Fluorine distribution

A detailed analysis of the partially fluorinated products formed by the ECF of triethylamine (TEA) [184], in particular the fluorine distribution throughout the TEA skeleton during the course of the reaction, has led the authors to compare the striking similarity to the product distribution known for free radical halogenations. 

The chemical composition of a BF3 NHC5H10 sample was also investigated by 19F NMR. Three fluorine-containing environments were found with fluorine distributed as follows BF3 NHC5H10 (87.3%), BF NH C5H,0 (11.5%), and BF3(OH)-NH2+C5H10 (0.2%). 

The epoxy resin of a Hercules 3501 sample was dissolved in DMSO and investigated by 19F NMR. The 19F peaks associated with BF3 NH2C2H5 were absent and the 1 1 1 1 quartet associated with BF3 NHC5H10 was found at an 19F chemical shift value of — 155.17 ppm. The fluorine distribution among species found in this sample was BF3(OH) NH2+ CjH10 (2.8%), BF4-NH2+C5H10 (9.9%), BF3 NHCSH10 (78.3%), and epoxide-fluorine products (9.0%). 

Archaeological fragments of bones and teeth take up fluorine from the surrounding soil and accumulate it in their mineral phase when they are exposed to a humid environment. Geological time spans are needed for this process to reach equilibrium and for the fluorine distribution to become uniform. In cortical parts of long bone diaphysis, an initially U-shaped fluorine concentration profile can be observed, which decreases from the outer surface and the marrow cavity towards the inner parts of the bone and carries information on the exposure duration of the buried object in its shape. The time dependence of the profile slope is usually described in a simplified way by a diffusion model. The quantitative mathematical evaluation of these profiles may provide information on the exposure duration and the physical condition of the samples. Therefore, several attempts to use fluorine profiling as a dating method have been undertaken [3,39], The distribution of... 

Rutherford Backscattering Spectroscopy (RBS) is an established technique for analysis of inorganic materials. Recently, several applications of RBS on polymer films have been reported however, the effect of ion beams on these surfaces has not been well documented. RBS has been used to determine fluorine distribution in polymers. Since ion beam irradiation of polymers can induce chemical changes, instrumental parameters need to be optimized to minimize damage. 

Figure 2. RBS signal intensity representative of fluorine distribution, as a function of time in 02 rich plasma.

Yttrium oxyfluoride and several similar compounds have the fluorite type of structure with the oxygen and the fluorine distributed among the anion positions. Both Templeton (118) and Hoppe (51) have considered the Madelung constants of the crystals. There are three forms, tetragonal, rhombohedral, and cubic. Their Madelung constants are given in Table VII. 

More recently - P- F REDOR has been used to examine the connectivity of the different atoms via the dipolar coupling (Pan 1995). The method was used to compare the effect of fluoride treatment of hydroxyapatite with fluoroapatite itself. The results suggest that a layer of fluoroapatite less than 1 unit cell thick is formed on the hydroxyapatite and illustrate the potential of this approach for more detailed modelling of the fluorine distribution in these materials. 

A similar advantage of SALI over SIMS is seen at solid-solid interfaces. Monitoring the migration of implanted F in SiOi/Si structures during annealing is a technologically important issue, unattainable in SIMS because of the matrix-enhanced peak at the Si-SiOi interface. Analysis of the same sample with SALI yields a smooth fluorine distribution across the interface as expected. 

Laser-microprobc mass spectrometry has an unusually high sensitivity (down to 10 g), is applicable to both inorganic and organic (including biological) samples, has a spatial resolution of about I pm, and produces data at a rapid rate. Some typical applications of laser-microprobe mass spectrometry include determination of Na/K concentration ratios in frog nerve fiber, determination of the calcium distribution in retinas, classification of asbestos and coal mine dusts, determination of fluorine distributions in dental hard tissue, analysis of amino acids, and study of polymer surfaces. ... 

Cross section through a GDL (a) SEM picture, (b) Carbon distribution, (c) Fluorine distribution (from EDX measurements). 

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