Polymeric precursor synthesis of Ba2Ti9O20

Ba₂Ti₉O₂₀ was synthesized by Pechini method using citric acid as a chelating agent and ethylene glycol as an esterification agent. The effects, of the pH of the starting solutions and the molar ratio of citric acid to total metal cations concentration on the formation of Ba₂Ti₉O₂₀, were investigated. Increasing the pH of the starting solutions enhances the formation of Ba₂Ti₉O₂₀, but the increase of the molar ratio of citric acid to total metal cations concentration retards the formation of Ba₂Ti₉O₂₀ due to increased diffusion distances. Single-phase Ba₂Ti₉O₂₀ was obtained at 1200 °C for 4 h when the molar ratio of citric acid to total metal cations concentration was unity, regardless of the pH of the starting solutions. Increasing the molar ratio of citric acid to total metal cations concentration up to 2, single-phase Ba₂Ti₉O₂ was synthesized at 1200 °C for 6 h for the precursors with pH 3.5 and 6, but not for the precursors with pH 2.0. DTA, TG, XRD, FT–IR spectroscopy and Raman spectroscopy were used to characterize the precursors and the derived oxide powders. Details of the synthesis and characterizations of the resultant products were given.     

Evolution of the formation of barium titanate in the citrate process: the effect of the pH and the molar ratio of barium ion and citric acid

In this investigation, several experiments were conducted to study the effects of the molar ratio of barium ion and citric acid and the pH value on the formation of BaTiO3 by the citrate process. It was found that the molar ratio of barium ion and citric acid and the pH value could affect the chelation of carboxylate groups and Ba/Ti ions at temperatures below 450 °C but they seemed not to influence the formation of BaTiO3. The development of an oxycarbonate intermediate during the thermal decomposition of (Ba,Ti) gel was confirmed, which was suggested to possess a structure of BaTiO3, whereby CO–23 was located inside the layer structure.     

The effect of the concentration of citric acid and pH values on the preparation of MgAl2O4 ultrafine powder by citrate sol-gel process

Ultrafine MgAl₂O₄ was synthesized by citrate sol-gel process. A model was presented to evaluate the concentration of species in a citric solution for preparing MgAl₂O₄ ultrafine powder. The evaluated concentration of species can provide valuable information and help in selecting the optimal condition for preparation of MgAl₂O₄ powder by citrate sol-gel process. The influence of molar ratio of cations, citric acid and pH on the formation of MgAl₂O₄ was studied. The spinel precursor gel and the ultrafine MgAl₂O₄ spinel were characterized by X-ray diffraction (XRD), differential thermal analysis, thermogravimetric (TG-DTA) and scanning electron microscope (SEM). The results show that the MgAl₂O₄ spinel phase begins to form at 600 °C, and most of MgAl₂O₄ crystals are spherical with a crystal size about 30-50 nm.     

Synthesis and characterization of nano crystalline BaFe12O19 powders by low temperature combustion

Nano crystalline BaFe₁₂O₁₉ powders have been prepared at a relatively low calcination temperature by a gel combustion technique using citric acid as a fuel/reductant and nitrates as oxidants. The effects of processing parameters, such as Ba/Fe ratio, citric acid/nitrates ratio, reaction temperature on the powder characteristics and magnetic properties of the resultant barium ferrites were investigated. By controlling the molar ratio of citric acid to metal nitrates, nano crystalline BaFe₁₂O₁₉ powders with different particle sizes have been obtained. Phase attributes, microstructures and magnetic properties of the powders were characterized using X-ray diffraction analysis, X-ray line-broadening technique, Fourier transform infrared spectroscopy measurements, transmission electron microscopy and vibrating sample magnetometer. The maximum saturation magnetization value and intrinsic coercivity value for the obtained barium hexaferrites are 59.36 emu/g and 5540 Oe.     

Low temperature preparation of nanocrystalline Sr0.5Ba0.5Nb2O6 powders using an aqueous organic gel route

Nano-sized Sr_0.5Ba_0.5Nb₂O₆ (SBN50) ceramic powders have been synthesized by an aqueous organic gel route. Homogeneous Sr-Ba-Nb precursor gels are prepared with Ba-EDTA, Sr-EDTA, and Nb-citrate complex as source of Sr, Ba, and Nb, respectively. Citric acid and ethylenediaminetetraacetic acid (EDTA) were used as the chelating agents. The structural variation of the SBN powder with annealing temperature was studied by TG-DTA, FT-IR and XRD. The precursor gel on calcination at 800 °C for 2 h produces a pure tungsten bronze SBN phase and the corresponding average particle size is 30-50 nm. The influences of the pH and the molar ratio of citric acid:Nb cation on the formation of homogeneous Sr-Ba-Nb precursor gels were also studied. The results show that a homogeneous Sr-Ba-Nb precursor gel with no precipitate is formed at pH 8 and the optimum molar ratio of citric acid and the metal cations is 3:1.     

Synthesis of Ba6-3xNd8+2xTi18O54 ceramic powders via citric acid precursor

Ba_6-3xNd_8+2xTi₁₈O₅₄ ceramic powders have been synthesized by the Pechini method. The precursors and derived oxide powders were characterized by DTA, TG, XRD and TEM. The effect of the molar ratio of citric acid to total metal cation concentration on the crystallization behavior of Ba_6-3xNd_8+2xTi₁₈O₅₄ was investigated. Single-phase and well crystallized Ba_6-3xNd_8+2xTi₁₈O₅₄ powders were obtained from pulverized resin at 900 °C for 3 h, without the formation of any intermediate phase, when the correct molar ratio of citric acid to total metal cations concentration is used.     

Preparation of M-Ba-ferrite fine powders by sugar-nitrates process

In this paper, fine M-type barium hexaferrite (M-Ba-ferrite) particles were synthesized from sugar and nitrates by simple route, which revealed the feasibility of using sugar as chelating agent in forming solid precursors of BaFe₁₂O₁₉. The effects of factors, such as the molar ratio of Fe/Ba, calcination temperature and time, on the morphology, the phase component and the magnetic properties of M-type barium hexaferrite particles were studied by means of X-ray diffraction, infrared spectroscopy, transmission electron microscopy and physical property measurement system. The results showed that the molar ratio of Ba²⁺ to Fe³⁺ influenced significantly on the formation of the single phase barium ferrite. The hexagonal platelet barium ferrite particles with a specific saturation magnetization of 64.48 emu/g, remanence magnetization (Mr) of 33.84 emu/g, and coercive force (Hc) of 1848.85 Oe were obtained when the molar ratio of Fe/Ba was 11.5 and the calcination temperature was 1100 °C for 2 h.     

Hydrothermal synthesis of barium ferrite fine particles from goethite

Barium ferrite fine particles were prepared from aqueous suspensions containing goethite (-FeOOH) and barium hydroxide by a hydrothermal method. Barium ferrite particles of thin hexagonal plate shape could be produced from commercially available goethite with an Fe: Ba molar ratio of 7.2, whereas barium ferrite particles could be produced from synthesized goethite with a molar ratio of unity. The effects on the size of hexagonal platelike particles of such reaction conditions as temperature, stirring speed and alkali concentration were investigated. Particles of 0.6 to 0.8 m mean size were prepared under the reaction conditions covered here.     

溶胶-凝胶自燃烧制备CoY0.1Fe1.9O4铁氧体的反应特性

研究了溶胶-凝胶自燃烧法制备CoY0.1Fe1.9O4的成胶热力学条件和自燃烧的过程,从理论和实验讨论了pH值和柠檬酸量对产物的影响.利用热重/差热综合分析仪及X射线衍射仪对干凝胶的热反应特性和晶体结构进行了测试和分析.利用振动样品磁强计研究了不同柠檬酸量产物的矫顽力.实验结果表明,由Fe、Co和Y元素与水的二元体系的平衡电势(E)-pH图确定的溶液成胶pH值与实验结果相符合;通过计算氧化剂正价态和燃料的负价态的平衡系数,获得混合硝酸盐与柠檬酸的理论比值为2.3.取过量的柠檬酸量,能够合成尖晶石结构的CoY0.1Fe1.9O4纳米粉末.随着柠檬酸量的继续增加,产物中有Fe2O3的出现,且矫顽力减小.     

Synthesis and Formation Mechanisms of Calcium Ferrite Compounds

Calcium ferrite compounds were prepared using calcium nitrate and iron nitrate with different molar ratios, 1:1, 0.5:1, and 1:0.5, respectively. The reactions of formation were investigated at different temperatures following the differential thermal analysis (DTA) results. Calcium ferrite compounds are CaFeO3, Ca2FeO3.5, Ca2Fe2O5, CaFe2O4, CaFe4O7, Ca7.2Fe0.8Fe30O53, Ca3Fe15O25, Ca4Fe14O25, and Ca4Fe9O17. Other reactive species of calcium nitrate are still present after firing at 450℃. Compounds were characterized using X-ray diffraction (XRD), DTA, TG, magnetic susceptibility, infrared spectra and scanning electron microscope (SEM). It is concluded that the formation mechanism of Ca-ferrite compounds depends mainly on the valency of iron cations which in role depends on its molar ratio and the existing atmosphere.     

Synthesis of SrAl2O4 from a mixed-metal citrate precursor

A mixed-metal citrate precursor method was used to synthesize SrAl₂O₄. The effects of the pH of the starting solutions and the molar ratio of citric acid to total metal cations concentration (CA/M) on the formation of SrAl₂O₄ were studied. DTA, TG, FT-IR, XRD and field emission scanning electron microscopy (FESEM) were used to characterize the precursors and the derived oxide powders. XRD analysis showed that single-phase SrAl₂O₄ was synthesized from CA/M = 2 precursors at a temperature of 900 °C for 2 h, without the formation of any intermediate phase.     

吸附钡铁氧体的多孔陶粒吸波材料制备及其性能

以硝酸铁、硝酸钡、柠檬酸为原料,采用溶胶-凝胶法合成钡铁氧体溶胶,将其吸附于多孔陶粒表面和微孔中,经焙烧制备得到电磁吸波功能陶粒;再将该功能陶粒用作集料制备新型水泥基复合吸波材料。研究了合成的钡铁氧体的物相、形貌、复介电常数和复磁导率;结果表明合成的钡铁氧体纯度高,合成温度对其结晶度和晶体形貌有影响,经1000℃煅烧制得的钡铁氧体具有良好的吸波能力;对制得的功能陶粒进行了测试,结果表明钡铁氧体能包覆至陶粒表面和孔壁上;采用弓形法测得的功能陶粒水泥基吸波材料在8~18GHz频率范围内的电磁波反射率明显优于采用碎石和普通陶粒制备的试样。     

M型锶铁氧体中空纤维的制备和表征

以柠檬酸和金属盐为原料,采用有机凝胶先驱体转化法制备了M型锶铁氧体（SrFe₁₂O₁₉）中空纤维. 通过FTIR、TG/DSC、XRD、SEM和VSM等技术对所得纤维进行了表征. 结果表明,凝胶的可纺性与其化学组成和pH值有关,当柠檬酸与金属离子的摩尔比为1.5∶1.0,pH=4.2左右时,凝胶的可纺性最好. 经1100℃焙烧后,制备的M型锶铁氧体中空纤维具有较大的长径比,直径可小于1μm,中空孔径约为纤维直径的一半,组成纤维的晶粒形貌为六角片状,晶粒尺寸为236nm,在室温下的饱和磁化强度为53.5A·m²/kg,矫顽力为386.96kA/m. 纤维显示出一定的形状各向异性,当定向排列的纤维平行和垂直磁场时,矫顽力分别为391.66和358.72kA/m.     

Preparation and magnetic properties of barium ferrite fineparticles by the coprecipitation salt-catalysis method

The authors describe catalytic action by NaCl in the reaction between α-Fe₂O₃ and BaCO₃ and the development of a new process for manufacturing barium ferrite fine particles. Pure α-FeOOH and reagent-grade BaCO₃ are mixed and heated at temperatures from 300 to 800°C with and without NaCl. The BaCO₃ and α-Fe₂O₃ powders which are formed during heating react and change to barium ferrite at temperatures 100°C lower than NaCl than without it. A hematite defect structure is maintained up to a relatively high temperature due to the presence of the salt, which promotes the formation of barium ferrite. The manufacturing process involves mixing an aqueous solution of metallic chlorides with a mixture of NaOH and Na ₂CO₃. This alkaline coprecipitate slurry is then neutralized by HCl solution, filtered, and dried. The dried powder, containing salts produced by the reaction, is heated at 840°C. After the salts are dissolved in water, barium ferrite fine particles are obtained     

纳米钛酸钡粉体的水热合成研究

采用氢氧化钡和四氯化钛作为钡源和钛源,氨水作矿化剂,在200～280℃保温4h条件下合成粒径为60～90nm钛酸钡粉体。TEM、XRD、钡/钛摩尔比(Ba/Ti)和比表面积的测试结果表明,在单一水介质中水热合成钛酸钡晶体的结晶过程遵循“溶解-结晶”机制,存在第II类聚集长大过程。前驱体浓度、合成温度和合成反应时间是影响粉体粒径的重要因素。粉体的Ba/Ti比过低会导致粉体中出现BaCO3杂质相,且Ba/Ti越低,钛酸钡晶体晶胞膨胀程度越大。     

Preparation of La(Zn0.5Ti0.5)O3 powders via citric acid precursor

La(Zn_0.5Ti_0.5)O₃ powders were synthesized by the Pechini process using citric acid as a complexing agent. The effect of the molar ratio of citric acid to total metal cations concentration (CA/M) and the pH of the starting solution on the crystallization behavior of La(Zn_0.5Ti_0.5)O₃ was investigated. Homogeneously mixed gel was obtained and transferred into resin through charring. Single-phase and well-crystallized La(Zn_0.5Ti_0.5)O₃ powders were obtained at 1000 °C for 2 h. DSC, TG and XRD were used to characterize the precursors and derived powders.     

Effect of Barium on Morphological Transition and Magnetic and Dielectric Properties in Ferrite Nanoparticles

Barium ferrite (BaFe₂O₄) nanoparticles were synthesized by auto combustion method under different weight percentages of barium. The role of barium in the behavior of spinel ferrite property is identified from this study. XRD exhibits prominent orientation of (212) for BaFe₂O₄ has confirmed especially in 20 and 30 wt% of barium. The addition of barium metal induced the specific vibration in FTIR spectra and such changes coincide well with the particle size. Further, the EDX spectrum reflects the atomic percentage of elemental presence in the samples of barium ferrite. Addition of barium on ferrite nanoparticles reduces the intensity of fluorescence. The morphological changes occurred due to increasing doping concentration of barium and is visualized from the FESEM and TEM images. The formation of different morphologies such as spherical, hexagonal platelets and small rectangular bar shape are observed only due to inclusion of barium at surfactant medium. The magnetic properties of the barium ferrite samples are studied by VSM. It reveals that 35.11 emu/g saturation magnetization (M _s ) with 3775.08 Oe coercivity. The change in values of coercivity (H _c ) from 3775.08 to 1572.95 Oe due to the variation of barium levels confirmed that the role of barium induced the hard magnetic behavior. The dielectric study also indicates the significance of barium ferrite in the variation of dielectric constant.     

硫酸盐还原法制备La_2O_2S∶Yb,Er及其上转换发光性能

采用硫酸盐还原法制备了Yb、Er双掺的La2O2S粉体,考察了柠檬酸用量、前驱体煅烧温度、碳还原温度、Er3+离子浓度和Yb3+离子浓度对粉体的影响。分别采用X-射线衍射分析(XRD)、扫描电子显微镜(SEM)、比表面积分析(BET)、紫外可见光分光光度计(UVPC)和荧光光谱分析(PL)对粉体的相组成、形貌、颗粒尺寸、反射率和上转换发光性能进行表征。研究结果表明,800℃时可以得到纯相的La2(SO4)3;碳还原温度为900℃以上可以得到纯相的结晶较好的La2O2S;样品的粒径大约为100～200nm,颗粒存在一定的团聚;柠檬酸与硝酸盐的最佳摩尔比为1.5∶1;Er3+离子掺杂浓度为2mol%、Yb3+离子掺杂浓度为12mol%时粉体的上转换发光强度最强。     

Acrylamide assisted polymeric citrate route for the synthesis of nanocrystalline ZrO2 powder

Nanocrystalline ZrO₂ powders have been prepared using acrylamide assisted polymeric citrate combustion (autoignition) route. Process parameters (i.e., total metal ions to citric acid ratio) were varied for the formation of polymeric resin in order to obtain the final product with desired properties (organic free, smaller crystallite size, etc.). The effect of three different citric acid amounts in the formation of nanocrystalline ZrO₂ powder was investigated using FTIR, XRD, TG/DTA and SEM-EDS, respectively, to identify the structural coordination, phase, thermal behavior and microstructure of the polymeric intermediates as well as the final ZrO₂ powders. Organic free ZrO₂ powder with two different phases of metastable t-ZrO₂ and m-ZrO₂ were prepared by calcining the polymeric intermediates at 600 °C. The lowest crystallite was found to be 18 and 16 nm, respectively, for the t-ZrO₂ and m-ZrO₂ phases prepared with total metal ions to citric acid ratio of 1:3.     

Synthesis of Nanocrystalline Barium Ferrite in Ethanol/Water Media

Nanocrystalline particles of barium ferrite magnetic material have been prepared by co-precipitation route using aqueous and non-aqueous solutions of iron and barium chlorides with a Fe/Ba molar ratio of 11 and subsequent drying-annealing treatment.Water and ethanol/water mixture with volume ratio of 3:1 were used as solvents in the process.Coprecipitated powders were annealed at various temperatures for 1 h.FTIR(Fourier transform infrared spectroscopy),XRD(X-ray diffraction),DTA/TGA(differential thermal an...