Formation of synthetic analogues of double metal-hydroxy carbonate minerals under controlled pH conditions: I. The synthesis of pyroaurite and reevesite

Clay Minerals ◽  
1990 ◽  
Vol 25 (2) ◽  
pp. 161-179 ◽  
Author(s):  
H. C. B. Hansen ◽  
R. M. Taylor
Keyword(s):  
Oxidation Rate ◽  
Reasonable Agreement ◽  
Single Phase ◽  
Morphological Features ◽  
Air Oxidation ◽  
Synthetic Analogues ◽  
Synthesis Technique ◽  
Homogeneous Product ◽  
Ph Conditions ◽  
Hydroxy Carbonate

AbstractTwo-layered Fe(III)-M(II) hydroxy carbonates (M(II) = Ni or Mg) have been synthesized by induced hydrolysis using controlled air oxidation of an aqueous Fe(II)-M(II) mixture (M(II)/Fe(II) ratio >3) at a pH below which the hydroxide of the M(II) cation precipitates. The crystalline, homogeneous product can be a single phase consisting of very thin circular to hexagonal plates (0·2–0·8 µm diam.). For synthetic reevesite (Ni(II)-Fe(III) hydroxy carbonate), stable spherular aggregates are formed. The well crystallized products have an M(II)/Fe(III) ratio of about two. However, by varying the pH, the initial M(II)-Fe(III) ratio and the oxidation rate, the M(II)/Fe(III) ratio in the product and its crystallinity can be varied. The derived formulae are in reasonable agreement with the known composition of pyroaurite-type compounds. Possible synthesis pathways are discussed. The ability to control some physical and morphological features of the products indicates that the synthesis technique could prove advantageous in the preparation of certain catalyst precursors.

Formation of synthetic analogues of double metal-hydroxy carbonate minerals under controlled pH conditions: II. The synthesis of desautelsite

Clay Minerals ◽  
1991 ◽  
Vol 26 (4) ◽  
pp. 507-525 ◽  
Author(s):  
H. C. B. Hansen ◽  
R. M. Taylor
Keyword(s):  
General Formula ◽  
Oxidation State ◽  
Particle Shape ◽  
Indirect Evidence ◽  
Aeration Rate ◽  
Synthesis Product ◽  
Aerial Oxidation ◽  
Ph Stat ◽  
Ph Conditions ◽  
Hydroxy Carbonate

AbstractDesautelsite, a Mg(II)Mn(III) hydroxy carbonate first described in 1979 and represented by the general formula Mg(8−x)Mn(III)x(OH)16(CO3)x/2(in which 2 <x< 2·67), has been synthesized under controlled pH conditions (induced hydrolysis) and coprecipitation techniques. In the pH-stat syntheses, the desautelsite is formed by aerial oxidation of MnCO3in 0·05–0·15mMg(NO3)2solutions at ∼pH 9 and temperatures of 35°C where, in the absence of Mg, manganite would normally form. The synthesis product from this technique is generally more crystalline than that formed by the coprecipitation method. Composition, particle shape and aggregation may be controlled through variations of the Mg concentration, pH, aeration rate or temperature. Indirect evidence suggests Mn to be present in the +3 oxidation state in the desautelsite.

Air Oxidation of Porous Cu-35wt.%Ni-(5,10,15) wt%Cr Alloys at 650°C

2013 ◽  
Vol 365-366 ◽  
pp. 987-990
Author(s):  
Jian Chen ◽  
Zi Han Huang ◽  
Yan Jie Ren ◽  
Wen Wen ◽  
Xiang Wu Xiao ◽  
...  
Keyword(s):  
Oxidation Rate ◽  
Oxidation Behavior ◽  
Air Oxidation ◽  
Internal Oxide ◽  
Rate Law ◽  
Cr Content ◽  
Ni Content ◽  
Initial Stage ◽  
Parabolic Rate

The oxidation behavior of porous Cu-Ni-Cr alloys containing approximately 5,10 and 15 wt.%Cr, but with a similar Ni content of 35 wt.%, was studied at 650°C in air. The results showed that the oxidation of alloys follows linear law at initial stage and then the parabolic rate law. Continuous external scales of CuO and Cu2O formed on the alloys. Some internal oxide of were observed. In addition, with increase of Cr content, the oxidation rate decreased slightly.

scholarly journals Synthesis and Application of Inverse Spinel NiFe2O4 Produced by EDTA-citrate Method: Structural, Vibrational, Magnetic, and Electrochemical Properties

2021 ◽  
Author(s):  
Maitê Medeiros de Santana e Silva ◽  
Rafael A. Raimundo ◽  
Luciena S. Ferreira ◽  
Daniel A. Macedo ◽  
Marco A. Morales ◽  
...  
Keyword(s):  
Electrochemical Properties ◽  
Single Phase ◽  
Crystal Size ◽  
Band Gap Energy ◽  
Inverse Spinel ◽  
Microstructural Characteristics ◽  
Crystallite Sizes ◽  
Ph Conditions ◽  
Synthesized Materials ◽  
Discharge Curves

Abstract In this paper we studied the production of single-phase NiFe2O4 powders synthesized by the complexation method combining EDTA-citrate. The structural, optical, magnetic, and electrochemical properties of were studied as a function of the synthesis pH. Powders obtained with pH 9 showed larger crystallite sizes (73 nm) in comparison to those produced with pH 3 (21 nm). The band gap energy was found to be inversely proportional to the crystal size (1.85 and 2.0 eV for powders with crystallites of 73 nm and 21 nm, respectively). The synthesized materials presented an inverse spinel crystalline structure. The samples obtained at higher pH conditions were found to be fully magnetic saturated with a saturation magnetization of 50.5 emu g-1, while that synthesized at pH 3 is unsaturated with a maximum measured magnetization of 48.4 emu g-1. Cyclic voltammetry and charge-discharge curves indicate a battery-type behavior, with an better performance for the material obtained at pH 9 (65 C g-1 at a specific current of 3 A g-1). The remarkable performance of the associated with its by microstructural characteristics (particle size, particle agglomeration and porosity). This work offers an alternative synthesis route for obtaining spinel ferrites for magnetic and electrochemical applications.

scholarly journals Tunable single-phase magnetic behavior in chemically synthesized AFeO3–MFe2O4 (A = Bi or La, M = Co or Ni) nanocomposites

Nanoscale ◽  
2018 ◽  
Vol 10 (48) ◽  
pp. 22990-23000 ◽  
Author(s):  
T. Sarkar ◽  
G. Muscas ◽  
G. Barucca ◽  
F. Locardi ◽  
G. Varvaro ◽  
...  
Keyword(s):  
Magnetic Properties ◽  
Single Phase ◽  
Magnetic Behavior ◽  
Oxide Systems ◽  
Synthesis Technique ◽  
Correlated Electron ◽  
Novel Synthesis

Tailoring the magnetic properties of nanocomposites consisting of correlated electron oxide systems via a novel synthesis technique.

Oxidation of Zirconium-Yttrium Alloys

1964 ◽  
Vol 8 ◽  
pp. 143-150 ◽  
Author(s):  
D. I. Phalen ◽  
D. A. Vaughan ◽  
N. A. Richard
Keyword(s):  
Single Phase ◽  
Phase Distribution ◽  
Zirconium Alloys ◽  
Metallic Elements ◽  
Air Oxidation ◽  
X Ray Diffraction ◽  
Metal Interface ◽  
Two Phase ◽  
Anion Diffusion ◽  
Metal Composition

AbstractThe phase and elemental distributions on zirconium alloys containing 5, 10, 25, 35, and 50 at.%. yttrium, oxidized in dry air at 1200 and 1600°C, have been studied by X-ray diffraction, fluorescence, and electron-microprobe techniques. Zirconium-yttrium alloys, which are entirely solid at 1200°C, and zirconium 5 and 25 at.% yttrium alloys, which aire two-phase solid plus liquid at 1600°C, form a multiphase scale of ZrO2, Y2O3, and ZrN. The phase distribution varies with yttrium content, while the average metal composition remains constant throughout the oxide scale and base metal. In contrast, zirconium 35 and 50 at.% yttrium alloys, which are entirely liquid at 1600°C, form a single-phase Y2O3 layer.The mechanism of air oxidation of solid zirconium-yttrium alloys, up to 50 at. % yttrium, is one of anion diffusion to the oxide-metal interface with little or no diffusion of the metallic elements. The oxidation of liquid alloys differs in that, as a result of yttrium diffusion to the oxide-liquid interface, Y2O3 is the only oxide formed. Ternary Zr-Y-O isotherms are presented to illustrate the phase distribution and mode of formation.

Formation and properties of Fe(II)Fe(III) hydroxy-carbonate and its possible significance in soil formation

Clay Minerals ◽  
1980 ◽  
Vol 15 (4) ◽  
pp. 369-382 ◽  
Author(s):  
R. M. Taylor
Keyword(s):  
Soil Formation ◽  
Oxidation Products ◽  
Ph Values ◽  
Carbonate Solutions ◽  
Freeze Dried ◽  
Colour Changes ◽  
Ph Conditions ◽  
Related Compounds ◽  
Magnetite Phase ◽  
Hydroxy Carbonate

AbstractSmall amounts of Fe(III) induce precipitation of Fe(II) from carbonate solutions around neutral pH values. The reaction involves the formation of Fe(II)Fe(III) hydroxycarbonate, a green, layer-structured compound of the pyroaurite group of minerals. Variations in the concentration of Fe(II) in the solution phase, and in the form and amounts of the total Fe(III) in the system, may cause other phases such as magnetite and siderite to form also. Freeze-dried Fe(II)Fe(III) hydroxy-carbonate undergoes topotactic alteration to a magnetic phase, presumably maghemite, when stored under vacuum. The compound is readily oxidized in air in either the moist or dry state, rapidly becoming yellow or yellow-brown in colour. Oxidation leads to the formation of either goethite, lepidocrocite, ferrihydrite or mixtures of these phases, depending on the mode of oxidation and the impurities present. The similarity between the rapid colour changes and the oxidation products of the blue-green precipitates in gleyed soil horizons and this Fe(II)Fe(III) hydroxy-carbonate leads to the speculation that this and related compounds may be the meta-stable precipitates in such soils, rather than a previously postulated hydro-magnetite phase. Eh and pH conditions for the formation of Fe(II)Fe(III) hydroxy-carbonate are given, and are in the range encountered in the soil environment.

Air and Wet Air Oxidation of 9Cr-3Co-3W Creep Resistant Ferritic Steel at 650 °C

2013 ◽  
Vol 634-638 ◽  
pp. 1685-1689
Author(s):  
Shan Tang ◽  
Xi Tang ◽  
Z.D. Xiang
Keyword(s):  
Oxidation Kinetics ◽  
Oxidation Rate ◽  
Ferritic Steel ◽  
Air Oxidation ◽  
Wet Air Oxidation ◽  
Rate Law ◽  
Cr2o3 Scale ◽  
Weight Measurement ◽  
Experimental Creep ◽  
Power Rate

The new experimental creep resistant ferritic steel of the 9Cr-3Co-3W type was oxidised at 650 °C in air and wet air. The oxidation kinetics was measured by intermittent weight measurement. The scales formed were analysed using techniques of XRD, SEM and EDS. The results showed that the oxidation rate was more than a magnitude faster in wet air than in air. The oxidation kinetics in air obeyed the parabolic rate law of oxidation only in a limited oxidation period of up to 1726 h whereas it did not follow any power rate law of oxidation in wet air. The steel cannot form a protective Cr2O3 scale either in air or in wet air at 650 °C. Instead, the scale formed in air consisted of an outer (Fe0.6Cr0.4)2O3 layer and an inner Cr-rich (Fe,Cr)2O3 layer containing Cr2O3 particles, but in wet air it consisted of an outer Fe3O4 layer and an inner (Fe,Cr)3O4 layer.

scholarly journals Morpho-structural and luminescence investigations on yttrium silicate based phosphors prepared with different precipitating agents

2014 ◽  
Vol 12 (10) ◽  
pp. 1023-1031 ◽  
Author(s):  
Laura Muresan ◽  
Adrian Cadis ◽  
Ioana Perhaita ◽  
Emil Indrea
Keyword(s):  
Single Phase ◽  
Ammonium Carbonate ◽  
Ammonium Oxalate ◽  
Blue Emission ◽  
Yttrium Silicate ◽  
Order Degree ◽  
Ft Ir ◽  
Xrd Patterns ◽  
Uv Excitation ◽  
Hydroxy Carbonate

AbstractYttrium silicate doped with cerium (Y2SiO5:Ce) was obtained from Y-Ce-Si based precursors prepared by the simultaneous addition of reagents (SimAdd) technique. The synthesis of the precursors was done in well controlled conditions using ammonium oxalate, ammonium carbonate or urea as precipitating agents. Results regarding the influence of precipitating agents on the morpho structural and photoluminescent characteristics of Y2SiO5:Ce are reported. The TG analysis in correlation with EGA, FT-IR and XRD investigations reveals the formation of oxalate, hydroxy-carbonate or hydroxy-nitrate based compounds, the same as the conversion of the precursors to well crystallized yttrium silicate. XRD patterns show that the precursors are amorphous except for the sample prepared with ammonium oxalate. Depending on the precipitation conditions, the phosphors phase composition varies from single phase (X2-Y2SiO5) to a mixture of phases (X2-Y2SiO5, X1-Y2SiO5, Y2O3). Under UV excitation, phosphors exhibit the specific blue emission of cerium with an intensity that varies from 175.8% (urea) to 96.0% (ammonium carbonate) and to 78.5% (ammonium oxalate). The emission intensity depends on the phase purity and order degree of the phosphors. PACS Classification codes:78.55 Hx, 81.20Fw

scholarly journals Microwave-assisted synthesis of bismuth oxide

2007 ◽  
Vol 1 (1-2) ◽  
pp. 29-33 ◽  
Author(s):  
Eva Bartonickova ◽  
Jaroslav Cihlar ◽  
Klara Castkova
Keyword(s):  
Phase Composition ◽  
Bismuth Oxide ◽  
Single Phase ◽  
Ph Value ◽  
Chelating Agent ◽  
Microwave Assisted Synthesis ◽  
Reaction Products ◽  
Transformation Mechanism ◽  
Microwave Assisted ◽  
Ph Conditions

Single phase and ultrafine bismuth oxide was synthesized via microwave-assisted hydrothermal synthesis. The effect of reaction parameters (temperature/pressure and pH) on the product phase composition and morphology was discussed. The transformation of bismuth hydroxide into bismuth oxide was controlled by pH value and it was accelerated by time and temperature. The phase composition of reaction products was strongly dependent on pH value. The amorphous products were obtained at acidic pH conditions and the crystalline single phase product ?-Bi2O3 phase was obtained at pH ?12. The particle size was reduced from micrometric to nanometric size in the presence of a chelating agent. The bismuth hydroxides into bismuth oxides transformation mechanism, consisting in polycondensation of Bi - OH bounds to Bi-O-Bi bridges and crystallization of Bi2O3, was proposed.

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