Microstructure analysis of microwave and conventionally fired porcelain

The evolution of porcelain closed porosity during microwave and electric fast-firing is investigated and compared with that of conventionally gas-fired porcelain (taken as reference). Samples were fired in less than 70 min and are considered to be fast-fired as their processing takes less than one-half of the conventional heating time (similar to 210 min). The closed porosity relationship with the porcelain functional properties explains some of the observed differences between microwave and electrically fired porcelain. Electrically-fired samples at 1100 degrees C present a microstructure like that of the biscuit reference, fired at similar to 1000 degrees C in 460 min, whereas microwave-fired samples already show some vitrification at this temperature. The samples microwave fired between 1300 degrees C and 1380 degrees C, in 70 min, present a microstructure similar to that of reference samples fired at 1380 degrees C in 210 min. Electric fast-firing requires similar to 80 degrees C higher firing temperatures (between 1350 degrees C and 1380 degrees C than microwave fast-firing to reach similar features. Both electrically and microwave fast-fired porcelain show similar microstructure evolutions and densifications (similar to 95% of the real density, equal to 2.57 g.cm(-3)), the microwave-fired samples presenting a more developed microstructure state for the same firing temperature.