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19F
Published in Guillaume Madelin, X-Nuclei Magnetic Resonance Imaging, 2022
Until World War II, there was no real commercial production of elemental fluorine, but as uranium enrichment is the largest application of fluorine gas, industrial production of fluorine began during the Manhattan Project as a step in the making of atomic bombs. Fluorine was used to produce uranium hexafluoride (UF6), which in turn was used to separate two uranium isotopes, 235U and 238U, from each other, and is still used nowadays to produce enriched uranium for nuclear power applications. Other commercial applications use fluorine compounds such as fluorite instead of pure fluorine (due to its difficult production), with about half of it used in steelmaking. Its very active chemistry makes fluorine useful in many products, such as polymers, pesticides, antibiotics and toothpastes (fluoride ion F− inhibits dental cavities). Compounds containing a carbon-fluorine (C–F) bond, called fluorocarbons or perfluorocarbons (PFCs), often have very high chemical and thermal stability and can be used as refrigerants, electrical insulation and cookware (such as Teflon). However, PFCs, as well as sulfur hexafluoride (SF6), are greenhouse gases with atmospheric lifetimes of more than 1000 years and global-warming potential. Though their concentrations are very small compared to the main greenhouse gas carbon dioxide, this very long lifespan in the atmosphere makes them important actors in the global greenhouse effect.
Atomic and Molecular Origins of Color
Published in Mary Anne White, Physical Properties of Materials, 2018
As an example, consider the sometimes violet color of fluorite, CaF2. This color arises when some F− ions are missing from their usual lattice sites, giving rise to an extra electron in the lattice. This can happen in one of several ways: the crystal might have been grown in the presence of excess Ca; the crystal might have been exposed to high-energy radiation that displaced an ion from the usual lattice site; or the crystal might have been in an electric field that was strong enough to remove F− electrochemically. In any case, electrons exist in the places where F− would be in a perfect lattice. These electrons give rise to the color, as the electrons absorb yellow light, leaving behind a violet color.
Rock Forming Minerals
Published in Aurèle Parriaux, Geology, 2018
Fluorite forms beautiful cubic or octahedral crystals with perfect cubic cleavage (Fig. 5.30). It has a value of 4 on the hardness scale, and a density of 3.2 · 103 kg/m3. Fluorite is transparent to translucent with vitreous luster. Its most common color is purple, but it can also be yellow, green or blue. It often has double coloring: green by reflection and blue by transparence. It occurs in hydrothermal veins or more rarely in limestones (important deposits in the USA). It is used for the manufacture of hydrofluoric acid and as a flux in metallurgy.
Genesis of geogenic contaminated groundwater: As, F and I
Published in Critical Reviews in Environmental Science and Technology, 2021
Yanxin Wang, Junxia Li, Teng Ma, Xianjun Xie, Yamin Deng, Yiqun Gan
The geogenic hazardous elements can be leached from rocks/sediments and enriched in groundwater in the recharge areas and/or fault zones. This genetic type can be applied to explain the occurrence of high F groundwater in mountain areas of crystalline rocks, as observed in India, Pakistan, Sri Lanka, and several countries from Africa such as Cameroon, Ghana, and Ethiopia (Table 2). The bedrock and weathered rocks/soils in the mountain area contain substantial quantities of F-bearing minerals, such as mica, apatite and amphibole, which substitutes for hydroxyl in the crystal lattices. Ramamohana Rao et al. (1993) reported that F concentration ranges in granitic rocks from Nalgonda district were from 325 to 3200 mg/kg with a mean of 1440 mg/kg. Fluorite (CaF2) is the principal fluoride mineral, mostly present as an accessory mineral in granitic rocks. Significant deformation can produce a network of intersecting fractures in the weathered zone and provide voids for groundwater permeation. Due to fluorine-containing bedrock weathering and water-rock interactions, F ions can be leached out into groundwater. Dissolution of such minerals can constitute a major source of F in groundwater (Abu Rukah & Alsokhny, 2004; Edmunds & Smedley, 2013; Shaji et al., 2007; Subba Rao & John Devadas, 2003). Relatively high F concentrations have been found even in deeply circulating groundwater along deep faults (Kim & Jeong, 2005; Kundu et al., 2001).
Effects of CeO2 geometry on corrosion resistance of epoxy coatings
Published in Surface Engineering, 2020
Wenbo Zhang, Huaiyuan Wang, Chongjiang Lv, Xixi Chen, Zhiqiang Zhao, Yongquan Qu, Yanji Zhu
To further probe into the crystal structures of the nanofillers, the XRD patterns of CeO2 nanospheres, CeO2 nanorods, FCNS, FCNR and EP composite coatings (EP, PVDF, FCNS/PVDF/EP and FCNR/PVDF/EP) are typically depicted in Fig. S3. CeO2 nanospheres and CeO2 nanorods both exhibit a strong sharp crystalline peak of the (111) plane at 2θ =28.4° and the peak of CeO2 nanospheres is higher, suggesting CeO2 nanospheres are more crystallised than CeO2 nanorods [27]. Moreover, the characteristic planes of (200), (220), (311), (222), (400), (331), (420) and (422) are attributed to the cubic fluorite structure according to CDD (PDF2.DAT) (CeO2/Cerianite, syn, DB card number 00-043-1002). The XRD patterns of FCNS and FCNR both remain almost the same after functionalisation, indicating the chemical modification did not change the crystal structure. For pure EP, a broad peak at 2θ of 21° resulted from the scattering of the cross-linking network of EP matrix, which indicates the amorphism of EP. Moreover, FCNS/PVDF/EP and FCNR/PVDF/EP show all characteristic peaks of PVDF and CeO2, which may be attributed to the homogenous dispersion of nanofillers in the entire EP matrix [28].
Fluorite and translucent beads in Iberian Late Prehistory
Published in Materials and Manufacturing Processes, 2020
J. A. Garrido-Cordero, C. P. Odriozola, A. C. Sousa, V. S. Gonçalves
Fluorite occurs worldwide, it is relatively frequent in western Europe and the Iberian Peninsula. From a mineralogical standpoint, fluorite [CaF2] has a cubic face-centered lattice and may be regarded as a simple cubic lattice of F− ions with a Ca2+ ion at the center of every other cube.[10] In nature, it most commonly forms granular to massive aggregates or cubic crystals. Natural fluorites exhibit every color of the rainbow in various shades: from colorless to white, yellow to orange, pink to purple–red, purple to violet, blue, pale green, brown or violet-black.[11–13]