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Hydrothermal alteration
Hydrothermal alteration, also called wallrock alteration, is the change in a rock's minerals and chemistry from reaction with hot fluid, ranging from isochemical change to metasomatism, important in ore formation.
Hydrothermal carbonization
Hydrothermal carbonization (HTC) is a thermochemical conversion method that heats wet biomass in water under pressure at 180–250 °C, producing hydrochar, a carbon-rich solid used as fuel and functional carbon material.
Hydrothermal circulation
Hydrothermal circulation: seawater moving through oceanic crust, driven by thermal gradients, exchanging heat and chemicals; accounts for 20–25% of Earth's heat loss and sustains chemosynthetic vent ecosystems discovered in 1977.
Hydrothermal deposition
Hydrothermal deposition is a materials synthesis method that grows films, coatings, and crystal layers on substrates from aqueous solutions sealed in a heated autoclave, where elevated temperature and pressure drive dissolution and recrystallization.
Hydrothermal liquefaction
Hydrothermal liquefaction (HTL) is a thermochemical conversion method that heats wet biomass in hot, pressurized water at 250–374 °C, decomposing it into liquid biocrude, gases, and solids.
Hydrothermal synthesis
Hydrothermal synthesis, also called hydrothermal reaction, makes inorganic materials by reacting in water in a sealed pressure vessel above 100 °C, producing zeolites, ceramics, and nanoparticles.
Hydrothermal treatment
Hydrothermal treatment is a family of waste-destruction processes that uses hot, pressurized water to break down persistent organic pollutants such as PFAS into inorganic end products.
Hydrothermal vent
A hydrothermal vent, also known as a deep-sea vent, is a seafloor opening where seawater heated by magma reemerges as mineral-rich fluid, discovered near the Galápagos Islands in 1977.
Hydrotrope
A hydrotrope is a small amphiphilic molecule added to water in large amounts to boost the solubility of poorly soluble organic compounds without forming micelles.
Hydroxamic acid
A hydroxamic acid, or hydroxamate, is an N-hydroxy amide that strongly chelates metal ions, making it a major pharmacophore in medicinal chemistry and an iron-binding group of bacterial siderophores.
Hydroxide
Hydroxide, also called the hydroxide anion or OH⁻ ion, is the diatomic anion that is the conjugate base of water; its compounds include sodium hydroxide, hydroxide minerals, and layered double hydroxides.
Hydroxide anomaly
The hydroxide anomaly is the anomalously high mobility of the hydroxide ion in water, explained by structural diffusion, though it still moves slower than hydronium.
Hydroxy group
The hydroxy group, also called the OH or alcohol group, is the –OH functional group made of oxygen bonded to hydrogen; compounds with it on a saturated carbon are alcohols.
Hydroxyacetone
Hydroxyacetone, also called acetol, is the simplest hydroxy ketone, a colorless liquid that forms in the atmosphere from isoprene oxidation, occurs in human metabolism, and appears in e-cigarette aerosols.
Hydroxyapatite
Hydroxyapatite, also known as calcium hydroxyapatite or hydroxylapatite, is a calcium phosphate mineral with formula Ca10(PO4)6(OH)2 that forms most of human bone and tooth enamel.
Hydroxycitric acid
Hydroxycitric acid (HCA), or hydroxycitrate, is a tricarboxylic acid and the principal acid of Garcinia cambogia fruit rinds, used in weight-loss supplements with at best a small, questionable effect.
Hydroxyl number
The hydroxyl number, also called hydroxyl value or OH value, gives the hydroxyl content of a substance in mg KOH per gram and is the key polyol specification.
Hydroxyl radical
The hydroxyl radical, also known as the OH radical, is a highly reactive diatomic molecule, HO, best known as the atmosphere's primary cleansing oxidant of methane, carbon monoxide, and pollutants.
Hydroxylamine
Hydroxylamine (NH2OH, also called oxammonium) is an inorganic compound of ammonia bearing a hydroxy group, a white solid that is thermally unstable and used mainly to make caprolactam for nylon.
Hydroxylysine
Hydroxylysine (5-hydroxylysine) is an amino acid formed by hydroxylation of lysine residues in proteins, best known as a component of collagen, the structural protein of connective tissue.
Hydroxymethylfurfural production
Hydroxymethylfurfural production is the manufacture of 5-hydroxymethylfurfural (HMF), a bio-based platform chemical made by acid-catalyzed dehydration of sugars such as fructose; no large-scale commercial plant was running as of 2020.
Hydroxynorketamine
Hydroxynorketamine (HNK) is a hydroxylated metabolite of ketamine, formed in the body after ketamine administration. Twelve stereoisomers exist; the (2R,6R) form is studied as a rapid-acting antidepressant without dissociation.
Hydroxyproline
Hydroxyproline is a non-proteinogenic amino acid made by post-translational hydroxylation of proline by prolyl hydroxylase. It stabilizes collagen, the main protein of connective tissue, and occurs in plant cell walls.
Hydroxypropyl cellulose
Hydroxypropyl cellulose (HPC, CAS 9004-64-2), a non-ionic cellulose ether soluble in water below its 45°C LCST and in organic solvents; used as a food thickener, pharmaceutical excipient, and the discontinued Lacrisert dry-eye insert.
Hydroxytyrosol
Hydroxytyrosol is a phenolic compound found principally in olives and olive oil, formed from oleuropein during ripening and valued for antioxidant, anti-inflammatory, and antibacterial properties in laboratory studies.
Hydrus
Hydrus (abbreviation Hyi) is a small far-southern constellation, the Male Water Snake, distinct from Hydra, introduced by Johann Bayer in 1603 with brightest star Beta Hydri.
Hye Kyung C. Timken
Hye Kyung C. Timken is an American physical chemist who spent a 38-year career at Chevron developing refining catalysts, including the ISOALKY ionic liquid alkylation technology.
Hye Ryung Byon
Hye Ryung Byon (변혜령) is a South Korean chemist and professor at KAIST who works on lithium batteries, redox flow batteries, and electrocatalysts, after leading a research unit at RIKEN.
Hygrometer
A hygrometer, also called a humidity meter, is an instrument that measures the water vapor content of air, typically as relative humidity or dew point.
Hygroscopy
Hygroscopy is the tendency of a substance to absorb water from the atmosphere, through adsorption, absorption, or capillary condensation; a substance that does so is hygroscopic.