Aluminate Hydrate Research Articles

Evolution of elastic and thermal properties of cementitious composites containing micro-size lightweight fillers after exposure to elevated temperature

This paper studies the evolution of elastic and thermal properties of cementitious composites containing micro-size lightweight fillers after exposure to elevated temperatures (up to 800 °C). A multiscale investigation is carried out to study the thermal degradation of cementitious composite materials at multiple scale levels: at cement past level, the dehydration kinetics of cement hydrates (i.e., C–S–H, CH and aluminate hydrates) and development of microcracks are studied as functions of exposure temperatures. The damage mechanism of the inclusion phases and damages within the interfacial transition zone (ITZ) under elevated temperature are also investigated. In addition, the change of mechanical (i.e., elastic moduli, compressive strengths) and thermal (thermal conductivities) properties are measured as functions of the exposure temperature. Based on the experimental studies, a multiscale thermal degradation model is developed where the thermal degradations of cement paste (including water composition, porosity, and solid phase changes), inclusion phases, and the interfaces are captured through a multiscale sub-stepping homogenization scheme. The thermal degradation model is validated through multiple sets of experimental data. Finally, the influence of key parameters including the particle size distribution of the inclusions, the chemical composition, as well as the effects of ITZ damage are studied.

Strength evolutions of varying water content-dredged sludge stabilized with alkali-activated ground granulated blast-furnace slag

The variation of water content significantly affects the strength development of stabilized dredged sludge (DS), as well as the rational use of binder. This paper experimentally studies the strength and microstructure evolutions of DS stabilized with alkali-activated ground granulated blast-furnace slag (GGBS) under different water contents, via a range of unconfined compressive strength (UCS), X-ray diffraction (XRD) and scanning electron microscopy (SEM) tests. The sodium hydroxide (SH) and sodium silicate (SS) were used as single and composite activators for GGBS, and their roles on the stabilization efficacy were mainly focused. The results illustrated that the optimum single activator content tended to increase with the increase of water content. Composite activators were more effective than single activator in activating GGBS for achieving higher UCS of stabilized DS. The optimum mass ratio of SH to SS (H/S) in composite activators was 2/3, 2/3 and 1/4 at water content of 60, 70 and 80%, respectively. The linear empirical equations for predicting 60- and 90-day UCS based on 28-day UCS were proposed. XRD and SEM results confirmed that calcium silicate hydrate and calcium aluminate hydrate were the major hydrations, which undertook the cementation and filling roles. Furthermore, the micro-mechanisms revealing the strength evolutions of stabilized DS were analyzed and discussed. The results recommended that using 20% SH/SS-GGBS binder with optimum H/S of 2/3, 2/3 and 1/4 as the substitute of equivalent PC for stabilizing DS with water content of 60, 70 and 80%, respectively.

Effects of calcium formate on early-age strength and microstructure of high-volume fly ash cement systems

Replacement of Portland cement (PC) by fly ash (FA) is currently limited to 15–30% by mass, mainly due to low early age strength development of concrete. This research uses calcium formate (Ca(HCO2)2; CF) as an admixture to high-volume FA (HVFA) composites to improve its strength properties. HVFA represents 60–70% of cement replaced by FA and dosage of CF varies from 0.5% up to high dosage of 9% of cement content. Compressive strength, isothermal calorimetry, thermogravimetric analysis, X-ray diffraction and scanning electron microscopy were conducted to investigate the effects of CF on hydration and microstructural aspects. The results show that both HVFA pastes with 60% and 70% FA achieved the highest strength at the CF dosage of 3%. At the age of 28 days, adding 3% CF to HVFA mixes led to higher consumption of FA as well as higher formation of calcium hydroxide (Ca(OH)2), calcium silicate hydrates, calcium carbonate (CaCO3) and ettringite, which contribute to the increase of strength. The addition of very high dosages of CF at 9% increased the hydration of tricalcium aluminate but could hinder the hydration of tricalcium silicate in both PC and HVFA pastes with 60% and 70% FA.

Unground granulated slag as a substitute for natural aggregate during concrete production

Styrene-butadiene copolymer [SB] modified cement-based materials are widely used, but the addition of SB can delay the setting and hardening of cement, which limits its application in some projects. In this paper, nanosilica was selected as the modifying component to study its influence on the early hydration, setting and hardening of SB/cement composite material. By measuring the setting time and early strength of nanosilica modified SB/cement composite material, the influence of nanosilica on the setting and hardening process of composite cementitious material was analyzed. The hydration heat of nanosilica modified SB/cement composite material was determined by isothermal calorimetry, and its hydration products were examined by X-ray diffraction, so as to analyze the influence of nanosilica on the early hydration process of composite cementitious material. The results show that the addition of nanosilica can effectively promote the setting and hardening process of composite cementitious material, and the higher the dosage is, the more significant the effect is. It also indicates that addition of nanosilica accelerates the formation of ettringite and calcium hydroxide, by promoting the hydration of tricalcium aluminate and tricalcium silicate. Shortens the hydration induction period and acceleration period of the composite cementitious material and accelerates the hydration process, thereby shortening the setting time and increasing the early strength.

Preparation and Performance of a Fluorine-Free and Alkali-Free Liquid Accelerator for Shotcrete

Based on aluminum sulfate, a fluorine-free and alkali-free liquid accelerator (FF-AF-A) was prepared in this study. The setting time and compressive strength of three cement types with different FF-AF-A dosages were fully investigated. The compatibility of the FF-AF-A with the superplasticizers were also investigated, and the early hydration behavior and morphology of the hydration products of reference cement paste with the FF-AF-A were explored by hydration heat, X-ray diffractometry (XRD), and scanning electron microscopy (SEM). Test results indicated that adding the FF-AF-A at 8 wt% of the cement weight resulted in 2 min 35 s initial setting time and 6 min 30 s final setting time. The 1-day compressive strength of the cement mortar with 8 wt% of FF-AF-A reached 13.5 MPa, which represents an increase of 35% as compared to the strength of cement mortar without the FF-AF-A, and the 28-day compressive strength ratio was 119%. In addition, the FF-AF-A also showed good compatibility with different superplasticizer dosages. The results show that, when the FF-AF-A was added to the cement paste, it promoted the formation of ettringite crystals due to the aluminum ions (Al3+) and sulfate ions (SO4 2-) reacted with gypsum in the cement, as well as promoted the hydration of tricalcium aluminate (C3A) and tricalcium silicate (C3S) leading to the overall structure becomes more compact. As a consequence, the hydration heat rate of the cement sharply increased, the cement paste setting time is shortened, and the compressive strength of cement mortar is improved.

Influence of calcium and alumina-based pozzolanas on the strength properties of low calcium fly ash geopolymer concrete

This work presents the effect of Ground granulated blast furnace slag (GGBS), fly ash (FA) and metakaolin (MK) on the strength properties of geopolymer concrete (GPC). Geopolymer concrete made with FA produces calcium aluminosilicate hydrate (C-A-S-H) product due to presence of alumina and sodium aluminosilicate hydrate (N-A-S-H) gel as main reaction product of polymerization. Geopolymer concrete made with FA and GGBS, calcium silicate hydrate (C-S-H) also gets produced additionally with calcium aluminosilicate hydrate (C-A-S-H) gel and sodium aluminosilicate hydrate (N-A-S-H) gel due to presence of high content of CaO in GGBS. This additional product imparts more strength performance in GPC. In geopolymer concrete made with FA and MK, the more amount of calcium aluminosilicate hydrate (C-A-S-H) is produced due to presence of high amount of alumina in metakaolin along with sodium aluminosilicate hydrates (N-A-S-H) giving more strength to GPC. Metakaolin is recommended to be used for the development of GPC because it has high amount of alumina.

Study of the influence of magnetized ferromagnetic additives on the processes of cement hydration

One of the essential tasks for a sustainable future is to reduce harmful emissions into the atmosphere significantly. Cement production is the world’s largest industrial carbon pollutant, accounting for 8 % of global emissions. More than 2.2 gigatons of carbon dioxide are emitted into the atmosphere every year. Therefore, reducing the energy intensity of products and reducing the number of harmful emissions in cement production is becoming critical. One strategy to reduce cement production emissions is to reduce the most energy-consuming component in cement – clinker. In this case, various activation methods are used for maintaining the same level of cement activity. One of these methods is the impact on the hardening binder with magnetic fields. The paper presented a study of hydration processes of blast-furnace cement activated by a magnetized ferromagnetic additive. The work established that the introduction of pre-magnetized ferromagnetic dust into blast-furnace cement composition has an activating effect on binder hydration. It shows that activation occurs both in the initial and long periods of hardening. The nature of the mutual influence of the components of the hydration system alite-lime-slag in a modified binder was revealed. The investigation determined that the ferromagnetic additive, intensifying the process of slag hardening, increases the proportion of hydrated slag by 1.5-2 times. It was revealed that the formation of the ettringite framework in the modified binder’s gel is completed within one day. It is shown that in the subsequent periods, hydration of aluminates occurs mainly due to the formation of tricalcium aluminate hexahydrate (C3AH6), which excludes destructive processes in the late periods of binder hardening. It has been established that under the action of a ferromagnetic additive, the degree of crystallization of hydro silicates in the modified binder increases.

Microstructural behavior of expansive soil using calcium chloride and alccofine

Expansive soils are extensively found in arid and semi-arid regions of the world. One of the key problems associated with these expansive soils is their swelling characteristics to an increase in their natural water content. The present study is to elucidate and efficacy of alccofine-1203 and CaCl2 in ameliorating the engineering properties of expansive soils. An experimental program has evaluated the effects of alccofine-1203 (4%, 8%, & 12%) and CaCl2 (0.5% & 1%) contents on the Atterberg limits, compaction, unconfined compressive strength test of an intrinsic soil and artificially mixes soil were examined. Both admixtures were added independently and blended to the expansive soil. It was found that the liquid limit, plasticity index, and swelling behaviour of the expansive soil decreased considerably with the addition of binder, while the unconfined compressive strength improved with adding a Calcium Chloride and alccofine-1203. The improvement of strength is due to the formation of Calcium Silicate Hydrate (C-S-H), Calcium Aluminate Hydrates (C-A-H), Calcium Aluminate Silicate Hydrate (C-A-S-H), and other cementitious compounds that are observed in Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) studies. From this investigation, it is concluded that the addition of 1% Calcium Chloride and 8% alccofine-1203 binders is a potential stabilizer for expansive soil.

Study of copper fixation mechanisms on Bayer Process Electrostatic precipitator Microparticles (BPEM) using 1H and 27Al NMR spectroscopy

The removal of heavy metals from natural, mining, or industrial ponds or water flows is a problem for metallurgical industries. The reason is that heavy metals represent a risk for the health of people living close to these industries. One of these heavy metals is copper, whose removal was widely studied using different aluminous materials (clays, zeolites, smectites or power plant ashes). In this manuscript, a different aluminous material is proposed to remove copper from water, the Bayer Process Electrostatic precipitator Microparticles (BPEM). The BPEM mainly consists of alpha alumina (min. 6.5 % and max. 53 %), aluminum hydrates (min. 12 % and max. 72 %) and intermediate or gamma alumina. The adsorption of Cu2+ by different BPEMs was studied using Nuclear Magnetic Resonance (NMR) technique. The NMR 1H and 27Al spectra were tested to identify the presence of oxides and hydroxides and their bonding structures, and how the spectra varied once the copper had been captured by the BPEMs. A huge attenuation of the 1H spectrum was found in all the studied BPEMs when copper is adsorbed. There does not seem to be any Cu2+ adsorbed related to 27Al, although some spectra show a slight attenuation of the corresponding peak, but not comparable with that observed in the case of the 1H. Thus, Cu fixation is produced by replacement of hydrogen bonding, present on the surface of the hydrated alumina, by the Cu cations.

Optimization of California bearing ratio of tropical black clay soil treated with cement kiln dust and metakaolin blend

The study showcase the optimization of California bearing ratio (CBR) values of expansive soil treated with cement kiln dust (CKD) and metakaolin (MTK) blend based on Scheffe optimization method. The CBR values utilized in the design of road infrastructure is an important parameter because it provides the rating of soil material for use as subgrade, sub-base and/or base course of road pavement. Therefore, applying Scheffe optimization technique will eliminate the random selection of design mix ratios and other associated disadvantages during CBR tests. Based on the optimization exercise and it results, the maximum CBR (unsoaked and soaked) values of 69 and 50 % were achieved with a corresponding mix ratio of 1.0:0.30:0.35:0.50 for black cotton soil, water, cement kiln dust and metakaolin respectively. During the course of this study, the laboratory results were used to develop two CBR models. The scheffe models developed are Ŷ = 34X1 + 46X2 + 40X3 + 69X4 − 8X1X2 − 4X1X3 + 34X1X4 + 8X2X3 + 34X2X4 + 30X3X4 and Ŷ = 17X1 + 28X2 + 22X3 + 50X4 − 10X1X2 − 6X1X3 + 42X1X4 + 8X2X3 + 40X2X4 + 40X3X4 for CBR unsoaked and soaked, respectively. In addition, the mathematical models were statistically scrutinized, confirmed for the adequacy and validity based on the outcomes of student t-test and analysis of variance (ANOVA). Also, the scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) techniques were used to explore the morphological and composition variations of the natural soil in contrast with the typically optimized soil-CKD-MTK blend. However, the SEM of the unaltered soil sample showed a smooth like surface, whereas the soil mixture optimally treated does not show same but rather demonstrated a rough like surfaced morphology. Thus, the observed variations might be due to the alterations of the soil fabrics possibly enhanced by the development of cementitious compounds (calcium silicate hydrate and calcium aluminate hydrate) as a result of pozzolanic reaction.

The Role of Hydrated Alumina Layer on the Incorporation of Electrolyte Species in Anodizing of Aluminum

Hydration treatment of aluminum is often used for corrosion protection of aluminum alloys and for the formation of dielectric alumina layer in aluminum electrolytic capacitors. Hydrated alumina layer is usually formed by immersing aluminum with and without a porous anodic alumina layer in hot water. The hydrated alumina layer plays an important role in enhancing the corrosion resistance and forming crystalline γ’-alumina in subsequent barrier-type anodic film growth by anodizing. However, the properties of the hydrated layer are not yet well understood. In this study, we examined the influence of anion incorporation properties into the barrier-type anodic alumina films through the hydrated alumina layer, which was formed in hot water.High purity (99.99%) aluminum plate was used in this study. After electropolishing in a HClO4–ethanol mixed solution below 283 K, a hydrated alumina layer was formed by immersing the electropolished aluminum in hot water (95ºC) for 10 min. The resultant hydrated layer consists of two layers, comprising a flake-like outer porous layer and a relatively dense inner layer. The thickness of the hydrated layer was ~430 nm. Then the aluminum with the hydrated layer was anodized in boric acid and tungstate electrolytes to grow the barrier-type anodic films. When the boric acid electrolyte was used, boron species were incorporated into the outer part of the barrier-type anodic films through the hydrated alumina layer. In contrast, no incorporation of tungsten species into the barrier-type anodic film through the hydrated layer occurred in the tungstate electrolyte. Phosphate anions are known to be incorporated into the 70% of the film thickness in the anodic amorphous alumina film, but in the present study, phosphate anions were not incorporated into the barrier-type anodic films through the hydrated layer. It is likely from the GDOES elemental depth profile analysis suggests that the inner hydrated layer becomes a barrier for the incorporation of tungsten and phosphorus species. Thus, apparently, the inner hydrated alumina layer has cation-selective permeation properties so that anion incorporation is limited. In boric acid electrolyte, the acid dissociation is limited, and non-charged boric acid species can be penetrated through the hydrated layer.

First-principles study of dehydration interfaces between diaspore and corundum, gibbsite and boehmite, and boehmite and γ-Al2O3: Energetic stability, interface charge effects, and dehydration defects

Aluminum hydrate dehydration interfaces were studied using a van der Waals density functional. The interface configurations investigated here as a first exploration of possible interface geometries, were all found to have a reasonable probability of occurring. From gibbsite/boehmite and boehmite/γ-Al2O3 interface simulation cells, the formation of dehydration-related defects during relaxation was observed. H transfer between hydroxyl groups, and separation of hydroxyl groups and H atoms from the lattice, resulted in the formation of chemisorbed H2O and OH2 groups in gibbsite; in boehmite, the formation of OH2 groups and interstitial H was observed. All interfaces show a transfer of small amounts of charge across the interface. Accumulation of charge in spaces interstitial to the lattice was found to play a role in the dehydration process as well. The present study shows the potential of interface studies for elucidating dehydration pathways at the atomic scale, and offers various starting-points for follow-up studies.

The potential use of drinking water sludge ash as supplementary cementitious material in the manufacture of concrete blocks

The effect of drinking water sludge ash (DWSA) on the properties of DWSA-cement pastes is investigated in this study using x-ray diffraction, scanning electron microscopy coupled with energy-dispersive spectrometry, and thermogravimetry techniques. The pozzolanic reactivity of DWSA is confirmed; the filler effect of DWSA can significantly and rapidly accelerate the hydration reaction at an early curing age. The presence of DWSA in blended pastes promotes the incorporation of aluminum into the C-(A)-S-H gel; the original ‘Al-minor’ C-(A)-S-H gel in pure cement paste is converted to ‘Al-rich’ C-(A)-S-H gel. The added DWSA leads to the formation of aluminum-bearing hydrates, such as ettringite and calcium aluminate hydrates (C-A-H). The compressive strength of sludge-derived concrete blocks is studied; blocks containing 10% DWSA exhibited higher compressive strength at a curing age of 90 d than the reference samples. Such benefits are not observed in block samples with 20 and 30% DWSA, which is attributed mainly to the physical effect of unreacted DWSA particles.

Microstructure evolution of hydration products and strength change of hydratable alumina‐bonded castables below 1250°C

AbstractThere have been reports that strength of hydratable alumina (HA)‐bonded castables without silica fume drops significantly at 600°C and decreases substantially again at 1000°C. But the strength variation of the HA‐bonded castables during the intermediate temperature range has not been investigated and elaborated from the perspective of phase evolution and microstructural change in the castables. In this work, the relationship between the change in the strength of castables and the microstructural characteristics of the HA‐bonded castables was investigated. The phase and microstructure evolution of HA‐bonded castables between 110°C and 1250°C were investigated by X‐ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analysis (TG). It has been found that strength drops of the HA‐bonded castables during heating process do not mainly happen at the temperature at which HA hydrates decompose, but at the temperature at which the structure of dehydrated HA hydrates disintegrates.

Effect of grinding on the hydration of hydratable alumina and properties of hydratable alumina-bonded castables

Hydratable alumina (HA) is a superior Ca-free refractory binder, but the quick hydration rate restricts the working time of castables bonded with HA. In this work, HA was grounded for 1 h and 6 h by a rotational ball mill to study the effect of grinding on the hydration of HA and properties of HA-bonded castables. HA samples with and without grinding were cured at 30 °C and then terminated by freeze-vacuum drying. The phase composition and microstructure of the dried HA samples were then examined. Moreover, flow ability and mechanical strength of castables containing ungrounded and grounded HA were also investigated. The results indicate that the specific area of HA particles were decreased by grinding as the micro-pores and micro-cracks on the surface of HA particles were blocked by smaller HA particles, thereby decreasing the hydration rate of HA and increasing the flow ability of castables.

Optimal Mixture Designs for Heavy Metal Encapsulation in Municipal Solid Waste Incineration Fly Ash

Mixing municipal solid waste incineration fly ash (MSWIFA) with industrial by-products such as ground granulated blast furnace slag (GGBFS) and ladle furnace slag (LFS) can lead to a hardened system which can encapsulate the heavy metals present in the MSWIFA. The objective of this study is to find optimal mixture designs to effectively encapsulate these heavy metals. The nature of the hydrates and the strength of the mixtures are studied to develop a sustainable and practical construction material incorporating MSWIFA. Heavy metals including Cr, Cu, Zn and Cd are safely encapsulated in several developed mixtures with leachate concentration below EPA drinking water limit. The encapsulation behavior is complex and depends on metal type, age of testing, and hydration products. In general, mixtures containing LFS have more aluminate hydrates, and show greater encapsulation capacity for most heavy metals. However, they also generally show significant Sb leaching. Mixtures which show satisfactory encapsulation for all ions and adequate strength development are identified. Three ideal mixtures, including one containing zero cement, are identified which satisfy both leaching and strength requirements.

Influence of sulphate ions on the crystal chemistry of white cement mortars with a high content of marble filler powder

Objects of this research are white cement mortars, characterized by both of high content of addition of marble powder and reduced water-cement ratio. The hardened cement mortars, formed after 28-and 120-day curing under standard conditions, are studied. The newly formed phases, containing [SO4]2-, [CO3]2-, [OH]-, etc., are identified using X-ray powder diffraction, infrared spectroscopy and thermal analysis (coupled with analysis of the outgoing gas mixture by mass spectrometry). Based on of the formed calcium silicate hydrates, calcium aluminate hydrates, the influence of sulphate ions is analysed and the mechanism of the thermal decomposition reaction at high temperatures in an oxidizing gas environment is studied. This allows us to establish that the hydration of Portland cement depends on the addition of marble powder (technically calcium carbonate CaCO3), as well as mono- and hemicarboaluminates are formed instead of monosulphoaluminates.

Enhanced biodeterioration and biofouling resistance of nanoparticles and inhibitor admixed fly ash based concrete in marine environments

In this paper, we report the enhanced biodeterioration and biofouling resistance of a modified fly ash based concrete, formulated by the addition of fly ash, nano-TiO2, nano-CaCO3, and corrosion inhibitor into conventional concrete. After six months of exposure in natural seawater, the modified fly ash based concrete showed a three to four order reduction in aerobic and anaerobic bacterial density, which was confirmed by epifluorescence and confocal microscopic investigations. The FESEM micrographs showed a characteristic surface morphology with uniform distribution of more calcium silicate hydrate (CSH) gels and aluminate hydrates, absence of discontinuities, pits, and cracks on the modified concrete surface which helped to resist the ingress of aggressive ions from seawater. The comparatively lesser reduction in surface pH, low water/cement ratio, better bulk thermal properties, and low surface roughness facilitated the improvement in the antimicrobial and antifouling properties of modified concrete. The addition of nanoparticles and inhibitor increased the hydration of cement resulting in the formation of more portlandite which got converted into more hydration products, producing a pore free morphology. The inherent photocatalytic activity of nano-anatase TiO2 and bactericidal activity of sodium nitrite due to the presence of reactive nitrogen species (RNS) together enhanced the biofouling and biodeterioration resistance.

N,N-dimethylformamide assisted facile hydrothermal synthesis of boehmite microspheres for highly effective removal of Congo red from water

A series of boehmite microspheres with highly effective adsorption performance for Congo red (CR) were successfully prepared via amides assisted hydrothermal method at 180 °C. Effects of dosages and hydrolysates of N,N-dimethylformamide (DMF), amides species including DMF, N-methylformamide (MF) and formamide (FA), and reaction times on their physicochemical properties were studied in detail. It was found that increase on their crystallinity and shell thickness results from the different hydrolysis rates of the amides; amorphous alumina hydrate, boehmite core-shell structure and hollow microspheres were obtained at hydrothermal times of 60, 140 and 360 min, respectively due to the Ostwald ripening. Especially, dimethylamine (DMA) as a hydrolysate of DMF, can effectively regulate the morphologies of the boehmites together with the sulfate ions, and make their pore sizes distribution (PSD) centering at 3–4 nm. Importantly, the boehmite microspheres with specific surface area of 221.3 m2/g shows the maximum adsorption capacity of 847.5 mg/g for CR calculated from Langmuir isotherm model, and its adsorption amount reached a high value of 484.1 mg/g at 60 min due to the mentioned PSD. This template-free hydrothermal method using DMF as precipitant provides an alternative approach for preparing high-performance hydrated alumina for environmental applications.

Calcium aluminate cement conversion analysed by ptychographic nanotomography

Calcium aluminate cements are used for special applications but are nowadays banned for general structural purposes due to the calcium aluminate hydrate conversion, that has led, for concretes fabricated with high water contents, to building collapses. The stoichiometries of these conversion chemical reactions are relatively well established but the consequences in porosity, key to predict durability, were unknown. Here, we have used hard X-ray ptychographic nanotomography to study the hydration of CaAl2O4 at different temperatures and chiefly, at 4 °C and then at 50 °C to provoke conversion similar to field conditions. The mass densities of the resulting Al (OH)3 gels were 1.94, 1.98 and 2.23 g·cm−3, for samples hydrated at 4, 20 and 50 °C, respectively. These values are lower than that of gibbsite, 2.42 g·cm−3. Above all, this 3D imaging technique has allowed measuring the secondary water porosity developed in the conversion, which has an average pore dimension close to 140 nm.