Influence des additions nanométriques sur les propriétés thermodynamiques et structurales des matériaux.

Abstract

The objective of the work undertaken within the framework of this thesis is the study of the thermodynamic and structural characteristics of a class of nanocomposites. The characteristics of luminescent materials based on microcrystalline cellulose (MCC) containing oxides and rare earth elements were investigated. In order to highlight the role of multi-walled carbon nanotubes (MWCNT) in the improvement of physical properties of materials (portland cement, FeCu), several thermodynamic and structural techniques have been carried out. • For luminescent materials: Several series (A, B, C and D) of samples were studied. Several non-destructive testing methods have been used. The results obtained are a contribution to the development of cellulose/oxide composites studied as luminescent transformers of violet and blue light and of a new type of electroluminescent diodes of white light. • For Portland cement + plasticizer nanocomposites / MWCNT: Two samples underwent several characterizations to study the effect of the addition of multi walled carbon nanotubes (MWCNT) on the thermodynamic and structural properties of the samples produced. The DSCs of the two samples are similar. The two curves contain the same number of anomalies and they appear at the same temperatures. This can mean that only one mechanism is operational. The effect of MWCNT dispersion plays a significant role. TG has shown that MWCNTs well stabilize the matrix. The agglomeration of MWCNTs blocks the expansion of the matrix which can lead to contraction and occupation of different types of defects. The XRD showed a remarkable increase in the intensity of the peaks of the spectrum of the sample containing the MWCNTs. This may be related to the increase in the degree of crystallinity of the CH formed and/or to the increase in the rate of its formation. • For FeCu / MWCNT nanocomposites: Four FeCu-based nanocomposites containing different concentrations of MWCNT (0%, 0.25%, 0.75% and 1% MWCNT) were synthesized by high energy ball milling, then underwent characterizations using different techniques. XRD has shown that crystallite sizes vary from 26 to 84 nm and the stresses are negligible. The FeCu + 1% MWCNT sample has the best refinement. SERS characterization revealed that the 1% concentration of MWCNT is responsible for the homogeneous distribution of MWCNT. In addition, the ID/IG ratio decreased with the increasing of MWCNT concentration. A decrease in the expansion of the three nanomaterials was observed compared to conventional materials. The introduction of 1% MWCNT is the cause of the lower expansion. At low temperatures, the TG curves are line segments. As the temperature rises, TG increases slightly. At high temperatures, the effect of oxidation depends on the concentration of MWCNT. The FeCu/1% MWCNT nanomaterial has the lowest TG. The DSC results showed the same observation as that of the TG analysis.