Additives for densification of fine-grained Y2O3: from solid state to liquid phase sintering
NAJAFZADEHKHOEE A. 1, TALIMIAN A. 2, GIRMAN V. 3, POYATO R. 4, GALLARDO-LÓPEZ A. 4,5, GUTIÉRREZ-MORA F. 4,5, HVIZDOš P. 3, MACA K. 6,7, GALUSEK D. 1,2
1 Joint Glass Centre of the IIC SAS, TNUAD, and FChPT STU, Tren?ín, Slovakia; 2 Centre for Functional and Surface Functionalised Glass, Alexander Dub?ek University of Tren?ín, Študentská 2, 91150 Tren?ín, Slovakia, Tren?ín, Slovakia; 3 Institute of Materials Research, Slovak Academy of Sciences, Watsonova 47, 040 01 Košice, Slovakia , Košice, Slovakia; 4 Instituto de Ciencia de Materiales de Sevilla (CSIC-US), Américo Vespucio 49, Sevilla,41092, Spain, Sevilla, Spain; 5 Dpto. de Física de la Materia Condensada, Universidad de Sevilla, Apdo. 1065, Sevilla, 41080, Spain, Sevilla, Spain; 6 Central European Institute of Technology, Brno University of Technology, Purky?ova 123, 612 00 Brno, Czech Republic, Brno, Czechia; 7 Faculty of Mechanical Engineering, Brno University of Technology, Technická 2, 612 00 Brno, Czech Republic, Brno, Czechia
Although sintering additives modify the properties of sintered powder and make the sintering energy efficient by shortening the process, yttrium oxide bodies produced with the addition of sintering aids are often characterized by large grains. In the present work, we revisit the role of sintering additives in the densification and grain growth of nano-sized yttrium oxide during solid-state and liquid-phase sintering. Commercial nano-sized yttria was doped with various concentrations of transition metals. The doped powders were consolidated using spark plasma sintering; the effects of dopants were investigated in terms of densification behaviour and grain growth as a function of dopant concentration. The results showed that the electron structure and ionicity of doping cations determine their impact on defects chemistry, “critical concentration,” and sintering behaviour of doped-Y2O3. All solid-state dopants have a similar effect on densification and grain growth.
Liquid phase sintering was carried out by using limited amounts of Al2O3 and SiO2, up to 1 wt.%, as sintering additives producing a liquid phase by reacting with Y2O3 at high temperatures. Using the SiO2-Al2O3 additive simultaneously reduces the sintering temperature and time and suppresses grain growth; the samples containing SiO2-Al2O3 additive exhibited finer microstructure than additive-free samples after sintering at 1650°C for 2 min. The reactions during liquid phase sintering were investigated by measuring the wetting behaviour of liquids in Y2O3-Al2O3-SiO2 and the precipitation of crystalline phases at high temperatures upon continuous changes in chemical composition during sintering. The crystallization of yttria-rich aluminium-silicate phases at the grain boundaries at high temperatures is responsible for suppressing the grain boundary motion.
Acknowledgement:
This research work has been supported by the Research Agency of the Ministry of Education, Science, Research and Sport of the Slovak Republic, by the project: Advancement and support of R&D for "Centre for diagnostics and quality testing of materials" in the domains of the RIS3 SK specialization, Acronym: CEDITEK II., ITMS2014+ code 313011W442. This project has also received funding from the European Union´s Horizon 2020 research and innovation programme under grant agreement No 739566.
