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Magnesium Oxide (magnesium + oxide)
Selected AbstractsAsymmetric Epoxidation of Olefins by Manganese(III) Complexes Stabilised on Nanocrystalline Magnesium OxideADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 9 2006M. Choudary Abstract The asymmetric epoxidation of unfunctionalised olefins to epoxides is realised by using manganese(III) complexes stabilised on nanocrystalline magnesium oxide in the presence (1R,2R)-(,)-diaminocyclohexane as a chiral ligand in good yields and up to 91,% enantiomeric excess. [source] Effect of Segregating Impurities on the Grain-Boundary Character Distribution of Magnesium OxideJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2009Francine Papillon The grain-boundary character distribution (GBCD) of undoped MgO has been measured and compared with samples containing small concentrations of Ca, Sr, Ba, and Y. Auger electron spectroscopy measurements of intergranular fracture surfaces verified that Ca, Ba, and Y segregated anisotropically to grain boundaries (GBs). The segregation of Sr was not detected. The GBCDs of Ca, Ba, and Y doped MgO have more GBs comprised of {100} planes than the undoped material and the fractional area of these planes was highest in the Ca-containing samples. Sr impurities, on the other hand, have no measurable influence on the GBCD. The results demonstrate that GB plane distributions can be controlled through impurity additions. [source] ChemInform Abstract: Transfer Hydrogenation of Carbonyl Compounds Catalyzed by Ruthenium Nanoparticles Stabilized on Nanocrystalline Magnesium Oxide by Ionic Liquids.CHEMINFORM, Issue 8 2009M. Lakshmi Kantam Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Matrimid®/MgO mixed matrix membranes for pervaporationAICHE JOURNAL, Issue 7 2007Lan Ying Jiang Abstract For the first time, porous Magnesium oxide (MgO) particles have been applied to generate mixed matrix membranes (MMM) for the dehydration of iso-propanol by pervaporation. A modified membrane fabrication procedure has been developed to prepare membranes with higher separation efficiency. FESEM and DSC characterizations confirm that the MMMs produced have intimate polymer/particle interface; the nanosize crystallites on MgO surface may interfere with the polymer chain packing and induce chains rigidification upon the particle surface. It is observed that Matrimid®/MgO MMMs generally have higher selectivity, but lower permeability relative to the neat Matrimid® dense membrane. The highest selectivity is obtained with MMM containing 15 wt. % MgO. The selective sorption and diffusion of water in the MgO particles, and the polymer/particle interface properties combine to lead to the earlier phenomena. The investigation on the effect of feed water composition on the pervaporation performance reveals that the addition of MgO can show the selectivity-enhancing effects if the feed water concentration is lower than 30 wt. %. In the dehydration of isopropanol aqueous solution with 10 wt. % water, the selectivity of the MMMs is around 2,000, which is more than twice of 900 of neat polymeric membrane. This makes MMMs extremely suitable for breaking the azeotrops of water/iso-propanol. Gas permeation tests are also conducted using O2 and N2 to determine the microscopic structure of the MMMs, and to investigate the relationship between pervaporation and gas separation performance. © 2007 American Institute of Chemical Engineers AIChE J, 2007 [source] Space Charge Measurement in MgO/LDPE Nanocomposite up to Breakdown under DC Ramp VoltageIEEJ TRANSACTIONS ON ELECTRICAL AND ELECTRONIC ENGINEERING, Issue 4 2010Yoshinobu Murakami Member Abstract To understand the basic electric properties of nanosized magnesium oxide (MgO)/low-density polyethylene (LDPE) nanocomposites under an applied DC voltage, the DC breakdown strength and space charge up to the breakdown under a DC ramp voltage were investigated. Compared to that of the LDPE sample, the sample containing a MgO nanofiller (hereafter, called a nanocomposite) had a higher DC breakdown strength. In the case of the LDPE sample, the homo charges, which contained a large negative charge and a small positive charge, were only observed near the electrodes just prior to breakdown. However, in the case of the nanocomposite sample, the positive charge increased as the average field increased until the average field reached a certain value. After that, the positive charge decreased as the average field increased until breakdown occurred. The field enhancement rate (=maximum field/average field) of the nanocomposite sample increased with the average field, until it became saturated. After peaking, the field enhancement rate of the nanocomposite sample decreased as the average field increased. These observations suggest that, instead of the MgO nanofiller suppressing the electronic avalanche, it suppresses the conduction current, which was determined by the space charge, leading to the higher DC breakdown strength. Copyright © 2010 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [source] Heterogeneous Palladium Catalysts for a New One-Pot Chemical Route in the Synthesis of Fragrances Based on the Heck ReactionADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2007Maria Jose Climent Abstract The one-pot synthesis of the fragrance 4-(p -methoxyphenyl)butan-2-one, with raspberry scent, has been carried out using palladium on different supports such as magnesium oxide (MgO), hydrotalcite, hydroxyapatite (HA), aluminium oxide (,-Al2O3) and titanium dioxide (TiO2). The first pathway consists of a Heck coupling between 4-methoxyiodoanisole and methyl vinyl ketone followed by hydrogenation. Palladium supported on titanium dioxide showed the best performance for carrying out both consecutive steps giving 4-(p -methoxyphenyl)butan-2-one with high yields and selectivity. The Pd-TiO2 catalyst is more active than a homogeneous palladium complex that is well accepted in the literature as being highly active for performing Heck reactions. [source] Asymmetric Epoxidation of Olefins by Manganese(III) Complexes Stabilised on Nanocrystalline Magnesium OxideADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 9 2006M. Choudary Abstract The asymmetric epoxidation of unfunctionalised olefins to epoxides is realised by using manganese(III) complexes stabilised on nanocrystalline magnesium oxide in the presence (1R,2R)-(,)-diaminocyclohexane as a chiral ligand in good yields and up to 91,% enantiomeric excess. [source] Ionic elastomers based on carboxylated nitrile rubber and magnesium oxideJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2007L. Ibarra Abstract The crosslinking of carboxylated nitrile rubber (XNBR) with magnesium oxide (MgO) leads to an ionic elastomer with thermoplastic nature and better physical properties than the ones obtained with other metallic oxides. The crosslinking reaction leads to the formation of a metallic salt as unique product, as it could be seen on the ATR analysis of the samples, prepared at different reaction times. The mechanical properties of the material increase with the amount of crosslinking agent and segregation of an ionic microphase takes place. The presence of this microphase is demonstrated by a relaxation at high temperatures. The apparent activation energy of this relaxation is smaller than the activation energy of the glass transition of the elastomer, the former being more dependent on the amount of metallic oxide than is the latter. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1894,1899, 2007 [source] Lactobacillus casei rhamnosus Lcr35 in children with chronic constipationPEDIATRICS INTERNATIONAL, Issue 4 2007LING-NAN BU Abstract Background: The purpose of the present paper was to evaluate the efficacy of probiotics (Lactobacillus casei rhamnosus, Lcr35) for treating children with chronic constipation and to compare its effect with magnesium oxide (MgO) and placebo. Methods: This double-blind placebo-controlled, randomized study enrolled 45 children under 10 years old with chronic constipation. They were randomly assigned to receive Lcr35 (8 × 108 c.f.u./day; n = 18), MgO (50 mg/kg/day; n = 18), or placebo (n = 9) orally twice daily for 4 weeks. Lactulose use (1 mL/kg per day) was allowed when no stool passage for 3 days was noted. Glycerin enema was used only when no defecation was noted for >5 days or abdominal pain was suffered due to stool impaction. Bacterial cultures of stool were performed before and after treatment to evaluate the change of intestinal flora. Comparisons of the frequency of defecation, consistency of stool and the use of lactulose or enema during the period of treatment were made among the three groups. Results: The patients who received MgO or probiotics had a higher defecation frequency (P = 0.03), higher percentage of treatment success (P = 0.01), less use of glycerin enema (P = 0.04) and less hard stool (P = 0.01) than the placebo group. There was no significant difference between MgO and probiotic groups in the aforementioned comparisons. The first effect of MgO (second week) on constipation was slightly earlier than that of probiotic (second to third week). Abdominal pain occurred less frequently in the probiotic group than in both the MgO and the placebo groups (P = 0.03). There was no statistically significant difference among the three groups in the use of lactulose, episodes of fecal soiling, and change of appetite. No adverse effect was noted in probiotic and placebo groups. Only one patient in the MgO group suffered from mild diarrhea. Conclusion: Lcr35 was effective in treating children with chronic constipation. There is no statistically significant difference in efficacy between MgO and Lcr35, but less abdominal pain occurred when using Lcr35. Study with larger case number and longer follow up is needed in the future. [source] Evidence for 2,4-D mineralisation in Mediterranean soils: impact of moisture content and temperaturePEST MANAGEMENT SCIENCE (FORMERLY: PESTICIDE SCIENCE), Issue 9 2009Bachir Bouseba Abstract BACKGROUND: The 2,4-D degradation ability of the microbiota of three arable Mediterranean soils was estimated. The impact of soil moisture and temperature on 2,4-D degradation was investigated. RESULTS: The microbiota of the three soils regularly exposed to 2,4-D were able rapidly to mineralise this herbicide. The half-life of 2,4-D ranged from 8 to 30 days, and maximum mineralisation of 14C-2,4-D ranged from 57 to 71%. Extractable 14C-2,4-D and 14C-bound residues accounted for less than 1 and 15% respectively of the 14C-2,4-D initially added. The highest amounts of 14C-2,4-D bound residues were recorded in the soil with the lowest 2,4-D-mineralising ability. Although all three soils were able to mineralise 2,4-D, multivariate analysis revealed that performance of this degrading microbial activity was dependent on clay content and magnesium oxide. Soil temperature affected the global structure of soil microbial community, but it had only a moderate effect on 2,4-D-mineralising ability. 2,4-D-mineralising ability was positively correlated with soil moisture content. Negligible 2,4-D mineralisation occurred in all three soils when incubated at 10 or 15% soil moisture content, i.e. within the range naturally occurring under the Mediterranean climate of Algeria. CONCLUSION: This study shows that, although soil microbiota can adapt to rapid mineralisation of 2,4-D, this microbial activity is strongly dependent on climatic parameters. It suggests that only limited pesticide biodegradation occurs under Mediterranean climate, and that arable Mediterranean soils are therefore fragile and likely to accumulate pesticide residues. Copyright © 2009 Society of Chemical Industry [source] Effect of Halide and Acid Additives on the Direct Synthesis of Hydrogen Peroxide using Supported Gold,Palladium CatalystsCHEMSUSCHEM CHEMISTRY AND SUSTAINABILITY, ENERGY & MATERIALS, Issue 6 2009Edwin Ntainjua N. Dr. Abstract Acidity is crucial: The effect of halide and acid addition on the direct synthesis of hydrogen peroxide is studied for magnesium oxide- and carbon-supported bimetallic gold,palladium catalysts. When using a Au,Pd/C catalyst, the acidity of the methanol/water solvent has a profound effect on the productivity (P). The effect of halide and acid addition on the direct synthesis of hydrogen peroxide is studied for magnesium oxide- and carbon-supported bimetallic gold,palladium catalysts. The addition of acids decreases the hydrogenation/decomposition of hydrogen peroxide, and the effect is particularly pronounced for the magnesium oxide-supported catalysts whilst for carbon-supported catalysts the pH requires close control to optimize hydrogen peroxide synthesis. The addition of bromide leads to a marked decrease in the hydrogenation/decomposition of hydrogen peroxide with either catalyst. These effects are discussed in terms of the structure of the gold,palladium alloy nanoparticles and the isoelectric point of the support. We conclude that with the highly active carbon-supported gold,palladium catalysts these additives are not required and that therefore this system presents the potential for the direct synthesis of hydrogen peroxide to be operated using green process technology. [source] Flame-retardant action of red phosphorus/magnesium oxide and red phosphorus/iron oxide compositions in recycled PETFIRE AND MATERIALS, Issue 5 2006F. Laoutid Abstract Red phosphorus was combined with metallic oxides Fe2O3 and MgO to improve the fire properties of recycled PET. Both Fe2O3 and MgO act as co-synergist agents at a total loading of 5 wt%. The analysis by diffraction X of the char formed during combustion shows that transformation of Fe2O3 to Fe3O4 occurs. Fe2O3 favours the oxidation and improves the effectiveness of red phosphorus. It is suggested that MgO interacts with acidic end groups of PET and forms a thermal stable residue. The thermal decomposition of recycled PET containing red phosphorus combined with Fe and Mg oxides was studied by thermal analysis and leads to an increase in char formation. While the incorporation of Fe2O3 in this ternary blend maintains the mechanical properties of PET, the reactivity of MgO leads to a brittle material. The use of reinforcements (talc and glass fibres) to mechanically stabilize the char formed during combustion of ternary blend with Fe2O3 entails a further decrease in heat release rate, nevertheless impact resistance of the material decreases dramatically. Copyright © 2005 John Wiley & Sons, Ltd. [source] | ||||||||||||||||