Abstract

Pressure slip casting is state of the art for the production of ceramics containing clay minerals such as sanitary ware and whiteware. Recently, pressure slip casting was presented as a forming technique for coarse grained oxide ceramics using a xanthan/guar gum solution as a stabilizer and binder. Subsequently, graded refractories consisting of two layers with a different maximum grain size were successfully produced by pressure slip casting.

The present contribution presents the further developments of the pressure slip casting of graded composites for refractory applications by demonstrating the manufacturing and characterizing of filter cakes with three layers, which have a maximum grain size of 3 mm, 1 mm and 0.5 mm, respectively.

To study the rheological behavior of the slips, an adapted falling sphere viscosimeter was designed, which uses the sphere’s acceleration phase to measure the viscosity of the slips. By repeated measurements, the thixotropy of the slips can be determined. Afterwards, the effect of the added amount of water, binder and dispersant on the thixotropy of the slips was evaluated using full factorial experimental designs.

Subsequently, the casting of graded coarse grained filter cakes was investigated in a pressure filtration cell, which uses pressurized air as the pressure medium. To study the filtration behavior of the filter cakes, the effects of the filtration pressure and filtration time of the three slip layers were firstly determined. In addition, the application of a small layer of the xanthan/guar gum binder solution as a filtration aid was evaluated. Eventually, the effects of the type of the dispersant, particle size distribution and of the used refractory raw material were analyzed.

For all three particle size distributions, a slip composition with a minimal thixotropy and fast filtration behavior was developed. Later on, stable filter cakes with an excellent bonding without cracks, pores or delamination of the three filter cake layers were achieved, which was confirmed by X-ray computed tomography investigations. Finally, thermal shock resistance investigations were performed by comparing X-ray computed tomography images before and after thermal shock, whereas a special focus was a possible delamination of the three filter cake layers.