Oxygen Gas (oxygen + gas)

Distribution by Scientific Domains


Selected Abstracts


Growth of ZnO single crystals by an induced nucleation from a high temperature solution of the ZnO-PbF2 system

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 3 2007
Xinhua Li
Abstract To grow ZnO single crystals from a high temperature solution of the ZnO-PbF2 system, a gas cooling system was assembled at the bottom of the crucible to induce nucleation in the initial growth stage. The growth experiments were carried out in a homemade vertical Bridgman furnace and Pt crucible of 28 mm in diameter was used. The furnace temperature was set to 1100°C and the flow rate of the oxygen gas was optimized as 3.0 l/min. ZnO crystal up to 5,8mm in the thickness was obtained with the lowering rate of 0.3 mm/h. XRD patterns showed that the as-grown crystal was pure ZnO Wurtzite phase. The impurity ions were analyzed by the glow discharge mass spectroscopy (GDMS) as 390.0 ppm and 40.0 ppm for Pb2+ and F - , respectively. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Co3O4 Nanostructures with Different Morphologies and their Field-Emission Properties,

ADVANCED FUNCTIONAL MATERIALS, Issue 12 2007
B. Varghese
Abstract We report an efficient method to synthesize vertically aligned Co3O4 nanostructures on the surface of cobalt foils. This synthesis is accomplished by simply heating the cobalt foils in the presence of oxygen gas. The resultant morphologies of the nanostructures can be tailored to be either one-dimensional nanowires or two-dimensional nanowalls by controlling the reactivity and the diffusion rate of the oxygen species during the growth process. A possible growth mechanism governing the formation of such nanostructures is discussed. The field-emission properties of the as-synthesized nanostructures are investigated in detail. The turn-on field was determined to be 6.4 and 7.7,V,,m,1 for nanowires and nanowalls, respectively. The nanowire samples show superior field-emission characteristics with a lower turn-on field and higher current density because of their sharp tip geometry and high aspect ratio. [source]


Studies on the oxygen atom transfer reactions of peroxomonosulfate: Catalytic effect of hemiacetal

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 10 2009
S. Shailaja
The reaction of peroxomonosulfate (PMS) with glycolic acid (GLYCA), an alpha hydroxy acid, in the presence of Ni(II) ions and formaldehyde was studied in the pH range 4.05,5.89 and at 31°C and 38°C. When formaldehyde and Ni(II) ions concentrations are ,5.0 × 10,4 M to 10.0 × 10,4 M, the reaction is second order in PMS concentration. The rate is catalyzed by formaldehyde, and the observed rate equation is (,d[PMS])/dt = (k,2[HCHO][Ni(II)][PMS]2)/{[H+](1+K2[GLYCA])}. The number of PMS decomposed for each mole of formaldehyde (turnover number) is 5,10, and the major reaction product is oxygen gas. The first step of the reaction mechanism is the formation of hemiacetal by the interaction of HCHO with the hydroxyl group of nickel glycolate. The peroxomonosulfate intermediate of the Ni-hemiacetal reacts with another molecule of PMS in the rate-limiting step to give the product. This reaction is similar to the thermal decomposition of PMS catalyzed by Ni(II) ions. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 642,649, 2009 [source]


Physico-chemical characterisation of 99mTc-tin fluoride colloid agent used for labelling white cells

JOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 6 2006
Chris Tsopelas
Abstract 99mTc,tin fluoride colloid is an agent used to label leucocytes, for the imaging and diagnosis of inflammatory conditions including Crohn's disease. Despite previous investigations, this radiolabelling agent is still poorly characterised. The aim of this work was to examine the process of formation and stability of 99mTc,tin fluoride colloid using mass spectrometry, membrane filtration and atomic absorption spectrophotometric techniques. Tin-oxide bonds in tin clusters were identified in the stannous fluoride reagent vial by mass spectrometry. From radioactive particle size distribution experiments, the facile disruption of radiocolloid particles with excess oxygen gas contrasted to the partial hydrolysis of Sn(II) during the formation process. Under the standard conditions, 10% of particles were determined as 1,3 µm, and this population coordinated 96% of the 99mTc added. Colloid particle formation and the reduction of 99mTc-pertechnetate is discussed. Sodium fluoride may optimise 1,3 µm radioactive particle size, by regulating particle growth. 99mTc,tin fluoride colloid is affected by positive or negative charge, as either Al, Mo ions or solid membranes, resulting in either coagulation and/or deflocculation of the particles. Copyright © 2006 John Wiley & Sons, Ltd. [source]


Terephthalic acid synthesis at higher concentrations in high-temperature liquid water.

AICHE JOURNAL, Issue 6 2009

Abstract We synthesized terephthalic acid (TPA) from p -xylene at an initial concentration above its solubility limit in high-temperature liquid water (HTW). The nominal p -xylene loading at the reaction conditions was 0.4 mol L,1, which is the highest reported to date for generation of high TPA yields (>70 mol %) in HTW. The presence of two liquid phases during the reaction did not appear to accelerate the rate, unlike behavior reported for some other organic reactions done "on water" at lower temperatures. Adding oxygen gas in a large increment during synthesis produced a black liquid and a black solid byproduct, which is a previously undocumented problem. Adding oxygen in smaller increments prevented formation of the liquid and solid byproducts and also provided high selectivities (90 mol %) and yields (>70 mol %) of TPA. These results demonstrate the feasibility of HTW as a medium for TPA synthesis at p -xylene concentrations even higher than its solubility limit. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source]


Terephthalic acid synthesis at higher concentrations in high-temperature liquid water.

AICHE JOURNAL, Issue 3 2009

Abstract We conducted terephthalic acid (TPA) synthesis from p-xylene in high-temperature liquid water (HTW) at 300°C. The p-xylene concentration at the reaction condition was 0.2 mol L,1, which is the highest to date in research that achieved at least 80 mol % yields of TPA in HTW. Pure oxygen gas was the oxidant. Increasing the MnBr2 catalyst concentration increased the rate of TPA formation only slightly. In contrast, whether oxygen was fed in small, quick, discrete bursts, or fed continuously significantly affected the p-xylene conversion and the TPA selectivity. Adding oxygen in quick bursts and small increments led to high selectivities (>90 mol %) of TPA. Continuous addition of oxygen failed to do so. In addition to identifying the sensitivity of this synthesis to the oxygen feed method, these results also demonstrate the feasibility of HTW for TPA synthesis at higher concentrations, and hence high TPA production per unit reactor volume. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source]


Hydroxyapatite Coating on Thermally Oxidized Titanium Substrates

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2001
Minkmas Vatanatham
Titanium substrates were oxidized in oxygen or air at temperatures of 600°,800°C, then immersed in solutions of 2.0mM, 20.7mM CaCl2 and 1.2mM,12.4mM KH2PO4 for aging periods of 0.5,10 d. The titanium surface was successfully coated with hydroxyapatite (HAP) when the substrates were oxidized in oxygen gas at 610°C for 1 h and then aged in a solution of 2.00mM Ca2+ and 1.20mM PO43,. The Ca/P ratio of the surface coating increased toward its stoichiometric HAP value (return 10/6) as the aging time increased; the Ca/P ratio attained a value of 1.66 after 10 d. [source]