Carbonate-salt-based composite materials for medium- and high-temperature thermal energy storage

This paper discusses composite materials based on inorganic salts for medium- and high-temperature thermal energy storage application. The composites consist of a phase change material （PCM）, a ceramic material, and a high thermal conductivity material. The ceramic material forms a microstructural skeleton for encapsulation of the PCM and structural stability of the composites; the high thermal conductivity material enhances the overall thermal conductivity of the composites. Using a eutectic salt of lithium and sodium carbonates as the PCM, magnesium oxide as the ceramic skeleton, and either graphite flakes or carbon nanotubes as the thermal conductivity enhancer, we produced composites with good physical and chemical stability and high thermal conductivity. We found that the wettability of the molten salt on the ceramic and carbon materials significantly affects the microstructure of the composites.     

Effect of mixing structure on the hygroscopic behavior of ultrafine ammonium sulfate particles mixed with succinic acid and levoglucosan

Understanding the interactions between water and atmospheric aerosols is critical for estimating their impact on the radiation budget and cloud formation. The hygroscopic behavior of ultrafine(100 nm)ammonium sulfate particles internally mixed with either succinic acid〔slightly soluble) or levoglucosan(soluble) in different mixing structures(core-shell vs. well-mixed) were measured using a hygroscopicity tandem differential mobility analyzer(HTDMA). During the hydration process(6-92% relative humidity(RH)), the size of core-shell particles(ammonium sulfate and succinic acid) remained unchanged until a s|ow increase in particle size occurred at 79% RH; however, an abrupt increase in size(i.e., a clear deliquescence) was observed at ~72% RH for well-mixed particles with a similar volume fraction to the core-shell particles(80:20 by volume). This increase might occur because the shell hindered the complete dissolution of the core-shell particles below 92% RH. The onset RH value was lower for the ammonium sulfate/levoglucosan core-shell particles than the ammonium sulfate/succinic acid core-shell particles due to levoglucosan's higher solubility relative to succinic acid. The growth factor(GF) of the core-shell particles was lower than that of the well-mixed particles, while the GF of the ammonium sulfate/levoglucosan particles was higher than that of ammonium sulfate/succinic acid particles with the same volume fractions. As the volume fraction of the organic species increased, the GF decreased. The data suggest that the mixing structure is also important when determining hygroscopic behavior of the mixed particles.     

Novel synthesis with an atomized microemulsion technique and characterization of nano-calcium carbonate （CaCO3）/poly（methyl methacrylate） core-shell nanoparticles

The synthesis of hard-core/soft-shell calcium carbonate （CaCO3）/poly（methyl methacrylate） （PMMA） hybrid structured nanoparticles （〈100nm） by an atomized microemulsion polymerization process is reported. The polymer chains were anchored onto the surface of nano-CaCO3 through use of a cou- pling agent, triethoxyvinyl silane （TEVS）. Ammonium persulfate （APS）, sodium dodecyl sulfate （SDS） and n-pentanol were used as the initiator, surfactant and cosurfactant, respectively. The polymeriza- tion mechanism of the core-shell latex particles is discussed. The encapsulation of nano-CaCO3 by PMMA was confirmed using a transmission electron microscope （TEM）. The grafting percentage of the core-shell particles was investigated by thermogravimetric analysis （TGA）. The nano-CaCO3/PMMA core-shell par- ticles were characterized by Fourier transform infrared （FTIR） spectroscopy and differential scanning calorimetry （DSC）. The FTIR results revealed the existence of a strong interaction at the interface of the nano-CaCO3 particle and the PMMA, which implies that the polymer chains were successfully grafted onto the surface of the nano-CaCO3 particles through the link of the coupling agent, In addition, the TGA and DSC results indicated an enhancement of the thermal stability of the core-shell materials compared with that of the pure nano-PMMA, The nano-CaCO3/PMMA particles were blended into a polypropylene （PP） matrix by melt processing. It can also be observed using scanning electron microscopy （SEM） that the PMMA chains grafted onto the CaCO3 nanoparticles interfere with the aggregation of CaCO3 in the polymer matrix （PP matrix） and thus improve the compatibility of the CaCO3 nanoparticles with the PP matrix.     

Facile aqueous synthesis and thermal insulating properties of low-density glass/TiO2 core/shell composite hollow spheres

Anatase TiO2 shells assembled on hollow glass microspheres(HGM)with tunable morphologies were successfully prepared through a controllable chemical precipitation method with urea as the precipitator. Thus,glass/TiO2 core/shell composite hollow spheres with low particle density(0.40 g/cm3)were fabricated.The phase structures,morphologies,particle sizes,shell thicknesses,and chemical compositions of the composite microspheres were characterized by X-ray diffraction(XRD),scanning electron microscopy (SEM),and energy dispersive X-ray spectroscopy(EDS).The morphology of the TiO2 shell can be tailored by properly monitoring the reaction system component and parameters.The probable growth mechanism and fabrication process of the core/shell products involving the nucleation and oriented growth of TiO2 nanocrystals on hollow glass microspheres was proposed.A low infrared radiation study revealed that the radiation properties of the products are greatly influenced by the unique product shell structures. A thermal conductivity study showed that the TiO2/HGM possess low thermal conductivity that is similar to that of the pristine HGMs.This work provides an additional strategy to prepare low-density thermal insulating particles with tailored morphologies and properties.     

Synthesis and characterization of magnetic polymer microspheres with a core-shell structure

Non-porous magnetic polymer microspheres with a core-shell structure were prepared by a novel micro-suspension polymerization technique. A stable iron oxide ferrofluid was used to supply the magnetic core, and the polymeric shell was made of glycidyl methacrylate （GMA monomer） and ethylene dimethacrylate （cross-linker）. In the preparation, polyvinyl alcohol was used as the stabilizer, and a lauryl alcohol mixture as the dispersant. The influence of various conditions such as aqueous phase volume, GMA and initiator amounts, reaction time and stirring speed on the character of the microspheres was investigated. The magnetic microspheres were then characterized briefly. The results indicate that the microspheres with active epoxy groups had a narrow size distribution range from 1 to 10 μm with a volume-weighted mean diameter of 4.5 μm. The saturation magnetization reached 19.9 emu/g with little coercivity and remanence.     

Self-assembly with varying hydrophobic centers:Synthesis of red blood cell-like basic magnesium carbonate microspheres

Basic magnesium carbonate microspheres with a red blood cell(RBC)-like appearance and diameters of ~3μm were synthesized by amphiphilic molecule-participated self-assembly under hydrothermal conditions.In the self-assembly,sodium dodecyl benzene sulfonate served as a template for the formation of Mg(OH)_2 spherical micelles and also as a reactant precursor that releases CO_2 to react with Mg(OH)_2.The growth of the microspheres is driven by the continuous generation of new hydrophobic centers because of the consumption of hydrophilic poles(—SO_3~-).The surfactant-directed self-assembly can be applied to the synthesis of other carbonate or metallic oxide self-assemblies,indicating that it is a universal self-assembly method for amphiphilic molecules.     

Highly dispersed Mn_2O_3 microspheres:Facile solvothermal synthesis and their application as Li-ion battery anodes

Nanostructured transition metal oxides are promising alternative anodes for lithium ion batteries.Li-ion storage performance is expected to improve if high packing density energy particles are available.Herein,Mn_2O_3 microspheres with a ca.18 μm diameter and a tapped density of 1.33 g/cm~3 were synthesized by a facile solvothermal-thermal coversion route.Spherical MnCO_3 precursors were obtained through solvothermal treatment and they decomposed and converted into Mn_2O_3 microspheres at an annealing temperature of 700 C.The Mn_2O_3 microspheres consisted of Mn_2O_3 nanoparticles with an average 40 nm diameter.These porous Mn_2O_3 microspheres allow good electrolyte penetration and provide an ion buffer reservoir to ensure a constant electrolyte supply.The Mn_2O_3 microspheres have reversible capacities of590 and 320 mAh/g at 50 and 400 mA/g,respectively.We thus report an efficient route for the fabrication of energy particles for advanced energy storage.     

Micromechanical properties of poly(N-isopropylacrylamide)hydrogel microspheres determined using a simple method

Temperature-responsive poly(N-isopropylacrylamide)(PNIPAM) hydrogel microspheres have attracted extensive attention because of their promising diverse biomedical applications.A quantitative understanding of the micromechanical properties of these microspheres is essential for their practical application.Here,we report a simple method for the characterization of the elastic properties of PNIPAM hydrogel microspheres.The results show that PNIPAM hydrogel microspheres exhibit elastic deformation and the obtained force-deformation experimental data fits the Hertz theory well.The moduli of elasticity of the PNIPAM hydrogel microspheres prepared under different conditions were systematically investigated in this work for the first time.The PNIPAM hydrogel microsphere composition significantly affects their micromechanical properties and their temperature sensitivity behavior.PNIPAM hydrogel microspheres with a larger equilibrium volume change have a lower modulus of elasticity.The modulus of elasticity of the PNIPAM hydrogel microspheres at body temperature(37 ℃,above the lower critical solution temperature(LCST) of PNIPAM) is much higher than that at room temperature(25 ℃,below the LCST of PNIPAM) because of thermo-induced volume shrinkage and an increase in stiffness.These results provide valuable guidance for the design of smart materials for practical biomedical applications.Moreover,the simple microcompression method presented here also provides a versatile way to investigate the micromechanical properties of microscopic biomedical materials.     

Audio-frequency heating of particulate magnetic systems

This paper presents theoretical and experimental studies on the magnetodynamics and energy dissipation in suspensions of small ferromagnetic particles with magnetic hysteresis and mechanical mobility in an AC magnetic field. Energy absorption by particles suspended in a solid, liquid or gas environment and subjected to high frequency magnetic fields is of great interest for cancer treatment by hyperthermia, chemical technology, biotechnology and smart materials science. Sub-micron needle-like γ-Fe2O3 particles dispersed in liquid were subjected in this study to a 430 Hz magnetic field with an intensity of up to 10^5 A/m. Dynamic magnetization loops were measured in parallel to the energy dissipated in the samples. Combined magnetomechanical dynamics of particle dispersions was simulated by using a chain-of-spheres model allowing for incoherent magnetic field reversal. In liquid dispersions, within the kilohertz frequency range, the mechanical mobility of particles does not interfere with their hysteretic magnetic reversal that makes heat release comparable to that observed with solids; for instance, in the present study using γ-Fe2O3 particles in liquid subjected to 10^4 Hz field exhibited heat release rates from 250 up to 600W oer 1 cm^3 of the dry oarticle content.     

Synthesis and characterization of PMMA/Al2O3 composite particles by in situ emulsion polymerization

In order to improve its dispersibility, superfine alumina （A1203） was encapsulated with poly（methyl methacrylate） （PMMA） by in situ emulsion polymerization. It was found that only when the concentration of sodium dodecyl sulfate （SDS） was much higher than its critical micelle concentration, could PMMA/Al2O3 composite particles with high percentage of grafting （PG） be prepared. The same results were obtained between the experimental and stoichiometric amounts of tris（dodecylbenzenesulfonate） isopropoxide （NDZ）, indicating that single-molecule-layer adsorption had taken place between NDZ and Al2O3. Analysis using FTIR, TEM and XPS showed that PMMA/Al2O3 composite particles with core-shell structure had been successfully synthesized by in situ emulsion polymerization. Compared to Al2O3, thermal stability and dispersibility of the composite particles showed marked improvement.     

Effect of system parameters on the size distributions of hollow nickel microspheres produced by an ultrasound-aided electrical discharge machining process

Ultrasound-aided electric discharge machining（EDM） is an emerging technology for producing hollow nickel microspheres.This technology combines traditional EDM with the cavitation and vibration effects of ultrasound to produce hollow microspheres.In this paper,ultrasound-aided EDM was carried out in a kerosene medium（the working solution）.The effects of various parameters on the sizes of microspheres were investigated using scanning electronic microscopy（SEM）.Smileview software was used to measure the sizes of the microspheres.Originpro software was used for statistical analysis to determine the size distributions of the microspheres.To study the effects of the system parameters on the sizes of the microspheres,we first investigated the necessity of using an ultrasonic wave with EDM.After comparing the experimental results with and without the ultrasonic field,we found that ultrasound-induced cavitation and vibration effects reduced the diameters of the microspheres.We then studied the effects of several electrical parameters,including the arc current,pulse width,and gap voltage,on the sizes of the microspheres at an ultrasound frequency of 40 kHz.Smaller microspheres could be obtained by lowering the arc current,pulse width,and gap voltage.     

Mesoporous composite of LiFePO4 and carbon microspheres as positive-electrode materials for lithium-ion batteries

Mesoporous LiFePO4/C microspheres consisting of LiFePO4 nanoparticles are successfully fabricated by an eco-friendly hydrothermal approach combined with high-temperature calcinations using cost-effective LiOH and Fe3＋ salts as raw materials.In this strategy,pure mesoporous LiFePO4 microspheres,which are composed of LiFePO4 nanoparticles,were uniformly coated with carbon（1.5nm）.Benefiting from this unique architecture,these mesoporous LiFePO4/C microspheres can be closely packed,having high tap density.The initial discharge capacity of LiFePO4/C microspheres as positive-electrode materials for lithium-ion batteries could reach 165.3 mAh/g at 0.1 C rate,which is notably close to the theoretical capacity of LiFePO4 due to the large BET surface area,which provides for a large electrochemically available surface for the active material and electrolyte.The material also exhibits high rate capability（100 mAh/g at 8 C） and good cycling stability（capacity retention of 92.2%after 400 cycles at 8 C rate）.     

Size effect of lattice material and minimum weight design

The size effects of microstructure of lattice materials on structural analysis and minimum weight design are studied with extented multiscale finite element method（EMsFEM） in the paper. With the same volume of base material and configuration, the structural displacement and maximum axial stress of micro-rod of lattice structures with different sizes of microstructure are analyzed and compared.It is pointed out that different from the traditional mathematical homogenization method, EMsFEM is suitable for analyzing the structures which is constituted with lattice materials and composed of quantities of finite-sized micro-rods.The minimum weight design of structures composed of lattice material is studied with downscaling calculation of EMsFEM under stress constraints of micro-rods. The optimal design results show that the weight of the structure increases with the decrease of the size of basic sub-unit cells. The paper presents a new approach for analysis and optimization of lattice materials in complex engineering constructions.     

Direct transformation of FGD gypsum to calcium sulfate hemihydrate whiskers:Preparation,simulations,and process analysis

Calcium sulfate hemihydrate（CSH） whiskers were synthesized by phase transition in CaCl₂ solution under atmospheric pressure.Analytical-grade calcium sulfate dihydrate（AR CSD） was used as the raw material for the synthesis of CSH whiskers,according to orthogonal experiments.The effects of reaction temperature,AR CSD content,H₂SO₄ content,and reaction time were investigated,and the crystallization conditions were optimized.The as-prepared CSH whiskers displayed a regular morphology and a highly uniform size,with an aspect ratio of 105.A simulation system was also established by blending various sulfates with AR CSD,to evaluate the effects of impurities in flue gas desulfurization（FGD） gypsum.The main aim was to prepare CSH whiskers directly from FGD gypsum,without any purification,using the optimized conditions.This is a facile potential alternative process for large-scale production of CSH whiskers using abundant FGD gypsum as source materials.     

Hierarchical structure observation and nanoindentation size effect characterization for a limnetic shell

In the present research, hierarchical structure observation and mechanical property characterization for a type of biomaterial are carried out. The investigated biomaterial is Hyriopsis cumingii, a typical limnetic shell, which consists of two different structural layers, a prismatic "pillar"structure and a nacreous "brick and mortar" structure. The prismatic layer looks like a "pillar forest" with variationsection pillars sized on the order of several tens of microns.The nacreous material looks like a "brick wall" with bricks sized on the order of several microns. Both pillars and bricks are composed of nanoparticles. The mechanical properties of the hierarchical biomaterial are measured by using the nanoindentation test. Hardness and modulus are measured for both the nacre layer and the prismatic layer, respectively.The nanoindentation size effects for the hierarchical structural materials are investigated experimentally. The results show that the prismatic nanostructured material has a higher stiffness and hardness than the nacre nanostructured material.In addition, the nanoindentation size effects for the hierarchical structural materials are described theoretically, by using the trans-scale mechanics theory considering both strain gradient effect and the surface/interface effect. The modeling results are consistent with experimental ones.     

Preparation of slightly crosslinked monodisperse poly(maleic anhydride-cyclohexyl vinyl ether-divinylbenzene)functional microspheres with anhydride groups via precipitation polymerization

Slightly crosslinked monodisperse poly（maleic anhydride-cyclohexyl vinyl ether-divinylbenzene）（MA-CHVE-DVB） microspheres were prepared via precipitation polymerization while using 2,2-azobisisobutyronitrile as an initiator in a mixture of methyl ethyl ketone and n-heptane without any stabilizer.The number-average diameter of the resultant poly（MA-CHVE-DVB） microspheres ranged from 0.478 to 1.386 μm with a polydispersity index of 1.00 to 1.02 that depended on the feed ratios of the MA/CHVE/DVB monomers.The introduction of one electron donor monomer cyclohexyl vinyl ether strongly affected the yield,size,and morphology of these slightly crosslinked microspheres.Quinolinetype chelating resins were obtained after combining the poly（MA-CHVE-DVB） with 8-hydroxyquinoline;the adsorption properties of these materials were measured through their ability to remove Cu²⁺ ions from water.The poly（MA-CHVE-DVB） microspheres with low degrees of crosslinldng provided more effective functional groups and therefore better ion removal capabilities.These slightly crosslinked microspheres may have applications in water treatment as well as in sensing and drug delivery.     

Effects of high order deformations on the strength of planar lattice materials

Lattice materials have been attractive over the last decade for use as load-carrying structures, energy absorbing elements and heat exchanging structures because of their excellent mechanical properties and multifunctional characters. However, the quantitative analysis accounting for high order deformations upon the collapse of lattice materials, which is important for their applications, has not been reported. An analytical investigation of yield surfaces with respect to the high order deformations was carried out for two typical planar lattice materials： triangular and Kagome lattices separately. The analytical results were validated by the finite element method （FEM） simulations. It was found that the effect of high order deformation on the yield strength increases with the relative density. The bending effect of the Kagome lattice is more obvious than that of the triangular one with the same relative density and stress state. The yield strength of the Kagome lattice calculated by neglecting the bending effect overestimates the result by more than 10% when the relative density is higher than about 11.1%, which may not be ignored in engineering applications. The yielding surfaces of the two lattice materials demonstrated in the paper also confirm the analytical results.     

Preparation and functionalization of mesoporous silica spheres as packing materials for HPLC

This paper presents the integrated results of a series of new methods for preparing mesoporous silica spheres as high-performance liquid chromatography （HPLC） packing materials. The separation performance of the mesoporous spheres materials has also been determined. Micrometer- sized silica spheres with uniform spherical morphologies and ordered mesostructures were first successfully synthesized by the method employing a water-soluble polymer-assisted assembly. Then the templates for getting ordered mesoporous materials with high-density silanol groups were removed by using hydrothermal oxidation. Finally the silica spheres were functionalized with C8 alkyl groups by surface modification under hydrothermal conditions. The resultant functionalized silica spheres were demonstrated to be excellent oacking materials for HPLC.     

SYNTHESIS OF MESOPOROUS TiOz MATERIALS WITH HIGH SPECIFIC AREA USING INORGANIC ACIDS AS CATALYSTS

This paper presents a synthesis process for preparing mesoporous titanium dioxide materials in the absence of any templates and using inorganic acids as catalysts. Tetrabutyl titanate was used as the precursor at ambient temperature, and four different inorganic acids, i.e., hydrochloric, nitric, sulfuric and phosphoric, were used as catalysts.The as-prepared mesoporous TiO2 materials were characterized by SEM, XRD and nitrogen adsorption/desorption measurements, The influences of different inorganic acids on the properties of TiO2 were discussed and compared in details. Experiments showed that the inorganic acids have significant effects on the surface area, pore volume, pore size,and pore size distribution of the products. The mesoporous TiO2 materials catalyzed by phosphoric acid exhibited the largest specific surface area and largest pore volume with narrow pore size distribution. Vacuum and infrared drying methods tested in the process were found to have subtle impact on the structure of the TiO2 materials prepared,     

Effect of chemical composition of PM2.5 on visibility in Guangzhou,China, 2007 spring

The object of this study was to investigate the correlation of visibility with chemical composition of PM2.5 in Guangzhou. In April 2007, 28 PM2.5 samples were collected daily at the monitoring station of the South China Institute of Environmental Sciences （SCIES）, in urban Guangzhou. Water-soluble ionic species （CI^-, NO3^-, SO4^2-, NH4^＋, K^＋, Na^＋, Ca^2＋, and Mg^2＋） and carbonaceous contents （OC and EC） of the PM2.5 samples were determined to characterize their impact on visibility impairment. The results showed that sulfate was the dominant species that affected both light scattering and visibility. The average percentage contributions of the visibility-degrading species to light scattering coefficient were 40% for sulfate, 16% for nitrate, 22% for organics, and 22% for elemental carbon. Because of its foremost effect on visibility, sulfate reduction in PM2.5 would effectively improve the visibility of Guangzhou.