Introduction of Closed Pores into Pottery Body by Addition of Microspherical Hollow Flyash Powder

The microstructures of ceramics obtained by firing a pottery material blended with hollow ceramic microspheres of flyash origin to introduce closed pores into the ceramics were examined. The bulk density of the ceramics was found to decrease proportionally to the flyash balloon content, and it was slightly bigger than the apparent density when the firing temperature was set to 1260°C (standard temperature for firing the pottery material). The addition of flyash balloon resulted in the formation of both open and closed pores in the ceramics. The open pore ratio increased linearly with flyash content up to 57 vol%, and the ratio upturned further above 57%. The closed pore ratio increased approximately with the volume of the flyash balloons. The pore formation mechanism was investigated by scanning electron microscopy, energy dispersive X-ray analysis and X-ray diffraction measurements. The optimum firing temperature for achieving a well-vitrified body increased with decreasing potassium content due to the diffusion of potassium from the pottery material to the flyash balloons. Interspaces among the balloons contributed to the open pore volume at the balloon concentrations larger than 57 vol%. Light ceramics were successfully produced by firing at 1350°C which caused the sealing of the open pores.