TY - CONF A1 - Höhne, Patrick A1 - Kuchenbecker, Petra A1 - Lindemann, Franziska A1 - Güther, Wolfgang A1 - Rabe, Torsten T1 - Strategies to improve spray dried multi-component granules N2 - Dry pressing of ceramic materials requires homogeneously soft granules with good flowability to allow rapid die filling and to avoid packing defects. Spray-drying granulation appears to be the best method for obtaining granules with high flowability in industrial scale. But, strength reducing internal microstructural defects caused by spray-dried granules with hollow and hard shells are often observed using nano and/or multi-component starting powders. Using the example of a ZTA composite, the potential of slurry optimization, ultrasound atomization and infrared drying for better granule properties and compaction behavior were investigated. Starting granules produced in a conventional spray dryer (Niro, Denmark) with a two fluid nozzle showed typical defects like large central pores and dimples. The early step of slurry preparation already possesses an essential optimization possibility in the form of stability adjustments. Granule compaction was clearly improved upon a specific reduction in slurry stability. The second optimization opportunity to improve the granule quality was the atomization step. Implementation of an ultrasound atomizing unit into the conventional spray dryer positively affected granule size distribution and therefor flowability and as well granule yield. But, a combination of both process optimizations delivered the best sinter bodies with highest density and strength due to further reduction in maximum size and fraction of pores. As last step of a spray drying process, the drying is the focus of further investigations. A current setup implying a spray dryer prototype utilizes stacked infrared heater in a countercurrent setup delivering a further increase in granule yield and enduring spraying process stability. T2 - 93. Jahrestagung der Deutschen Keramischen Gesellschaft CY - München, Germany DA - 10.04.2018 KW - Spray drying KW - Granules KW - Destabilization KW - Ultrasound PY - 2018 AN - OPUS4-44700 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Höhne, Patrick A1 - Kuchenbecker, Petra A1 - Rabe, Torsten T1 - Superior granule properties by spray drying controlled destabilized slurries with ultrasound N2 - Homogeneous introduction of organic additives is a key of ceramic powder processing. Addition of organics to ceramic slurries holds advantages compared to dry processing like organic content reduction and a more homogeneous additive distribution on the particle surface. Investigations of the alumina slurries were primarily based on zeta potential measurements and sedimentation analysis by optical centrifugation. Both methods were combined to determine a suitable additive type, amount and composition, whereas the spray drying suitability has been ensured by viscosity measurements. Granules, yielded by spray drying of such ideally dispersed alumina slurries, are mostly hollow and possess a hard shell. Those granules cannot easily be processed and can only hardly be destroyed in the following shaping step, leading to sinter bodies with many defects and poor strength and density. The precise slurry destabilization, carried out after ideally dispersing the ceramic powder, shows a strong influence on the drying behavior of the granules and hence on the granule properties. A promising degree of destabilization and partial flocculation was quantified by optical centrifugation and resulted in improved granule properties. Spray drying the destabilized alumina slurries yielded homogeneous “non-hollow” granules without the above mentioned hard shell. Sample bodies produced of these granules exhibited a reduction of defect size and number, leading to better results for sinter body density and strength. The positive effect of the slurry destabilization has been further improved, by exchanging the atomizing unit from a two-fluid one to an ultrasound atomizer with only minor slurry adjustments necessary. The controlled destabilization and ultrasound atomization of the ceramic slurry show excellent transferability for zirconia and even ZTA (zirconia toughened alumina) composite materials. T2 - Partec 2019 CY - Nuremberg, Germany DA - 09.04.2019 KW - Destabilization KW - Slurry KW - Ultrasound KW - Atomization PY - 2019 AN - OPUS4-48291 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Höhne, Patrick A1 - Kuchenbecker, Petra A1 - Lindemann, Franziska A1 - Güther, Wolfgang A1 - Rabe, Torsten T1 - Advanced spray drying process by controlled slurry destabilization and ultrasonic atomization N2 - Spray drying of ceramic slurries aims for soft and free-flowing granules with homogenous microstructure suitable for uniaxial and isostatic pressing. A stable and continuous spray drying process of slurries with maximized solids content is a further development target, since a reduction of the energy intensive drying procedure is desirable. First part of the investigation focuses on the development of an appropriate zirconia slurry for spray drying with optimized organic additive contents (dispersant + binder + pressing and lubricating agents). Characterization and improvement of slurries are based on zeta potential measurements and investigations of the sedimentation behavior in an optical centrifuge. Therefor the slurries were spray dried with a conventional spray dryer with a two stream nozzle run in fountain mode. The controlled destabilization of the slurries was introduced, since the unwanted formation of hard granules with donut-like shape could be circumvented. Spray drying of such modified slurries resulted in soft granules without voids and finally leaded to sintered bodies with improved microstructure, density and bending strength. Expectedly, the destabilization process causes a significant increase in viscosity of the ceramic slurry. Hence, an alternative spraying concept utilizing an ultrasonic nozzle was tested. Indeed, the ultrasonic nozzle seems able to atomize slurries with viscosities beyond the capability of the regular two stream nozzles due to the slurry’s shear thinning behavior. In second part of the investigation the integration of the ultrasonic nozzle in a commercial spray dryer is shown and first results of the spraying tests are discussed. Continuous spraying processes of highly viscous alumina, zirconia and ZTA slurries were realized over an extended production period. T2 - 92. Jahrestagung der deutschen keramischen Gesellschaft CY - Berlin, Germany DA - 20.03.2017 KW - Ceramics KW - Slurry KW - Granulation KW - Spray drying KW - Ultrasound KW - Destabilization PY - 2017 AN - OPUS4-39587 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -