水热法合成锰锌铁氧体纳米球包覆的碳纳米管磁性材料的研究

用水热法分别在160℃和220℃下反应5 h制备了锰锌铁氧体纳米球包覆的碳纳米管复合材料。用X射线衍射分析样品的物相,用高分辨透射电镜和电子衍射分析样品的形貌和结构,用振动样品磁强计表征磁性能。结果表明：锰锌铁氧体为球形,粒径约为13 nm。磁滞回线结果表明：复合材料粒子的饱和磁化强度为10.92 em u/g,剩磁为4.25 em u/g,矫顽力为381.43O e。     

Hydrothermal Synthesis of Manganese Zinc Ferrites

Hydrothermal synthesis has been used to synthesize nano-sized manganese zinc ferrite powder. The results show that the pH value of the starting suspension has a decisive influence on the composition of the hydrothermally prepared manganese zinc ferrite powder. At a pH value of ∼8.5, stoichiometric amounts of manganese and zinc can be incorporated in the manganese zinc ferrite. The grain size of the powder increases with the temperature and time of hydrothermal treatment. The nanosized manganese zinc ferrite produced is superparamagnetic and becomes ferri-magnetic after the ferrite grains become larger than ∼100 nm. The nanosized ferrite grains are very prone to oxidation and disintegrate at 600°C in air. The surfaces of the synthesized ferrite grains are covered with a thin film of water.     

Preparation of Manganese Zinc Ferrite Powders by Alcoholic Dehydration of Citrate/Formate Solution

Chemically homogeneous manganese zinc ferrite powders of submicrometer size and desired stoichiometry were achieved using alcoholic dehydration and subsequent calcination of citrate/formate solution. The successful powder preparation was dependent on the water content in the starting solution, the pH of the solution, the amount of alcohol used, and the washing and drying step. Calcination temperature was also critical since the evaporation of ZnO took place above 1000°C. A two-step calcination process was utilized to develop submicrometer ferrite powders without any Zn loss.     

用废旧锌锰干电池制取软磁铁氧体

报道了用废旧南孚牌锌锰电池为主要原料制备软磁铁氧体的方法。具体方法是,先用物理分离方法将锌锰干电池的外壳、集电体及一些塑料件与电池的含锌锰成分分离开来,然后将锌锰氧化物焙烧以除去其中的石墨。用酸溶解获得的锌锰氧化物,并加足够量的铁粉共同反应已得到含Zn、Mn、Fe的水溶液,然后用碱性溶液将它们共沉淀得到前驱体。焙烧前驱体即得到需要的软磁铁氧体。     

Sol-Gel Coating of Lithium Zinc Ferrite Powders

Lithium zinc ferrite powders of composition Li_0.3Zn_0.4Mn_0.05− Fe_2.25O₄ were prepared by solid—state synthesis. Liquid-phase borosilicate sintering additives were applied to the ferrite particle surfaces at room temperature via a sol—gel coating technique. Calcined and comminuted ferrite powder was dispersed in methanol with predetermined quantities of tetraethyl orthosilicate and triethyl borate. Hydrofluoric acid was used to catalyze the sol—gel reactions. Amorphous coatings of 10 to 20 nm thickness were observed on particle surfaces by TEM. Chemical bonding in the coatings was studied using diffuse reflectance FTIR spectroscopy.     

Aqueous Processing and Stabilization of Manganese Zinc Ferrite Powders via a Passivation–Dispersion Approach

A dispersion scheme for aqueous processing of manganese zinc ferrite suspensions is presented. The addition of oxalic acid leads to the formation of a uniform negative charge on the surface such that a cationic polyelectrolyte, polyethyleneimine (PEI), adsorbs and provides electrosteric dispersion. At 0.5 w/w (weight percent with respect to the dry powder) oxalic acid addition, there is a relatively uniform negative surface charge (approximately −30 mV) within the suspension pH range investigated (3–10), eliminating the isoelectric point (pH ∼7.6) present for the as-received metal oxide powder. At the addition of 0.5 w/w PEI on an oxalate-treated surface, the surface charge is constant and positive (∼20 mV) through a wide pH range, ∼5–10. The resulting rheological data for passivation–dispersion of relatively high-solids manganese zinc ferrite suspensions (∼80 wt%) demonstrate improved colloid stability with improved rheological properties. The resulting apparent viscosity and Bingham yield point is 0.01 Pa·s (12.0 cP) and 0.24 Pa (2.4 dynes/cm²), respectively. A sulfonated napthalene-based dispersant, typically used in industry, gives an apparent viscosity and Bingham yield point of 0.03 Pa·s (32 cP) and 3.1 Pa (31 dynes/cm²), respectively.     

Hydrothermal Soft Chemical Process for Synthesis of Manganese Oxides with Tunnel Structures

A soft chemical process is used for the synthesis of manganese oxides with tunnel structures. This process comprises two steps: the first step is the preparation of a precursor with layered structure and insertion of templates (structure-directing agents) into its interlayer space by a soft chemical reaction [1], and the second step is the transformation of the template-inserted precursor into a tunnel structure by hydrothermal treatment. The usefulness of this process was demonstrated by synthesizing six kinds of tunnel manganese oxides from a birnessite-type manganese oxide with layered structure. The transformation reactions from layered structure to tunnel structures were investigated by X-ray, DTA-TG, and chemical analyses, and IR spectroscopy. Spinel-, hollandite-, romanechite-, and todorokite-type manganese oxides, which have (1^×3), (2^×2), (2^×3), and (3^×3) tunnel structures, can be obtained by using Li⁺, K⁺, Ba²⁺, and Mg²⁺ ions as the templates, respectively. Pyrolusite- and ramsdellite-type manganese oxides with (1^×1) and (1^×2) tunnel structures can be obtained in acidic solutions. The size of the resulting tunnels correspond to the size of the templates.     

纳米铁酸锌粉体的制备研究进展

铁酸锌粉体是一种重要的磁性材料,不仅具有良好的气敏和光催化特性,而且具有良好的光电转换性能。由于具有这些特殊的性能,人们越来越重视铁酸锌粉体的制备以及应用。本文对纳米铁酸锌粉体的主要制备技术进行了简单介绍,并分析了各种制备方法的发展现状、优势及不足。     

Hydrothermal Synthesis of Bismuth Titanate Powders

Bismuth titanate was synthesized under hydrothermal conditions from an amorphous bismuth–titanium precursor gel. The gel was formed by mixing a bismuth acetate complex with titanium butoxide and then adding the solution dropwise into 6 M NaOH. The resulting gel suspension was reacted under hydrothermal conditions at temperatures ranging from 160° to 200°C to form crystalline bismuth titanate. The gel crystallization kinetics increased with temperature, which resulted in 100% crystalline bismuth titanate in 5 h at 200°C. Wavelength-dispersive spectroscopy data indicated that sodium was incorporated into bismuth titanate during processing, and X-ray diffractometry suggested that the powder was composed of the Bi₅Ti₄O₁₅ phase. Transmission electron microscopy micrographs showed that the gel particles decomposed to 100–200 nm crystalline bismuth titanate particles during hydrothermal processing.     

水热法制备KNbO3粉体的研究

以KOH和Nb2O5为原料, KOH作为矿化剂,通过水热法合成了结晶度高﹑晶粒发育完整的KNbO3微晶.借助XRD分析了钾铌比、反应温度和反应时间对晶相和粒度的影响;并通过SEM分析了KNbO3的晶粒形貌.研究结果表明:钾铌比和反应温度是水热合成铌酸钾粉体的关键因素,所得铌酸钾为斜方晶相的微晶.     

水热法制备BiFeO3粉体

以FeC l3.6H2O和B i(NO3)3.5H2O为原料,氨水为沉淀剂,KOH为矿化剂,采用共沉淀法制备前驱物,水热法合成了纯相的B iFeO3粉体。X射线衍射结果表明,在160℃,碱浓度仅为0.15 mol/L的水热条件下,即可合成纯相的B iFeO3粉体。该工艺大大降低了水热温度,减小了碱浓度,从而节约了能源,降低了成本,减轻了碱对水热设备的腐蚀。扫描电镜显示,前驱沉淀物陈化时间为1 d时,水热制备的B iFeO3粉体中有发育良好的六方短柱状晶体形成;陈化时间增加到3 d时,所得B iFeO3粉体呈双层板状。差热-失重分析表明,所得B iFeO3粉体的尼尔温度(TN)为301℃,居里温度(TC)为828℃,分解温度为964℃。     

水热法制备球形二氧化锆粉体的研究

以氯氧锫为前躯体通过水热法制备出了粒径在5μm左右,粒度分布均匀的球形二氧化锆粉体.研究结果表明水热温度、水热时间以及醇水比例对产物的微观结构均有影响.140℃水热处理24h获得产物为无定型态的氢氧化锆粉体,而200℃水热处理24h可获得单斜和四方混相的二氧化锆粉体.随水热时间的延长,产物相结构经历了由无定型氢氧化锆向单斜与四方混相的二氧化锆转变,相转变机制则经历了由均匀饱和析出机制到溶解沉淀为主、原位结晶为辅机制再到原位结晶为主、溶解沉淀为辅机制的变化过程.     

Low-Temperature Hydrothermal Synthesis of Yttrium-Doped Zirconia Powders

The feasibility of low-temperature synthesis of yttrium-doped zirconia (Y-ZrO₂) crystalline powders in aqueous solutions at lessthan equal to100°C has been evaluated, and the hydrothermal crystallization mechanism for Y-ZrO₂ powders also has been investigated. Coprecipitated (Y,Zr) hydroxide gel, mechanical mixtures of Y(OH)₃ and Zr(OH)₄ gel, and Y(OH)₃ gel have been reacted in boiling alkaline solutions. Coprecipitated (Y,Zr) hydroxide gel crystallized to cubic or tetragonal Y-ZrO₂ at pH 13.9. The yttrium content in the powder synthesized from coprecipitated (Y,Zr) hydroxide is consistent with the initial precursor solution composition, as expected from the similarity in solubility of Zr(OH)^-₅ and Y(OH)^-₄. A diffusionless mechanism for the transformation of the (Y,Zr) hydroxide gel to Y-ZrO₂ is proposed, and the phase stability in aqueous solution is discussed in terms of an in situ crystallization model. It is also demonstrated through thermodynamic arguments with experimental verification that the stable form of the Y-ZrO₂ at 25°C is the anhydrous phase, not the metal hydroxide as previously thought.     

水热法合成镍锌铁氧体工艺研究

以硫酸镍、硫酸亚铁、硫酸锌和氢氧化钠为原料,采用水热合成法制备纳米镍锌铁氧体粉体,利用正交实验法考察考察pH、水热温度、水热反应时间和Zn的含量（x）对产物性能的综合影响,结合XRD和SEM结果,确定水热法合成镍锌铁氧体的最佳工艺为：共沉淀pH=10,水热温度为180℃,水热反应时间为10h,Zn的含量（x）=0．65。     

Phase Evolution in Synthesis of Manganese Ferrite Nanoparticles

Physico-chemical equilibria that influence oxide powders' precipitation from an aqueous solution can be substantially altered when the process is carried out in a microemulsion system. To obtain nanosized MnFe₂O₄ and gain information about the physico-chemical characteristics of products, Mn²⁺ and Fe³⁺ metal ions were induced to precipitate in a toluene/water/sodium dodecylbenzenesulfonate microemulsion system. Portions of the precipitated powder were differently treated, both in solution and in the solid state, and the role of restricted aqueous domains in the obtained materials was investigated. X-ray diffraction profile-fitting methods and chemical analysis were applied to characterize the powder particles. Samples obtained from the selected microemulsion were identified as nanosized mixed hydroxide compounds. A low metal content and a limited matter exchange among aqueous nanodroplets appear to inhibit hydroxide to oxide transformation inside the selected micellar system. A calcination process of precipitated powder was required to obtain a manganese ferrite compound.     

Hydrothermal Synthesis of Spherical Perovskite Oxide Powders Using Spherical Gel Powders

Spherical perovskite oxide powders, composed of fine particulates, were prepared by using spherical gel powders under hydrothermal conditions. Spherical PbTiO₃, BaTiO₃, and SrTiO₃ powders were synthesized from spherical TiO₂ gel powders, and spherical PbZrO₃ powder from spherical ZrO₂ gel powder. Spherical Pb(Zr_0.5, Ti_0.5)O₃ and Ba(Zr_0.5,Ti_0.5)O₃ powders were prepared from spherical ZrTiO₄ gel powders. Lead acetate trihydrate, barium hydroxide octahydrate, and strontium hydroxide octahydrate were used as the sources of A-site ions in each perovskite oxide (ABO₃). The spherical TiO₂ and ZrO₂ gel powders were prepared by thermal hydrolysis of titanium tetrachloride and zirconium oxychloride, respectively, and spherical ZrTiO₄ gel powder by thermal hydrolysis of a mixture of them in alcohol-water mixed solvent. During the hydrothermal treatment, the spherical gel powders retained their spherical shape to produce spherical perovskite oxide powders, composed of nanometer-sized particulates.     

水热法制备铁锡纳米复合氧化物及表征

以Fe(NO3)3·9H2O,SnCl4·5H2O为原料,通过改变水热反应的条件合成了铁锡纳米复合氧化物.用X射线衍射仪和透射电镜对产物的结构和微观形貌进行了表征.结果表明:在水热制备铁锡复合氧化物的过程中,通过分步控制温度法和使用不同的沉淀剂可以控制产物的粒径大小和形貌.最终得到以棒状的α-Fe2O3晶体为核,附着有SnO2粒子的纳米复合氧化物.并对复合物形成机理进行了初步探讨.     

Interface Reactions between Silicon Dioxide-Lead Oxide Glass and Manganese Zinc Ferrite

The interface reations between SiO₂–PbO melt and Mn-Zn ferrite were studied using electron probe microanalysis (EPMA) and X-ray diffraction (XRD). Intermediate layers were formed at the interface between the glass and the Mn-Zn ferrite which were heated at 800° and 900°C, although those layers were not found in specimens heated at 1000°C. Using EPMA and XRD, the intermediate layers were found to be Pb₂(Mn, Fe)₂Si₂O₉ and Pb₈(Mn, Fe)Si₆O₂₁. The mechanisms of interface reactions are discussed, related to glassforming regions. It was concluded that the interface reaactions between SiO₂–PbO melt and Mn-Zn ferrite are controlled by the dissolution of Zn ions and Mn ions from the Mn-Zn ferrite.     

Hydrothermal Synthesis of Acicular Lead Titanate Fine Powders

A pure, acicular lead titanate (PbTiO₃) fine powder with a white color has been prepared by hydrothermal synthesis. It is a new phase of PbTiO₃ with I 4 symmetry, cell parameters of a = 12.358 Å and b = 14.541 Å, and a density of 6.80 g.cm⁻³. The influences of pH (12.5 to 14.4), Pb/Ti ratio (1.0 to 1.6) in the feedstock, reaction temperature (130° to 230°C), time (0.25 to 4 h), starting materials, and additives on the formation of acicular PbTiO₃ under hydrothermal conditions have been investigated. The acicular PbTiO₃ with I 4 symmetry, referred to as the PX phase, can be converted to the perovskite-type (PE phase) of PbTiO₃ at about 605°C while its acicular morphology is essentially unchanged. The preferable conditions for preparing pure acicular PX-phase PbTiO₃ are that the pH is 13.0 to 14.0, Pb/Ti ratio is >1.3, reaction temperature is 170° to 200°C, time is 0.5 to 1.0 h, titanium butoxide (Ti[O(CH₂)₃CH₃]₄) is the starting material, and poly(vinyl alcohol) is an additive. The acicular grain of the PX phase is usually less than 100 nm in diameter and more than 1000 nm in length.