Effect of calcium carbonate addition on the properties of mambong clay by using slip casting method

Kelantan state, Malaysia has several traditional heritages including Mambong pottery, that originally from Kampung Mambong, Kuala Krai, Kelantan. This pottery is made of Mambong clay to produce steam pots, covered jars, and other products using hand building and wheel throwing techniques in which the production process is slower with ununiformed shapes and sizes. The traditional products have thicker pottery that make them heavier. They are also very weak, less durable, and fragile. In fact, the low demand of this pottery is due to these weaknesses. A research had been carried out to improve the strength, shrinkage percentage, density and porosity, and also the fabrication technique of Mambong clay to overcome these weaknesses. The different CaCO3 contents which are 0, 5, 10, and 15 wt% were added into Mambong clay as an additive and fired with different firing duration (4, 8, and 12 hours) to get the optimum duration to improve the physical and mechanical properties in order to strengthen the flexural strength, lower the linear shrinkage and weight, and increase the production rate by using slip casting method. The sample preparation started by preparing the fine clay powder with the size under 425 μm followed by the clay mixing process with CaCO3 and water to form the slip. The POP mould was used to form the bar shaped samples and dried completely with oven at 80 °C for 24 hours. The samples were fired at 900 °C in the furnace for 4, 8, and 12 hours. XRF analysis result shows that the highest element existed in the Mambong clay is SiO2 with 55.3 wt%. XRD analysis shows the results of 10wt% CaCO3 content from each firing duration as compared to the raw Mambong clay. The main crystalline phases are quartz, muscovite and calcite. Furthermore, the increasing of CaCO3 composition causes the decrement trend for bulk density and the shrinkage percentage and also the increment in apparent porosity percentage of samples. SEM analysis shows that the increasing of CaCO3 content has increased the pores distribution. The strength analysis shows that sample 10 wt% from all firing durations is the best sample. MOR test shows the results of 6554.359, 9599.263, and 9663.613 N/mm2 for 4, 8, and 12 hours respectively. Bending strength analysis resulted in 5.985, 8.344, and 8.576 N/mm2 respectively. Then, the impact strength for 10 wt% samples are 50.210, 59.183, 70.000 kJ/m2 respectively. For the toughness of sample, 10 wt% samples showed 2510.500, 2959.125, and 3500.000 kJ/m3 respectively. Based on the overall results, 12 hours firing duration is the best sample with the highest strength among all samples.