Electrochemical treatment of wastewater from a phosphoric acid manufacturing plant

Phosphoric acid plant wastewater containing fluoride, phosphate and chemical oxygen demand etc., was treated using electrooxidation and electroflocculation methods. A maximum of 82% F- and 22.7% COD were removed using Ti/Pt(5c) under electrooxidative conditions. Electrooxidation with respect to F- removal is found mass-transfer limited, and removals below 5-6 mg/L F- are not achievable. Electroflocculation using Al anode resulted in better removal of F-, COD and PO4(3-). The various results obtained are discussed in this paper.     

Isotope effect for transport and magnetic properties of La 0.35 Pr 0.35 Ca 0.3 MnO 3 thin films

The effect of ¹⁶ O → ¹⁸ O isotope substitution on electrical resistivity, magnetoresistance, and ac magnetic susceptibility was studied for La_0.35Pr_0.35Ca_0.3MnO₃ epitaxial thin films deposited onto LaAlO₃ and SrTiO₃ substrates. For the films on LaAlO₃, the isotope substitution resulted in the reversible transition from a metal-like to insulating state. The applied magnetic field ( H ≥ 2 T) transformed the sample with ¹⁸O back to the metallic state. The films on SrTiO₃ remained metallic at low temperatures for both ¹⁶O and ¹⁸O, but the shift of the resistivity peak corresponding to onset of metallic state exceeded 63 K after ¹⁶ O → ¹⁸ O substitution. The temperature dependence of both resistivity and magnetic susceptibility was characterized by hysteresis, especially pronounced in the case of the films on LaAlO₃. Such a behavior gives certain indications of the phase separation characteristic of interplay between ferromagnetism and charge ordering. Received 11 February 2000 and Received in final form 13 September 2000     

Logarithmic correction to the bekenstein-hawking entropy

The exact formula derived by us earlier for the entropy of a four dimensional nonrotating black hole within the quantum geometry formulation of the event horizon in terms of boundary states of a three dimensional Chern-Simons theory is reexamined for large horizon areas. In addition to the semiclassical Bekenstein-Hawking contribution proportional to the area obtained earlier, we find a contribution proportional to the logarithm of the area together with subleading corrections that constitute a series in inverse powers of the area.     

Kinetic effects in manganites La1 − x Ag y MnO3 (y ≤ x)

We have measured the resistivity, magnetoresistance, and thermopower of ceramic manganite samples La_{1 ? x} Ag _y MnO₃ (y ≤ x) doped with silver as functions of temperature (4.2–350 K) and magnetic field (up to 26 kOe). A metal-insulator phase transition is observed in all investigated samples at temperatures close to room temperature. The behavior of the resistivity and thermopower in the high-temperature paramagnetic region is interpreted using the concept of small radius polaron; the activation energy decreases with increasing doping level. The resistivity in the low-temperature ferromagnetic region is approximated by the expression ρ_FM(T) = ρ₀ + AT ² + BT ^4.5 presuming the existence of electron-electron and electron-magnon interactions. A resistivity minimum and a strong magnetoresistive effect are observed at low temperatures. The latter effect is associated with scattering of charge carriers at grain boundaries, which are antiferromagnetically ordered relative to one another. The temperature dependence of thermopower in the magnetically ordered phase is described in the framework of a model taking into account the drag of charge carriers by magnons.     

Investigation of BiFeO3 Multiferroic thin films prepared by metalloorganic chemical vapor deposition

BiFeO₃ thin oriented films are grown on SrTiO₃(001) and ZrO₂(Y₂O₃)(001) substrates by metalloorganic chemical vapor deposition (MOCVD) in the temperature range T= 500–800°C. Iron dipivaloylmethanate Fe(thd)₃ and triphenylbismuth Bi(C₆H₅)₃ are used as volatile precursors. It is shown that the high thermal stability of Bi(C₆H₅)₃ leads to significant deviations of the Bi: Fe ratio in the film from their ratio in the precursor flow. An increase in the residence time of the precursor flow in the reactor makes this ratio close to unity. The film-substrate epitaxial relations are determined. It is found that the film orientation on the ZrO₂(Y₂O₃)(001) substrate changes with increasing temperature. Optical second harmonic generation (SHG) measurements show the presence of ferroelectric ordering in the films. A significant decrease in the Curie temperature due to epitaxial stress is found. At the same time, the magnetization noticeably increases as compared to a BiFeO₃ single crystal.     

Search for anomalous interaction mean free paths of charge, 2≦Z≦18 projectile fragments in emulsions exposed to 1.8 A GeV40Ar ions

⁴⁰Ar-emulsion interactions are studied, to investigate the question of anomalons, in twoG- 5 emulsion stacks. In about 4600 primary interactions, projectile fragments of Z≧2 for all generations have been followed until they interact or leave the stack. After careful estimation of charges of these fragments, variation of their mean free paths is studied as a function of distance from the preceding interaction. Generation effect,N _h dependence and production angle effect are investigated. In addition multi-chain events are analysed separately. Our results do not show anomalons at the 6% level and are consistent with non-occurrence of anomalons. However, this experiment is not sensitive enough to rule out anomalons (with a mfp of the order of 2 to 3 cm) produced at about 1% (or less) level.     

Correlation of electrical, magnetic, and thermal properties of the La0.85Ag0.15MnO3 manganite near the phase transition temperature

The correlation between electrical, magnetic, and lattice properties of manganites has been studied by analyzing the temperature dependence of the electrical resistivity of the La_0.85Ag_0.15MnO₃ manganite. The results have been discussed within the model of a phase-separated manganite in terms of the percolation theory. It has been shown that, from analyzing the temperature and magnetic field dependences of the electrical resistivity, it is possible to predict the behavior of the magnetization and specific heat, as well as the change of magnetic entropy near the phase transition temperature, and that the obtained agreement with experimental data for this analysis is quite reasonable.     

Is gadolinium a helical antiferromagnet or a collinear ferromagnet?

Controversial issues concerning the nature of magnetic ordering in gadolinium are briefly reviewed. The recent experimental results are shown to resolve most of such issues in that they rule out the possibility of a helical spin structure in Gd and clearly bring out the role of longrange dipolar interactions in stabilising collinear ferromagnetic order for temperatures between the spin-reorientation temperature and the Curie point Article presented at the International Symposium on Advances in Superconductivity and Magnetism: Materials, Mechanisms and Devices, ASMM2D-2001, 25–28 September 2001, Mangalore, India.