Study on kaolin geopolymer ceramic using powder metallurgy method

Geopolymer is an inorganic polymeric material synthesized from the dissolution and polycondensation of aluminosilicates in alkaline solutions at ambient temperature yielding an amorphous, three-dimensional polymeric framework. Geopolymers become an interest due to environmental friendly, low cost production, high early strength, durability and high chemical resistance. Kaolin is used as the aluminosilicate source in this study. The selection of kaolin offers a few advantages towards the common source materials used in geopolymer such as metakaolin. Dehydroxylation cause the decomposition of kaolinite crystals to a partially disordered structure to produce metakaolin. This reaction requires calcining of kaolin at temperatures between 500°C - 900 °C. Calcining kaolin limits the commercial application of metakaolin due to the added cost and consume much energy. Recent technology has been focusing on widening the application of geopolyrner by conversion to ceramics upon heating to higher temperature. In order to overcome problem arise, the effective method was to use powder metallurgy method whereby to sinter ground and compressed geopolymer powder. There are three parameters that involved to produce kaolin geopolyrner ceramics with optimum properties which are NaOH concentration, Na2Si03/NaOH ratios and sintering temperatures. The properties and characterization of kaolin ceramic and kaolin geopolyrner ceramic has been done using a flexural strength, density measurement, water absorption measurement, phase analysis and microstructural analysis. Results showed that NaOH molarity of 12 M, Na2Si03/NaOH ratio of 0.24:1 and sintering temperature of 1200 oc gives the highest flexural strength of 88.47 MPa, a density of 2.13 g/cm3 and water absorption of 1.2 %. Phase analysis show that the highest peak intensity of nepheline contributed to this high strength of kaolin geopolymer ceramic. Microstructural analysis show that sintering the geopolymer to 1200 °C resulted in the formation of pores possibly due to the decomposition of the material on sintering. As a conclusion, this study provides a better understanding on how NaOH concentration, Na2Si03/NaOH ratios and sintering temperature influence the properties (flexural strength, density measurement, volumetric shrinkage measurement and water absorption measurement) and characteristics (microstructure and phase) of kaolin geopolyrner ceramic. For future research, another aluminosilicate materials can be proposed for geopoJymer ceramic.