karima horchani | National Center of Researches in Materials Sciences (original) (raw)
Papers by karima horchani
Journal de Physique IV (Proceedings), 2004
Étude des propriétés de conduction électrique des phosphates condensés mixtes éléments monovalent... more Étude des propriétés de conduction électrique des phosphates condensés mixtes éléments monovalentsterres rares : LiDy (pro3) 4, NaNd (pro3) 4, AgLa (pro3) 4, NH4Dy (P03) 4
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2002
Single crystals of CsPrP4O12 and RbPrP4O12 cyclotetraphosphates have been grown using the flux me... more Single crystals of CsPrP4O12 and RbPrP4O12 cyclotetraphosphates have been grown using the flux method. Selective excitations in the Pr3+ (4f2) 3P0 and 3P2 levels using an excimer-pumped dye laser mainly result in intense line emissions in both materials. Though originating from transitions within the Pr3+ 4f2 ground configuration, these emissions have very short decay times, on the order of 50ns.
Thermochimica Acta, 2009
A new neodymium cyclotriphosphate pentahydrate powder, NdP 3 O 9 ·5H 2 O, has been prepared using... more A new neodymium cyclotriphosphate pentahydrate powder, NdP 3 O 9 ·5H 2 O, has been prepared using a classical chemistry method and characterized by X-ray diffraction and infrared spectroscopy techniques. The IR spectrum shows the characteristic bands of cyclotriphosphates as the triplet in the range 1055-1007-917 cm −1 .
: Ce travail est consacre a l'etude physico-chimique de phosphates condenses de terres rares.... more : Ce travail est consacre a l'etude physico-chimique de phosphates condenses de terres rares. Il est divise en deux parties principales. La premiere est consacree a la synthese des materiaux, aux etudes structurales et thermodynamiques des cyclotetraphosphates, CsPrP4O12 (cubique), RbPrP4O12 (cubique et monoclinique), KDyP4O12 (monoclinique), et des polyphosphates en phase monoclinique : CsPr(PO3)4, RbPr(PO3)4, LiLu0,9Pr0,1(PO3)4, TlTm(PO3)4 et Rb2Pr(PO3)5. L'etude structurale a montre que les distances entre les ions terres rares les plus proches sont relativement grandes et que les polyedres LnO8 sont bien isoles les uns des autres, ce qui ne favorise pas les processus de transferts d'energie entre ions terres rares. L'etude par spectroscopie infrarouge et spectroscopie de diffusion Raman nous a permis de differencier les cyclotetraphosphates des polyphosphates et de faire des previsions sur la symetrie des anions cyclotetraphosphates. La seconde concerne les proprietes optiques de l'ion praseodyme present a l'etat trivalent dans les composes consideres. Les transitions intraconfigurationnelles 4f2-->4f2 donnent lieu a des emissions de fluorescence intenses dont les spectres sont interpretes en utilisant le programme de calcul de niveaux d'energie SPECTRA. Les durees de vie des emissions observees correspondantes sont tres breves pour des transitions dipolaires electriques " forcees " et ne dependent que tres peu de la temperature. Un calcul des probabilites des transitions non radiatives 3P0-->1D2 internes a l'ion Pr3+ a montre que celles-ci varient tres peu entre 300 et 6 K et que la rapidite des declins des fluorescences issues du niveau 3P0 peut s'expliquer par l'intervention de ces processus non radiatifs. Sous excitation a l'aide d'une source de rayons X, les materiaux consideres presentent des emissions ultraviolettes tres intenses associees aux transitions 4f15d1-->4f2 permises a l'ordre dipolaire electrique et caracterisees par des declins de fluorescence tres rapides, de l'ordre de quelques nanosecondes. La comparaison avec le materiau scintillateur de reference, Bi4Ge3O12, conduit a la conclusion que ces materiaux possedent des potentialites certaines pour des applications dans le domaine des materiaux scintillateurs rapides.
Journal of Luminescence, 2001
Single crystals of CsPrP 4 O 12 and RbPrP 4 O 12 cyclotetraphosphates have been grown using the f... more Single crystals of CsPrP 4 O 12 and RbPrP 4 O 12 cyclotetraphosphates have been grown using the flux method. Selective excitations in the Pr 3+ (4f 2) 3 P 0 and 3 P 2 levels using an excimer-pumped dye laser mainly result in intense line emissions in both materials. Although originating from transitions within the Pr 3+ 4f 2 ground configuration, these emissions have very short decay times, of the order of 50 ns. Both compounds also exhibit intense ultraviolet band emissions in the 200-300 nm spectral range when using either a xenon lamp or an X-ray source for optical excitation. The decays of these emissions under pulsed X-ray excitation were measured using the start-stop technique. They exhibit a main fast component (decay time t f) and a minor slower one (decay time t s), the decay times of which are t f D9 and 5 ns, t s D30 and 20 ns, in the Cs and Rb compounds, respectively.
Journal de Physique IV (Proceedings), 2004
Crystals of RbEr(PO 3) 4 have been grown by the flux technique and characterized by X-ray diffrac... more Crystals of RbEr(PO 3) 4 have been grown by the flux technique and characterized by X-ray diffraction, UV-Vis absorbance and infrared spectroscopy. Single crystal structure of RbEr(PO 3) 4 has been solved, it crystallizes in the monoclinic P2 1 /n space group with lattice parameters : a = 10,2419(2), b = 8,8349(2), c = 10,9361(2) Å, ß = 106,229(2)°, Z = 4. The crystal structure has been refined yielding a final R(F 2) = 0.026 for 2206 independent reflections (F o 2 ≥ 2σ(F o 2)). The RbEr(PO 3) 4 structure is characterized by helical ribbons (PO 3) ∞ running along the c-axis. The erbium ions have an eightfold coordination. The ErO 8 polyhedra are isolated from each other in the sense that they do not share any oxygen atom. The minimal distance between two atoms of erbium is 6,2583 Å. Résumé. Le polyphosphate RbEr(PO 3) 4 est synthétisé, sous forme monocristalline, par la méthode de flux ; ce composé est caractérisé par diffraction RX, spectroscopie d'absorption optique et spectroscopie de vibration IR. L'étude structurale de RbEr(PO 3) 4 a montré que ce polyphosphate cristallise dans le système monoclinique, de groupe d'espace P2 1 /n, les paramètres de maille sont : a = 10,2419(2), b = 8,8349(2), c = 10,9361(2) Å, ß = 106,229(2)°, Z = 4. L'affinement conduit à un facteur de confiance R(F 2) = 0.026, pour 2206 réflexions indépendantes (F o 2 ≥ 2σ(F o 2)). La structure de RbEr(PO 3) 4 est caractérisée par une chaîne hélicoïdale (PO 3) ∞ se développant le long de l'axe c. Les atomes d'erbium ont un environnement de 8 oxygènes. Les polyèdres ErO 8 sont isolés les uns des autres, ils ne présentent aucun atome d'oxygène en commun. La distance Er-Er la plus courte mesure 6,258 (Å).
Journal de Physique IV (Proceedings), 2004
Crystals of NaHo(PO 3) 4 have been grown by the flux technique and characterized by X-ray diffrac... more Crystals of NaHo(PO 3) 4 have been grown by the flux technique and characterized by X-ray diffraction and infrared spectroscopy. Single crystal structure of NaHo(PO 3) 4 has been solved, it crystallizes in the monoclinic P2 1 /n space group with lattice parameters : a = 9,699(4), b = 13,0441(5), c = 7,1614(3) Å , ß = 89,314(1)° , Z = 4. The crystal structure has been refined yielding a final R(F 2) = 0.033 for 2064 independent reflections (F o 2 ≥ 2σ(F o 2)). The NaHo(PO 3) 4 structure is characterized by helical ribbons (PO 3) ∞ running along the c-axis. The HoO 8 and NaO 7 polyhedra form zigzag chains with common faces and surrounded by four (PO 3) ∞ chains Résumé. Le polyphosphate NaHo(PO 3) 4 est synthétisé, sous forme de monocristaux, par la méthode de flux; ce composé est caractérisé par diffraction RX et spectroscopie de vibration IR. L'étude structurale de NaHo(PO 3) 4 a montré que ce polyphosphate cristallise dans le système monoclinique, de groupe d'espace P2 1 /n, les paramètres de maille sont : a = 9,699(4), b = 13,0441(5), c = 7,1614(3) Å , ß = 89,314(1)° , Z = 4. L'affinement conduit à un facteur de confiance R 1 = 3,3 % pour 2064 réflexions indépendantes. La structure de NaHo(PO 3) 4 est caractérisée par une chaîne hélicoïdale (PO 3) ∞ se développant le long de l'axe c. Les polyèdres HoO 8 et NaO 7 forment des chaînes en zigzag possédant des faces en commun et entourés par quatre chaînes (PO 3) ∞ .
Optical Materials, 2006
The optical properties of Pr3+ ions in cyclotetraphosphates M1PrP4O12 (M1=Cs, Rb), cyclotriphosph... more The optical properties of Pr3+ ions in cyclotetraphosphates M1PrP4O12 (M1=Cs, Rb), cyclotriphosphate PrP3O9·3H2O and diphosphate NaPrP2O7 have been investigated. Emission spectra under selective laser excitation in the 3PJ multiplets (J=0,1,2) have been measured both at room and low temperatures. The resulting fluorescent emissions originating mainly from the 3P0 level exhibit very fast decay times shorter than 100ns at 6K. The results concerning cyclotetraphosphates are compared with those obtained for the corresponding polyphosphates M1Pr(PO3)4 with the aim of understanding the possible role of the cyclic structure. In the same way, the results concerning the hydrated cyclotriphosphates are compared with those obtained for the corresponding anhydrous polyphosphate Pr(PO3)3, in order to point out the role of water molecules. All the materials under consideration (cyclotriphosphate PrP3O9·3H2O excepted) exhibit intense ultraviolet emissions under X-ray or VUV synchrotron radiation e...
Journal of Essential Oil Research
Membranes
In recent years, numerous studies have been conducted to develop biopolymer-based membranes, high... more In recent years, numerous studies have been conducted to develop biopolymer-based membranes, highlighting the challenges to prepare porous structures with control porosity. In this paper an innovative method that relies on the generation of Pickering emulsions was developed to prepare porous membranes from gelatin for filtration purpose. Hexagonal boron nitride nanosheets (h-BNNS) were used to stabilize micro-droplets of castor oil in a continuous homogeneous gelatin solution. Two steps in the membrane preparation process strongly influenced the porous structure. Specifically, the duration of the drying time after emulsion casting and the duration of the cross-linking step affected membrane pore size, hydrophobicity, water swelling, and water permeability. By controlling these two steps, membranes could be designed with pore size between 0.39 and 1.60 μm and display pure water permeability between 150 and 506 L h−1 m−2 bar−1. These membranes have been tested for complexation–ultrafi...
New Journal of Chemistry
The proposal of a method for converting the phosphogypsum waste (PG) remains the focus of many re... more The proposal of a method for converting the phosphogypsum waste (PG) remains the focus of many researchers since its quantity, growing considerably, is causing serious environmental problems.
Journal of Electronic Materials
International Journal of Biological Macromolecules
Journal of Asian Ceramic Societies
Among La 1-x Ca x FeO 3-δ (0 ≤ x ≤ 0.5) compounds, the optimal value of the direct current conduc... more Among La 1-x Ca x FeO 3-δ (0 ≤ x ≤ 0.5) compounds, the optimal value of the direct current conductivity was registered for a 20% substituted amount. We therefore attempted to study the impedance and dielectric properties of 20% calcium-substituted lanthanum ferrite. We investigated the electric properties in depth between 5 Hz and 13 MHz from 350 to 800°C. The results reveal interesting properties. Indeed, the perovskite shows a huge dielectric constant which promotes its utilization in high-performance dielectric material applications. At a given temperature, ε' and tan(δ) decrease with increases in frequency. This trend was explained based on the Maxwell Wagner polarization model. The variations in dielectric loss (ε") with frequency obey the Giuntini theory based on the hopping model. As the temperature increases from 350 to 800°C, the binding energy increases from 0.22 to 0.34 eV, while the minimum hopping distance decreases from 2.16 to 0.12 pm. Consideration of the electric modulus analyzes showed that the relaxation mechanism is dominated at below 400°C by a shortrange movement of charge carriers, whereas at above that temperature, a long-range movement of charge carriers is dominant. This study presents a solid foundation for the polarization and dielectric properties of lanthanum ferrite, which is a lead-free, environmentally friendly material and a promising candidate for use in nonlinear optical applications and microwave devices.
Korean Journal of Chemical Engineering
Journal of African Earth Sciences
Advances in Biochemical Engineering/Biotechnology
Chemistry Africa
Phosphogypsum (PG) is classified as the main hazardous waste present in large quantities in Tunis... more Phosphogypsum (PG) is classified as the main hazardous waste present in large quantities in Tunisia. It is a by-product of the fertilizer industry produced by a sulfuric acid attack on calcium phosphate. Storage and management of this toxic waste are environmental problems that concern many countries producing phosphate fertilizer, especially since waste is, in principle, prohibited by international law. Therefore, finding out a solution for the valorization or the removal of phosphogypsum has become a universal preoccupation and a topical research field. In this work, a fresh produced PG sample was firstly characterized by various analytical methods to determine its chemical composition as well as its rare earth elements (REEs) amount. Then, a hydrothermal conversion of the PG allowed obtaining an insoluble residue of calcium carbonate richer in REEs than the starting sample such that the enrichment rate was 66%. The obtained residue, considered after that as an interesting source of rare earths, was leached with a hydrochloric solution (5-6%) in the presence of ascorbic acid as reducing agent. The leaching method favored the migration of 89% of REEs to the leach liquor.
Journal de Physique IV (Proceedings), 2004
Étude des propriétés de conduction électrique des phosphates condensés mixtes éléments monovalent... more Étude des propriétés de conduction électrique des phosphates condensés mixtes éléments monovalentsterres rares : LiDy (pro3) 4, NaNd (pro3) 4, AgLa (pro3) 4, NH4Dy (P03) 4
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2002
Single crystals of CsPrP4O12 and RbPrP4O12 cyclotetraphosphates have been grown using the flux me... more Single crystals of CsPrP4O12 and RbPrP4O12 cyclotetraphosphates have been grown using the flux method. Selective excitations in the Pr3+ (4f2) 3P0 and 3P2 levels using an excimer-pumped dye laser mainly result in intense line emissions in both materials. Though originating from transitions within the Pr3+ 4f2 ground configuration, these emissions have very short decay times, on the order of 50ns.
Thermochimica Acta, 2009
A new neodymium cyclotriphosphate pentahydrate powder, NdP 3 O 9 ·5H 2 O, has been prepared using... more A new neodymium cyclotriphosphate pentahydrate powder, NdP 3 O 9 ·5H 2 O, has been prepared using a classical chemistry method and characterized by X-ray diffraction and infrared spectroscopy techniques. The IR spectrum shows the characteristic bands of cyclotriphosphates as the triplet in the range 1055-1007-917 cm −1 .
: Ce travail est consacre a l'etude physico-chimique de phosphates condenses de terres rares.... more : Ce travail est consacre a l'etude physico-chimique de phosphates condenses de terres rares. Il est divise en deux parties principales. La premiere est consacree a la synthese des materiaux, aux etudes structurales et thermodynamiques des cyclotetraphosphates, CsPrP4O12 (cubique), RbPrP4O12 (cubique et monoclinique), KDyP4O12 (monoclinique), et des polyphosphates en phase monoclinique : CsPr(PO3)4, RbPr(PO3)4, LiLu0,9Pr0,1(PO3)4, TlTm(PO3)4 et Rb2Pr(PO3)5. L'etude structurale a montre que les distances entre les ions terres rares les plus proches sont relativement grandes et que les polyedres LnO8 sont bien isoles les uns des autres, ce qui ne favorise pas les processus de transferts d'energie entre ions terres rares. L'etude par spectroscopie infrarouge et spectroscopie de diffusion Raman nous a permis de differencier les cyclotetraphosphates des polyphosphates et de faire des previsions sur la symetrie des anions cyclotetraphosphates. La seconde concerne les proprietes optiques de l'ion praseodyme present a l'etat trivalent dans les composes consideres. Les transitions intraconfigurationnelles 4f2-->4f2 donnent lieu a des emissions de fluorescence intenses dont les spectres sont interpretes en utilisant le programme de calcul de niveaux d'energie SPECTRA. Les durees de vie des emissions observees correspondantes sont tres breves pour des transitions dipolaires electriques " forcees " et ne dependent que tres peu de la temperature. Un calcul des probabilites des transitions non radiatives 3P0-->1D2 internes a l'ion Pr3+ a montre que celles-ci varient tres peu entre 300 et 6 K et que la rapidite des declins des fluorescences issues du niveau 3P0 peut s'expliquer par l'intervention de ces processus non radiatifs. Sous excitation a l'aide d'une source de rayons X, les materiaux consideres presentent des emissions ultraviolettes tres intenses associees aux transitions 4f15d1-->4f2 permises a l'ordre dipolaire electrique et caracterisees par des declins de fluorescence tres rapides, de l'ordre de quelques nanosecondes. La comparaison avec le materiau scintillateur de reference, Bi4Ge3O12, conduit a la conclusion que ces materiaux possedent des potentialites certaines pour des applications dans le domaine des materiaux scintillateurs rapides.
Journal of Luminescence, 2001
Single crystals of CsPrP 4 O 12 and RbPrP 4 O 12 cyclotetraphosphates have been grown using the f... more Single crystals of CsPrP 4 O 12 and RbPrP 4 O 12 cyclotetraphosphates have been grown using the flux method. Selective excitations in the Pr 3+ (4f 2) 3 P 0 and 3 P 2 levels using an excimer-pumped dye laser mainly result in intense line emissions in both materials. Although originating from transitions within the Pr 3+ 4f 2 ground configuration, these emissions have very short decay times, of the order of 50 ns. Both compounds also exhibit intense ultraviolet band emissions in the 200-300 nm spectral range when using either a xenon lamp or an X-ray source for optical excitation. The decays of these emissions under pulsed X-ray excitation were measured using the start-stop technique. They exhibit a main fast component (decay time t f) and a minor slower one (decay time t s), the decay times of which are t f D9 and 5 ns, t s D30 and 20 ns, in the Cs and Rb compounds, respectively.
Journal de Physique IV (Proceedings), 2004
Crystals of RbEr(PO 3) 4 have been grown by the flux technique and characterized by X-ray diffrac... more Crystals of RbEr(PO 3) 4 have been grown by the flux technique and characterized by X-ray diffraction, UV-Vis absorbance and infrared spectroscopy. Single crystal structure of RbEr(PO 3) 4 has been solved, it crystallizes in the monoclinic P2 1 /n space group with lattice parameters : a = 10,2419(2), b = 8,8349(2), c = 10,9361(2) Å, ß = 106,229(2)°, Z = 4. The crystal structure has been refined yielding a final R(F 2) = 0.026 for 2206 independent reflections (F o 2 ≥ 2σ(F o 2)). The RbEr(PO 3) 4 structure is characterized by helical ribbons (PO 3) ∞ running along the c-axis. The erbium ions have an eightfold coordination. The ErO 8 polyhedra are isolated from each other in the sense that they do not share any oxygen atom. The minimal distance between two atoms of erbium is 6,2583 Å. Résumé. Le polyphosphate RbEr(PO 3) 4 est synthétisé, sous forme monocristalline, par la méthode de flux ; ce composé est caractérisé par diffraction RX, spectroscopie d'absorption optique et spectroscopie de vibration IR. L'étude structurale de RbEr(PO 3) 4 a montré que ce polyphosphate cristallise dans le système monoclinique, de groupe d'espace P2 1 /n, les paramètres de maille sont : a = 10,2419(2), b = 8,8349(2), c = 10,9361(2) Å, ß = 106,229(2)°, Z = 4. L'affinement conduit à un facteur de confiance R(F 2) = 0.026, pour 2206 réflexions indépendantes (F o 2 ≥ 2σ(F o 2)). La structure de RbEr(PO 3) 4 est caractérisée par une chaîne hélicoïdale (PO 3) ∞ se développant le long de l'axe c. Les atomes d'erbium ont un environnement de 8 oxygènes. Les polyèdres ErO 8 sont isolés les uns des autres, ils ne présentent aucun atome d'oxygène en commun. La distance Er-Er la plus courte mesure 6,258 (Å).
Journal de Physique IV (Proceedings), 2004
Crystals of NaHo(PO 3) 4 have been grown by the flux technique and characterized by X-ray diffrac... more Crystals of NaHo(PO 3) 4 have been grown by the flux technique and characterized by X-ray diffraction and infrared spectroscopy. Single crystal structure of NaHo(PO 3) 4 has been solved, it crystallizes in the monoclinic P2 1 /n space group with lattice parameters : a = 9,699(4), b = 13,0441(5), c = 7,1614(3) Å , ß = 89,314(1)° , Z = 4. The crystal structure has been refined yielding a final R(F 2) = 0.033 for 2064 independent reflections (F o 2 ≥ 2σ(F o 2)). The NaHo(PO 3) 4 structure is characterized by helical ribbons (PO 3) ∞ running along the c-axis. The HoO 8 and NaO 7 polyhedra form zigzag chains with common faces and surrounded by four (PO 3) ∞ chains Résumé. Le polyphosphate NaHo(PO 3) 4 est synthétisé, sous forme de monocristaux, par la méthode de flux; ce composé est caractérisé par diffraction RX et spectroscopie de vibration IR. L'étude structurale de NaHo(PO 3) 4 a montré que ce polyphosphate cristallise dans le système monoclinique, de groupe d'espace P2 1 /n, les paramètres de maille sont : a = 9,699(4), b = 13,0441(5), c = 7,1614(3) Å , ß = 89,314(1)° , Z = 4. L'affinement conduit à un facteur de confiance R 1 = 3,3 % pour 2064 réflexions indépendantes. La structure de NaHo(PO 3) 4 est caractérisée par une chaîne hélicoïdale (PO 3) ∞ se développant le long de l'axe c. Les polyèdres HoO 8 et NaO 7 forment des chaînes en zigzag possédant des faces en commun et entourés par quatre chaînes (PO 3) ∞ .
Optical Materials, 2006
The optical properties of Pr3+ ions in cyclotetraphosphates M1PrP4O12 (M1=Cs, Rb), cyclotriphosph... more The optical properties of Pr3+ ions in cyclotetraphosphates M1PrP4O12 (M1=Cs, Rb), cyclotriphosphate PrP3O9·3H2O and diphosphate NaPrP2O7 have been investigated. Emission spectra under selective laser excitation in the 3PJ multiplets (J=0,1,2) have been measured both at room and low temperatures. The resulting fluorescent emissions originating mainly from the 3P0 level exhibit very fast decay times shorter than 100ns at 6K. The results concerning cyclotetraphosphates are compared with those obtained for the corresponding polyphosphates M1Pr(PO3)4 with the aim of understanding the possible role of the cyclic structure. In the same way, the results concerning the hydrated cyclotriphosphates are compared with those obtained for the corresponding anhydrous polyphosphate Pr(PO3)3, in order to point out the role of water molecules. All the materials under consideration (cyclotriphosphate PrP3O9·3H2O excepted) exhibit intense ultraviolet emissions under X-ray or VUV synchrotron radiation e...
Journal of Essential Oil Research
Membranes
In recent years, numerous studies have been conducted to develop biopolymer-based membranes, high... more In recent years, numerous studies have been conducted to develop biopolymer-based membranes, highlighting the challenges to prepare porous structures with control porosity. In this paper an innovative method that relies on the generation of Pickering emulsions was developed to prepare porous membranes from gelatin for filtration purpose. Hexagonal boron nitride nanosheets (h-BNNS) were used to stabilize micro-droplets of castor oil in a continuous homogeneous gelatin solution. Two steps in the membrane preparation process strongly influenced the porous structure. Specifically, the duration of the drying time after emulsion casting and the duration of the cross-linking step affected membrane pore size, hydrophobicity, water swelling, and water permeability. By controlling these two steps, membranes could be designed with pore size between 0.39 and 1.60 μm and display pure water permeability between 150 and 506 L h−1 m−2 bar−1. These membranes have been tested for complexation–ultrafi...
New Journal of Chemistry
The proposal of a method for converting the phosphogypsum waste (PG) remains the focus of many re... more The proposal of a method for converting the phosphogypsum waste (PG) remains the focus of many researchers since its quantity, growing considerably, is causing serious environmental problems.
Journal of Electronic Materials
International Journal of Biological Macromolecules
Journal of Asian Ceramic Societies
Among La 1-x Ca x FeO 3-δ (0 ≤ x ≤ 0.5) compounds, the optimal value of the direct current conduc... more Among La 1-x Ca x FeO 3-δ (0 ≤ x ≤ 0.5) compounds, the optimal value of the direct current conductivity was registered for a 20% substituted amount. We therefore attempted to study the impedance and dielectric properties of 20% calcium-substituted lanthanum ferrite. We investigated the electric properties in depth between 5 Hz and 13 MHz from 350 to 800°C. The results reveal interesting properties. Indeed, the perovskite shows a huge dielectric constant which promotes its utilization in high-performance dielectric material applications. At a given temperature, ε' and tan(δ) decrease with increases in frequency. This trend was explained based on the Maxwell Wagner polarization model. The variations in dielectric loss (ε") with frequency obey the Giuntini theory based on the hopping model. As the temperature increases from 350 to 800°C, the binding energy increases from 0.22 to 0.34 eV, while the minimum hopping distance decreases from 2.16 to 0.12 pm. Consideration of the electric modulus analyzes showed that the relaxation mechanism is dominated at below 400°C by a shortrange movement of charge carriers, whereas at above that temperature, a long-range movement of charge carriers is dominant. This study presents a solid foundation for the polarization and dielectric properties of lanthanum ferrite, which is a lead-free, environmentally friendly material and a promising candidate for use in nonlinear optical applications and microwave devices.
Korean Journal of Chemical Engineering
Journal of African Earth Sciences
Advances in Biochemical Engineering/Biotechnology
Chemistry Africa
Phosphogypsum (PG) is classified as the main hazardous waste present in large quantities in Tunis... more Phosphogypsum (PG) is classified as the main hazardous waste present in large quantities in Tunisia. It is a by-product of the fertilizer industry produced by a sulfuric acid attack on calcium phosphate. Storage and management of this toxic waste are environmental problems that concern many countries producing phosphate fertilizer, especially since waste is, in principle, prohibited by international law. Therefore, finding out a solution for the valorization or the removal of phosphogypsum has become a universal preoccupation and a topical research field. In this work, a fresh produced PG sample was firstly characterized by various analytical methods to determine its chemical composition as well as its rare earth elements (REEs) amount. Then, a hydrothermal conversion of the PG allowed obtaining an insoluble residue of calcium carbonate richer in REEs than the starting sample such that the enrichment rate was 66%. The obtained residue, considered after that as an interesting source of rare earths, was leached with a hydrochloric solution (5-6%) in the presence of ascorbic acid as reducing agent. The leaching method favored the migration of 89% of REEs to the leach liquor.