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Preparation of fine spinel and cordierite ceramic powders by mechano-chemical techniques
Low temperature synthesis of cordierite and magnesium aluminate spinel powders has been attracting attention in recent years due to new potential applications. The use of mechanochemical methods to achieve partial or complete structural disorder as a tool to lower the sintering temperatures has also been increasingly reported. In this study, spinel was produced by intense milling of a mixture of Mg(OH)2 and Al(OH)3. Detailed phase characterization of the synthesized loose powder spinel was performed using XRD and DTA. SEM was used for the analysis of ground powder morphology and particle size. Amorphization was observed after 50 minutes of grinding at 600 rpm. 110 minutes of grinding led to partial growth of spinel. Temperatures less than 1000oC were able to produce spinel powders. In the second part of the study, cordierite was synthesized by mixing proper amounts of various combinations of alumina or Al(OH)3 (as a source of Al2O3), kaolin (as a source of SiO2 and Al2O3), and talc (as a source of MgO and SiO2). Detailed microstructural characterization of the synthesized pellets was performed by using SEM. Other techniques used for analysis of powder products were XRD, DTA and FTIR. One of the four possible mixture combinations was processed by using mechanochemical synthesis. This technique was analyzed by the use of statistical experimental design (SED) in order to understand the effects of process variables on the amount of synthesized product. Temperature was the most important factor and grinding speed-grinding time interaction was the next significant variable. These results were expected because lower grinding speed and longer grinding time generates a similar amount of grinding action compared to higher speeds and lower times. The cordierite mixture was completely amorphized by grinding at 300 rpm for 60 minutes based on XRD peak intensity measurements. Temperatures as low as 1150oC were able to produce cordierite ceramic. In addition to the mechanochemical technique, the effect of additive use and the combined effect of additive use and grinding on cordierite synthesis were also studied. These factors further decreased the synthesis temperature down to about 1050oC.