Volume 2 Issue 2
Authors: S. N. Kharin
Abstract: The mechanism of thermionic emission from the cathode surface based on Richardson-Dushman equation is corrected by addition of another emission mechanism due to electrochemical phenomena in melted pool on the cathode. It is important for thermo-chemical cathodes based on such materials as copper, zirconium, hafnium and their alloys. Mathematical model describing phenomena in opening electrical contacts takes into account ion bombardment of cathode, arc column radiation, heat conduction inside contacts, inverse electrons etc. The new element of this model is the component of electron current caused by oxidation-reduction phenomena on melted electrode surface. It is possible in the frame of this model to explain decreasing of work function and measured values of contact erosion. Results of calculations using new model are compared with data presented in the book R. Holm “Electric Contacts” as well as with other experimental data.
Keywords: Thermochemical Cathodes; Electric Arc Phenomena; Mathematical Modeling
Authors: Razieh Fazaeli; Hamid Aliyan; Mona Masoudinia; Zahra Heidari
Abstract: The direct encapsulation of tungstophosphoric acid (PW12) into MIL-101 was done (PW12@MIL(101)en). The addition of PW12 to the synthesis mixture of MIL-101 yielded the direct encapsulation of chromium-containing polyoxometalates (POMs) inside the metal organic framework (MOF) structure, with a good distribution over the MIL-101 crystals. Another PW12 composite (PW12@MIL(101)im) was prepared via the impregnation of the polyoxometalate in MIL-101. The structural and textural characterizations of PW12@MIL(101) were done using FTIR, X-ray diffraction, N2 adsorption-desorption, and TEM. XRD and adsorption–desorption analysis showed that the mesostructure of MIL-101 remains intact after vanadium oxide modifications, while spectral technique showed the successful immobilizing of the neat vanadium oxide inside the MIL-101 cavities. PW12@MIL(101) has emerged as highly efficient and heterogeneous catalyst for selective oxidation of sulfides to sulfoxides and sulfones because of its high specific surface area, tuneable pore size, and unique structure.
Keywords: Metal-organic Frameworks (MOFs); MIL-101; Heterogeneous Catalyst; Phosphotungstic Acid (PW12); Encapsulation; Impregnation
Authors: Zina Al-Shadidi; I.H. Khdayer
Abstract: Generally the a.c. conductivity shows a power law in frequency where the exponent s ≤ 1. As the frequency goes to zero the conductivity become frequency independent. The a.c. conductivity was studied for the Ge1-xSex thin films to see how the selenium contents affect the permittivity and the permeability for the Ge1-x Sex. The thin films prepared by thermal evaporation at room temperature and under vacuum (~2 x10-5toor) using Edward coating unit model 306A. From the relation between ln conductivity and ln w, the effect of selenium contents in Ge1-x Sex thin films on the exponent value, the relaxation time and the maximum barrier height. An algebric fitting method for circles and circular arcs was used to find the permittivity and the permeability from cole-cole diagram, and to see how the selenium content affects these parameter values of Ge1-x Sex thin films. It was clear that there were direct proportions between the selenium content in the Ge1-x Sex structure and each of the following factors: The exponent S, the barrier height, and the permittivity. It was also possible to note the presence of inverse proportion between the selenium content in the Ge1-x Sex structure and each of the polarizability and the charge carrier relaxation time.
Keywords: a.c. Conductivity; Cole-cole Diagram; Thin Films; Matlab
Authors: Liliane Schier de Lima; Laura Techy; Sueli Pércio Quináia
Abstract: The present work evaluated the simultaneous adsorption of the metallic ions Cd(II), Cu(II) and Cr(VI) onto bamboo activated carbon. The main and interactive factors studied were determined as the initial concentration of metallic ions, pH, and contact time, by using a factorial design. The analysis of variance (ANOVA) was applied in the factorial design and the statistics data showed adequate models. The kinetic model of pseudo-second-order fitted better for both single and simultaneous adsorption. The adsorption of Cr(VI) was positively improved by the presence of other ions in solution, while the adsorption of Cd(II) was repressed.
Keywords: Bamboo Activated Carbon; Adsorption; Metallic Ions; Multi-component Sorption