The grain growth behavior in the (1-x)K_0.5Na_0.5NbO₃-xCaZrO₃ (KNNCZ-x) system is studied as a function of the amount of CZ and grain shape. The (1-x)K_0.5Na_0.5NbO₃-xCaZrO₃ (KNNCZ-x) powders are synthesized using a conventional solid-state reaction method. A single orthorhombic phase is observed at x = 0 – 0.03. However, rhombohedral and orthorhombic phases are observed at x = 0.05. The grain growth behavior changes from abnormal grain growth to the suppression of grain growth as the amount of CaZrO₃ (CZ) increases. With increasing CZ content, grains become more faceted, and the step-free energy increases. Therefore, the critical growth driving force increases. The grain size distribution broadens with increasing sintering time in KNNCZ-0.05. As a result, some large grains with a driving force larger than the critical driving force for growth exhibit abnormal grain growth behavior during sintering. Therefore, CZ changes the grain growth behavior and microstructure of KNN. Grain growth at the faceted interface of the KNNCZ system occurs via two-dimensional nucleation and growth.

In this study, the effects of kaolin addition on the properties of reticulated porous diatomite-kaolin composites are investigated. A reticulated porous diatomite-kaolin composite is prepared using the replica template method. The microstructure and pore characteristics of the reticulated porous diatomite-kaolin composites are analyzed by controlling the PPI value (45, 60, and 80 PPI) of the polyurethane foam (which are used as the polymer template), the ball-milling time (8 and 24 h), and the amount of kaolin (0–50 wt. %). The average pore size decreases as the amount of kaolin increases in the reticulated porous diatomite-kaolin composite. As the amount of kaolin increases, it can be determined that the amount of inter-connected pore channels is reduced because the plate-shaped kaolin particles connect the gaps between irregular diatomite particles. Consequently, a higher kaolin percentage affects the overall mechanical properties by improving the pore channel connectivity. The effect of kaolin addition on the basic properties of the reticulated porous diatomite-kaolin composite is further discussed with characterization data such as pore size distribution, scanning electron microscopy images, and compressive strength.

The grain growth behavior of M-type Sr hexaferrite (SrM) grains is investigated with the addition of MnCO₃. First, the SrM powder is synthesized by a conventional solid-state reaction. The powder compacts of SrM are sintered at 1250°C for 2 h with various amounts of MnCO₃ (0, 0.5, 1.0, and 4.0 mol%). There is no secondary solid phase in any of the sintered samples. Relative density increases when MnCO₃ is added to the SrM. Obvious abnormal grain growth does not appear in any of the SrM samples with MnCO₃. The average grain size increases when 0.5 mol% MnCO₃ is added to the SrM. However, as the amount of MnCO₃ increase to over 0.5 mol%, the average grain size decreases. These observations allow us to conclude that the growth of SrM grains is governed by the two-dimensional nucleation grain growth mechanism, and the critical driving force for the growth of a grain decreases as the amount of MnCO₃ increases.

Fe₃O₄/SiO₂/YVO₄:Eu³⁺ multifunctional nanoparticles are successfully synthesized by facile stepwise sol-gel processes. The multifunctional nanoparticles show a spherical shape with narrow size distribution (approximately 40 nm) and the phosphor shells are well crystallized. The Eu³⁺ shows strong photoluminescence (red emission at 619 nm, absorbance at 290 nm) due to an effective energy transfer from the vanadate group to Eu. Core-shell structured multifunctional nanoparticles have superparamagnetic properties at 300 K. Furthermore, the core-shell nanoparticles have a quick response time for the external magnetic field. These results suggest that the photoluminescence and magnetic properties could be easily tuned by either varying the number of coating processes or changing the phosphor elements. The nanoparticles may have potential applications for appropriate fields such as laser systems, optical amplifiers, security systems, and drug delivery materials.

Grain-growth behavior in the 95Na_1/2Bi_1/2TiO₃-5BaTiO₃ (mole fraction, NBT-5BT) system has been investigated with the addition of Na₂CO₃. When Na₂CO₃ is added to NBT-5BT, the growth rate is higher than desired and grains are already impinging each other during the initial stage of sintering. The grain size decreases as the sintering temperature increases. With the addition of Na₂CO₃, a liquid phase infiltrates the interfaces between grains during sintering. The interface structure can be changed to be more faceted and the interface migration rate can increase due to fast material transport through the liquid phase. As the sintering temperature increases, the impingement of abnormal grains increases because the number of abnormal grains increases. Therefore, the average grain size of abnormal grains can be decreased as the temperature increases. The phenomenon can provide evidence that grain coarsening in NBT-5BT with addition of Na₂CO₃ is governed by the growth of facet planes, which would occur via mixed control.

Citations

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• Growth of single crystals in the (Na1/2Bi1/2)TiO3–(Sr1–xCax)TiO3 system by solid state crystal growth
  Phan Gia Le, Huyen Tran Tran, Jong-Sook Lee, John G. Fisher, Hwang-Pill Kim, Wook Jo, Won-Jin Moon
  Journal of Advanced Ceramics.2021; 10(5): 973.     CrossRef
• Sintering Behavior of M-type Sr-Hexaferrite by MnCO₃ Addition
  MinSeok Jeong, Changjae You, Jung Young Cho, Kyoung-Seok Moon
  Journal of Korean Powder Metallurgy Institute.2020; 27(2): 126.     CrossRef

Citations

Citations to this article as recorded by  

• Effect of Na₂CO₃ Addition on Grain Growth Behavior and Solid-state Single Crystal Growth in the Na_0.5Bi_0.5TiO₃-BaTiO₃ System
  Kyoung-Seok Moon
  Journal of Korean Powder Metallurgy Institute.2018; 25(2): 104.     CrossRef