“Beryllium fluoride”的意思、由来-开放百科全书

Beryllium fluoride is the inorganic compound with the formula BeF₂. This white solid is the principal precursor for the manufacture of beryllium metal. Its structure resembles that of quartz, but BeF₂ is highly soluble in water.

Properties

Beryllium fluoride has unique optical properties. In the form of fluoroberyllate glass it has the lowest refractive index for a solid at room temperature of 1.275. It dispersive power is the lowest for a solid at 0.0093, and the non linear coefficient is also the lowest at 2 × 10⁻¹⁴.

Structure and bonding

The structure of solid BeF₂ resembles that of cristobalite. Be²⁺ centers are four coordinate and tetrahedral and the fluoride centers are two-coordinate.^[6] The Be-F bond lengths are about 1.54 Å.^[7] Analogous to SiO₂,BeF₂ can also adopt a number of related structures. An analogy also exists between BeF₂ and AlF₃: both adopt extended structures at mild temperature.

Gaseous and liquid BeF₂

Gaseous beryllium fluoride adopts a linear structure, with a Be-F distance of 143 pm.^[10] BeF₂ reaches a vapor pressure of 10 Pa at 686 °C, 100 Pa at 767 °C, 1 kPa at 869 °C, 10 kPa at 999 °C, and 100 kPa at 1172 °C.^[8]

'Molecules' of liquid beryllium fluoride have a fluctuating tetrahedral structure. Additionally, the density of liquid BeF₂ decreases near its freezing point, as Be²⁺ and F⁻ ions begin to coordinate more strongly with one another, leading to the expansion of voids between formula units.^[9]

Production

The processing of beryllium ores generates impure Be(OH)₂. This material reacts with ammonium bifluoride to give ammonium tetrafluoroberyllate:

Tetrafluoroberyllate is a robust ion, which allows its purification by precipitation of various impurities as their hydroxides. Heating purified (NH₄)₂BeF₄ gives the desired product:

In general the reactivity of BeF₂ ions with fluoride are quite analogous to the reactions of SiO₂ with oxides.^[10]

Applications

Reduction of BeF₂ at 1300 °C with magnesium in a graphite crucible provides the most practical route to metallic beryllium:^[11]

The chloride is not a useful precursor because of its volatility. {{cn|reason = The page on Beryllium specifically states that electrolysis of BeCl2 is a practical industrial path to metallic beryllium.|date=November 2018}}

Niche uses

Beryllium fluoride is used in biochemistry, particularly protein crystallography as a mimic of phosphate. Thus, ADP and beryllium fluoride together tend to bind to ATP sites and inhibit protein action, making it possible to crystallise proteins in the bound state.^[12]^[13]

Beryllium fluoride forms a basic constituent of the preferred fluoride salt mixture used in liquid-fluoride nuclear reactors. Typically beryllium fluoride is mixed with lithium fluoride to form a base solvent (FLiBe), into which fluorides of uranium and thorium are introduced. Beryllium fluoride is exceptionally chemically stable and LiF/BeF₂ mixtures (FLiBe) have low melting points (360 C - 459 C) and the best neutronic properties of fluoride salt combinations appropriate for reactor use. MSRE used two different mixtures in the two cooling circuits.

Safety

Beryllium compounds are highly toxic. The increased toxicity of beryllium in the presence of fluoride has been noted as early as 1949.^[14] The {{LD50}} in mice is about 100 mg/kg by ingestion and 1.8 mg/kg by intravenous injection.

References

1. ^{{RubberBible87th}}
2. ^{{cite journal|doi=10.1016/0022-4596(88)90113-2|title=The preparation and structure of the α- and β-quartz polymorphs of beryllium fluoride|year=1988|last1=Wright|first1=Albert F.|last2=Fitch|first2=Andrew N.|last3=Wright|first3=Adrian C.|journal=Journal of Solid State Chemistry|volume=73|issue=2|pages=298|bibcode = 1988JSSCh..73..298W }}
3. ^{{Cite web|url=https://pubchem.ncbi.nlm.nih.gov/compound/24589|title=Beryllium Difluoride|last=|first=|date=|website=PubChem|publisher=National Institute of Health|archive-url=|archive-date=|dead-url=|access-date=October 13, 2017}}
4. ^{{IDLH|7440417|Beryllium compounds (as Be)}}
5. ^¹²{{PGCH|0054}}
6. ^Wells A.F. (1984) Structural Inorganic Chemistry 5th edition Oxford Science Publications {{ISBN|0-19-855370-6}}
7. ^Pallavi Ghalsasi, Prasanna S. Ghalsasi, "Single Crystal X-Ray Structure of BeF2: α-Quartz" Inorg. Chem., 2011, 50 (1), pp 86–89. {{DOI|10.1021/ic101248g}}
8. ^Vapor pressure, physics.nyu.edu, p. 6-63, from Ohe, S. (1976) Computer Aided Data Book of Vapor Pressure, Data Book Publishing Co., Tokyo.
9. ^{{cite journal| title = Waterlike Structural and Excess Entropy Anomalies in Liquid Beryllium Fluoride|author1=Agarwal, M. |author2=Chakravarty C | journal = J. Phys. Chem. B| year = 2007| volume = 111| pages = 13294–300| doi = 10.1021/jp0753272| pmid = 17963376| issue = 46}}
10. ^{{Greenwood&Earnshaw}}
11. ^¹Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. {{ISBN|0-12-352651-5}}.
12. ^{{cite journal| title = The structure of bovine F1-ATPase inhibited by ADP and beryllium fluoride| author = Reiko Kagawa| author2 = Martin G Montgomery| author3 = Kerstin Braig| author4 = Andrew G W Leslie| author5 = John E Walker| last-author-amp = yes| journal =The EMBO Journal| year = 2004| volume = 23| issue = 5| pages = 2734–2744| doi = 10.1038/sj.emboj.7600293| pmid = 15229653| pmc = 514953}}
13. ^{{cite journal | title=Fluoride complexes of aluminium or beryllium act on G-proteins as reversibly bound analogues of the gamma phosphate of GTP. |vauthors=Bigay J, Deterre P, Pfister C, Chabre M | journal = The EMBO Journal | year=1987 | volume=6 | issue=10 | pages=2907–2913| pmid=2826123 | pmc=553725}}
14. ^{{Cite book|url=https://www.nap.edu/read/11571|title=Fluoride in Drinking Water: A Scientific Review of EPA's Standards|last=|first=|publisher=The National Academies Press|year=2006|isbn=978-0-309-10128-8|location=https://www.nap.edu/catalog/11571/fluoride-in-drinking-water-a-scientific-review-of-epas-standards|pages=51-52|language=en|doi=10.17226/11571}}