Servicenavigation

Detailseite

Zurück

Projekt Druckansicht

New ceramic processes and their mechanical characterization

Fachliche Zuordnung Glas und Keramik und darauf basierende Verbundwerkstoffe
Metallurgische, thermische und thermomechanische Behandlung von Werkstoffen
Förderung Förderung von 2006 bis 2015
Projektkennung Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 27296763
 
Erstellungsjahr 2015

Zusammenfassung der Projektergebnisse

In this project a rigorous investigation of ceramic processing methods was performed. The first part focused on the retention of nanocrystallinity and investigated the effect of electric field on sintering. However, no evidence for a supporting effect from electric current or field was found for comparative study about FAST/SPS sintering. Three different types of oxide materials (insulator, ion conductor and semiconductor) show the same activation energy, sintering mechanism and grain growth behavior in comparison to hot pressing. Surprisingly, the sintering of nanocrystalline ZnO is highly promoted by adsorbed water. Here, hydroxyl ion diffusion mechanism is identified to support densification, which reduces activation energy for diffusion and finally results into a reduction of sintering temperature from 800 °C to 400 °C for full densification. Hence, retention of nanocrystallinity is permitted, which depends on a low sintering temperature. Moreover, this hydroxide ion diffusion enhanced densification is expected to be applied on several other metal oxide systems during sintering. Anyway, only a limited temperature-time window exists as the diffusion process is activated by elevated temperatures, but the desorption of water increases simoultaneously. Thus, high heating rates are necessary as provided by FAST/SPS sintering method. Interestingly, nanocrystalline ZnO shows a high sensitivity concerning flash sintering under electrical current/field. Second, the size dependend melting point and evaporation behavior was analysis on bismuth oxide. Here, an innovative calorimetric device was developed, which extends phase transition investigations on oxide materials (which was only accessible for metallic materials up to now). A better understanding and calculation of the multiphase equilibrium would be helpful for any high temperature application and vacuum processes. Furthermore surfaces play a decisive role for evaporation and for properties of nanomaterials. Since they are responsible for most changes at the nanoscale a better understanding of surface structures, or at least knowledge of the average surface energy from independent methods are important. Adsorbates, atmosphere and temperature have a decisive impact on these properties and should be considered, too. Such knowledge would allow a better assessment of models and the size-dependent properties could be determined much more accurately. In summary no definite statements can be given at the current state of research with the chip calorimeter. But once working, the possibilities are manifold and would contribute to complete the picture of size-, and atmosphere-dependent phase transitions in (bismuth) oxide nanoparticles. It would also add valuable thermodynamic information about the phase transitions. Third, the drying behavior of thin films was investigated. New types of characterization methods were used/developed to evaluate in-situ the mechanical properties of those ceramic films. The presence of PVA binder has significant influence on the drying behavior of aqueous alumina films. It was observed that the end of shrinkage, maximum viscosity, elastic modulus and drying stress of the films coincides with the end of the constant rate period (CRP). The addition of PVA to alumina lowers shrinkage, elastic modulus and drying stress and increases viscosity. A theoretical framework was proposed to calculate the shrinkage, densification rate and drying stress for the films up to the end of CRP.

Projektbezogene Publikationen (Auswahl)

 
 

Zusatzinformationen

© 2024 DFG Kontakt / Impressum / Datenschutz

Textvergrößerung und Kontrastanpassung