All articles starting with H
20,046 articles
Hydrosilylation
Hydrosilylation is the addition of a silicon–hydrogen bond across an alkene or alkyne to form an organosilane, first reported in 1947 and now central to the multibillion-dollar silicones industry.
Hydrosphere
The hydrosphere is all of Earth's water in liquid and solid form at and beneath the surface, including oceans, rivers, lakes, groundwater, glaciers, and ice sheets.
Hydrostatic bearing
A hydrostatic bearing, also called an externally pressurized bearing, is a fluid-film bearing in which a pump supplies the pressure that keeps the surfaces separated, even at zero speed.
Hydrostatic drive
A hydrostatic drive, or hydrostatic transmission, converts engine rotation into hydraulic pressure at a pump and back into rotation at a motor, giving stepless speed control without gears.
Hydrostatic equilibrium
Hydrostatic equilibrium, also called hydrostatic balance, is the state of a fluid at rest where internal pressure balances gravity. It applies to oceans, atmospheres, and stars.
Hydrostatic mass bias
Hydrostatic mass bias is the systematic underestimate of galaxy-cluster masses inferred from X-ray observations assuming hydrostatic equilibrium, an assumption violated by non-thermal pressure from turbulent gas motions.
Hydrostatic pressure
Hydrostatic pressure is the pressure in a fluid at rest, produced by the weight of fluid above, increasing linearly with depth according to p = p₀ + ρgh.
Hydrostatic shock
Hydrostatic shock, also called hydraulic shock, is the contested hypothesis that a bullet's ballistic pressure wave injures tissue remote from the wound track; critics attribute remote damage to temporary cavitation instead.
Hydrostatic stress
Hydrostatic stress is the average of the three normal stress components at a point in a material, equal to the pressure a fluid at rest experiences, and it drives volume change.
Hydrostatic test
A hydrostatic test, also called hydrotesting, is a pressure test in which a vessel, pipe, or component is filled with water and pressurized above its operating pressure to check for leaks.
Hydrostatic test (pipelines)
A hydrostatic test of a pipeline fills a segment with water and pressurizes it above its maximum operating pressure to prove the pipe and welds will not leak or rupture.
Hydrostatics
Hydrostatics is the branch of fluid mechanics that studies fluids at rest, explaining how pressure increases with depth and giving rise to Pascal's principle and Archimedes' principle of buoyancy.
Hydrotalcite
Hydrotalcite is a carbonate-bearing magnesium–aluminum hydroxide mineral, first described in 1842 from the Urals, and the archetype of the layered double hydroxides, or anionic clays.
Hydrotalcite anhydrous
Hydrotalcite anhydrous is the water-free form of the magnesium-aluminum hydroxycarbonate mineral Mg6Al2(OH)16CO3·4H2O, a layered double hydroxide used as the antacid Talcid for heartburn, gastritis, and acid-peptic disease.
Hydrotalcite catalyst
Hydrotalcite catalyst is a layered magnesium–aluminum hydroxide (layered double hydroxide) used as a reusable heterogeneous solid base catalyst, above all for transesterifying vegetable oils and waste fats into biodiesel.
Hydrotherapy
Hydrotherapy (aquatic physiotherapy, balneotherapy): therapeutic external use of water, from cold immersion (11–15 °C) and warm baths (38–40 °C) to pool exercise. Small trial benefits for osteoarthritis and fibromyalgia pain; not FDA-regulated; no cure claims proven.
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 gasification
Hydrothermal gasification is a thermochemical conversion method that reacts wet biomass or organic waste in hot, pressurized water to produce gas rich in hydrogen or methane, with pilot plants only.
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 liquefaction of plastics
Hydrothermal liquefaction of plastics (plastic HTL) is a thermochemical recycling process that decomposes waste polymers in hot, pressurized water into an oil refined into fuels and chemicals.
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.
Hydrotreated vegetable oil
Hydrotreated vegetable oil (HVO), also known as renewable diesel or green diesel, is a liquid biofuel made by hydrogenating vegetable oils and waste fats, usable in diesel engines without modification.
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.
Hydroureter
Hydroureter is the abnormal enlargement of the ureter, the tube carrying urine from kidney to bladder, most often caused by a blockage; it occurs at all ages.
Hydrovolt
Hydrovolt is a Norwegian battery recycling company founded in 2020 as a joint venture of Hydro and Northvolt, operating Europe's largest EV battery recycling plant in Fredrikstad.