Characterizing macropore structure of agrosoddy-podzolic soil using computed tomography

AbstractThe agrosoddy-podzolic soil (Eutric Albic Glossic Retisol (Abruptic, Loamic, Aric, Cutanic)) is typical for Moscow Oblast and is used for agricultural purposes, resulting in use of various agrochemicals and pesticides. The presence of macropores and cracks in such soils leads to preferential water and substance transfer and nonequilibrium conditions. Therefore, it is important to study the numerical characteristics of the pore space of soils to adjust mathematical models of substance transfer. Undisturbed soil monoliths 10 cm in diameter taken from Ap (from 0 to 30 cm) and E, BE horizons (from 30 to 50 cm) were investigated under the field moisture conditions and after saturation using the tomographic core analyzer RKT-180 with the resolution of 200 μm/pixel. Using the X-ray computer tomography, it has been established that the plough layer of the agrosoddy-podzolic soil contains over 7% of macropores larger than 1 mm, while the subsurface layer has a porosity of about 3%. After saturation, some of the inter-aggregate pores overlap, which leads to a decrease in the total porosity to 4% in the upper and 2% in lower horizons, as well as increase in the average pore diameter. The number of macropores determined by tomographic analysis is one third higher than the values calculated using pedotransfer functions for this soil. The data obtained in this paper are recommended for use in national scenarios of migration of substances (pesticides, agrochemicals, salts) in soils.

Download Full-text

Effect of Macroporosity on Physical Property Estimates for Peat Soils

10.5194/egusphere-egu21-5238 ◽

2021 ◽

Author(s):

Miaorun Wang ◽

Haojie Liu ◽

Bernd Lennartz

Keyword(s):

Hydraulic Conductivity ◽

Soil Properties ◽

Total Porosity ◽

Pedotransfer Functions ◽

Parameter Estimates ◽

Model Parameters ◽

Soil Water Retention ◽

Peat Soils ◽

Undisturbed Soil ◽

Wide Range

Hydrophysical soil properties play an important role in regulating the water balance of peatlands and are known to be a function of the status of peat degradation. The objective of this study was to revise multiple regression models (pedotransfer functions, PTFs) for the assessment of hydrophysical properties from readily available soil properties. We selected three study sites, each representing a different state of peat degradation (natural, degraded and extremely degraded). At each site, 72 undisturbed soil cores were collected. The saturated hydraulic conductivity (Ks), soil water retention curves, total porosity, macroporosity, bulk density (BD) and soil organic matter (SOM) content were determined for all sampling locations. The van Genuchten (VG) model parameters (&#952;s,&#160;&#945;,&#160;n) were optimized using the RETC software package. Macroporosity and the&#160;Ks&#160;were found to be highly correlated, but the obtained functions differ for differently degraded peatlands. The introduction of macroporosity into existing PTFs substantially improved the derivation of hydrophysical parameter values as compared to functions based on BD and SOM content alone. The obtained PTFs can be applied to a wide range of natural and degraded peat soils. We assume that the incorporation of macroposity helps to overcome effects possibly resulting from soil management. Our results suggest that the extra effort required to determine macroporosity is worth it, considering the quality of parameter estimates for hydraulic conductivity as well as the soil hydraulic VG model.

Download Full-text

USO DE FUNÇÕES DE PEDOTRANSFERÊNCIA PARA ESTIMATIVA DA RETENÇÃO DE ÁGUA EM UM LATOSSO NO ESTADO DE RONDÔNIA [ Use of pedotransfer functions for estimation of the water retention in Oxisol on the Rondônia state ]

REEC - Revista Eletrônica de Engenharia Civil ◽

10.5216/reec.v14i2.51385 ◽

2018 ◽

Vol 14 (2) ◽

Author(s):

Petrus Luiz de Luna Pequeno ◽

Flávio de Paula Fagundes ◽

Raiany Cardoso dos Santos ◽

Cláudio Luiz do Amaral Santini ◽

Marcelo Augusto Rambo ◽

...

Keyword(s):

Water Retention ◽

Pearson Correlation ◽

Total Porosity ◽

Pedotransfer Functions ◽

Pedotransfer Function ◽

Undisturbed Soil ◽

Physical Attributes ◽

Development And Validation ◽

Porto Velho

RESUMO: A presente pesquisa objetivou testar funções de pedotransferência desenvolvidas para as condições brasileiras identificando a de melhor ajuste para determinação da retenção de água de um Latossolo do município de Porto Velho-RO. O banco de dados inicial constou de resultados analíticos do RADAMBRASIL e SIGTERON, onde a classe de solo Latossolo Vermelho Amarelo foi escolhida. Para melhorar a qualidade do banco de dados, foram coletadas amostras indeformadas de solo, e nestas determinados atributos físicos do solo, tais como: granulometria, densidade do solo, porosidade total, macroporosidade e microporosidade, além do conteúdo volumétrico de água retido nas tensões de -0,006 e -0,01 MPa utilizando-se mesa de tensão. Os dados determinados (observados) e os preditos (por meio das funções de pedotransferências - FPT) foram comparados graficamente através da relação 1:1, também por meio dos indicadores estatísticos: coeficiente de correlação de Pearson (r²), erro médio (ME) e raiz quadrada do erro médio (RMSE). As FPT desenvolvidas por Pequeno (2016) apresentaram acurácia regular para predição do conteúdo de água retido. As funções de pedotransferências desenvolvidas por Urach (2007) foram as que melhores se ajustaram para predição do conteúdo e água retido nas condições edafoclimáticas analisadas. Considerando o comportamento dos modelos testados, a qualidade dos dados obtidos, as peculiaridades regionais, este trabalho possibilitou a observância da necessidade de desenvolvimento e validação de modelos específicos para as condições edafoclimáticas locais, o que poderá mostrar melhores ajustes e precisão para uso na estimativa da retenção de água no solo.ABSTRACT: The present research aimed to test pedotransfer functions developed for the Brazilian conditions identifying the model of the best adjustment in the determination of water retention on the Ferrasol of the municipality of Porto Velho-RO. The initial database consisted of the analytical results of RADAMBRASIL and SIGTERON, where was chosen the Ferrasol soil class. In order to improve the quality of the database, undisturbed soil samples were collected and in these samples physical attributes of the soil was determinated: granulometry, soil density, total porosity, macroporosity and microporosity, as well as water volumetric content retained at -0.006 And -0.01 MPa using tension table. The determined (observed) and predicted (through pedotransfer function - FPT) data were compared graphically through the 1:1 ratio, as well as through statistical indicators: Pearson correlation coefficient (r²), mean error (ME) and root-mean-square error (RMSE). The pedotransfer function developed by Pequeno (2016) showed a regular accuracy to predict the water content retained. The pedotransfer function developed by Urach (2007) were the best fit for predicting the content and water retained in the edaphoclimatic conditions analyzed. Considering the behavior of the models tested, the quality of the data obtained, the regional peculiarities, this work allowed for the observance the need for development and validation of specific models for the local edaphoclimatic conditions, which may will show better adjustments and accuracy for to use on the estimating water retention on soil.

Download Full-text

Petrographic and Petrophysical Characteristics of the Upper Devonian Three Forks Formation, Southern Nesson Anticline, North Dakota

The Mountain Geologist ◽

10.31582/rmag.mg.54.3.181 ◽

2017 ◽

Vol 54 (3) ◽

pp. 181-201

Author(s):

Rebecca Johnson ◽

Mark Longman ◽

Brian Ruskin

Keyword(s):

Relaxation Time ◽

Pore Size ◽

Water Saturation ◽

Average Pore Size ◽

Total Porosity ◽

Average Pore ◽

Pore Sizes ◽

Three Forks Formation ◽

Three Forks ◽

Intercrystalline Pores

The Three Forks Formation, which is about 230 ft thick along the southern Nesson Anticline (McKenzie County, ND), has four “benches” with distinct petrographic and petrophysical characteristics that impact reservoir quality. These relatively clean benches are separated by slightly more illitic (higher gamma-ray) intervals that range in thickness from 10 to 20 ft. Here we compare pore sizes observed in scanning electron microscope (SEM) images of the benches to the total porosity calculated from binned precession decay times from a suite of 13 nuclear magnetic resonance (NMR) logs in the study area as well as the logarithmic mean of the relaxation decay time (T2 Log Mean) from these NMR logs. The results show that the NMR log is a valid tool for quantifying pore sizes and pore size distributions in the Three Forks Formation and that the T2 Log Mean can be correlated to a range of pore sizes within each bench of the Three Forks Formation. The first (shallowest) bench of the Three Forks is about 35 ft thick and consists of tan to green silty and shaly laminated dolomite mudstones. It has good reservoir characteristics in part because it was affected by organic acids and received the highest oil charge from the overlying lower Bakken black shale source rocks. The 13 NMR logs from the study area show that it has an average of 7.5% total porosity (compared to 8% measured core porosity), and ranges from 5% to 10%. SEM study shows that both intercrystalline pores and secondary moldic pores formed by selective partial dissolution of some grains are present. The intercrystalline pores are typically triangular and occur between euhedral dolomite rhombs that range in size from 10 to 20 microns. The dolomite crystals have distinct iron-rich (ferroan) rims. Many of the intercrystalline pores are partly filled with fibrous authigenic illite, but overall pore size typically ranges from 1 to 5 microns. As expected, the first bench has the highest oil saturations in the Three Forks Formation, averaging 50% with a range from 30% to 70%. The second bench is also about 35 ft thick and consists of silty and shaly dolomite mudstones and rip-up clast breccias with euhedral dolomite crystals that range in size from 10 to 25 microns. Its color is quite variable, ranging from green to tan to red. The reservoir quality of the second bench data set appears to change based on proximity to the Nesson anticline. In the wells off the southeast flank of the Nesson anticline, the water saturation averages 75%, ranging from 64% to 91%. On the crest of the Nesson anticline, the water saturation averages 55%, ranging from 40% to 70%. NMR porosity is consistent across the entire area of interest - averaging 7.3% and ranging from 5% to 9%. Porosity observed from samples collected on the southeast flank of the Nesson Anticline is mainly as intercrystalline pores that have been extensively filled with chlorite clay platelets. In the water saturated southeastern Nesson Anticline, this bench contains few or no secondary pores and the iron-rich rims on the dolomite crystals are less developed than those in the first bench. The chlorite platelets in the intercrystalline pores reduce average pore size to 500 to 800 nanometers. The third bench is about 55 ft thick and is the most calcareous of the Three Forks benches with 20 to 40% calcite and a proportionate reduction in dolomite content near its top. It is also quite silty and shaly with a distinct reddish color. Its dolomite crystals are 20 to 50 microns in size and partly abraded and dissolved. Ferroan dolomite rims are absent. This interval averages 7.1% porosity and ranges from 5% to 9%, but the pores average just 200 nanometers in size and occur mainly as microinterparticle pores between illite flakes in intracrystalline pores in the dolomite crystals. This interval has little or no oil saturation on the southern Nesson Anticline. Unlike other porosity tools, the NMR tool is a lithology independent measurement. The alignment of hydrogen nuclei to the applied magnetic field and the subsequent return to incoherence are described by two decay time constants, longitudinal relaxation time (T1) and transverse relaxation time (T2). T2 is essentially the rate at which hydrogen nuclei lose alignment to the external magnetic field. The logarithmic mean of T2 (T2 Log Mean) has been correlated to pore-size distribution. In this study, we show that the assumption that T2 Log Mean can be used as a proxy for pore-size distribution changes is valid in the Three Forks Formation. While the NMR total porosity from T2 remains relatively consistent in the three benches of the Three Forks, there are significant changes in the T2 Log Mean from bench to bench. There is a positive correlation between changes in T2 Log Mean and average pore size measured on SEM samples. Study of a “type” well, QEP’s Ernie 7-2-11 BHD (Sec. 11, T149N, R95W, McKenzie County), shows that the 1- to 5-micron pores in the first bench have a T2 Log Mean relaxation time of 10.2 msec, whereas the 500- to 800-nanometer pores in the chlorite-filled intercrystalline pores in the second bench have a T2 Log Mean of 4.96 msec. This compares with a T2 Log Mean of 2.86 msec in 3rd bench where pores average just 200 nanometers in size. These data suggest that the NMR log is a useful tool for quantifying average pore size in the various benches of the Three Forks Formation.

Download Full-text

Numerical analysis of soil microstructure reveals conditions for natural attenuation in aged tar oil contaminated soil

10.5194/egusphere-egu21-4810 ◽

2021 ◽

Author(s):

Pavel Ivanov ◽

Karin Eusterhues ◽

Kai Uwe Totsche

Keyword(s):

Soil Solution ◽

Contaminated Soil ◽

Natural Attenuation ◽

Pore Space ◽

Total Porosity ◽

Control Soil ◽

Soil Microstructure ◽

Cell Counts ◽

Good Protection ◽

Tar Oil

Understanding of ongoing biogeochemical processes (natural attenuation) within contaminated soils is crucial for the development of plausible remediation strategies. We studied a tar oil contaminated soil with weak grass vegetation at a former manufactured gas plant site in Germany. Despite of the apparent toxicity (the soil contained up to 120 g kg-1 petroleum hydrocarbons, 26 g kg-1 toxic metals, and 100 mg kg-1 polycyclic aromatic hydrocarbons), the contaminated layers have 3-5 times as much cell counts as an uncontaminated control soil nearby. To test, if the geometry of the pore space provides favourable living space for microorganisms, we applied scanning electron microscopy to the thin sections and calculated on sets of 15 images per layer three specific Minkowski functionals, connected to soil total porosity, interface, and hydraulic parameters.Our investigation showed that the uncontaminated control soil has a relatively low porosity of 15-20 %, of which 50-70 % is comprised of small (< 15 &#181;m) pores. These pores are poorly connected and show high distances between them (mean distance to the next pore 10 &#181;m). The dominating habitats in the control soil are therefore created by small pores. They provide good protection from predators and desiccation, but input of dissolved organic C and removal of metabolic products are diffusion limited. Coarser pores (>15 &#181;m) provide less space (< 50 % of total porosity) and solid surface area (< 20 %), are prone to desiccation and offer less protection from predators. However, they serve as preferential flow paths for the soil solution (input of nutrients) and are well aerated, therefore we expect the microbial activity in them to appear in &#8220;hot moments&#8221;, i.e. after rain events.All layers of the contaminated profile have higher porosities (20-70 %) than the control. Coarse pores comprise 83-90 % of total pore area and create 34-52 % of total interface. Pores are also more connected and tortuous than in the control soil, which implies a better aeration and circulation of soil solution. The loops of pore channels may retain soil solution and be therefore preferably populated with microorganisms. The small (< 15 &#181;m) pores comprise less than 17 % of total porosity but represent a substantial proportion of the interface (48-66 % vs 82-91 % in control). In the uppermost layer of the contaminated profile, such pores occur in plant residues, are close to the largest pores (mean distance to the next pore 4 &#181;m) and therefore, along with good protection, are supplied with air, water, and non-tar C. In the middle of the profile, the small pores, presumably constantly filled with water, are located within dense tar pieces remote from the neighbouring pores (mean distance to the next pore 22 &#181;m), and therefore, with hindered aeration and no supply of non-tar C, may create anaerobic domains of tar attenuation.Our results show that the contaminated soil offers more favourable conditions for microorganisms than the control soil, probably because the hydrocarbons provide suitable energy and nutrition sources and a beneficial pore space geometry.

Download Full-text

Physical and optical characteristics of heavily melted “rotten” Arctic sea ice

The Cryosphere ◽

10.5194/tc-13-775-2019 ◽

2019 ◽

Vol 13 (3) ◽

pp. 775-793 ◽

Cited By ~ 2

Author(s):

Carie M. Frantz ◽

Bonnie Light ◽

Samuel M. Farley ◽

Shelly Carpenter ◽

Ross Lieblappen ◽

...

Keyword(s):

Light Scattering ◽

Sea Ice ◽

Pore Space ◽

Total Porosity ◽

Arctic Sea Ice ◽

Micro Computed Tomography ◽

Structural Anisotropy ◽

Scattering Coefficients ◽

Ice Melt ◽

Arctic Sea

Abstract. Field investigations of the properties of heavily melted “rotten” Arctic sea ice were carried out on shorefast and drifting ice off the coast of Utqiaġvik (formerly Barrow), Alaska, during the melt season. While no formal criteria exist to qualify when ice becomes rotten, the objective of this study was to sample melting ice at the point at which its structural and optical properties are sufficiently advanced beyond the peak of the summer season. Baseline data on the physical (temperature, salinity, density, microstructure) and optical (light scattering) properties of shorefast ice were recorded in May and June 2015. In July of both 2015 and 2017, small boats were used to access drifting rotten ice within ∼32 km of Utqiaġvik. Measurements showed that pore space increased as ice temperature increased (−8 to 0 ∘C), ice salinity decreased (10 to 0 ppt), and bulk density decreased (0.9 to 0.6 g cm−3). Changes in pore space were characterized with thin-section microphotography and X-ray micro-computed tomography in the laboratory. These analyses yielded changes in average brine inclusion number density (which decreased from 32 to 0.01 mm−3), mean pore size (which increased from 80 µm to 3 mm), and total porosity (increased from 0 % to > 45 %) and structural anisotropy (variable, with values of generally less than 0.7). Additionally, light-scattering coefficients of the ice increased from approximately 0.06 to > 0.35 cm−1 as the ice melt progressed. Together, these findings indicate that the properties of Arctic sea ice at the end of melt season are significantly distinct from those of often-studied summertime ice. If such rotten ice were to become more prevalent in a warmer Arctic with longer melt seasons, this could have implications for the exchange of fluid and heat at the ocean surface.

Download Full-text

Morphological and physicochemical properties of various tropical soils from east-central Puerto Rico

The Journal of Agriculture of the University of Puerto Rico ◽

10.46429/jaupr.v36i2.12797 ◽

1969 ◽

Vol 36 (2) ◽

pp. 167-178

Author(s):

M. A. Lugo López ◽

M. B. Martínez ◽

A. R. Riera

Keyword(s):

Organic Matter ◽

Puerto Rico ◽

Laboratory Data ◽

High Capacity ◽

Total Porosity ◽

Tropical Soils ◽

Drainage Water ◽

Low Fertility ◽

Undisturbed Soil ◽

East Central

This report presents the results of a preliminary soil reconnaissance in east-central Puerto Rico. It contains soil-profile observations made on several deep pits dug for the purpose. It also includes the results of various infiltration tests conducted in the major soil types of the area. The laboratory data reported include organic matter, pH, nitrogen, and total exchange capacity, and also the following measurements conducted on undisturbed soil cores dug with a Kelley (Utah) soil sampling machine: Permeability, quick drainage, water retained at pF 1.78, maximum saturation, and bulk density. Additional data are presented on water retained at pF 2.7 and pF 4.2, available water, total porosity, and air porosity. The soils of east-central Puerto Rico are rather deep, medium- or heavy-textured, acid, and of medium to low fertility. They are not generally well supplied with organic matter and nitrogen. In many cases they have compact, tight subsoil layers near the surface which considerably reduce the permeability of the profile and induce poor drainage. Laboratory soil-moisture studies confirmed field observations indicating that the majority of the soils of this region have a moderately high capacity to store water available for crop growth.

Download Full-text

Effect of time of application and continuity of rainfall on leaching of surface applied nutrients

Soil Research ◽

10.1071/sr9910001 ◽

1991 ◽

Vol 29 (1) ◽

pp. 1 ◽

Cited By ~ 18

Author(s):

CDA Mclay ◽

KC Cameron ◽

RG Mclaren

Keyword(s):

Preferential Flow ◽

Pore Space ◽

Natural Soil ◽

Sufficient Time ◽

Undisturbed Soil ◽

Time Of Application ◽

Applied Pulse ◽

Time Periods ◽

Soil Lysimeters ◽

Continuous Rainfall

The effect of time of rainfall relative to solute application, and the effect of rainfall continuity, was studied using undisturbed soil lysimeters. Immediate leaching with a surface-applied pulse of nitrate was compared with delayed (24 h) leaching of sulfate in a non-adsorbing soil. Preferential flow of water and solutes through natural soil macropores resulted in: (i) peak solute concentrations occurring before 1.0 pore volume of drainage, and (ii) incomplete leaching of applied solutes after 2.0 pore volumes of drainage. The immediate application of rainfall resulted in faster leaching rates compared with a delayed application. It is considered likely that the delay before rainfall allowed sufficient time for some solute to diffuse into intra- and inter-aggregate pore space and thus be bypassed by water flowing through soil macropores. Under intermittent rainfall, there was a series of time periods during which diffusion could occur into soil micropores and therefore the rate of leaching of surface-applied solute was slower than under continuous rainfall.

Download Full-text

Laboratory Evaluation of the Stress-Strain relationship of Permeable Concrete

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.243-249.3259 ◽

2011 ◽

Vol 243-249 ◽

pp. 3259-3262 ◽

Cited By ~ 1

Author(s):

Manal Hussin ◽

Zhu Ge Yan ◽

Frank Bullen ◽

Weena Lokuge

Keyword(s):

Pore Space ◽

Strain Curve ◽

Laboratory Evaluation ◽

Fine Aggregate ◽

Stress Strain ◽

Average Pore ◽

Water To Cement Ratio ◽

Strain Relationship ◽

New Type ◽

Relationship Of

The authors conducted research aimed at developing a new type of permeable concrete material with enhanced structural strength. This paper presents and discusses the results of their investigation on the unaxial compressive stress-strain relationship of porous concrete made with two different mix designs with constant water to cement ratio. The concrete mixes were designed with a target compressive strength between 15-25 MPa and target porosity between 10-15% to study the effect of pore sizes on the stress-strain curve. The average pore space was increased by increasing the relative amount of large aggregate. The reduction in the relative amount of fine aggregate increased the average pore space and resulted in a reduction in mix stiffness and a marginal increase in ultimate strength.

Download Full-text

Physical and optical characteristics of heavily melted "rotten" Arctic sea ice

10.5194/tc-2018-141 ◽

2018 ◽

Author(s):

Carie M. Frantz ◽

Bonnie Light ◽

Samuel M. Farley ◽

Shelly Carpenter ◽

Ross Lieblappen ◽

...

Keyword(s):

Light Scattering ◽

Sea Ice ◽

Pore Space ◽

Total Porosity ◽

Arctic Sea Ice ◽

Micro Computed Tomography ◽

Structural Anisotropy ◽

Scattering Coefficients ◽

Ice Melt ◽

Arctic Sea

Abstract. Field investigations of the properties of heavily melted "rotten" Arctic sea ice were carried out on shorefast and drifting ice off the coast of Utqiaġvik (formerly Barrow), Alaska during the melt season. While no formal criteria exist to qualify when ice becomes "rotten", the objective of this study was to sample melting ice at the point where its structural and optical properties are sufficiently advanced beyond the peak of the summer season. Baseline data on the physical (temperature, salinity, density, microstructure) and optical (light scattering) properties of shorefast ice were recorded in May and June 2015. In July of both 2015 and 2017, small boats were used to access drifting "rotten" ice within ~ 32 km of Utqiaġvik. Measurements showed that pore space increased as ice temperature increased (−8 °C to 0 °C), ice salinity decreased (10 ppt to 0 ppt), and bulk density decreased (0.9 g cm-3 to 0.6 g cm-3). Changes in pore space were characterized with thin-section microphotography and X-ray micro-computed tomography in the laboratory. These analyses yielded changes in average brine inclusion number density (which decreased from 32 mm-3 to 0.01 mm-3), mean pore size (which increased from 80 μm to 3 mm) as well as total porosity (increased from 0 % to > 45 %) and structural anisotropy (variable, with values generally less than 0.7). Additionally, light scattering coefficients of the ice increased from approximately 0.06 cm-1 to > 0.35 cm-1 as the ice melt progressed. Together, these findings indicate that Arctic sea ice at the end of melt season is physically different from the often-studied summertime ice. If such rotten ice were to become more prevalent in a warmer Arctic, this could have implications for the exchange of fluid and heat at the ocean surface.

Download Full-text

Magnetic Resonance Pore Imaging, a new tool for porous media research

10.26686/wgtn.17009354 ◽

2021 ◽

Author(s):

◽

Stefan A. Hertel

Keyword(s):

Porous Media ◽

Magnetic Resonance ◽

Pore Space ◽

Biological Tissues ◽

Porous System ◽

Two Dimensional ◽

Phase Problem ◽

Average Pore ◽

Wide Range ◽

Pgse Nmr

Porous media are highly prevalent in nature and span a wide range of systems including biological tissues, chemical catalysts or rocks in oil reservoirs. Imaging of the structure of the constituent pores is therefore highly desirable for life sciences and technological applications. This thesis presents the new development and application of a nuclear magnetic resonance (NMR) technique to acquire high resolution images of closed pores. The technique is a further development of diffusive-diffraction Pulsed Gradient Spin Echo (PGSE) NMR, which has been shown to image the pore auto-correlation function averaged over all pores. Until recently it was conventional wisdom that diffusive-diffraction PGSE NMR can only measure the magnitude of the form factor, due to its similarity to diffraction techniques such as x-ray and neutron scattering. In diffraction applications the loss of phase information is commonly referred to as the “phase problem”, which prevents the reconstruction of images of the pore space by inverse Fourier transform. My work is based on a recently suggested modification of the diffusive-diffraction PGSE NMR method, which creates a hybrid between Magnetic Resonance Imaging (MRI) and PGSE NMR. Therefore, we call this approach Magnetic Resonance Pore Imaging (MRPI). We provide experimental confirmation that MRPI does indeed measure the diffractive signal including its phase and thus the “phase problem” is lifted. We suggest a two-dimensional version of MRPI and obtain two-dimensional average pore images of cylindrical and triangular pores with an unprecedented resolution as compared to state of the art MRI. Utilizing a laser machined phantom sample we present images of microscopic pores with triangular shape even in the presence of wall relaxation effects. We therefore show that MRPI is able to reconstruct the pore shape without any prior knowledge or assumption about the porous system under study. Furthermore, we demonstrate that the MRPI approach integrates seamlessly with known MRI concepts. For instance we introduce “MRPI mapping” which acquires the MRPI signal for each pixel in an MRI image. This enables one to resolve pore sizes and shapes spatially, thus expanding the application of MRPI to samples with heterogeneous distributions of pores.

Download Full-text