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Kaolinite–urea complexes obtained by mechanochemical and aqueous suspension techniques—A comparative study

“…In the first step up to 125 • C the adsorbed water is removed. The melting of urea takes place at 134 • C, and then the adsorbed and intercalated urea, as well as the rest of the water, are liberated in the second mass loss steps (up to about 370 • C) [30]. Finally, the thermally deintercalated kaolinite dehydroxylates between 370 and 700 • C. Although urea and the hydroxyl groups decompose separately, a decrease of ca.…”

“…The intercalation of kaolinites-i.e., the separation of kaolinite layers by reactive guest molecules such as urea, formamide, dimethyl sulfoxide, and potassium acetate-has been studied by numerous authors [23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38]. One of the earliest practical applications of the urea intercalation of kaolinite was during the Sung period in China (production of thin-walled (egg-shelled) porcelain) [23,24].…”

“…At 77 K, the layers are closer together, resulting in the formation of additional hydrogen bonds between the carbonyl groups and the hydroxyls of the octahedral layer. The kaolinite-urea intercalate can be thermally decomposed completely without dehydroxylating the mineral, although further treatments are necessary to regain the original unexpanded structure [30].…”

“…Different techniques have been used to intercalate kaolinite with urea [25][26][27][28][29][30][31][32][33][34][36][37][38]. The most common technique is the aqueous suspension method [25,[27][28][29][30].…”

“…The most common technique is the aqueous suspension method [25,[27][28][29][30]. In this case kaolin is mixed with a concentrated aqueous urea solution at 60-110 • C for 3-8 days.…”