Browsing by Author "Djafar, Rabah"

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Cu2O addition and sintering temperature dependence of structural, microstructural and dielectric properties of CaCu3Ti4O12 ceramics
(Elsevier, 2020) Djafar, Rabah; Boumchedda, K.; Chaouchi, A.; Fasquelle, D.; Sedda, K.; Brahimi, S.; Khalfaoui, K.; Bououdina, M.
This study is aimed in the replacement of commonly used (CuO) by Cu2O in the synthesis of perovskite CaCu3Ti4O12 (CCTO) phase by the solid-state reaction method. The XRD analysis of powder calcined at 1100 °C and ceramics sintered at different temperatures show that the CCTO phase was well crystallized with the presence of small quantities of additional phases. The SEM/EDS analysis of prepared pellets show that the formation of Cu2O/CuO phase occurs above 950 °C, resulting in enhanced densification at 1050 °C (>96%). However, it is found that the Cu2O-based CCTO begins to degrade around 1090 °C. The densification after sintering at 1050 °C reaches 96%, meanwhile dielectric constant and loss tangent values are optimum in the low frequency range (<103 Hz); i.e. 13378 and 0.177, respectively. This favors the use of Cu2O instead of CuO in CCTO ceramics for applications at low frequencies
Développement et caractérisation de céramiques à grandes capacités électriques du type pérovskite de CaCu3 Ti4 O12(CCTO)
(Université M'Hamed Bougara Boumerdès : Faculté de Technologie, 2023) Djafar, Rabah; Boumchedda, Khaled(Directeur de thèse)
Au cours de cette étude, nous nous sommes intéressés à l’élaboration et à la caractérisation des céramiques de titanate de calcium et de cuivre CaCu 3 Ti 4 O 12 (CCTO) et à l’étude de l’influence des conditions de synthèse sur les propriétés structurales, micro-structurales et diélectriques de cette céramique, dans le but d’obtenir des matériaux de propriétés optimales par la méthode solide. Cette étude a mis en évidence l’aptitude de ce matériau à être utilisé en tant que condensateur. Dans notre étude, plusieurs composants sont élaborés, a base de poudres commerciales généralement utilisées (CaCO 3 , CuO et TiO 2 ) ou par le remplacement de CaCO 3 par le calcaire naturel de Guelma en vue de leur intégration au sein des condensateurs et valorisation de ce dernier, ainsi la synthèse et l’élaboration de CCTO par le remplacement de CuO par le Cu 2 O a été effectuée. Pour le composant CCTO, L’échantillon CCTO14h présente des meilleures propriétés diélectriques, des valeurs colossales de la permittivité (?'=95867 et 84762 à 20 Hz et à 1 KHz respectivement) et des très faibles valeurs des pertes (tg? =0,045 et 0.14 à 20 Hz et à 1 KHz respectivement) sont obtenues. L’analyse FRX montre que le calcaire naturel de Guelma est de haute pureté (dépasse 98.4% en CaCO 3 ) avec une bonne cristallinité (>73%), La phase CCTO pure a été bien synthétisée sans présence de phase secondaires pour les céramiques élaborées à base de calcaire naturel de Guelma, des valeurs de densité supérieurs à 92% sont trouvées. Ces analyses montrent que le calcaire naturel de Guelma peut constituer un candidat potentiel pour remplacer les carbonates commerciales (CaCO 3 ) pour la synthèse de matériaux CCTO. La phase CCTO a été synthétisée avec succès et avec la présence de phases secondaires en faibles quantité pour les céramiques CCTO fabriquées avec l'ajout de Cu 2 O au lieu de CuO. Un frittage complet a été réalisé à une température optimale de 1050 °C avec un taux de densification élevé (>96%). De plus, CCTO1050 a présenté les valeurs de constante diélectrique les plus élevées à basse fréquence (~13 400) et des pertes diélectriques assez faibles (tg? ~ 0.17). Les échantillons frittés à 1050 °C pendant 24 heures montrent la meilleure valeur de constante diélectrique (21392), tandis que les échantillons frittés à 14h montrent une valeur de pertes très faible (0.08).
Dielectric properties of nanocrystalline CaCu3Ti4O12 (CCTO) ceramics fabricated from Algerian limestone raw material
(Elsevier, 2023) Djafar, Rabah; Boumchedda, K.; Fasquelle, D.; Chaouchi, A.; Sedda, K.; Bououdina, M.; Bellucci, S.; Bánhegyi, G.
Algerian natural limestone was used to fabricate the perovskite CaCu3Ti4O12 phase (CCTO) to replace commercial calcium carbonate (CaCO3) powder by a solid-state method. X-ray diffraction analysis of CCTO ceramics sintered at 1010 °C manifested the formation of well-crystallized pure (CCTO) phase with narrow crystallite size (43–99 nm) without any additional phases after sintering beyond 4 h. Thermal analysis by DSC indicated that CCTO phase is stable up to 1151 °C, afterwards it decomposes into CaTiO3 and TiO2 and accompanied by the segregation of the CuO/Cu2O phase. Scanning electron microscopy observations of the ceramics sintered at 1010 °C showed that most of the grains have an average particle size in the narrow range of 1–2 μm. The sintered pellet at 1010 C° for 14 h showed the optimum density (>94%). This study highlights the importance of using natural calcium carbonates (extracted from Guelma limestone in Algeria) as potential replacement to commercial counterpart for the fabrication of dense well-crystallized perovskite-type ceramics with controlled particle size distribution as promising candidates for electronic applications
Preparation and characterization of biocomposites based on chitosan and biomimetic hydroxyapatite derived from natural phosphate rocks
(Elsevier, 2021) Brahimi, Salim; Ressler, Antonia; Boumchedda, Khaled; Hamidouche, Mohamed; Kenzour, Abdeghani; Djafar, Rabah; Antunović, Antunovic; Bauer, Leonard; Hvizdoš, Pavol; Ivanković, Hrvoje
Highly porous chitosan/hydroxyapatite (CS/HA) biocomposite scaffolds were prepared using the freeze-gelation method. A starting biomimetic HA powder was synthesized by a wet precipitation method using an abundant natural phosphate (NP) ore as raw material. Then, CS/HA scaffolds with different weight ratios (100/0; 90/10; 80/20; 70/30) have been prepared. The used powders and synthesized scaffolds were characterized by XRF, ICP-MS, FTIR, TG-DSC, XRD, SEM, and cell viability. The results showed that the precipitated raw powder was mainly composed of HA and amorphous calcium phosphate (ACP) with some traces of Mg2+, SiO42−, Sr2+, Na+ and Fe2+ ions which were usually found in such mineral NP precursors. The heat treatment of the raw powder at more than 750 °C leads to the formation of Mg-substituted β-tricalcium phosphate (β-TCMP). Moreover, the culture of human embryonic kidney cells indicated the non-cytotoxicity of the as-prepared powder. On the other hand, the elaborated CS/HA scaffolds exhibited a highly porous structure with well-interconnected pores and homogeneously dispersed HA particles. The measurement of swelling capacity under physiological conditions revealed that the addition of HA to the CS matrix effectively decreased the swelling percentage. The obtained results suggest that the elaborated CS/HA composites may have effective potential as biocompatible scaffolding materials for bone tissue engineering
The Synergistic Effect of Algerian Na-Bentonite/Potato Starch/Grass Powder on the Enhancement of Aged Water-based Drilling Fluids
(Springer, 2022) Sid, Asma Nour El Houda; Benalia, Kouin; hazourli, Abdelkrim; Djafar, Rabah; Gherraf, Noureddine; Bououdina, Mohamed
Nowadays, the use of eco-friendly additives in drilling fluids to improve rheological properties is widespread. This work aims to examine and assess the rheological characteristics and fluid loss of drilling fluid suspensions containing Algerian Na-Bentonite (NaB) and potato starch (PS) as viscosifier upon the addition of grass powder (GP). The obtained results indicate that the aging tests applied on different drilling fluid suspensions during 192 h at (20 °C) reduce the values of apparent viscosity by an average of (14.3%), plastic viscosity (22.2%), yield point (6.7%), and shear stress (47.3%) when varying the (PS) concentration in the suspensions (0.6, 1.2, 2%) as well as the values of fluid loss (9.5%); meanwhile, the values of initial and final gel strength are increased (32.6% and 19.6%, respectively). Subsequently, the possibility to further improve the rheological properties of drilling fluid suspensions using an environment eco-friendly additive (GP) has been studied. The introduction of (3, 6, 9 g) GP in the aged suspensions increases the values of rheological properties, i.e., the highest efficiency of 18.4% has been achieved by adding 9 g of GP to 2% (PS) aged suspension. The fluid loss test indicates that increasing the (GP) concentration in the (NaB+PS) suspension reduces the fluid loss volume by 36.42%. This study demonstrates the synergy of combining cost-effective GP to (NaB+PS) in aged drilling fluids by enhancing significantly its rheological properties besides a better environmental protection.
Tuning the dielectric properties of CaCu3Ti4O12 ceramic by Cu2O addition and microstructural modifications
(Elsevier, 2023) Djafar, Rabah; Boumchedda, K.; Fasquelle, D.; Chaouchi, A.; Sedda, K.; Bououdina, M.; Bellucci, S.
Cuprous (I) oxide (Cu2O) was used instead of Cupric (II) oxide (CuO) for the synthesis of CCTO ceramic by solid-state reaction. The impact of sintering time on the structure stability, grain size, and dielectric performance of Cu2O-based CCTO ceramics was discussed. XRD analysis indicates that the CaCu3Ti4O12 cubic phase was successfully synthetized. The studied samples manifested high permittivity and quite low dielectric loss values in the frequency range (20–106 Hz); with optimum values of 15,423 and 0.083 respectively achieved after sintering at 1050 °C for 14 h while for longer sintering times of 19 h and 24 h resulted in higher values of permittivity of 19,943 and 21,392 respectively were obtained and associated with an improved loss tangent of ∼0.114 and 0.127, respectively. It was found that a longer sintering time of Cu2O-based CCTO ceramics resulted in an important improvement of the dielectric properties