Hafsia Ben Rhaiem

Correlation between Electrochemical Impedance Spectroscopy and Structural Properties of Amorphous Tunisian Metanacrite Synthetic Material

In the present work, we report the structural and electrochemical properties of metanacrite. Metanacrite is a synthetic material originated by heating (550°C) of a clay mineral (Tunisian nacrite) belonging to the kaolin group. The structure of the amorphous synthetic product was corroborated by X-ray diffraction (disappearing of nacrite peaks) and infrared spectroscopy (disappearing of Al–OH and water bands). The decomposition of the silicate framework was confirmed by transmission electron microscope (TEM). The obtained metanacrite synthetic material was also examined by electrochemical impedance spectroscopy (EIS). Accordingly, the electronic conduction is followed by the correlated barrier hopping (C.B.H.) model. Therefore, by combining ac and dc electrical conductivity, a semiconductor behavior is evidenced. The dependence of the dielectric constant () and dielectric loss () on both temperature and frequency is also discussed.

Quantitative XRD analysis of the dehydration–hydration performance of (Na+, Cs+) exchanged smectite

AbstractThe clay mineral membrane is increasingly used, as a natural geological barrier, in wastewater treatment. The variation of the environmental condition (T, P, RH, etc.) induces probably several change on the materials structure. This work aims at characterizing the link between dehydration–hydration behavior, charge location, and the ionic radius, in the case of dioctahedral smectites, exchanged with Na+ and Cs+ cation, which are occurred from industrial waste. A natural montmorillonite and beidellite, with different charge location (respectively, dioctahedral and trioctahedral), are selected. The exchange process is directed using Na+ and Cs+ cations. The hydration hysteresis is investigated “in situ” as a function of relative humidity condition rates. All samples are studied using quantitative X-ray diffraction (XRD) analysis. This method allows us to determine the structural parameters obtained from the theoretical mixed layer structure used to fit experimental XRD patterns. For both Na+ and/or ...

Structural and Electrochemical Properties of Cementitious and Hybrid Materials Based on Nacrite

This chapter gives possible valorization of a well-crystallized Tunisian nacrite as an interesting clay mineral belonging to the kaolin group: The first part of the chapter aims to produce a new synthetic material labeled ‘‘metanacrite”. Metanacrite is a supplementary cementitious material originated by heating a raw Tunisian nacrite at 823 K. The structure of the amorphous synthetic product was corroborated by X-ray diffraction (XRD) and infrared spectroscopy (IR). The decomposition of the silicate framework was confirmed by transmission electron microscope (TEM). The obtained metanacrite was also examined by electrochemical impedance spectroscopy (EIS). Accordingly, a semiconductor behavior of the novel synthetic material is evidenced. The second part of this chapter deals with the intercalation of lithium chloride salt between the planar layers of this Tunisian nacrite. The intercalation leads to a stable hybrid material that after calcination under inert atmosphere at 723–873 K induces an amorphous hybrid. The structural identification of the obtained nacrite–LiCl hybrid was determined by means of XRD, IR, TGA, and EIS. Finally, the resulting amorphous hybrid shows a superionic behavior with high ionic conductivity up to 10–2 S.m–1, good electrochemical stability, and can be used as an innovative solid electrolyte in lithium batteries and other electrochemical devices.

Interlamellar space configuration under variable environmental conditions in the case of ni-exchanged montmorillonite: quantitative XRD analysis

Interlamellar space organization of low-charge montmorillonite was studied by modeling of X-ray diffraction (XRD) patterns recorded under controlled relative humidity (RH) conditions on Ni saturated specimens. The quantitative XRD investigation, based on an indirect method consisting of the comparison of experimental 00l reflections with the other calculated from structural models, is used to characterize eventual nanostructural changes along c* axis of Ni-exchanged montmorillonite. This method allowed us to determine, respectively, the relative layer types contribution, the layer thickness, nanoconfiguration of the interlamellar space, and position, amount, and organization of water molecules and exchangeable cations. Obtained theoretical models exhibit heterogeneous hydration state which is the dominating character detected all over studied cycles. Along RH cycle a modification in the main structure of the host materials is performed and the presence of a mixed layer structure (MLS) is noted. The hydration hysteresis at the low and the high RH range can be explained by fluctuations in the water retention mechanism and hydration heterogeneities created within the smectite crystallite.

Synthesis, characterization and applications of a new nanohybrid composite: Nacrite/MgCl 2 .6H 2 O/ethanol

In this paper, we present an experimental study about the functionalization of a Tunisian nacrite with a hydrated magnesium chloride salt. The elaborated nanomaterial composite have been studied via X-ray diffraction, IR spectroscopy and EDXS. The quantitative XRD analysis allowed us to determine the structural parameters related to the number and position along the normal of the layers of the alkaline bivalent cations Mg2+, halide anions Cl- and water molecules in the interlamellar space. The obtained results showed that the basal spacing value shifted from 0.72 nm related to the unexpanded nacrite to 1.5 nm attributed to the nacrite/MgCl2.6H2O composite. The existence of intercalated water is verified by infrared spectroscopy, and revealed that the active groups on the nacrite layers and the intercalated species are linked by hydrogen bonds. Moreover, microstructure investigation by transmission electron microscopy (TEM) coupled with energy dispersive X-ray spectroscopy (EDXS) were carried out. TEM analyses confirm the intercalation of MgCl2.6H2O into the nacrite matrix. The main objective of this paper was to elucidate the influence of the new physicochemical properties of the modified nacrite layers that allows the evaluation of the applicability of this innovative composite material “nacrite/MgCl2.6H2O/ethanol”.

Morphological Analysis of White Cement Clinker Minerals: Discussion on the Crystallization-Related Defects.

The paper deals with a formation of artificial rock (clinker). Temperature plays the capital role in the manufacturing process. So, it is useful to analyze a poor clinker to identify the different phases and defects associated with their crystallization. X-ray fluorescence spectroscopy was used to determine the clinkers chemical composition. The amounts of the mineralogical phases are measured by quantitative XRD analysis (Rietveld). Scanning electron microscopy (SEM) was used to characterize the main phases of white Portland cement clinker and the defects associated with the formation of clinker mineral elements. The results of a study which focused on the identification of white clinker minerals and defects detected in these noncomplying clinkers such as fluctuation of the amount of the main phases (alite (C3S) and belite (C2S)), excess of the free lime, occurrence of C3S polymorphs, and occurrence of moderately-crystallized structures are presented in this paper.