Microwave hydrothermal synthesis of nanosize Ta2O5 added Mg-Cu-Zn ferrites

Tantalum oxide added MgCuZn ferrite powders were synthesized by a co-precipitation method using NaOH in a microwave-hydrothermal (M-H) apparatus. The phase identification of the prepared samples was done by X-ray diffraction and crystal size and morphology were determined by transmission electron microscopy (TEM). Nano-phase ferrites with high surface area were synthesized at 160°C after a treatment time of 1 hour. The M-H synthesized powders were conventionally sintered at a temperature of 900°C/4h. The variations of the sintered density, initial permeability and electrical resistivity as a function of additive concentration at room temperature have been investigated.     

Dispersant-assisted hydrothermal synthesis of MnZn ferrites from raw oxides

MnZn-ferrite powders were prepared using hydrothermal syntheses of a homogenous mixture of the raw oxides, i.e., Fe₂O₃, ZnO and Mn₃O₄, at 280°C in air. The hydrothermal synthesis was performed in the presence of various amounts of an anionic dispersant. The final results of the hydrothermal reaction between the raw oxides were fine powders with a heterogeneous phase composition mostly composed of iron oxide and spinel products. The composition of the spinel products depended to a great extent on the amount of dispersant in the hydrothermally treated suspension. Without the dispersant addition, Zn ferrite and Zn manganate spinel products were formed, while in the presence of the dispersant, the ferrimagnetic MnZn-ferrite spinel product was obtained. A larger amount of the dispersant in the reaction mixture increased the conversion rate of the raw oxides into the Mn,Zn ferrite spinel product. Additionally, polyvinyl alcohol (PVA) was used during the hydrothermal synthesis in order to bind the chlorine impurities, introduced into the hydrothermally prepared powder with the raw Fe₂O₃. With the PVA burnout, the level of chlorine impurities was decreased by approximately 50%.     

Microwave hydrothermal synthesis of nanocrystalline rutile

Titanium dioxide of the rutile phase has been synthesized using titanium tetrachloride and hydrochloric acid by means of microwave hydrothermal method. The mixture solution is processed in microwave hydrothermal autoclave first at 120 °C for 1.5 h and then at 180 °C for 1 h to precipitate rutile powders. It was revealed that well-dispersed and shuttle-like rutile TiO₂ with the average diameter of 10 nm was formed by means of XRD and TEM.     

Distribution of cations in nanosize and bulk Co-Zn ferrites

The structural and magnetic properties of Co(1-x)Zn(x)Fe2O4 ferrites (Co-Zn ferrites) are investigated in a narrow compositional range around x = 0.6, which is of interest because of applications in magnetic fluid hyperthermia. The study by x-ray and neutron diffraction, M?ssbauer spectroscopy and magnetization measurements is done on nanoparticles prepared by the coprecipitation method and bulk samples sintered at high temperatures. In spite of the known preference of Zn2+ for tetrahedral (A) sites and Co2+ for octahedral [B] sites, the cations are distributed nearly evenly over the two sites of spinel structure and there is also a variable number of [B] site vacancies (see text), making cobalt ions trivalent. In particular for x = 0.6, the cationic distribution is refined to [Formula: see text] and [Formula: see text] for the 13 nm particles (T(C) = 335 K) and bulk sample (T(C) = 351 K), respectively.     

自组装花状结构Ni(OH)2的微波水热合成与表征

以六水合硝酸镍为镍源,尿素为水解控制剂及聚乙二醇(PEG)为表面活性剂,采用微波水热法成功合成了由亚微米片自组装而成的花状结构Ni(OH)2,并通过进一步的热处理得到相同结构形貌的NiO.利用XRD、SEM、TEM、FTIR、UV-Vis等方法对产物进行了表征,结果表明,自组装花状结构Ni(0H)2的直径为2.5-4....     

Microwave ferrites for phase shifters

The electronically steerable phased array radars (PARs) are finding extensive use in military, communication and civilian applications. A PAR system typically comprises a regular arrangement of a large number of phase controlled radiating elements. Ferrite-based phase shifters in various designs are employed in these systems operating at frequencies above 5 GHz due to their superior power rating and insertion loss characteristics. Under DRDO’s integrated missile programme considerable success has been achieved in the country on the development of ferrite materials, phase shifters and array system. The work done at SSPL on the development of ferrite materials for both X- and C-band phase shifters is described. The effect of various substituents in the chemical composition of the lithium-titanium ferrites and of the process parameters to evolve the grades with required magnetic, electrical and microstructural properties are discussed. The investigations carried out to enhance optimally the r.f. power handling capability of the material for meeting the desired specifications of the C-band phase shifter are also given.     

Microwave properties of planar hexagonal ferrites

A large number of samples of hexagonal ferrite, with planar anisotropy incorporating various metal ions, were synthesized and tested for FMR (ferromagnetic resonance). Measurements were made at room temperature in transmission cavities at frequencies between 10 and 35 Gc/s on magnetically oriented polycrystalline compounds. Of the possible crystal forms for hexagonal ferrite, those designated asW, Y, andZwere investigated. TheYcompounds were found to have the most useful microwave properties. The resonance line width was found to vary between 100 and 1200 Oe, and the anisotropy field varied from zero to 40000 Oe. TheWandZcompounds have planar or uniaxial anisotropy, depending on the composition. The region of zero anisotropy was determined. The magnetically oriented polycrystalline materials resemble single crystals in having easy and hard directions of magnetization which require different magnetic field values for FMR. Qualitative information about how well the crystallites are aligned with each other can be obtained from the examination of two FMR absorption curves made with the sample turned so that its easy and hard directions, respectively, are aligned with the magnetic field. Curves are shown to illustrate the difference between nonoriented, partially oriented, and well-oriented materials.     

中空NiO微球的微波水热制备及其表征

以六水合硝酸镍为镍源,聚乙烯吡咯烷酮（PVP）为表面活性剂,采用微波辅助水热方法制备前驱体α-Ni（OH）2,经过500℃热处理之后得到具有中空微纳结构NiO粉体。以XRD、SEM、TEM、UV-Vis测试手段,对样品进行了分析,并对其电化学性能进行初步的测试。结果表明合成的样品为立方晶系的NiO,其结构为中空球形。C-V曲线表明了样品具有典型的法拉第准电容,可逆性良好,具有良好的电化学稳定性。     

Microwave hydrothermal synthesis of nanoporous cobalt oxides and their gas sensing properties

In this paper, the precursors were synthesized by microwave hydrothermal method using Co(NO₃)₂·6H₂O as raw material, CO(NH₂)₂ and KOH as precipitants, respectively. The precursors and calcined products were characterized by XRD, FESEM, and BET-BJH. The results show that both constituent and synthetic condition can determine the products morphology. When using KOH as precipitant, hollow Co₃O₄ nanorings were obtained whose precursor was synthesized at 140 °C for 3 h and calcined at 500 °C in air for 2 h. While using CO(NH)₂, Co₃O₄ like-nanochains were obtained whose precursor was synthesized at 110 °C for 1 h and calcined at 420 °C in air for 2 h, and Co₃O₄ nanosheets were obtained while their precursor was synthesized at 140 °C for 3 h and calcined at 500 °C in air for 2 h. The sensitivity test of Co₃O₄ to alcohol reveals that the hollow Co₃O₄ nanorings show the best sensitivity, porous Co₃O₄ like-nanochains are superior to that of the porous nanosheets.     

ZnO纳米球的微波水热合成及纯丙乳液改性研究

以六水合硝酸锌和三乙醇胺为原料,采用微波水热法快速合成出形貌规则的ZnO纳米球。利用XRD、SEM、TEM等分析手段对样品进行表征。结果表明ZnO纳米球直径约150nm且单分散性良好;TEM分析显示ZnO纳米球是由10～20nm的晶粒堆积而成的疏松球形结构;在较大的水热温度和水热时间范围内,所得产物均为100～200nm的颗粒。将ZnO纳米粒子改性后掺入到纯丙乳液中形成复合乳液,其涂膜的抗张强度和断裂伸长率均有较大提高,涂膜浸泡48h后的吸水率也降低约10%。     

Microwave ferrites, part 1: fundamental properties

Ferrimagnets having low RF loss are used in passive microwave components such as isolators, circulators, phase shifters, and miniature antennas operating in a wide range of frequencies (1–100 GHz) and as magnetic recording media owing to their novel physical properties. Frequency tuning of these components has so far been obtained by external magnetic fields provided by a permanent magnet or by passing current through coils. However, for high frequency operation the permanent part of magnetic bias should be as high as possible, which requires large permanent magnets resulting in relatively large size and high cost microwave passive components. A promising approach to circumvent this problem is to use hexaferrites, such as BaFe₁₂O₁₉ and SrFe₁₂O₁₉, which have high effective internal magnetic anisotropy that also contributes to the permanent bias. Such a self-biased material remains magnetized even after removing the external applied magnetic field, and thus, may not even require an external permanent magnet. In garnet and spinel ferrites, such as Y₃Fe₅O₁₂ (YIG) and MgFe₂O₄, however, the uniaxial anisotropy is much smaller, and one would need to apply huge magnetic fields to achieve such high frequencies. In Part 1 of this review of microwave ferrites a brief discussion of fundamentals of magnetism, particularly ferrimagnetism, and chemical, structural, and magnetic properties of ferrites of interest as they pertain to net magnetization, especially to self biasing, are presented. Operational principles of microwave passive components and electrical tuning of magnetization using magnetoelectric coupling are discussed in Part 2.     

Transport properties of microwave sintered pure and glass added MgCuZn ferrites

A series of pure stoichiometric and 1 wt% lead borosilicate (PBS) glass added MgCuZn ferrite with the general formula Mg_0.5Cu_xZn_0.5−xFe₂O₄ with x = 0.05, 0.1, 0.15, 0.2, 0.25 and 0.3 were synthesized by microwave sintering technique. Single phase spinel structure is exhibited by the XRD patterns of these ferrites. DC and AC conductivity were investigated as a function of composition, temperature and frequency. DC conductivities were also estimated using the impedance spectroscopy analysis of Cole–Cole plots. The DC conductivities thus obtained are in good agreement with the experimental results. All the investigated samples exhibited two regions of conductivity one in the low temperature and the second in the high temperature region. It is observed that PBS glass added samples have lower conductivities than pure samples. Due to their lower conductivities and sintering temperatures the 1 wt% PBS glass added samples are suitable for multilayer chip inductor (MLCI) and high definition TV deflection yoke material application.     

Microwave hydrothermal synthesis of AgInS2 with visible light photocatalytic activity

AgInS₂ nanoparticles with superior visible light photocatalytic activity were successfully synthesized by a microwave hydrothermal method. This method is a highly efficient and rapid route that involves no organic solvents, catalysts, or surfactants. The photocatalytic activity of AgInS₂ nanoparticles was investigated through the degradation of dyes under visible light irradiation. Compared with TiO_2−xN_x, AgInS₂ has exhibited a superior activity for photocatalytic degradation MO under the same condition. The experiment results showed that superoxide radicals (O₂⁻), hydrogen peroxides (H₂O₂) and holes (h⁺) were the mainly active species for the degradation of organic pollutants over AgInS₂. Through the determination of flat band potential, the energy band structure of the sample was obtained. A possible mechanism for the degradation of organic pollutant over AgInS₂ was proposed.     

Microwave assisted hydrothermal synthesis of mesoporous SnO2 nanoparticles for ethanol sensing and degradation

We report the synthesis of mesoporous SnO₂ nanoparticles by a microwave assisted hydrothermal process and their application as a gas sensor. The synthesized materials were characterized by transmission electron microscopy, X-ray diffraction technique, X-ray photoelectron spectroscopy, and Photoluminescence spectroscopy. As the results, we found that as-synthesized SnO₂ was synthetic Cassiterite with tetragonal structure and spherical in shape with the primary crystallite size of 6–8 nm, and the SnO₂ embedded material was mesoporous with average pore sizes of ≈15 nm. Moreover, this material showed excellent thermal stability from 80 to 800 °C and its crystal structure after heat treatment was preserved even at ultrahigh temperature of 800 °C. We demonstrated that this material could be used for detection of the ethanol gas because of its stability and nanoscale size at high temperature. Additionally our investigations also suggest that the processed materials can be used for the photocatalytic oxidation of ethanol. These results propose the potential application of the material for a sense and shoot kind of approach for indoor air purification in pharmaceutical and fermentation monitoring and vehicular control through breath analyzer.     

Phase evolution of bismuth ferrites in the process of hydrothermal reaction

Bismuth ferrite crystallites were prepared by the hydrothermal method. The phase evolution in the process of hydrothermal reactions was investigated for different conditions. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis indicates that sillenite Bi₂₅FeO₄₀ could be the intermediate products, while perovskite BiFeO₃ was the target crystallite. The phase evolution could be controlled by adjusting KOH concentration, reaction temperature and duration time et al. The dissolution of Fe(OH)₃ plays an important role to control the phase formation of bismuth ferrites. Bi₂₅FeO₄₀ and BiFeO₃ crystallites have the cubic and sphere-like morphologies respectively. The formation of perovskite BiFeO₃ crystallites was based on the dissolution of sillenite Bi₂₅FeO₄₀.     

Electrochemical synthesis of nanosize polyaniline from aqueous surfactant solutions

Electrochemical polymerization of aniline was carried out in micellar solutions of camphor sulphonic acid (CSA, anionic surfactant), cetyltrimethylammonium bromide (CTAB, cationic surfactant) and TritonX 100 (Tx100, nonionic surfactant), to reveal the morphology against the nature of the surfactant molecule. The resultant polyaniline film was characterized by Fourier transform infrared (FTIR) spectroscopic and cyclic voltammetric techniques. The surface morphology observed from different surfactant molecules was found to be distinctly different. Polyaniline synthesized from CSA and Tx100 solutions, showed uniform nanosized (100 nm) globular structures.     

Phase and morphology evolution of bismuth ferrites via hydrothermal reaction route

Phase-controlled synthesis of bismuth ferrites has been achieved via hydrothermal route by adjusting the KOH concentration. The as-prepared powders were characterized by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, and selected area electron diffraction. The particle morphologies of the as-prepared powders evolve from nanoflakes, to self-assembled particles, and microparticles when the concentration of KOH was changed from 1.5 M, 2.5 M, to 3.5 M, and 5 M. Correspondingly, the main phase of the samples changed from orthorhombic Bi₂Fe₄O₉, both Bi₂Fe₄O₉ and BiFeO₃, to pure rhombohedral BiFeO₃. On the basis of these experiments, the phase formation and morphology evolution mechanism of the samples are discussed. Furthermore, the photocatalytic activity of the as-prepared samples was investigated by the photo-degradation of rhodamine-B solution.     

纳米烧绿石型钛酸铅的水热合成

钙钛矿结构的钛酸铅是重要的电子陶瓷材料,在合成钙钛矿型钛酸铅的过程中,经常出现烧绿石结构的钛酸铅物相,但目前尚未见到合成单一物相烧绿石结构的钛酸铅报道.本文报道了用水热法制备烧绿石型钛酸铅纯相的结果,以及体系的碱度对产物的种类和形貌的影响.