Micro-CT-based identification of double porosity in fired clay ceramics

Kariem, Hawraa; Hellmich, Christian; Kiefer, Thomas; Jäger, Andreas; Füssl, Josef

doi:10.1007/s10853-018-2281-9

Cited by 21 publications

(10 citation statements)

References 33 publications

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“…The results for mercury intrusion porosimetry and total porosity agree well with a former report of Kariem et al, who also investigated pore structures of clay samples with organic additives . Rörig-Dalgaard et al reported an open porosity of clay bricks of about 33% (water saturation), which is in accordance with the porosity of the pure clay in Table .…”

Section: Resultssupporting

confidence: 90%

“…The porosity of the individual specimens was examined by mercury intrusion porosimetry, including pore diameters smaller than 150 μm, as presented in Table . Bigger pores are beyond the measurement range; hence, the remaining part of pores was calculated by relating the apparent densities from weighing specimens with reference to the density of the pure clay, a method described elsewhere . Calculated total porosities are also indicated in Table .…”

Section: Resultsmentioning

confidence: 99%

“…17 Nevertheless, in the present subject of various different organic substances used for pore forming of which each may exhibit different size distributions, reactivity, ash formation, and so forth, the SCM seems the more general approach. In fired clay bricks, porosity can reach substantial values, 25,26 while due to the wide particle size distribution of clays, 27 the pore structure of the solid matrix is fine (e.g., compared to sintered materials) and, consequently, effective diffusion coefficients can be expected to be low. This leads to a situation where diffusion is the limiting reaction step, which favors the application of the SCM.…”

Section: ■ Introductionmentioning

confidence: 99%

See 2 more Smart Citations

An Unreacted Shrinking Core Model Serves for Predicting Combustion Rates of Organic Additives in Clay Bricks

et al. 2020

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The present study investigates the suitability and restrictions of the unreacted shrinking core model to describe the combustion of a fixed organic substance in a clay matrix, as found in the firing process of clay bricks. The model was applied to the experimental data of isothermal measurements and validated by the model prediction of nonisothermal experiments, which were examined by combustion of mixed clay containing several organic additives in a fluidized bed combustor. Besides reactivity measurements, the shrinking core proceeding was also indicated by apparent separated phases within partially reacted clay specimens. The reaction site moves from the surface toward the inner site dividing a reacting solid into two distinct zones with different organic carbon concentrations, which was confirmed by separated analyses. Mass transfer and reactivity parameters of the model were found to be both exponentially related to temperature (Arrhenius law). The apparent chemical activation energies were determined to be 39.8−59.3 kJ/mol and, therefore, relatively small compared to literature data derived from the experimental procedure with low heating rates, but similar to values of experimental data associated with fast warming rates similar to the present investigation. The determined chemical pre-exponential factors seemed to reflect the specific surface of the organic substance incorporated in the clay matrix. The porosity of the clay samples was investigated by means of mercury intrusion porosimetry and found to be dependent on the amount of added organic substance. The porosity of the pure clay sample was 36.4%, while moderately higher values were found for mixed samples (41.0−44.2%). The effective diffusion coefficients appeared to be directly related to the portion of the total porosity generated by the organic additives. The diffusion coefficients found were around 0.002− 0.02 cm 2 /s for a temperature range of 350−650 °C, which is in the same order of magnitude as reported in comparable studies. The presented model provides an important item for the simulation of the firing process of ceramic goods in oxidizing atmospheres and explains mass transfer mechanisms evolving inside ceramic material blended with organic substances under heat exposure.

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Section: Resultssupporting

confidence: 90%

Section: Resultsmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

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An Unreacted Shrinking Core Model Serves for Predicting Combustion Rates of Organic Additives in Clay Bricks

et al. 2020

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“…However, micropores of size below the resolution of the SEM-images with 0:192 lm pixel size may still prevail. This is suggested by an intravoxel microCT-image analysis which was experimentally validated by weighing tests and mercury intrusion porosimetry [52]. Correspondingly obtained porosity values are about 8% higher than those obtained from present SEM-EDX results of Fig.…”

Section: Sem-edx Image Analysissupporting

confidence: 66%

EDX/XRD-based identification of micrometer-sized domains in scanning electron micrographs of fired clay

et al. 2020

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The thermal and mechanical properties of bricks are strongly dependent on both the chemical composition and the microstructural features of the used fired clay material. Focussing on the latter, we here identify, in terms of volume fraction, shape, and orientation characteristics, one-to-several micrometer-sized subdomains (''material phases'') within the SEM-imaged microstructure of two raw clays fired at 880 and 1100 centigrades: (1) quartz grains, (2) muscovite, (3) Fe-Mg mica, (4) feldspar grains, (5) decarbonated dolomite, (6) pores, or (7) binding matrix. This identification rests on the simultaneous use of Scanning Electron Microscopy (SEM) and Energy-dispersive X-ray spectroscopy (EDX), with correspondingly obtained data entering statistical analyses based on the Otsu algorithm, and complemented by minimum grain size and grain shape requirements, as well as by logical exclusion criteria. Crystalline and amorphous phase shares were additionally confirmed by X-ray powder diffraction measurements (PXRD). As for the investigated clays, an increased firing temperature results in dehydroxylation of muscovite, and in a reduced appearance of feldspar grains.

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“…For a constant applied voltage of the X-ray tube, there is a linear relationship between the greyscale level and the material density [47]. By virtue of this relationship, X-ray tomography can be used to measure local density variations within the material given proper calibration [48][49][50]. However, due to the complex material structure of cement paste, purely analytical solution mapping the attenuation to physical density has not been achieved to date.…”

Section: Experimental Results and Assumptionsmentioning

confidence: 99%

Experimentally informed micromechanical modelling of cement paste: An approach coupling X-ray computed tomography and statistical nanoindentation

Zhang

Šavija

Luković

et al. 2019

Composites Part B: Engineering

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This work proposes a method for numerically investigating the fracture mechanism of cement paste at the microscale based on X-ray computed tomography and nanoindentation. For this purpose, greyscale level based digital microstructure was generated by X-ray microcomputed tomography with a resolution of 2 μm/voxel length. In addition, statistics based micromechanical properties (i.e. Young's modulus and hardness) were derived from the grid nanoindentation test which was set to have an interaction volume the same as the resolution of the digital microstructure. A linear relationship between the two probability density functions of greyscale level and local Young's modulus was assumed and verified by the two-sample Kolmogorov-Smirnov (KeS) statistic. Based on this assumption, the fracture and deformation of a digital cubic volume with a dimension of 100 μm under uniaxial tension was simulated using a lattice fracture model. In addition, the influence of heterogeneity on fracture response was studied. Furthermore, the proposed method was compared with the results obtained from a traditional approach used previously by the authors in which discrete phases (capillary pore, anhydrous cement clinker, outer and inner hydration products) were considered. The two methods show similar crack patterns and stress-strain responses. The proposed method is regarded more promising as it captures also the gradient of material properties (within the discrete phases) in the cement paste.

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Micro-CT-based identification of double porosity in fired clay ceramics

Cited by 21 publications

References 33 publications

An Unreacted Shrinking Core Model Serves for Predicting Combustion Rates of Organic Additives in Clay Bricks

An Unreacted Shrinking Core Model Serves for Predicting Combustion Rates of Organic Additives in Clay Bricks

EDX/XRD-based identification of micrometer-sized domains in scanning electron micrographs of fired clay

Experimentally informed micromechanical modelling of cement paste: An approach coupling X-ray computed tomography and statistical nanoindentation

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