Effect of additives on porosity of alumina materials obtained by freeze casting

Lebreton, K.; Rodríguez-Parra, J. M.; Moreno, Rodrigo; Nieto, Marı́a Luisa

doi:10.1179/1743676115y.0000000006

Cited by 23 publications

(20 citation statements)

References 31 publications

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“…Figure shows low magnification SEM images of the sintered ZrB 2 produced by freeze casting 45 vol% solids aqueous suspensions. Large lamellar and dendritic pores were observed for the slowest freezing with slightly finer features observed for faster freezing consistent with previous work . The large pores which were produced when ZrB 2 particles were rejected in front of the growing ice crystals were too large to be eliminated during sintering as discussed in detail later.…”

Section: Resultssupporting

confidence: 88%

“…This liquid phase formed during sintering is likely to have enabled particle rearrangement, improved removal of large pores and reduced crack formation explaining the high sintered density achieved in their work. Also, many of the ceramics produced by Ceramic Process Systems (CPS) 1 contained a liquid phase sintering aid, such as the silicon nitride and SiAlON compositions or were “easier” to densify oxides such as alumina or zirconia. The alumina freeze cast by Sofie and Dogan reached 98% theoretical density most likely because it was an easy to densify oxide.…”

Section: Discussionmentioning

confidence: 99%

“…Freeze‐drying is used to remove the solvent by sublimation. Most investigations on freeze casting focus on ice templating to produce porous bodies . In those investigations the aim is to produce a macroporous green body where the solvent crystals (ice in the case of water) act as pore formers.…”

Section: Introductionmentioning

confidence: 99%

“…Most investigations on freeze casting focus on ice templating to produce porous bodies. [3][4][5][6][7][8][9][10][11][12][13] In those investigations the aim is to produce a macroporous green body where the solvent crystals (ice in the case of water) act as pore formers. This research has provided deep understanding about the role of freezing rate and solids concentration of the suspension on controlling microstructure of macroporous ceramics.…”

Section: Introductionmentioning

confidence: 99%

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Freeze casting for near‐net‐shaping of dense zirconium diboride ceramics

et al. 2018

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Zirconium diboride (ZrB2) was formed into dense complex shapes using freeze casting as a near‐net‐shaping technique. Aqueous‐based formulations were compared with nonaqueous (cyclohexane) based formulations in terms of rheological behavior, particle packing in the green body, sintered density, macroscale porosity, and cracking. The influence of particle solids concentration and freezing rate was investigated. The aqueous formulations were found to be deficient in that they produced macroscale porosity that could not be eliminated during sintering resulting in low density and large pores in the final shaped objects. The nonaqueous‐based system was able to produce complex shaped objects with significantly reduced macroscale porosity. The higher concentration of solids in the nonaqueous‐based formulations was primarily responsible for the reduced macroscale porosity and enabled higher sintered densities (up to 90%‐91.5% of theoretical density for fast freezing). The microstructure of the ZrB2 formed at fast freezing rates and high solids content typically had isolated pores in the order of 5‐10 μm in size, mainly found along grain boundaries (grain sizes between 20 and 50 μm). Although this rapid freezing produced denser components, it tended to produce objects with internal cracks. When slower freezing rates were used, intricate complex shaped objects could be produced without cracks but their density was only between 65% and 80% of theoretical density.

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Section: Resultssupporting

confidence: 88%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Freeze casting for near‐net‐shaping of dense zirconium diboride ceramics

et al. 2018

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“…During the ice (or frozen crystal) growth, particles are pushed ahead of the advancing freezing front (induced phase separation), typically producing an interconnected type of porosity. The morphology of the frozen crystals can be modified by the addition of cryoprotectants or binders, salts, and other molecules to create different porous structures such as; lamellae, hexagonal crystals, or dendritic patterns . Once the sample is completely frozen, it is subjected to sublimation (freeze drying), to remove the frozen solvent and leave a porous structure behind, which corresponds to the volume previously occupied by the frozen solvent.…”

Section: Macroporous Ceramic Structures Enabled By Colloidal Processingmentioning

confidence: 99%

Colloidal processing: enabling complex shaped ceramics with unique multiscale structures

et al. 2017

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Colloidal processing of fine ceramic powders enables the production of complex shaped ceramics with unique micro and macro structures which are not possible to produce via conventional dry processing routes. Because of this enhanced structural control and shaping capabilities, colloidal processing has been exploited to produce ceramic components with ever increasing complexity and functionalities. In this review, we revisit some of the research efforts on this topic to highlight its relevance and growing importance for the advanced manufacturing of functional ceramics. Selected examples of colloidal systems with increasing level of complexity are discussed to showcase the wide range of structures that can be generated through wet processing approaches. The historical development and background knowledge pertaining to colloids and surface interactions is first briefly reviewed. The major colloidal shape forming and additive manufacturing processes that utilize colloidal pastes and inks are then reviewed, highlighting the control of suspension rheology needed in these techniques. Next, methodologies that combine suspended particles with a pore‐forming phase are discussed as a means to produce porous ceramic materials. Further control over the interactions between anisotropic particles and their alignment in suspensions can be gained via externally applied fields (such as magnetic) to produce texturally aligned green bodies. This leads to bioinspired ceramics that can programmably morph into complex shaped objects upon sintering. Hierarchical porous structures with high mechanical efficiency are also shown as an example of the multiscale designs that can be generated through advanced colloidal processing. As drying of ceramic bodies is an inevitable consequence of wet colloidal processing, the current understanding of this critical processing step is reviewed. Finally, the gaps in knowledge in these fields are discussed to provide our perspective on where the field may support advances in ceramics in the future.

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Advancing the Mechanical Performance of Glasses: Perspectives and Challenges

et al. 2022

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in terms of deciphering structure-property relationships and the nonaffine nature of glass mechanical behavior, of computational and computer-assisted methods for accelerated materials discovery, and of physicochemical insight at glass formation and synthesis in unconventional types of materials. Despite this progress, significant questions remain as to the fundamental role of structural heterogeneity and its consequences for the predictability of mechanical properties underlying the many applications of glass. Today's challenge is to translate new understanding of the physics of disorder, glass chemistry, and surface mechanics into tools that enable future glass products with adapted elasticity, strength, and toughness. We will therefore consider fundamental advances in relation to emerging glass applications. While the aforementioned physical insights have mostly been obtained by computational simulation of model systems, and often through the examination of metallic glasses, we will here focus on glasses suitable for visible transparency, in particular silicate glasses, such as a representative of today's most prolific glass devices, ranging from ultrathin substrates to strong and visually transparent cover materials. We will further consider hybrid glasses and glass-like composite materials as emerging alternatives that may overcome the ubiquitous conflict between strength and toughness. [1] Glasses are materials that lack a crystalline microstructure and long-range atomic order. Instead, they feature heterogeneity and disorder on superstructural scales, which have profound consequences for their elastic response, material strength, fracture toughness, and the characteristics of dynamic fracture. These structure-property relations present a rich field of study in fundamental glass physics and are also becoming increasingly important in the design of modern materials with improved mechanical performance. A first step in this direction involves glass-like materials that retain optical transparency and the haptics of classical glass products, while overcoming the limitations of brittleness. Among these, novel types of oxide glasses, hybrid glasses, phase-separated glasses, and bioinspired glass-polymer composites hold significant promise. Such materials are designed from the bottom-up, building on structure-property relations, modeling of stresses and strains at relevant length scales, and machine learning predictions. Their fabrication requires a more scientifically driven approach to materials design and processing, building on the physics of structural disorder and its consequences for structural rearrangements, defect initiation, and dynamic fracture in response to mechanical load. In this article, a perspective is provided on this highly interdisciplinary field of research in terms of its most recent challenges and opportunities.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adma.202109029.

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Effect of additives on porosity of alumina materials obtained by freeze casting

Cited by 23 publications

References 31 publications

Freeze casting for near‐net‐shaping of dense zirconium diboride ceramics

Freeze casting for near‐net‐shaping of dense zirconium diboride ceramics

Colloidal processing: enabling complex shaped ceramics with unique multiscale structures

Advancing the Mechanical Performance of Glasses: Perspectives and Challenges

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