Papers by Author: Teresa Marcelo

Abstract: The present paper focus on preliminary work carried out at INETI concerning the use of microwave radiation applied to sintering of both ceramic and metal powders. Due to the characteristics of materials-radiation interaction, microwaves can become an interesting power source in powder technology and other processing routes, since it is possible to lower the sintering temperature and shorten the sintering cycles, leading to time and energy savings. Alumina, hydroxyapatite, titanium and stainless steel powder compacts were sintered in a modified commercial oven of 2.45GHz and 1000W nominal power. Microwave susceptors were used to enable temperature rise during the initial stage of the sintering cycles. Results on densification and microstructural evaluation of microwave sintered samples are reported and compared to conventionally sintered ones, when available. For similar porosity levels upon sintering, microwave radiation generally reduces sintering times from several hours to minutes. The results obtained so far are quite encouraging since in the case of alumina and stainless steel compacts, a decrease of about 200°C in the sintering temperature was achieved. It was also found that the green density plays a key role in the densification of both metallic and ceramic powders.

Abstract: Hydroxyapatite (HA) is widely used as a bone repair material. The use of microwave radiation as energy source for powders densification opens new opportunities for sintering HA at lower temperatures than by conventional sintering (electric furnace). The aim of this work was to compare the densification behaviour of a commercial hydroxyapatite powder under microwave and conventional heating conditions through evaluation of the elastic properties of the resulting sintered materials. The effect of green density, sintering temperature and dwell time on the Young’s modulus E (measured by the impulse excitation of vibration method) of microwave sintered HA was evaluated by using the Taguchi method. Under the set of controlled parameters investigated, green density was the most significant factor affecting E. It was verified that the highest E values obtained with each sintering process are similar (104 and 105 GPa for microwave and conventional sintering, respectively). These values were obtained at 1250°C for 2 h in conventional sintering and at 1200°C for 10 min with microwave sintering. This illustrates the advantage of microwave processing on energy and time savings over conventional sintering.