The effect of gelation on statically and dynamically freeze‐cast structures

Cathrine D. Christiansen*, Kaspar K. Nielsen, Rajendra K. Bordia, Rasmus Bjørk

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

Freeze‐casting is a technique used to produce structures with anisotropic porosity in the form of well‐defined microchannels throughout a sample. Here, this technique is used on the magnetocaloric ceramic La0.66Ca0.26Sr0.07 Mn1.05O3. We show that a dynamic freezing profile, where the temperature is decreased continuously at −10 K/min, results in homogeneous, lamellar channels with widths of 15 µm, while static freezing, where the temperature is kept constant at 177 K, results in channels of increasing size away from the initial ice crystal nucleation site. The effect of gelation before freeze‐casting is also investigated. Gelation inhibits ice crystal growth, which significantly changes the morphology by making channel cross sections less elongated, while additionally introducing more dendrites and ceramic bridges in the structure. The latter significantly dominates the flow path through the gelated structures, affecting the calculated tortuosity, which increases to τ ≈ 4 when compared to non‐gelated samples where calculated tortuosities are in the range of 1.3 to 3. Finally, we present a systematic and automatic approach for evaluating channel and wall sizes and calculating tortuosities. This is based on analysis of images obtained by scanning electron microscopy using a continuous particle size distribution method and the TauFactor application in MATLAB®.
Original languageEnglish
JournalJournal of the American Ceramic Society
Volume102
Issue number10
Pages (from-to)5796-5806
Number of pages11
ISSN0002-7820
DOIs
Publication statusPublished - 2019

Keywords

  • Directional porosity
  • Dynamic freezing
  • Freeze‐casting
  • Gelation
  • Gelation‐freeze‐casting
  • Ice‐templating
  • Magnetocaloric
  • Static freezing

Cite this

@article{536aec1f1ff348d9a8d812af64471fbc,
title = "The effect of gelation on statically and dynamically freeze‐cast structures",
abstract = "Freeze‐casting is a technique used to produce structures with anisotropic porosity in the form of well‐defined microchannels throughout a sample. Here, this technique is used on the magnetocaloric ceramic La0.66Ca0.26Sr0.07 Mn1.05O3. We show that a dynamic freezing profile, where the temperature is decreased continuously at −10 K/min, results in homogeneous, lamellar channels with widths of ∼15 µm, while static freezing, where the temperature is kept constant at 177 K, results in channels of increasing size away from the initial ice crystal nucleation site. The effect of gelation before freeze‐casting is also investigated. Gelation inhibits ice crystal growth, which significantly changes the morphology by making channel cross sections less elongated, while additionally introducing more dendrites and ceramic bridges in the structure. The latter significantly dominates the flow path through the gelated structures, affecting the calculated tortuosity, which increases to τ ≈ 4 when compared to non‐gelated samples where calculated tortuosities are in the range of ∼1.3 to ∼3. Finally, we present a systematic and automatic approach for evaluating channel and wall sizes and calculating tortuosities. This is based on analysis of images obtained by scanning electron microscopy using a continuous particle size distribution method and the TauFactor application in MATLAB{\circledR}.",
keywords = "Directional porosity, Dynamic freezing, Freeze‐casting, Gelation, Gelation‐freeze‐casting, Ice‐templating, Magnetocaloric, Static freezing",
author = "Christiansen, {Cathrine D.} and Nielsen, {Kaspar K.} and Bordia, {Rajendra K.} and Rasmus Bj{\o}rk",
year = "2019",
doi = "10.1111/jace.16500",
language = "English",
volume = "102",
pages = "5796--5806",
journal = "Journal of the American Ceramic Society",
issn = "0002-7820",
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}

The effect of gelation on statically and dynamically freeze‐cast structures. / Christiansen, Cathrine D.; Nielsen, Kaspar K.; Bordia, Rajendra K.; Bjørk, Rasmus.

In: Journal of the American Ceramic Society, Vol. 102, No. 10, 2019, p. 5796-5806.

Research output: Contribution to journalJournal articleResearchpeer-review

TY - JOUR

T1 - The effect of gelation on statically and dynamically freeze‐cast structures

AU - Christiansen, Cathrine D.

AU - Nielsen, Kaspar K.

AU - Bordia, Rajendra K.

AU - Bjørk, Rasmus

PY - 2019

Y1 - 2019

N2 - Freeze‐casting is a technique used to produce structures with anisotropic porosity in the form of well‐defined microchannels throughout a sample. Here, this technique is used on the magnetocaloric ceramic La0.66Ca0.26Sr0.07 Mn1.05O3. We show that a dynamic freezing profile, where the temperature is decreased continuously at −10 K/min, results in homogeneous, lamellar channels with widths of ∼15 µm, while static freezing, where the temperature is kept constant at 177 K, results in channels of increasing size away from the initial ice crystal nucleation site. The effect of gelation before freeze‐casting is also investigated. Gelation inhibits ice crystal growth, which significantly changes the morphology by making channel cross sections less elongated, while additionally introducing more dendrites and ceramic bridges in the structure. The latter significantly dominates the flow path through the gelated structures, affecting the calculated tortuosity, which increases to τ ≈ 4 when compared to non‐gelated samples where calculated tortuosities are in the range of ∼1.3 to ∼3. Finally, we present a systematic and automatic approach for evaluating channel and wall sizes and calculating tortuosities. This is based on analysis of images obtained by scanning electron microscopy using a continuous particle size distribution method and the TauFactor application in MATLAB®.

AB - Freeze‐casting is a technique used to produce structures with anisotropic porosity in the form of well‐defined microchannels throughout a sample. Here, this technique is used on the magnetocaloric ceramic La0.66Ca0.26Sr0.07 Mn1.05O3. We show that a dynamic freezing profile, where the temperature is decreased continuously at −10 K/min, results in homogeneous, lamellar channels with widths of ∼15 µm, while static freezing, where the temperature is kept constant at 177 K, results in channels of increasing size away from the initial ice crystal nucleation site. The effect of gelation before freeze‐casting is also investigated. Gelation inhibits ice crystal growth, which significantly changes the morphology by making channel cross sections less elongated, while additionally introducing more dendrites and ceramic bridges in the structure. The latter significantly dominates the flow path through the gelated structures, affecting the calculated tortuosity, which increases to τ ≈ 4 when compared to non‐gelated samples where calculated tortuosities are in the range of ∼1.3 to ∼3. Finally, we present a systematic and automatic approach for evaluating channel and wall sizes and calculating tortuosities. This is based on analysis of images obtained by scanning electron microscopy using a continuous particle size distribution method and the TauFactor application in MATLAB®.

KW - Directional porosity

KW - Dynamic freezing

KW - Freeze‐casting

KW - Gelation

KW - Gelation‐freeze‐casting

KW - Ice‐templating

KW - Magnetocaloric

KW - Static freezing

U2 - 10.1111/jace.16500

DO - 10.1111/jace.16500

M3 - Journal article

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EP - 5806

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