Morsi M. Mahmoud

Microwave Crystallization of Lithium Aluminum Germanium Phosphate Solid-State Electrolyte

Lithium aluminum germanium phosphate (LAGP) glass-ceramics are considered as promising solid-state electrolytes for Li-ion batteries. LAGP glass was prepared via the regular conventional melt-quenching method. Thermal, chemical analyses and X-ray diffraction (XRD) were performed to characterize the prepared glass. The crystallization of the prepared LAGP glass was done using conventional heating and high frequency microwave (MW) processing. Thirty GHz microwave (MW) processing setup were used to convert the prepared LAGP glass into glass-ceramics and compared with the conventionally crystallized LAGP glass-ceramics that were heat-treated in an electric conventional furnace. The ionic conductivities of the LAGP samples obtained from the two different routes were measured using impedance spectroscopy. These samples were also characterized using XRD and scanning electron microscopy (SEM). Microwave processing was successfully used to crystallize LAGP glass into glass-ceramic without the aid of susceptors. The MW treated sample showed higher total, grains and grain boundary ionic conductivities values, lower activation energy and relatively larger-grained microstructure with less porosity compared to the corresponding conventionally treated sample at the same optimized heat-treatment conditions. The enhanced total, grains and grain boundary ionic conductivities values along with the reduced activation energy that were observed in the MW treated sample was considered as an experimental evidence for the existence of the microwave effect in LAGP crystallization process. MW processing is a promising candidate technology for the production of solid-state electrolytes for Li-ion battery.

Determination of Effective Constitutive Properties of Metal Powders at 2.45 GHz for Microwave Processing Applications

Abstract A reflection-transmission based rectangular waveguide approach for measuring the effective constitutive properties of metal powders at 2.45 GHz is presented. The measured effective dielectric properties of these metal powders are quite important for sintering of metal powders using microwaves, which is a new area of research. The proposed method is based on placing the metal powders of varying density into a standard glass tube, which is then positioned inside a specially designed waveguide holder for measuring the scattering coefficients at 2.45 GHz using a vector network analyser. The effective constitutive properties of the metal powders are obtained in terms of the measured scattering coefficients using the proposed two step approach. In order to validate the accuracy of the measured material properties, an electromagnetic core-shell model of the metal powders is developed. Finally, the effective dielectric properties of Cu and stainless steel powders are measured and compared with the values obtained using the electromagnetic model.