S. H. Salah

Study of the high iron concentrations in cement clinker by Mössbauer spectroscopy

Determination par spectrometrie Mossbauer de la teneur en fer de clinkers obtenus a partir de melanges de matieres premieres contenant differentes teneurs en cendres de pyrite

Study of magnetic properties and lattice dynamics of the Cd x Co1−x ferrite system by Mössbauer effect

The magnetic properties and lattice dynamics of the spinel ferrite system CdxCox−1Fe2O4 (x=0.0, 0.1,…, and 1) were studied in the temperature range between 78 K to 800 K. The results showed that the samples withx=0.0 up to 0.5 are antiferromagnetic at room temperature, and a magnetic disorder transformation started to appear atx=0.6. The Neel temperature was found to decrease with increasing cadmium concentration. The reduced hyperfine magnetic fields for A and B sites were found to follow the Brillouin function and One-Third-Power Law. The results showed that the introduction of the Cs2+ ions decreased thef-value and Debye temperature. The anisotropic energy, for 0.1≤x≤0.9 was found to be of the order of 2×10−21 J.

Superparamagnetic behaviour of cement clinker and its ferrite phase doped with different impurities

Two oxide mixtures of clinker and its ferrite phase of compositions (66.5 wt.% CaO+24.5 wt.% SiO2+6.0 wt.% Al2O3+3.0 wt.% Fe2O3) and (60.4 wt.% CaO+15.4 wt.% Al2O3+24.2 wt.% Fe2O3) respectively were divided into protions and were mixed individually with 0.5, 1, 1.5 or 3 wt.% of LiF, MgF2, CaF2, CaCl2 or ZnO. Each portion of clinker was fired at 1450°C and each portion of ferrite was fired at 1350°C for 30 min. then quenched in air. Mössbauer effect and X-ray diffraction measurements were performed on each sample. The impurities doping produced small particle size. The LiF doping gave the smallest particle size and the highest blocking temperature. The ferrite with LiF exhibited two Fe3+ sites while the other used impurities gave one site only. The superparamagnetic relaxation appeared only in the spectra of ferrite with impurities, which means that the impurities in clinker have a tendency to combine with the calcium silicate phases not with C4AF.

Mössbauer studies on Al−Co ferrites

Mössbauer spectroscopy studies have been performed on the spinel CoAlxFe2−xO4 (2<-x<-1.7) in the temperature range 77–750 K using either a liquid nitrogen bath cryostat or a furnace. The samples are magnetic at 77 K giving spectra that have magnetic sextets coexisting with a central line which increases in population with the Al-content indicating relaxation effects. The data shows that Al possesses no preference to either tetrahedral or octahedral sites of the ferrite over the whole range of concentration. The Mössbauer hyperfine interaction parameters and magnetic transition temperatures were determined. As expected the hyperfine field and Curie temperature decrease when the Al-content increases.

Mössbauer effect and electron spin resonance study of CdxMg1−xFe2O4 system

This work deals with the application of Mossbauer Effect (ME) in studying the crystal electric field and the cation distribution among tetrahedral (A) and the octahedral (B) sites of the spinal structure in the ferrite system Cdx Mg1−x Fe2O4 (x=0, 0.2,...1). The electron spin resonance technique (ESR) was also applied for studying this ferrite system. It was possible to characterize the ESR spectra of ferrite through the combination with the ME spectra.The ESR spectra of magnesium ferrite showed two resonance positions of Fe3+ ions and indicated that a strong exchange interaction is dominant in the pure Mg-ferrite. For high Cd concentration ferrites only single resonance line was observed. These results could be interpretted on the basis of the ME results where it indicated that Cd2+ ions prefer tetrahedral positions, forcing the Fe3+ ions from these positions to join those in the octahedral sites. The complete site occupation with different types of cations was successfully achieved from the ME spectra. The values of the quadrupole splitting indicated that for each ferrite in the system there exists an electric field gradient surrounding the Fe3+ ions in each of the octahedral and tetrahedral sites. The increase in the Mg-concentration increases the symmetry of the electric field at these sites.

Mössbauer effect study of co-ferrite formation

The activation energy (Q) for the formation of CoFe2O4 was calculated from a series of Mössbauer effect spectra measured during the formation process. This was calculated by applying the Jander’s reaction kinetics equation to determine the reaction rate constant, on applying the Arrhenius equation. The obtained value ofQ was found to be 56 K · cal/mol.

Variation of Some Physical Properties of Brownmillerite Doped with a Transition Metal Oxide

Cement clinker is the main component of Portland cement. It is composed of four main phases. One of them is the brownmillerite or the ferrite phase of cement clinker. It is prepared according to the formula (4CaO)(Al2O3)(Fe2O3)l−x (M) x , where M represents transition metal oxides (TMO): TiO2, Cr2O3, Mn2O3 and WO3, where x = 1, 2, 3, 4 and 5 mol%. Each mixture was fired at 1300°C for 30 minutes in a platinum crucible. The samples were pulverized for Mossbauer spectroscopy, X-ray diffraction and a.c. conductivity measurements. A shift in the position of the characterized peaks of pure brownmillerite appears in the X-ray diffraction patterns of brownmillerite doped with a transition metal oxide. The a.c. conductivity showed a maximum value for the samples containing 3 mol% TiO2, Cr2O3 and Mn2O3, and 2 mol% WO3. The Mossbauer parameters for the sample containing 5 mol% M showed a gradual increase in the isomer shift values. The number of electrons in d-orbital for the doped transition atoms, as the nearest neighbor atoms increased from 2 to 5 electrons. The hyperfine magnetic field at Fe3+ (Oh) iron nucleus decreases with increasing M content. This may be due to the decrease of the particle size of brownmillerite.

Study of the dehydration of Portland Cement by Mössbauer spectrometry

Egyptian Portland Cement in the form of one inch cube was hydrated at different times of hydration. Nine cubes of each period of hydration were heated for five minutes 200, 300, 400 up to 1000°C then were quenched in air. The compressive strength was measured for these samples and related to unheated ones. These cubes were ground and measured by Mössbauer spectrometry to correlate the effect of dehydration of cement pastes on the states of iron, with the decrease of compressive strength. It was observed that starting from 400°C the central doublet characteristic of the hydration process decreased as the dehydration temperature was increased. At 1000°C the dehydration process was complete, the central doublet disappeared and the compressive strength vanished. The hydration process was found to be reversible. The application of Mössbauer spectrometry to estimate the degree of fire in concrete building was demonstrated.