Synthesis of Mg_2B_2O_5 whiskers via coprecipitation and sintering process

Mg2B2O5 whiskers with high aspect ratio were synthesized by coprecipitation and sintering process using MgCl2-6H2O, H3BO3, and NaOH as raw materials and KCl as a flux. Their formation process was investigated by thermogravimetry and differential scanning calo- rimetry （TG-DSC）, X-ray diffraction （XRD）, and scanning electron microcopy （SEM）. It is found that the products synthesized at 832℃ are monoclinic Mg2B205 whiskers with a diameter of 200-400 nm and a length of 50-80 μm. Transmission electron microscopy （TEM） and selected area electron diffraction （SAED） analyses show that the whiskers obtained at 832℃ are single crystalline and grow along with the [010] direction. The growth mechanism of Mg2B2O5 whiskers was also presented.

Simultaneous determination of some trace metal impurities in high-purity sodium tungstate using coprecipitation and inductively coupled plasma atomic emission spectrometry

A method based on the combination of coprecipitation with inductively coupledplasma atomic emission spectrometry (ICP-AES) was developed for the determination of impurities inhigh-purity sodium tungstate. Six elements (Co, Cu, Fe, Mn, Ni, and Pb) were coprecipitated bylanthanum hydroxide so as to be concentrated and separated from the tungsten matrix. Effects of somefactors on the recoveries of the analytes and on the residual amount of sodium tungstate wereinvestigated, and the optimum conditions for the coprecipitation were proposed. Matrix-matchingcalibration curve method was used for the analysis. It is shown that the elements mentioned abovecan be quantitatively recovered. The detection limits for Co, Cu, Fe, Mn, Ni, and Pb are 0.07, 0.4,0.2, 0.1, 0.6, and 1.3 μg·g^(-1), respectively. The recoveries vary from 92.5% to 108%, and therelative standard deviations (RSDs) are in the range of 3.1%-5.5%.

Growth of carbon nanotubes on the novel FeCo-Al_2O_3 catalyst prepared by ultrasonic coprecipitation

FeCo-Al2O3 catalyst was prepared by an ultrasonic coprecipitation （UC） method for the growth of carbon nanotubes （CNTs） from catalytic decomposition of methane.Its catalytic performance was compared with that of the FeCo-Al2O3 catalyst counterparts prepared by stepwise impregnation （I） and conventional coprecipitation （C） methods,respectively.The structure and properties of the catalysts and the CNTs as produced thereon were investigated by means of XRD,XPS,TEM and N2 adsorption techniques.It was found that the catalyst prepared by the ultrasonic coprecipitation method was more active,and the yield and purity of the synthesized CNTs were promoted evidently.The XPS results revealed that there were more active components on the surface of the catalyst prepared by the ultrasonic coprecipitation method.On the other hand,N2 adsorption demonstrated that the catalyst prepared by the ultrasonic coprecipitation method conferred larger specific surface area,which was beneficial to dispersion of active components.TEM images further confirmed its higher dispersion.These factors could be responsible for its higher activity for the growth of CNTs from catalytic decomposition of methane.

Comparison of the Sol-gel Method with the Coprecipitation Technique for Preparation of Hexagonal Barium Ferrite

Hexagonal barium ferrite BaFe12O19 particles were prepared by sol-gel and coprecipitation methods, respectively. The composition of the so-obtained materials was investigated by means of XRD. By the sol-gel method, non-anticipated intermediate crystalline phases, such as γ-Fe2O3, α-Fe2O3, BaCO3, and BaFe2O4 etc., were formed with the delay of the formation of BaFe12O19. The formation of single phase BaFe12O19 required calcination at 850 oC for 4 h. On the other hand, using coprecipitation technique, amorphous hydroxide precursor was directly transferred into BaFe12O19 almost without the formation of intermediate crystalline phases. BaFe12O19 was prepared by calcining at 700 oC for 3 h. The results were confirmed by ESEM and VSM analyses. Based on the already reported results and the observed results in this study, it can be concluded that the coprecipitaion technique is easier to control than the sol-gel method for preparation of BaFe12O19 at a low temperature.

A Coprecipitation Coating Synthesis of SiC/YAG Composites

The α-SiC in 0.5μm size powders were coated with Al_2O_3 and Y_2O_3 by a coprecipitation coating (CPC) method forfabrication of SiC/YAG composites. The same powder preparation was carried out by conventional mechanical mixing(MM) method for comparison. Two kinds of SiC/YAG composites were manufactured by pressureless sintering usingthe different powders, named CPC composite and MM composite thereafter respectively. It is shown that the CPCcomposite has the advantages of homogeneous distribution of YAG phase and of being sintered to high density ata low temperature, 100℃ lower than that of MM composite. The strength (573 MPa) and hardness (23.3 GPa) ofthe CPC composite are significantly higher than those (323 MPa and 13.5 GPa) of the MM composite, respectively.

Studies on State and Structure of Noble Metals in Electrocatalyst Made by Coprecipitation Method

The electrocatalysts of Pt/C, PtRu/C and Ru/C were prepared by the impregnation method. The facet characterization, the dispersion and the particle size for the catalysts were determined by means of X ray diffraction and transmission electron microscopy. X ray photoelectron spectroscopy was also used to analyze the state and the valency of the noble metals. The results show that the particle size was in nanometer range and the binary metals have come into being an alloy. The platinum in the catalysts existed in zero valency. The valency of the ruthenium on the surface is different from that in the body, while the ruthenium on the surface existed in oxide form. PtRu/C and Pt/C are of good activity to the electrooxidation of hydrogen except Ru/C. PtRu/C is more tolerant of CO than Pt/C, and CO is only adsorbed on Pt.

Characterization of (Y,Gd)B_xV_(1-x)O_(4-x)∶Eu Phosphor Prepared by Coprecipitation Reaction

White body-color （Y, Gd）BxV1-xO4-x ：Eu^3＋ phosphors were prepared by coprecipitation reaction. Under VUV excitation at 147 nm, the red emission colorimetric purity of （Y, Gd） BxV1-xO4-x： Eu^3＋ phosphor is much better than that of commercial PDP （plasma display panels） phosphor （Y, Gd）BO3：Eu^3＋ . But its relative emission intensity is only about 90% of the commercial phosphor.

Acidithiobacillus ferrooxidans enhanced heavy metals immobilization efficiency in acidic aqueous system through bio-mediated coprecipitation

This study investigated the promotion effect of A.ferrooxidans on complex heavy metals coprecipitation process.A.ferrooxidans significantly enhanced the ferrous oxidation,which also promoted the formation of iron-oxyhydroxysulphate.Cu(II)concentration reduced to0.058mmol/L in A.ferrooxidans inoculated system,and Cd also reduced to the lowest concentration(0.085mmol/L).Pb was mainly immobilized as anglesite and iron-oxyhydroxysulphate promoted the removal of remanent Pb in solution.The precipitates are characterized by XRD,SEM,and FTIR analysis.The main component of the iron-oxyhydroxysulphate was well crystallized jarosite.A.ferrooxidans contributed to the formation of schwertmannite in later monovalent cation lack stage.Higher ferrous iron oxidation rate and Fe(III)supply rate in A.ferrooxidans inoculated system facilitated polyhedron crystal formation and the increase of particle diameter.Complex heavy metals could be incorporated into iron oxyhydroxysulphate crystal,and efficiently removed from acidic wastewater through A.ferrooxidans mediated coprecipitation.

Microstructure and magnetic characteristics of nanocrystalline Ni0.5Zn0.5 ferrite synthesized by a spraying-coprecipitation method

Nanocrystalline Ni0.5Zn0.5 ferrite with average grain sizes ranging from 10 to 100 nm is prepared by using a spraying-coprecipitation method. The results indicate that the nanocrystalline Ni0.5Zn0.5 ferrite is ferromagnetic without the superparamagnetic phenomenon observed at room temperature. Specific saturation magnetization of nanocrystalline Nio.sZno.5 ferrite increases from 40.2 to 75.6 emu/g as grain size increases from 11 to 94nm. Coercivity of nanocrystalline Ni0.5Zn0.5 ferrite increases monotonically when d 〈 62 nm.The relationship between the coercivity and the mean grain size is well fitted into a relation Hc - d^3. A theoretically evaluated value of the critical grain size is 141nm larger than the experimental value 62nm for nanocrystalline Ni0.5Zn0.5 ferrite. The magnetic behaviour of nanocrystalline Ni0.5Zn0.5 ferrite may be explained by using the random anisotropy theory.

COPRECIPITATION PREPARATION AND VOLTAGE SENSITIVE CHARACTERISTICS OF DOPED ZnO VARISTOR

A process of preparing ZnO voltage sensitive ceramics doped with some oxides by coprecipitation was described in the paper. The thermal properties of ZnO nanometer powders and the current voltage characteristics of the ceramics have been investigated. The results showed that the six additive ZnO powders with hexagonal system were homogeneous grain size distribution in microstructure, the optimal reaction pH is 6.90±0.05, the temperature for calcining and sintering was at about 500 ℃ and 1100 ℃, respectively. The powders were also examined by SEM, IR and XRD etc, and the effect of doping La 2O 3 on the electrical properties of ZnO varistor was investigated too.

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.

Agglomeration Control of Ultrafine Y_2O_3-ZrO_2 and (MgO, Y_2O_3)-ZrO_2 Powders Synthesized by Coprecipitation Process

Chemical coprecipitation was used to produce ultrafine and easily sinterable Y2O3-stabilized and （Y2O3,MgO）-stabilized ZrO2 powders. Six precipitation processes for preparation of ZrO2-based ultrafine powders were designed separately, meanwhile different techniques used to control the agglomeration formation were proposed. By means of TEM, SEM, Raman spectroscopy and IR spectroscopy, the mechanisms of agglomeration control in the precipitation processes and post-precipitation and drying process were investigated. The experimental results show that adding appropriate anion surface active agents （such as PAA1460） or polymer （PEG1540 matching with PEG200） in aqueous solution systems during precipitation processes could reinforce charge effect and location effect for gel particles interface. Adding wetting agents to wet gels washing with distilled water during drying process could change interface structure of gel particles and decrease surface tension between gel particles. The agglomeration control in the precipitation, post-precipitation and drying processes had remarkable influence on the characteristics of powders. By adding various macromolecules in the processes, the agglomeration state could be controlled efficiently, and the characteristics of powders were improved.

Assessment of the conventional molybdenum-blue and magnesium-induced coprecipitation procedures in phosphorus measurement in various aquatic environments

Phosphorus （P） is an essential nutrient utilized by all organisms for energy transport and growth. Both the conventional molybdenum-blue method and the magnesium-induced coprecipitation （MAGIC） procedures were applied for the measurement of dissolved inorganic phosphorus （DIP） and total dissolved phosphorus （TDP） in more than 840 water samples collected between 2003 and 2005, including seawater （the Huanghai Sea, the East China Sea, and the northern South China Sea）, water from rivers and estuaries （the Changjiang, the Huanghe, and the major rivers emptying into the Jiaozhou Bay）, groundwater （in the drainage basin surrounding the Jiaozhou Bay）, rain-water, and aquaculture water samples. The MAGIC method allows the investigation of phosphorus distributions and cycling for systems in which DIP is below the detection limits of conventional methods. Comparison between the two methods demonstrated that the concentrations obtained with both methods were significantly correlated. The differences of DIP and TDP concentrations measured with the two methods were higher when the concentrations of DIP and TDP were lower, implying the lower reproducibility at low concentrations. The concentration differences increase with the increase in the proportion of DOP in TDP, which indicates that the discrepancy of DIP concentrations measured with the two methods increases when the DOP concentration is high. The discrepancies indicated that the composition of P compounds differs depending on sample sources and water type; it would be useful to infer the presence of different phosphorus compound pools from differences between the two methods. This study indicates the potential presence of a pool of alkaline-labile compounds for samples from rainwater and rivers and estuaries surrounding the Jiaozhou Bay; the potential presence of acid-labile compounds that were adsorbed by Mg（OH）2 for samples from the Changjiang Estuary, Huanghai Sea, East China Sea, and groundwater; the potential presence of a substantial pool of acid-labile compounds that were not adsorbed by Mg（OH）2 for samples from the Huanghe Estuary, aquaculture water, the East China Sea algal bloom water, and the northern South China Sea.

Preparation of tetragonal CaO-ZrO_2 nano-powder by chemical coprecipitation method

With zirconium oxychloride, nitrate of lime and ammonia as raw materials, nano powder of CaO ZrO 2 was prepared by chemical coprecipitation method. By use of azeotropic distillation processing, chemical coprecipitation precursor was obtained. Phase transformation of the precursor was observed at the temperature of 593.81 ℃ and 1 234.56 ℃ respectively with DTA analyses. Phase structure was analyzed through XRD and Raman spectra. The average particle size of tetragonal zirconium oxide powder was 9.8 and 43.7 nm after calcination at 600 and 1 100 ℃ respectively which was tested by TEM and BET analyses. Furthermore, the influences of the doping of nitrate of lime and the average particle size of zirconium oxide on the stability of tetragonal zirconium oxide were also discussed.

Effect of Zn^(2+) Content on the Microstructure and Magnetic Properties of Nanocrystalline Ni_(1-x)Zn_xFe_2O_4 Ferrite by a Spraying-coprecipitation Method

Nanocrystalline Ni1-xZnxFe2O4 ferrites with 0≤x≤1 were successfully prepared by a spraying-coprecipitation method.The microstructure was investigated by using XRD and TEM.Magnetic properties were measured with vibrating sample magnetometer（VSM） at room temperature.The results show that the grain size of nanocrystalline Ni1-xZnxFe2O4 ferrite calcined at 600 ℃ for 1.5 h is about 30 nm.Lattice parameter and specific saturation magnetization Ms of nanocrystalline Ni1-xZnxFe2O4 ferrite increase with the Zn^2＋ ions content at room temperature,and maximum Ms is 66.8 A·m^2·kg^-1 as the Zn^2＋ ions content is around 0.5,and coercivity Hc of the nanocrystalline Ni1-xZnxFe2O4 ferrite decreases with Zn^2＋ ions content.

Morphology and photoluminescence of BaMoO_4 micro-and nano-crystals synthesized by coprecipitation method

Barium molybdate（Ba Mo O4） micro- and nano-crystals were synthesized by the coprecipitation method. Utilizing the water as the solvent provides octahedron-like nanostructures. These nano-crystals were structurally characterized by X-ray diffraction, energy dispersive X-ray micro-analysis, Fourier transform infrared spectra. The size and shape were observed by scanning electron microscopy. The optical properties were studies by ultraviolet-visible diffuse reflectance spectroscopy and photoluminescence measurements at room temperature. The effects of temperature, solvent, surfactant and barium source were considered to obtain a controlled shape. It is found that the morphology, particle size and phase of the final products are extremely affected by these parameters.

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

A new method for the determination of vanadium in high purity Y2O3 by fluorination assisted electrothermal vaporization-ICP-AES is presented in this paper. After the sample dissolved,the vanadium in the sample solution was coprecipitated with Bi(PDC)_3 at pH 3. 7. The precipitates were made into a slurry with the fluorinating agent PTFE and directly introduced into the graphite furnace for determination. The analytical results were obtained by aqueous calibration curve method. The detection limit of the method is 1. 1 ng/mL, the RSD is 2. 8% (n=10,1 5 ng/mL vanadium solution), and the recovery of vanadium added to real sample is more than 96%.

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 and Tribological Properties of Copper-alumina Nanocomposites Prepared by Coprecipitation Technique

The objective of this work is to study the synthesis of copper-alumina nanocomposites using the coprecipitation process and hot-pressing method, and investigate their mechanical properties. The effects of calcination temperature on the average size of composite particles and chemical composition after calcination were also analyzed. The sintering parameters including sintering temperature, hot pressure and packing time were optimized to fabricate the alumina nanoparticles reinforced copper matrix composites（CMCs）. The density, microhardness and tribological properties of the CMCs reinforced with 1 wt%, 2 wt%, 3 wt%, 4 wt% and 5 wt% of alumina nanoparticles were investigated correspondingly. The results showed that the optimum preparation parameters for the CMCs were 900 ℃ of hot pressing temperature, 27.5 MPa of hot pressure and 2 hrs of packing time. The CMC reinforced with 2 wt% of alumina nanoparticles had the lowest wear rate, with the relative wear resistance of 3.13.

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.