Empty Pores Research Articles

Optical properties of uniform, porous, amorphous Ta2O5 coatings on silica: temperature effects

We present spectroscopic ellipsometry (SE) results, in the 0.75–5 eV spectral range, obtained on highly uniform Ta2O5 coatings deposited on high-quality silica substrates by ion sputtering. The study was motivated mainly by issues related to the exploitation of Ta2O5–SiO2 λ/4 multilayers in detectors of gravitational waves. Two sets of samples with nominal thicknesses of 40 and 500 nm were considered. A sub-set of samples was treated with post-growth annealing in air for several hours at temperatures Tann up to 600 °C. The SE data were complemented with photothermal common-path interferometry measurements at 1064 nm providing data about absorption losses in the 1–4 ppm range. SE data, taken at room temperature, were analysed by exploiting three different three-phase (substrate/film/surface) models (Cody–Lorentz, Tauc–Lorentz and Herzinger–Johs) of the fundamental absorption edge. Following the literature (Stenzel 2009 J. Phys. D: Appl. Phys. 42 055312) the simulations exploited a graded nano-porosity inside the coating, testing both the shape and composition of the pores. The best simulation of data was obtained using the Cody–Lorentz approach and a quasi-uniform density (6–7.5%) of empty spherical pores, slowly degrading from the substrate/film interface towards the film/ambient interface. A comparison with the literature indicated a high stoichiometric quality of the coatings. The analysis of samples annealed to increasingly higher Tann showed (i) a slight blue-shift of the energy gap (ii) an increase in the pore volume fraction, (iii) an increase (1–2%) in the coating thickness, (iv) a small (less than 1%) reduction in the index of refraction in the transparency region and (v) a limited increase in absorption losses. These findings were interpreted in terms of a release of the compressive strain inherent to the deposition process.

Membranes with Highly Ordered Straight Nanopores by Selective Swelling of Fast Perpendicularly Aligned Block Copolymers

Membranes with uniform, straight nanopores have important applications in diverse fields, but their application is limited by the lack of efficient producing methods with high controllability. In this work, we reported on an extremely simple and efficient strategy to produce such well-defined membranes. We demonstrated that neutral solvents were capable of annealing amphiphilic block copolymer (BCP) films of polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) with thicknesses up to 600 nm to the perpendicular orientation within 1 min. Annealing in neutral solvents was also effective to the perpendicular alignment of block copolymers with very high molecular weights, e.g., 362 000 Da. Remarkably, simply by immersing the annealed BCP films in hot ethanol followed by drying in air, the originally dense BCP films were nondestructively converted into porous membranes containing highly ordered, straight nanopores traversing the entire thickness of the membrane (up to 1.1 μm). Grazing incident small-angle X-ray spectroscopy confirmed the hexagonal ordering of the nanopores over large areas. We found that the overflow of P2VP chains from their reservoir P2VP cylinders and the deformation of the PS matrix in the swelling process contributed to the transformation of the solid P2VP cylinders to empty straight pores. The pore diameters can be tuned by either changing the swelling temperatures or depositing thin layers of metal oxides on the preformed membranes via atomic layer deposition with a subnanometer accuracy. To demonstrate the application of the obtained porous membranes, we used them as templates and produced centimeter-scale arrays of aligned nanotubes of metal oxides with finely tunable wall thicknesses.

Strength homogenization of matrix-inclusion composites using the linear comparison composite approach

A homogenization procedure to estimate the macroscopic strength of nonlinear matrix-inclusion composites with different strength characteristics of the matrix and inclusions, respectively, is presented in this paper. The strength up-scaling is formulated within the framework of the yield design theory and the linear comparison composite (LCC) approach, introduced by Ponte Castaneda (2002) and extended to frictional models by Ortega et al. (2011), which estimates the macroscopic strength of composite materials in terms of an optimally chosen linear thermo–elastic comparison composite with a similar underlying microstructure. In the paper various combinations for the underlying material behavior for the individual phases of the composite are considered: The matrix phase can be a quasi frictional material characterized either by a Drucker–Prager-type (hyperbolic) or an elliptical strength criterion, which predicts a strength limit also in hydrostatic compression, while the inclusion phase either may represent empty pores, pore voids filled with a pore fluid, rigid inclusions, or solid inclusions, whose strength characteristics also maybe described by a Drucker–Prager-type or an elliptical strength criterion. For generating the homogenized strength criterion efficiently in such general cases of matrix-inclusion composites, a novel algorithm is proposed in the paper. The validation of the proposed strength homogenization procedure for selected combinations of strength characteristics of the matrix material and the inclusions is conducted by comparisons with experimental results and alternative existing strength homogenization models.

PEMANFAATAN ZEOLIT DIAKTIFKAN DENGAN LARUTAN ASAM UNTUK PEMURNIAN BIODIESEL

Utilization of zeolite activated by acid solution for biodiesel purification has been done. This research is conducted to find the mechanism of biodiesel purification from catalyst with activated zeolite, the effectiveness of the activated zeolite of various particle size, soaking time and purification temperature, the economic feasibility of biodiesel production by using this method and the more economical method by comparing the cost and performance of biodiesel purification using activated zeolite and using water and acid solution.This research has used cooking oil, methanol and sodium hydroxide to make biodiesel, sulfuric acid as activator and zeolite from Gunung Kidul which is filled into wash column with support from vacuum pump to purify biodiesel. The variable of the research is particle size of zeolite among others: 12 mesh <De< 20 mesh, 20 mesh <De< 40 mesh and 40 mesh <De< 80 mesh, soaking time 0, 15 minutes, 30 minutes, 1 hour and 2 hours, and purification temperature 27oC, 40oC and 60oC.Mechanism of activated zeolite for purifying biodiesel from catalyst has been investigated that activated zeolite is using the absorption rate where catalyst will fill the empty pores of zeolite and its cation exchange capacity where it will exchange cation in zeolite surface with cation of catalyst so that zeolite can purify the unwashed biodiesel from catalyst. Optimization of biodiesel purification using zeolite activated by acid solution method can be achieved with particle size of the zeolite 20 mesh <De< 40 mesh, 30-minute soaking time and purification temperature at 27oC. Economic analysis of the use of zeolites in the optimum condition within one year resulted Payback Period 8.68 months, Benefit Cost Ratio 1.86, Net Present Value Rp 431,173,257.44 and Return of Investment -138 % and the use of zeolite activated by acid solution more economical than the use of water and acid solution as purifying biodiesel because of cost savings can be made up to 86% of method of using water and acid solution.

Deformation and Damage of Composites with Anisotropic Components (Review)

A statistical model describing the coupled deformation and damage of composites with porous transversely isotropic and orthotropic components is proposed. The mechanism of microdamage of such composites is studied assuming that the microstrength of the material is inhomogeneous. A singlemicrodamage is modeled by an empty quasispherical pore forming in place of a microvolume damaged in accordance with the Huber–Mises failure criterion. The ultimate microstrength is assumed to be a random function of coordinates with Weibull one-point distribution density. The method of conditional moments, the damage balance equations, and the Newton–Raphson method are used to set up an algorithm to calculate the effective deformation characteristics of composite materials depending on macrostrains. The effect of the damage of the material on the macrostress–macrostrain relationship is established. The influence of the mechanical characteristics of the material, the volume fraction and porosity of its components, the geometrical parameters of its structure, and the distribution of microstrength on the damage and macrostress–macrostrain curves of the material is analyzed

Charging Dynamics and Optimization of Nanoporous Supercapacitors

An improved mean-field model used earlier (J. Phys.: Condens. Matter2011, 23, 022201) to explain the anomalous increase of capacitance in nanoporous supercapacitors is extended to the study of charging dynamics. We find that charging of initially empty (i.e., ionic liquid-phobic) pores proceeds in a front-like way, while charging of filled (i.e., ionophilic) pores is diffusive; in both cases, however, the accumulated charge grows as a square root of time. We also discuss two-step complementary optimization of porous electrodes for supercapacitors. In a first step, the optimal pore width is chosen to maximize the stored energy density; in a second step, the optimal pore depth/length (that is, electrode’s thickness) is chosen to satisfy the requirement on charging times. In addition, the use of “nanoporous channels” in a “multilayered” configuration is suggested to decrease the volume and to increase the capacitance, stored energy, and power density of a supercapacitor.

Phenanthrene removal from aqueous solutions using well-characterized, raw, chemically treated, and charred malt spent rootlets, a food industry by-product

Malt spent rootlets (MSR) are biomaterials produced in big quantities by beer industry as by-products. A sustainable solution is required for their management. In the present study, MSR are examined as sorbents of a hydrophobic organic compound, phenanthrene, from aqueous solutions. Raw MSR sorb phenanthrene but their sorptive properties are not competitive with the respective properties of commercial sorbents (e.g., activated carbons). Organic petrography is used as a tool to characterize MSR after treatment in order to produce an effective sorbent for phenanthrene. Chemical and thermal (at low temperature under nitrogen atmosphere) treatments of MSR did not result in highly effective sorbents. Based on organic petrography characterization, the pores of the treated materials were filled with humic colloids. When pyrolysis at 800 °C was used to treat MSR, a sorbent with new and empty pores was produced. Phenanthrene sorption capacity was 2 orders of magnitude higher for the pyrolized MSR than for raw MSR.

Adsorption induced transitions in soft porous crystals: An osmotic potential approach to multistability and intermediate structures

Soft porous crystals are flexible metal-organic frameworks that respond to physical stimuli (temperature, pressure, and gas adsorption) by large changes in their structure and unit cell volume. We propose here a thermodynamic treatment, based on the osmotic ensemble, of the interplay between guest adsorption and host deformation, where the bare host material can undergo elastic deformation, as well as structural transitions between metastable phases in the case of a multistable material. We show that in addition to structural transitions between metastable phases of bistable or multistable host frameworks, a new guest-stabilized host phase can be created when the size of the adsorbate is larger than the empty material's pore size. We then confront the findings of our approach with experimental data for systems exhibiting phenomena such as gate opening and breathing.

Fibrillar structure and elasticity of hydrating collagen: A quantitative multiscale approach

It is well known that hydration of collagenous tissues leads to their swelling, as well as to softening of their elastic behavior. However, it is much less clear which microstructural and micromechanical “rules” are involved in this process. Here, we develop a theoretical approach cast in analytical mathematical formulations, which is experimentally validated by a wealth of independent tests on collagenous tissues, such as X-ray diffraction, vacuum drying, mass measurements, and Brillouin light scattering. The overall emerging picture is the following: air-drying leaves water only in the gap zones between the triple-helical collagen molecules; upon re-hydration, the extrafibrillar space is established at volumes directly proportional to the hydration-induced swelling of the (micro) fibrils, until the maximum equatorial distance between the long collagen molecules is reached. Thereafter, the volume of the fibrils stays constant, and only the extrafibrillar volume continues to grow. At all these hydration stages, the elastic behavior is governed by the same, hydration-invariant mechanical interaction pattern of only two, interpenetrating mechanical phases: transversely isotropic molecular collagen and isotropic water (or empty pores in the vacuum-dried case).

High electrochemical performance of carbon black-bonded carbon nanotubes for electrode materials

Carbon–carbon nanocomposites were prepared by the chemical reduction of strongly oxidized multi-walled carbon nanotubes (O-MWNTs) and acid-treated carbon blacks (A-CBs). To apply the electrode materials, the electrochemical performance of the MWNTs–CBs was examined as a function of the CB content. The chemically converted MWNTs–CBs were formed successfully by physical interaction during the reduction of the functional groups of O-MWNTs and A-CBs, resulting in the conjugation of CBs onto the MWNT surface with a high aspect ratio. The electrical properties of the MWNTs increased with increasing CB content, resulting from the condensed MWNT networks by the CBs deposited on the MWNTs. In addition, MWNTs–CBs showed higher current density than the pristine MWNT alone. This suggests that the incorporation of CBs onto MWNTs could have a compacting effect on the empty pores in MWNT networks, leading to MWNTs-based electrodes with enhanced electrochemical performance.

Permittivity estimation over Mars by using SHARAD data: the Cerberus Palus area

Cerberus Palus is a thoroughly studied region of Mars, characterized by evident platy textures that were interpreted either as evidence for a frozen sea close to Mars' equator or as being resultant of lava, mud or ice‐flows coming from Cerberus Fossae through Athabasca Valles. Radargrams provided by radar sounder SHARAD clearly show the presence of subsurface layers in the area. By exploiting the great amount of available data, authors have performed an accurate quantitative analysis aimed to estimate electromagnetic properties of surface and subsurface layers, in terms of permittivity and attenuation. To this aim, a simplified electromagnetic approach has been used, but taking into account effects of scattering due to surface roughness, for avoiding overestimated results. This has been done by using theory of electromagnetic scattering from fractal surfaces and by estimating needed parameters from topographic data provided by MOLA. Three distinct geologic formations have been analyzed, namely a part of Zephyria Planum, the Cerberus plains and the bedrock beneath the plains. The retrieved electromagnetic parameters have been also modeled as a mixture of volcanic rocks with either ice or air. The Zephyria Planum material was found to be significantly porous [50–60%] with an attenuation more likely compatible with empty pores. Ambiguous results were obtained for the plains material, being the resulting porosity high in both the cases of empty [40–50%] and of ice‐filled [80%] pores. The obtained results do not allow for evidence of a frozen sea on Cerberus Palus area.

The use of small angle neutron scattering with contrast matching and variable adsorbate partial pressures in the study of porosity in activated carbons

The porosity of a typical activated carbon is investigated with small angle neutron scattering (SANS), using the contrast matching technique, by changing the hydrogen/deuterium content of the absorbed liquid (toluene) to extract the carbon density at different scattering vector (Q) values and by measuring the p/p0 dependence of the SANS, using fully deuterated toluene. The contrast matching data shows that the apparent density is Q-dependent, either because of pores opening near the carbon surface during the activation processor or changes in D-toluene density in nanoscale pores. For each p/p0 value, evaluation of the Porod Invariant yields the fraction of empty pores. Hence, comparison with the adsorption isotherm, shows that the fully dry powder undergoes densification when liquid is added. An algebraic function is developed to fit the SANS signal at each p/p0 value hence yielding the effective Kelvin radii of the liquid surfaces as a function of p/p0. These values, when compared with the Kelvin equation, show that the resultant surface tension value is accurate for the larger pores but tends to increase for small (nanoscale) pores. The resultant pore size distribution is less model-dependent than for the traditional methods of analyzing the adsorption isotherms.

Deformation and damage of composite materials of stochastic structure: physically nonlinear problems (Review)

The studies on the theory of deformation and short- and long-term damage of physically nonlinear homogeneous and composite materials are systematized. In the case of short-term damage, a single microdamage is modeled by an empty quasispherical pore occurring in place of a microvolume damaged by the Huber–Mises criterion. The ultimate microstrength is assumed to be a random function of coordinates. In the case of long-term damage, the damage criterion for a single microvolume is characterized by its stress-rupture strength determined by the dependence of the time to brittle fracture on the difference between the equivalent stress and its limit, which is the ultimate strength. The equation of porosity balance at an arbitrary time and the equations relating macrostresses and macrostrains constitute a closed system. Algorithms of calculating microdamage and macrostresses as functions of time and macrostrains are developed. The effect of nonlinearity on the curves is studied

Effective-medium theory of elastic waves in random networks of rods

We formulate an effective medium (mean field) theory of a material consisting of randomly distributed nodes connected by straight slender rods, hinged at the nodes. Defining wavelength-dependent effective elastic moduli, we calculate both the static moduli and the dispersion relations of ultrasonic longitudinal and transverse elastic waves. At finite wave vector k the waves are dispersive, with phase and group velocities decreasing with increasing wave vector. These results are directly applicable to networks with empty pore space. They also describe the solid matrix in two-component (Biot) theories of fluid-filled porous media. We suggest the possibility of low density materials with higher ratios of stiffness and strength to density than those of foams, aerogels, or trabecular bone.

Formation Mechanism for a Hybrid Supramolecular Network Involving Cooperative Interactions

A novel mechanism of hybrid assembly of molecules on surfaces is proposed stemming from interactions between molecules and on-surface metal atoms which eventually got trapped inside the network pores. Based on state-of-the-art theoretical calculations, we find that the new mechanism relies on formation of molecule-metal atom pairs which, together with molecules themselves, participate in the assembly growth. Most remarkably, the dissociation of pairs is facilitated by a cooperative interaction involving many molecules. This new mechanism is illustrated on a low coverage Melamine hexagonal network on the Au(111) surface where multiple events of gold atoms trapping via a set of so-called "gate" transitions are found by kinetic Monte Carlo simulations based on transition rates obtained using ab initio density functional theory calculations and the nudged elastic band method. Simulated STM images of gold atoms trapped in the pores of the Melamine network predict that the atoms should appear as bright spots inside Melamine hexagons. No trapping was found at large Melamine coverages, however. These predictions have been supported by preliminary STM experiments which show bright spots inside Melamine hexagons at low Melamine coverages, while empty pores are mostly observed at large coverages. Therefore, we suggest that bright spots sometimes observed in the pores of molecular assemblies on metal surfaces may be attributed to trapped substrate metal atoms. We believe that this type of mechanism could be used for delivering adatom species of desired functionality (e.g., magnetic) into the pores of hydrogen-bonded networks serving as templates for their capture.

Study of the porous structure of white chocolate by confocal Raman microscopy

AbstractConfocal Raman microscopy has been shown to be a useful technique for investigation of white chocolate surfaces. The appearance of protrusions and pores, and the distribution of fat, sucrose, and milk powder at and below the surface of white chocolate pralines were investigated using confocal Raman microscopy. Raman horizontal and depth scans showed that the protrusions and pores continue at least 10 µm into the chocolate shell and that some protrusions and channels mainly consist of fat, while some consisted of a fat layer, leaving a hollow space underneath. Further, the pores and their continuing channels consisted of nothing but air. These findings indicate that the protrusions might be connected to channels where we suggest a pressure driven convective flow of liquid fat from within the chocolate matrix that, depending on temperature, moves up to the surface or goes back into the matrix, leaving an empty pore with a shell of fat at the surface, which in some cases collapse and leaves a hollow pore and channel. Therefore, these findings support that the protrusions could be connected to oil migration in chocolate and, thus, further to fat bloom development.Practical applications: Confocal Raman microscopy can be used to investigate the local distribution of different components in white chocolate. This technique offers the possibility to acquire the local distribution of different components within the sample, with a resolution down to the optical diffraction limit. Further, the analysis can be performed at ambient conditions, without requiring any special sample preparation or marker molecules. The results obtained by using this technique suggest that specific surface imperfections on chocolate could be part of a network of pore structures at and beneath the chocolate surface, which could be related to oil migration and thus, to fat bloom formation.

4-Phenoxyphenol: A Porous Molecular Material

4-Phenoxyphenol is a simple organic molecule that crystallizes as a porous material with channels running throughout the structure. The channels are constructed by a 6-fold hydrogen bonded ring and can host solvent molecules incorporated during crystal growth, with a minimum channel diameter of 5.8–5.9 A; each channel usually contains a single solvent molecule per unit cell. The hydrogen bonded ring shows surprising flexibility, being able both to breathe and to sustain its crystalline integrity even when grown with empty pores. This is particularly surprising given that the remainder of the interactions within the crystal structure are C–H···π interactions and are weak in nature. It is also possible to grow “dry” porous 4-phenoxyphenol crystals by using a bulky solvent in the recrystallization.

Deformation and damage of linear elastic homogeneous and composite materials (review)

The studies on the deformation and short- and long-term damage of homogeneous and composite materials are systematized. In the case of short-term damage, a single microdamage is modeled by an empty quasispherical pore formed in place of a microvolume damaged in accordance with the Huber–Mises or Schleicher–Nadai failure criterion. The ultimate microstrength is assumed to be a random function of coordinates. In the case of long-term damage, the damage of a single microvolume is characterized by its stress-rupture strength determined by the dependence of the time to brittle fracture on the difference between the equivalent stress and its limit, which is the ultimate strength. The equation of porosity balance at an arbitrary time and the equations relating macrostresses and macrostrains constitute a closed system. Algorithms of calculating the dependence of microdamage and macrostresses on time and macrostrains are developed. The effect of temperature and the resistance of particles of damaged material on the curves is studied

Improvement in Coating Quality and Corrosion Characteristics of Galvanized Steels by Pre-Electrodeposition of Cu

A dual-phase steel was electrodeposited with Cu prior to reduction annealing in order to improve coating quality and resultant corrosion characteristics of the galvanized material. This pre-eletrodeposition process allowed a tenfold reduction in coating defects (typically found in uncoated areas and empty pores), thereby yielding a 8.4% coating weight gain and a noticeable decrease (24%) in the average spangle diameter. However, the Cu pre-electrodeposition layer acted as an inter-diffusion barrier, thereby limiting Fe-Al interactions during galvanization, and resulted in the formation of imperfect Fe-Al compounds. Nevertheless, this Cu layer could extend the incubation time of the Fe-Zn phases. Consequently, the presence of this Cu electrodeposition layer could effectively prevent concentration polarization, thereby decreasing corrosion current density even after 4 days of immersion in 3.5% NaCl solution.

New integrated 2D–3D physical method to evaluate the porosity and microstructure of carbonate and dolomite porous system

We propose here a method which concerns the characterization of carbonate porous systems from image analysis of wood’s metal intrusion. The wood’s metal is an alloy which at a low melting point (70°C) and in fact in fusion phase (liquid phase) this alloy can be injected into the geological porous space of materials with the aim of making a quantification by microscopic image. It is thus possible to solidify the pores and the cracks in various conditions of fluid pressure. The study of numeric images of this preparation on a scanning electron microscope has the advantage of presenting a strong contrast and thus facilitating the image segmentation in three phases (substance, empty porous space and pores filled with wood’s metal).We show the results of this new method of investigation on samples of the carbonates types and for various pressures of injection. These results are then compared with traditional measurements of porosity mercury.We obtain a very good correlation between physical measurements (porosity, pore-throat size) given in porosity mercury and measurements resulting from the image processing. We have moreover the possibility to visualize in 2D and thus to determine the proportion of closed pores i.e. pores which are found insulated without connection. The proportions of these pores do cannot be given with traditional methods and they represent an increasingly important data for many properties.