Single Hollow Spheres Research Articles

In-situ regulation of hollow TiO2 with tunable anatase/rutile heterophase homojunction for promoting excellent photocatalytic degradation of pesticides

Constructing phase junction is an effective strategy to increase photocatalytic performance of titanium dioxide (TiO2) because it can promote charge separation. However, both low surface area and unstable phase interface limit its further application. In this investigation, we introduce a structural regulation strategy to prepare anatase/rutile TiO2 (A/R–TiO2) hollow photocatalyst through in-situ growth of rutile TiO2 on anatase TiO2 hollow microspheres byheat treatment. The as-synthesized A/R–TiO2 photocatalyst was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and ultraviolet–visible (UV–vis) spectroscopy. The results reveal that the A/R–TiO2 hollow photocatalyst significantly promotes efficient charge separation due to the intimate contact of two phases within a single hollow sphere. Notably, A/R–TiO2 exhibits more efficient than commercial TiO2 (P25) towards the photodegradation of various pesticide pollutants, which suggests that such a structural design can be an effective method for rationally constructing TiO2-based photocatalyst with advanced performance.

On the compressive properties of aluminum and magnesium syntactic foams: Experiment and simulation

The influence of the materials of Al and Mg-based syntactic foams on the compressive behavior was investigated. Two different kinds of foams of cp-Al and cp-Mg in combination with ceramic hollow spheres (Al2O3 or Al2O3/SiO2/mullite) were manufactured by infiltration technique. A full-scale finite element model was established to explain the experimental results and to explore the effect of matrix and hollow sphere properties up to the peak strain. In this full-scale model, the ceramic hollow spheres’ effective elastic and fracture properties were used, determined from compression tests and micromechanical model of single hollow spheres. The finite element model predicted the compression curve with high precision in the investigated deformation range for the highly ductile foams with Al matrix, indicating that fracture becomes the dominant failure mode only near the peak stress. The model of Mg matrix syntactic foams showed that fracture in the early stage of compression did not change the strength of the material; however, it significantly lowered the stiffness in the case of Al2O3 hollow sphere having a diameter of ∼4 mm and thin (150 µm) wall. If significant reactions occurred between the matrix and hollow spheres during manufacturing, the model could estimate the formed complex interface’s effect on the syntactic foams’ strength.

Deposition of hollow sphere In2O3 coatings by liquid flame spray

ABSTRACT Hollow sphere In(OH)3 coatings were deposited by a simple liquid flame spray with hollow sphere In(OH)3 suspension, which was synthesized by improved soft template methods. The morphology of the In(OH)3 was well preserved and oxygen vacancies were produced in the harsh thermomechanical environment of the flame spraying process. The In2O3 coatings and In2O3 powder were obtained by calcinating the In(OH)3 coatings and In(OH)3 precursor, respectively. The thickness of the coatings increased from 12 to 22 μm as the diameter of the feed nozzle increased, and the interconnection between the single hollow spheres In2O3 in the coatings was better than that of the as-synthesized In2O3 powder. The diameter of the single hollow spheres In2O3 in the coatings was about 1.2∼1.4 μm, which is similar to the as-synthesized In2O3 powder. The In2O3 coatings with hollow spheres possessed a very high specific surface area, excellent interconnections, controllable thickness and numerous oxygen defects.

Magnetic Reversal by Mixed Modes in Two-Dimensional Hexagonal Array of Hollow Cobalt Nanospheres

Magnetization reversal in two-dimensional hexagonal arrays of cobalt hollow spheres occurs by mixed coherent and curling-vortex modes. Micromagnetic analysis was based on values of exchange, demagnetizing, and anisotropy energy. Arrays of 20 nm and 30 nm radius spheres were modeled, with sphere separations of 0, 2, and 4 nm, which controlled the dipolar interactions. The results demonstrate that solutions for magnetization reversal of single hollow spheres cannot be applied to arrays of hollow spheres.

Effects of size and shell thickness of TiO2 hierarchical hollow spheres on photocatalytic behavior: An experimental and theoretical study

Through a self-sacrificing template method, highly uniform hollow-spheres of TiO2 anatase are synthesized with controllable diameter from 365nm to 930nm. Compared to large hollow spheres, a large enhancement in the photocatalytic activity is reported for the small hollow spheres (with a thickness of 50nm). By extending Mie's scattering theory from solid- to hollow-spheres, for a spherical scatter with a diameter of 300–900nm, theoretical calculation reveal that each singular hollow sphere has absorption power equivalent to a solid sphere as the shell thickness parameter reaches a critical value of 0.3–0.6. This critical thickness parameter is independent to the size of a single hollow sphere, demonstrating that hollow spheres have quantitative advantages over solid spheres of the same weight. Moreover, calculation supported that small hollow spheres have stronger absorption power than large hollow spheres due to higher thickness. This greatly enhance the performance of small hollow spheres under a photocatalytic test. Our theoretical results showed good agreement to the experimental measurements, and provided a framework for the design of hollow-sphere nano-particles for optimized absorption power.

Experimental investigations on the weakening effect of magnetic fields on surface‐enhanced Raman scattering

Currently, because of the wide use of magnetic/metal hybrid materials in the field of surface‐enhanced Raman scattering (SERS), magnetic fields (MFs) as a kind of surrounding environments of SERS substrates have been not ignored. And enormous attentions for the effect of MFs on SERS are very necessary. Our analysis from previous reports shows SERS signals are closely associated with MFs; yet the study of the exact effect of MFs on SERS is still in need of detail and broadening. In this work, we demonstrate that the use of Ni/Au microparticles (MPs) and Au hollow spheres (HSs) to study the effect of MFs on SERS signals. The experiments are preformed from three aspects, including the comparison of SERS signals of Ni/Au MPs with different Ms values, the comparison of SERS signals of Au HSs and Ni/Au MPs under different external MFs, and the comparison of SERS signals of single Au HS particle and single Ni/Au particle in the absence and presence of an external MF. Thereinto, under different external MFs from 0, 0.01, 0.02, 0.04 to 0.08 T, SERS signals of Au HSs and Ni/Au MPs are gradually weaker. According to the experiments, the weakening effect of MFs on SERS is confirmed. It is suggested that the weakening effect is originated from the blue‐shift of surface plasmon resonance and the locking of charge‐transfer from Au to probe molecules. Copyright © 2012 John Wiley & Sons, Ltd.

A refined finite element analysis on the thermal conductivity of perforated hollow sphere structures

This work addresses the thermal properties of perforated hollow sphere structures. Hollow sphere structures are a new material with significant areas of application in thermal insulation , structural and acoustic damping and controlled deformation at low stress levels. The structures are assembled by single hollow spheres and can be joined for example by sintering. Finite element analysis is performed in order to determine the effective thermal conductivity . Special focus is given to the influence of the sintered contact area and the relative density on the thermal properties. In addition, different contact topologies are accounted for. The maximum observed thermal conductivity is only 1.82% of the base material conductivity λ b which confirms the usability of the material for the purpose of thermal insulation.

Experimental Investigation of Mechanical Properties of Metallic Hollow Sphere Structures

Metallic foam was fabricated from 316L stainless steel spheres, where the bonding of the spheres was achieved by a sintering process. The mechanical behavior of a low-density material (0.3 g/cm3) with 2- and 4-mm sphere diameter and a high-density material (0.6 g/cm3) with 4-mm sphere diameter was investigated in compression and tension. The cell wall material of this hollow sphere structure (HSS) had different morphologies: dense and porous sintered walls were investigated. The cell wall morphology affects the Young’s modulus (stiffness) and the ductility of the HSS material. Defects, such as the cell wall porosity, lower the ductility of the material. Besides the quasi-static measurements, the HSS material was tested with a resonance frequency method (dynamic measurement), to obtain detailed information on the stiffness at different temperatures up to 700 °C. In-situ compression and tension tests were carried out to understand the deformation mechanisms on the scale of the single hollow spheres. The failure mechanisms in the vicinity of the sintering neck of the spheres was investigated. A doubling of the density leads to an increase of the plateau stress and the ultimate tensile stress of the material, whereas the ductility (strain to fracture) depended mainly on the cell wall morphology. Due to the mainly tensile loading of the cell walls in the vicinity of the sinter neck, the ultimate tensile strength doubled for the high-density HSS, in good agreement with theoretical considerations. In compression, the gain in the plateau stress was not as distinctive compared with the theoretical considerations assuming a bending dominated deformation. The influence of structural parameters, such as cell wall morphology, cell wall thickness, and sphere diameter, on the mechanical behavior is discussed.

Budded, Mesoporous Silica Hollow Spheres: Hierarchical Structure Controlled by Kinetic Self‐Assembly

Recently, mesoporous materials with hierarchical structures and well-defined morphologies have attracted much attention. Besides possible practical applications, studies of mesoporous materials may also shed light on fundamental mechanisms of biomineralization. Among the many types of mesoporous materials, hollow spheres are of significance because of their potential uses in encapsulation, drug-delivery, and controlled-release applications. Although many articles have been published describing the interior templating of mesoporous hollow particles using hard templates, vesicles, or emulsions, the fabrication of hierarchical structures on the shell has rarely been reported. In this Communication, we report a novel, single-step, emulsion-templating method to fabricate a unique, hierarchical morphology. Our products consist of budded, mesoporous silica hollow spheres. What distinguishes these structures from the traditional ones is that they combine two separate, distinct mesophases with different-sized mesovoids in a single hollow sphere. Specifically, the shell of the sphere is based on wormholelike mesoporous structures, while the protruding buds are formed from lamellar (vesicular) mesostructures. Our process utilizes the sodium salt of the anionic surfactant N-lauroylsarcosine (Sar-Na), which is commonly used in cosmetic and pharmaceutical industries due to its biodegradability and low toxicity. Instead of employing the usual emulsion-templating methods with nonpolar fluids such as trimethylbenzene, we employ a novel process in which the emulsion is generated by the acidification of a Sar-Na solution. As shown in Scheme 1, the addition of acid converts a portion of the Sar anions to Sar-H, which is an amphiphilic polar oil that behaves as droplets. The condensation of the added silica precursors (3aminopropyltrimethoxysilane (APMS) and tetraethylorthosilC O M M U N IC A TI O N

Analysis of the Initial Slope of the Small‐Angle Scattering Correlation Function of a Particle

AbstractThe small‐angle scattering correlation function of a particle γ(r) results from scattering experiments. This function possesses a well‐defined slope γ′(0) at the origin. This slope is defined by the particle volume V and the whole surface area S of the particle via γ′(0) = –S/(4V).In this paper it is demonstrated that this slope defines the mean chord length of the particle, $ \bar l=-1/\gamma \prime (0)=4V/S $. This theorem involves non‐convex particles, especially the case of particles with hollow parts. Consequently, for a large class of particle shapes the mean chord length is defined in terms of V and S.This extension of the Cauchy theorem is developed by closer analysis of the set covariance C(r), of the small‐angle scattering correlation function γ(r), and of the so‐called linear erosion P(r) near the origin r→0. The cases of a single hollow sphere, of two touching spheres, and of the single hollow cylinder are discussed.

Compressive Properties and Energy Absorption of Hollow Sphere Aluminum

Manufactured cellular aluminums have been developed for a wide range of automotive applications where weight savings, improved safety, crashworthiness and comfort are required. The plateau deformation behavior of cellular aluminums under compressive loading makes this new class of lightweight materials suitable for energy absorption and comes close to ideal impact absorbers. In the present study, aluminum hollow hemispheres were firstly processed by pressing. Hollow sphere aluminum samples with a body-centered cubic (BCC) packing were then fabricated by bonding together single hollow spheres, which were prepared by adhering together hollow hemispheres. Hollow sphere aluminum samples with various kinds of sphere wall thicknesses of 0.1 mm, 0.3 mm and 0.5 mm but the same outside diameter of 4 mm were investigated by compressive tests. The effects of the sphere wall thickness on the mechanical properties and energy absorption characteristics were investigated.

Behavior of a random hollow sphere metal foam

The quasistatic uniaxial compression behavior of both single hollow spheres and bulk metal foams comprised of the same hollow spheres is examined experimentally. The spheres are nominally the composition of a 405 stainless steel (Fe–12Cr), with a 2 mm outside diameter and 0.1 mm thick walls, and are sintered together to process the bulk foam. It is shown that to first order the bulk foam stress–strain behavior, Poisson effects, and densification may be understood on the basis of simple experiments performed on single spheres between parallel platens. These hollow sphere foams appear to behave similar to open-cell foams. Finite element modeling of finite compression of a single sphere lends further insight into the deformation process and the role of plastic bending and contact of cell walls during the process of densification.

Linear simulation models for real-space interpretation of small-angle scattering experiments of random two-phase systems

A procedure is presented for modelling and interpreting small-angle scattering experiments of random isotropic two-phase media. There are applications in structure research. Based on the curvature behaviour of the small-angle scattering correlation function γ(r), the distribution laws of random distances between the interfaces of the phases are analysed. Furthermore, the function of occupancy Z(r) Z(r), defined by Porod (see Porod G 1951, 1952 Z. Kolloid 124 83–114, 125 51–122), is simulated. This includes the connection with the volume fraction c of the microparticles. Both functions are studied by use of a linear finite symmetrical one-dimensional model. A Mathematica program allows the numerical simulation of these functions for a large class of phase correlation functions (indicator functions). In this way, a scattering experiment can be interpreted in the light of chord length distribution. Explanations of this strategy for two types of discrete inhomogeneity are included: discussion of γ″(r) γ″(r) of a single hollow sphere and the analysis of an experimental γ(r) γ(r) function of an amorphous AlDy(6 at.%)Ni(10 at.%) alloy.