Distribution Of Macropores Research Articles

Porous materials from oppositely charged nanoparticle gel emulsions

Sol–gel processing is an important colloidal processing route for the synthesis of macroporous materials of tunable microstructure. More recently, methods that use particle stabilized foams or emulsions have been developed. However, such methods generally involve the use of an external surface active additives that bind the particles together during processing. In this work, we present a simple and scalable additive-free method for the fabrication of porous materials that are both macroporous and microporous in nature. In particular, we show that silica-alumina porous materials can be fabricated by processing oppositely charged nanoparticle gel emulsions which are a dispersion of oil droplets in a space spanning network of colloidal particles. The nanoparticle gel emulsions obtained are initially characterized by optical microscopy and oscillatory rheology. The water and oil in these emulsion gels are removed by drying and it is finally sintered at 1000 °C to obtain porous material. The pore size and their distribution in the three-dimensional porous material is characterized using scanning electron microscopy (SEM) and X-ray tomography. Microscopy observations revealed a homogeneous distribution of macro-pores of 20–40 μm in diameter along the width, breadth and thickness of the porous material with an average porosity of 40% measured from 2D X-ray computed tomography images. One of the important features of the porous materials thus fabricated is the presence of nanosized pores due to the inherent porosity of the nanoparticle gel as well as micron sized pores due to the oil droplets.

Separation of proteins from complex bio-matrix samples using a double-functionalized polymer monolithic column.

A double-functionalized polymer monolithic column was fabricated within the confines of a stainless-steel column (50 mm × 4.6 mm i.d.) via a facile method using iron porphyrin, ionic liquid (1-allyl-3-methylimidazolium chloride) and 1,10-decanediol dimethacrylate as tri-monomers; ethylene dimethacrylate as a crosslinker; polyethylene glycol 400 and N,N-dimethylformamide as co-porogens; benzoyl peroxide and N,N-dimethyl aniline as the redox initiation system. Results obtained from scanning electron microscopy, nitrogen adsorption-desorption, and mercury intrusion porosimetry confirmed the uniform pore structure and the pore size distribution of macro-pores. The home-made monolith was further characterized by elemental analysis to investigate the elemental composition of Fe supplied by iron porphyrin, confirming the synthetic process. The resulting optimized monolithic column was used as the stationary phase in high performance liquid chromatography for separating proteins, such as mixture of standard proteins, egg white, and human plasma, exhibiting good selectivity and high performance. It is worth noting that the home-made double-functionalized polymer monolithic column shows excellent selectivity for fractionation separation of human plasma proteins, and it is a promising separation tool for complex bio-samples in proteomic research.

A Novel Model for Carbonate Formation Acidizing Based on Equivalent Permeability

Based on the equivalent permeability tensor theory, a novel carbonate acidizing mathematical model is developed, which can be adopted to simulate the simulation process for carbonate matrix-acidizing and vuggy carbonate acidizing. Wormhole-channel in the core BC21 and BC10 was simulated based on the Omer Izgec experimental data. The comparative result between the experiment and the simulation shows that the two dominating wormhole-channels, the variation of pressure-drop curve and the pressure values at the inlet of the core are almost the same. The acid-flowing channel is significantly influenced by mineral distribution heterogeneity and macropore distribution pattern in the core. The acid breakthrough volume is defined as 1.5 PV divided by pore volume of core (PV is the acid volume consumed to form the dominating wormhole channel.). If the acid is injected continuously while the wormhole has completely broken through the core, the wormhole shape only changes a little, but the end-face dissolution will be formed at the end of the core. And the conclusion could be used to optimize the acid consumption volume.

Structure characterisation of catalytic particulate filters for automotive exhaust gas aftertreatment

Modern automobiles with internal combustion engine are equipped with several different converters of exhaust gas and a particulate filter. The size and cost of exhaust aftertreatment system can be reduced by coating the catalytically active material on or into the porous filter walls. The characterisation of filter morphology including the distribution of catalytic material inside the filter wall is a key prerequisite for the development of porous structures with optimum performance with respect to pressure loss, filtration efficiency and catalytic activity.Three SiC filter samples with different amount of SCR catalyst were characterised by X-ray tomography (XRT), scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP). Combination of the techniques provides detailed and consistent information on filter and coating hierarchical pore structure. The segmented XRT image revealed 3D distribution of catalytic material and larger macropores inside filter wall. The 3D XRT images were further used as the input for mathematical models evaluating porosity, pore size distribution (PSD), effective diffusivity and tortuosity. Maximum sphere inscription method applied to XRT data gave PSD shifted to larger pore sizes in comparison with the MIP results, in line with the bottleneck limitation of MIP. On the other hand, MIP was able to determine also smaller internal pores in the catalyst layer. Pressure loss of the filters measured in lab reactor increased non-linearly with the amount of catalytic coating. The PSD and XRT suggest that a large number of substrate pores is filled up completely by catalytic material.

Triple-Confined Well-Dispersed Biactive NiCo2S4/Ni0.96S on Graphene Aerogel for High-Efficiency Lithium Storage.

Layered double hydroxides (LDHs), also known as hydrotalcite-like anionic clay compounds, have attracted increasing interest in electrochemical energy storage, in the main form of LDH precursor-derived transition metal oxides (TMOs). One typical approach to improve cycling stability of the LDH-derived TMOs is to introduce one- and two-dimensional conductive carbonaceous supports, such as carbon nanotubes and graphene. We herein demonstrate an effective approach to improve the electrochemical performances of well-dispersed biactive NiCo2S4/Ni0.96S as anode nanomaterials for lithium-ion batteries (LIBs), by introducing a three-dimensional graphene aerogel (3DGA) support. The resultant 3DGA supported NiCo2S4/Ni0.96S (3DGA/NCS) composite, obtained by sulfuration of NiCo-layered double hydroxide (NiCo-LDH) precursor in situ grown on the 3DGA support (3DGA/NiCo-LDH). Electrochemical tests show that the 3DGA/NCS composite indeed delivers the greatly enhanced electrochemical performances compared with the NiCo2S4/Ni0.96S counterpart on two-dimensional graphene aerogel, i.e., a high reversible capacity of 965 mA h g-1 after 200 cycles at 100 mA g-1 and especially a superlong cycling stability of 620 mA h g-1 after 800 cycles at 1 A g-1. The enhancements could be ascribed to the compositional and structural advantages of boosting electrochemical performances: (i) well-dispersed NiCo2S4/Ni0.96S nanoparticles with interfacial nanodomains resulting from both the dual surface confinements of the 3DGA support and the crystallographic confinement of NiCo-well-arranged LDH crystalline layer, (ii) an appropriate specific surface area and a wide pore size distribution of mesopores and macropores, and (iii) highly conductive 3DGA support that is measured experimentally by using electrochemical impedance spectra to underlie the enhancement. Our results demonstrate that the tunable LDH precursor-derived synthesis route may be extended to prepare various transition metal sulfides and even transition metal phosphides for energy storage with the aid of tunable cationic type and molar ratio.

Effects of heavy weight waste glass recycled as fine aggregate on the mechanical properties of mortar specimens

The quantities of heavy weight waste glass have increased over time due to rapid industrialization and changes in the quality of life. Moreover, most of this waste is not recycled. Concrete is the most widely used construction material, the huge amounts of natural resources are required to make concrete. Therefore, it is necessary to investigate the possibility of recycling of heavy weight waste glass as an ingredient in the manufacturing of concrete.In this study, the suitability of heavy weight waste glass as a fine aggregate material is considered. The results of flow test, unit volume weight, radiation shielding performance, compressive strength, flexural strength, and micropore and macropore distribution of mortar are compared and evaluated. It was found that when the heavy weight waste glass substitution ratio increases, the fluidity, unit volume weight and radiation shielding performance also increase. However, the compressive and flexural strength of mortar gradually decrease with an increase in the substitution ratio of heavy weight waste glass. Moreover, the micro pore size distribution is significantly affected by the substitution of heavy weight waste glass.

Dye tracer infiltration technique to investigate macropore flow paths in Maka Mountain, Yunnan Province, China

In order to investigate the differences of macropores vertical distribution under different surface plants, and to assess the influences of root systems, organic matter and texture on macropore flow paths, two dye tracer infiltration experiments were performed in slopes under two different plants (Campylotropis polyantha (Franch.) Schindl vs. Cynodon dactylon (Linn.) Pers). Dye tracer infiltration experiments with field observations and measurements of soil properties were combined. Results show that the discrepancy in macropores distribution between two slopes under different plants is significant. Root systems have significant effects on macropore flow paths distribution and the effect become more pronounced as the diameter of roots become larger. Organic matter and stone are important factors to affect macropores distribution. Root-soil interface, inter-aggregate macropore and stone-soil interface are important macropore flow paths in well vegetated slopes.

X-ray microtomography analysis of soil structure deformation caused by centrifugation

Abstract. Centrifugation provides a fast method to measure soil water retention curves over a wide moisture range. However, deformation of soil structure may occur at high angular velocities in the centrifuge. The objective of this study was to capture these changes in soil structure with X-ray microtomography and to measure local deformations via digital volume correlation. Two samples were investigated that differ in texture and rock content. A detailed analysis of the pore space reveals an interplay between shrinkage due to drying and soil compaction due to compression. Macroporosity increases at moderate angular velocity because of crack formation due to moisture release. At higher angular velocities, corresponding to capillary pressure of ψ < −100 kPa, macroporosity decreases again because of structure deformation due to compression. While volume changes due to swelling clay minerals are immanent in any drying process, the compaction of soil is a specific drawback of the centrifugation method. A new protocol for digital volume correlation was developed to analyze the spatial heterogeneity of deformation. In both samples the displacement of soil constituents is highest in the top part of the sample and exhibits high lateral variability explained by the spatial distribution of macropores in the sample. Centrifugation should therefore only be applied after the completion of all other hydraulic or thermal experiments, or any other analysis that depends on the integrity of soil structure.

Hierarchical emulsion based hybrid ceramics synthesized with different siloxane precursor and with embedded nickel nanoparticles

An emulsion-based synthesis route for the generation of organo-silica-based monolithic hybrid ceramics with a high content of different organic groups and embedded nickel nanoparticles is presented. By this route hybrid ceramics with a hierarchical pore size distribution and tailorable surface characteristics can be obtained. Mixtures of methyl polysiloxane (MK), tetraethyl orthosilicate (TEOS) and (3-aminopropyl)triethoxysilane (APTES) with varying ratios are selected as precursors, cross-linked, and subsequently pyrolyzed at 500 or 600 °C. In this way monolithic emulsion based hybrid ceramics with three different organo-functionalized siloxane precursor can be synthesized. Additionally, by adding the metal precursor NiCl2, metal-containing emulsion-based hybrid ceramics can be achieved. By adjusting the oil/water ratio and using high- or low internal phase emulsions (HIPEs or LIPEs), controlled micro-, meso-, and macropore distributions are obtained. After pyrolysis, materials achieve specific BET surface areas of up to 550 m2/g. Adjustable surface characteristics in terms of hydrophobicity and hydrophilicity of the material surface by thermal decomposition behavior of precursors is demonstrated. Nickel is incorporated through the formation of complexes with APTES, resulting in well-distributed metal nanoparticles with average particle sizes between 35 and 69 nm. The material properties are pivotal features for catalysis and gas separation applications.

Optimisation of thermoporometry measurements to evaluate mesoporous organic and carbon xero-, cryo- and aerogels

Thermoporometry (TPM) was used for characterisation of porous structure of organic and carbon materials (based on melamine or cellulose acetate) by examining melting behaviour of water inside the pores. Due to specific porous features (low pore volumes, broad distribution of mesopores and small macropores), an optimisation of TPM measurements by a sample pretreatment and adjustment of experimental parameters was necessary. Removing the soluble impurities before a TPM measurement was required as the impurities affected melting of water in the pores and thus also the calculated pore size distribution (PSD). Heating rate of 1°Cmin−1 was optimal for resolution and separation of the peaks originating from melting in the pores and in the bulk. The best ratio of water to a sample mass ranged from 4:14 for the samples with lower mesopore volumes (≈0.1cm3g−1) to 12:12 for the samples with higher volumes (≈0.4cm3g−1). A simple procedure without separation of the overlapping peaks was used for the assessment of pore volumes and PSDs. The results of TPM measurements are reasonably in agreement with the findings from nitrogen adsorption and SEM. Only supercritically dried organic aerogel was not measurable by TPM due to shrinkage of its porous structure after wetting.

Preparation of ordered macroporous cinchonine molecularly imprinted polymers and comparative study of their structure and binding properties with traditional bulk molecularly imprinted polymers

Three-dimensionally ordered macroporous molecularly imprinted polymers (MMIPs) were prepared by a combination of the colloidal crystal template method and the molecular imprinting technique. Traditional bulk molecularly imprinted polymers (BMIPs) were simultaneously synthesized with the same recipe as the MMIPs by using methacrylic acid as functional monomer, ethylene glycol dimethacrylate as crosslinker and chloroform as porogen. SEM and Brunauer − Emmett − Teller measurements show that MMIPs have a more regular macroporous structure, a narrower macropore distribution and a greater surface area and porosity compared with BMIPs. The isothermal and kinetic data of both polymers can be fitted with the Freundlich model and a pseudo-second-order equation, respectively. Their specificities to the template molecules are also similar. However, the binding capability, adsorption rate coefficient and internal effective diffusion coefficient of the MMIPs are higher than for the BMIPs when the particle size is above 54 µm. © 2015 Society of Chemical Industry

Microstructural changes of an undisturbed, reconstituted and compacted high plasticity clay subjected to wetting and drying

The behaviour of soil, and in particular compacted clay fill, can have significant implications on the safe and reliable operation of man-made infrastructure. The mechanical behaviour of soil (e.g. volume change and shear strength) is widely recognised as being associated with the microstructural arrangement (fabric/structure). In the case of high plasticity clays, despite the large amount of research carried out, soil microstructure and its evolution along mechanical and hydraulic paths are still not well understood. This makes incorporation of microstructural analysis difficult in engineering practice and highlights the need for further research. A comprehensive microstructural analysis of Maryland clay, a high plasticity residual soil, based on mercury intrusion porosimetry tests, is presented in this paper. Experimental results obtained from undisturbed, reconstituted and compacted specimens subjected to different hydraulic and mechanical paths are described. As with mechanical investigations, the reconstituted state is proposed to be used routinely as a reference state for comparison of undisturbed and compacted soil. The microstructural evolution of the compacted clay, prepared on the wet side of standard Proctor optimum water content, with an initially high void ratio, is examined along the main drying path. Importantly, a monotonic suction increase from the as-compacted state is shown to have negligible effect on the distribution of macro-pores. However, a new insight is provided based on the evolution of the dominant micro-pore entrance diameter which is shown to reduce with increased suction. This micro-pore entrance diameter is shown to correspond with the theoretical suction back-calculated from a simple capillary tube model, up to a limit. It is observed that, under oedometric conditions, the as-compacted microstructure is erased during saturation (soaking) and resembles the reconstituted microstructure. For this particular material and preparation conditions, it is demonstrated that a bimodal microstructure is not recovered on drying from a saturated state.

Surfactant assisted syntheses of monolithic hybrid ceramics with hierarchical porosity

A surfactant assisted emulsion-based syntheses route is presented for obtaining organo-silica-based monolithic hybrid ceramics with a hierarchical pore size distribution and tailorable surface characteristics. Methyl polysiloxane (MK) and methyl-phenyl polysiloxane (H44) with varying mixing ratios are selected as precursors, cross-linked and subsequently pyrolyzed at 500°C or 600°C, respectively. By adjusting the oil/water ratio and by tailoring the surfactant concentration controlled micro and macropore distributions with mesoscopic cell windows are obtained. After pyrolysis, specific surface areas of up to 600m2/g are achieved. In addition, due to the distinguished pyrolysis decomposition behavior of MK and H44, the adjustment of the surface characteristics in terms of hydrophobicity or hydrophilicity is demonstrated. The presented surfactant assisted emulsion-based process is hence highly suitable for tailoring pore size distribution and surface characteristics at the same time. Both material properties are pivotal features for catalysis and gas separation applications.

Unified method for the total pore volume and pore size distribution of hierarchical zeolites from argon adsorption and mercury intrusion.

A generalized approach to determine the complete distribution of macropores, mesopores, and micropores from argon adsorption and mercury porosimetry is developed and validated for advanced zeolite catalysts with hierarchically structured pore systems in powder and shaped forms. Rather than using a fragmented approach of simple overlays from individual techniques, a unified approach that utilizes a kernel constructed from model isotherms and model intrusion curves is used to calculate the complete pore size distribution and the total pore volume of the material. An added benefit of a single full-range pore size distribution is that the cumulative pore area and the area distribution are also obtained without the need for additional modeling. The resulting complete pore size distribution and the kernel accurately model both the adsorption isotherm and the mercury porosimetry. By bridging the data analysis of two primary characterization tools, this methodology fills an existing gap in the library of familiar methods for porosity assessment in the design of materials with multilevel porosity for novel technological applications.

Structure and properties of porous films based on aliphatic copolyamide developed for cellular technologies.

The effect of concentration and viscosity of the copolyamide (copolymer of ε-caprolactam and hexamethylendiaminadipate) solutions in aqueous/alcoholic solvents on its phase state was studied. The films obtained by the coagulation method were characterized by monodisperse pore distribution with an average pore size of 1.3 μm. The films processed by electrospinning from copolyamide solutions were characterized by a bimodal distribution of macropores with one peak of pore radius at 2.0 μm and second peak of pore radius at 20 μm. The adhesion and proliferation of mesenchymal adhesion stem cells (ASCs) stem cells to copolyamide matrix were studied. With the help of scanning electron microscopy it was shown that both tapes porous films were characterized by good adhesion of mesenchymal ASCs stem cells. It was shown that the porous structure, transport and mechanical properties of these copolyamide films allow their use as two-dimensional matrices for cellular technology.

Effect of acid treatment on the chemical composition and the structure of Egyptian diatomite

In this study Egyptian diatomaceous earth from Kasr El-Sagha locality in El Fayium province, Egypt was used. A highly purified diatomite has been prepared successfully by using a two stage process. In the first stage, samples of Egyptian diatomite were subjected to several mechanical techniques (attrition scrubbing and hydrocyclone classification) to remove most of the accompanied gangue minerals like inorganic carbonate, silica sand, and clay. The fraction with a particle size of −45μm was then submitted to a thermo-chemical treatment. This second stage started with a calcination of the diatomite samples at 1023K for 1h. Three modified forms of diatomite were then prepared by hot acidification of the calcined diatomite samples with aqua regia (5M HCl+5M HNO3), 5M sulphuric acid or 5M hydrochloric acid. The refined products were characterized by X-ray diffraction, X-ray fluorescence, low temperature nitrogen adsorption, mercury intrusion and scanning electron microscopy. Silica materials with high purity (>96wt.% SiO2) and an accessible and interconnected mesopore structure could be obtained. Additionally, all samples displayed a large amount of macropores of about 1μm diameter and a broad distribution of larger interstitial macropores. The treatment with hydrochloric acid led to products with a specific surface area between 120 and 150m2g−1 and 63wt.% of amorphous phase.

Characterizing preferential flow in cracked paddy soils using computed tomography and breakthrough curve

Soil cracks generated in paddy fields may change soil structure and provide pathways for preferential flow. However, the quantitative relationship between soil cracks and preferential flow remain unclear in paddy soils. The objectives of this study were to (1) reveal the effect of soil cracking on soil structure and preferential flow, (2) find a quantitative relationship between characteristics of soil structure and preferential flow in two paddy fields. Two paddy fields, one cultivated for 20 years (YPF) and the other cultivated for more than 100 years (OPF), were subjected to either alternate flooding and drying (AFD) or continuous flooding (CF) (as a control) during rice growing season. Undisturbed soil columns (10cm in diameter and 20cm in height) were sampled in the four plots. Macropores (including cracks) were quantified using computed tomography (CT), and preferential flow was assessed by breakthrough curve (BTC). The results showed that the presence of soil cracks under the AFD increased average macropore length but decreased the number of macropores significantly (P<0.05), and it also changed macropore size distribution and macropore area density distribution with soil depth. The three-dimensional structures of soil cracks were complicated but can be quantified using CT. The BTCs were well fitted by the convection-dispersion model (CDE) as well as by the two-region (mobile–immobile) transport model. Quick breakthrough, long tail and asymmetrical shape of BTCs for all soil columns indicated the extensiveness of preferential flow in these paddy fields. The relationships between soil macropore features and solute dispersivity parameters (λ and λeff) were poor (P>0.05). Both the shape of BTCs and fitting parameters demonstrated that soil cracks (5.31–11.9cm depth) did not increase preferential flow because they did not perforate through the dense plow pan. Soil columns in the CF plots displayed a bit more preferential flow due to a deeper macropore distribution as compared with the AFD plots. While macropore features were different at the two paddy soils, the difference in preferential flow was reduced due to the presence of plow pan. This study demonstrates that soil cracks significantly affect macropore structure but their impact on preferential flow may be poor when they do not penetrate through the plow pan.

The investigation of desired product properties of polycaprolactone-hydroxy apatite composites for tissue engineering applications

Biomaterials are used to perform or support the function of living tissues and contact with body fluids [1-3]. For temporary implants, biodegradation products of scaffolds have to be compatible with the body, and biodegradation time must be sufficient for regeneration of the tissue [4,5]. The aim of this study is to produce composites with improved product properties by using Polycaprolactone (PCL, hydrophobic and long biodegradation time) and Hydroxy apatite (HA, weak mechanical properties) that are not sufficient alone. Oleic Acid (OA) and Glycerol Monooleate (GMO) as organic additives were selected to provide a homogeneous distribution of the ceramic material in the polymer matrix. Desired product properties of prepared composites using different concentrations of these inorganic and organic additives and affecting parameters on these product properties were investigated for tissue engineering. Biocomposite materials were prepared with solvent casting technique using dichloromethane as the solvent. Salt was used as the porosifier. FTIR and EDX analyses for chemical characterization, tensile and compressive tests for determining mechanical properties, SEM analyses for determining surface properties, and BET analyses for pore sizes, total surface areas and total pore volumes of scaffolds were performed. Materials were kept in 5 times concentrated simulated body fluid (SBF) at 37°C for 2 days to determine the bioactivity. FTIR, EDX, and SEM analyses were performed again for characterization after SBF treatment. MTT test for determining toxicity and cell proliferation experiments for testing tissue regeneration will be performed. Composite materials which have micro and macro pore distribution are required for tissue engineering applications. Optical microscope images showed that prepared scaffolds had porous structure. Neat PCL is biocompatible with human body because of the increment of Ca/P ratio after SBF from zero to 2. Scaffolds that contain 3 wt% HA are more compatible than scaffolds that contain 20 wt% HA, and OA is more effective than GMO to form a new HA layer. Obtained results show that the composites are suitable for soft tissue applications.

秦岭火地塘林区土壤大孔隙分布特征及对导水性能的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 秦岭火地塘林区土壤大孔隙分布特征及对导水性能的影响 DOI: 10.5846/stxb201210281493 作者: 作者单位: 西北农林科技大学资源环境学院;陕西秦岭森林生态系统国家野外科学观测研究站,西北农林科技大学资源环境学院,西北农林科技大学水土保持研究所,西北农林科技大学资源环境学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家林业局林业公益性行业科研专项（201004036） Distribution of soil macropores and their influence on saturated hydraulic conductivity in the Huoditang forest region of the Qinling Mountains Author: Affiliation: College of Resources and Environment,Northwest A F University,Yangling;China;National Forest Ecosystem Research Station in Qinling of Shaanxi,Yangling;China,College of Resources and Environment,Northwest A F University,Yangling,Institute of soil and water conservation,Northwest A F University,Yangling,College of Resources and Environment,Northwest A F University,Yangling Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:大孔隙广泛分布于森林土壤中，是定量研究与土壤水分运动有关的重要因素，其研究可深化森林涵养水源机理的认识。基于田间持水量到饱和含水量之间的土壤孔隙作为大孔隙的标准，利用土壤水分穿透曲线和Poiseulle方程研究了秦岭火地塘林区森林土壤大孔隙分布特征及其对土壤饱和导水率的影响。结果表明，林区土壤大孔隙当量孔径主要分布在0.3-3.8 mm之间；当量孔径>1.5 mm的大孔隙密度较小，其数量仅占大孔隙总数量的5.37%；各当量孔径的大孔隙密度随土层分布基本呈现为上层大、下层小的特点，且垂直分布差异显著，其与有机质含量分布有极显著的相关性。0-60 cm土层大孔隙平均面积比顺序为：针阔混交林>油松林>落叶阔叶林>华山松林。不同当量孔径的大孔隙密度与饱和导水率呈显著正相关关系，当量孔径大于1.5 mm 的大孔隙密度决定了饱和导水率84%的变异；大孔隙率平均在1.6%-13.3%之间，当其小于5%时，饱和导水率随着大孔隙率增大而增大。 Abstract:Macroporosity is an important factor related to soil water movement. Relatively little is known abut soil macroporosity in the Huoditang forest region of the Qinling Mountains. Although they contribute relatively little to total soil porosity, macropores have a very important influence on saturated hydraulic conductivity and on subsurface flow. The study of macropores is important for understanding the characteristics of soil water movement and the mechanism of water conservation under forest vegetation. At the microscopic scale, the flow of water in all soil macropores is related to the size of the void. Furthermore, water flow rates are controlled by the smallest void in any single continuous flow path (i.e., pore neck). The objectives of this experiment were to study the distribution of soil macropores in the Huoditang Forest region and to determine the influence of these macropores on saturated hydraulic conductivity. The volume of soil macropores is equivalent to the volume of water in a soil at saturation minus the volume of water in the same soil at field capacity. This definition, along with water breakthrough curves and the Poiseulle formula were used in this study. The results showed that the equivalent radii of soil macropores in the Huoditang Forest ranged from 0.3 to 3.8 mm. Macropores with equivalent radii > 1.5 mm made up only 5.37% of the total macropore content. The order of average area proportion of 0-60 cm layer was mixed forest > Pinus tabulaeformis forest > deciduous broadleaf forest > Pinus armandii forest. Heavy clay may restrict the development of macropores in the P. armandii forest soil. Macropore density was significantly greater in the upper soil layers than in the lower soil layers. There was significant correlation between macropore density and the soil organic matter content. Macropore distribution in the root zone differed significantly among the different forest types. The content of rock fragments in deeper soil layers also affected macropore distribution. The average densities of macropores with different equivalent radii were positively related with saturated hydraulic conductivity. The density of macropores with radii > 1.5 mm accounted for 84% of the variability in saturated hydraulic conductivity. Soil porosity ranged from 1.6 to 13.3%. The saturated hydraulic conductivity increased with porosity when porosity was less than 5%. This is because the possibility of such discontinuous behavior increased both as the size and connectivity of the macropores increased and as the effect of capillary tension within the macropores became smaller. Pore structure is of crucial importance. In general, macropores, especially those with radii >1.5 mm, play a critical role in conserving water in forest soils. 参考文献 相似文献 引证文献

Macropores and Macropore Transport

Preferential transport of water through soil macropores is a governing process in the facilitated transport of strongly sorbing compounds. The aim of this study was to investigate the relationships between macropore density and the hydraulic conductivity of the soil and to test the sampling representativeness of soil columns for the measurement of saturated hydraulic conductivity. Macropore density was determined in three horizons in four typical Danish soil types (third year of pasture), and saturated hydraulic conductivity and near-saturated hydraulic conductivity were measured in the laboratory on undisturbed soil columns (6,280 cm) in the same three horizons. A strong relationship between macropore density and the mean particle diameter was found in the B and C horizons. A poor relationship was found between macropore density and the hydraulic conductivity at a matric potential of −10 hPa, whereas a stronger relationship was found at saturation. Results of the test of the number of soil columns needed for a representative distribution of macropores for the measurement of saturated hydraulic conductivity indicated that approximately six soil columns were enough. Our work suggests that integrating knowledge of the abundance of macropores in relation to soil type and land use will increase the performance of pedotransfer functions in predicting saturated hydraulic conductivity.