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34. Simultaneous control of mechanical strength and hierarchical structure in freeze‐casted porous alumina by two‐step sintering.

Author

Jeon, Sang‐Chae, Woo, Jong‐Won, Kim, Sung‐Hyun, Ha, Jang‐Hoon, Yang, Dong‐Yeol, Moon, Kyoung‐Seok, Wu, Haoyue, Yang, Jae‐Hwan, and Kim, Dong‐Kyu

Subjects
SINTERING, FINITE element method, COMPRESSIVE strength, ACTIVATION energy
Abstract

To increase mechanical strength of porous ceramics, here, an effective two‐step sintering (TSS) technique capable of producing highly porous alumina with enhanced mechanical strength is suggested. Based on the sintering theories, here, a significantly lower activation energy for densification at low temperature region allowed a beneficial temperature range for the TSS to be deduced. With a specific TSS regime (T1 = 1550°C and T2 = 1400°C), significantly higher compressive strength levels (8.00–15.24 MPa) were measured with an apparent porosity of 56.49% compared to conventional sintering (1.03–1.86 MPa) with similar apparent porosity of 57.84%. Specifically, another TSS regime (T1 = 1550°C and T2 = 1380°C) left submicron‐sized open pores within the lamellar walls, providing a hierarchical porous structure with enhanced mechanical strength. An evaluation of the mechanical stability by a finite element analysis indicated outstanding compressive strength even with small pores in the lamella walls. [ABSTRACT FROM AUTHOR]

Published
2024
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44. Manufacturing and properties evaluation of Al2O3/ZrO2granules derived from sodium alginate gelation

Author

Lucio, Maria Dolores Sosa, Oh, Eun-Ji, Ha, Jang-Hoon, Lee, Jongman, Lee, Hong-Joo, Jung, Seung Hwa, Shin, Jun Young, and Song, In-Hyuck

Abstract

Spherical millimeter-sized ceramics with porous and dense microstructure are materials of interest in approaches related to catalytic supports and milling media. The reliability of these operations depends on key characteristics of these materials, including high sphericity to ensure efficient process designing, ease of handling, facile separation and/or recyclability, abrasion resistance, and uniform packing. This is accompanied by the structural stability and microstructure tailoring to secure its functionality. The Al2O3/ZrO2system has been applied in powdered form for catalytic support applications, and in both porous and dense ceramics for structural applications, highlighting the performance and functionality of the Al2O3/ZrO2system in these approaches. Based on this analysis, the present study explores the optimized preparation of spherical millimeter-sized Al2O3/ZrO2granules along with the assessment of their microstructural, mechanical, and pore-related outcomes as a function of the heat treatment conditions. Optimized Al2O3/ZrO2granules with high sphericity, processed through sodium alginate gelation at 900 °C and 1100 °C displayed a hierarchical macro/mesoporosity which can provide potential functionality for catalytic supports-related applications. In comparison Al2O3/ZrO2granules similarly processed at a sintering temperature of 1600 °C exhibited a tailored mechanical strength and high relative density ensured by a refined microstructure, as well as a high sphericity which are features preferred for milling media applications.

Published
2024
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45. Processing of millimeter-sized spherical ZrO2granules through sodium alginate cross-linking and an assessment of their resultant properties

Author

Lucio, Maria Dolores Sosa, Oh, Eun-Ji, Ha, Jang-Hoon, Lee, Jongman, Lee, Hong-Joo, Jung, Seung Hwa, Shin, Jun Young, and Song, In-Hyuck

Abstract

ZrO2–based porous and dense engineering ceramics exhibit a wide range of applications due to their remarkable features. Specifically, applications related to catalytic supports, inert matrix fuel pellets, and structural materials (milling media) require the preparation of millimeter-sized ZrO2-based spherical granules with high sphericity. This ensures easy handling and recovery, improved mass transfer, uniform packing density, and efficient designs of processes. However, commonly applied granulation methods involve the use of toxic and corrosive reagents and severe processing conditions, which can impede safe industrial manufacturing. The present study investigates the processing of millimeter-sized spherical ZrO2granules based on ZrO2as a raw material in the form of a solid network and with sodium alginate cross-linked through ion exchange as a patterned structure. The results suggest that optimized spherical ZrO2granules, with high sphericity processed between 1000 and 1200 °C, exhibit characteristics preferable for catalytic supports, including good structural stability and hierarchical meso/macro porosity. Furthermore, spherical ZrO2granules processed between 1400 and 1500 °C displayed low residual porosity and a refined microstructure, resulting in high compressive strength, comparable to ZrO2granules potentially suitable for structural applications such as milling media and inert matrix fuels.

Published
2024
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