AP0859 Structural and Mechanical Properties of Porcelain Prepared from Iraqi Raw Materials with Non-plastic Clay Additives

Abstract

Porcelain is one of the most important technical ceramics, but the shrinkage in dimensions after firing resulting from plastic clays is one of the shortcomings that manufacturers suffer from.  Therefore, this work aims to reduce shrinkage by adding non-plastic powder (fired kaolin (Grog): prepared by firing plastic clay up to 1100°C) and extend their effect on some other properties of porcelain. The composition of hard porcelain is: 60 wt.% kaolin, 20 wt.% flint and 20 wt.% potash feldspar as Iraqi raw materials. Non-plastic clay was added to the porcelain by 25, 30, 35 and 40 wt.% instead of kaolin. Forming the samples by axial pressing into discs then fired at 1300°C. FE-SEM images showed the emergence and increasing of the mullite phase as a result of the porcelain firing with the addition of fired clays. XRD analysis confirmed the presents of mullite phase in addition to the cristobalite phase. Increasing the non-plastic clay from 25 to 40 wt.% led to a significant decrease in linear shrinkage from 12.6 to 5.4%, increased the porosity from 12.2 to 15.1%, decreased the bulk density from 2.25 to 2.16 g/cm³, this clearly affected the decrease in the diametral strength from 23.26 to 10.48 MPa. The results obtained determined the possible application range for construction, to include thermal insulation, wall tiles and decoration.