Search Results (4)

Doping semiconducting oxides, such as LaFeO₃ (LF), with metallic elements is a good strategy to improve the performance of photocatalysts. In this study, LF and ten different nanopowders metal-doped at the La or Fe site of LaFeO₃ were evaluated in the photocatalytic degradation of ciprofloxacin (CP) and oxytetracycline (OTC). The following metals were used in the doping (mol%) process of LF: Pd 3% and 5%; Cu 10%; Mg 5%, 10%, and 20%; Ga 10%; Y 10% and 20%; and Sr 20%. The doped samples were synthetized using a citrate auto-combustion technique. From the X-ray diffraction (XRD) data, only a single crystalline phase, namely an orthorhombic perovskite structure, was observed except for trace amounts of PdO in the sample with Pd 5%. The specific surface area (SSA) ranged from 9 m² g⁻¹ (Ga 10%) to 20 m² g⁻¹ (Mg 20%). SEM images show that all samples were constituted from agglomerates of particles whose sizes ranged from ca. 20 nm (Mg 20%) to ca. 100 nm (Pd 5%). Dilute aqueous solutions (5 × 10⁻⁶ M) prepared for both CP and OTC were irradiated for 240 min under visible-light and in the presence of H₂O₂ (10⁻² M). The results indicate a 78% removal of OTC with Cu 10% doped LF in a phosphate buffer (pH = 5.0). The degradation of CP is affected by pH and phosphate ions, with 78% (in unbuffered solution) and 54% (in phosphate buffer, pH = 5.0) removal achieved with Mg 10% doped LF. The reactions follow a pseudo-first order kinetic. Overall, this study is expected to deepen the assessment of photocatalytic activity by using substrates with different absorption capacities on photocatalysts. Full article

In this study, the combination of hydrothermal technique and seed-doping method was conducted to coordinately control the formation of fine MgO-Y₂O₃ powders, which are promising mid-infrared materials applied to hypersonic aircraft windows due to their excellent infrared transmissions over wide regions. Y(NO₃)₃·6H₂O, Mg(NO₃)₂·6H₂O, Y₂O₃ seeds and MgO seeds were used as raw materials to prepare the MgO-Y₂O₃ composite powders (50:50 vol.%), and the influences of the seed contents and hydrothermal treatment temperatures on the final powders and hot-pressed ceramics were investigated by XRD, SEM and TEM techniques. The results show that powders with a seed content of 5% that are hydrothermally synthesized at 190 °C can present a better uniformity and dispersion with a particle size of ~125 nm. Furthermore, the ceramics prepared with the above powders displayed a homogenous two-phase microstructure, fewer pores and a fine grain size with Y₂O₃ of ~1 µm and MgO of ~620 nm. The present study may open an avenue for developing transparent ceramics based on MgO-Y₂O₃ nanopowders prepared by hydrothermal technique. Full article

In the present work, a study was carried out to investigate the key factors that determine the uniformity, mass, thickness, and density of compacts obtained from nanopowders of solid solutions of yttrium and lanthanum oxides ((La_xY_1−x)₂O₃) with the help of the electrophoretic deposition (EPD). Nanopowders were obtained by laser ablation of a mixture of powders of yttrium oxide and lanthanum oxide in air. The implemented mechanisms of the EPD and factors of stability of alcohol suspensions are analyzed. It has been shown that acetylacetone with a concentration of 1 mg/m² can be used as a dispersant for stabilization of isopropanol suspensions of the nanoparticles during the EPD. It was shown that the maximum density of dry compacts with a thickness of 2.4 mm reaches 37% of theoretical when EPD is performed in vertical direction from a suspension of nanopowders with addition of acetylacetone. Full article

Oxygen-rich SiAlON ceramics doped with various nanosized metal oxide (MO) stabilizers were synthesized with a view to examine their effect on thermal and mechanical characteristics. The nanosized starting powder precursors comprising Si₃N₄, AlN, Al₂O₃, and SiO₂ along with oxides of Ba, Y, Mg, La, Nd, Eu, Dy, Er, and Yb as the MO charge stabilizer were employed in developing different SiAlON samples. Ultrasonic probe sonication was utilized to develop a homogenous mixture of initial powder precursors followed by spark plasma sintering (SPS) of the samples at the low temperature of 1500 °C coupled with 30 min of isothermal treatment. Sample compositions (according to general formula of alpha SiAlON: M_m/v^v+Si_12−(m+n)Al_m+nO_nN_16−n) selected in the present study are represented by m value of 1.1 and n value of 1.6. The synthesized samples were evaluated for their physical behavior, microstructural and crystal structure evolution, and thermal and mechanical characteristics. More specifically, the sintered ceramics were examined by X-ray diffraction and electron microscopy to comprehend and relate the structural characteristics with the densification, thermal conductivity, hardness, and fracture toughness. The high reactivity of the nanopowders and the localized heating provided by SPS resulted in densified ceramics with relative densities in the range of 92–96%. Vickers hardness values were found to be in the range of 12.4–17.0 GPa and were seen to be profoundly influenced by the grain size of the alpha SiAlON (primary) phase. The fracture toughness of the samples was measured to be in the range of 4.1–6.2 MPa·m^1/2. SiAlON samples synthesized using Er and Yb charge stabilizers were found to have the highest fracture toughness of 5.7 and 6.2 MPa·m^1/2, primarily due to the relatively higher content of the elongated beta phase. While there was no obvious relationship between the thermal conductivity and the alpha SiAlON metal charge stabilizers, the values were seen to be influenced by the grain size of alpha phase where Dy-SiAlON had the lowest thermal conductivity of 5.79 W/m⋅K and Er-SiAlON showed the highest value of thermal conductivity (6.91 W/m⋅K). It was concluded that scientifically selected metal oxide charge stabilizers are beneficial in developing SiAlON ceramics with properties tailored according to specific applications. Full article