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Topic Review
Osmium-167
Osmium (76Os) has seven naturally occurring isotopes, five of which are stable: 187Os, 188Os, 189Os, 190Os, and (most abundant) 192Os. The other natural isotopes, 184Os, and 186Os, have extremely long half-life (1.12×1013 years and 2×1015 years, respectively) and for practical purposes can be considered to be stable as well. 187Os is the daughter of 187Re (half-life 4.56×1010 years) and is most often measured in an 187Os/188Os ratio. This ratio, as well as the 187Re/188Os ratio, have been used extensively in dating terrestrial as well as meteoric rocks. It has also been used to measure the intensity of continental weathering over geologic time and to fix minimum ages for stabilization of the mantle roots of continental cratons. However, the most notable application of Os in dating has been in conjunction with iridium, to analyze the layer of shocked quartz along the Cretaceous–Paleogene boundary that marks the extinction of the dinosaurs 66 million years ago. There are also 30 artificial radioisotopes, the longest-lived of which is 194Os with a half-life of six years; all others have half-lives under 94 days. There are also nine known nuclear isomers, the longest-lived of which is 191mOs with a half-life of 13.10 hours. All isotopes and nuclear isomers of osmium are either radioactive or observationally stable, meaning that they are predicted to be radioactive but no actual decay has been observed.
  • 598
  • 15 Nov 2022
Topic Review
Osmium-189
Osmium (76Os) has seven naturally occurring isotopes, five of which are stable: 187Os, 188Os, 189Os, 190Os, and (most abundant) 192Os. The other natural isotopes, 184Os, and 186Os, have extremely long half-life (1.12×1013 years and 2×1015 years, respectively) and for practical purposes can be considered to be stable as well. 187Os is the daughter of 187Re (half-life 4.56×1010 years) and is most often measured in an 187Os/188Os ratio. This ratio, as well as the 187Re/188Os ratio, have been used extensively in dating terrestrial as well as meteoric rocks. It has also been used to measure the intensity of continental weathering over geologic time and to fix minimum ages for stabilization of the mantle roots of continental cratons. However, the most notable application of Os in dating has been in conjunction with iridium, to analyze the layer of shocked quartz along the Cretaceous–Paleogene boundary that marks the extinction of the dinosaurs 66 million years ago. There are also 30 artificial radioisotopes, the longest-lived of which is 194Os with a half-life of six years; all others have half-lives under 94 days. There are also nine known nuclear isomers, the longest-lived of which is 191mOs with a half-life of 13.10 hours. All isotopes and nuclear isomers of osmium are either radioactive or observationally stable, meaning that they are predicted to be radioactive but no actual decay has been observed.
  • 588
  • 14 Oct 2022
Topic Review
Osmium-182
Osmium (76Os) has seven naturally occurring isotopes, five of which are stable: 187Os, 188Os, 189Os, 190Os, and (most abundant) 192Os. The other natural isotopes, 184Os, and 186Os, have extremely long half-life (1.12×1013 years and 2×1015 years, respectively) and for practical purposes can be considered to be stable as well. 187Os is the daughter of 187Re (half-life 4.56×1010 years) and is most often measured in an 187Os/188Os ratio. This ratio, as well as the 187Re/188Os ratio, have been used extensively in dating terrestrial as well as meteoric rocks. It has also been used to measure the intensity of continental weathering over geologic time and to fix minimum ages for stabilization of the mantle roots of continental cratons. However, the most notable application of Os in dating has been in conjunction with iridium, to analyze the layer of shocked quartz along the Cretaceous–Paleogene boundary that marks the extinction of the dinosaurs 66 million years ago. There are also 30 artificial radioisotopes, the longest-lived of which is 194Os with a half-life of six years; all others have half-lives under 94 days. There are also nine known nuclear isomers, the longest-lived of which is 191mOs with a half-life of 13.10 hours. All isotopes and nuclear isomers of osmium are either radioactive or observationally stable, meaning that they are predicted to be radioactive but no actual decay has been observed.
  • 567
  • 21 Nov 2022
Topic Review
Osmium-168
Osmium (76Os) has seven naturally occurring isotopes, five of which are stable: 187Os, 188Os, 189Os, 190Os, and (most abundant) 192Os. The other natural isotopes, 184Os, and 186Os, have extremely long half-life (1.12×1013 years and 2×1015 years, respectively) and for practical purposes can be considered to be stable as well. 187Os is the daughter of 187Re (half-life 4.56×1010 years) and is most often measured in an 187Os/188Os ratio. This ratio, as well as the 187Re/188Os ratio, have been used extensively in dating terrestrial as well as meteoric rocks. It has also been used to measure the intensity of continental weathering over geologic time and to fix minimum ages for stabilization of the mantle roots of continental cratons. However, the most notable application of Os in dating has been in conjunction with iridium, to analyze the layer of shocked quartz along the Cretaceous–Paleogene boundary that marks the extinction of the dinosaurs 66 million years ago. There are also 30 artificial radioisotopes, the longest-lived of which is 194Os with a half-life of six years; all others have half-lives under 94 days. There are also nine known nuclear isomers, the longest-lived of which is 191mOs with a half-life of 13.10 hours. All isotopes and nuclear isomers of osmium are either radioactive or observationally stable, meaning that they are predicted to be radioactive but no actual decay has been observed.
  • 551
  • 01 Nov 2022
Topic Review
Osmium-183
Osmium (76Os) has seven naturally occurring isotopes, five of which are stable: 187Os, 188Os, 189Os, 190Os, and (most abundant) 192Os. The other natural isotopes, 184Os, and 186Os, have extremely long half-life (1.12×1013 years and 2×1015 years, respectively) and for practical purposes can be considered to be stable as well. 187Os is the daughter of 187Re (half-life 4.56×1010 years) and is most often measured in an 187Os/188Os ratio. This ratio, as well as the 187Re/188Os ratio, have been used extensively in dating terrestrial as well as meteoric rocks. It has also been used to measure the intensity of continental weathering over geologic time and to fix minimum ages for stabilization of the mantle roots of continental cratons. However, the most notable application of Os in dating has been in conjunction with iridium, to analyze the layer of shocked quartz along the Cretaceous–Paleogene boundary that marks the extinction of the dinosaurs 66 million years ago. There are also 30 artificial radioisotopes, the longest-lived of which is 194Os with a half-life of six years; all others have half-lives under 94 days. There are also nine known nuclear isomers, the longest-lived of which is 191mOs with a half-life of 13.10 hours. All isotopes and nuclear isomers of osmium are either radioactive or observationally stable, meaning that they are predicted to be radioactive but no actual decay has been observed.
  • 538
  • 24 Oct 2022
Topic Review
Osmium-165
Osmium (76Os) has seven naturally occurring isotopes, five of which are stable: 187Os, 188Os, 189Os, 190Os, and (most abundant) 192Os. The other natural isotopes, 184Os, and 186Os, have extremely long half-life (1.12×1013 years and 2×1015 years, respectively) and for practical purposes can be considered to be stable as well. 187Os is the daughter of 187Re (half-life 4.56×1010 years) and is most often measured in an 187Os/188Os ratio. This ratio, as well as the 187Re/188Os ratio, have been used extensively in dating terrestrial as well as meteoric rocks. It has also been used to measure the intensity of continental weathering over geologic time and to fix minimum ages for stabilization of the mantle roots of continental cratons. However, the most notable application of Os in dating has been in conjunction with iridium, to analyze the layer of shocked quartz along the Cretaceous–Paleogene boundary that marks the extinction of the dinosaurs 66 million years ago. There are also 30 artificial radioisotopes, the longest-lived of which is 194Os with a half-life of six years; all others have half-lives under 94 days. There are also nine known nuclear isomers, the longest-lived of which is 191mOs with a half-life of 13.10 hours. All isotopes and nuclear isomers of osmium are either radioactive or observationally stable, meaning that they are predicted to be radioactive but no actual decay has been observed.
  • 537
  • 03 Nov 2022
Topic Review
Osmium-176
Osmium (76Os) has seven naturally occurring isotopes, five of which are stable: 187Os, 188Os, 189Os, 190Os, and (most abundant) 192Os. The other natural isotopes, 184Os, and 186Os, have extremely long half-life (1.12×1013 years and 2×1015 years, respectively) and for practical purposes can be considered to be stable as well. 187Os is the daughter of 187Re (half-life 4.56×1010 years) and is most often measured in an 187Os/188Os ratio. This ratio, as well as the 187Re/188Os ratio, have been used extensively in dating terrestrial as well as meteoric rocks. It has also been used to measure the intensity of continental weathering over geologic time and to fix minimum ages for stabilization of the mantle roots of continental cratons. However, the most notable application of Os in dating has been in conjunction with iridium, to analyze the layer of shocked quartz along the Cretaceous–Paleogene boundary that marks the extinction of the dinosaurs 66 million years ago. There are also 30 artificial radioisotopes, the longest-lived of which is 194Os with a half-life of six years; all others have half-lives under 94 days. There are also nine known nuclear isomers, the longest-lived of which is 191mOs with a half-life of 13.10 hours. All isotopes and nuclear isomers of osmium are either radioactive or observationally stable, meaning that they are predicted to be radioactive but no actual decay has been observed.
  • 529
  • 19 Oct 2022
Topic Review
Osmium-170
Osmium (76Os) has seven naturally occurring isotopes, five of which are stable: 187Os, 188Os, 189Os, 190Os, and (most abundant) 192Os. The other natural isotopes, 184Os, and 186Os, have extremely long half-life (1.12×1013 years and 2×1015 years, respectively) and for practical purposes can be considered to be stable as well. 187Os is the daughter of 187Re (half-life 4.56×1010 years) and is most often measured in an 187Os/188Os ratio. This ratio, as well as the 187Re/188Os ratio, have been used extensively in dating terrestrial as well as meteoric rocks. It has also been used to measure the intensity of continental weathering over geologic time and to fix minimum ages for stabilization of the mantle roots of continental cratons. However, the most notable application of Os in dating has been in conjunction with iridium, to analyze the layer of shocked quartz along the Cretaceous–Paleogene boundary that marks the extinction of the dinosaurs 66 million years ago. There are also 30 artificial radioisotopes, the longest-lived of which is 194Os with a half-life of six years; all others have half-lives under 94 days. There are also nine known nuclear isomers, the longest-lived of which is 191mOs with a half-life of 13.10 hours. All isotopes and nuclear isomers of osmium are either radioactive or observationally stable, meaning that they are predicted to be radioactive but no actual decay has been observed.
  • 513
  • 10 Nov 2022
Topic Review
Osmium-195
Osmium (76Os) has seven naturally occurring isotopes, five of which are stable: 187Os, 188Os, 189Os, 190Os, and (most abundant) 192Os. The other natural isotopes, 184Os, and 186Os, have extremely long half-life (1.12×1013 years and 2×1015 years, respectively) and for practical purposes can be considered to be stable as well. 187Os is the daughter of 187Re (half-life 4.56×1010 years) and is most often measured in an 187Os/188Os ratio. This ratio, as well as the 187Re/188Os ratio, have been used extensively in dating terrestrial as well as meteoric rocks. It has also been used to measure the intensity of continental weathering over geologic time and to fix minimum ages for stabilization of the mantle roots of continental cratons. However, the most notable application of Os in dating has been in conjunction with iridium, to analyze the layer of shocked quartz along the Cretaceous–Paleogene boundary that marks the extinction of the dinosaurs 66 million years ago. There are also 30 artificial radioisotopes, the longest-lived of which is 194Os with a half-life of six years; all others have half-lives under 94 days. There are also nine known nuclear isomers, the longest-lived of which is 191mOs with a half-life of 13.10 hours. All isotopes and nuclear isomers of osmium are either radioactive or observationally stable, meaning that they are predicted to be radioactive but no actual decay has been observed.
  • 500
  • 18 Oct 2022
Topic Review
Energy Dispersive X-Ray Spectroscopy
Energy-dispersive X-ray spectroscopy (EDS, also EDX or EDAX) is an analytical microanalysis technique used for the elemental characterization of a sample. When a focused beam of high-energy electrons is directed at a specimen — typically within a scanning electron microscope (SEM) or electron probe microanalyzer (EPMA) — inner-shell ionization of the atoms in the interaction volume produces characteristic X-rays whose photon energies are element-specific [1]. An energy-dispersive spectrometer, usually a cooled silicon drift detector or Si(Li) detector, records the emitted X-rays by energy simultaneously, producing a spectrum in which peak energies identify the elements present and peak areas quantify their concentrations [2]. The technique is conventionally applied to elements heavier than sodium (Z ≥ 11), although modern detectors extend routine light-element detection to beryllium [3]. EDS is distinguished from wavelength-dispersive X-ray spectroscopy (WDS) by its parallel acquisition of the full X-ray energy spectrum, shorter acquisition time, and generally lower energy resolution; quantitative analysis requires correction for atomic number effects, absorption, and secondary fluorescence, as specified in ASTM E1508 [3].
  • 29
  • 17 Sep 2026
Topic Review
Crosslinking Density
Crosslinking density is the number of network junctions per unit volume of a polymer, or equivalently the molar concentration of elastically effective chains [1]. It is obtained from the equilibrium swelling ratio through the Flory-Rehner relation or from the rubbery plateau modulus through rubber-elasticity theory, and both routes assume affine deformation of the network [1]. The value sets the distance between junctions relative to the contour length of the chain, and with it the modulus, the solvent uptake and the resistance to creep [2]. Junctions formed by covalent bonds, by ionic aggregates or by physical entanglements count differently, so the quantity is defined against the junction type it counts [2]. Probe diffusion through the network slows as the density rises, because the mesh size limits transport [3].
  • 6
  • 06 Nov 2026
Topic Review
Epoxy Vitrimer
Epoxy vitrimers are crosslinked epoxy networks whose junctions are dynamic covalent bonds that exchange without dissolving the network [1]. The resin is cured with a hardener carrying the exchangeable linkage, typically an ester, a disulfide or a boronate ester, so the topology rearranges while the crosslink density is preserved [1]. Above the topology freezing transition the exchange rate exceeds the relaxation of the network, and the solid flows as a glass-forming liquid while remaining insoluble [1]. Below that temperature the same network behaves as a conventional thermoset [2]. Because the exchange is associative, the number of bonds stays constant throughout the rearrangement [3].
  • 5
  • 06 Nov 2026
Topic Review
Fire Retardant
A fire retardant is a substance that slows ignition or reduces the rate at which a polymer burns, without necessarily preventing combustion [1]. The action follows four chemical routes: a halogen or phosphorus species interrupts the radical chain of the gas-phase flame, a filler releases water or an inert gas on heating, a char-forming agent promotes a carbonaceous layer at the surface, and a diluent lowers the fuel fraction reaching the flame [1]. The char layer separates the condensed phase from the heat flux and from oxygen, so its continuity governs the residual performance [2]. Additives are described by the loading needed to reach a limiting oxygen index and a vertical burn rating, and by whether they are reactive or merely blended into the host polymer [3]. Bio-based additives act through intumescence or through phosphorus released on decomposition [3].
  • 5
  • 06 Nov 2026
Topic Review
Cellulose Dissolution
Cellulose dissolution is the disruption of the hydrogen-bond network that holds glucan chains in crystalline microfibrils, so that the chains disperse as individual molecules in a liquid medium [1]. Intramolecular bonds stiffen each chain while intermolecular bonds stack neighbouring chains into sheets, and a solvent must break both without derivatising the hydroxyl groups [1]. Effective media pair a hydrogen-bond acceptor with a cation or a base, among them aqueous alkali-urea, N-methylmorpholine-N-oxide, ionic liquids and deep eutectic mixtures [2]. Dissolution is distinct from swelling, in which the network loosens while crystalline order survives, and from derivatisation, which alters the chain chemistry [3]. Recovery of the polymer from solution regenerates the cellulose II polymorph rather than the native form [3].
  • 5
  • 06 Nov 2026
Topic Review
Dialdehyde Cellulose
Dialdehyde cellulose is cellulose whose anhydroglucose units carry two aldehyde groups at C2 and C3, produced by oxidative cleavage of the vicinal diols of the glucopyranose ring [1]. Cleavage opens the ring, so the product is a chain of 2,3-dialdehydic residues whose aldehyde content is expressed per anhydroglucose unit [1]. Because the aldehydes hydrate and form hemiacetals with neighbouring hydroxyls, the polymer is partly crosslinked and its crystallinity falls as oxidation proceeds [2]. The dialdehyde groups condense with amines and hydrazides to give imines and hydrazones, and that reactivity separates the material from carboxymethyl or hydroxyethyl cellulose [3]. Over-oxidation shortens the chain and introduces carboxyl groups [3].
  • 3
  • 06 Nov 2026
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