Formation Mechanism Of Hollow Microspheres Research Articles

Synthesis of hollow carbonyl iron microspheres via pitting corrosion method and their microwave absorption properties

In this paper, we report a new method to prepare hollow carbonyl iron microspheres, which is called pitting corrosion method. The comparison of the morphology, specific surface area and apparent density of the initial and pitting corroded carbonyl iron microspheres demonstrate that the pitting corroded carbonyl iron has a hollow structure. The pitting corrosion process is uncovered through the concentration change of ferrous ion in the reaction solution and the TEM images with different pitting corrosion time. The formation mechanism of hollow microspheres via pitting corrosion is analyzed. Furthermore, this pitting corrosion method can also be used to prepare other hollow metal particles, such as Ni, Co, and Cu particles. The electromagnetic parameters of the samples before and after pitting corrosion are measured. The calculated reflection loss of the pitting corroded sample for single layer of 0.5mm or 1.0mm thickness at 2–18GHz is much better than that of the initial one. The mechanism of the improvement of the microwave absorption properties is discussed.

基于动态溶胀法制备中空聚合物微球

Hollow polymer microspheres about 5 m in diameter were synthesized by dynamic swelling method using micron-sized polystyrene spheres with positive charges on surfaces as seeds. The synthesis process included swelling by organic solvents such as toluene and divinylbenzene, polymerizing and coating. The influences of variety and dosage of organic solvents on diameter, size distribution and hole structure of hollow microspheres were investigated, and the formation mechanism of hollow microspheres was discussed. It is indicated that some volatile organic solvents, such as toluene and dimethylbenzene, are crucial to hollow structure formation. Experimental results show that, more toluene leads to larger hollow structure after swelling, and dimethylbenzene is good for hollow structure formation, owing to its low solubility.

Formation mechanism of hollow microspheres consisting of ZnO nanosheets

Hydrangea-like hollow microspherical ZnO has been synthesized via a transformation from layered basic zinc acetate (LBZA) and characterized using X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Investigation of the early stages of the crystal growth revealed a non-classic growth mechanism. With increasing reaction time, (1) amorphous spherical aggregates formed initially, followed by (2) surface multiple nucleation, (3) crystallization into LBZA nanosheets which are vertical to the microspheres' surface, (4) surface condensation leading to the formation of hollow microspheres, (5) extension of the crystallization both inwards and outwards, and (6) transformation to zinc oxide during annealing in air. The detailed formation mechanism of the hydrangea-like microspheres, consisting of thin (∼5.4 nm) LBZA nanosheets, is proposed. The hydrangea-like ZnO exhibited superior photocatalytic performance in dye degradation due to its unique construction and high specific surface area. This work may shed light on crystal engineering of porous microspheres, hollow crystals and thin nanosheets of other materials.

One-pot template-free synthesis, formation mechanism, and lithium ions storage property of hollow SnO2 microspheres

In this work, we report a facile one-pot template-free approach to prepare hollow rutile SnO2 microspheres using SnCl4 as the precursor in a condensed H2SO4–EtOH mixed solvent. The formation mechanism of the hollow microspheres was proposed on the basis of characterizations. First, the controlled hydrolysis and condensation of SnCl4 to SnO2 nanocrystals was realized by the formation of water via catalytic dehydration of EtOH in the presence of condensed H2SO4. These SnO2 nanocrystals rapidly aggregated to form microspheres in order to minimize their surface energies. Then, Ostwald ripening mechanism governed the subsequent growth and recrystallization of the nanocrystals to form the hollow structure. The resulting hollow SnO2 microspheres exhibited better cycle performance than the pristine SnO2 nanoparticles when used as anode materials in lithium ion batteries.

A Fast and Template Free Synthesis of Tb:Y2O3 Hollow Microspheres Via Supercritical Solvothermal Method

The design of template-free hollow microspheres in a very short period of time will be of great importance to save energy and time and allow rapid production. We succeeded in the rapid synthesis of precursor material via a supercritical solvothermal method followed by subsequent heating to obtain Tb:Y2O3 hollow microspheres. The prepared precursor material was actually composed of Y(OH)3 and Y(OH)CO3 phases. The hollow microspheres seemed to be formed through the aggregation of nanoparticles under supercritical conditions. The formation mechanism of hollow microspheres in the present synthesis is the Ostwald ripening process. Effects of reaction temperature and pH of the starting solution were investigated to understand the effect on the formation of hollow microspheres. Well-shaped Tb:Y2O3 hollow microspheres showed strong green emission at 540 nm under 304 nm light excitation. The effect of doping concentrations and calcinations temperature was investigated.

Polyhedral construction of hollow ZnO microspheres by CO 2 bubble templates

A new type of complex ZnO hollow structures constructed by polyhedral particles has been prepared via a facile solution-phase route, in which ZnO precursors (ZnCO 3) are synthesized through the reaction between Zn(CH 3COOH) 2 and NH 4HCO 3 in aqueous solution. Similar morphology of hollow ZnO microspheres can be effectively obtained simply by the pyrolysis method. The formation mechanism of hollow microspheres is mainly via an oriented aggregation process. CO 2 bubble templates produced during the reaction to form the aggregation centers help the small particles to aggregate and form hollow microspheres. The surface morphology and size of these microspheres can be tuned by simply varying the reaction temperature. The hollow ZnO microspheres constructed by polyhedral particles may bring novel physical and chemical properties in the field of microscale electronics and photonics.

Surfactant-assisted preparation of hollow microspheres of mesoporous TiO 2

Hollow microspheres of mesoporous titania with a thin shell of anatase structure have been prepared by a simple procedure of surfactant poly(ethylene oxide) assisted nanoparticle assembly in nonaqueous system. A high surface area of 378 m 2/g and pore volume of 0.34 cm 3/g was obtained in the as-prepared sample with pore size of 2.6 nm. A large number of surface hydroxyl groups and a reduced band gap were found, which should be significant for multi-functionalisation of the surface and photocatalysis applications. A formation mechanism of hollow microspheres was proposed.