COPRECIPITATION PREPARATION AND VOLTAGE SENSITIVE CHARACTERISTICS OF DOPED ZnO VARISTOR

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Coprecipitation of metal ions into calcite: an estimation of partition coefficients based on field investigation

Trace elements(and their isotopes)in carbonates are commonly used to reconstruct paleoenvironment and paleoclimate.Understanding the processes and mechanisms of element incorporation into carbonates is thus crucial for using such geochemical parameters as paleoclimate proxies.In contrast to laboratory-based experimental results,the partitioning of trace metals between solid and solution phases in natural carbonate precipitation systems has rarely been reported.In this study,we investigated the partition coefficients of metal ions between solid and solution in the channel of the natural Baishuitai travertine system,Yunnan,China.Our results show that the partition coefficients of Li+,Na+,Mg2+,Sr2+and Ba2+are<1,that of Ni2+is approximately 1,and those of Co2+,Mn2+,Zn2+and Cu2+are>1,consistent with the results found in previous experimental studies.Although the substitution for Ca2+is likely the main uptake process of these metals into calcite,depending on their ionic radius and charge,trace elements may also be incorporated by adsorption or physical entrapment.Our study shows that unlike laboratory experiments performed under specific conditions,the partitioning of metals between two phases in the natural travertine system could be controlled by several,even multiple,environmental factors(e.g.,carbonate deposition rate,temperature,and pH),which should be taken into account when using trace metals(and their isotopes)in carbonate archives as a paleoclimate proxy.

Synthesis of (1-x)Pb[(Mg,Zn)_(1/3)Nb_(2/3)] O_3-PbTiO_3 DielectricCeramic Powder by a Coprecipitation Process

A coprecipitation method was used for preparation of 0.95Pb[(Mg0.8,Zn0.2) 1/ 3 Nb2 /3]O3-0.05PbTiO3(PMZN-PT),dielectric ceramic powder. X-ray powder diffraction and electron probe energy dispersive, X-ray analyzer revealed that the powder calcinated at 800℃ for 2 h is the PMZN-PT with 100% single perovskite phase, and the order of magnitude of atomic proportion of Mg to Zn reaches approximately 10: 1. In addition, the influence of Zn and Ti content on the perovskite phase and pyrochlore phase formation namely : 0.95Pb[(Mg1-x Znx) 1 /3Nb,2/3]O3 -0.05PbTiO3, (1-y)Pb[(Mg0.7Zn0.3) 1 /3Nb2 /3] O3-yPbTiO3 was also analysed.

Determination of Trace Amount of Vanadium in High Purity Y_2O_3 by Electrothermal Vaporization－ICP－AES With Bi（PDC）_3 Coprecipitation

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Method to Study the Primary Nucleation for Solid Solution: Application to Uranium-Neodymium Oxalate Coprecipitation

Actinides co-precipitation is currently investigated in order to synthesize solid solutions of actinides mixed oxalates. This paper deals with the thermodynamic and kinetic study of the precipitation of uranium-neodymium oxalate system. Based on an analysis of the theories developed in the literature, a new expression for the determination of the supersaturation ratio for the solid solutions is presented. An experimental study of the nucleation kinetics was performed on the mixed uranium-neodymium oxalates. Homogeneous and heterogeneous primary nucleation laws are obtained using a specific stopped flow apparatus. The experimental results are consistent with the classical behaviour of nucleation phenomena. The values of the kinetic parameters for the solid solution point out that the formation of the uraniumneodymium mixed oxalates is kinetically favoured compared with the simple uranium and neodymium oxalates.

Modified coprecipitation process of synthesizing Bi-system superconductor precursor powder and its stoichiometry

A modified coprecipitation process is presented based on the stoichiometry study of oxalate coprecipitation process in water medium to synthesize Bi-Pb-Sr-Ca-Cu-O multi-component powder.Its characteristic is that the coprecipitation reaction takes place in a mixed solution medium composed of water and a kind of organic solvent (volume percentage 】90%).Thus,it overcomes the serious shortcoming of inability to maintain stoichiometry in Bi-system superconductor powder synthesized by water-medium coprecipitation.The effects of pH value,oxalic acid concentration and aging time on stoichiometry maintenance in precipitate are systematically studied.Bulk material made from the powder prepared by the new modified coprecipitation also shows the success of the new process.

Enhanced thermal stability of Ce_(0.33)Zr_(0.55)(LaNdY)_(0.12)O_(2) mixed oxides prepared by sulfate-aided coprecipitation method

Ceria-zirconia based mixed oxides(CZs)have been applied in three-way catalysts(TWCs)for their high surface area and oxygen storage capacity(OSC).In this work,enhanced thermal stability of Ce_(0.33)Zr_(0.55)(LaNdY)_(0.12)O_(2)mixed oxides was realized via a facile and scalable approach,namely,sulfateaided coprecipitation method was labelled as CZ-S.Sulfate ion(SO_(4)^(2-))was added into raw solution in the form of sulfuric acid and acted as coordination agent.The control sample was prepared by conventional coprecipitation method without sulfuric acid added and labelled as CZ.The promotion effect of sulfate ion was analyzed systematically by X-ray diffraction(XRD),transmission electron microscopy(TEM),scanning electron microscopy(SEM),N_(2)adsorption-desorption,Fourier transform infrared spectroscopy(FT-IR),X-ray photoelectron spectroscopy(XPS),OSC and hydrogen temperatureprogrammed reduction(H_(2)-TPR)analysis.XRD and high resolution TEM results reveal that CZ-S have homogeneous distributions of elements.TEM and SEM images show that fresh samples of CZ-S have narrower distributions of grain sizes and larger pore sizes than those of CZ.Through cross analysis of structure and morphology of CZ and CZ-S,we find that the introduction of sulfate ions results in uniform distributions of elements,narrows distributions of grain sizes,and enables the formation of secondary loose packing of sub-particles,which lead to enhanced thermal stability of the samples of CZ-S upon aging process at high temperature.After aging treatment at 1100℃for 10 h,aged samples of CZ-S present larger specific surface areas and pore volumes than the aged sample prepared by conventional coprecipitation method without sulfate ions added.Furthermore,the aged sample of CZ-S2(SO_(4)^(2-)/Zr=1)possesses the highest specific surface area of 21.9 m2/g and the biggest pore volume of 0.035 mL/g among all aged samples.

A new type-γ'/γ''coprecipitation behavior and its evolution mechanism in wrought Ni-based ATI 718Plus superalloy

In the precipitation-hardened Ni-based superalloy,typified by ATI 718 Plus,the nano-scaleγandγphase in duplet or triple coprecipitate morphology can provide superior high-temperature strength.Thus,it is of great sense to study the evolution ofγ’/γ’’coprecipitate during long term service at elevated temperature.In this study,the new-typeγ’/γ’’coprecipitates with a sandwich or compact configuration were found firstly in wrought ATI 718 Plus superalloy during long term thermal exposure at 705℃.These co-structure of theγ’/γ’’precipitates evidently inhibit the coarsening ofγ’phase.The increase of thermal exposure time evidently leads to the increase of the volume fraction ofγ’/γ’’coprecipitate and transformation of sandwich-typeγ’/γ’’coprecipitate to compact-typeγ’/γ’’coprecipitate,which is characterized asγphase precipitate at several faces of theγphase.The main evolution mechanism ofγ’/γ’’coprecipitates is element segregation,especially the composition variations of Al+Ti and Nb and their ratio of Al+Ti/Nb.In addition,the interfacial energy betweenγ’’phase andγmatrix also plays a key role on theγ’/γ’’coprecipitates evolution.The calculated results show that the longer thermal exposure time leads to the higher interfacial energy,which is beneficial for nucleation and precipitation ofγ’’phase on the faces ofγ’phase.

非负载和氧化铝负载的纳米CeO_2-ZrO_2和CeO_2-Te_2O_3固溶体催化CO氧化(英文)

Ceria-zirconia(CZ)and ceria-terbia(CT)and alumina-supported ceria-zirconia(CZA)and ceria-terbia(CTA)solid solutions were synthesized by coprecipitation and deposition precipitation methods,respectively.Structural characteristics and catalytic activity of the synthesized samples have been investigated using X-ray diffraction(XRD),high resolution transmission electron microscopy(HRTEM),X-ray photoelectron spectroscopy(XPS),Raman spectroscopy(RS),and Brunauer-Emmett-Teller(BET)surface area measurements.To evaluate the catalytic properties,total oxygen storage capacity and CO oxidation activity measurements were carried out.The XRD analyses revealed the formation of Ce0.75Zr0.25O2 phase for CZ and Ce0.5Zr0.5O2 and Ce0.6Zr0.4O2 phases for CZA samples,respectively.While the formation of only Ce0.8Tb0.2O2-δphase was noted for both CT and CTA samples.All the supported and unsupported samples adopted a fluorite-type structure and exhibited cell parameters with respect to Vegard's rule.The HRTEM results indicated well-dispersed particles of the size around 5 nm.The RS measurements suggested the presence of oxygen vacancies due to defective structure formation.The XPS studies revealed the presence of cerium in both Ce 4+ and Ce 3+ oxidation states in different proportions.It was found that CO oxidation for CTA occurs at very much lower temperature than CT,CZ,and CZA samples.Details of these findings by correlating with the structural characterization studies are consolidated.

PREPARATION OF NANOMETER ZrO_2-8% Y_2O_3 POWDERS BY AZEOTROPIC DISTILLATION PROCESSING

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Synthesis and Properties of La and Sb Doped SnO_2 Conductive Nanoparticles

La and Sb doped SnO2 conductive nanoparticles were prepared by the coprecipitation method with SnCl4·5H2O, SbCl3 and La2O3 as the raw materials. Thermal behavior, crystal phase, and structure of the prepared conductive nanoparticles were characterized by TG/DSC/DTG, FTIR, XRD and TEM techniques, respectively. The resistivity of the prepared conductive nanoparticles is 2.5 Ω·cm. TG/DSC/DTG curves show that the precursors lose weight completely before 750 ℃. FTIR spectrum show that the vibration peak are wide peak in 718～615 cm -1, and the La and Sb doped SnO2 conductive nanoparticles have intense absorption in 4000～2000 cm -1. X-ray powder diffraction pattern of the conductive nanoparticles indicates that the Sb-doping in SnO2 is replacement doping and La 3+ combines with Sn 4+ and O 2- form La2Sn2O7. TME shows that the particles are weakly agglomerated, and the size of the particles calcined at 1000 ℃ ranged about 20～30 nm.

A new candidate as the cathode material for intermediate and low temperature SOFCs

In order to develop the new cathode materials suitable for intermediate and low temperature solid oxide fuel cells (IT/LTSOFCs), LaNi1-xFexO3 (x=0.4-0.8) (LNF) materials were synthesized using coprecipitation method. Their structures and morphologies were investigated by XRD and SEM, and their electronic conductivities at different temperatures were measured by dc four terminal method. Fuel cells were fabricated to evaluate the electrochemical properties of the LNF materials as cathodes at different temperatures. The performance of 450-497 mW·cm-2 was obtained in the temperature region of 580-650 ℃ for the LaNi0.2Fe0.8O3 cathode, and of 209-227 mW·cm-2 at 400-500 ℃ for the LaNi0.4Fe0.6O3. The excellent fuel cell performances indicate that the LNF materials are good cathodes for IT/LTSOFCs.

Enrichment of lanthanides in aragonite

Using the constant addition technique,the coprecipitation of lanthanum,gadolinium,and lutetium with aragonite in seawater was experimentally investigated at 25 ℃.Their concentrations in aragonite overgrowths were determined by inductive coupled plasma mass spectrometer.All these lanthanides were strongly enriched in aragonite overgrowths.The amount of lanthanum,gadolinium,and lutetium incorporated into aragonite accounted for 57%-99%,50%-89%,and 40%-91% of their initial total amount,respectively.With the increase of aragonite precipitation rate,more lanthanides were incorporated into aragonite while their relative fraction in aragonite overgrowths decreased consistently.It indicated that the coprecipitation of lanthanides with aragonite was controlled by the kinetics of aragonite precipitation.

SEPARATION AND PURIFICATION OF ULTRAMICROGRAM URANIUM FROM SATURATED NaCl SOLUTION

This paper summarizes the results of the coprecipitation of ultramicrogram uranium with Fe（OH）3 from saturated NaCl solution and separation of uranium from Fe（Ⅲ） by solvent extraction with TBP as extractant. In the first step, the coprecipitation efficiency of uranium is more than 95%; in the second step, extraction percentage of uranium is more than 98%, and stripping efficiency of uranium is nearly 100% （twice stripping） and separation factor （separation of Fe（Ⅲ） from uranium） is more than 103.

Matrix Induced Synthesis of Eu^(3+) Doped Zn_3(PO_4)_2 and LaPO_4 Phosphors by in-Situ Composing Hybrid Precursors

Using rare earth and zinc coordination polymers with aromatic carboxylic acids as the precursors, composing with the polyethylene glycol （PEG） as the dispersing media, micro crystalline phosphors Zn3（PO4）2∶Eu 3+ and LaPO4∶Eu 3+ were synthesized by in-situ co-precipitation method. X-ray diffraction and scanning electronic micrograph were used to characterize the resultant samples, whose particle size are in the range of micrometer. The emission spectra of Zn3（PO4）2∶Eu 3+ （λ ex=245 nm） and LaPO4∶Eu 3+ （λ ex=390 nm） shows that the emission for Eu 3+ in Zn3（PO4）2 is dominated by the 5D0→7F1 （592 nm） magnetic-dipole transition,While the dominant emission for Eu 3+ in LaPO4 is the typical hypersensitive transition 5D0→7F2 （618 nm）.

Pb(Mg_(1/3)Nb_(2/3))O_3-PbTiO_3-BaTiO_3 Complex Perovskite Ferroelectric Ceramics with High Dielectric Constant and Low Firing Temperature

The effects of different firing temperatures on the stability of perovskite phase, grain size, and dielectric properties were investigated by XRD, TEM, SEM and dielectric measurements. The dielectric ceramics of Pb(Mg1/3Nb2/3)O3-PbTiO3-BaTiO3 system were obtained by chemical coprecipitation in water. The ceramics have higher dielectric constant (7003-9714), lower firing temperature(950-1150℃), quite uniform microstructure with grain size less than 2.5 mp, and lower temperature coefficients of capacitance. As a re-sult, it was confirmed that the simple and low cost chemical route used namely coprecipitation in water is a desired method for preparinghigh property dielectfic materials applicable to multilayer capacitors.

Preparation of zirconia-alumina powder by co-precipitation

A zirconia alumina powder with a near spherical shape and an average size of 0.1～0.2 μm was prepared by co precipitation. XRD analysis shows that α Al 2O 3 phase may be directly transformed from amorphous in calcining the hydroxide composite. The ZrO 2 Al 2O 3 composite ceramics manufactured from this powder has the maximum fracture toughness of 9 MPa·m -1/2 at 15% ZrO 2 and 740 MPa fracture strength at 5% ZrO 2. Zirconia grains about 1 μm in diameter are dispersed uniformly in the alumina ceramic matrix.

CoMnMgAl Hydrotalcite-like Compounds and their Complex Oxides: Facile Synthesis and FCC SO_x Removal

The X-CoMnMgAl hydrotalcite-like precursors(X-LDHs) were first synthesized by the coprecipitation method using Cl-, CO32-, NO3- and SO42- as the corresponding guest anions, which were further used to prepare X-CoMnMgAl complex oxides(X-LDOs) through calcination. The structure and the surface morphology of the as-prepared samples were characterized by FT–IR, XRD, N2 adsorption-desorption and SEM. These as-prepared X-LDOs could act as sulfur-transfer catalysts for desulfurization. The activity of SOx adsorption and regeneration was evaluated via a self-assembled fixed-bed reactor simulating the conditions found in the fluid catalytic cracking units. These four types of sulfur-transfer catalysts with the same phase but different structure displayed the following order of desulfurization efficiency: CO3-LDO >Cl-LDO >NO3-LDO > SO4-LDO.

Preparation and Analysis of Porous Oxychloride Titanium Oxide Precursor Material

Oxychloride titanium oxide precursor material is one of the key substances produced by the giant electrorheological effect. In this paper, tetrabutyl titanate and oxalic acid and anhydrous ethanol are used to prepare porous titanyl oxalate precursor powder by precipitation method. The materials, morphology and grain size were analyzed by X-ray diffraction and electron microscope method. Conductivity was measured by a four-probe method, and then the infiltration property of water and silicone oil on the surface of the powder was investigated. The results show that Oxychloride titanium oxide precursor has good wettability to water and silicone oil. The wettability has little to do with the bath temperature and the pH of the solution. The contact angle of water on oxychloride titanium oxide precursor surface does not change greatly with the change of the bath temperature and pH, ranging from 26.8? to 31.1?. Similarly, the contact angle of silicone oil on the surface of the sample ranges from 9.5? to 11.5?. So, silicone oil has better wettability on the surface of the sample than water. Porous titanium oxalate is an insulating material having a resistivity more than 1 GΩ?cm. Oxychloride titanium oxide precursor is poor thermal stability, and it breaks down to generate TiO2 when the temperature is higher than 70?C.

The Role of CeO₂-Doping of Fe₂O₃/Co₃O₄System on Its Structural Characteristics

The role of ceria doping (0.75 - 3 mol%) on solid-solid interactions between ferric and cobaltic oxides was investigated. The investigated solids were characterized by TGA, DTA, XRD and HRTEM. The results revealed that ceria much enhanced the formation of nanosized CoFe2O4 (10 - 30 nm). The stimulation effect of ceria towards cobalt ferrite formation was evidenced from analysis of DTA and XRD investigations. In fact, the area of endothermic peak located at 575℃- 680℃ relative to solid-solid interaction between ferric and cobaltic oxide increased by increasing the dopant concentration. This treatment decreased the activation energy of formation of the produced ferrite from 33 - 9.2 kJ/mol upon doping with 3 mol% CeO2. HRTEM analysis revealed the formation of homogenous nanosized CoFe2O4. The formation effect of ceria dopant towards the formation of CoFe2O4 has been tentatively attributed to an effective increase in the mobility of the reacting cations.