A novel approach for the synthesis of nanocrystalline zinc oxide powders by room temperature co-precipitation method

A single step co-precipitation route has been employed for the first time in the preparation of ZnO nanoparticles using ammonium hydroxide and zinc nitrate tetrahydrate. The X-ray diffraction analysis revealed that the synthesized powder has the hexagonal (wurtzite) structure. The as-prepared ZnO powder was well crystalline, without any calcination. This is a promising result compared to those mentioned in the literature, in which crystallization of ZnO nanoparticles was detected at > 300 °C. The average crystallite size of the as-prepared ZnO nanopowder is 20-40 nm. The nanocrystalline ZnO could be sintered to ~ 95% of the theoretical density at 1300 °C in 4 h.     

Effect of different solvents in the synthesis of LaCoO3 nanopowders prepared by the co-precipitation method

This paper describes the obtention of LaCoO₃ nanopowders by the co-precipitate method with ammonium hydroxide from solvent such as water, ethyl alcohol and ethylene glycol. The crystalline structure and average particle size are dependent of type-solvent. The XRD patterns indicated that the LaCoO₃ nanopowders prepared with water and ethyl alcohol exhibit a pure perovskite-type LaCoO₃ in the rhombohedra structure. The average diameter of the particles prepared with ethyl alcohol and water are 27 ± 4.49 nm and 64.4 ± 12.92 nm respectively. High resolution transmission electron microcopy revealed an oriented attachment mechanism for the growth of aggregated LaCoO₃ nanocrystals. Room temperature magnetization results of the heat treated LaCoO₃ nanopowders exhibited a paramagnetic behavior. The average particle size and formation temperature of LaCoO₃ obtained in this study is comparatively lower than those reported in the literature.     

Structural and properties of hydrothermally synthesised M-type hexaferrites

Magnetoplumbite-type (M-type) hexagonal strontium ferrite particles were synthesized by hydrothermal method as the materials. Then, the precursors were calcinated at 1000 °C for two different time (200 and 300 min). The phase composition, micro-morphology and magnetic properties of the particles were investigated by X-ray powder diffraction analysis, scanning electron microscopy, and vibrating sample magnetometer. At hydrothermal temperature ranging from 220 to 230 °C, the phase of M-type hexaferrites includes small amounts of impurities phases, such as α-Fe₂O₃. The result shows that the single M-type phase was obtained when the hydrothermal temperature is 240 °C. The particles appear in hexagonal plate-like shape and the size of grain is about 400 nm. The effect of sintering time on magnetization and coercivity was studied in this paper.     

微通道反应-共沉淀法制备YAG纳米粉体

以碳酸氢铵为沉淀剂,采用微通道反应与共沉淀法相结合的方法制备出了钇铝石榴石纳米粉体。实验考查了溶液浓度、pH值、Nd3+掺杂等因素对合成纯相YAG纳米粉体的影响。结果表明增大沉淀剂浓度不利于纯相YAG粉体的制备,当沉淀剂浓度为0.4mol/L,Al 3+浓度范围为0.1～0.4mol/L的条件下均得到纯相YAG纳米粉体;采用优化的实验条件,体系pH值维持在8左右,以2%(原子分数)的Nd3+取代YAG中的Y3+,900℃保温4h得到纯相Nd∶YAG粉体,粉体平均粒径在40nm左右,分布均匀,呈近球形。     

A novel method for preparation of barium strontium titanate nanopowders

Ba_0.6Sr_0.4TiO₃ (BST) nanopowders have been prepared using the modified citrate method with ammonium nitrate as a combustion promoter, and the formation mechanism, phase evolution, and particle size have been investigated using TG/DTA, XRD, and SEM. It is found that the peaks of barium carbonate disappear when the precursor powders are calcined at 650 °C. The fine particles of the nanopowders calcined with the combustion promoter addition are homogeneous and well-dispersed and their narrow size distribution is about 60-90 nm. Comparatively, the particles of the powder calcined without the ammonium nitrate addition are inhomogeneous, with an evident agglomeration. The mechanism for the above results is attributed to that a reaction can generate soft and loose precursor powders by the adoption of ammonium nitrate, and hence a pure BST phase could occur at the low synthesis temperature of 650 °C.     

A comparative study on the magnetic properties of Fe-doped CuO nanopowders prepared by sol-gel and co-precipitation method

The Fe-doped CuO nanopowders (Cu_0.95Fe_0.05O) were prepared by the sol-gel and the co-precipitation methods. The effects of synthesis methods on the structure, magnetic property and exchange bias effect of Cu_0.95Fe_0.05O nanopowders were investigated. The microstructure and magnetic properties of the two types of nanopowders were characterized by X-ray diffraction and physics property measuring systems, respectively. It was found that the sol-gel method tended to lead the formation of CuFe₂O₄ phase, which dominated the magnetic behaviors of the sample; the co-precipitation tended to lead larger exchange bias field at low temperature in samples, comparing with sol-gel method.     

Characterization and synthesis of pure ZrO2 nanopowders via sonochemical method

Pure ZrO₂ nanopowders have been synthesized via sonochemical method, which is a simple and energy efficient way to synthesize inorganic materials. The as-synthesized samples (hydrous zirconia, ZrO₂·nH₂O) are characterized by several techniques: X-ray diffraction (XRD), thermogravimetric analysis (TGA), photoluminescence spectrometer (PLS) and Raman spectrometer (RS). It is shown that t-ZrO₂ samples have two photoluminescence (PL) bands corresponding to the wavelengths of excitations of 254 and 412 nm. The structure of as-synthesized samples (ZrO₂·nH₂O) and the formation mechanism of ZrO₂ nanopowders are also discussed.     

Mixture of fuels approach for the solution combustion synthesis of LaAlO3 nanopowders

A modified solution combustion approach was used in the preparation of nanosize LaAlO₃ (～23.6 nm) using mixture of citric acid and oxalic acid as fuels with corresponding metal nitrates. The synthesized and calcined powders were characterized by Fourier transform infra red spectrometry (FTIR), Differential thermal analysis-Thermogravimetry analysis (DTA–TGA), X-ray diffractometry (XRD) and Transmission electron microscopy (TEM). The FTIR spectra show the lower frequency bands at 656 and 442 cm^?1corresponds to metal–oxygen bonds (possible La–O and Al–O stretching frequencies) vibrations for the perovskite structure compound. DTA confirms the formation temperature of LaAlO₃ varies between 830–835 °C. XRD results show that mixture of fuels ratio is influential on the crystallite size of the resultant powders. The average particle size of LaAlO₃-1 as determined from TEM was about 41 nm, whereas for LaAlO₃-2 and LaAlO₃-3 samples, particles are seriously aggregated.     

Synthesizing nano LaAlO3 powders via co-precipitation method

Co-preparation method has been applied to synthesize nano LaAlO₃ powders. By using La(NO₃)₃ and Al(NO₃)₃ as raw materials and keeping the pH≈9, the co-preparation process could be finished at room temperature. Pure LaAlO₃ nano powders with a size of about 50 nm could be obtained after calcining at 700–800 °C. These nano LaAlO₃ powders could be sintered at 1550 °C for 4 h, a high relative density of about 97% could be reached.     

A novel approach to prepare tetragonal BaTiO3 nanopowders

BaTiO₃ nanopowders were attempted to synthesize by using a novel straight-forward, solvent free reactions under autogenic pressure at elevated temperature (RAPET) approach. The as-prepared BaTiO₃ nanoparticles were characterized by X-ray diffraction, transmission electron microscopy, high-resolution TEM, and convergent-beam electron diffraction. It was found that Ba(OH)₂·8H₂O and Ti(OBu)₄ could be appropriate starting materials to synthesize BaTiO₃ at 973 K for 2 h by using RAPET approach. Pure tetragonal BaTiO₃ nanopowders could be obtained by exceeding moderate amount of Ba(OH)₂·8H₂O in the starting materials. The obtained BaTiO₃ nanoparticles had well dispersion and crystallinity, possessed a tetragonal perovskite structure at room temperature and relatively narrow particle size distribution.     

Dielectric properties of cobalt substituted M-type barium hexaferrite prepared by co-precipitation

Barium hexaferrite was synthesised via the co-precipitation method using high purity nitrates, oxides and carbonates of iron (III), barium (II) and ammonium hydroxide. Once a phase pure sample of barium hexaferrite was obtained, it was doped, by weight, with 1, 2, 3, 5, 10, 15, 20 and 30% cobalt oxide (Co₃O₄). The addition of cobalt to the BaM had the effect of reducing the permittivity and loss tangent until a doping of 10% whereupon it remained constant at around 9. Thermogravimetric (TG) studies of green bodies showed decarboxilation to occur at around 825°C and the transformation of residual Co₃O₄ to Co₂O₃ at around 900°C. The X-ray diffraction (XRD) studies confirmed the Co ions substituting in the iron sites until a doping level, of 10–15% where the structure underwent a transition to one more closely resembling the W-type hexaferrite. The measured densities were found to vary with doping levels, with a maximum of 4.45 g/cm³ at 1% Co doping.     

Synthesis and characterization of magnetite nanoparticles via the chemical co-precipitation method

Magnetite nanoparticles were synthesized via the chemical co-precipitation method using ammonium hydroxide as the precipitating agent. The size of the magnetite nanoparticles was carefully controlled by varying the reaction temperature and through the surface modification. Herein, the hexanoic acid and oleic acid were introduced as the coating agents during the initial crystallization phase of the magnetite. Their structure and morphology were characterized by the Fourier transform infrared spectroscopy (FTIR), the X-ray diffraction (XRD) and the field-emission scanning electron microscopy (FE-SEM). Moreover, the electrical and magnetic properties were studied by using a conductivity meter and a vibrating sample magnetometer (VSM), respectively. Both of the bare magnetite and the coated magnetite were of the cubic spinel structure and the spherical-shaped morphology. The reaction temperature and the surface modification critically affected the particle size, the electrical conductivity, and the magnetic properties of these particles. The particle size of the magnetite was increased through the surface modification and reaction temperature. In this study, the particle size of the magnetite nanoparticles was successfully controlled to be in the range of 10–40 nm, suitable for various biomedical applications. The electrical conductivity of the smallest particle size was 1.3 × 10^?3 S/cm, within the semi-conductive materials range, which was higher than that of the largest particle by about 5 times. All of the magnetite nanoparticles showed the superparamagnetic behavior with high saturation magnetization. Furthermore, the highest magnetization was 58.72 emu/g obtained from the hexanoic acid coated magnetite nanoparticles.     

Synthesis of sulfated zirconia nanopowders via polyacrylamide gel method

In the present study, polyacrylamide gel method was applied for synthesis nanosized sulfated zirconia powders, first time. An assessment of the influence of calcination temperature and sulfate ion loading on the properties of synthesized powders was performed and the samples were characterized by X-ray diffraction, infrared spectroscopy, scanning electron microscopy and thermal analysis. The results revealed that tetragonal phase was obtained on calcination at 500 °C and was stable towards higher temperatures (650 °C). The increase of crystallite size with increasing calcination temperature was observed. Calcination for long duration time led to evolution of some sulfur species, furthermore results in higher particle size (∼100–200 nm) as compared to calcination for short duration time resulting in lower particle size (<50 nm). The presence of sulfate had no significant effect on thermal stability of polyacrylamide gel network whereas structure and the nature of the sulfur species bound with the zirconia surface are affected by the sulfur content.     

A novel method for synthesis of microstructure MoO3

One-dimensional microstructures of orthorhombic molybdenum trioxide (α-MoO₃) have been synthesized via acidification of ammonium heptamolybdate tetrahydrate. A solution of precursor compound, ammonium heptamolybdate tetrahydrate, is acidified to pH 3.5 using diluted glacial acetic acid. Then the intermediate compound is sintered at 300 and 600 °C to give the final α-MoO₃, and the SEM shows that it still keeps its micrometer fibers structure.     

溶剂热合成纳米钛酸钡及其表征

为满足钛酸钡纳米陶瓷的需求,本文用TiCl4和Ba(OH)2作前驱体,乙醇和乙二醇甲醚作混合溶剂,溶剂热合成了钛酸钡纳米粉体,并使用TEM、XRD和Raman光谱对产物进行了表征.结果表明,在本文条件下可以得到粒径为10~80 nm纳米粉体,通过控制反应条件可以达到控制颗粒尺寸的目的,反应时间和反应温度对颗粒尺寸有显著的影响.     

A novel method for the synthesis of polyamide 6 magnetic microspheres

Polyamide 6 (PA6) magnetic microspheres were firstly prepared via successively in situ polymerization using phase inversion technology of polymer pairs polyamide 6/polystyrene (PA6/PS) at extremely low PS content. The properties of PA6 magnetic microspheres, such as morphologies, diameter size distribution, magnetic properties, thermal stability, and the functional groups of the magnetic microspheres, were investigated by different techniques (i.e. SEM, TEM, DLS, VSM, FTIR, and DSC). The results indicated that the diameter distribution of PA6 magnetic microspheres was narrow, and the mean diameter size was about 7.7 μm. The saturation magnetization of magnetic microspheres reached 12.50 emu/g. Furthermore, the magnetic microspheres had abundant functional groups and better thermal stability.     

配位均匀共沉淀法制备Ag/ZnO纳米复合材料的研究

采用配位均匀共沉淀法成功制备出了粒径20～50nm的Ag/ZnO纳米复合材料,用TG-DTA、XRD、IR及TEM等技术对前驱物及不同温度下焙烧前驱物所得的产品进行了表征分析.结果表明,当前驱物的焙烧温度为300℃时,粒子呈球形,粒径小,且其粒径随前驱物焙烧温度的升高而增大.对Ag/ZnO晶粒生长动力学的研究发现,在较低温度范围内,晶粒生长速度较快,其晶粒生长动力学指数为1.32.