Yttrium oxide ceramics have properties that allow us to use them in different areas, in particular as a host for luminescent materials [1]. In this case, Y2O3 ceramics must be highly dense to reach high transparency, which is achieved only if there are no defects in the material volume. An example of such defects can be porosity, which reduces the value of the optical transmittance of ceramics due to light scattering and affects the density of the material [2]. The choice of raw materials and parameters of their processing significantly affects the microstructure and optical properties, and therefore is a very relevant issue. In this regard, the purpose of this work is to study the influence of the morphology of the initial powders and the way of their treatment on the quality of IR-transparent Y2O3 ceramics. In our research, we investigated the morphology of four commercial powders (Nippon, Stanford, US Research Nanomaterials (further US RN), Solvay) under different milling conditions. 3 mol.% ZrO2 was chosen as a sintering additive. Samples were obtained by uniaxial pressing followed by cold isostatic pressing (CIP) and vacuum sintering at 1735 °C for 32 h. At the first stage, morphology of these powders was investigated. It was found that Stanford has large and hard agglomerates, which are difficult to break during pressing. Nippon, Solvay and US RN powders are characterized by a fairly homogeneous morphology with soft agglomerates. Among all samples, only Y2O3-Nippon ceramics were transparent, which explains by optimal specific surface area (SSA; BET) of this powder. The favorable particle size distribution and SSA allow to obtain a denser compact that can then sinter to pore-free transparent ceramics. Solvay and US RN powders are characterized by high SSA values, which cause the formation of inhomogeneities in the sample volume during pressing. Thus, Y2O3 Nippon powder was chosen for the next step and the effect of milling conditions (speed and time of the process) was investigated for the selected Y2O3 powder. It was established that milling at 300 rpm for 65 min gives the best result. SEM, BET and DLS data confirm that this powder has optimal parameters. In this case, SSA is 21.3 m2/g and average particle and agglomeration size is about 70 and 480 nm, respectively. Ball milling at 100 and 200 rpm at 65 min finally leads to larger particles size. Conversely, the increase of milling time to 10 h provides finer particles. However, too small particle size and high SSA of powder lead to formation of some defects in green bodies during pressing. Y2O3 ceramics obtained from this powder is characterized by a relative density of 100% and the highest value of optical transmittance among all those tested (78.3% at 1100 nm). Acknowledgments: The authors are grateful to the JECS Trust for funding (Contract No. 2021293) [1] J. Petry, R. Komban, C. Gimmler, et al, Nanoscale Adv. 4, (2022) 858-864. [2] S. H?íbalová, W. Pabst, J. Eur. Ceram. Soc. 41 (2021) 2169-2192.
IR-transparent yttrium oxide ceramics, the effect of raw powders and powder processing
J Hostasa
2023
Abstract
Yttrium oxide ceramics have properties that allow us to use them in different areas, in particular as a host for luminescent materials [1]. In this case, Y2O3 ceramics must be highly dense to reach high transparency, which is achieved only if there are no defects in the material volume. An example of such defects can be porosity, which reduces the value of the optical transmittance of ceramics due to light scattering and affects the density of the material [2]. The choice of raw materials and parameters of their processing significantly affects the microstructure and optical properties, and therefore is a very relevant issue. In this regard, the purpose of this work is to study the influence of the morphology of the initial powders and the way of their treatment on the quality of IR-transparent Y2O3 ceramics. In our research, we investigated the morphology of four commercial powders (Nippon, Stanford, US Research Nanomaterials (further US RN), Solvay) under different milling conditions. 3 mol.% ZrO2 was chosen as a sintering additive. Samples were obtained by uniaxial pressing followed by cold isostatic pressing (CIP) and vacuum sintering at 1735 °C for 32 h. At the first stage, morphology of these powders was investigated. It was found that Stanford has large and hard agglomerates, which are difficult to break during pressing. Nippon, Solvay and US RN powders are characterized by a fairly homogeneous morphology with soft agglomerates. Among all samples, only Y2O3-Nippon ceramics were transparent, which explains by optimal specific surface area (SSA; BET) of this powder. The favorable particle size distribution and SSA allow to obtain a denser compact that can then sinter to pore-free transparent ceramics. Solvay and US RN powders are characterized by high SSA values, which cause the formation of inhomogeneities in the sample volume during pressing. Thus, Y2O3 Nippon powder was chosen for the next step and the effect of milling conditions (speed and time of the process) was investigated for the selected Y2O3 powder. It was established that milling at 300 rpm for 65 min gives the best result. SEM, BET and DLS data confirm that this powder has optimal parameters. In this case, SSA is 21.3 m2/g and average particle and agglomeration size is about 70 and 480 nm, respectively. Ball milling at 100 and 200 rpm at 65 min finally leads to larger particles size. Conversely, the increase of milling time to 10 h provides finer particles. However, too small particle size and high SSA of powder lead to formation of some defects in green bodies during pressing. Y2O3 ceramics obtained from this powder is characterized by a relative density of 100% and the highest value of optical transmittance among all those tested (78.3% at 1100 nm). Acknowledgments: The authors are grateful to the JECS Trust for funding (Contract No. 2021293) [1] J. Petry, R. Komban, C. Gimmler, et al, Nanoscale Adv. 4, (2022) 858-864. [2] S. H?íbalová, W. Pabst, J. Eur. Ceram. Soc. 41 (2021) 2169-2192.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
