Promotional effects of samarium on Co3O4 spinel for CO and CH4 oxidation

A series of Co3O4 spinel catalysts modified by Sm were prepared by co-precipitation method and tested for CH4 and CO oxidation.The addition of a small amount of Sm into Co3O4 led to an improvement in the catalytic activity for both reactions.Co0.98Sm0.02 and Co0.95Sm0.05,the two samples with Co/Sm molar ratio of 0.98/0.02 and 0.95/0.05 in sequence,showed the similar and the highest activity for CH4 oxidation,with CH4 complete conversion at 450 oC.In contrast,Co0.90Sm0.10 was the most active sample for CO oxidation,with CO complete conversion at 120 oC.The catalysts were characterized by techniques of N2 adsortion-desorption with Brunauer-Emmett-Teller technique(N2-BET),X-ray powder diffraction(XRD),thermal gravity analysis-differential scanning calorimetry(TGA-DSC),H2 temperature programmed reduction(H2-TPR) and X-ray photoelectron spectroscopy analysis(XPS).Compared with pure Co3O4,for Co1–x Smx catalysts with 0.02≤x≤0.10,the addition of a small amount of Sm resulted in the formation of spinel Co3O4 and amorphous SmCoO3,hence increasing the number of Co3+ and the active surface oxygen species,which was responsible for the improvement of the activity.Co0.95Sm0.05 catalyst showed not only high thermal stability and activity but also good reaction durability in the presence of 5% water vapor for CH4 oxidation.     

Density of Na3AlF6–AlF3–LiF–MgF2–Al2O3–Sm2O3 molten salt melt for Al–Sm alloy

Samarium (Sm) has been widely used in making aluminum (Al)–Sm magnet alloy materials. The research team for this study developed a molten salt electrolyte system which directly produces Al–Sm alloy to replace the energy intensive conventional distillation technology. In this study, molten melt density was measured and operation conditions were optimized to separate Al–Sm alloy product from the fluoride molten melt electrolysis media based on density differences. Archimedes' principle was applied to measure density for the basic molten fluoride system (BMFS: Na₃AlF₆–AlF₃–LiF–MgF₂) electrolysis media in the temperature range from 905 to 1055 °C. The impact of temperature (t) and the Al₂O₃ and Sm₂O₃ addition ratio (w_(Al2O3), w_(Sm2O3)) in the basic fluoride system on molten melt density was examined. The fluoride molten melt density relationship was determined to be: ρ = 3.11701 ? 0.00802w_(Al2O3) + 0.027825w_(Sm2O3) ? 0.00117t. The test results showed that molten density decreases with increase in temperature and Al₂O₃ addition ratio, and increases with the addition of Sm₂O₃, and/or Al₂O₃ + Sm₂O_3. The separation of Al–Sm (density 2.3 g/cm³) product melt from the BMFS melt is achieved by controlling the BMFS density to less than 2.0 g/cm³. It is concluded that the optimal operation conditions to control the BMFS molten salt density to less than 2.0 g/cm³ are: maintain addition of Al₂O₃ + Sm₂O₃ (w_(Al2O3) + w_(Sm2O3)) < 9% of Na₃AlF₆, Al₂O₃/Sm₂O₃ ratio (w_(Al2O3):w_(Sm2O3)) > 7:3, and temperature between 965 and 995 °C.     

Phase Transformation and Microstructure of Zn2Ti3O8 Nanocrystallite Powders Prepared Using the Hydrothermal Process

This paper examines the phase transformation and microstructure of Zn₂Ti₃O₈ nanocrystallite powders prepared using the hydrothermal process that includes TiCl₄ and Zn(NO₃)₂·6H₂O as the initial materials. Differential thermal analysis, X-ray diffraction, transmission electron microscopy (TEM), selected area electron diffraction, nanobeam electron diffraction, and high resolution TEM were utilized to characterize the transition behavior of zinc titanate precursor powders after calcination. Nanocrystalline Zn₂Ti₃O₈ powders with a size range of about 5.0 to 8.0 nm were obtained when the precursor powders were calcined at 773 K (500 °C) for 1 hour. When the zinc titanate precursor powders were calcined at 1073 K (800 °C) for 1 hour, the cubic crystal of Zn₂Ti₃O₈ with a _o = 0.8399 ± 0.0003 nm still remained the predominant crystalline phase and the crystallite size increased to 20.0 nm. In addition, ZnTiO₃ phase first appeared because of the 13.8 pct of Zn₂Ti₃O₈ decomposition when the zinc titanate precursor powders were calcined at 1073 K (800 °C) for 1 hour. When the zinc titanate precursor powders were calcined at 1073 K (800 °C) for 9 hours, the Zn₂Ti₃O₈ crystallites grew continuously to 80.0 nm and enhanced the crystallinity. When the precursor powders were calcined at 1273 K (1000 °C) for 1 hour, Zn₂TiO₄ crystallites with a _o = 0.8461 ± 0.0002 nm were the predominant crystalline phase.     

Iron(II) oxidation by SO2/O2 for use in uranium leaching

Iron(III) can be used as an oxidant in the leaching of uranium ore in an acid medium. The oxidation of iron(II) to iron(III) using an SO₂/O₂ gas mixture was investigated in order to provide an iron(III) stream for uranium extraction. The effects of pH, temperature and SO₂/O₂ volumetric ratios were considered. Oxidation of iron(II) by SO₂/O₂ was controlled by diffusion of SO₂ or O₂ at pH 2 and 40 °C. However as the pH decreased below pH 1, the reaction was controlled by a slow chemical step and the reaction rate decreased. Increasing the temperature increased the oxidation rate at pH 0.8, and at 70 °C the rate again became dependent on SO₂ or O₂ diffusion. The oxygen efficiency for a fixed reactor set-up was dependent on the SO₂/O₂ ratio and total flow rate of the gas. In leach tests, the uranium extraction achieved with iron(III) solution prepared by SO₂/O₂ oxidation was the same as that for a standard uranium leach with conventional oxidant.     

Sintering characteristics and microwave dielectric properties of 0.5Ca0.6La0.267TiO3-0.5Ca(Mg1/3Nb2/3)O3 ceramics prepared by reaction-sintering process

0.5 Ca_(0.6)La_(0.267)TiO_3-0.5 Ca(Mg_(1/3)Nb_(2/3))O_3(5 CLT-5 CMN) ceramics were prepared by a reaction-sintering process and their sintering characteristics, microwave dielectric properties were investigated in detail.Without any calcination stage involved,a mixture of CaCO_3, La_2 O_3, TiO_2, MgO and Nb_2 O_5 was pressed and sintered directly. Pure phase 5 CLT-5 CMN ceramics with high density and dense microstructure can be obtained after sintered at 1400 ℃ for 4 h. Compared with those prepared by the conventional ceramic route, 5 CLT-5 CMN ceramics produced by the reaction-sintering process exhibit slightly higher dielectric constant and Q×f value. Fine microwave dielectric properties of ε_r= 56.4, Q×f= 48,550 GHz and T_f = +8.7 ppm/℃ for 5 CLT-5 CMN ceramics sintered at 1400 ℃ for 4 h are obtained, suggesting reactionsintering process is a simple and efficient method to produce pure phase 5 CLT-5 CMN ceramics as a potential candidate for the fabrication of microwave devices.     

Preparation and luminescence properties of orange-red Ba3Y4O9:Sm3+ phosphors

A novel orange-red emitting Ba₃Y₄O₉:Sm³⁺ phosphors were prepared by a high temperature solid-state reaction in air. X-ray diffraction (XRD), photoluminescence spectra, fluorescence decay and temperature-dependent emission spectra were utilized to characterize the structure and luminescence properties. The results show that the excitation spectrum includes a series of linear peaks at 350, 367, 382, 410, 424, 445, 470 and 495 nm, respectively. Under 410 nm excitation, the emission peaks were located at 574 nm (⁴G_5/2—⁶H_5/2), 608 nm (⁴G_5/2—⁶H_7/2), 659 nm (⁴G_5/2—⁶H_9/2) and 722 nm (⁴G_5/2—⁶H_11/2), respectively. The concentration quenching occurs when x equals 0.08 for Ba₃Y_4–xO₉:xSm³⁺ phosphor and its mechanism is ascribed to the dipole–dipole interaction. The chromaticity coordinates of Ba₃Y_3.92O₉:0.08Sm³⁺ phosphor are in the orange-red region. The temperature-dependent study shows that this phosphor has excellent luminescence thermal-stability. And the luminescence intensity of Ba₃Y_3.92O₉:0.08Sm³⁺ phosphor at 473 K only declines by about 25.75% of its initial intensity. The experimental data indicate that Ba₃Y₄O₉:Sm³⁺ phosphor may be promising as an orange-red emitting phosphor for white light emitting diodes.     

Effect of Er,Gd, and Nd Co-Dopants on the Properties of Sm-Doped Ceria Electrolyte for IT-SOFC

Doped ceria electrolytes of Ce_0.8Sm_0.20O_1.90 (SDC), Ce_0.8Er_0.08Sm_0.12O_1.90 (ESDC), Ce_0.8Gd_0.08Sm_0.12O_1.90 (GSDC), and Ce_0.8Nd_0.08Sm_0.12O_1.90 (NSDC) were prepared by a citric–nitrate combustion process. The thermal decomposition of the precursor was investigated by simultaneous thermogravimetric analysis and differential thermal analysis experiments. The phase structure of the calcined and sintered powders was characterized by X-ray diffraction analysis. All of the samples were fluorite-type ceria-based solid solutions. The calcined and sintered powders were also characterized by Fourier transform infrared spectroscopy. Scanning electron microscopy was used to characterize the samples after calcination and sintering. A relative density over 95 percent of the theoretical density was achieved after the sintering process. Electrical conductivities of the sintered samples were measured using the impedance spectra method. The highest ionic conductivity value was found to be 5.28 × 10^?2 S cm^?1 at 1023 K (750 °C) for GSDC sintered at 1673 K (1400 °C) for 6 hours.     

Phase diagram of the Al2O3-ZrO2-Sm2O3 system. I. Triangulation and isothermal sections at 1250 and 1650°C

Isothermal sections at 1250 and 1650 °C have been constructed for the Al₂O₃-ZrO₂-Sm₂O₃ phase diagram, and phase equilibria at those temperatures have been demonstrated. No ternary compounds are found and nor are areas of solid solutions based on components and binary compounds in the system. Partially quasibinary sections Al₂O₃-F, SmAlO₃-(66.7% ZrO₂ · 33.3% Sm₂O₃), and Sm₄Al₂O₉-F have been detected, which triangulate the ternary system, and a demonstration is given of the mechanism for penetration of a phase Sm₂Zr₂O₇ with the structure of the pyrochlore into the middle of the Al₂O₃-ZrO₂-Sm₂O₃ system.     

Preparation and Evaluation of High-Purity La2O3

A separation procedure based on extraction chromatography using the di(2-ethylhexyl) phosphoric acid (D2EHPA) impregnated resin, anion exchange with DIAION SA 10 resin, and oxalate precipitation has been developed for the preparation of high-purity La₂O₃ in hydrochloric acid media at a high La concentration. The metallic impurities Ce, Pr, Nd, Sm, K, Mg, Ca, Zn, Cu, Co, Mn, Pb, Al, In, and Fe, but not Bi, were removed efficiently from La by extraction chromatography using a D2EHPA impregnated resin. The Bi was separated from the La by anion exchange (DIAION SA 10) separation. Thus, a high-purity LaCl₃ solution was obtained by anion exchange separation and extraction chromatography. La₂O₃ was prepared from the purified LaCl₃ solution by oxalate precipitation. Glow discharge mass spectrometry was applied for purity evaluation of the prepared La₂O₃. The purity of the prepared La₂O₃ was more than 99.9998 pct total rare earth oxide.     

Mechanism of oxidation-sulfation reactions of coo in the presence of na2so4

Sulfation studies were conducted on CoO samples coated with a thin film of Na₂SO₄ and exposed at 600 to 900 °C in O₂-SO₂-SO₃ environments containing 0.02 to 2 pct (SO₂+SO₃). Within this range of conditions, Co₃O₄ (s), CoSO₄ (s), and liquid Na₂SO₄-CoSO₄ solutions were observed as reaction products. At lower concentrations of SO₃ where CoSO₄ (s) was unstable, the reaction product consisted of a thick Co₃O₄ layer close to the CoO, a layer of Na₂SO₄-CoSO₄ liquid, and large Co₃O₄ particles at the gas/salt interface. At higher concentrations of SO₃, the reaction procuct was a two phase mixture of solid CoSO₄ and an Na₂SO₄-CoSO₄ liquid. In gas mixtures containing 0.15 pct and 1 pct (SO₂+SO₃), the highest reaction rates were observed at about 750 to 800 °C. Some of these results are quite similar to those observed during low temperature hot corrosion of cobalt-base alloys. The overall reaction mechanism has been described in terms of two processes: oxidation of CoO to Co₃O₄ and sulfation of cobalt oxides.     

Ferroelectric and Dielectric Behavior of Samarium-Substituted Bi<Subscript>4</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> Nanomaterials Synthesized by Gel Combustion Method

Samarium (Sm) substituted bismuth titanate (Bi₄Ti₃O₁₂, BT) nanoparticles with compositions of Bi_4?xSm_xTi₃O₁₂ (BSmT) (where x = 0.0, 0.25, 0.50, 0.75, 1.0) were prepared by using the gel combustion method. X-ray diffraction pattern of prepared nanoparticles confirmed that all the BSmT compositions were of the single phase orthorhombic structure with the space group of B2ab. The dielectric loss at 100 Hz varied from 0.0925 to 0.056 with an increase in Samarium content. Dielectric loss confirmed the lower leakage current of BSmT nanoparticles. The ferroelectric behavior of BSmT nanoparticles showed that the Bi_3.50Sm_0.50Ti₃O₁₂ had good ferroelectric property and also had minimum leakage current. The increase of coercive field (Ec) and the increase of remnant polarizations (Pr) were pronounced with the increase in Sm content confirming to the fact that the substitution of Sm³⁺ had improved the ferroelectric properties of BT.     

Hydrochloric acid-hydrogen peroxide leaching and metal recovery from a Greek zinc-lead bulk sulphide concentrate

A zinc-lead bulk sulphide concentrate from Kirki (Greece) was leached in aqueous solution with HClH₂O₂at atmospheric pressure and 95°C to extract up to 97% zinc, 40% lead, 80% silver and less than 12% iron after 6 h. Highly pure PbCl₂ crystallized from the leach filtrate on cooling. Sulphur was oxidized to the elemental form; its loss as sulphate ion in solution and residue was 7.5%. During leaching no emission of H₂S or SO₂ was detected. Conditions were determined for producing a pregnant solution (130 g/L Zn) low in iron and lead, to facilitate zinc extraction by electrolysis. Leaching experiments were conducted at 40% solids, 0.55 g HCl and 0.26 g H₂O₂ per gramme concentrate in a 1-L reactor. After a second leaching of the residue in aqueous solution with HCl (1 M) for 1 h at 90°C, the residual lead sulphate was extracted, so that total lead recovery was over 98%. Other values, such as silver and sulphur, could be recovered by additional treatment of either the leach solution or leach residue.     

Luminescence Property of ZnWO4:Sm Nanopowders Synthesized with Wet Chemical Methods

ZnWO₄:Sm powders with a Sm content of 0 to 10 at. pct have been prepared with wet chemical methods, and a variation of their luminescence property with the Sm content was studied for the first time. X-ray diffraction (XRD) analysis indicated that the synthesized powders all were single-phase sanmartinite ZnWO₄ with monoclinic structure. The doped Sm³⁺ ions have not caused any significant change in the host structure, indicating Sm³⁺ ions were incorporated in the ZnWO₄ structure. A scanning electron microscope (SEM) micrograph indicated that powders had uniform morphology and particle size approximately 10 to 150 nm, which decreased with increasing Sm³⁺ content. The synthesized ZnWO₄ nanopowders showed broad emissions at blue-green bands near 460 nm and red emissions at 568.4 nm, 610.4 nm, and 649.4 nm. The blue-green emission decreased with increase in Sm³⁺ content, and the red emission reached maximum at Sm³⁺ content of 5 at. pct.     

Response to Thermal Exposure of Ball-Milled Cu-Mg/B2O3 Powder Blends

The response to thermal exposure of ball-milled Cu-Mg/B₂O₃ powder blends was investigated in the current study to explore the potential of powder metallurgy route to produce Cu-B alloys. Cu-20Mg alloy powder was mixed with B₂O₃ and subsequently ball milled for 1 hour. Ball milling alone failed to establish a reaction between Cu-Mg compounds and B₂O₃. When the ball-milled powder blend was heated, however, B₂O₃ was reduced by CuMg₂ <773 K (500 °C). The Cu₂Mg intermetallic phase, which has survived until 773 K (500 °C), was involved in the reduction of the remaining B₂O₃ at still higher temperatures, while excess Mg reacted with B to produce MgB₂ and MgB₆ compounds. Cu-Mg alloy with predominantly the CuMg₂ phase must be utilized to take advantage of the capacity of the CuMg₂ (Cu-43 wt pct Mg) compound to reduce B₂O₃ at temperatures as low as 773 K (500 °C). Once the Cu-43Mg alloy powder is mixed with B₂O₃ and the powder blend thus obtained is ball milled and subsequently heated at 500 °C, B₂O₃ is readily reduced by CuMg₂ to yield Cu, B, and MgO. The latter can be easily removed from the powder blend by acid leaching.     

Zersetzungsgleichgewichte im System Fe2O3—Fe3O4

Neue isothermische Abbauten und Aufbauten des Fe₂O₃ und Fe₃O₄ zwischen 1170 °C und 1420 °C. Wechselwirkungen zwischen Proben und Schiffchenmaterial. Randlöslichkeiten des Fe₂O₃ und Fe₃O₄. Keimbildungshemmungen der Hämatitphase. Aktivitäten des Fe₃O₄ in seinem Homogenitätsbereich. Erörterung des γ-Fe₂O₃ um 1350 °C als Kryptomodifikation.     

Isothermal section of Gd-Sm-Co ternary system at 773 K

The isothermal section of the phase diagram of the Gd-Sm-Co ternary system at 773K was investigated by X-ray powder diffraction(XRD),differential thermal analysis(DTA),optical microscopy and scanning electron microscopy(SEM) techniques.The result shows that the isothermal section consists of 12 single-phase regions,16 two-phase regions and 5 three-phase regions.Five pairs of corresponding compounds of Gd-Co and Sm-Co systems,i.e.,Gd2Co17 and Sm2Co17,Gd2Co7 and Sm2Co7,GdCo3 and SmCo3,GdCo2 and SmCo2,Gd3Co and SmCo form continuous series of solid solutions.The maximum solid solubility of Sm in Gd 4Co3 and Gd12Co7 were about 7.2 at.% and 47.8 at.% Sm,respectively.The maximum solid solubility of Gd in Sm5Co19 and Sm5Co2 were about 4.7 at.% and 7.6 at.% Gd,respectively.The binary compounds Sm9Co4,GdCo5 and SmCo5 were not observed at 773K.No ternary compound was found.     

Decomposition of monazite concentrate in sulphuric acid

A sulphuric acid bake-leach process was investigated for the extraction of rare earth elements (REEs), uranium, and thorium from a monazite concentrate. X-ray diffraction analysis showed the formation of water-soluble sulphates that readily dissolved during the water leach step. Nearly complete extraction of REEs, uranium, and thorium was achieved when the concentrate was baked at 250°C for 4?h with a sulphuric acid to concentrate (S/C) weight ratio of 4:1. At the 1:1 sulphuric acid to concentrate ratio ～65% of REEs were leached while only ～2–5% of uranium and thorium were extracted. Temperature (180–250°C) had little effect on the extraction of REEs, but greatly affected the extraction of thorium and uranium. In general, the extraction of thorium and uranium decreased with an increase in temperature. The effect of particle size (48–137?µm) was also tested and found to have little effect on the extraction of REEs. Acid consumption was calculated and found to increase with longer baking times (0.3–0.8?g acid/g concentrate). The major mineralogical phases formed because of the sulphation reaction included potassium cerium sulphate hydrate (2K₂SO₄·Ce(SO₄)₂·2H₂O), lanthanum sulphate hydrate (La₂(SO₄)₃·2H₂O), sodium praseodymium sulphite hydrate (NaPr(SO₃)₂·2H₂O), and neodymium sulphate hydrate (Nd₂(SO₄)₃·5H₂O), all of which were water-soluble.     

Comparative studies on promotional effect of Pr6O11,Nd2O3 and Sm2O3 on Ni-SiO2 for pressurized carbon dioxide reforming of methane

The 7 wt% rare earth metal oxide promoted Ni-SiO₂ catalysts of Ni-7Pr₆O₁₁-SiO₂,Ni-7Nd₂O₃-SiO₂,and Ni-7Sm₂O₃-SiO₂ were prepared by the complex-decomposition method,and were comparatively evaluated for pressurized carbon dioxide reforming of methane(CRM) under severe conditions of 750℃,1.0 MPa,CH₄/CO₂=1,and gas hourly space velocity of 53200 mL/(g·h).The addition of r...     

Interfacial Molten Reactivity of Aluminum in Contact with (0001) Al2O3 and (111) Al2MgO4 Single Crystal Surfaces

The present work studies (0001) Al₂O₃ and (111) Al₂MgO₄ wetting with pure molten Al by the sessile drop technique from 1073 K to 1473 K (800 °C to 1200 °C) under Ar at PO₂ 10^?15 Pa. Al pure liquid wets a smooth and chemically homogeneous surface of an inert solid, the wetting driving force (t,T) can be readily studied when surface solid roughness increases in the system. Both crystals planes (0001) Al₂O₃ and (111) Al₂MgO₄ have crystallographic surfaces with identical O^?2 crystalline positions however considering Mg²⁺ content in Al₂MgO₄ structure may influence a reactive mode. Kinetic models results under similar experimental conditions show that Al wetting on (0001) Al₂O₃ is less reactive than (111) Al₂MgO₄, however at >1273 K (1000 °C) (0001) Al₂O₃ transformation occurs and a transition of wetting improves. The (111) Al₂MgO₄ and Al system promotes interface formations that slow its wetting process.     

Synthesis of Dy2O3 nanoparticles via hydroxide precipitation： effect of calcination temperature

This work described the preparation of dysprosium oxide, Dy2O3, nanoparticles using the homogeneous precipitation method. Dy3+ ions were precipitated using NaOH solution. The obtained product was filtered, dried, and then calcined for 1 h at the temperature range of 300–700 °C in static air. The calcination temperature of the Dy-precursor was chosen based on its decomposition as indicated by the TGA analysis. The crystalline structure and surface morphology of the calcined solids were studied by X-ray diffraction(XRD), field emission scanning electron microscopy(FE-SEM), transmission electron microscopy(TEM) and X-ray photoelectron spectroscopy(XPS). The obtained results revealed that Dy2O3 with crystallites size of 11–21 nm was formed at 500 °C. Such value increased to 25–37 nm for the sample calcined at 700 °C.