Production and characterization of porous mullite ceramics

In this thesis study, production and characterization of müllite (3Al2O3.2SiO2) ceramics with macroporous, needle-like morphology capable of controlling pore size and distribution were carried out by polymeric sponge method. CC31 kaolin has been used because of its economic advantages in producing porous mullite ceramics, its relatively low formation temperature for mullite formation, and its significant advantages such as allowing a very good microstructure. Kaolen is a relatively pure clay that has been used for centuries in the production of ceramic materials and forms mullite phase when sintered at high temperatures. In this study, polymeric sponge method is preferred because it is economical to produce mullite based porous ceramic materials and easily applicable. Depending on the desired application area, the amount of pores, pore size and distribution expected from the porous material are changing. In this thesis, porous mullite ceramics with uniform pore size and porous mullite ceramics with functional graded material design were produced. A preferred type of sponge polyurethane foam for the polymeric sponge process. Polyurethane foam is preferred in the current study because it can be easily removed from the structure at relatively low temperatures. Thermal behaviors of polymeric sponge was investigated by TG-DTA analysis. The effect of sintering temperature, time and rate on the development of mullite morphology in kaolin mullite production process was studied by sintering porous ceramic samples at 1300-1600°C. The phase compositions of the sintered samples were analyzed by XRD analysis. Microstructure studies of mullite ceramics were carried out by SEM analysis. The shrinkage behavior, density and compressive strength of porous mullite ceramics were determined depending on the production conditions.