When an incident x-ray strikes the detector, it creates a charge pulse that is proportional to the energy of the x-ray. The charge pulse is converted to a voltage pulse which remains proportional to the x-ray energy by a charge-sensitive preamplifier. The signal is then sent to a multichannel analyzer where the pulses are sorted by voltage. The energy, as determined from the voltage measurement, for each incident x-ray is sent to a computer for display and further data evaluation.
The spectrum of x-ray energy versus counts is evaluated to determine the elemental composition of the sampled volume. Qualitative Analysis - The sample x-ray energy values from the EDS spectrum are compared with known characteristic x-ray energy values to determine the presence of an element in the sample. Elements with atomic numbers ranging from that of beryllium to uranium can be detected. The minimum detection limits vary from approximately 0.
Quantitative Analysis - Quantitative results can be obtained from the relative x-ray counts at the characteristic energy levels for the sample constituents. Semi-quantitative results are readily available without standards by using mathematical corrections based on the analysis parameters and the sample composition. The accuracy of standardless analysis depends on the sample composition. Greater accuracy is obtained using known standards with similar structure and composition to that of the unknown sample.
Elemental Mapping - Characteristic x-ray intensity is measured relative to lateral position on the sample. Variations in x-ray intensity at any characteristic energy value indicate the relative concentration for the applicable element across the surface. One or more maps are recorded simultaneously using image brightness intensity as a function of the local relative concentration of the element s present.
Line Profile Analysis - The SEM electron beam is scanned along a preselected line across the sample while x-rays are detected for discrete positions along the line. Feldspar grains anorthite : The orthoclase and the anorthite identified by the PXRD cannot be distinguished from each other within the backscattered scanning electron micrograph. Plus, the feldspar grains and the quartz grains cannot be visually separated. This allows for identifying the feldspar grains as all grain-type objects which were not qualified as quartz grains according to the method described before.
Fine anorthite grains mineralizing due to higher burning temperatures are, as some quartz particles, dispersed in the matrix and therefore not captured by the SEM-EDX. Iron-magnesium mica Fe—Mg mica : All plate-shaped features in the backscattered scanning electron micrographs, which contained iron, as indicated by the corresponding elemental maps, were identified as Fe—Mg mica.
Light mica muscovite : All plate-shaped features in the backscattered scanning electron micrographs, which did not contain iron, as indicated by the corresponding elemental maps, were identified as light mica, namely muscovite [ 39 ].
Decarbonated dolomite: This phase was identified as comprising all non-platy features containing magnesium. Accordingly, a cost function representing the discrepancy between the original map and the binary map, as well as the number of bits required for the binary image, was minimized.
Afterwards, Mg pixel agglomerations of fewer than ten pixels as well as with a circularity below two, were deleted by means of the particle analyser plug-in of ImageJ [ 38 ].
Within the remaining structures of the decarbonated dolomite, gehlenite, and, with higher burning temperature, diopside as identified by the PXRD may occur. Accordingly, the brightness value histogram was considered as a bimodal distribution, and the threshold separating pixels of one class belonging to the background, representing anything but pores from those of the other class belonging to the foreground, representing pores was determined such that the inter-class variance becomes a maximum.
However, corresponding foreground objects, appearing as dark objects on the SEM, may also contain parts of the decarbonated dolomite phase, so that all sections of the foreground which overlap with the previously determined carbonated dolomite phase, are subtracted from what is considered as the pore space. Such is necessary for a correct identification of the phase morphology.
The latter concludes the phase identification description. Matrix: Structures that could not be uniquely assigned to one of the aforementioned phases were considered to be part of the fired clay matrix.
This matrix phase consists of the amorphous fractions, small amounts of minerals, such as haematite and diopside, which cannot be assigned to self-contained structures observable with the SEM-EDX, as well as of fine dispersed mineral particles like quartz and feldspar.
Plus, remaining structures of clay minerals forming new crystal or melting phases, are assigned to the matrix phase. However, all this constituent phases within the glassy matrix phase cannot further be resolved, the microheterogeneous matrix is therefore considered as a quasi-homogeneous subdomain in the framework of continuum mechanics. In sections through the anisotropy axis of fired clay z -axis in Fig. Color figure online. When calculating the weighted orientation distribution by means of the standard deviation, defined via:.
Using this transformation rule, we can transform Eq. According to the PXRD results on the unfired samples, clay A contained carbonates calcite and dolomite, see Table 2 , while clay B is free of such, containing more quartz. Additionally, both show some shares of phyllosilicates chlorite, muscovite and kaolinite as well as some feldspars albite and microcline , see Table 2.
In contrast, Clay B poor in Ca , is dominated by vermiculite, with some constituents of illite, chlorite and kaolinite see Table 3. Clay A, representing a clay rich in carbonates, shows, in agreement with literature [ 42 ], a wide compositional variability with respect to the carbonate-poor clay B Table 4 , Fig. With higher burning temperature, clay A shows a significant decrease in the quartz content, something which can be typically expected for carbonate-containing clays [ 45 , 46 ].
Riccardi et al. The highest amount of newly forming crystals within clay A is represented by anorthite, which has also been previously reported by other authors [ 45 ], followed by small amounts of diopside and the aforementioned cristobalite.
With higher burning temperatures, and the former dolomite and calcite grains fully reacted, only ring-like textures remain still visible see Fig. The muscovite and orthoclase then dissolve, as expected from literature [ 47 , 49 ], at high burning temperatures.
Regarding the constant amount of hematite, the following can be stated: all calcium-aluminum silicates accept varying amounts of iron within their mineral structures [ 45 , 50 ], which is why only little amounts of pure hematite are found, and no new crystallization can be observed at higher temperatures.
Clay B, which is poor in carbonates, shows a substantial different behaviour. As iron is not trapped within the lattice of calcium-aluminum silicates in clay B, an increase in hematite content can be found with higher burning temperature [ 43 ]. Cultrone et al. This is caused by the decomposition of carbonates in clay A, promoting the fast crystallization of calcium-aluminum silicates, at the expense of the formation of a melt phase [ 43 ].
To derive the chemical composition of the matrix, containing the amorphous fraction, mineral structures decomposed during burning as well as fine dispersed mineral grains, the PXRD data can be used to estimate the chemical composition.
Comparison of the results with the XRF data see Table 5 reveals the chemical composition of the amorphous fraction, given in Table 6. Overlaying plate-shaped features in the backscattered scanning electron micrographs see Fig. As the aforementioned binary maps are representative for the entire spatial clay samples, their mean grey values give direct access to the phase volume fraction, see Fig.
This indicates that at this lower firing temperature, quartz appears not only in grain form, but also as fine dispersed particles within the matrix phase. This indicates that at this higher firing temperature, quartz appears virtually exclusively in the form of several micrometer-sized grains. The higher porosity of clay A compare Fig.
Carbonate-bearing clays are known to be rather heterogeneous [ 45 ], which is consistent with clay A exhibiting indeed more material phases than clay B compare Fig. This is suggested by an intravoxel microCT-image analysis which was experimentally validated by weighing tests and mercury intrusion porosimetry [ 52 ].
These additional pores of clearly sub-micrometer size are part of the matrix phase. Simultaneous vanishing of the muscovite phase is probably due to dehydroxylation and weakening the long range structural organization of the latter, as reported by Gridi-Bennadji et al. Colour-based phase identification, on representative areas shown in Fig. Regarding these SEM images, the following can be stated: the induced secondary porosity in clay A due to the decarbonation of dolomite and calcite see [ 42 , 49 ] , can be observed, while porosity in clay B at lower burning temperatures seems to be mainly driven by shrinkage of the clay matrix Fig.
Quantitative morphological information for all distinguished material phases is given in Tables 7 and 8 , and reveals the preferential orientation to be with the extrusion axis, something which has already been observed by previous authors [ 7 , 13 ]. In general, it can be stated that the more elongated the inclusions are, the more their preferential orientation is with the extrusion axis. While the less elongated inclusions quartz, feldspar and decarbonized dolomite show a huge weighted standard deviation of the preferential orientation, the elongated inclusions phyllosilica are aligned almost parallel to the extrusion axis.
Conclusively, our new phase identification protocol, stemming from the combination of SEM-EDX images with a preliminary conducted PXRD, is fully consistent with many previous investigations, while marking, at the same time, a new level of completeness, as the entire space of SEM-resolved microstructure is clearly assigned to one of up to seven phases with different shapes. Additionally, the chemical composition of the matrix phase has been calculated using obtained data by PXRD and XRF measurements, confirming the assumption of finely dispersed quartz and feldspar particles below the resolution threshold of the SEM.
Plus, these results are in line with the mineralogical analysis of the unfired raw material and the fired clay at different burning temperatures. Finally, the morphological evaluation of all material phases allows for a thorough description of the morphometrics of the latter. This opens the way towards a more quantitative understanding of structure-property relations in fired clay, in particular for mechanical and thermal properties predicted with tools of continuum micromechanics or homogenization theory [ 15 ].
The latter proved as very suitable for this purpose, in the context of various construction materials. With the presented identification of the material phases and their morphology, the first step towards such a physically based multiscale material model able to estimate macroscopic elastic and thermal properties of fired clay [ 26 ] is taken. Bergaya F, Lagaly G Chapter 1 general introduction: clays, clay minerals, and clay science. Pusch R Chapter 6 mechanical properties of clays and clay minerals.
Coletti C, Cultrone G, Maritan L, Mazzoli C How to face the new industrial challenge of compatible, sustainable brick production: study of various types of commercially available bricks. Appl Clay Sci Supplement C — Appl Clay Sci 42 1 — Appl Clay Sci — Wilson W, Sorelli L, Tagnit-Hamou A a Automated coupling of nanoindentation and quantitative energy-dispersive spectroscopy ni-qeds : a comprehensive method to disclose the micro-chemo-mechanical properties of cement pastes.
Cem Concre Res — Wilson W, Sorelli L, Tagnit-Hamou A b Unveiling micro-chemo-mechanical properties of c- a -s-h and other phases in blended-cement pastes.
Cem Concr Res — Hisseine OA, Wilson W, Sorelli L, Tolnai B, Tagnit-Hamou A Nanocellulose for improved concrete performance: a macro-to-micro investigation for disclosing the effects of cellulose filaments on strength of cement systems.
Constr Build Mater — J Am Ceram Soc 93 5 — J Am Ceram Soc 94 9 — Article Google Scholar. Hill R Continuum micro-mechanics of elastoplastic polycrystals. J Mech Phys Solids 13 2 — Zaoui A Continuum micromechanics: survey.
Int J Solids Struct 44 9 — Constantinides G, Ulm FJ The effect of two types of C—S—H on the elasticity of cement-based materials: results from nanoindentation and micromechanical modeling. Cem Concr Res 34 1 — Pichler B, Hellmich C Upscaling quasi-brittle strength of cement paste and mortar: a multi-scale engineering mechanics model.
Cem Concr Res 41 5 — Hofstetter K, Hellmich C, Eberhardsteiner J Development and experimental validation of a continuum micromechanics model for the elasticity of wood. Bader T, Hofstetter K, Hellmich C, Eberhardsteiner J Poromechanical scale transitions of failure stresses in wood: from the lignin to the spruce level.
J Theor Biol 4 — Fritsch A, Dormieux L, Hellmich C, Sanahuja J Mechanical behavior of hydroxyapatite biomaterials: an experimentally validated micromechanical model for elasticity and strength. Abdalrahman T, Scheiner S, Hellmich C Is trabecular bone permeability governed by molecular ordering-induced fluid viscosity gain? Arguments from re-evaluation of experimental data in the framework of homogenization theory.
J Theor Biol — Schultz L Quantitative interpretation of mineralogical composition from X-ray and chemical data for the Pierre Shale. Constr Build Mater J Eur Ceram Soc. Oliver W, Pharr G An improved technique for determining hardness and elastic modulus using load and displacement sensing indentation experiments. J Mater Res 7 6 — Fischer H Quantitative determination of heat conductivities by scanning thermal microscopy. Thermochim Acta 1—2 — Buehler Ltd. Rietveld HM A profile refinement method for nuclear and magnetic structures.
J Appl Crystallogr — Russ JC Fundamentals of energy dispersive X-ray analysis. Microsc Microanal 12 1 :2— Scanning 35 3 — Springer US. Otsu N A threshold selection method from gray-level histograms. Nat Meth 9 7 — American Association of Petroleum Geologists. Appl Clay Sci 15 3 — J Eur Ceram Soc 27 16 — Some microtextures and related phase compositions.
Thermochim Acta 1 —
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