TheInfoList

Porosity or void fraction is a measure of the
void Void may refer to: Science, engineering, and technology * Void (astronomy) Cosmic voids are vast spaces between filaments (the largest-scale structures in the universe The universe ( la, universus) is all of space and time and their c ...
(i.e. "empty") spaces in a
material Material is a substance Substance may refer to: * Substance (Jainism), a term in Jain ontology to denote the base or owner of attributes * Chemical substance, a material with a definite chemical composition * Matter, anything that has mass and t ...

, and is a fraction of the volume of voids over the total volume, between 0 and 1, or as a
percentage In mathematics Mathematics (from Greek: ) includes the study of such topics as numbers (arithmetic and number theory), formulas and related structures (algebra), shapes and spaces in which they are contained (geometry), and quantities a ...

between 0% and 100%. Strictly speaking, some tests measure the "accessible void", the total amount of void space accessible from the
surface File:Water droplet lying on a damask.jpg, Water droplet lying on a damask. Surface tension is high enough to prevent floating below the textile. A surface, as the term is most generally used, is the outermost or uppermost layer of a physical obje ...
(cf.
closed-cell foam Foam is an object formed by trapping pockets of in a or . A and the are examples of foams. In most foams, the volume of is large, with thin films of liquid or solid separating the regions of gas. Soap foams are also known as suds. Solid ...
). There are many ways to test porosity in a substance or part, such as
industrial CT scanning Industrial computed tomography (CT) scanning is any computer-aided tomographic process, usually X-ray computed tomography, that uses irradiation Irradiation is the process by which an object is exposed to radiation upThe international sym ...
. The term porosity is used in multiple fields including
pharmaceutics Pharmaceutics is the discipline of pharmacy Pharmacy is the clinical health science The following outline is provided as an overview of and topical guide to health sciences: Health sciences – are those sciences which focus on heal ...
,
ceramics A ceramic is any of the various hard, brittle, heat-resistant and corrosion-resistant Corrosion is a Erosion, natural process that converts a refined metal into a more chemically stable form such as oxide, hydroxide, carbonate or sulfide. It ...
,
metallurgy Metallurgy is a domain of materials science and engineering ''Materials Science and Engineering'' may refer to several journals in the field of materials science and engineering: * '' Materials Science and Engineering A'' * '' Materials Science ...
,
materials Material is a substance Substance may refer to: * Substance (Jainism), a term in Jain ontology to denote the base or owner of attributes * Chemical substance, a material with a definite chemical composition * Matter, anything that has mass and t ...
,
manufacturing Manufacturing is the creation or Production (economics), production of goods with the help of equipment, Work (human activity), labor, machines, tools, and chemical or biological processing or formulation. It is the essence of secondary sector ...
,
petrophysics Petrophysics (from the Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is app ...
,
hydrology Hydrology (from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approxi ...
,
earth sciences Earth science or geoscience includes all fields of natural science related to the planet Earth. This is a branch of science dealing with the physical and chemical constitution of Earth and its atmosphere. Earth science can be considered to be a b ...
,
soil mechanics Soil mechanics is a branch of soil physics Soil physics is the study of soil File:Stagnogley.JPG, Surface-water-Gley soil, gley developed in glacial till, Northern Ireland. Soil is a mixture of organic matter, minerals, gases, liquids, a ...
, and
engineering Engineering is the use of scientific principles to design and build machines, structures, and other items, including bridges, tunnels, roads, vehicles, and buildings. The discipline of engineering encompasses a broad range of more speciali ...

.

# Void fraction in two-phase flow

In gas-liquid
two-phase flow In , two-phase flow is a of and — a particular example of . Two-phase flow can occur in various forms, such as flows transitioning from pure liquid to vapor as a result of external ing, separated flows, and dispersed two-phase flows where on ...
, the void fraction is defined as the fraction of the flow-channel volume that is occupied by the gas phase or, alternatively, as the fraction of the cross-sectional area of the channel that is occupied by the gas phase. Void fraction usually varies from location to location in the flow channel (depending on the two-phase flow pattern). It fluctuates with time and its value is usually time averaged. In separated (i.e., non-
homogeneous Homogeneity and heterogeneity are concepts often used in the sciences Science () is a systematic enterprise that Scientific method, builds and organizes knowledge in the form of Testability, testable explanations and predictions about th ...
) flow, it is related to
volumetric flow rate In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and time, and the related entities of energy and force. ...
s of the gas and the liquid phase, and to the ratio of the velocity of the two phases (called ''
slip ratio Slip ratio is a means of calculating and expressing the slipping behavior of the wheel of an automobile A car (or automobile) is a wheeled motor vehicle A motor vehicle, also known as motorized vehicle or automotive vehicle, is a self-prop ...
'').

# Porosity in earth sciences and construction

Used in
geology Geology (from the Ancient Greek Ancient Greek includes the forms of the Greek language Greek ( el, label=Modern Greek Modern Greek (, , or , ''Kiní Neoellinikí Glóssa''), generally referred to by speakers simply as Greek ...

,
hydrogeology Hydrogeology (''hydro-'' meaning water, and ''-geology'' meaning the study of the Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is lan ...
,
soil science Soil science is the study of soil Surface-water- gley developed in glacial till, Northern Ireland.">Northern_Ireland.html" ;"title="glacial till, Northern Ireland">glacial till, Northern Ireland. Soil is a mixture of organic matter, mine ...
, and
building science Building science is the collection of scientific knowledge Science (from the Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the ...
, the porosity of a
porous medium A porous medium or a porous material is a material containing (voids). The skeletal portion of the material is often called the "matrix" or "frame". The pores are typically filled with a ( or ). The skeletal material is usually a , but structure ...

(such as
rock Rock most often refers to: * Rock (geology) A rock is any naturally occurring solid mass or aggregate of minerals or mineraloid matter. It is categorized by the minerals included, its Chemical compound, chemical composition and the way in w ...
or
sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently sediment transport, transported by the action of wind, water, or ice or by the force of gravity acting on the particles. ...

) describes the fraction of void space in the material, where the void may contain, for example, air or water. It is defined by the
ratio In mathematics, a ratio indicates how many times one number contains another. For example, if there are eight oranges and six lemons in a bowl of fruit, then the ratio of oranges to lemons is eight to six (that is, 8∶6, which is equivalent to ...

: :$\phi = \frac$ where ''V''V is the volume of void-space (such as fluids) and ''V''T is the total or bulk volume of material, including the solid and void components. Both the
mathematical symbols A mathematical symbol is a figure or a combination of figures that is used to represent a mathematical object, an action on mathematical objects, a relation between mathematical objects, or for structuring the other symbols that occur in a formula. ...
$\phi$ and $n$ are used to denote porosity. Porosity is a fraction between 0 and 1, typically ranging from less than 0.005 for solid
granite Granite () is a coarse-grained (phanerite, phaneritic) intrusive rock, intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cool ...

to more than 0.5 for
peat Peat (), also known as turf (), is an accumulation of partially decayed vegetation Vegetation is an assemblage of species and the they provide. It is a general term, without specific reference to particular , life forms, structure, ...
and
clay Clay is a type of fine-grained natural soil Surface-water- gley developed in glacial till, Northern Ireland.">Northern_Ireland.html" ;"title="glacial till, Northern Ireland">glacial till, Northern Ireland. Soil is a mixture of organic m ...

. The porosity of a rock, or sedimentary layer, is an important consideration when attempting to evaluate the potential volume of
water Water (chemical formula H2O) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known li ...

or
hydrocarbon In organic chemistry Organic chemistry is a branch of chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, prop ...
s it may contain. Sedimentary porosity is a complicated function of many factors, including but not limited to: rate of burial, depth of burial, the nature of the
connate fluids In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock (geology), rocks of which it is composed, and the processes ...
, the nature of overlying sediments (which may impede fluid expulsion). One commonly used relationship between porosity and depth is given by the Athy (1930) equation: : $\phi\left(z\right) = \phi_0 e^\,$ where $\phi_0$ is the surface porosity, $k$ is the compaction coefficient (m−1) and $z$ is depth (m). A value for porosity can alternatively be calculated from the
bulk densityBulk density, also called apparent density or volumetric density, is a property of powders, granules, and other "divided" solid Solid is one of the four fundamental states of matter (the others being liquid, gas and plasma). The molecu ...
$\rho_$, saturating
fluid density The density (more precisely, the volumetric mass density; also known as specific mass), of a substance is its mass per unit volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter Rho (letter), rho), although the L ...
$\rho_$ and particle density $\rho_$: :$\phi = \frac$ If the void space is filled with air, the following simpler form may be used: :$\phi = 1-\frac$ Normal particle density is assumed to be approximately 2.65 g/cm3 (
silica Silicon dioxide, also known as silica, is an oxide An oxide () is a chemical compound A chemical compound is a chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any su ...

), although a better estimation can be obtained by examining the
lithology The lithology of a Rock (geology), rock unit is a description of its physical characteristics visible at outcrop, in hand or core sample, core samples, or with low magnification microscopy. Physical characteristics include colour, texture, grain ...
of the particles.

## Porosity and hydraulic conductivity

Porosity can be proportional to
hydraulic conductivity Hydraulics (from Greek language, Greek: Υδραυλική) is a technology and applied science using engineering, chemistry, and other sciences involving the mechanical properties and use of liquids. At a very basic level, hydraulics is the ...
; for two similar
sand Sand is a granular material composed of finely divided rock (geology), rock and mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer ...

y
aquifer An aquifer is an underground layer of -bearing , rock fractures or unconsolidated materials (, , or ). can be extracted using a water . The study of water flow in aquifers and the characterization of aquifers is called . Related terms include a ...

s, the one with a higher porosity will typically have a higher
hydraulic conductivity Hydraulics (from Greek language, Greek: Υδραυλική) is a technology and applied science using engineering, chemistry, and other sciences involving the mechanical properties and use of liquids. At a very basic level, hydraulics is the ...
(more open area for the flow of water), but there are many complications to this relationship. The principal complication is that there is not a direct proportionality between porosity and hydraulic conductivity but rather an inferred proportionality. There is a clear proportionality between pore throat radii and hydraulic conductivity. Also, there tends to be a proportionality between pore throat radii and pore volume. If the proportionality between pore throat radii and porosity exists then a proportionality between porosity and hydraulic conductivity may exist. However, as grain size or sorting decreases the proportionality between pore throat radii and porosity begins to fail and therefore so does the proportionality between porosity and hydraulic conductivity. For example: clays typically have very low hydraulic conductivity (due to their small pore throat radii) but also have very high porosities (due to the structured nature of
clay minerals Clay minerals are hydrous aluminium Aluminium (aluminum in American English, American and Canadian English) is a chemical element with the Symbol (chemistry), symbol Al and atomic number 13. Aluminium has a density lower than thos ...
), which means clays can hold a large volume of water per volume of bulk material, but they do not release water rapidly and therefore have low hydraulic conductivity.

## Sorting and porosity

Well sorted Sorting describes the distribution of grain size of sediments, either in unconsolidated deposits or in sedimentary rocks. This should not be confused with crystallite size, which refers to the individual size of a crystal in a solid. Crystallite i ...
(grains of approximately all one size) materials have higher porosity than similarly sized poorly sorted materials (where smaller particles fill the gaps between larger particles). The graphic illustrates how some smaller grains can effectively fill the pores (where all water flow takes place), drastically reducing porosity and hydraulic conductivity, while only being a small fraction of the total volume of the material. For tables of common porosity values for earth materials, see the "further reading" section in the
Hydrogeology Hydrogeology (''hydro-'' meaning water, and ''-geology'' meaning the study of the Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is lan ...
article.

## Porosity of rocks

Consolidated rocks (e.g.,
sandstone Sandstone is a clastic sedimentary rock of a clast (sand grain), derived from a basalt Basalt (, ) is a fine-grained extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron ('' mafic ' ...

,
shale Shale is a fine-grained, clastic Clastic rocks are composed of fragments, or clasts, of pre-existing minerals In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defi ...

,
granite Granite () is a coarse-grained (phanerite, phaneritic) intrusive rock, intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cool ...

or
limestone Limestone is a common type of carbonate In chemistry, a carbonate is a salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of Salt (chemistry), salts; salt in its na ...

) potentially have more complex "dual" porosities, as compared with alluvial sediment. This can be split into connected and unconnected porosity. Connected porosity is more easily measured through the volume of gas or liquid that can flow into the rock, whereas fluids cannot access unconnected pores. Porosity is the ratio of pore volume to its total volume. Porosity is controlled by: rock type, pore distribution, cementation, diagenetic history and composition. Porosity is not controlled by grain size, as the volume of between-grain space is related only to the method of grain packing. Rocks normally decrease in porosity with age and depth of burial.
Tertiary Tertiary ( ) is a widely used but obsolete term for the Period (geology), geologic period from 66 million to 2.6 million years ago. The period began with the demise of the non-bird, avian dinosaurs in the Cretaceous–Paleogene extincti ...

age
Gulf Coast The Gulf Coast of the United States is the coastline The coast, also known as the coastline or seashore, is defined as the area where land meets the sea or ocean, or as a line that forms the boundary between the land and the ocean T ...

sandstones are in general more porous than
Cambrian The Cambrian Period ( ; sometimes symbolized Ꞓ) was the first geological period A geological period is one of the several subdivisions of geologic time enabling cross-referencing of rocks and geologic events from place to place. These peri ...
age sandstones. There are exceptions to this rule, usually because of the depth of burial and thermal history.

## Porosity of soil

Porosity of surface soil typically decreases as particle size increases. This is due to soil aggregate formation in finer textured surface soils when subject to soil biological processes. Aggregation involves particulate adhesion and higher resistance to compaction. Typical bulk density of sandy soil is between 1.5 and 1.7 g/cm3. This calculates to a porosity between 0.43 and 0.36. Typical bulk density of clay soil is between 1.1 and 1.3 g/cm3. This calculates to a porosity between 0.58 and 0.51. This seems counterintuitive because clay soils are termed ''heavy'', implying ''lower'' porosity. Heavy apparently refers to a gravitational
moisture content Image:soil-phase-diagram.svg, 300px, Soil morphology, Soil composition by Volume and Mass, by phase: air, water, void (pores filled with water or air), soil, and total. Water content or moisture content is the quantity of water contained in a materi ...
effect in combination with terminology that harkens back to the relative force required to pull a
tillage Tillage is the agricultural Agriculture is the practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary Image:Family watching television 1958.jpg, Exercise trends, Increases in sedentary ...
implement through the clayey soil at field moisture content as compared to sand. Porosity of subsurface soil is lower than in surface soil due to compaction by gravity. Porosity of 0.20 is considered normal for unsorted gravel size material at depths below the biomantle. Porosity in finer material below the aggregating influence of
pedogenesis Pedogenesis (from the Greek ''pedo''-, or ''pedon'', meaning 'soil, earth,' and ''genesis'', meaning 'origin, birth') (also termed soil development, soil evolution, soil formation, and soil genesis) is the process of soil formation as regulated ...
can be expected to approximate this value. Soil porosity is complex. Traditional models regard porosity as continuous. This fails to account for anomalous features and produces only approximate results. Furthermore, it cannot help model the influence of
environmental factor An environmental factor, ecological factor or eco factor is any factor, abiotic or biotic, that influences living organisms. Abiotic factors include ambient temperature, amount of sunlight, and pH of the water soil in which an organism lives. Biot ...
s which affect pore geometry. A number of more complex models have been proposed, including
fractal In mathematics Mathematics (from Greek: ) includes the study of such topics as numbers (arithmetic and number theory), formulas and related structures (algebra), shapes and spaces in which they are contained (geometry), and quantities a ...

s,
bubble Bubble or Bubbles may refer to: Physical bubbles * Bubble (physics), a globule of one substance in another, usually gas in a liquid ** Soap bubble, commonly referred to as a "bubble" People * Bubbles, a contestant on ''Real Chance of Love ( ...
theory, theory, Boolean grain process, packed sphere, and numerous other models. The
characterisation of pore space in soilThe pore space of soil contains the liquid A liquid is a nearly incompressible fluid In physics, a fluid is a substance that continually Deformation (mechanics), deforms (flows) under an applied shear stress, or external force. Fluids are ...
is an associated concept.

## Types of geologic porosities

;Primary porosity: The main or original porosity system in a
rock Rock most often refers to: * Rock (geology) A rock is any naturally occurring solid mass or aggregate of minerals or mineraloid matter. It is categorized by the minerals included, its Chemical compound, chemical composition and the way in w ...
or unconfined
alluvial deposit Alluvium (from the Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Roman Re ...
. ;Secondary porosity: A subsequent or separate porosity system in a rock, often enhancing overall porosity of a rock. This can be a result of chemical leaching of minerals or the generation of a fracture system. This can replace the primary porosity or coexist with it (see dual porosity below). ;Fracture porosity: This is porosity associated with a fracture system or faulting. This can create secondary porosity in rocks that otherwise would not be reservoirs for hydrocarbons due to their primary porosity being destroyed (for example due to depth of burial) or of a rock type not normally considered a reservoir (for example igneous intrusions or metasediments). ;Vuggy porosity: This is secondary porosity generated by dissolution of large features (such as
macrofossil Macrofossils, also known as megafossils, are preserved organic remains large enough to be visible without a microscope A microscope (from the grc, μικρός, ''mikrós'', "small" and , ''skopeîn'', "to look" or "see") is a laboratory i ...
s) in
carbonate rock 250px, Carbonate ooids on the surface of a limestone; Carmel Formation (Middle Jurassic) of southern Utah, USA. Largest is 1.0 mm in diameter. Carbonate rocks are a class of sedimentary rocks composed primarily of carbonate minerals. The two major ...
s leaving large holes,
vug A vug, vugh, or vugg (pronounced ) is a small to medium-sized cavity inside rock Rock most often refers to: * Rock (geology) A rock is any naturally occurring solid mass or aggregate of minerals or mineraloid matter. It is categorized by ...
s, or even
cave A cave or cavern is a natural void in the Earth#Surface, ground, specifically a space large enough for a human to enter. Caves often form by the weathering of rock and often extend deep underground. The word ''cave'' can also refer to much small ...

s. ;
Effective porosity Effective porosity is most commonly considered to represent the porosityPorosity or void fraction is a measure of the Void (composites), void (i.e. "empty") spaces in a material, and is a volume fraction, fraction of the volume of voids over the to ...
(also called ''open porosity''): Refers to the fraction of the total volume in which
fluid flow In physics and engineering, fluid dynamics is a subdiscipline of fluid mechanics that describes the flow of fluids—liquids and gases. It has several subdisciplines, including ''aerodynamics'' (the study of air and other gases in motion) and h ...
is effectively taking place and includes
catenary forming multiple Elastic deformation, elastic catenaries. In physics and geometry, a catenary (, ) is the curve that an idealized hanging chain or wire rope, cable assumes under its own weight when supported only at its ends. The catenary cu ...

and dead-end (as these pores cannot be flushed, but they can cause fluid movement by release of pressure like gas expansion) pores and excludes closed pores (or non-connected cavities). This is very important for groundwater and petroleum flow, as well as for solute transport. ;Ineffective porosity (also called ''closed porosity''): Refers to the fraction of the total volume in which fluids or gases are present but in which
fluid flow In physics and engineering, fluid dynamics is a subdiscipline of fluid mechanics that describes the flow of fluids—liquids and gases. It has several subdisciplines, including ''aerodynamics'' (the study of air and other gases in motion) and h ...
can not effectively take place and includes the closed pores. Understanding the morphology of the porosity is thus very important for groundwater and petroleum flow. ;Dual porosity: Refers to the conceptual idea that there are two overlapping reservoirs which interact. In fractured rock aquifers, the rock mass and fractures are often simulated as being two overlapping but distinct bodies. Delayed yield, and leaky aquifer flow solutions are both mathematically similar solutions to that obtained for dual porosity; in all three cases water comes from two mathematically different reservoirs (whether or not they are physically different). ; Macroporosity: In solids (i.e. excluding aggregated materials such as soils), the term 'macroporosity' refers to pores greater than 50  nm in diameter. Flow through macropores is described by bulk diffusion. ; Mesoporosity: In solids (i.e. excluding aggregated materials such as soils), the term 'mesoporosity' refers to pores greater than 2 nm and less than 50 nm in diameter. Flow through mesopores is described by Knudsen diffusion. ;
MicroporosityPorosity or void fraction is a measure of the Void (composites), void (i.e. "empty") spaces in a material, and is a volume fraction, fraction of the volume of voids over the total volume, between 0 and 1, or as a percentage between 0% and 100%. Stric ...
: In solids (i.e. excluding aggregated materials such as soils), the term 'microporosity' refers to pores smaller than 2 nm in diameter. Movement in micropores is activated by diffusion.

# Porosity of fabric or aerodynamic porosity

The ratio of holes to solid that the wind "sees".
Aerodynamic study at Wallops Flight Facility, Wallops Island in 1990. A vortex is created by passage of an aircraft wing, revealed by smoke. Vortices are one of the many phenomena associated with the study of aerodynamics. Aerodynamics, from Greek language, ...
porosity is less than visual porosity, by an amount that depends on the constriction of holes.

# Die casting porosity

Casting porosity is a consequence of one or more of the following: gasification of contaminants at molten-metal temperatures; shrinkage that takes place as molten metal solidifies; and unexpected or uncontrolled changes in temperature or humidity. While porosity is inherent in die casting manufacturing, its presence may lead to component failure where pressure integrity is a critical characteristic. Porosity may take on several forms from interconnected micro-porosity, folds, and inclusions to macro porosity visible on the part surface. The end result of porosity is the creation of a leak path through the walls of a casting that prevents the part from holding pressure. Porosity may also lead to out-gassing during the painting process, leaching of plating acids and tool chatter in machining pressed metal components.

# Measuring porosity

Several methods can be employed to measure porosity: * Direct methods (determining the bulk volume of the porous sample, and then determining the volume of the skeletal material with no pores (pore volume = total volume − material volume). * Optical methods (e.g., determining the area of the material versus the area of the pores visible under the microscope). The "areal" and "volumetric" porosities are equal for porous media with random structure. * Computed tomography method (using
industrial CT scanning Industrial computed tomography (CT) scanning is any computer-aided tomographic process, usually X-ray computed tomography, that uses irradiation Irradiation is the process by which an object is exposed to radiation upThe international sym ...
to create a 3D rendering of external and internal geometry, including voids. Then implementing a defect analysis utilizing computer software) *
Imbibition Imbibition is a special type of diffusion that takes place when water is absorbed by solids-Colloid, colloids causing an increase in volume. Examples include the absorption of water by seeds and dry wood. If there is no pressure due to imbibition, ...
methods, i.e., immersion of the porous sample, under vacuum, in a fluid that preferentially wets the pores. ** Water saturation method (pore volume = total volume of water − volume of water left after soaking). * Water evaporation method (pore volume = (weight of saturated sample − weight of dried sample)/density of water) * Mercury intrusion
porosimetry Porosimetry is an Measurement, analytical technique used to determine various quantifiable aspects of a material's Porosity, porous structure, such as pore diameter, total pore volume, surface area, and Bulk density, bulk and absolute density, densi ...
(several non-mercury intrusion techniques have been developed due to toxicological concerns, and the fact that mercury tends to form amalgams with several metals and alloys). * Gas expansion method.F.A.L. Dullien, "Porous Media. Fluid Transport and Pore Structure",
Academic Press Academic Press is an academic An academy (Attic Greek: Ἀκαδήμεια; Koine Greek Ἀκαδημία) is an institution of secondary education, secondary or tertiary education, tertiary higher education, higher learning, research, or honor ...
, 1992.
A sample of known bulk volume is enclosed in a container of known volume. It is connected to another container with a known volume which is evacuated (i.e., near vacuum pressure). When a valve connecting the two containers is opened, gas passes from the first container to the second until a uniform pressure distribution is attained. Using
ideal gas An ideal gas is a theoretical gas Gas is one of the four fundamental states of matter In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion ...
law, the volume of the pores is calculated as :$V_V = V_T-V_a-V_b$, where :VV is the effective volume of the pores, :VT is the bulk volume of the sample, :Va is the volume of the container containing the sample, :Vb is the volume of the evacuated container, :P1 is the initial pressure in the initial pressure in volume Va and VV, and :P2 is final pressure present in the entire system. :The porosity follows straightforwardly by its proper definition :$\phi = \frac$. :Note that this method assumes that gas communicates between the pores and the surrounding volume. In practice, this means that the pores must not be closed cavities. * Thermoporosimetry and cryoporometry. A small crystal of a liquid melts at a lower temperature than the bulk liquid, as given by the Gibbs-Thomson equation. Thus if a liquid is imbibed into a porous material, and frozen, the melting temperature will provide information on the pore-size distribution. The detection of the melting can be done by sensing the transient heat flows during phase-changes using
differential scanning calorimetry Differential scanning calorimetry (DSC) is a thermoanalytical technique in which the difference in the amount of heat In thermodynamics, heat is energy in transfer to or from a thermodynamic system, by mechanisms other than Work (thermodynam ...

– (DSC thermoporometry), measuring the quantity of mobile liquid using
nuclear magnetic resonance Nuclear magnetic resonance (NMR) is a physical phenomenon A phenomenon (; plural phenomena) is an observable In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ...
– (NMR cryoporometry) or measuring the amplitude of
neutron scattering Neutron scattering, the irregular dispersal of free neutrons by matter, can refer to either the naturally occurring physical process itself or to the man-made experimental techniques that use the natural process for investigating materials. The ...
from the imbibed crystalline or liquid phases – (ND cryoporometry).

*
Void ratio The void ratio of a mixture is the ratio of the volume of voids to volume of solids. It is a dimensionless quantity In dimensional analysis, a dimensionless quantity is a quantity to which no physical dimension is assigned, also known as a bare, ...
*
Petroleum geology Petroleum geology is the study of origin, occurrence, movement, accumulation, and exploration of hydrocarbon fuels. It refers to the specific set of geological disciplines that are applied to the search for hydrocarbons In organic chemistry Org ...
* Poromechanics *
Bulk densityBulk density, also called apparent density or volumetric density, is a property of powders, granules, and other "divided" solid Solid is one of the four fundamental states of matter (the others being liquid, gas and plasma). The molecu ...
*
Particle density (packed density) {{refimprove, date=September 2016 The particle density of a particulate solid or powder A powder is a dry, bulk solid Solid is one of the four fundamental states of matter (the others being liquid, gas and plasma). The molecules in ...
*
Packing densityA packing density or packing fraction of a packing in some space is the fraction of the space filled by the figures making up the packing. In packing problems, the objective is usually to obtain a packing of the greatest possible density. In comp ...
*
Void (composites) A void is a pore that remains unfilled with polymer and fibers in a composite material A composite material (also called a composition material or shortened to composite, which is the common name) is a material Material is a substance Substan ...
*
Coherent diffraction imaging Coherent diffractive imaging (CDI) is a "lensless" technique for 2D or 3D reconstruction of the image of nanoscale structures such as nanotubes, nanocrystals, porous nanocrystalline layers, defects, potentially proteins, and more. In CDI, a highly ...

* * * * * * *