Homogeneous Pore Size Distribution Research Articles

Time of reactions in a lime treated clayey soil and influence of curing conditions on its microstructure and behaviour

A research programme has been set up to investigate the sequence of physical and chemical reactions in compacted soil–lime mixtures and their influence on the mechanical and hydraulic performance with time. The paper illustrates a method set up to monitor sequence and development of soil–lime reactions with curing time based on pH measurement. The method was also used, together with SEM observations and chemical analyses, to properly analyse results of hydraulic conductivity and oedometer tests performed on compacted soil–lime samples cured in saturated and unsaturated conditions. It was found that the hydraulic conductivity significantly decreases by increasing the time spent in unsaturated condition and it tends to appreciably reduce with time. In terms of compressibility, higher compression index resulted in saturated curing conditions. These differences were found to be due to a different microstructure. A crystalline, more brittle structure was detected in the case of immediate saturation with an ununiformed distribution in pore size. Unsaturated curing conditions give rise to amorphous, uniformly distributed pozzolanic products, with a more homogeneous pore size distribution.

Thermal-crosslinked porous chitosan scaffolds for soft tissue engineering applications

The aim of this study was to demonstrate the feasibility of using a steam autoclave process for sterilization and simultaneously thermal-crosslinking of lyophilized chitosan scaffolds. This process is of great interest in biomaterial development due to its simplicity and low toxicity. The steam autoclave process had no significant effect on the average pore diameter (~70μm) and overall porosity (>80%) of the resultant chitosan scaffolds, while the sterilized scaffolds possessed more homogenous pore size distribution. The sterilized chitosan scaffolds exhibited an enhanced compressive modulus (109.8kPa) and comparable equilibrium swelling ratio (23.3). The resultant chitosan scaffolds could be used directly for in vitro cell culture without extra sterilization. The data of in vitro studies demonstrated that the scaffolds facilitated cell attachment and proliferation, indicating great potential for soft tissue engineering applications.

Cost-effective nanoporous SiO2–TiO2 coatings on glass substrates with antireflective and self-cleaning properties

Simultaneous antireflective and self-cleaning properties have been realized by depositing double-layered SiO2–TiO2 coatings onto glass substrates using a combined sol–gel dip-coating process in which the two oxide layers were deposited in succession. The first layer is composed of a hybrid methyl-functionalized nanoporous SiO2 material that provides on average a 6% anti-reflection gain. The degree of antireflectivity can be controlled by adjusting the thickness and refractive index by selecting suitable solvents and pore-forming agents in the coating mixture. The second layer is an ultrathin TiO2 nanoporous layer deposited on top of antireflective layer. The high hardness of the TiO2 top layer acts as a protection barrier toward mechanical damage and ensures the surface is self-cleaning. An average anti-reflectivity of 3.4% achieved over a spectrum range of 400–800nm for the optimal SiO2–TiO2 bilayers is obtained. It is found that a homogeneous pore size distribution in the SiO2 layer introduced by using isopropanol as the solvent can compensate for the TiO2 band edge absorption based on the optical interference that occurs between the two layers. These systems are easy to produce on a large scale at low cost and exhibit high mechanical and chemical durability. These materials are thus suitable for use as bifunctional antireflective and self-cleaning coatings for use as large substrates for solar cells.

Development of Nanocomposite Membranes with Photocatalytic Surfaces

In 2030, 47% of the world population will be living in areas of high water stress (UN World Water Development Report 3, 2009). The global water shortage results in an emerging need for novel, more efficient and cost saving water purification methods. Membrane technology with its very low use of chemical substances and secure retention of contaminants represents a promising water cleaning method. The approach presented focuses on the application of nanocoating procedures to membrane processes which aims at reducing the fouling potential of membranes and destroying water contaminants. Photocatalytic titanium dioxide nanoparticles are applied. Novel suitable microsieves including a homogeneous pore size distribution and high robustness were developed from metallic material. An appropriate multilayer coating system was developed and applied on a new nanocomposite filter resulting in high photocatalytic activities with maximum photon efficiencies of 0.0733. The coating layer do not have a negative influence on the permeate flux. The effectiveness of the nanocomposite filter was proven in a 12 days biofouling experiment with activated sludge suspensions.

Effects of sintering temperature on pore characterization and strength of porous cordierite–mullite ceramics by a pore-forming in-situ technique

AbstractPorous cordierite–mullite ceramics with high strength were prepared by a pore-forming in-situ technique. The phase compositions, pore characteristics, and strength were investigated through X-ray diffractometry, scanning electron microscopy, and a microscopy measurement method. It is found that the sintering temperature strongly affects the formation of cordierite and mullite and the sintering, and thus changes the pore characteristics and strength. The formation of cordierite and mullite takes place on a large scale at 1430°C. The pore size distributions are bimodal in specimens sintered at 1370°C, 1400°C, and 1430°C, and mono-modal in a specimen sintered at 1450°C. The strength increases slightly when the sintering temperature increases from 1370°C to 1400°C, and increases significantly when the sintering temperature is increased to 1430°C. The most appropriate mode is a specimen sintered at 1430°C which has high cordierite (42 wt.%) and mullite content (53 wt.%), high apparent porosity (44%), high compressive strength (30.6 MPa) and a relatively homogeneous pore-size distribution.

Effect of particle size on microstructure and strength of porous spinel ceramics prepared by pore-forming in situ technique

The porous spinel ceramics were prepared from magnesite and bauxite by the pore-forming in situ technique. The characterization of porous spinel ceramics was determined by X-ray diffractometer (XRD), scanning electron microscopy(SEM), mercury porosimetry measurement etc and the effects of particle size on microstructure and strength were investigated. It was found that particle size affects strongly on the microstructure and strength. With decreasing particle size, the pore size distribution occurs from multi-peak mode to bi-peak mode, and lastly to mono-peak mode; the porosity decreases but strength increases. The most apposite mode is the specimens from the grinded powder with a particle size of 6·53 μm, which has a high apparent porosity (40%), a high compressive strength (75·6 MPa), a small average pore size (2·53 μm) and a homogeneous pore size distribution.

Preparation and Characterization of Porous Cordierite Ceramics with Well-distributed Interconnected Pores

Porous cordierite ceramics with well-distributed interconnected pores were prepared by pore forming in situ technique coordinated with adding pore forming agent. The phase, microstructure, strength and gas permeability were investigated through X-ray diffractometer, scanning electron microscopy, mercury porosimetry measurement, etc. The proper sintering temperature was found to be 1360°C when the porous cordierite ceramics were fabricated through pore forming in situ technique. The porous cordierite ceramics sintered at 1360°C has high cordierite phase content, high apparent porosity (40.3%), homogeneous pore size distribution and interconnected pores, thus the porous cordierite ceramics also has high compressive strength (54.5 MPa) and high gas permeability (2.31 m2). With the addition of sawdust as pore forming agent, the porosity and the gas permeability of the porous cordierite ceramics sintered at 1360°C increased, however, the strength decreased. For example, addition of 6% sawdust resulted in 47.9% porosity, 4.61 m2 gas permeability, while the compressive strength was reduced to 23.6 MPa.

Porous alginate/poly(ε-caprolactone) scaffolds: preparation, characterization and in vitro biological activity

In bone tissue engineering, scaffolds with controlled porosity are required to allow cell ingrowth, nutrient diffusion and sufficient formation of vascular networks. The physical properties of synthetic scaffolds are known to be dependent on the biomaterial type and its processing technique. In this study, we demonstrate that the separation phase technique is a useful method to process poly(ε-caprolactone) (PCL) into a desired shape and size. Moreover, using poly(ethylene glycol), sucrose, fructose and Ca2+ alginate as porogen agents, we obtained PCL scaffolds with three-dimensional porous structures characterized by different pore size and geometry. Scanning electron microscopy and porosity analysis indicated that PCL scaffolds prepared with Ca2+ alginate threads resemble the porosity and the homogeneous pore size distribution of native bone. In parallel, MicroCT analysis confirmed the presence of interconnected void spaces suitable to guarantee a biological environment for cellular growth, as demonstrated by a biocompatibility test with MC3T3-E1 murine preosteoblastic cells. In particular, scaffolds prepared with Ca2+ alginate threads increased adhesion and proliferation of MC3T3-E1 cells under basal culture conditions, and upon stimulation with a specific differentiation culture medium they enhanced the early and later differentiated cell functions, including alkaline phosphatase activity and mineralized extracellular matrix production. These results suggest that PCL scaffolds, obtained by separation phase technique and prepared with alginate threads, could be considered as candidates for bone tissue engineering applications, possessing the required physical and biological properties.

Comparative study of the textural characteristics of oil palm shell activated carbon produced by chemical and physical activation for methane adsorption

The objective of this study is to relate textural and surface characteristics of microporous activated carbon to their methane adsorption capacity. Oil palm shell was used as a raw material for the preparation of pore size controlled activated carbon adsorbents. The chemical treatment was followed by further physical activation with CO 2. Samples were treated with CO 2 flow at 850 °C by varying activation time to achieve different burn-off activated carbon. H 3PO 4 chemically activated samples under CO 2 blanket showed higher activation rates, surface area and micropore volume compared to other activation methods, though this sample did not present high methane adsorption. Moreover, it was shown that using small proportion of ZnCl 2 and H 3PO 4 creates an initial narrow microporosity. Further physical activation grantees better development of pore structure. In terms of pore size distribution the combined preparation method resulted in a better and more homogenous pore size distribution than the conventional physical activation method. Controlling the pore size of activated carbon by this combined activation technique can be utilized for tuning the pore size distribution. It was concluded that the high surface area and micropore volume of activated carbons do not unequivocally determine methane capacities.

Superbase catalysts from thermally decomposed sodium azide supported on mesoporous γ-alumina

Mesoporous γ-alumina because of its homogeneous pore size distribution, represents a good support for alkali metals. Controlled thermal decomposition of impregnated sodium azide on such support yields a superbasic catalyst for the double bond migration of vinylcyclohexane to ethylidene cyclohexane in continuous liquid flow operation. After slurry impregnation of the azide in methanol, 23Na MAS NMR shows the presence of resonance lines corresponding to Na metal particles and sodium oxide on the support. When dry mixing of the catalyst components is done, only supported sodium oxide is found, in association with decreased catalytic activity. It is concluded that both species are necessary components of the superbasic sites required for the isomerization reaction mentioned. In the transesterification of soybean oil with methanol in a batch reactor, the same differences in activity are encountered. The 23Na MAS NMR spectrum of the former catalyst remained unchanged after the transesterification reaction.

ポリアクリロニトリル（ＰＡＮ）ナノファイバー不織布セパレータを用いたリチウムイオン電池の特性

Two types of polyacrylonitrile (PAN) nano-fiber based nonwovens as separator for lithium ion battery, which consist of different fiber diameters, have been developed by an electrospinning technique. SEM observation exhibited that the electrospun PAN nano-fibers had homogeneous thicknesses, and their diameters were around 250 and 380 nm. The physical, electrochemical and thermal properties of the PAN nonwovens were characterized. The nonwovens possessed homogeneous pore size distribution with similar pore sizes to a polyolefin membrane separator. Moreover, they showed higher porosities, lower Gurley values than that of the polyolefin one. Cyclic voltammetry revealed that they were electrochemically stable in the voltage range of −0.5 to 4.5 V vs. Li0/Li+. They showed higher ionic conductivities than that of the polyolefin one in the temperature range of −10 to 60°C. Any internal short circuit was not observed for cells using them during charge-discharge tests. Cells using them showed better cycleabilities than that with the polyolefin one at −10 and 30°C. Besides, they showed better rate capabilities than a cell with the polyolefin one.

Electrophoretic deposition as rapid prototyping method

Electrophoretic deposition is a near-net shaping technique leading to excellent green body properties such as high green density and homogeneous pore size distribution that also affect the features of the sintered sample. It has been used in a wide range of applications from optical to biomedical ones. However, it was used as standardized method so that individually tailored geometries have not been fabricated yet. The present work modifies this promising method so that a rapid prototyping process is possible. First of all, the local application of an electric field was investigated and simulated in order to achieve a structure as fine as possible using commercially available coaxial cable. Afterwards, two different ways of fabricating prototype structures with optimized parameters were investigated. The first one was the combination of the developed electrode with a CAM unit. The second one was arranging 16 independent electrodes in a 4 × 4 array in order to parallelize deposition. In all cases, structural integrity as well as height distribution and shape were studied.

Development of hyaluronic acid-based scaffolds for brain tissue engineering

Three-dimensional biodegradable porous scaffolds play vital roles in tissue engineering. In this study, a hyaluronic acid–collagen (HA–Coll) sponge with an open porous structure and mechanical behavior comparable to brain tissue was developed. HA–Coll scaffolds with different mixing ratios were prepared by a freeze–drying technique and crosslinked with water-soluble carbodiimide to improve mechanical stability. The pore structure of the samples was evaluated by light and scanning electron microscopy, and the mechanical behavior was analyzed by mechanical compression and tension testing. The degree of crosslinking was determined by the water absorption and trinitrobenzene sulfonic assay, and the HA content was determined by a carbazole assay. The results showed that HA–Coll scaffolds containing an open porous structure with a homogeneous pore size distribution could be fabricated. Certain features of the mechanical properties of HA–Coll scaffolds prepared with a Coll:HA mixing ratio of 1:2, and pure HA sponges, were comparable with brain tissue. Neural stem cells (NSCs) were expanded in number in monolayer culture and then seeded onto the three-dimensional scaffolds in order to investigate the effects of the different types of scaffolds on neurogenic induction of the cells. This study contributes to the understanding of the effects of HA content and crosslink treatment on pore characteristics, and mechanical behavior essential for the design of HA–Coll scaffolds suitable for NSC growth and differentiation for brain tissue engineering.

Battery performances and thermal stability of polyacrylonitrile nano-fiber-based nonwoven separators for Li-ion battery

The microporous polyacrylonitrile (PAN) nonwoven separators have been developed by using electrospun nano-fibers with homogeneous diameter of 380 and 250 nm. The physical, electrochemical and thermal properties of the PAN nonwovens were characterized. The PAN nonwovens possessed homogeneous pore size distribution with similar pore size to the conventional microporous membrane separator. Moreover, the PAN nonwovens showed higher porosities, lower gurley values and better wettabilities than the conventional polyolefin microporous separator. Cells with the PAN nonwovens showed better cycle lives and higher rate capabilities than that of a cell with conventional one. Any internal short circuit was not observed for the cells with the PAN nonwovens during charge–discharge test. Hot oven tests for the charged cells up to 4.2 V have revealed that the PAN nonwoven was thermally stable at 120 °C, but showed shrinkage of about 26% isotropically after the test at 150 °C for 1 h. The Celgard membrane showed uniaxial shrinkage of about 30% along the machine direction at 150 °C for 1 h.

Deposition conditions in tailoring the morphology of highly porous reticular films prepared by electrostatic spray deposition (ESD) technique

Spongy-like reticular structure is a unique morphology fabricated by electrostatic spray deposition (ESD) technique. The effects of solvent, substrate temperature, precursor feeding rate, static electric field strength, and deposition time on tailoring the reticular structure were investigated. Scanning electron microscopy was used to observe the film morphology. MnO x or LiMn 2O 4 were selected as the model materials. It is found that in addition to the conventional solvent butyl carbitol, other kinds of solvents such as ethylene glycol and propylene glycol can also be used to obtain reticular films at a suitable substrate temperature. Porous films with a low cross-linking degree pore structure can be prepared by increasing precursor feeding rate or decreasing substrate temperature. Increasing the deposition time or the electric field strength helps to obtain reticular films with more homogeneous pore size distribution. In addition, the addition of a high boiling-point solvent in mixed alcohol solvent results in the increase of proper substrate temperature. It is concluded that the fluidity of the spray droplets on the surface of a hot substrate is an important factor to form a reticular film.

Activated Carbon Materials of Uniform Porosity from Polyaramid Fibers

Activated carbon fibers derived from polyaramids exhibit an outstandingly homogeneous pore size distribution. Here, we review the work carried out on the porosity characteristics of carbons prepared from these polymers, specifically Kevlar [poly(p-phenylene terephthalamide)] and Nomex [poly(m-phenylene isophthalamide)]. First, studies on the thermal decomposition of both polyaramid fibers and the reactivity of the resulting chars are reviewed in connection with the properties of the resulting products. Then, the porous texture of activated carbon fibers (ACFs) prepared by different methods (physical and chemical activation) is examined, with particular emphasis on the use of some novel methods to investigate microporosity in solids. Finally, the relationship between porosity and behavior of polyaramid-based carbons in several different types of application is analyzed.

Effect of freezing temperature, thawing and cooking rate on water distribution in two pork qualities

The effects of freezing temperature (−20 versus −80 °C) in combination with long-term freezer storage (−20 °C) on water mobility and distribution in pork of two qualities (normal and high ultimate pH) were explored using low-field NMR T 2 relaxometry. A marked effect of freezing temperature on the characteristics of intra- and extramyofibrillar water ( T 2 relaxation times) in the thawed pork was demonstrated, implying that the freezing temperature in combination with prolonged freezer storage affects the distribution and chemical–physical state of water in the thawed meat. Determination of technological properties (thawing and cooking loss) revealed that the observed T 2 variations related to water distribution and water properties, which were found to be consistent with the degree of structural damage assessed by light microscopy, also were reflected in the technological quality of the meat. Low freezing temperature in combination with prolonged freezer storage was associated with increased thawing and cooking loss. In addition, pH in the fresh meat had a pronounced effect on the distribution of myofibrillar water, as a more homogenous pore size distribution was evident in meat with high pH compared with normal pH. A clear effect of cooking rate on the T 2 relaxation characteristics in the cooked pork was also demonstrated, probably reflecting a cooking rate-induced effect on the myofibrillar structures. The effect of cooking rate on water distribution resulted in a significantly lower cooking loss upon a slow cooking rate (0.5 °C/min from 25 to 65 °C and 0.3 °C/min from 65 to 80 °C) compared with a fast cooking rate (1 °C/min).

Cost-effective fabrication of porous α-SiAlON bonded β-SiAlON ceramics

Porous sialon ceramics have been cost-effectively prepared by pressureless sintering from a mixture of elongated SHS β-sialon powders with an α-sialon precursor composition composed of α-Si3N4, AlN, Y2O3 and Al2O3. The obtained porous sialon ceramics exhibited low shrinkage and homogeneous pore size distribution. The results of X-ray diffraction and scanning electron microscopy showed that a uniform microstructure with elongated and intermingled β-SiAlON grains, which were strongly connected by α-SiAlON phase, has been obtained.

Improvement of the silica aerogel strengthening process for scaling-up monolithic tile production

Previously published results have shown that washing and aging treatments (respectively in water/ethanol and water/polyethoxydisiloxane solutions) of silica gels (synthesized from polyethoxydisiloxane precursors through HF catalysis) significantly enhance both the permeability and mechanical properties of the wet gels. Unfortunately, scaling-up the process induces severe cracks during supercritical drying. This phenomenon has been related to a pore-size distribution gradient between the surface and the bulk of the gel that appears after aging of thick gels. We report efforts to optimize the aging step. Aging in less-concentrated polyethoxydisiloxane solutions yields gels with a more homogeneous pore-size distribution and has enabled us to obtain large monolithic and crack-free aerogels that remain light and transparent.

Changing of network characteristics of acrylamide/maleic acid hydrogels by alteration of irradiation dose rate

Poly(acrylamide/maleic acid) P(AAm/MA) hydrogels were prepared by irradiating the ternary mixtures of AAm/MA and water by gamma rays at ambient temperature at very low (0.18 kGy/h), and moderate dose rate (3.0 kGy/h). The equilibrium degree of swelling (EDS) of hydrogels prepared at 3.0 kGy/h dose rate increased from 520% to 3900% with increasing MA mole content in the gel system from 0% to 5.2%. On the other hand, no systematic dependence of swelling on MA content was observed for hydrogels obtained at low dose rate irradiation due to formation of inhomogeneous network structure and large pores in the gel. Pore structure of hydrogels was monitored by using scanning electron microscope. Systematic swelling of P(AAm/MA) hydrogels prepared at moderate dose rates can be explained with homogeneous pore size distribution of network.