Resumo em Inglês:

Abstract A new solid solution Bi1.56-xCaxSb1.48Co0.96O7-δ (0≤x≤0.3) with a pyrochlore-like structure (A2B2O7) was synthesized in air by chemical solid-state reaction. The solution crystallized in the cubic system with the Fd-3m space group. A regular decrease of the lattice parameter was observed when calcium replaced bismuth in the A site. The electric measurements showed that the electrical conductivity increased with the temperature and that high values of relative permittivity and dielectric loss were put in evidence. Measurements of magnetic susceptibility indicated a paramagnetic behavior of the samples with an effective moment included between 4.81 and 5.12 μB and at a low temperature para-ferromagnetic transition was observed for fractions x= 0.2 and 0.3.

Resumo em Inglês:

Abstract The need for the reconstruction of large bone defects is an issue that arouses great interest in the field of materials science. The development of synthetic grafts similar to bone tissue is a promising option. Thus, this study proposes the synthesis of a zinc oxide and calcium phosphate composite in order to evaluate both its properties and its potential for bone applications. The synthesis of the HAp/TCP@ZnO composite was carried out in two stages; first, the precipitation method was employed. In the second stage, the ZnO was incorporated into the powder produced in the first stage. After the characterization of the material, the presence of HAp in its X-ray diffractogram as the major phase and TCP as the secondary phase was verified; moreover, ZnO peaks were also detected. Tests in a simulated body fluid indicated that the composite was highly bioactive, whereas hemolysis tests confirmed its non-toxicity. The addition of 10.0% of ZnO to the biomaterial provided it with antimicrobial properties.

Resumo em Inglês:

Abstract Microstructure, texture, and mechanical and fracture characterization of three insulating commercial refractories were carried out in order to establish a correlation between these properties. The materials were characterized using X-ray powder diffraction (XRD) with Rietveld and Le Bail approximation to perform phase quantification, mercury intrusion porosimetry, and scanning electron microscopy. The mechanical behavior of insulating commercial refractories was studied with a multi-technique approach that involved a three-point bending test, uniaxial compression test, and single-edge notched beam (SENB) test. Stable fracture tests were successfully performed. The obtained results showed that the main differences between the materials studied were pore size distribution and mineralogical composition. Materials with the major amount of mullite had the highest values of the mechanical parameters in the different performed tests.

Resumo em Inglês:

Abstract A study of ZnO-based ceramic films prepared by the spray-pyrolysis technique is presented. Pure and Ni-doped thin film samples were deposited as a coating on a glass substrate and experimentally characterized using scanning electron and atomic force microscopies, X-ray diffraction, and UV-vis-NIR spectroscopy. The morphologic, crystallographic, and optical properties were analyzed. Structural and electronic properties were compared to predictions obtained from computational calculations based on the density functional theory plus U approach (DFT+U). All these simulations provided additional data that could be used as a reference for material modeling and a better understanding of the experimental results. It was found that spray pyrolysis can be used to produce thin film ceramic samples (~300 nm) with low amounts (<5%) of Ni impurities substitutionally located at the cationic sites of the ZnO wurtzite host structure. The results of this investigation showed that an experimental and theoretical study aided in a better characterization of the thin films, and helped to outline a more robust model of the samples.

Resumo em Inglês:

Abstract Some experimental results concerning the performance of fiber-reinforced soil composites made of soil and shredded fibers from waste tires are presented. The composite mixtures were prepared with fiber addition of 0, 15, 30, and 45 wt%. After molding, the specimens were oven-dried and tested for unconfined compressive strength and water immersion durability. The results showed an improvement in durability with the addition of fiber. The results also indicated good compressive strength performance for the composites with a fiber content of 15 and 30 wt%. The 30 wt% fiber addiction was the best choice because of the environmental sustainability appeal to solid waste reduction.

Resumo em Inglês:

Abstract Adhesion and homogeneity of the coating-substrate were analyzed on the basis of the establishment of coating mineralogy. Substrate raw materials used were kaolin clay and a calcined alumina 4 µm; a series of higher density ceramic coatings were deposited using calcined aluminas 0.5 µm and 4 µm, silica fume, and talc. The dip coating technique was applied to all substrates and later sintered at 1300 ºC. Shrinkage and density of coatings mixtures and substrate were separately evaluated. X-ray diffraction was utilized to identify the crystalline phases present in the coatings, while optical and electron microscopy were employed for the structural characterization of the coatings. Coatings exhibited lower shrinkage compared to the substrate. Among the specimens that exhibited good adhesion, cracks were observed to extend parallel to the substrate surface. The presence of cristobalite on the coating indicated that the failure mechanism involved buckling. The crack dimension presented on the coating decreased after adding talc to the mixture.

Resumo em Inglês:

Abstract This study aimed to describe the preparation of Nb2O5 pellets by uniaxial pressing, to investigate the influence of heat treatment at different temperatures (800, 900, and 1000 °C) on the physical, surface, microstructural, and adsorptive properties of the materials, and to assess their potential as reusable adsorbents for methylene blue removal. Specimens treated at 800 °C contained a mixture of monoclinic and hexagonal phases, with a predominance of monoclinic structures. By contrast, heat treatment at 900 °C and above resulted in complete conversion to the monoclinic phase. The surface of Nb2O5 particles contained basic groups, possibly oxygen ions (O-). Experimental investigations showed that methylene blue adsorption followed second-order kinetics, suggesting chemical diffusion as the dominant process. Maximum adsorption occurred at pH 6.0. Pellets remained intact after the adsorption test. A study was carried out to determine the reusability of pellets over five adsorption cycles in methylene blue solutions at different concentrations. The maximum adsorbed concentration was 10.4 mg.L-1. The adsorption capacity of Nb2O5 specimens gradually decreased from 56% in the first cycle to 25% in the fifth cycle. Despite this reduction in removal efficiency, Nb2O5 pellets showed promise as reusable adsorbents in heterogeneous processes because of their high potential adsorption capacity and easy separation from the reaction medium.

Resumo em Inglês:

Abstract This work examines the impact of mordenite-rich tuff (MT) on the technological properties of fired clay brick. These specimens were obtained by substituting clay with MT in various proportions (0, 5, 10, 15, 20, 50, and 100 wt%). They were pressed at 10 MPa, air-dried in the laboratory, and fired at 900 °C using two different clays: clay of Remila (CR) and clay of Adjiba (CA), Algeria. The mechanical, thermal, and physical properties of fired bricks were determined and compared to those of control bricks (0 wt%). According to the finding, the partial and total substitution of clay by MT reduced the sample’s thermal conductivity and bulk density. Thus, the MT increased the apparent porosity and the water absorption of clay brick while maintaining the compressive strength within the limits of the Algerian standards. This research revealed the possibility of producing bricks containing up to 100% by weight of MT with the required technical and environmental properties.

Resumo em Inglês:

Abstract Lead-based (PZT) ferroelectric ceramic materials were prepared utilizing the solid-state reaction method as a pure and doped with different additives. As a pure form, the composition with the chemical formula Pb1.03(Zr0.56Ti0.44)O3 characterized as rhombohedral structure according to the PZT phase diagram region was investigated systematically. Different strategies of doping were followed to investigate the influence of donor and acceptor ions in addition to complex doping on structural and microstructure properties of the parent composition: for the soft ceramic, 2 mol% lanthanum-doped PZT at A-site (PLZT), whereas 2 mol% of scandium-doped PZT at B-site to produce hard ceramic (PSZT). In terms of complex doping, 2 mol% of both La3+ and Sc3+ substituted A- and B-site, respectively (PLSZT). All samples showed dense and homogeneous microstructures, except PSZT ceramic displayed a small grain size. X-ray diffraction results showed that the addition of Sc3+ induced phase transformation and formation of a coexistence region consisting of tetragonal and rhombohedral phases. This region was recognized in both PSZT and PLSZT compositions. Hard ceramic (Sc3+-doped PZT) exhibited the highest values of relative permittivity and lowest dielectric loss at a frequency of 100 kHz.

Resumo em Inglês:

Abstract It is described for the first time the synthesis and characterization of NiMn2O4 employing the Mn ores from the Amazon Region as starting material, instead of using commercial reagents as normally occurs in its synthesis process. Initially, an Mn ore was transformed into a single product, the octahedral layer (OL) manganese oxide with Ni2+ ions interlayer (Ni-OL-2), which was used as a matrix to obtain NiMn2O4 by thermal decomposition. The following techniques were used for characterization: X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), infrared spectroscopy (FTIR), thermal analysis (TG-DTA), scanning (SEM) and transmission (TEM) electron microscopies. The results revealed that Mn oxide ore composed of nsutite mineral transformed into a well-ordered crystalline Ni-OL-2 phase, after the hydrothermal and cation exchange process. The thermal decomposition of Ni-OL-2 produced the nickel manganite phase at 850 °C with spherical ball morphology and crystal sizes in the range of 200-300 nm.

Resumo em Inglês:

Abstract Graphene oxide (GO) is one of the main precursors for the production of graphene and other graphene-based materials. We report a simple, safe, and fast synthesis method to obtain graphene oxide as a functional material for battery-type electrodes. Washing and lyophilization processes were performed to evaluate their effects on exfoliation and removal of functional groups from graphene sheets. Sample GO1 consisted of a 10-layer stack of oxidized graphene, while sample GO2 had 8 stacked layers. The difference between them was an extra washing and lyophilization process in the GO2 sample. The electrochemical performance of graphene oxide-based electrodes, classified as battery-type, indicated an improved specific capacity of 10.15 C.g-1 for GO1 against 4.55 C.g-1 for GO2 at a specific current of 0.5 A.g-1. This superior battery-type behavior of the GO1 electrode, also confirmed by electrochemical impedance spectroscopy, was most likely due to a higher degree of oxygenated groups on its surface, as shown by energy dispersive spectroscopy (EDS) and Fourier transform infrared spectroscopy (FTIR) studies.