Pore Volume Size Distribution Research Articles

Synthesis of ordered mesoporous γ-alumina – Effects of calcination conditions and polymeric template concentration

Mesoporous alumina was one-pot synthesized via polymeric surfactant template assisted sol-gel and Evaporation-Induced Self-Assembly (EISA) using aluminum isopropoxide (Al(O-i-Pr)3) as aluminum source. Among several experimental parameters affecting the properties of the synthesized aluminas, the effect of calcination temperature and the triblock copolymer template (Pluronic P123) content in the gel were studied. The effects of calcination temperature in the range of 700°C–1050 °C, on such parameters as surface area, pore volume, pore size distribution, phase transformation, and crystal size were experimentally investigated. The influence of P123/Al(O-i-Pr)3mass ratio in the range of 0.49–1.96 on the textural properties of the synthesized alumina was studied. The synthesized mesoporous alumina was characterized using N2 adsorption-desorption analysis, TGA/DTG and DSC/DTA. The phase identification and crystal domain size were determined using XRD. The morphology of the calcined samples was analyzed using SEM and TEM. The TEM observations and SAXS measurements revealed the mesostructured pore lattice of the samples. The pore diameter distributions were estimated by numerical image analysis of TEM images. The pore lengths distributions were also estimated using the scale bar of TEM images and found to be averaged around 800 nm. The calculated volume pore size distributions (PSD) were found in reasonable agreement with the PSDs obtained from NLDFT analysis of nitrogen adsorption-desorption isotherms. The synthesized γ-aluminas exhibited thermal stability up to 950 °C. At higher temperatures, the α-phase was formed, and the mesostructure collapsed. Samples obtained with P123/Al(O-i-Pr)3 = 0.98 and 1.47, calcined at 700 °C with 3 h soaking time exhibited a surface area of 259 m2/g and 238 m2/g respectively.

COMPUTER SIMULATION OF RANDOM PACKINGS FOR SELF-SIMILAR PARTICLE SIZE DISTRIBUTIONS IN SOIL AND GRANULAR MATERIALS: POROSITY AND PORE SIZE DISTRIBUTION

A 2D computer simulation method of random packings is applied to sets of particles generated by a self-similar uniparametric model for particle size distributions (PSDs) in granular media. The parameter p which controls the model is the proportion of mass of particles corresponding to the left half of the normalized size interval [0,1]. First the influence on the total porosity of the parameter p is analyzed and interpreted. It is shown that such parameter, and the fractal exponent of the associated power scaling, are efficient packing parameters, but this last one is not in the way predicted in a former published work addressing an analogous research in artificial granular materials. The total porosity reaches the minimum value for p = 0.6. Limited information on the pore size distribution is obtained from the packing simulations and by means of morphological analysis methods. Results show that the range of pore sizes increases for decreasing values of p showing also different shape in the volume pore size distribution. Further research including simulations with a greater number of particles and image resolution are required to obtain finer results on the hierarchical structure of pore space.

Porous structure of carbon-carbon friction composites studied by gas adsorption and standard contact porosimetry techniques

Using low-temperature nitrogen adsorption measurements and standard contact porosimetry, we determined parameters of the pore structure of a carbon-carbon friction composite: specific surface area, total pore volume, and pore volume-size distribution. The results demonstrate that the material is macroporous, with predominant pore radii in the range 1 to 100 μm. Using two saturating fluids, octane and water, we established distinctions between the hydrophilic properties of the surface of different groups of pores in the composite material.

Formation of porous vanadium- and molybdenum-containing oxides during mechanochemical activation of pore-free powders

Porous V- and Mo-containing oxides have been produced by mechanochemical processing of pore-free coarse powders in different environments: air, water, and ethanol. The materials have been characterized by nitrogen adsorption-desorption measurements, mercury porosimetry, scanning electron microscopy, atomic force microscopy, and X-ray diffraction. The results demonstrate that the only effect of air milling is to reduce the particle size of the powders, whereas wet milling leads to the formation of meso- and macropores with several maxima in the pore volume-size distribution.

Pore Properties of Eco-Material for Erosion Control of Slope and its Fractal Features

The pore properties of the porous material are important factors influencing the vegetation to grow. The pore properties of an artificial planting material and soil were studied by a mercury intrusion test. Based on the fractal concept of Menger-sponge, the fractal dimensions characterizing pore volume-size distribution of planting material and soil are obtained from the experimental data, and the different of both of the fractal dimensions is compared. The testing results show that the total porosity of planting material varies from 30.27 % to 32.11%, and the total porosity of soil is 24.87%. The law of their pore volume-size distribution in different range of pore-size is identical. The fractal research exhibits that the fractal dimensions have a different value in all the range of pore-size for planting material or soil, and small fractal dimension corresponds to small pore-size. As compared with soil, the fractal dimension of planting material is larger slightly in range of small pore, and is same basically in range of micro and medium pore. These results indicate that the fractal dimension is a useful measure of pore grading, which divides the pore into four groups with micro pore, small pore, medium pore and large pore. And the pore properties of eco-material for erosion control of slope are helpful to the vegetation growth.

Freeze-casting technique in the development of solid drug delivery systems

The aim of the present study was to develop a fast-dissolving solid dosage form containing theophylline as active ingredient using the freeze-casting technique. The structure, the physical properties and mechanism of drug release from the freeze-casted units were investigated. The examined properties of the samples were compared with those of tablets compressed by an eccentric tableting machine using three different compression pressures. The freeze-casting technique proved to be an appropriate alternative for the development of porous solid drug delivery systems. The mechanical strength of the matrices could be improved by using water-soluble additives, which stabilized the solid bodies during recrystallization upon drying. As compared with the tablets, the freeze-casted units revealed a highly porous nature and a remarkable difference in pore volume size distribution. The results demonstrated that the drug–solvent interaction, enhanced by the structural properties, resulted in a rapid delivery of the theophylline from the solid units into artificial gastric juice.

Rényi dimensions of soil pore size distribution

The existence of fractal scaling for pore volume-size distribution has been empirically shown, and several fractal models have been constructed to replicate it, deriving also other important physical properties. One step forward may be given by using multifractal analysis, which achieves a better characterization of a distribution by means of a singularity spectrum whenever suitable scaling properties are present. Rényi dimensions are a classical tool to characterize complex distributions that are closely related to the multifractal singularity spectrum but having an easier handling and interpretation. In this article, Rényi dimensions of pore size distributions are computed from data obtained by 2-D image analysis of soil samples. Analyzed samples show suitable scaling properties. The Rényi dimensions D q appear defined with R 2 greater than 0.95 within a significative range of q's. The variation of D q with respect to q and the shape of the Rényi spectrum reveal that pore size distributions have properties close to multifractal self-similar measures. These results show that Rényi dimensional analysis is an appropriate tool for characterizing soil pore size distribution and thus may be used as indicator of soil structure as well as for deriving important soil physical properties. Moreover, this characterization opens the possibility of simulating the real distributions by adequate self-similar models of fractal geometry, as iterated function systems and related ones, with the corresponding benefits for prediction purposes.

Mercury porosimetry of microcrystalline cellulose tablets: effect of scanning speed and moisture

The effect of pretreatment and scanning speed of mercury porosimetry on the porosity result of microcrystalline cellulose tablets was studied. The porosity parameters followed were total pore volume, mean and median pore size, and volume pore size distribution. Scanning speed did not affect the total pore volume of tablets compressed from microcrystalline cellulose. With increasing speed, the smallest pores of powder tablets were not properly determined, which increased the mean pore size. The median pore size of tablets compressed from powder and granules decreased and the maximum at the pore size range 500–1000 nm changed towards smaller pores with increasing scanning speed. Scanning speed appears to affect in different ways the samples with different physical structures. In tablet samples, scanning speed affects the volume of the pores at the whole pore size range determined. Thus, it is important to use about the same, reasonably low scanning speed in the measurements when comparing the samples. Swelling of microcrystalline cellulose in tablet samples is observed by mercury porosimetry measurement; a change in the pore structure is detected after storage at 88% relative humidity as increased total pore volumes and median pore sizes. Due to swelling, the maximum at the pore size range 500–2000 nm changed towards larger pores with increasing moisture. Swelling is observed similarly in tablets manufactured from powder and granules. When storing in humid conditions, water fills the smallest pores of microcrystalline cellulose powder tablets, hinders the intrusion of mercury and, thus, the mean pore size increases. Contrary to this, the volume of the smallest pores of granule tablets compressed with the highest compression pressure increased with increasing moisture. Careful pretreatment before the measurements is important.

Pore structure and surface area of mannitol powder, granules and tablets determined with mercury porosimetry and nitrogen adsorption

Two methods used in pore structure characterisation, mercury porosimetry and nitrogen adsorption, were compared. Pore structure and surface area of mannitol powder, granules produced in wet granulation and tablets compressed with three compression pressures were studied. Greater surface area, more porous structure and greater number of small pores in granules, when compared with powder, increased the compactibility of mannitol granules in tableting. Plastic deformation and fragmentation of powder and granules in compression were observed in volume pore size distributions and surface areas measured with these methods. Pore volume and volume pore size distribution obtained with mercury porosimetry describe densification of mass better than those obtained with nitrogen adsorption. In spite of differences between the methods, the volume pore size distribution curves of samples in the overlapping pore size range had the same shape. The specific surface area of tablets, measured by the nitrogen gas adsorption method described well the deformation under compression. Fragmentation increased the surface area of powder, and plastic deformation decreased the surface area of granules in the pore size range determined. Surface area values measured with mercury porosimetry were larger than those determined with nitrogen adsorption.

Application of mercury porosimetry in evaluation of extrusion-spheronisation process

In this study we evaluated the applicability of mercury porosimetry on the properties of extradates and pellets. We investigated the effect of thickness of the screen, speed of the agitator and spheronisation time as well as the effect of re-extrusion. The extruder variables had no systematic effect on the porosity parameters of the pellets. Spheronisation was such a drastic process that it eliminated differences in the porosity parameters of extradates. With increasing spheronisation time, the total pore volume and mean pore diameter of the pellets decreased significantly. Due to the loose structure of the extrudates, the centrifugal force caused the wet mass to migrate towards the surface. This contributed to the formation of a cavity inside the pellets which became larger with increasing spheronisation time. Due to re-extrusion, the volume of the large pores decreased and that of the small pores increased. Although all the porosity parameters studied were useful in characterising the pore structure of pellets, the most sensitive parameter was the pore-volume size distribution. The use of microscopy in the interpretation of mercury porosimetry results is recommended.

Porosity parameters of lactose, glucose and mannitol tablets obtained by mercury porosimetry

The effect of compression force, compression speed and the amount of granulation liquid on the porosity parameters determined from lactose, glucose and mannitol tablets by high-pressure mercury porosimetry was investigated. Compression force affected all parameters measured, except the total pore surface area of lactose tablets. The changes in tablet microstructure with increasing compression force were particularly well detected from the pore volume size distributions of tablets. Compression speed affected the total pore volume of lactose tablets, both mean and median pore diameters of lactose tablets and mannitol tablets compressed from granules produced with a low amount of liquid, and the median pore diameter of glucose tablets. The compression speed dependence of these parameters was a sign of the time-dependent deformation of materials during compression. The amount of granulation liquid affected the total pore surface area of lactose and mannitol tablets. With a high amount of liquid, the surface area of pores was greater. The mean pore size of all tablets and the median pore diameter of mannitol tablets were smaller when a high amount of granulation liquid was used. Even when compressed with a high force, the pore volume size distributions of mannitol tablets with a low amount of granulation liquid were broader and the maxima were at larger pore diameters. It was concluded that each porosity parameter measured characterised the pore structure of compressed tablets from a different aspect. Thus, the use of all porosity parameters proved to be useful.

Change in porosity parameters of lactose, glucose and mannitol granules caused by low compression force

The change in porosity parameters, i.e., total pore volume, porosity percentage and pore volume size distribution of lactose, glucose and mannitol granules caused by compression with a low force was investigated. In compression, fragmentation of lactose and glucose granules increased total pore volume and porosity percentage, whereas the total pore volume and porosity percentage of mannitol granules was clearly decreased. This was due to the highly porous structure of mannitol granules, which densified easily in compression. Lactose and glucose granules were shown to resist deformation more. The pore volume size distributions of lactose and glucose tablets showed that large pores ( > 14 μm) decreased in size. For mannitol tablets, the large pores vanished and simultaneously the small granule pores ( < 14 μm) reduced in size. The features of the pore structure of granules were detected in the pore volume size distributions of compressed tablets. Mercury porosimetry, assisted by scanning electron microscopy, was shown to be an adequate method to evaluate the deformation of granules in compression.

Relationship between breaking force and pore structure of lactose, glucose and mannitol tablets

The aim of this study was to determine the relationship between the breaking force of lactose, glucose and mannitol tablets and the pore structure characterised by numeric porosity parameters: total pore volume, total pore surface area, mean pore diameter, median pore diameter and volume-size distribution of pores, obtained by mercury porosimetry. A clear overall relationship was found between breaking force of tablets and the median of the cumulative pore volume-pore diameter curve and pore volume-size distribution. The dependence of the breaking force on total surface area of pores was less evident. Fragmentation of granules contributes to the creation of large intergranular and intragranular pores, and further fragmentation and plastic deformation of the primary particles contributes to their reduction in number and size. According to pore volume-size distributions, the decrease in the volume of large pores and the shift of the maximum for volume-size distribution towards smaller pore diameter were related to the increased breaking force of tablets.

Correlation between carrier porous structure and gas-sensitive properties of thermocatalytic gas sensors

In order to determine the correlation between the gas-sensitive properties of the thermocatalytic gas sensor (TGS) and the porous structure of the carrier, two types of carriers have been investigated. Their sorptional parameters at different calcination temperatures have been studied. The parameters of the porous structure and the gas-sensitive properties of the TGS are characterized by measurements of benzene vapour adsorption and methane oxidation using methane/air mixtures, respectively. The obtained data indicate that the sensitivity of the TGS is related in some way with the structural parameters of the carrier (pore size and diameter distribution). Carriers must have a sorption capacity no less than 0.30 cm 3 g −1, surface area of 100–140 m 2 g −1 and possess biporous pore-volume size distribution.

The Role of Liquid Water Uptake by an Insoluble Tablet Containing a Disintegrant

AbstractThe hydration capacity of each of four disintegrants including microcrystalline cellulose (Avicel PH102), corn starch, croscarmellose sodium (Ac-di-sol) and sodium starch glycolate (Primojel) was determined to express the hydrophilicity. The complete pore structure, and the water uptake of unmilled dicalcium phosphate dihydrate (Di-Tab) tablets containing one of above disintegrants at 15% w/w level were studied It was found that the majority of the tablet porosity was made up by macropores which were accessed by mercury intrusion There was no statistically significant difference among pore volume-size distributions of table samples The water uptake results were treated by the empirical form of Washburn liquid penetration equation with appropriate experimental setup. It was possible to determine the significance of the empirical parameters drawn from the equation It was found that the hydrophilic nature of excipients present in a tablet played a major role in water uptake phenomenon It was suggeste...

Microstructure determination of cement pastes by NMR and conventional techniques

Applicability of NMR relaxation analysis to the characterization of pore structure in hydrating white cement pastes has been investigated. Measurements of transverse magnetization relaxation were made in specimens saturated and partially filled with water for periods of hydration between 1 and 28 days. The fast diffusion model successfully accounts for all relaxation measurements. The transverse surface relaxation rate was determined. A two-component pore volume size distribution was found. Comparison was made with mercury porosimetry and nitrogen sorption experiments and the results were correlated with compressive strength.

Surface tension nonuniformity effect on fluid distribution in a porous body

Surface forces nonuniformity within the volume of a capillary system for a given structure has been examined in terms of its effect on a wetting fluid distribution. This approach enables the distribution for a porous body with a uniform structure to be quantified using a specific function for the pore volume size distribution. The surface forces nonuniformity effect is illustrated using a fibrous structure impregnated with molten copper.

Mesure de la perméabilité aux gaz des revêtements de pyrocarbone isotrope

Gas permeability of pyrocarbon (PyC) coatings of Biso fuel particles for high temperature gas cooled reactors has been evaluated by various methods both physical and physical chemistry measurements. It was established that the gaseous chlorine leach method associated with ceramographic examinations of ThO 2 kernels is more suitable than PyC texture tests for routine control; the flow measurement of a labelled gas ( 14CO 2) accross the PyC coating is a technique available only in the laboratory. Moreover, it seems that the pore volume-size distribution is related to the permeability which would be rather attributed to the micropores.