M. Khitouni

Characterization of mechanically alloyed nanocrystalline fe(Al): crystallite size and dislocation density

A nanostructured disordered Fe(Al) solid solution was obtained from elemental powders of Fe and Al using a high-energy ball mill. The transformations occurring in the material during milling were studied with the use of X-ray diffraction. In addition lattice microstrain, average crystallite size, dislocation density, and the lattice parameter were determined. Scanning electron microscopy (SEM) was employed to examine the morphology of the samples as a function of milling times. Thermal behaviour of the milled powders was examined by differential scanning calorimetry (DSC). The results, as well as dissimilarity between calorimetric curves of the powders after 2 and 20 h of milling, indicated the formation of a nanostructured Fe(Al) solid solution.

Enhancement of the dielectric response through Al-substitution in La1.6Sr0.4NiO4 nickelates

The structures and dielectric properties of La1.6Sr0.4Ni1−xAlxO4 (x = 0, 0.2 and 0.4) ceramics elaborated using the Pechini method were studied for the first time. The same unique tetragonal phase was found in all compounds. The lattice parameters were found using Rietveld refinement. The surface morphology characterization and elemental analysis of these samples were respectively carried out using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). A giant dielectric response was observed in these ceramics, and one dielectric relaxation was found. The substitution of nickel with aluminum results in a colossal dielectric constant value (>106). The dielectric loss also drops with the increasing Al content; for x = 0.4 it is divided by 100 at room temperature for low frequencies. The giant dielectric response and low-temperature relaxation were mainly attributed to thermally activated small polaronic hopping in these compounds.

Thermal and Structural Analysis of Mn49.3Ni43.7Sn7.0 Heusler Alloy Ribbons

The martensitic transformation and the solidification structures of Mn49.3Ni43.7Sn7.0 alloy ribbons prepared by melt-spinning were investigated by means of scanning electron microscopy, X-ray diffraction and differential scanning calorimetry. In those experiments special attention was given to melt spinning processing parameters such as the linear surface speed of the copper wheel rotating, the injection overpressure and the distance between wheel and injection quartz tube. Transformation entropy was found higher when increasing linear surface speed or the distance from injection point to wheel. The resulting samples showed chemical compositions close to the nominal ones and, at room temperature, crystallized in a monoclinic single-phase martensite with 14M modulation (without a significant variation in the cell parameters). Strong dependence of ribbon thickness on processing parameters was found. The average grain size varied between 1.6 and 6.6 μm, while the start temperature of the martensitic temperature varied from 394 to 430 K.

Rapid degradation of azo-dye using Mn–Al powders produced by ball-milling

This study was conducted on the reduction reaction of the azo dye Reactive Black 5 by means of the Mn85Al15 particles prepared by melt-spinning and ball-milling processes. The morphology, the surface elementary composition and the phase structure of the powders were characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction. The degradation efficiency of the ball milled powder was measured by using an ultraviolet-visible absorption spectrophotometer and the collected powder was analyzed by means of Fourier transform infrared spectroscopy technique to characterize the functional groups in the extract. The degradation of Reactive Black 5 and the analysis of the aromatic by-products were investigated by high performance liquid chromatography coupled with tandem mass spectrometry. The ball-milled powder shows higher degradation efficiency and the Reactive Black 5 solution was completely decolorized after 30 min. The degradation kinetics and the formation by-products depend on the pH and temperature of the solution. The analyses of the extracted product confirmed the cleavage of the (–NN–) bonds. Our findings are expected to pave the way for a new opportunity with regard to the functional applications of nanostructured metallic particles.

Nanofibrillated cellulose as nanoreinforcement in Portland cement: Thermal, mechanical and microstructural properties:

Nanofibrillated cellulose from eucalyptus pulp, produced by high-pressure homogenization, was used as cement partial replacement for cement paste at a content ranging from 0% to 0.5% by weight of cement. The effect of the content of nanofibrillated cellulose on porosity, thermal properties, compressive strength and degree of cement hydration was investigated. Results have shown an improvement in the compressive strength by more than 50% with 0.3 wt% of added nanofibrillated cellulose. The porosity was reduced by nanofibrillated cellulose addition, and the greatest result was achieved with mixture incorporating 0.3 wt% nanofibrillated cellulose. The coefficient of thermal expansion and the thermal conductivity measurements, relative to nanofibrillated cellulose-reinforced cement pastes, have pointed out the reinforcement effectiveness of nanofibrillated cellulose. The degree of cement hydration has increased with nanofibrillated cellulose content. This trend was confirmed by X-ray diffraction and Fourier Transform Infrared spectroscopy. These analyses have revealed that the presence of nanofibrillated cellulose promoted the hydration of cement, by producing more portlandite and calcium silicate gel, which is likely the main reason accounting for the strong enhancement in the compressive strength.

Inhibitive action of stored olive mill wastewater (OMW) on the corrosion of copper in a NaCl solution

HPLC analysis shows that stored OMW is greatly enriched in phenolic compounds, mainly hydroxytyrosol (HT) (2.54 g L−1) and tyrosol (0.775 g L−1). But, after 4 years these compounds decrease in concentration. Potentiodynamic polarization measurements show that OMW acts as a mixed-type corrosion inhibitor for copper in 3 wt% NaCl solution. The exceptional effect of this inhibitor is above Ecorr. The full passivation range greatly increases upon the addition of inhibitor and increases further with increasing OMW concentration. For sufficiently-high OMW concentrations, a notable absence of trans-passivation phenomenon until 2500 mV is detected and no pits are observed on the samples’ surface.

Recovery, grain growth and recrystallization of mechanically alloyed FeAl alloy

A nanostructured disordered Fe(Al) solid solution was obtained by mechanical alloying (MA) for 20 h in a high-energy planetary ball-mill. The phase transformations and structural changes occurring in the studied material during MA and during subsequent heat treatments were investigated by X-ray diffraction. The recovery and the recrystallization of this compound are occurred due to the ordered nature of the grain boundaries after annealing at temperature ranging from 250 and 650 oC. The evolution of the thermal behaviour of the milled and heated powders was examined by differential scanning and calorimetry. We have shown that the occurrence of Fe2Al5 Fe4Al13and Fe3Al nanocrystalline phases at elevated temperature.

Effect of Amorphization Degree on Mechanical and Microstructural Properties of Portland Cement Paste

AbstractThis paper shows that besides the particle size reduction, prolonged high-energy ball milling of portland cement leads to mechanically induced phase transformation from the crystalline to t...