Kaolin intercalated by urea. Ceramic applications

• The intercalation degree of kaolinite by urea is 69% when aqueous mixing is used.
• Bonds are formed between inner-surface hydroxyls of kaolinite and NH groups of urea.
• Intercalation increases the densification rate and reduces the sintering temperature.
• Intercalated kaolinite behaves similarly to intensively grounded kaolinite.
• A high intercalation degree of kaolin can be attained in industrial processes.

Kaolinite–urea complexes were prepared with kaolinite from KGa-1 kaolin by two techniques, mixing and ball-milling at room temperature in water. The intercalation degree was found to be 72% and 69% respectively. Urea-intercalated kaolinite has potential applications in industry, since it change most of the chemical and thermal behaviors. Particularly, ion intercalation into kaolinite structure changes the amount of reactive acidic and basic sites on the internal and external surfaces. In this study XRD patterns and infrared spectroscopy of kaolinite–urea complexes confirm the intercalation of urea into kaolinite by the expansion of the basal spacing of kaolinite from 0.715 nm to 1.069 nm. The expansion of kaolinite is due to entering urea into interlayers that confirms the occurrence of hydrogen bonding between urea and kaolinite. Thermal analyses (TG, DSC and thermodilatometry) evidence changes in transformation temperatures of intercalated kaolinite. The sintering densification is shifted to lower temperature and kaolinite–urea complexes can be used in new ceramics for building with lower CO2 specific emission.