Non-uniform Pore Size Distribution Research Articles

Characteristics of Pumice from Cicurug and Its Application as a Bleacher for Crude Palm Oil

Pumice is relatively abundant in Indonesia, especially in Cicurug District, Sukabumi. Pumice has unique characteristics, so it has the potential to be an alternative bleaching agent or a bleacher for crude palm oil. Bleaching is one of the stages in processing crude palm oil into palm cooking oil. In the cooking oil industry, the bleaching of crude palm oil generally uses bentonite as a bleacher. This research aims to determine the characteristics of pumice and the optimum conditions for the bleaching process of crude palm oil with pumice as a bleacher. The research method consists of pumice activation, activated pumice characterization, degumming of crude palm oil, bleaching of crude palm oil, and analysis of processed palm oil. The results show that the metal oxide composition in activated pumice is dominated by silica (62.99%) and alumina (14.79%) and has a non-uniform pore size distribution. Optimum bleaching conditions are achieved when using 30% pumice and a bleaching temperature of 105 oC for 30 minutes. Under optimal bleaching conditions, pumice can reduce the color brightness level of crude palm oil from 600 to 125 mg/L Pt, or a bleaching power of 79.2%.

Wood chip sound absorbers: Measurements and models

Normal incidence absorption coefficient spectra of samples made from glued wood chips have been measured for various mesh sizes, bulk densities, thicknesses, and air gaps. Increasing thickness introduces additional layer resonance peaks and shifts the initial peak towards lower frequencies. The wood chip samples composed of the smallest mesh sizes were found to offer the highest sound absorption, comparable with that of the same thickness of materials made from synthetic fibers. Measured absorption spectra are compared with predictions of four models for the acoustical properties of rigid porous media. These include a model for slanted parallel identical uniform slits (SS), the Johnson-Champoux-Allard (JCA) and Johnson-Champoux-Allard-Lafarge (JCAL) models for arbitrary pore structures, and model for a non-uniform pore size distribution (NUPSD). Porosity and flow resistivity values have been determined non-acoustically. However, the tortuosity and characteristic lengths required for the JCA model have been obtained by fitting the measured absorption spectra. The thermal permeability required for the JCAL model has been deduced indirectly from the fitted tortuosity through a relationship with standard deviation of the pore size distribution due to the NUPSD model. JCAL and JCA models give the best agreement overall, but predictions of the SS and NUPSD models that use only the fitted tortuosity in addition to measured porosity and flow resistivity are found to give comparable agreement with data for many samples. SS and NUPSD predictions are improved by increasing the tortuosity values compared with those obtained by fitting the JCA model. The study should encourage the creation of sustainable sound-absorbing materials from wood chip wastes.

Adsorption behavior of serum proteins on anodized titanium is driven by surface nanomorphology.

Protein adsorption behavior can play a critical role in defining the outcome of a material by affecting the subsequent in vivo response to it. To date, the effect of surface properties on protein adsorption behavior has been mainly focused on surface chemistry, but research on the effect of nanoscale surface topography remains limited. In this study, the adsorption behavior of human serum albumin, immunoglobulin G, and fibrinogen in terms of the adsorbed amount and conformational changes were investigated on bare and anodized titanium (Ti) samples (40 and 60 V applied voltages). While the surface chemistry, RMS surface roughness, and arithmetic surface roughness of the anodized samples were similar, they had distinctly different nanomorphologies identified by atomic force microscopy and scanning electron microscopy, and the surface statistical parameters, surface skewness Ssk and kurtosis Sku. The Feret pore size distribution was more uniform on the 60 V sample, and surface nanostructures were more symmetrical with higher peaks and deeper pores. On the other hand, the 40 V sample surface presented a nonuniform pore size distribution and asymmetrical surface nanostructures with lower peaks and shallower pores. The amount of surface-adsorbed protein increased on the sample surfaces in the order of Ti < 40 V < 60 V with the predominant factor affecting the amount of surface-adsorbed protein being the increased surface area attained by pore formation. The secondary structure of all adsorbed proteins deviated from that of their native counterparts. While comparing the secondary structure components of proteins on anodized surfaces, it was observed that all three proteins retained more of their secondary structure composition on the surface with more uniform and symmetrical nanofeatures than the surface having asymmetrical nanostructures. Our results suggest that the nanomorphology of the peaks and outer walls of the nanotubes can significantly influence the conformation of adsorbed serum proteins, even for surfaces having similar roughness values.

Zeolite Coated Separators for Improved Performance and Safety of Lithium Metal Batteries

Lithium (Li) metal batteries are attractive due to their high gravimetric and volumetric energy densities. However, they can fail catastrophically due to dendritic nucleation, growth, and penetration through the polypropylene (PP) or polyethylene (PE) separators. Poor electrolyte wetting and non-uniform Li ion flux are known to affect Li dendrite formation, especially since the PP/PE separators have non-uniform pore size distribution and typical organic electrolytes do not wet them well. In this work, we demonstrate that a porous zeolite coating on a commercial PP separator can improve electrolyte wettability and through plane ionic conductivity, giving rise to more uniform Li flux. Consequently, coated separator can delay dendrite penetration and enhance cell performance and safety. We tested Celgard 2400 (uncoated) and zeolite-coated separator (coated) in high energy NMC||Li cells for their rate capability and cycle life performance. Rate capability test for these cells shows that the additional resistance due to the zeolite coating can negatively impact the cell performance at high C-rates. However, cells with the coated separator outperform those with uncoated separator in the cycle life test with improved capacity retention. Symmetric cell studies performed to understand the differences in Li plating morphology indicate initial lower overpotential for the coated separator cells, revealing improved electrolyte wetting and relatively uniform Li flux. Scanning electron microscopy (SEM) reveals zeolite-coating microstructure with evenly distributed zeolite particles and cycled Li metal electrode morphologies. SEM images show much smoother Li plating morphology on Li metal surface in the cells with coated separators. This study highlights the potential of using zeolite-coated separators to enhance lithium metal battery (LMB) performance and safety.

Measurement of Ultrasound Parameters of Bovine Cancellous Bone as a Function of Frequency for a Range of Porosities via Through-Transmission Ultrasonic Spectroscopy

The relationship between ultrasonic parameters (attenuation coefficients and velocity) and bone porosity in bovine cancellous bone is explored to understand the possibility of fracture risk diagnosis associated with osteoporosis by applying ultrasound. In vitro measurements of ultrasonic parameters on twenty-one bovine cancellous bone samples from tibia were conducted, using ultrasonic spectroscopy in the through-transmission mode. Transducers of three different center frequencies were used to cover a wide diagnostic frequency range between 1.0–7.8 MHz. The nonlinear relationship of porosity and normalized attenuation coefficient (nATTN) and normalized broadband attenuation coefficient (nBUA) were well described by a third-order polynomial fit, whereas porosity and the phase velocity (UV) were found to be negatively correlated with the linear correlation coefficients of −0.93, −0.89 and −0.83 at 2.25, 5.00 and 7.50 MHz, respectively. The results imply that the ultrasound parameters attain maximum values for the bone sample with the lowest porosity, and then decrease for samples with greater porosity for the range of porosities in our samples for all frequencies. Spatial variation in the ultrasound parameters was found to be caused by non-uniform pore size distribution, which was examined at five different locations within the same bone specimen. However, it did not affect the relationship of ultrasound parameters and porosity at these frequencies.

Estimation of Stagnosol Hydraulic Properties and Water Flow Using Uni- and Bimodal Porosity Models in Erosion-Affected Hillslope Vineyard Soils

Erosion has been reported as one of the top degradation processes that negatively affect agricultural soils. The study objective was to identify hydropedological factors controlling soil water dynamics in erosion-affected hillslope vineyard soils. The hydropedological study was conducted at identically-managed Jastrebarsko (location I), and Jazbina (II) and (III) sites with Stagnosol soils. Soil Hydraulic Properties (SHP) were estimated on intact soil cores using Evaporation and WP4C methods; soil hydraulic functions were fitted using HYPROP-FIT software. For Apg and Bg/Btg horizons, uni- and bimodal soil hydraulic models could be well fitted to data; although, the bimodal model performed better in particular cases where data indicated non-uniform pore size distribution. With these SHP estimations, a one-year (2020) water flow scenario was simulated using HYDRUS-1D to compare water balance results obtained with uni- and bimodal hydraulic functions. Simulation results revealed relatively similar flux distribution at each hillslope position between the water balance components infiltration, surface runoff, and drainage. However, at the bottom profile at Jastrebarsko, bimodality of the hydraulic functions led to increased drainage. Soil water storage was reduced, and the vertical movement increased due to modified soil water retention curve shapes. Adequate parameterization of SHP is required to capture the hydropedological response of heterogenous erosion-affected soil systems.

Incorporation of the Pore Size Variation to Modeling of the Elastic Behavior of Metallic Open-Cell Foams

Abstract In the present paper we present the approach for modeling of the elastic behavior of open-cell metallic foams concerning non-uniform pore size distribution. This approach combines design of foam structures and numerical simulations of compression tests using finite element method (FEM). In the design stage, Laguerre-Voronoi tessellations (LVT) were performed on several sets of packed spheres with defined variation of radii, bringing about a set of foam structures with porosity ranging from 74 to 98% and different pore size variation quantified by the coefficient of pore volume variation, CV(V), from 0.5 to 2.1. Each structure was numerically subjected to uni-axial compression test along three directions within the elastic region. Basing on the numerical response, the effective Young’s modulus, Eeff, was calculated for each structure. It is shown that the Eeff is not only dependent on the porosity but also on the pore size variation.

Anodic formation of highly ordered TiO2 nanotube arrays on conducting glass substrate: Effect of titanium film thickness

Highly ordered TiO2 nanotube arrays were successfully fabricated using ammonium fluoride electrolyte by galvanostatic anodization technique. The nanotube arrays were grown perpendicular to the titanium film deposited onto conducting glass substrate. The effect of the different titanium film thicknesses on the morphology, optical, and electrical properties of TiO2 nanotube arrays is investigated. It is found that the titanium film thickness is a crucial parameter for achieving highly ordered TiO2 nanotube arrays. Morphological investigations on the nanotube arrays reveal that anodization of 1.5 μm thick titanium films leads to formation of pores at the upper layer of the film with nonuniform pore size distribution and poor interconnectivity. Instead, anodization of 2.5 and 2.0 μm thick titanium films with the same conditions leads to formation of highly ordered TiO2 nanotube arrays with uniform size and sharp clear tubular structures, which are well connected to each other. The absorbance and optical band gap of the TiO2 nanotube arrays are also inferred from the diffuse reflectance spectra.Highly ordered TiO2 nanotube arrays were successfully fabricated using ammonium fluoride electrolyte by galvanostatic anodization technique. The nanotube arrays were grown perpendicular to the titanium film deposited onto conducting glass substrate. The effect of the different titanium film thicknesses on the morphology, optical, and electrical properties of TiO2 nanotube arrays is investigated. It is found that the titanium film thickness is a crucial parameter for achieving highly ordered TiO2 nanotube arrays. Morphological investigations on the nanotube arrays reveal that anodization of 1.5 μm thick titanium films leads to formation of pores at the upper layer of the film with nonuniform pore size distribution and poor interconnectivity. Instead, anodization of 2.5 and 2.0 μm thick titanium films with the same conditions leads to formation of highly ordered TiO2 nanotube arrays with uniform size and sharp clear tubular structures, which are well connected to each other. The absorbance and optical band ...

Synthesis and modification of reduced graphene oxide aerogels for biofuel cell applications

Abstract We have carried out the preparation of reduced graphene oxide aerogels using eco-friendly method that is based on the Hummers method of graphite oxidation without the use of NaNO3 that produces toxic gases. To obtain a porous 3D structure of reduced graphene oxide, we performed the hydrothermal reduction at elevated temperature. We also prepared the rGO aerogel/CNT composite using multiwalled carbon nanotubes as linkers. The rGO aerogels are promising materials as they possess good electrical conductivity (up to 100 S/m) and high surface area and porous structure (~500 m2/g). The main goal was to obtain the material for electrodes in enzymatic biofuel cells. Thus, the proper modification was performed using free radical functionalization. It was shown that in order to synthesize rGO aerogels modified with anthracene, the proper order of reactions needs to be provided. The morphology of anthracene modified electrodes was analyzed using scanning electron microscopy, which confirmed their porous structure with non-uniform pore size distribution that ranged between few nanometers to microns. Data obtained by Raman spectroscopy confirmed the successful oxidation and reduction of analyzed materials. UV-Vis spectra revealed the presence of anthracene moieties in examined materials. We also recorded preliminary cyclic voltammograms that confirm an electric conductivity of the obtained structures.

The catalytic performance of Ti-PILC supported CrOx–CeO2 catalysts for n-butylamine oxidation

A series of titanium pillared clays (Ti-PILC) materials are synthesized by different preparation conditions and the influence of the texture/structure nature of Ti-PILC on the catalytic performance of Ti-PILC supported CrOx–CeO2 mixed oxide (CrCe/Ti-PILC) catalysts for n-butylamine oxidation is investigated. The titanium pillared clays materials possess larger specific surface area and abundant porous structure with some irregular pore channel and nonuniform pore size distribution, due to the collapse of layered structure during pillaring process. The preparation conditions have significant impact on texture/structure properties of Ti-PILC. The synergistic effect between CrOx–CeO2 and Ti-PILC supports is promoted due to outstanding texture/structure properties of Ti-PILC, which enhances the catalytic activity for n-butylamine oxidation over Ti-PILC supported CrOx–CeO2 catalysts, especially for the 8CrCe(6:1)/Ti-PILC(12,20) catalyst. All the catalysts show a good control quality of NOx, and the yield of NOx is limited within 1 % at T98.

Prediction capability of different soil water retention curve models using artificial neural networks

Direct measurements of soil water retention curve (SWRC) are costly and time consuming. So far, less investigation has been carried out on the prediction capability of different models using artificial neural networks (ANNs). In this study in total 75 soil samples were collected from Guilan province, north of Iran. The basic soil properties namely sand, clay and bulk density were used as predictors and the parameters of ten SWRC models were forecasted by ANNs. The prediction capability of each model was examined based on three criteria in nine groups of samples: total, fine (clay and silty clay) and medium (clay loam, silt loam, silty clay loam and loam) textural groups and six soil texture classes. Overall, the Boltzman, Tani, Gardner, Campbell and van Genuchten models produced the best results. However, bimodal models (Durner, Seki and Dexter) established on non-uniform pore size distribution with two modes (peaks) in soils showed low prediction capability in this study. Therefore, further research is needed. Sensitivity analysis indicated that the residual and saturated water contents were largely dependent on clay content.

Soil-water characteristics and shear strength in constant water content triaxial tests on Yunnan red clay

The shear strength parameters for geotechnical designs are obtained mainly from consolidated drained (CD) or consolidated undrained (CU) triaxial tests. However, during construction, the excess pore-air pressure generally dissipates instantaneously while the excess pore-water pressure dissipates with time. This condition needs to be simulated in a constant water content (CW) triaxial test. The study on Yunnan red clay is carried out to investigate the soil-water characteristics and the shear strength characteristics under the constant water content condition. Osmotic technique is used to obtain the soil-water characteristic curve. A series of CW triaxial tests are conducted on statically compacted specimens. The experimental results show that the soil-water characteristic curve has a low air entry value of 7 kPa due to large pores in non-uniform pore size distribution, and a high residual value exceeding 10 MPa. In addition, the initial degree of saturation and net confining stress play an important role in affecting the shear characteristics under the constant water content condition. Finally, a new semi-empirical shear strength model in terms of degree of saturation is proposed and then applied to Yunnan red clay. Simulation result shows that the model is capable of capturing some key features of soils. The model can be used in whole engineering practice range, covering both unsaturated and saturated soils.

Prediction of the gaseous thermal conductivity in aerogels with non-uniform pore-size distribution

The gaseous thermal conductivity in nano-porous aerogel is an important contribution to the total thermal conductivity under normal temperature and pressure condition. Pore-size distribution in the aerogel has significant effect on the gaseous thermal conductivity. The pore-size in the porous materials generally presents random and non-uniform distribution, and large deviation will be caused if directly using the mean pore-size to calculate the gaseous thermal conductivity. We present a modified model based on the previous theoretical models to take into account the random and non-uniform pore-size distribution, and the predicted results from the present model are significantly better than those of existing models.

Material characterization and bioactivity evaluation of dental porcelain modified by bioactive glass

This study aimed at the chemical, microstructural and textural characterization of the sol–gel derived dental porcelain modified by bioactive glass and the evaluation of its bioactivity. Sol–gel derived specimens of the composite material were constructed and subjected to firing cycle. Specimens of bioactive glass and dental porcelain served as control. All the specimens were characterized using X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS) and N2 porosimetry. The assessment of in vitro bioactivity was carried out by incubating the composite specimens in DMEM solution. Apatite formation was evaluated by SEM/EDS, FTIR and XRD analysis. Microstructural analysis by SEM revealed irregularly shaped particles with broad size distribution, while complex porei network with large pore volume and non-uniform pore size distribution was evident. N2-adsorption isotherms were representative of non-nano-/meso-porous materials. A mixture of a- and b-wollastonite, apatite and leucite phases were detected by FTIR and Raman spectroscopy. The XRD analysis confirmed the previous results, though traces of cristobalite were identified too. The in vitro tests evidenced the bioactivity of the specimens in a 3-day-period. In conclusion, the physicochemical properties of the sol–gel derived composite result in a bioactive material, though further modifications need to be considered in order to fulfill the requirements of application in the clinical reality.

Esterification of 4-methoxyphenylacetic acid with dimethyl carbonate over mesoporous sulfated zirconia

Abstract Mesoporous zirconia was synthesized using cetyltrimethylammonium bromide as template under hydrothermal conditions. The surfactant was removed by ethanol extraction. The resultant mesoporous material was further treated with sulfuric acid and calcined in air at 450 °C for 5 h to obtain mesoporous sulfated zirconia (MSZ). The mesoporous sulfated zirconia was characterized by XRD and N 2 adsorption and desorption measurements. Esterification of 4-methoxyphenylacetic acid (4-MPAA) with dimethyl carbonate was carried out in a batch reactor under autogeneous pressure over this catalyst as a function of reaction temperature, catalyst loading and the results are also compared with conventional sulfated zirconia (CSZ). More than 98% selectivity for methyl 4-methoxyphenylacetate was observed in all the experiments. The CSZ catalyst shows very low conversion when compared to that of MSZ. This may be attributed to its low surface area, presence of micropores and non-uniform pore size distribution. The mesoporous sulfated zirconia comprises of large surface area and uniformly distributed mesopores, which facilitates the reaction of bulky organic molecules like 4-MPAA with DMC. In addition, MSZ catalyst shows higher acidity than that of CSZ catalyst and in turn a higher catalytic activity. The kinetics of the reaction over both the catalysts was studied. The rate constant for the reaction was found to be 4.7 × 10 −3 min −1 and 0.5 × 10 −3 min −1 for MSZ and CSZ, respectively. The activation energy of the reaction is 18.0 kcal/mol over MSZ catalyst.

Effect of Temperature on the Adsorption of Water in Porous Carbons

We report experimental and simulation studies to investigate the effect of temperature on the adsorption isotherms for water in carbons. Adsorption isotherms are measured by a gravimetric technique in carbon-fiber monoliths at 378 and 423 K and studied by molecular simulation in ideal carbon pores in the temperature range 298-600 K. Experimental adsorption isotherms show a gradual water uptake, as the pressure increases, and narrow adsorption-desorption hysteresis loops. In contrast, simulated adsorption isotherms at room temperature are characterized by negligible uptake at low pressures, sudden and complete pore filling once a threshold pressure is reached, and wide adsorption-desorption hysteresis loops. As the temperature increases, the relative pressure at which pore filling occurs increases and the size of the hysteresis loop decreases. Experimental adsorption-desorption hysteresis loops are narrower than those from simulation. Discrepancies between simulation and experimental results are attributed to heterogeneities in chemical composition, pore connectivity, and nonuniform pore-size distribution, which are not accounted for in the simulation model. The hysteresis phase diagram for confined water is obtained by recording the pressure-density conditions that bound the simulated hysteresis loop at each temperature. We find that the hysteresis critical temperature, i.e., the lowest temperature at which no hysteresis is detected, can be hundreds of degrees lower than the vapor-liquid critical temperature for bulk model water. The properties of confined water are discussed with the aid of simulation snapshots and by analyzing the structure of the confined fluid.

Modeling through Drying of Tissue—Effect of Pore Size Distribution on Drying Characteristics

A general model for through drying of tissue was developed based on the equations of continuity in combination with correlations for heat and mass transfer. The model incorporates different geometric descriptions together with corresponding heat and mass transfer correlations for flow through cylindrical conduits and flow through packed beds of cylindrical fibers. At low intensities, i.e., at low airflow rates and low drying air temperatures, the model shows very good agreement with experimental data found in the literature and accurately predicts a period of constant drying rate due to saturation of the drying air. However, at higher drying intensities, the model predicts drying rates that are generally higher than what is found in experimental studies described in the literature. The model also predicts a period of constant drying rate that has not been observed in experiments at higher drying intensities. To illustrate the effect of nonuniform pore size distribution on the average drying rate, a model including a variable pore size distribution was developed. The results show that the early onset of the falling rate period in through drying at higher intensities could be explained by channelling effects caused by a nonuniform pore size distribution.

Contemporary Ideas about the Role of the Geometric Factor during Sintering in the Light of Work by M. Yu. Bal'shin

The effect on sintering of two such basic geometric parameters of a powder body as pore size distribution and the magnitude of the interphase specific surface is demonstrated. Nonuniform pore size distribution is the basis of the phenomenon of local volumetric shrinkage during sintering. The amount of interphase surface affects volumetric shrinkage and alloy formation. It is suggested that sintering is a two-stage process. The first stage is sintering of unbound powder system, and the second is sintering of a bound porous body.

Theoretical model of the porosity of copolymer membranes

A theoretical model is developed to explore the porosity and chemical morphology of copolymer membranes. The size of the leaving group during polycondensation of the cross-links is found to have unexpected effects on the porosity, leading to a nonuniform pore-size distribution. The size and formation of microdomains with different chemistries and porosities can be predicted using this model. Such knowledge of a membrane’s physical and chemical morphology is useful in the development of fouling-resistant filtration membranes. Reverse osmosis and nanofiltration membranes commonly used today frequently undergo degradation due to fouling and thus experience a diminishing water flux. Additional control over the properties of the membrane can be achieved by combining two or more polymers to form a heteropolymer network.

The densification and morphology of cordierite-based glass-ceramics

In this study, five different proportion of a borosilicate glass (from 30 to 70 wt.%) were added to stoichiometric cordierite to improve the densification behaviour of cordierite-based glass-ceramica. The phase and microstructural evolution of the samples were characterised by DTA and SEM. The results show that glass content plays an important role in the sintering of cordierite-based glass-ceramics. The sintered density increases as the glass content increases at low temperature (950°C). At high temperatures, the sintered density passes through a maximum value when the glass content is about 60 wt.%, followed by a decrease as the glass content further increases. DTA results show that densification is a non-reactive liquid phase sintering process. The microstructural evolution of the samples is in good agreement with the measurements of sintered densities. At the lower glass content, the sample shows more pores and a non-uniform pore size distribution. With the glass content increasing, the pore size becomes more uniform and sintered density increases.