Absorption of boron

Palmer MR, Slack JF (1989) Boron isotopic composition of tourmaline from massive sulfide deposits and tourmalinites, Contr Miner Petrol 103 434 51 Palmer MR, Swihart GH (1996) Boron isotope geochemistry an overview. Rev Miner 33 709-744 Palmer MR, Spivack AJ, Edmond JM (1987) Temperature and pH controls over isotopic fractionation during the absorption of boron on marine clays, Geochim Cosmochim Acta 51 2319-2323 Palmer MR, London D, Morgan GB, Babb HA (1992) Experimental determination of fractionation of B/ °B between tourmaline and aqueous vapor a temperature- and pressure-dependent isotopic system, Chem Geol 101 123-129... 

Excessive absorption of boron oxide may lead to cardiovascular collapse, alterations in temperature regulation, and coma. ... 

Wester, R.C., T. Hartway, H.I. Maibach, M.J. Schell, D.J. Northington, B.D. Culver, and PL. Strong. 1998a. In vitro percutaneous absorption of boron as boric acid, borax, and disodium octaborate tetrahydrate in human skin. A summary. Biol. Trace Elem. Res. 66 111-120. 

Hu H and Brown PH (1997) Absorption of boron by plant roots. Plant Soil 193 49-58. 

Toxicity. Fluoroborates are excreted mostly in the urine (22). Sodium fluoroborate is absorbed almost completely into the human bloodstream and over a 14-d experiment all of the NaBF ingested was found in the urine. Although the fluoride ion is covalently bound to boron, the rate of absorption of the physiologically inert BF from the gastrointestinal tract of rats exceeds that of the physiologically active simple fluorides (23). 

Boron [7440-42-8] B, is unique in that it is the only nonmetal in Group 13 (IIIA) of the Periodic Table. Boron, at wt 10.81, at no. 5, has more similarity to carbon and siUcon than to the other elements in Group 13. There are two stable boron isotopes, B and B, which are naturally present at 19.10—20.31% and 79.69—80.90%, respectively. The range of the isotopic abundancies reflects a variabiUty in naturally occurring deposits such as high B ore from Turkey and low °B ore from California. Other boron isotopes, B, B, and B, have half-Hves of less than a second. The B isotope has a very high cross-section for absorption of thermal neutrons, 3.835 x 10 (3835 bams). This neutron absorption produces alpha particles. 

In the process of inhibition polypyrocatechin borate interacts with polyethylene macroradicals to form the B—O—C bonds. This is confirmed by the fact that the absorption spectrum of polyethylene inhibited with polypyrocatechin borate revealed the bands in the region of 1350 cm" characteristic for the B—O—C bond. There is no such a band in the spectrum of pure polypyrocatechin borate after heating under the same conditions. Chemical analysis of boron in polyethylene provides support for the IR-spectroscopy data concerning the presence of chemically bonded boron in polyethylene after destruction. 

Two pieces of direct evidence support the manifestly plausible view that these polymerizations are propagated through the action of car-bonium ion centers. Eley and Richards have shown that triphenyl-methyl chloride is a catalyst for the polymerization of vinyl ethers in m-cresol, in which the catalyst ionizes to yield the triphenylcarbonium ion (C6H5)3C+. Secondly, A. G. Evans and Hamann showed that l,l -diphenylethylene develops an absorption band at 4340 A in the presence of boron trifluoride (and adventitious moisture) or of stannic chloride and hydrogen chloride. This band is characteristic of both the triphenylcarbonium ion and the diphenylmethylcarbonium ion. While similar observations on polymerizable monomers are precluded by intervention of polymerization before a sufficient concentration may be reached, similar ions should certainly be expected to form under the same conditions in styrene, and in certain other monomers also. In analogy with free radical polymerizations, the essential chain-propagating step may therefore be assumed to consist in the addition of monomer to a carbonium ion... 

Consistent with the involvement of the boron 2pz-orbital in this transition is the almost total reduction of the long-wavelength absorption of (PhCH2)3B above 250 nm by its complexation with ammonia. Strong chemical support for a multiply bonded boron in the excited state (48b) can be deduced from photolysis results with tribenzylborane (49).48 While photolysis of... 

Naturally occurring boron consists of approximately 20% of 10B and 80% of UB, leading to an average atomic mass of 10.8 amu. Because 10B has a relatively large cross-section for absorption of slow (thermal) neutrons, it is used in control rods in nuclear reactors and in protective shields. In order to obtain a material that can be fabricated into appropriate shapes, boron carbide is combined with aluminum. 

Atomic absorption spectrometry has been used for the rapid determination of boron in seawater [113]. 

In the case of boron impurities a complementary situation occurs. Boron has only three outer bonding electrons instead of the four found on carbon. Each boron impurity atom occupies a carbon position, forming Be, which results in the creation of a set of new acceptor energy levels just 0.64 x 10 19 J (0.4 eV) above the valence band. The transition of an electron from the valence band to this acceptor level has an absorption peak in the infrared, but the high-energy tail of the absorption band spills into the red at 700 nm. The boron-doped diamonds therefore absorb some red light and leave the gemstone with an overall blue color. 

The fact that the boron trifluoride t-butyl fluoride (and chloride) system and the boron trifluoride isopropyl fluoride systems on thermal decomposition yielded polymer mixtures may indicate the equilibrium in equation (1). On measuring absorption spectra of boron trifluoride—... 

Borazine, substituted borazines and some boron hydrides are ionized by absorption of 121.5 mn radiation (H-a line). Types of ion sources used in these studies are illustrated in Fig. 16. The absorption process results in loss of an electron to form a cation without fragmentation ... 

The calibration graph at 510 nm is a straight line and Beer s law is obeyed from 0.5 to 5 [xg/ml of boron in the final measured solution (corresponding to 10-110 xg of boron in the aqueous phase). The molar absorptivity, calculated from the slope of the statistical working calibration graph at 510 nm, was 29051/mol/cm. The Sandell sensitivity was 0.011 xgcm2 of boron. The precision of the method for ten replicate determinations was 0.6%. The absorbance of the reagent blank solution at 510 nm was 0.010 d= 0.003 for ten replicate determinations. Therefore, the detection limit was 0.04 xg/ml of boron in the final measured solution. 

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