Optimization of the dispersion/flowing properties of ball clay used in sanitaryware ceramic productions and its influence on the properties of green and fired products

In this study, the commercial ESC-3 clay was used here with combination various dispersant (Na2SiO3, Dolapix PC67, Dolapix CE64, Dolapix SPC7, Darvan CN ve Darvan A821), the flowing behaviour (flow time and thixotropy) were investigated for optimum casting conditions (most appropriate dispersant and dispersant dose) were determined. The parameters kept constant during the ford cup measurements are solid ratio of slurry (% 60 as weight), temperature (27 ±1 oC), mixing speed (800 rpm). Considering the flow curves (flowing time versus the dispersant dose) of ESC-3 clay slurry it is determined that the most suitable dispersant is Dolapix PC67 and its dose is ~ % 0.1. Thereafter, in the constant experimental conditions which are present above and only with Dolapix PC67 (dispersant) dosages (on the solid base % 0, % 0.03, % 0.1,% 1) slurry samples were prepared and slip casted in to gypsum molds and thus the bar shaped (13.2 x 3.2 x 1.25 cm) samples were formed. The green samples were dried at 21-24±1 oC, afterward they were placed in the kiln for firing at 1200 oC for 1 hour. Some physical (shrinkage, water absorption, apparent porosity, bulk density) and mechanical strength (three point bending) tests were applied on both dried (green) and fired samples and also their micro structure were investigated using SEM. Some of the obtained results are as follows; (i) The dispersant addition to the slurry have positive effect on the properties of green and fired samples. For example: for the samples prepared with the clay slurry without dispersant the linear shrinkage and mechanical strength are average % 4.82 and 2.65 N/mm2 respectively, whereas they became average % 3.96 and 2.68 N/mm2, respectively with % 0.1 Dolapix PC67 addition. Similarly, physical and mechanical properties of the fired samples were improved. The total volume shrinkage and three point bending strength of the fired samples obtained from the dispersant free slurry were % 15.66 ve 18.78 N/mm2, respectively, whereas these values were became % 28.92 ve 22.78 N/mm2, respectively with with % 0.1 Dolapix PC67 addition. (ii) Determination of the optimum dispersant amount used in the ceramic slurry by slip casting is an important case. When the properties of green/final products and flowing curves measured by ford-cup are considered, it might be expressed that the dispersant dosage at which the shortest flowing duration was obtained does not always mean the best results in the physical/mechanical properties of green/final products. (iii) The relationship between the green and fired samples which were prepared from the slip with different dispersant dosages, and the flowing curves of these slips was not able to observe from their SEM images.