Evaluation of the pore morphology formation of the Freeze Foaming process by in situ computed tomography

Ahlhelm, Matthias; Werner, David; Maier, Johanna; Abel, Johannes; Behnisch, Thomas; Moritz, Tassilo; Michaelis, Alexander; Gude, Μaik

doi:10.1016/j.jeurceramsoc.2018.02.031

Cited by 9 publications

(14 citation statements)

References 13 publications

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“…Particular interest has been recently shown for the application of XCT in the field of AM, to evaluate AM methods, to control the geometry of the produced components or to characterize their microstructure [33][34][35][36][37]. In the field of ceramic materials, XCT have been particularly used for structural or damage characterization of ceramic matrix composites [38][39][40][41][42][43] and to evaluate pore morphology and interconnectivity of porous or cellular ceramics [44][45][46][47][48][49][50]. XCT analysis was also applied to follow the microstructural evolutions during the compaction process of [51] or their sintering [52][53][54], and to investigate indentation induced cracking in dense alumina [55].…”

Section: Introductionmentioning

confidence: 99%

X-ray tomography of additive-manufactured zirconia: Processing defects – Strength relations

Saâdaoui

Khaldoun

Adrien

et al. 2020

Journal of the European Ceramic Society

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Section: Introductionmentioning

confidence: 99%

X-ray tomography of additive-manufactured zirconia: Processing defects – Strength relations

Saâdaoui

Khaldoun

Adrien

et al. 2020

Journal of the European Ceramic Society

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“…Ahlhelm et al uses the Freeze Foaming technique for the manufacturing of ceramic foams for possible application in the biomedical technology. They focused on the controlled regulation of the pore morphology by controlling the preparation and process approach.…”

Section: Introductionmentioning

confidence: 99%

Hierarchical‐Porous Ceramic Foams by a Combination of Replica and Freeze Technique

Schelm

Fey²,

Dammler

et al. 2019

Adv Eng Mater

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Open-porous alumina foams with additional strut porosity are fabricated by a two-step sponge-replication based manufacturing process. As the first step, open cellular ceramic foams are prepared following the Schwarzwalder sponge replication technique. Therefore, organic foam templates are coated with different aqueous alumina slurries with a solid load between 20 and 40 vol% In a second step, an additional porosity is generated inside the foam struts by freezing of the foams at temperatures between À196 and À20 C and subsequent sublimation drying. The hierarchical structure of both, cell pores and strut pores in the freeze-dried material remains intact after drying, template removal, and sintering. Size, connectivity, and morphology of the strut pores strongly depend on the solid load of the alumina slurry and on the freezing temperature. Cellular structures with a strut porosity between 50% and 60% and a total porosity exceeding 90% are prepared, which show a compressive strength in between 0.4 to 0.6 MPa. Due to the additional strut porosity, the specific surface area of freeze-dried replica foams increases from 70 cm 2 g À1 for conventionally prepared foams to 200 cm 2 g À1 for freeze-dried foams, respectively.

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“…After crossing the triple point, the generated protofoam instantaneously freezes and dries via sublimation [7,8]. This freezing step can result in cryogenic structures (discussed in more detail in [9]) similar to typical freeze cast structures [10,11] and accounts for the microporosity of foamed structures. Therefore, the Freeze Foam's only pore formers are rising bubbles of processing air and water vapor as well as sublimated frozen water.…”

Section: The Freeze-foaming Process and Recent Achievementsmentioning

confidence: 99%

“…Already detailed in the previous contribution [9], CT analyses were used for the first time to monitor the Freeze-Foaming process and allow for evaluation of foam structuring phenomena. The first results report the successful manufacturing of a model suspension, of reproducible foam structures foamed at room temperature and the dependence of the porosity, pore size and the shape from the pressure reduction rate of the freeze dryer used.…”

Section: The Freeze-foaming Process and Recent Achievementsmentioning

confidence: 99%

“…The CT measurements were performed with the parameters given in Table 1. Using VGStudio Max, we quantified pore morphology data of scanned foams (Figure 3, top left) as also detailed in [9]: First a three-dimensional "Region of Interest" (ROI) is defined and the surface determined by automatic software-assisted grey value analyses (definition of pores, material and material surface; Figure 3, top right). A subsequent defect analysis shows the identified foam cells marked in yellow ( Figure 3, bottom left).…”

Section: Ct Evaluation Proceduresmentioning

confidence: 99%

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Deriving Principles of the Freeze-Foaming Process by Nondestructive CT Macrostructure Analyses on Hydroxyapatite Foams

et al. 2018

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Freeze Foaming is a direct foaming method that aims at manufacturing ceramic cellular scaffolds for diverse applications. Next to porous structures for a potential use as refractories, the focus lies on potential bone replacement material. The main challenge of this foaming method is to achieve a homogeneous and predictable pore morphology. That is why, in a current project, the authors report on the pore morphology formation and evolution of the foaming process by means of nondestructive testing. This contribution primarily compares the effect of the suspension’s temperature on the resulting foam structure (foaming at 5 and 40 °C). As a basis for computed tomographic analysis, a stable and reproducible model suspension was developed that resulted in reproducible foam structures. Characterized by viscosity, foam structure analyses and foaming rate, the resulting Freeze Foams became adjustable with regards to their porosity and pore shape/size. Under certain conditions, we succeeded in achieving a relatively homogeneous pore structure, as proven by computed tomography-derived quantitative analysis.

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Evaluation of the pore morphology formation of the Freeze Foaming process by in situ computed tomography

Cited by 9 publications

References 13 publications

X-ray tomography of additive-manufactured zirconia: Processing defects – Strength relations

X-ray tomography of additive-manufactured zirconia: Processing defects – Strength relations

Hierarchical‐Porous Ceramic Foams by a Combination of Replica and Freeze Technique

Deriving Principles of the Freeze-Foaming Process by Nondestructive CT Macrostructure Analyses on Hydroxyapatite Foams

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