RESUMO
Low loss Ruddlesden-Popper (RP) series, i.e., (Sr1-xCax)5Ti4O13, 0.0 ≤ x ≤ 0.06, has been synthesized by a mixed oxide route. In this work, the substitution of Ca2+ cation in Sr5Ti4O13 sintered ceramics was chosen to enhance the structural, optical, and dielectric properties of the product. It was found that the Ca2+ content has significant effects on enhancing the dielectric properties as compared to Mn and glass additions. It was observed that the relative density, band gap energy, and dielectric loss (tangent loss) increase while relative permittivity decreases along with Ca2+ content. High relative density (96.7%), low porosity, and high band gap energy (2.241 eV) values were obtained in (Sr1-xCax)5Ti4O13, 0.0 ≤ x ≤ 0.06 sintered ceramics. These results will play a key role in the application of dielectric resonators.
RESUMO
Nanofiltration and reverse osmosis are investigated as a possible alternative to the conventional methods of Cr(VI) removal from model water and industrial effluent. The influences of feed concentration, water recovery, pH, and the coexisting anions were studied. The results have shown that retention rates of hexavalent chromium can reach 99.7% using nanofiltration membrane (NF-HL) and vary from 85 to 99.9% using reverse osmosis membrane (RO-SG) depending upon the composition of the solution and operating conditions. This work was also extended to investigate the separation of Cr(VI) from car shock absorber factory effluent. The use of these membranes is very promising for Cr(VI) water treatment and desalting industry effluent. Spiegler-Kedem model was applied to experimental results in the aim to determine phenomenological parameters, the reflection coefficient of the membrane (σ), and the solute permeability coefficient (Ps ). The convective and diffusive parts of the mass transfer were quantified with predominance of the diffusive contribution.