Iron and steel slag: An alternative source of raw materials for porcelain ceramics

Iron and steel industry generates substantial amount of inorganic solid wastes namely blast furnace (BF), Linz-Donawitz (LD) slag from the metallurgical process and fly ash from thermal power plant which creates environmental pollution when dumped in open land. In this investigation, BF and LD slag are incorporated in quartz free fly ash based porcelain system and changes in their properties, phase and microstructural evolution were studied. The samples shown very high flexural strength (>50 MPa) in the temperature range of 1200-1300 °C. Appearance of anorthite crystals were observed when feldspar is gradually replaced by BF and LD slag.  The body with a combination of BF slag and feldspar possesses the highest strength (90 MPa) due to the presence of mullite grains and fewer fracture origins caused by large difference in the thermal expansion coefficient between the glassy matrix, quartz and anorthite grains during cooling process. Total replacement of feldspar by equal percentage of BF and LD slag resulted formation of almost 100% anorthite grains with distinct change in crystal morphology. A strong pre-stress is produced on the glassy phase that surrounds the anorthite grains by the large difference in thermal expansion coefficient between the glassy phase and anorthite grain.