodal microwave was used to processing (K0.5,Na0.5)NbO3 piezoelectrics system in one-single step by two permanency times corresponding to the calcination and the sintering temperatures. The conditions of dwell time, final temperature and power were variated to determinate its influence over the structural properties of KNN. By this new approach technology, the total time-cycle to obtain KNN material was 50 min and the XRD analysis and microstructural characterization reveal revolutionary results in the formation of perovskite structure.
11:15
15 mins
MICROWAVE MODIFICATION OF SITKA SPRUCE TIMBER FOR INCREASING WOOD PERMEABILITY
Grigory Torgovnikov, Peter Vinden
Abstract: MICROWAVE MODIFICATION OF SITKA SPRUCE TIMBER FOR INCREASING WOOD PERMEABILITY G. Torgovnikov and P. Vinden School of Ecosystem and Forest Sciences, University of Melbourne, 4 Water St. Creswick, Victoria 3363, Australia; e-mail: grigori@unimelb.edu.au Keywords: microwave wood modification, permeability, Sitka spruce, wood impregnation Abstract Sitka spruce (Picea sitchensis) is a non-durable species with a low permeability and difficult to treat with preservatives and resins and obtain a suitable distribution of preservatives. The controlled application of microwave energy can modify the wood structure creating new pathways for liquid flow and improving the permeability of the timber. Experimental study of Sitka wood microwave (MW) modification and impregnation showed opportunity to get required preservative distribution in timber cross section. MW processing provides preservative uptake increase by 3.7–5.6 times compared to controls. Microwave conditioning of the timber followed by impregnation with copper naphthenate solution results in a 34% reduction in modulus of rupture and modulus of elasticity. The strength reduction is a result of significant modification to the surface of the timber. Microwave energy required for timber conditioning is 81 kW-h/m3. Results highlight that a particular design of applicator is required to concentrate the MW energy in the outer layer of the timber allowing an envelope treatment to be achieved. Economic assessment of Sitka spruce MW modification for preservative treatment showed reasonable specific costs AU$ 19 to $33/m3 which are acceptable for industry and provide good commercial opportunities.
11:30
15 mins
MICROWAVE SINTERING OF Na-β’’-Al2O3 ELECTROLYTE IN SINGLE MODE CAVITIES
Cristina Leonelli, Roberto Rosa, Stefano Fasolin, Paolo Veronesi, Cecilia Mortalò, Georgios Dimitrakis, Monica Fabrizio
Abstract: Microwave assisted sintering of Na-β’’-Al2O3 solid electrolyte is here investigated in full details. The use of single mode cavities indeed allows an accurate monitoring of all the different parameters affecting the sintering process, like the forward, the reflected and the dissipated power, as well as the surface temperature evolution of the sample. Despite sintering experiments at the conventional 2450 MHz frequency, attempts to sinter pure Na-β’’-Al2O3 phase powders have also been conducted at the higher frequency of 5800 MHz. Dielectric properties of the loose powders have been previously measured as a function of temperature in order to both partially predict their experimental heating behaviour as well as obtain fundamental information needed for the simplified numerical simulation of the heating experiments, conducted also with the aim to investigate the better load configuration to assure the most homogeneous heating treatment. Hybrid microwave-assisted sintering resulted the best option to reach homogeneous and controllable heating avoiding as much as possible thermal runaway and arcing phenomena. The effect of the different frequencies, the heating rate employed, the temperature reached and the dwell time on the obtained density and on the resulting microstructure will be fully detailed.