Evolution Of Pore Volume Research Articles

Experimental investigation of dynamic drying in single pharmaceutical granules containing acetaminophen or carbamazepine using synchrotron X-ray micro computed tomography

Drying time, velocity, and temperature are important aspects of the drying process for pharmaceutical granules observed during tablet manufacturing. However, the drying mechanism of single granules is often limited to modelling and simulation, with the internal and physical changes difficult to quantify at an experimental level. In this study, in-situ synchrotron-based X-ray imaging techniques were used for the first time to investigate the dynamic drying of single pharmaceutical granules, quantifying internal changes occurring over the drying time. Two commonly used excipients (lactose monohydrate (LMH) and microcrystalline cellulose (MCC)) were used as pure components and binary mixtures with one of either two active pharmaceutical ingredients of differing hydrophilicity/hydrophobicity (acetaminophen (APAP) and carbamazepine (CBZ)). Water was used as a liquid binder to generate single granules of 25 % to 30 % moisture content. Results showed that for most samples, the drying time and composition significantly influences the pore volume evolution and the moisture ratio, with the velocity and temperature of the drying air possessing mixed significance on increasing the rate of pore connectivity and moisture removal depending on the sample composition. Effects of active ingredient loading resulted in minimal influence on the drying of CBZ and generated binary mixtures, with APAP and its respective mixtures’ drying behaviour dominated by the material’s hydrophilic nature.

Investigation of pore structure evolution and damage characteristics of high temperature rocks subjected to liquid nitrogen cooling shock

Liquid nitrogen (LN2) can be utilized in the development of enhanced geothermal systems, as well as for deep/ultra-deep hydrocarbon reservoir stimulation, fire suppression, and other high-temperature geological projects. It is a crucial issue in the utilization of LN2 to investigate the pore structure evolution, permeability, and damage characteristics of high-temperature rocks under the influence of LN2 cooling shock. These rocks were first slowly heated to 150∼600°C and held for 2 h, followed by LN2 or natural cooling. The evolution of pore volume in high-temperature rocks affected by liquid nitrogen cooling was quantified. T2 cutoff values were determined through centrifugal tests, while the contents of irreducible and mobile fluids were estimated. Based on the aforementioned analysis as well as changes in irreducible fluid saturation, pore throat, tortuosity, and permeability, this study examines the closure and development of pores along with permeability behavior. The findings suggest that, despite a more pronounced decrease in porosity at lower heating temperatures, LN2 cooling specimens exhibit superior pore connectivity and permeability compared to those cooled naturally. LN2 stimulation not only induces crack initiation and propagation but also results in further cooling induced densification based on heating densification. 225°C is considered to be the optimal temperature for cooling contraction induced densification in this study. At higher heating temperatures, the damage to rock cooled with LN2 is more severe than that of naturally cooled. This results in a greater increase in porosity, movable fluid content and proportion, and permeability of LN2 cooled specimens compared to naturally cooled specimens. The damage mechanism can be better understood by the constructed damage model that coordinates the pore increase/decrease and mutual pore transformation from the perspective of pore evolution.

Effect of the near-surface pore volume evolution on graphite migration of copper-based graphite composite during friction

The discrete element method was used to simulate the friction process of copper-based graphite composite materials in order to analyze the influence of pore structure on the solid lubricants migration in metal-based self-lubricating materials. And the near-surface pore volume evolution was considered in the simulation. The simulation results showed that the graphite particle motion depth and the migration channel increased gradually and tended to stable during friction. The near-surface pore structure has an important influence on the graphite migration and the tribological properties of the composite: the larger the migration channel was, the greater the graphite migration speed was; with the increase in migration channel, the graphite average critical migration depth decreased first then increased, the number of the film-forming particles first increased and then decreased; the greater the migration channel volume was, the more worn particles number were. The numerical simulation was confirmed by experimental analysis on a self-made in-situ observation tribometer, the experimental results were consistent with the numerical simulation results.

In-Situ observation and quantitative analysis on sintering process of Li4SiO4 sorbents

High-temperature CO2 adsorption has an attractive prospect in reducing CO2 emissions efficiently. As the core of CO2 adsorption technology, sorbents suffer from a well-known problem of capacity degradation as a result of sintering during cyclic CO2 adsorption and desorption at high temperatures. This work aims to understand the microstructural evolution of Li4SiO4, one of the most typical and promising sorbents, during CO2 capture. In-situ Transmission Electron Microscopy was used to directly capture the morphological variation of Li4SiO4 sorbents. Comprehensive characterization techniques were adopted to quantify microstructural parameters of Li4SiO4 under different conditions. The real-time shrinkage of Li4SiO4 particles was demonstrated and equations on grain growth, specific surface area reduction, and pore volume evolution were established. The work can not only reveal the reason for the reduction of CO2 capacity, but provide a theoretical guidance for the development of sintering-resistant CO2 sorbents.

Research on pore closure behavior and microstructure evolution during hot isostatic pressing of Ti6Al4V alloy casting

Hot isostatic pressing (HIP) has an important influence on the pore closure behavior and the microstructure evolution around pores in Ti6Al4V alloy castings. Therefore, experiments including the preparation of HIP samples and interrupted HIP experiments, and finite element numerical simulations were used to analyze the evolution of pore volume, distribution of stress and strain in Ti6Al4V alloy during HIP. After the mechanical closure of pores, molecular dynamics simulations were used to study the effect of temperatures and numbers of grains on the micropore closure. Finally, SEM/EBSD methods were applied to characterize the evolution of microstructure around the pore. The results show that creep is mainly contributed to the pore closure in the Ti6Al4V alloy during HIP, and the pore volume decreases by 96% after the step of raising temperature and pressure (first stage of HIP), the pore closure mainly occurs in the first stage of HIP. Grain boundary diffusion is the main mechanism for micropore closure. In addition, with the increase of HIP duration, the volume fraction of spheroidized α grains around pores is getting larger, the main mechanisms of spheroidization of α lamellae around the pore during HIP are continuous dynamic recrystallization and lamellae kinking.

Impact of thermal maturity on the concomitant evolution of the ultrafine structure and porosity of marine mudstones organic matter; contributions of electronic imaging and new spectroscopic investigations

This study aims to better understand the evolution of the organic matter (OM) ultrafine structure (designating the nanoscopic structure of the OM/macerals) and porosity with increasing thermal maturity of mudstones source-rocks. To this end, the particulate fractions of kerogen from organic-rich Kimmeridge clay mudstones were isolated by acidic treatment before and after laboratory thermal maturation. The evolution of the composition, the chemical structure and the porosity of kerogen from the immature stage (Ro = 0.42%) to the dry gas zone (Ro = 2.12%) were documented using a combination of elemental analysis, vitrinite reflectance measurements, Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM), Raman spectroscopy and Small Angle X-Ray Scattering (SAXS). The evolution of the porosity of OM was then compared to the evolution of the pore volume of the total rock measured by nitrogen adsorption. The results show that the progressive densification, reorganization and aromatization of the amorphous kerogen particles into a more ordered, but heterogeneous carbon-rich residue is responsible for significant variations in the kerogen porosity with increasing maturity. Contrary to the previous observations on these Kimmeridge clay mudstones, the variations that occur during the peak of oil generation (Ro of ca. 0.90%) mark the onset of the OM-hosted pores development. There appears to be a natural close relationship between the evolution of OM porosity and total pore volume of organic-rich mudstones during gas generation. Indeed, a similar alternation of pore collapse and pore development is observed in response to gas generation. The development and the evolution of pores in these organic-rich mudstones seems thus mainly driven by the evolution of the chemical structure and the composition of OM during thermal maturation. In the dry gas zone, the porosity and the specific surface area of the kerogen are significant (19% and 57.1 m2.g−2 respectively). This highlights the importance of the OM content, type and composition in the porosity and gas storage capacities of mudstone reservoirs, increasingly discussed in the available literature in recent years.

Effects of cement content and curing period on strength enhancement of cemented calcareous sand

Cement treatment is a promising and effective method to enhance strength of calcareous sand in regions where offshore foundations and coastal facilities are localized. In treatment, the added cement content and curing period influence the strength of cemented calcareous sand. In order to regulate the loading resistance of cemented calcareous sand, effects of cement content and curing period on strength enhancement are investigated experimentally. First, cemented specimens with 5%, 7.5%, and 10% cement contents and 1–28 days curing period are prepared. Then, unconfined compression test is conducted to measure strength. Nuclear magnetic resonance test is also performed to analyze microstructure change during hydration reaction. An empirical equation of strength is derived, considering the effects of cement content and curing period. This equation shows higher accuracy than existing empirical models. In addition, the microstructure change in hydration process is quantified by pore volume evolution. Void ratio is used to characterize the pore volume evolution. Hence, the dependence of strength on cement content and curing period is quantitatively explained by the change in void ratio. This sheds light on hydration reaction in cement treatment by cement content and curing period and the regulation of strength enhancement in cemented calcareous sand. Highlights Empirical equation on strength with effects of cement content and curing period Pore volume evolution by hydration reaction in cement treatment Characterization of microstructure change by void ratio Microscopic mechanism of strength enhancement for cemented calcareous sand

Distinct evolution trends of nanometer-scale pores displayed by the pyrolysis of organic matter-rich lacustrine shales: Implications for the pore development mechanisms

Organic matter (OM) compositions greatly affect hydrocarbon generation and expulsion processes, which are critical for the organic porosity development in shale. Lacustrine shale samples of low thermal maturity were pyrolyzed using two pyrolysis systems (closed and semi-closed systems). Pore development was measured by low-pressure gas adsorption and field emission-scanning electron microscopy (FE-SEM), and bulk porosity was modeled utilizing organic geochemical data. The gas adsorption analysis indicated that shale samples of different OM compositions differed in pore volume evolution with thermal maturity, mainly related to the different amounts of hydrocarbon generated and expelled. Residual bitumen significantly reduced the pore volume of OM-rich oil generative shale samples, and restricted the micro-, meso-, and macro-pore volumes to different extents. Calculations and experiments both showed that OM-rich and oil generative shale experienced a greater increase in pore volume after the oil peak. In addition, it was observed that variations in the main pore types were associated both with shale compositions and with exerted overburden pressure. Increase in overburden pressure were found to greatly facilitate the development of nanometer-size spongy and complex OM pores in shales containing type Ⅱ/Ⅲ kerogens, possibly as a result of the expulsion of gaseous hydrocarbons. By contrast, the shale with abundant type Ⅰ kerogen tended mainly to develop relatively large pores following oil expulsion regardless of overburden pressure. The modeled organic porosity of pyrolyzed samples of type III OM was similar to the porosity of geological shale, but the porosity of OM-rich oil generative shale samples with high expulsion efficiency at the oil generation stage was two to three times the measured porosity of the geological shale. In some cases, the higher modeled shale porosity might be related to the higher expulsion efficiency. For geological shales of expulsion efficiency comparable to the pyrolyzed samples, geological processes (e.g., compaction and cementation) may have greatly reduced the OM-associated pore volume.

In-situ pore size investigations of loaded porous concrete with non-destructive methods

Subject of this investigation is the in-situ evolution of pore volume and pore size distribution in Ytong (a porous concrete material) under increasing pressure with two different non-destructive analytical methods: Nuclear Magnetic Resonance (NMR) and X-ray Computed Tomography (CT). For both methods special strain devices to apply external pressure were constructed. The results from the two techniques yield complementary information on the pore size distribution and allows covering different pore size regions.

Experimental Investigation for Pore Structure and CH4 Release Characteristics of Coal during Pulverization Process

Qinshui coalfield is the largest coalbed methane and anthracite production base in China. In the process of mine gas prevention and control, there was a larger amount of gas that can be extracted, but even with this, the residual gas pressure is not up to standard. In this paper, in order to analyze its specific reasons, a series of experiments were carried out to investigate the pore structure, particle size distribution, and CH4 release characteristics of anthracite during the pulverization process. Results show that, compared with bituminous coal, anthracite can continuously release a certain concentration of CH4 during the pulverization process. The SEM test exhibits that anthracite possesses more secondary pores while bituminous shows more mineral pores. With the increase of total pulverizing time, the coal particle size is gradually decreased. Furthermore, compared with the pre-pulverized samples, the porosity, pore volume, and surface area of post-pulverized samples are increased, indicating that the closed pores are destroyed to be open pores during the pulverization process. In addition, by combining the gas release concentration and pore volume evolution, it can be inferred that the anthracite may contain more solid solution gas due to the fact that there is a certain amount of gas that can be released when the pore volume tends to be smooth. The research results can provide the theoretical basis for gas extraction in the anthracite mine.

Positron insight into evolution of pore volume and penetration of the polymer network by n-heptane molecules in mesoporous XAD4.

The adsorption and desorption of n-heptane on the mesoporous polymer resin Amberlite XAD4 were investigated in situ by positron annihilation lifetime spectroscopy (PALS). This technique allows the monitoring of porosity and subnanometer free volume changes as well as the amount of liquid adsorbate captured within an investigated sorbent, without causing any interference with the course of adsorption/desorption. In consequence, the conducted studies provide microscale insight into the sorption processes of n-heptane (which is a significant component of volatile organic compounds - VOCs) on the polymeric material. The total pore volume decreases parabolically with n-heptane pressure until it reaches zero just below the saturated vapor pressure. Simultaneously, the average pore size increases linearly until it has approximately doubled. However, much faster rates of change in both these parameters occur at relative pressures below 0.05. The PALS results can be properly explained only if the swelling of the polymer skeleton is taken into account during the alkane adsorption process. This is confirmed by long-term pumping, which was required to achieve stabilization of PAL spectra during the final phase of desorption. In addition, the evolution of subnanometer free volumes (located between polymer chains and formed in liquid n-heptane) support this interpretation of the results.

Understanding sintering characteristics of ZnO nanoparticles by FIB-SEM three-dimensional analysis

Abstract In this study, we utilize three-dimensional (3D) reconstruction by focused ion beam (FIB) cutting and SEM imaging to understand the evolution of pore volume, pore-solid interfacial area, pore shape, pore connectivity, and pore number during the two-step sintering of ZnO nanoparticles. After the first-step sintering, the density is 75% and all the pores are connected. During the second-step sintering, the decrease of pore volume leads to the segmentation of pores and formation of closed pores. The shape of closed pores is irregular. The pore number first increases with the formation of closed pores, and then decreases due to the disappearance of small pores. The pore-solid interfacial area keeps decreasing during sintering. FIB-SEM 3D reconstruction offers an opportunity to directly and quantitatively observe the pore evolution and understand the sintering process at nanoscale.

Effect of combined activation on the preparation of high porous active carbons from granulated post-consumer polyethyleneterephthalate

Activated carbons were prepared from granulated post-consumer PET by combined activation including heat treatment with sulphuric acid (chemical activation) followed by steam activation. The effect of activation time, temperature, impregnation coefficient in the activation process was studied in order to optimize those reception parameters. One of the most important parameter in combined activation of crushed PET was found to be impregnation coefficient. It was defined that the optimal impregnation coefficient is equal 28%. Activation temperature is another variability which has a significant effect on the pore volume evolution. The increasing of activation temperature enhances the surface area and pore volumes of active carbons. The yield of final product which composes of nearly 15% is the factor limited the activation temperature above 800 °C. Textural characteristics of the samples were carried out by performing N 2 adsorption isotherm at −196 °C. The obtained active carbons were mainly micro- and mesoporous and with BET apparent surface areas of up to 1030 m 2/g. The adsorption capacity on methylene blue reaches 1.0 mmol/g, the sorption activity on iodine comes to 77%.

A carbon activation model with application to longan seed char gasification

In this paper a new structural model is presented to describe the evolution of porosity of char during the gasification process. The model assumes the char structure to be composed of bundles of parallel graphite layers, and the reactivities of each layer with the gasification agent are assumed to be different to represent the different degree of heterogeneity of each layer (i.e. each layer will react with the gasification agent at a different rate). It is this difference in the reactivity that allows micropores to be created during the course of gasification. This simple structural model enables the evolution of pore volume, pore geometrical surface area and the pore size distribution to be described with respect to the extent of char burn-off. The model is tested against the experimental data of gasification of longan seed-derived char with carbon dioxide and it is found that the agreement between the model and the data is reasonably satisfactory, especially the evolution of surface area and pore volume with burn-off.

Radial distribution of porosity in spherical activated carbon particles

The radial distribution of porosity in spherical activated carbon particles and its relationship to both activation temperature and conversion of the reaction C–CO 2 are discussed. Char spheres, obtained by pelletizing Quercus agrifolia powdered char, were activated using CO 2 as activating agent at 820 and 860 °C. For both temperatures, the gasification reaction was run until the desired conversion (30, 50 and 70%) was reached. The activation process was performed using TGA apparatus. The porosity of the samples was measured by physical adsorption of nitrogen at −196 °C. BET and Dubinin–Raduskhevich equations were used to analyse the results. From each activated carbon sphere several samples were prepared, corresponding to different layers of the sphere; an outer layer, a middle layer and the core of the particle. From these results, the radial porosity evolution as a function of activation temperature and reaction conversion was obtained and a mathematical expression that correlates pore volume evolution and reaction conversion is proposed.

The preparation of activated carbon from macadamia nutshell by chemical activation

Different structured activated carbons were prepared from macadamia nutshell by chemical activation with potassium hydroxide and zinc chloride. The influence of process variables on the carbons' pore structure was studied in order to optimise these parameters. The results were also compared with those previously obtained on the chemical activation of coal. The most important parameter in chemical activation with both chemical agents was found to be the impregnation ratio. Carbonization temperature is the second important variable which had significant effect on pore volume evolution. Under the experimental circumstances studied, the optimum conditions in preparation of carbons with high surface area and pore volumes with both chemical agents are identified.

The preparation of active carbons from coal by chemical and physical activation

A series of activated carbons was prepared from bituminous coal by chemical activation with potassium hydroxide and zinc chloride and also by physical activation with carbon dioxide. The effect of process variables such as carbonization time, temperature, particle size, chemical agents, method of mixing and impregnation ratio in the chemical activation process was studied in order to optimize those preparation parameters. Partial gasification of the high surface area carbon obtained by zinc chloride activation in CO 2 with different exposure times shows some improvement in adsorption. The physical properties of the chemically activated carbon was also compared with those obtained purely by physical activation. The most important parameter in chemical activation of coal with both of the chemical agents was found to be impregnation ratio. Carbonization temperature is another variable which had a high effect on pore volume evolution. While increasing the carbonization temperature enhances surface area and pore volumes of KOH-activated carbon, it destroys carbon structure in the ZnCl 2 carbon series. Under the experimental conditions investigated, the optimum conditions for high surface area carbons with KOH and ZnCl 2 activation are identified.

Stages of surface and pore volume evolution during sintering: O. Blaschko et al (University of Vienna, Vienna, Austria) Acta Metall. Mater., Vol 42, No 1, 1994, 43–50

Stages of surface and pore volume evolution during sintering: O. Blaschko et al (University of Vienna, Vienna, Austria) Acta Metall. Mater., Vol 42, No 1, 1994, 43–50

Stages of surface and pore volume evolution during sintering

Sintering in compacted powders of Mo, Nb, Ta, and alumina is investigated using small angle neutron scattering. The scattering data permits to follow the evolution of the total pore surface F together with the total pore volume V in the course of the entire densification process. Characteristic changes in the relation between F and V suggest that sintering proceeds in three different stages. Quantitative evidence is presented that, in particular, third stage sintering (taking place if the pores can be considered isolated from each other) is governed by a universal relation between F

A random capillary model with application to char gasification at chemically controlled rates

AbstractPorous particles are described by a random capillary model predicting the frequency of pore intersections and the evolution of pore volume and surface area during reaction. The model is applied to char gasification at chemically controlled rates, and the results are compared with data from the literature.