Diameter Of Hollow Spheres Research Articles

Influence of welding residual stress on bending resistance of hollow spherical joints

Welded hollow spherical joints are widely used in large-span spatial structures because of their simple organization and convenient construction. However, in the sphere-pipe connection welds of the joints, welding residual stress is generated, which will adversely affect the mechanical properties of the joints and the overall structure. In this paper, the parametric model of welded hollow spherical joints was established by employing the geometric configuration dimensions of those joints frequently used in engineering. Through the combination of experimental research and numerical simulation, the welding residual stress of welded hollow spherical joints and its impact on joints' bending resistance were studied. First of all, based on the distribution pattern of the stress, bending test of the joints was carried out and revealed the influence of welding residual stress on the bending stiffness and ultimate bending capacity of the joints; Then, through the results of experimental analysis and finite element calculation, and with parametric analysis, the impact of welding residual stress on joints' bending resistance was clarified with the variation of parameters such as the hollow sphere diameter D, wall thickness t and the connecting steel pipe diameter d. It is shown that welding residual stress has a great impact on joints' bending stiffness, with a reduction more than 10%, while it doesn't affect their ultimate bending capacity much, with an influence no more than 5%. In addition, as D increases, t, and d decrease, its impact on the bending resistance rises.

Microstructure and mechanical properties of bimodal syntactic foams with different size combination and volume fraction of alumina hollow spheres

In this study, the stir casting method was used to prepare aluminum matrix bimodal syntactic foams by mixing alumina hollow spheres of different size ranges. Alumina hollow spheres of 1.0–4.0 mm were divided into six size ranges. In bimodal syntactic foams, the hollow spheres of different size ranges were mixed in equal volume to ensure that their average diameter was almost the same, or the hollow spheres of 1.5–2.0 mm and 3.0–3.5 mm were mixed in different volume ratios. The bimodal syntactic foams under quasi-static compression first fractured along the small-sized hollow spheres, presenting brittle fracture characteristics. When mixing hollow spheres with different size ranges in equal volume, the mechanical properties of bimodal syntactic foams strongly depended on the average diameter of hollow spheres. The mechanical properties of bimodal syntactic foams with 1.5–2.0 mm and 3.0–3.5 mm hollow spheres decreased linearly with the increase of 3.0–3.5 mm hollow sphere content.

Effects of volume fraction and diameter of hollow spheres on acoustic properties of Metallic-Hollow-Sphere/Polyurethane (MHSP) acoustic composites

Metallic hollow spheres and polyurethane resin are excellent sound insulation and sound absorption materials. In this study, the surface modified 316L stainless steel hollow spheres were added into polyurethane by casting method. The influence of the volume fraction and diameter of the hollow spheres on the sound insulation and sound absorption performance of the Metallic-Hollow-Sphere/Polyurethane (MHSP) acoustic composites was investigated by impedance tube method and the relevant acoustic mechanism was discussed. When the volume fraction of hollow spheres is 45% and the diameter is 2.5 mm, composite has the best sound insulation performance. And when the volume fraction of hollow spheres is 60% and the diameter is 2.5 mm, composite has the best sound absorption performance. Due to the mass effect, damping effect, change of acoustic impedance and multiple interface of composites, sound waves will reflect, refract and scatter many times in the process of propagation, thus losing lots of sound energy to improve the sound insulation performance. The sound absorption mechanism of MHSP is that the friction, viscosity and reflection of sound waves in the pores of polyurethane, cavities of the hollow spheres and interfaces will cause the loss of sound energy and turn it into heat energy.

Mechanical performance of welded hollow spherical joints with H-beams after elevated temperatures

Welded hollow spherical joints with H-beam (H-WHSJ), as a new connection pattern in space lattice structures, have been applied in practical engineering. This study aims to investigate the residual mechanical properties of H-WHSJ after loading in elevated-temperature environments and provide an important basis to evaluate the performance of space lattice structures after the occurrence of fire. The effects of temperature history, plastic residual deformation, sizes of WHSJ and H-beam, type of steel, and stiffening rib arrangement on the residual mechanical performance of H-WHSJs after exposure to elevated temperatures are determined via axial compression test by using 28 specimens and finite element (FE) parametric study. The major conclusions are as follows. (1) The residual characteristics of H-WHSJ after elevated temperature are rarely affected by temperature history, but mainly determined by the residual deformation at elevated temperature when the temperature is lower than 700 °C. (2) Plastic residual deformation can considerably reduce the residual bearing capacity (Nu,p) of the loaded H-WHSJ. In particular, Nu,p decreases by approximately 20% when the residual deformation is 6% of the hollow sphere diameter. (3) The formula to calculate the residual bearing capacity of H-WHSJ after loading in elevated-temperature environments has been proposed, and its prediction are in good agreement with the test and FE results.

Facile synthesis of hollow mesoporous MgO nanospheres as ultra-high performance and reusable adsorbent

A facile approach for fabrication of hollow mesoporous MgO nanospheres (HMMN) has been demonstrated. The employed protocol involves the coating of carbon spheres template with MgO nanoparticles, followed by the calcination in presence of air to remove the carbon core at elevated temperature. Scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) have been used to characterize the sample. Brunauer-Emmett-Teller (BET) method reveals the specific surface area and the average pore diameter of hollow spheres as 55.1 m2/g and 8.19 nm, respectively. The composite exhibits excellent adsorptive capacity toward Congo red (CR) at room temperature. The adsorption reaches equilibrium within 70 min with the maximum adsorption capacity of 5000 mg/g which is, to the best of our knowledge, the highest reported value. Additionally, the regeneration by calcination shows that adsorbent has high adsorption performance and superb reusability.

Study on compressive bearing capacity and axial stiffness of welded hollow spherical joints with H-shaped steel member

To study the compressive bearing capacity and stiffness of welded hollow spherical joints with H-shaped steel member(WHS-HSM joints), axial compression test was conducted on eight specimens of WHS-HSM joints. By verifying the correctness of the numerical model, the parametric analyses were done considering the following factors, such as the welded hollow sphere diameter (D), the wall thickness of the welded hollow sphere (t), and the height (h) and width (b) of the H-shaped steel member(HSM). The calculation methods of the compressive capacity and axial stiffness of WHS-HSM were proposed. The results show that the failure mode of the joints under axial compressive load is the hollow sphere’s concave failure starting from the flange edge of H-beam. Under axial compressive load, the joints show good ductility. The bearing capacity and initial axial stiffness of the joints are positively related with the wall thickness of the welded hollow sphere (t), the section height(h) and width(b) of HSM, but are negatively correlated with the diameter(D) of the welded hollow sphere. The formulas for calculating the compressive bearing capacity and initial axial stiffness proposed in this paper have high accuracy.

Synthesis and characterization of Fe-doped TiO2 hollow nanospheres prepared by carbon sphere as hard template

Fe-doped TiO2 hollow nanospheres (THs-Fe) with various Fe-dopant concentrations (0.25, 0.50, 0.75 and 1.00 mol%) were prepared using carbon spheres as templates. After calcination, the obtained hollow structure TiO2 were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), energy-dispersive X-ray spectroscopy (EDS) and ultraviolet-visible spectroscopy (UV-Vis). The analysis results revealed that the crystallite size and crystallinity of the samples decreased with increasing Fe content. Morphology and particle size were investigated by electron microscopic techniques and the results showed that dopant concentrations had a significant influence on average particle size. The average diameter of hollow spheres decreased from 146.92 to 61.57 nm when Fe-content increased from 0.25 to 1.00 mol%. The UV-Vis absorption spectra exhibited that the absorption edge of THs-Fe was shifted toward the visible light region with increased Fe content. The energy gap (Eg) was decreased from 2.85 to 1.84 eV when the dopant content increased from 0.25 to 1.00 mol%.

Dynamic responses and energy absorption of hollow sphere structure subjected to blast loading

Closed-cell and open-cell hollow spheres were designed to develop lightweight cellular structures with excellent blast resistance, and the mechanical response of the hollow sphere structure (HSS) under blast loading was investigated numerically using ANSYS®/LS-DYNA®17.0. In this paper, the blast wave pressure decay rate was served as the main index of blast resistance while areal specific energy absorption and frame deformation were used as auxiliary indexes. The results indicated that the weight of HSS was reduced by 37.7%–69.8% compared to solid structures with the same physical size, and the blast resistance of HSS was significantly affected by the hollow sphere diameter and wall thickness, frame length and width, opening size and opening density. Closed-cell HSS with smaller hollow sphere diameters and thicker wall, or smaller frame lengths and widths would achieve the optimal blast resistance. Meanwhile, the blast resistance of HSS could be improved by adopting a smaller opening size, but the effect of opening density did not follow any rule, which was affected by the number and position of openings. Comprehensively, the blast resistance of HSS was enhanced when there was opening only at the face blast surface rather than at both the face blast surface and back blast surface.

Effect of Co substitution and magnetic field on the morphologies and magnetic properties of CeO2 nanoparticles

Abstract Pure and Co-doped CeO2 nanoparticles were synthesized successfully by the solvothermal method. The effect of Co substitution and external magnetic field on the morphologies and magnetic properties of nanoparticles was investigated. Results showed that synthesized Co-doped CeO2 had the face-centered cubic structure and no other impurities existed in the samples with the increase of Co concentration from 5 to 75 wt%. The increasing Co concentration made the morphologies of Co-doped CeO2 nanoparticles vary from the hollow sphere, solid sphere to rod-like shape. The applied external magnetic field of 5T decreased the nanoparticle size effectively including the diameter of hollow sphere with low Co concentration and rod-like particles with high Co concentration. Moreover, the wall thickness of hollow sphere particles was also decreased from 35 nm to 18 nm for pure CeO2. The Co-doped CeO2 nanoparticles showed the weak ferromagnetic behavior. With the increase of Co concentration, the saturation magnetization (Ms) value increased first and then decreased. The Co-doped CeO2 with 30 wt% showed the highest value of 3.65 × 10−2 emu/g (Ms). The Ms value of Co-doped CeO2 prepared in 5T showed an increasing trend with the Co concentration. The highest value (Ms) reached 4.21 × 10−2 emu/g for doped CeO2 with 75 wt% Co.

The Processing and Structure of Steel Matrix Syntactic Foams Prepared by Infiltration Casting

Metal matrix syntactic foams are consisting of metal matrix and hollow spheres in closely or randomly packed, which own multifunctional properties with lightweight, damping, heat insulation, energy absorption and have a vast application prospect. Steel matrix can extend the potential of syntactic foams as a materials class to several new fields of application. In this paper, the hollow alumina spheres were introduced into the steel matrix by infiltration casting, the minimum diameter of hollow spheres for infiltration is analyzed in theory, the steel matrix syntactic foams were successfully prepared, which contain two different sphere types with average diameter sizes 3.97mm and 4.72mm, and the average densities of syntactic foams were calculated to be 4.39 (spheres occupy 43.7% of the volume) and 3.74 g/cm3 (spheres occupy 52.1% of the volume), respectively. The microstructure characteristics of the steel matrix syntactic foam were analyzed by means of scanning electron microscopy and energy spectrum.

Ultimate tensile and compressive performances of welded hollow spherical joints with H-beam

Welded hollow spherical joints with H-beam are a new type of spatial grid structural joints. Experiments and numerical simulation were conducted to investigate the axial tensile and axial compressive performances of the welded hollow spherical joints with H-beam. The influences of material strength, size of joint, and stiffening rib on the mechanical properties, were analyzed. The formulas were proposed to calculate the bearing capacity under axial tension and compression. The major conclusions are as follows: (1) Welded hollow spherical joints with H-beam developed strength fracture under axial tensile load, and hollow spheres developed buckling failure under axial compressive load. The failure mode was related to the strength of the material. (2) Proper arrangement of stiffening ribs can increase bearing capacity of welded hollow spherical joints with H-beam. The improvement coefficients were 1.1 under axial tension and 1.4 under axial compression. (3) The compression bearing capacity of welded hollow spherical joints with H-beam increased with the increase in height and flange width of H-beam, as well as wall thickness of the hollow spheres, but it decreased with the increase in diameter of hollow spheres. (4) The formula used to calculate tensile bearing capacity of welded hollow spherical joints with H-beam was proposed according to the punching shear model. (5) The design formula of compressive bearing capacity of welded hollow spherical joint with H-beam was obtained through the linear regression of abundant numerical simulation data.

Size control of aromatic polyamide hollow spheres prepared by reaction-induced phase separation

Size control of the poly (1,4-phenylene-5-hydroxyisophthalamide) hollow spheres was examined by tuning the polymerization condition, focusing on concentration, temperature and solvent. Higher concentration lowered the diameter owing to the higher degree of super-saturation for nucleation. Temperature drop during the polymerization just before the nucleation was so effective to make the diameter smaller. Moreover, the diameter was susceptive to the solubility of oligomers in the solvent, and higher content of liquid paraffin in the aromatic solvent lowered the solubility, resulting in the decrease in the diameter. Based on these results, the combination of the temperature drop and the solvent effect was the most desirable to prepare the smallest hollow spheres, and the diameter of hollow spheres could be controlled from 4.4 to 0.7 μm.

Facile Synthesis and High Photocatalytic Degradation Performance of ZnO-SnO2 Hollow Spheres.

ZnO-SnO2 hollow spheres were successfully synthesized through a hydrothermal method-combined carbon sphere template. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FT-IR). The average diameter of hollow spheres is about 150 nm. The photocatalytic activity of the as-prepared samples was investigated by photodegrading Rhodamine B. The results indicated that the photocatalytic activities of ZnO-SnO2 hollow spheres are higher than ZnO hollow spheres. The degradation efficiency of the hollow spheres could reach 99.85% within 40 min, while the ZnO hollow spheres need 50 min.

Novel inkjet droplet method generating monodisperse hollow metal oxide micro-spheres

A novel method to synthesize monodisperse hollow TiO2, SnO2 and ZnO microspheres was developed. Water droplets generated from an inkjet nozzle contain clusters of polystyrene latex (PSL) particles covered with metal oxide nanoparticles were continuously dried up forming PSL clusters decorated with metal oxide nanoparticles. By heating the clusters up to 400°C, the PSL particles are evaporated forming hollow spheres. Monodisperse hollow TiO2, SnO2 and ZnO spheres in the size range of 5.1–8.6μm were consequently generated with a narrow particle size distribution. And the hollow TiO2, SnO2 and ZnO spheres have 41.0nm, 30.0nm, and 85.3nm sized pores, respectively. The method enables us to have simpler and faster process to generate hollow TiO2, SnO2 and ZnO spheres and to control the diameter of hollow spheres easily by adjusting waveform applied to a nozzle compared to other processes. A potential applicability to photoelectrochemical cells was demonstrated for the prepared hollow TiO2 grown a Si substrate.

Synthesis and Quasi-Static Compressive Properties of Mg-AZ91D-Al₂O₃ Syntactic Foams.

Magnesium alloys have considerably lower density than the aluminum alloy matrices that are typically used in syntactic foams, allowing for greater specific energy absorption. Despite the potential advantages, few studies have reported the properties of magnesium alloy matrix syntactic foams. In this work, Al2O3 hollow particles of three different size ranges, 0.106–0.212 mm, 0.212–0.425 mm, and 0.425–0.500 mm were encapsulated in Mg-AZ91D by a sub-atmospheric pressure infiltration technique. It is shown that the peak strength, plateau strength and toughness of the foam increases with increasing hollow sphere wall thickness to diameter (t/D) ratio. Since t/D was found to increase with decreasing hollow sphere diameter, the foams produced with smaller spheres showed improved performance—specifically, higher energy absorption per unit weight. These foams show better performance than other metallic foams on a specific property basis.

Magnetic properties of Fe3O4 nano-hollow spheres

We prepared magnetite nano-hollow spheres with diameter 100–725nm using solvothermal method. We studied the magnetic domain structures of the spheres and found them to vary from single domain for smaller diameter to multi-domain structure for the spheres of larger diameter. We also reported the frequency dependence of their magnetic properties and interestingly, found a systematic power law variation in coercivity and hysteresis loss with frequency, magnetic field strength and also with hollow sphere diameter. The results clearly represent that the domain wall width or the number of domains depends not only on the sphere diameter but also on the applied field frequency.

Control of Particle Size of Hollow Silica-alumina Composite Spheres and Their Activity for Hydrolytic Dehydrogenation of Ammonia Borane

The influence of particle size of hollow silica-alumina composite spheres on their activity for hydrolytic dehydrogenation of ammonia borane (NH3BH3) was investigated. A silica-alumina composite shell was coated onto polystyrene (PS) template particles, before the removal of PS template particle by calcination. The diameter of the PS template particles decreased with an increase in the amount of poly (vinyl pyrrolidone) and the centrifugation speed, and the diameter of the obtained PS template particles was controlled between 150 and 400 nm. Hollow silica-alumina composite spheres with diameters of 180, 230, and 430 nm were prepared using these PS template particles; the shell thickness was controlled 15 nm by adjusting the amount of PS suspension and coating time. The hydrolytic dehydrogenation of NH3BH3 evolved 9.5, 9.0, and 7.0 mL hydrogen in the presence of hollow spheres with diameters of 180, 230, and 430 nm, respectively; the molar ratios of the generated hydrogen to the initial NH3BH3 in the presence of the hollow spheres were 2.5, 2.3, and 1.8, respectively. The results indicate that the activity increases with a decrease in the diameter of hollow spheres.

Effect of hollow sphere size and size distribution on the quasi-static and high strain rate compressive properties of Al-A380–Al2O3 syntactic foams

Metal matrix syntactic foams are promising materials for energy absorption; however, few studies have examined the effects of hollow sphere dimensions and foam microstructure on the quasi-static and high strain rate properties of the resulting foam. Aluminum alloy A380 syntactic foams containing Al2O3 hollow spheres sorted by size and size range were synthesized by a sub-atmospheric pressure infiltration technique. The resulting samples were tested in compression at strain rates ranging from 10−3 s−1 using a conventional load frame to 1720 s−1 using a Split Hopkinson Pressure-bar test apparatus. It is shown that the quasi-static compressive stress–strain curves exhibit distinct deformation events corresponding to initial failure of the foam at the critical resolved shear stress and subsequent failures and densification events until the foam is deformed to full density. The peak strength, plateau strength, and toughness of the foam increases with increasing hollow sphere wall thickness to diameter (t/D) ratio. Since t/D was found to increase with decreasing hollow sphere diameter, the foams produced with smaller spheres showed improved performance. The compressive properties did not show measurable strain rate dependence.

Production and modification of hollow powders in plasma under controlled pressure

Conducting plasma processes under high or low pressure is an efficient way to affect the heat, mass and momentum exchange in a two-phase flow and this technique is widely used in such well-developed technologies as low-pressure plasma spraying (LPPS) and high pressure plasma-chemical processes. In addition operating pressure is a key parameter in novel plasma process for modification of hollow powders properties. Plasma processing of porous ceramic powders is an effective method of producing hollow spheres (HOSP) with predefined properties. Regardless the method hollow powders were produced their geometric and structural properties can be adjusted by re-melting in plasma of certain pressure: low pressure processing will expand hollow spheres and high pressure – contract it. Regulating the outer diameter of hollow sphere allows adjusting its shell thickness, apparent density, gas pressure in the cavity etc. Preliminary experiments with zirconia hollow powders demonstrated good agreement with theoretical estimations of HOSP properties. The same technique can be used for adjusting properties of ceramic hollow powders produced by different methods, including cost effective fly-ash particles (cenospheres).

Building on size-controllable hollow nanospheres with superparamagnetism derived from solid Fe3O4 nanospheres: preparation, characterization and application for lipase immobilization

Monodisperse porous hollow nanospheres with superparamagnetism were prepared via a hydrothermal reaction based on solid Fe3O4 nanospheres. By investigating the effect of carbon precursors, the kinds and amounts of structure-directing agents and the reaction time on the formation of hollow spheres, it was proposed that the main formation mechanism of hollow spheres is a gas-bubble-assisted Ostwald ripening process. Additionally, it is found that the diameter of hollow spheres and the size of the hollow core could be adjusted by changing the above factors. The resulting hollow spheres were characterized by means of Brunauer–Emmett–Teller (BET) gas sorptometry, transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier-transform infrared spectrophotometer (FT-IR), thermogravimetric analysis (TG) and vibrating sample magnetometry (VSM). It is verified that the resulting hollow spheres are porous and have high saturation magnetization. For further application, these hollow spheres were utilized to immobilize Candida rugosa lipase (CRL) and they showed excellent immobilization capacities.