Physical world and mathematics

Metalation

Metalation is a chemical reaction that replaces a hydrogen atom on carbon with a metal, most often lithium, magnesium, or zinc, giving organometallic reagents used in synthesis.

Oct 21, 2026

Metaldehyde

Metaldehyde is a cyclic tetramer of acetaldehyde, a white crystalline solid with the formula C₈H₁₆O₄ used as the dominant molluscicide against slugs and snails, and formerly as solid camp-stove fuel.

A metalens is a flat optical lens that focuses light using a thin metasurface of subwavelength nanostructures rather than curved glass, enabling miniature, lightweight optics for cameras, sensors, and displays.

Metallaphotoredox catalysis

Metallaphotoredox catalysis is a dual-catalyst synthetic method combining a metal cross-coupling catalyst, usually nickel, with a visible-light photocatalyst, first reported in 2014 to couple sp3 fragments.

Metallaphotoredox decarboxylative coupling

Metallaphotoredox decarboxylative coupling is a dual-catalytic organic reaction, first reported in 2014 by the Doyle and MacMillan groups, combining a photocatalyst and nickel to couple carboxylic acids with aryl halides.

Metallaphotoredox decarboxylative cross-coupling

Metallaphotoredox decarboxylative cross-coupling is a dual-catalytic organic reaction in which a photoredox catalyst turns carboxylic acids into alkyl radicals that a nickel catalyst couples with organic halides.

Metallic bonding

Metallic bonding, first modeled by Paul Drude's early-1900s electron sea theory, is the electrostatic attraction between positive metal centers and delocalized valence electrons, explaining metals' conductivity and luster.

Metallic hydrogen

Metallic hydrogen, also called hydrogen metal, is a high-pressure phase of hydrogen that conducts electricity like a metal and is believed to fill Jupiter and Saturn.

Metallic microlattice

A metallic microlattice is an ultralight cellular material made of a periodic three-dimensional network of hollow metal struts, first reported by HRL Laboratories in Malibu, California, in 2011.

Metallic oxygen

Metallic oxygen is oxygen that conducts electricity like a metal, reached under extreme pressure of about 96 GPa in the solid or 1.2 Mbar as a hot dense fluid.

Metallic water

Metallic water is water that has acquired the electrical properties of a metal, first prepared under terrestrial conditions in 2021 as a transient gold-colored layer doped with electrons.

Metallicity

Metallicity, also called stellar metallicity, is the fraction of a star's or galaxy's baryonic mass made of elements heavier than helium, including non-metallic ones like carbon and oxygen.

Metallocene catalyst

A metallocene catalyst is an organometallic catalyst for olefin polymerization, typically a Group 4 metallocene activated by methylaluminoxane, producing polyethylene and polypropylene with narrow molecular weight distributions.

Metallography

Metallography is a materials characterization technique that reveals the microstructure of metals and alloys by sectioning, polishing, etching, and imaging with optical or electron microscopy.

Metalloid

A metalloid is a chemical element whose properties lie between those of metals and nonmetals; the most commonly cited members are boron, silicon, germanium, arsenic, antimony, and tellurium.

Metalloradical catalysis

Metalloradical catalysis is a catalytic method in organic chemistry in which open-shell transition-metal complexes, chiefly cobalt(II) porphyrins, generate and control radical intermediates to form chemical bonds selectively under neutral conditions.

Metallosupramolecular self-healing polymers

Metallosupramolecular self-healing polymers are polymer networks whose chains are joined by reversible metal-ligand coordination bonds rather than permanent covalent cross-links, so after a cut or scratch the network re-forms and recovers its mechanical function.

Metallurgical Laboratory

The Metallurgical Laboratory, or Met Lab, was a secret Manhattan Project laboratory at the University of Chicago, where the first nuclear chain reaction was achieved in 1942.

Metamagnetic transition

A metamagnetic transition is a field-driven first-order magnetic phase transition in which a material jumps discontinuously from an antiferromagnetic or paramagnetic state to a strongly magnetized state.

Metamaterial absorber

A metamaterial absorber is an artificial electromagnetic structure that absorbs waves at near unity while much thinner than the wavelength, introduced by Landy in 2008.

Metamaterial cloaking

Metamaterial cloaking is the use of artificially structured metamaterials to render objects undetectable to waves by steering fields around them, first demonstrated with a microwave cloak in 2006 and since extended to sound and heat.

Metamaterial fiber

A metamaterial fiber is an optical fiber with engineered subwavelength inclusions that give it optical properties not found in natural materials, such as artificial anisotropy.

Metamorphic core complex

A metamorphic core complex is a domal geological structure where deep metamorphic and granitic rocks are brought to the surface by extension on a low-angle detachment fault.

Metamorphic facies

A metamorphic facies is a set of mineral assemblages that characterizes a range of pressure and temperature conditions during metamorphism, a concept introduced by Finnish geologist Pentti Eskola in 1915.

Metamorphic grade

Metamorphic grade is the relative intensity of metamorphism recorded in a rock, used as a qualitative proxy for metamorphic temperature; index minerals such as garnet and staurolite mark increasing grades.

Metamorphic rock

Metamorphic rock, or metamorphosed rock, forms when heat, pressure, or hot fluids transform pre-existing rock in the solid state deep in the crust, producing rocks such as marble, slate, schist, and gneiss.

Metamorphism

Metamorphism is the geological process that changes pre-existing rocks in mineralogy and texture through heat, pressure, and fluids, without melting them, deep in the Earth's crust.

Metanephrine

Metanephrine, also called metadrenaline, is the O-methylated metabolite of epinephrine formed by COMT with no activity of its own; elevated plasma levels are a leading indicator of pheochromocytoma and paraganglioma.

Metaphilosophy

Metaphilosophy, also known as the philosophy of philosophy, is the study of philosophy itself: its methods, aims, scope, and foundations, including debates over intuition and experimental philosophy.