Crystallization and Quantification of Crystalline and Non-Crystalline Phases in Kaolin-Based Cordierites

Abstract

Kaolin is most often used as traditional raw material in ceramic industry. The purpose of the study was to obtain understanding of the structural and chemical variability of cordierite ceramics influenced by chemical and mineralogical properties of six raw kaolins taken from different localities when they are applied in ceramics mixtures with vermiculite and sintered up to 1300 °C. The X-ray diffraction and simultaneous thermogravimetric and differential thermal analysis were used to identify and characterize crystalline mineral phases and the course of reactions during the heating. The percentages of the crystalline and non-crystalline phases were newly determined by recalculation of the bulk chemical analyses of kaolins and cordierite ceramics using Chemical Quantitative Mineral Analysis (CQMA) method. Varying amounts of minerals in kaolins: kaolinite from 73.3 to 85.0, muscovite from 4.2 to 9.9, and quartz from 6.0 to 19.5 (mass %) affected amount of cordierite/indialite from 75.2 to 85.1, enstatite from 5.8 to 8.9 (when are calculated as their maximal possible percentages), and non-crystalline phases from 8.8 to 15.1 (mass %) in cordierite ceramics. Regression analysis predicted high relationship between quantity of: (a) kaolinite in kaolins and crystalline cordierite and (b) quartz in kaolins and non-crystalline phases in the ceramics. The migration of potassium from muscovite into the cordierite structure, melting point and crystallization of cordierite/indialite phases and pore size variability in relation to impurity of kaolins are documented and discussed.

Cordierite ceramic through glass and ceramic routes from kaolin and talc

“…Increasing the temperature up to 1200 °C/2h endorsed the crystallization of cordierite as the main phase with little protoenstatite, spinel and cristobalite. At 1300 °C/2h, cordierite was crystallized with spinel in both CS5 and CS6 ceramic samples (Fig 2 [17]. We can imagine the results of sintering between 1000 and 1300 °C temperatures as follow:…”

Alkali-Activated Metakaolin and Fly Ash as Unfired Ceramic Bonding Systems

“…The observed weight loss of 13% of the KA sample in the temperature range of 400-680 • C (Figure 1) is connected to the dehydroxylation process characterized by the loss of hydroxyl groups. The dehydroxylation of kaolinite is an endothermic process as evidenced by the shape of the corresponding peak on the DTA curve showing the minima at 506 • C. An additional exothermic peak at 1000 • C observed on the DTA curve at 1000 • C is connected to the formation of the mullite phase [42,43]. Based on the results of the TG/DTA analysis, the temperature of the KA calcination 550 • C was deliberately chosen to be slightly higher for the KA treatment to ensure the quantitative dehydroxylation of kaolinite in the whole volume of the sample.…”

Effects of Kaolin Additives in Fly Ash on Sintering and Properties of Mullite Ceramics

“…Two samples originating from the kaolin Pilsen Basin were marked K1 and K2 and one sample from the Karlovy Vary region was marked K3. These kaolins generally contain kaolinite in an average amount of 75% by mass and the original minerals, in particular quartz, muscovite/illite and feldspars from their original rocks [30,31].…”