Magnetic susceptibility, spin transition, and electrical conductivity of LaCo1 + xO3 and NdCo1 + xO3

The magnetic susceptibility of Nd₂O₃, NdCo_{1 + x} O₃, and LaCo_{1 + x} O₃ (x = 0, 0.05, 0.1, 0.15) has been measured at temperatures from 80 to 950 K, and the electrical conductivity of the neodymium and lanthanum cobaltites (enriched in cobalt relative to neodymium or lanthanum) with the general formulas Nd(La)Co_{1 + x} O_{3 + 1.5x} , or Nd_{1/(1 + x)}(La)_{1/(1 + x)}CoO_{(3 + 1.5x)/(1 + x)}, has been measured between 300 and 1050 K. The effective magnetic moments of paramagnetic ions have been determined in the temperature ranges of CurieWeiss behavior and have been used to evaluate the fractions of low-, intermediate-, and high-spin Co³⁺ ions. Raising the temperature from 320 to 660 K (non-Curie—Weiss behavior) increases the fraction of high-spin Co³⁺ ions in LaCo_{1 + x} O_{3 + 1.5x} (La_{1/(1 + x)}CoO_{(3 + 1.5x)/(1 + x)} from 27–43 to 56–61%. Moreover, in this temperature range the conductivity of the lanthanum cobaltites rises most steeply. In the range 660–950 K, no spin transition occurs in LaCo_{1 + x} O_{3 + 1.5x} , the slope of the conductivity versus temperature curves gradually decreases, and the conductivity gradually saturates. The conductivity of NdCo_{1 + x} O_{3 + 1.5x} (Nd_{1/(1 + x)}CoO_{(3 + 1.5x)/(1 + x)}) varies considerably in the range 550–950 K, and the spin transition in these cobaltites takes place between 260 and 760 K. Above 760 K, the NdCo_{1 + x} O_{3 + 1.5x} cobaltites with x = 0.05 and 0.10 contain, respectively, 72 and 83% high-spin Co³⁺ ions and 28 and 17% high-spin Co⁴⁺ ions, whereas neodymium cobaltite with x = 0.15 contains 83% high-spin and 17% intermediate-spin Co³⁺ ions. Original Russian Text ? S.V. Shevchenko, L.A. Bashkirov, G.S. Petrov, S.S. Dorofeichik, N.N. Lubinskii, 2008, published in Neorganicheskie Materialy, 2008, Vol. 44, No. 1, pp. 88–94.     

Two‐component “Onionlike” micelles with a PPO core,a PDMAEMA shell and a PEO corona: formation and crosslinking

BACKGROUND: Chemical or physical crosslinking of supramolecular assemblies gives them stability in a wide range of environments. Much attention is paid to multilayer (onion‐like) polymeric micelles because their functionality is higher than classic core‐shell micelles. This work reports on the formation and crosslinking of onion‐like micelles prepared by mixing two different block copolymers containing a crosslinkable poly(dimethylaminoethyl methacrylate) (PDMAEMA) block. RESULTS: Block copolymers of a crosslinkable PDMAEMA block were synthesized by atom transfer radical polymerization of 2‐(dimethylamino)ethyl methacrylate (DMAEMA) from poly(propylene oxide) (PPO) or poly(ethylene oxide) (PEO) macroinitiators. The (PDMAEMA₁₃)‐block‐PPO₆₉‐block‐(PDMAEMA₁₃) triblock formed wormlike core‐shell micelles, which were converted into ellipsoidal onion‐like micelles on mixing with the PEO₄₅‐block‐P(DMAEMA₈‐co‐MMA₄) diblock. Onion‐like micelles were crosslinked by quaternization of DMAEMA units. CONCLUSION: Formation of onion‐like micelles by mixing two different AB (ABA) and B′C block copolymers and their subsequent crosslinking is a valuable approach towards stabilized supramolecular assemblies of a higher complexity and functionality than the individual constitutive components. Copyright © 2008 Society of Chemical Industry     

Neutron-Physical Calculation of a Fresh Zone in the Natural Nuclear Reactor at Oklo

A full-scale computer model of zone 2 of the Oklo reactor with a realistic materials composition is constructed. Modern Monte Carlo programs are used to calculate the multiplication factor, the excess reactivity, and the neutron flux for the fresh reactor zone 2. The calculations are performed in a wide range of variation of the zone parameters: the uranium content in the contemporary Oklo zone is varied from 35 to 55 mass% and the water content from 0.355 to 455 g/cm³. The power effect is determined. The temperature of the fresh zone is found to be 725 ± 55 K, at which the reactor is critical and can operate in a stable manner for a long time. The power of the reactor is maintained by negative feedback. The neutron spectrum, over which the cross section of strong absorbers must be averaged, for example, ₆₂ ¹⁴⁹ Sm, in order to obtain the most accurate bounds on the possible shift of the samarium resonance as a result of a change in the fundamental constants, is found for 700 K.__________Translated from Atomnaya Energiya, Vol. 98, No. 4, pp. 306–316, April, 2005.     

Natural concentrates of Bi- and tricyclic naphthenes

Translated from Khimiya i Tekhnologiya Topliv i Masel, No. 5, pp. 7–8, May, 1989.     

Transformation of CH4 and liquid fuels into syngas on monolithic catalysts

Active components comprised of fluorite-like Ln_x(Ce_0.5Zr_0.5)_1−xO_2−y (Ln = La, Pr, Sm) and perovskite-like La_0.8Pr_0.2Mn_0.2Cr_0.8O₃ mixed oxides and their composites with yttria-doped zirconia (YSZ) promoted by precious metals (Pt, Ru) and/or Ni were supported on several types of heat-conducting substrates (compressed Ni-Al foam, Fecralloy foil or gauze protected by corundum layer, Cr-Al-O microchannel cermets, titanium platelets protected by oxidic layer) as well as on honeycomb corundum monolithic substrate. These structured catalysts were tested in pilot-scale reactors in the reactions of steam reforming of methane, selective oxidation of decane and gasoline and steam/autothermal reforming of biofuels (ethanol, acetone, anisole, sunflower oil). Applied procedures of supporting nanocomposite active components on monolithic/structured substrates did not deteriorate their coking stability in real feeds with a small excess of oxidants, which was reflected in good middle-term (up to 200 h) performance stability promising for further up-scaling and long-term tests. Equilibrium yield of syngas at short contact times was achieved by partial oxidation of decane and gasoline without addition of steam usually required to prevent coking. For the first time possibility of successive transformation of biofuels (ethanol, acetone, anisole, sunflower oil) into syngas at short contact times on monolithic catalysts was demonstrated. This was provided by a proper combination of active component, thermal conducting monolithic substrates and unique evaporation/mixing unit used in this research.     

Entrapment of Saccharomyces cerevisiae cells in u.v. crosslinked hydroxyethylcellulose/poly(ethylene oxide) double-layered gels

Double-layered gels, consisting of hydroxyethylcellulose cryogel core and poly(ethylene oxide) hydrogel shell, were synthesized with u.v. irradiation, using the same photoinitiator, (4-benzoylbenzyl) trimethylammoniumchloride (BBTMAC) for the both layers. The gels were characterized by measuring their rheological parameters, gel fraction yield, the degree of equilibrium swelling and diffusion coefficient. The diffusion coefficients for glucose and ethanol through the hydroxyethylcellulose cryogel were 3.9 × 10^?6 cm²/s and 0.97 × 10^?5 cm²/s, respectively. The applicability of these double-layered gels as carriers for immobilization was investigated by entrapment of Saccharomyces cerevisiae cells. The immobilization efficiency and cell retention were determined in batch fermentation for ethanol production from glucose. The operational stability of the gels was evaluated in batch fermentation with three consecutive runs. The ethanol yield was in the range from 60% to 77% of the theoretical yield.     

Trace metals in Phragmites australis and Phalaris arundinacea growing in constructed and natural wetlands

Constructed wetlands with horizontal subsurface flow (HF CWs) designed for treatment of municipal sewage have been monitored extensively with respect to removal of organics, suspended solids, nitrogen, phosphorus and bacteria. However, the information on the removal of various metals and metalloids in these systems is very limited. During the period 2002-2004 aboveground and belowground biomass of Phragmites australis (common reed) and Phalaris arundinacea (reed canarygrass) were sampled in three HF CWs in the Czech Republic. Concentrations of monitored elements in both aboveground and belowground plant tissues were similar to those found in plants growing in natural stands. The concentrations were much lower as compared to those found in plants growing in wetlands receiving acid mine drainage waters, waters from smelters or highway runoff. Concentrations decrease in the order of roots>rhizomes>leaves>stems. The leaf:stem concentration ratios were quite similar for all monitored elements ranging between 1.0 and 1.9. The root:leaf concentration ratio varied widely between 1.5 (Cu) and 54 (Cr) with a mean value of 20.0. Belowground/aboveground plant tissue concentration ratios varied from 2.2 (Cu) to 32 (Cr) with the average value of 9.9.