Exploring droplet coagulation for shaping ceramics: a physico-chemical study
4 May 2018
Campus Middelheim, A.143 - Middelheimlaan 1 - 2020 Antwerpen (route: UAntwerpen, Campus Middelheim
Organization / co-organization:
Faculty of Science
Vera Meynen, Bart Michielsen, Steven Mullens
PhD defence Judith Pype - Faculty of Science
Ceramic microspheres are widely used in a broad range of applications, all with their own demands concerning the ideal correlation between properties versus performance. In order to comply with these different requirements, the shaping method needs to offer good control of the microspheres properties. Droplet coagulation provides the opportunity of combining the physical aspects of the granulation with the chemical impact of the coagulation.
Applying the droplet coagulation in a vibrational nozzle set-up benefits the physical control of the granulation process, with the potential of tuning the microsphere size and architecture. The interaction of the feed pressure and frequency of the vibration facilitates the shaping of a wide range of ceramic microspheres.
The droplet coagulation makes use of the ionotropic gelation of sodium alginate with a multivalent cation. In this, the coagulation is controlled by the properties of the coagulation salt and sodium alginate. During this PhD study, an experimental approach is followed to study the flexibility of the coagulation chemistry in shaping ceramics. The coagulation parameters were defined by the development of a model system by using calcium as the multivalent cation, indicating the calcium incorporation in the ceramic microspheres as a hetero-element. Other coagulation salts were used to study their potential of either eliminating the hetero-element or using it as a functional element.
Another feature of the droplet coagulation is its generic use for various powder sources. The versatility was examined by selection of three different waste fines with distinct differences in origin, chemical composition and morphology. An apparent difference could be noticed on the pre-processing requirements, based in their origin. Waste fine which were produced in high temperature processes (ash residues), could be shaped without any pre-processing. Sludges from the wastewater treatment facilities needed several pre-processing steps to obtain a well disperse suspension for shaping the microspheres. The variation in polymorph composition after sintering caused by their unique chemical composition indicated the potential of shaping mullite microspheres by smart mixing the waste fines. The Al2O3 rich alum sludge was stoichiometric mixed with either fly ash or rice husk ash to examine the impact of the waste fines on the mullite formation and properties.
In summary, the flexibility of droplet coagulation for shaping ceramic microspheres was explored in this PhD. Its physico-chemical control provided the opportunity of shaping ceramics with a broad range of functionalities.