EFFECT OF QUARTZ ON THE SINTERING AND BEN DING STRENGTH OF THE PORCELAIN BODIES IN QUARTZ-FELDSPAR-KAOLIN SYSTEM

Effect of quartz on the sintering and bending strength of the porcelai n bodies in quartz-feldspar-kaolin system was investigated by the obse rvation of bulk density, 3-point bending strength test, X-ray diffract ion and the microstructures using a scanning electron microscope. Quar tz and feldspar mere jet-milled to mean particle sizes of 5 mu m and 4 .5 mu m respectively, before the wet-mixing of the raw materials. Porc elain bodies containing 45% feldspar and 55% kaolin showed full densif ication in long firing range. A mean bending strength of the body incr eased from 15 kg/mm(2) to 19 kg/mm(2) with the increase of firing temp erature from 1150 degrees C to 1300 degrees C. Quartz particles acted as inclusions before dissolution and restrained the sintering of the b ody to increase the maturing temperature. These particles hardly react ed on the eutectic melts; formed from decomposed kaolin and feldspar, and showed isolated microstructures. Therefore, the bending strength o f the body containing quartz never exceeded 16 kg/mm(2) in this experi mental conditions. These results were discussed in a viewpoint of micr ostructural developments, utilizing a phase diagram in K2O-Al2O3-SiO2 system.