Shell Porosity Research Articles

Influence of Granule Porosity during Fluidized Bed Spray Granulation

Fluidized bed spray granulation is an important process for the transformation of liquids into solid materials. Especially product properties like final particle size and structure of the granules are important. These properties are closely related to the selected process parameters such as temperature and spraying rate. By knowing the relationship between the thermal process conditions and resulting particle structure, the final product can be designed according to the wishes of the consumers. In the presented work, a correlation between the thermal process conditions and the achieved shell porosity, which is relevant for the particle structure, is revealed. Therefore two experimental series with different materials (non-porous glass particles and porous alumina) were performed in a lab-scale fluidized bed spray granulator. The lab-plant allows the precise measurement of the inlet and outlet temperatures and moisture contents of the gas. All process parameters were kept constant except the inlet gas temperature and the spraying rate. Although the amount of initial material as well as the amount of injected solution was the same for all experiments, the final particle size distribution and the structure of the formed shell were clearly different. The obtained experimental results were compared with a process model including a new expression for the growth kinetics, which takes into account an acceleration of the growth velocity due to the formation of a porous structure. The used model also considers the separation of the fluidized bed into two different zones, namely the spraying zone and the drying zone. With the given initial process conditions, the model calculates the time evolution of the particle size distribution, the theoretical outlet temperature and the moisture content of the gas. The introduction of the shell porosity into the growth kinetics reduces the underestimation of the particle size in the model, which occurs if the formed layer on the particle surface is assumed to be compact.

Effects of surface states over core-shell Ni@SiO2 catalysts on catalytic partial oxidation of methane to synthesis gas

In the present work, core-shell Ni@SiO2 catalysts were investigated in order to evaluate the relevance of catalytic activity and surface states of Ni core as well as Ni nanoparticles size to catalytic partial oxidation of methane (POM). The catalysts were characterized by N2 adsorption, H2-TPR, XRD, TEM and XPS techniques. The catalytic performance of the core-shell catalysts was found to be dependent on the surface states of catalyst, which influenced the formation of products. It was considered that carbon dioxide formed on the oxidized nickel sites (NiO) and carbon monoxide produced on the reduced sites (Ni). The surface states of active metal in the dynamic were influenced both by the size of Ni core and the porosity of silica shell. However, the catalytic activity would be debased when the size of Ni core was under a certain extent, which can be ascribed to the fact the carbon deposition increased with the increasing content of NiO. The effects of surface states of Ni@SiO2 catalyst on the catalytic performance were discussed and the reaction pathway over Ni core encapsulated inside silica shell was proposed.

Polymeric nanoparticle engineering: from temperature-responsive polymer mesoglobules to gene delivery systems.

A novel approach for the preparation of nano- and microcapsules in aqueous solutions by using thermoresponsive polymer (TRP) templates (mesoglobules) is described. The method comprised three steps: formation of mesoglobules, coating the templates by seeded radical copolymerization, followed by core dissolution and core removal upon cooling. When mesoglobule entraps biomacromolecules during the process of their formation, it makes it possible to load a controlled amount of bioactive compounds without covalent attachment. Special attention is paid to the mesoglobule dissolution upon cooling, as well as their loading efficiency. Details on the outer shell formation and the possibilities for targeting ligands incorporation and control of the shell porosity are discussed. Finally, the seeded radical copolymerization was used for covering DNA complexes with cationic copolymers bearing TRP blocks. This Review is an attempt to convince researchers of the promising perspectives for using mesoglobules as potential reservoirs, carriers, and transferring agents for biologically active substances.

Genetic and morphometric evidence for parallel evolution of the Globigerinella calida morphotype

Molecular genetic investigations of the highly abundant extant planktonic foraminifera plexus Globigerinella siphonifera/Globigerinella calida have recently shown this group to be the genetically most diverse one within planktonic foraminifera, separating it into 12 distinct genetic types belonging to three main genetic lineages. Independently, several morphological or physiological variants have been described within the group, but the correlation between the high genetic diversity and the phenotypic variability remains unclear. In this study, we combine genetic data with morphometric analyses of shell shape and porosity of genotyped individuals of the different genetic lineages. Our morphometric measurements suggest a differentiation of three morphotypes within the plexus, two of which possess the elongated chambers described as a typical trait of G. calida. These two morphotypes with elongated chambers are associated with two distinct genetic lineages. The G. calida morphology therefore appears to have evolved twice in parallel. Unexpectedly, we show that the two morphotypes with elongated chambers can be separated from each other by characters seen in the lateral view of their shells. This implies that the taxonomy of the extant members of the genus Globigerinella should be revised. A comparison with the original descriptions and type specimens of members of the genus shows that two genetic types of one major lineage correspond to G. calida. The second group with elongated chambers is associated with a recently diverged genetic type and we propose to reinstate the name Globigerinella radians for this distinct form. The remaining nine of the 12 genetic types correspond to the G. siphonifera morphology, and in the absence of evidence for morphological differentiation, they form a paraphyletic morpho-taxon. Our results highlight the prevalence of parallelism in the evolution of shell morphology in planktonic foraminifera even at the lowest level of relatedness represented by genetic types.

Microencapsulation of n-hexadecane phase change material by ethyl cellulose polymer

Microencapsulation of phase change materials (PCMs) is an attractive opportunity for broadening their applications. In this respect, a novel encapsulating polymer, ethyl cellulose (EC) was used to entrap n-hexadecane (HD) PCM by an emulsion-solvent evaporation method. Emulsifiers strongly influenced the size and morphology of the forming EC–HD composite microcapsules, and they also had a great impact on their thermal properties. All of the three emulsifiers were suitable to prepare quasi core–shell microparticles, though the high porosity of shells resulted in serious leakage in composites prepared by Tween 80, and permeability of particles manufactured by poly(vinyl alcohol) (PVA), as can be stated from scanning electron microscopy and differential scanning calorimetry analysis. Interfacial tension measurements and spreading coefficient analysis enabled the prediction of preparation conditions for usable core–shell microcapsules. Volume-weighted mean diameters of the microparticles were 319, 92 and 85 μm formed by Tween 80, PVA and poly(methacrylic acid sodium salt) (PMAA), respectively. A significantly higher HD content and latent heat storage capacity could be achieved using PVA and PMAA than with Tween 80. The thermal cycling test indicated good thermal reliability of microcapsules prepared by PMAA, while the energy-storing capacity of composites prepared by PVA decreased substantially, and a dramatic reduction was found in microparticles using Tween 80.

Co3O4@Mesoporous Silica for Fischer–Tropsch Synthesis: Core–Shell Catalysts with Multiple Core Assembly and Different Pore Diameters of Shell

A series of core–shell cobalt oxide catalysts were prepared by tuning the pore diameter of mesoporous silica shell and the influence of pore dimensions on Fischer–Tropsch synthesis was studied. TEM images of core–shell 20Co3O4@MSN-x catalysts showed an increase in the silica shell porosity with increasing molar ratio of the swelling agent to tetraethyl orthosilicate used during catalyst preparation. As a result of this porosity increase, the dispersion of congregated core Co oxide particles within the shell increased, resulting in multiple core centers. Reference catalysts were synthesized using conventional supports, and the effects of pore dimensions on the activity and hydrocarbon selectivity of the reference and the prepared core–shell catalysts were compared. In the experiments performed, 20Co3O4@MSN-x catalysts showed an increase in their CO conversion and C5+ selectivity with increasing silica shell porosity. Moreover, the prepared core–shell catalysts demonstrated higher selectivity toward C5–C18 hydrocarbon fractions than SBA–15- and SiO2-supported Co oxide catalysts. This could be due to the comparatively lower diffusion limitations and less probability of readsorption of intermediates in the confined space of the mesoporous silica shell. Further, the core–shell catalysts displayed higher stability (100 h on stream) than the reference catalysts, and this was attributed to their small diffusion length and less probability of metal sintering due to a protective silica shell around Co oxide particles.

Enhancement of Porosity of the Ceramic Shell in Investment Casting Process Using Needle Coke and Camphor

Investment casting process has been a widely used process for centuries. It is known for its ability to produce components of complex shapes with dimensional accuracy and excellent surface finish. Investment casting has been used to make manufacture weapons, jewellery and art castings during the ancient civilization and today it is used to manufacture engineering components. In Investment casting wax patterns are made by wax injection and then coating of the wax patterns are done by ceramic slurry, made with silica flour and binder. After dewaxing and firing molten metal is poured in the shell and solidified casting can be achieved. Investment casting can be cast any ferrous and non ferrous metal which is difficult in die casting. Finishing operations are negligible and very thin sections as.75mm can also be cast which is not possible in sand casting but there are many challenges in Investment casting. It is relatively slow process because preparation of ceramic shell consumes a lot of time, permeability of shell is very low which causes gas permeability. Incorporation of chills is very difficult. Among all these challenges gas porosity is main problem because of poor permeability, entrapment of gases due to complex geometry of the shell, reuse of scrap metal. In the present work porosity of the shell can be increase by addition of mixture of Camphor and needle coke. After firing of the shell camphor and needle coke will be burnt leaving pores for the escape of entrapped gases. Mechanical properties of the both shell will be compared with each other.

Controllable preparation and properties of mesoporous silica hollow microspheres inside-loaded Ag nanoparticles

The novel mesoporous silica hollow microspheres inside-loaded Ag nanoparticles (MSMAs) were fabricated through successively assembling Ag nanoparticles (AgNPs) and silica nanoparticles on the polystyrene beads and followed by the calcinations to remove the organics. The dosage of AgNO3, polyvinylpyrrolidone (PVP), tetraethoxysilane (TEOS) and ammonia was investigated to explore the variation in the morphology of the MSMAs such as the AgNP loading amount and the porosity of silica shell. Moreover, the Ag release property and long-term antibacterial activity of as-prepared MSMAs were also studied. The results show that the loading amount of AgNPs can be regulated by controlling the dosage of PVP or AgNO3, while the size of the pore in silica shell is increased with TEOS dosage. Lowering the PVP/AgNO3 mole ratio (>1.5) is favorable to obtain the MSMAs with high Ag loading density. High Ag loading amount as well as large pore size will increase the Ag+ ion release rate, leading to the more efficient diffusion of Ag+ ions from the interior of the silica hollow microsphere to the external medium through the pore channels in the shell. The long-term antibacterial activity is mainly determined by the Ag+ ion release rate, and the highest antibacterial activity can remain at a high level of up to 96% for long periods of six months.

Compressive and thermal characterization of syntactic foams containing hollow silicon carbide particles with porous shell

ABSTRACTSilicon carbide hollow particle (SiCHS) reinforced vinyl ester matrix syntactic foams are prepared and characterized for compressive properties and coefficient of thermal expansion (CTE). Two types of SiCHS were utilized in 60 vol % to prepare syntactic foams. These SiCHS had ratio of inner to outer radius of 0.91 and 0.84 for the thin and thick walled particles. The specific compressive strength values were 33.4 and 38.8 kPa/kg/m3 and the specific compressive modulus values were 0.8 MPa/kg/m3 and 0.6 MPa/kg/m3 for the thin and thick walled SiCHS‐filled syntactic foams, respectively. The shell of the hollow particles contained microporous voids, and the porosity was estimated as 16.6% and 24.8% in the walls of the thin and thick walled particles, respectively. The shell porosity adversely affected the specific compressive strength and the modulus of the syntactic foam. However, the SiCHS‐filled syntactic foams exhibited low CTE values (26.7 and 15.9 × 10−6/°C). These CTE values were 65.1% and 79.3% lower than the CTE of the neat resin. Such properties can be useful for applications where syntactic foams are exposed to high temperatures and dimensional stability is important. A theoretical model is used to estimate the porosity level in the SiC shells and estimate the effective mechanical properties of the porous SiC material that forms the particle shell. Such analysis can help in using the models as predictive tools to estimate the mechanical properties of syntactic foams. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40689.

Composition and structure of the shells of fly ash cenospheres from the combustion of coal of the Kuznetsk Basin

The chemical and phase composition and the structure of the shells of the narrow fractions of nonmagnetic and magnetic unperforated cenospheres in fly ash from the combustion of coal of the Kuznetsk Basin were studied. It was found that the fractions of nonmagnetic cenospheres were characterized by a low Fe2O3 content of 2.6–3.5 wt %, and they consisted of globules with uniform smooth or relief surfaces and shells with different degrees of porosity. The average diameter, thickness, and porosity of the vitrocrystalline shells of cenospheres decreased with increasing the aluminum content of the nonmagnetic fractions; in this case, the concentration of the crystalline phase of quartz as two modifications with different lattice parameters decreased. The narrow fractions of magnetic cenospheres contained 3–21 wt % Fe2O3, and they contained globules with a thick porous shell, on the external surface of which the heterogeneous regions of a ferrospinel phase were detected. The amount of the ferrospinel phase in the magnetic cenospheres increased with the iron content; in this case, an increase in the size of its crystallites and a decrease in the degree of magnesium and aluminum substitution for iron were observed.

α-Fe2O3multi-shelled hollow microspheres for lithium ion battery anodes with superior capacity and charge retention

Multi-shelled α-Fe2O3 hollow microspheres were synthesized using carbonaceous microsphere sacrificial templates and utilized for high capacity anode materials in lithium ion batteries (LIBs). Structural aspects including the shell thickness, number of internal multi-shells, and shell porosity were controlled by synthesis parameters to produce hollow microspheres with maximum lithium capacity and stable cycling behavior. Thin, porous, hollow microspheres with three concentric multi-shells showed the best cycling performance, demonstrating excellent stability and a reversible capacity of up to 1702 mA h g−1 at a current density of 50 mA g−1. The electrode performance is attributed to the large specific surface area and enhanced volumetric capacity of the multi-shelled hollow spheres that provide maximum lithium storage, while the porous thin shells facilitate rapid electrochemical kinetics and buffer mechanical stresses that accompany volume changes during de/lithiation.

A general and versatile procedure for coating of hydrophobic nanocrystals with a thin silica layer enabling facile biofunctionalization and dye incorporation.

Here we report a method for coating of hydrophobic nanocrystals (NCs) with a thin silica layer. By using this approach 11 nm NaGdF4 NCs were coated with a mesoporous silica shell thinner than 20 nm resulting in highly monodisperse core-shell nanocomposite particles smaller than 50 nm. The synthetic protocol used here is based on the two-phase system that ensures high repeatability of the nanoparticle morphology and can be conveniently adapted for large-scale production. The use of an organic solvent as a diluent for tetraethoxysilane allows us to control not only the thickness, but also the porosity of the uniform silica shell. This procedure can be applied for coating NCs of various sizes and can be generalized to encapsulate other nanocrystals, e.g. semi-conductor quantum dots, into silica spheres. Furthermore, it allows facile surface modification with -NH2 groups that can be then used to conjugate biomolecules to the nanoparticle surface, as well as straightforward incorporation of various organic molecules (e.g. dyes or drugs) into the silica shell during its growth. To demonstrate potential applications up-converting NaGd0.80Yb0.18Er0.02F4 NCs were used as cores and zinc phthalocyanine was incorporated into the silica shell as a photosensitizer. Under irradiation with a 980 nm laser diode efficient generation of singlet oxygen was observed indicating that such nanocomposite particles have the capability to be used for photodynamic therapy.

A Model for Allosteric Control of Pore Opening by Substrate Binding in the Eutl Microcompartment Shell Protein

The ethanolamine utilization microcompartment (eut MCP) is a giant protein assembly that acts as a metabolic organelle in enteropathogenic bacteria, allowing them to proliferate in the human gut. The eut MCP consists of a polyhedral shell, reminiscent of a viral capsid, which encapsulates several sequentially acting metabolic enzymes that convert ethanolamine to ethanol and acetyl phosphate. The tightly-packed molecular shell surrounding the eut MCP is believed to act as a semi-permeable barrier, allowing the passage of substrates, products, and larger cofactor molecules, while minimizing the efflux of a toxic acetaldehyde intermediate. Previous structural studies of the eut MCP demonstrated that a conformational change of the EutL shell protein opens a 10-15A pore through the shell. That observation led to a model for how the protein shell might interconvert between high and low permeability conformations, but the mechanism controlling the pore opening has remained unclear. Here we present structural and biophysical studies directed toward understanding how the conformational switch is regulated in EutL. The X-ray crystal structure of EutL bound to ethanolamine provides evidence that binding of this small metabolite stabilizes the closed-pore conformation by sterically blocking rearrangement to the open conformation. Specific binding of ethanolamine to EutL was verified by isothermal titration calorimetry (ITC). Thermodynamic parameters derived from ITC experiments were rationalized through analysis of molecular contacts revealed by X-ray crystallography and molecular dynamics simulations. We show that ethanolamine binding is specific; i.e. EutL does not bind to other small molecules associated with the metabolic reactions carried out in the eut MCP. Our results suggest a model for EutL function in which the presence of ethanolamine decreases the porosity of the MCP shell by modulating the interconversion between open and closed pore conformations.

Individual SERS substrate with core–satellite structure decorated in shrinkable hydrogel template for pesticide detection

Individual Au@PNIPAM/Ag composite has been designed and fabricated as surface‐enhanced Raman scattering (SERS) substrate in this paper. Because of the high porosity of the polymer shell and the driving force of the Au core to Ag+(H2O)n (n = 1–4) in aqueous solution, chemical reactions can be carried out while aggregation is completely avoided. Also, this makes the formation of vast and monodisperse Ag nanoparticles within PNIPAM and increases the colloidal stability. The Au cores with different sizes and the vast Ag nanoparticles then form core–satellite structures that can generate plasmon resonance. Moreover, this kind of individual Au@PNIPAM/Ag composite can be seen directly through Raman optical microscope, and uncertain effects on SERS signals resulting from variability of the configurations are minimized because these individual composite particles are relatively uniform. Importantly, the gaps between the Au and Ag nanoparticles can decrease because the PNIPAM shrinks from swollen to collapse state, so the substrate can also be used for inspecting pesticide residues accurately and rapidly. Copyright © 2014 John Wiley & Sons, Ltd.

Encapsulation of Au nanoparticles with well-crystallized anatase TiO2 mesoporous hollow spheres for increased thermal stability

Uniform Auencap/TiO2 hollow microspheres, in which sub-10 nm Au nanoparticles are coated with a mesoporous anatase TiO2 shell, are prepared by a protected-calcinating process. The method involves the preparation of SiO2@Au@TiO2 colloidal composites, sequential deposition of carbon and then SiO2 layers through solvothermal and sol–gel processes, crystallization of TiO2 by calcination and finally etching of the inner and outer silica layers to produce the hollow structure. The protected crystallization process suppresses the excessive growth of TiO2 and eventually produces mesoporous anatase shells with high surface area. Additionally, by simply controlling the crystallization temperature, it can be convenient to tune the porosity and crystallinity of the TiO2 shell, meanwhile maintaining the small size of Au nanoparticles. When used as the catalyst for the reduction of 4-nitrophenol, the synthesized Auencap/TiO2 catalysts exhibit significantly enhanced catalytic performance. Moreover, the obtained Auencap/TiO2 hollow spheres show a superior thermal stability, as it resists sintering during the additional calcination at 500 °C, whereas the sample prepared by deposited Au nanoparticles on commercial P25(Au/P25) was found to sinter severely.

Alloying effect on K-shell fluorescence parameters of porous NiTi shape memory alloys

The Kα,β shell production cross-sections and Kβ/Kα intensity ratios of porous Ni −49at% Ti shape memory alloys were determined using energy dispersive X-ray fluorescence (EDXRF) technique. Also, the alloying effect on the K shell fluorescence parameters was investigated. The samples were excited by 59.5keV γ-rays from an 241Am annular radioactive source. The K X-rays emitted by the samples were counted by an Ultra-LEGe detector with a resolution of 150eV at 5.9keV. The structure analyses of the samples were also made using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The deviations between the present results and theoretical values, calculated for pure Ti and Ni, were attributed to charge transfer phenomena and/or rearrangement of valance shell electrons and porosity.

Tailoring Porosity in Carbon Nanospheres for Lithium–Sulfur Battery Cathodes

Porous hollow carbon spheres with different tailored pore structures have been designed as conducting frameworks for lithium-sulfur battery cathode materials that exhibit stable cycling capacity. By deliberately creating shell porosity and utilizing the interior void volume of the carbon spheres, sufficient space for sulfur storage as well as electrolyte pathways is guaranteed. The effect of different approaches to develop shell porosity is examined and compared in this study. The most highly optimized sulfur-porous carbon nanosphere composite, created using pore-formers to tailor shell porosity, exhibits excellent cycling performance and rate capability. Sulfur is primarily confined in 4-5 nm mesopores in the carbon shell and inner lining of the shells, which is beneficial for enhancing charge transfer and accommodating volume expansion of sulfur during redox cycling. Little capacity degradation (∼0.1% /cycle) is observed over 100 cycles for the optimized material.

Ion Transport Through Polyelectrolyte Multilayers

Polyelectrolyte multilayer (PEM) films and capsules loaded with ion-sensitive fluorophores can be used as ion-sensors for many applications including measurements of intracellular ion concentration. Previous studies have shown the influence of the PEM films/shells on the specific response of encapsulated ion-sensitive fluorophores. PEM shells are considered as semipermeable barriers between the environment and the encapsulated fluorophores. Parameters such as the time response of the encapsulated sensor can be affected by the porosity and charge of the PEM shell. In this study, the time response of an encapsulated pH-sensitive fluorophore towards pH changes in the surrounding environment is investigated. Furthermore, the conductance of PEM films for potassium ions is determined.

SAXS characterization of polymer-embedded hollow nanoparticles and of their shell porosity

Size parameters of SiO2/TiO2hollow nanoparticles (HNPs) of 25–100 nm in diameter were characterized by small-angle X-ray scattering (SAXS). On the basis of the decoupling and the Percus–Yevick approximations, and using a hollow sphere model, size information on HNPs was extracted, including average outer diameter, average inner diameter and polydispersity. Application of an alternative form factor based on hollow ellipsoids, and of a sticky hard sphere structure factor, did not improve the fit significantly. The shell porosity of the HNPs and the size of the pores in the HNP shell were further characterized by combining SAXS with gas adsorption methods. The above HNPs were then supported on a porous poly(ethylene oxide) scaffold by freeze drying from aqueous solution. To characterize the product, a multishell model was applied to fit the experimental SAXS curves and extract the following morphological information: distribution of HNPs between the surface and interior of the polymer, thickness of the polymer layers lining the outer and inner surfaces of HNPs, and densities of the outer and inner polymer layers. The work demonstrates the versatility of SAXS in obtaining key information on dissolved and polymer-supported HNPs in applications such as drug delivery and catalysis.

Synthesis and catalytic activity of M@SiO2 (M = Ag, Au, and Pt) nanostructures via “core to shell” and “shell then core” approaches

M@SiO 2 (M = Ag, Au, and Pt) core-shell nanostructures were prepared by the “core to shell” and “shell then core” approaches. In the former, the metal core size could be controlled in the 6–9 nm range with a narrow size distribution, and the shell porosity was tunable. The preparation was straightforward and efficient, without requiring specialized high-speed centrifugation. Au@SiO 2 containing mesoporous SiO 2 shells (Au@meso-SiO 2 ) exhibited good thermal stability and high CO oxidation activity ( T 100 = 235 °C) even after being subjected to calcination in air at 550 °C. In the latter approach, the core size could be controlled at < 10 nm with a narrow size distribution, and the shell porosity was tunable to a fine degree. 4-Nitrophenol was readily reduced at room temperature in the presence of Au@meso-SiO 2 obtained through the “shell then core” approach. The SiO 2 shell mesoporosity minimized the diffusion limitation of 4-nitrophenol. The core-shell structures from both approaches were uniformly dispersed. Employing Si sources with differing functionality allowed the SiO 2 shell and metal core properties to be modified in these approaches, which is beneficial for application. “Core to shell” and “shell then core” approaches were used to prepare 6–9 nm diameter M@SiO 2 (M = Ag, Au and Pt) with tunable shell porosity for catalytic reactions.