Fluorine content

Bromine ttifluoride is commercially available at a minimum purity of 98% (108). Free Br2 is maintained at less than 2%. Other minor impurities are HF and BrF. Free Br2 content estimates are based on color, with material containing less than 0.5% Br2 having a straw color, and ca 2% Br2 an amber-red color. Fluoride content can be obtained by controlled hydrolysis of a sample and standard analysis for fluorine content. Bromine ttifluoride is too high boiling and reactive for gas chromatographic analysis. It is shipped as a Hquid in steel cylinders in quantities of 91 kg or less. The cylinders are fitted with either a valve or plug to faciUtate insertion of a dip tube. Bromine ttifluoride is classified as an oxidizer and poison by DOT. 

Fluorinated Alkanes. As the fluorine content increases, the chemical reactivity decreases until complete fluorination is achieved, after which they are inert to most chemical attack, including the highly reactive element fluorine. Their lack of reactivity leads to their use in certain commercial apphcations where stabiUty is valued when in contact with highly reactive chemicals. 

The high fluorine content contributes to resistance to attack by essentially all chemicals and oxidizing agents however, PCTFE does swell slightly ia halogenated compounds, ethers, esters, and selected aromatic solvents. Specific solvents should be tested. PCTFE has the lowest water-vapor transmission rate of any plastic (14,15), is impermeable to gases (see also Barrierpolymers), and does not carbonize or support combustion. 

Polyfluoroaroinatics show similar reactivity pauems, wherein the ease of electrophilic substitution generally decreases with increasing fluorine content Pentafluorobenzene undergoes substitution only under forcing conditions, and perfluoroaromadcs completely resist substitution, which would require displacement of F, but instead give addition products when they react with electrophiles [777, 772,126. ... 

Fluorgehalt, m. fluorine content, fluorhaltig, a. containing fluorine. 

In some cases, the degree of fluorine contamination of tantalum and niobium oxides containing increased fluorine levels is not very critical to the later application of the oxides. Applications related to the manufacturing of optic and electronic devices, however, require significant limitations of the fluorine content of tantalum and niobium oxides. 

Equations (141) and (142) describe the equilibrium between the hydrolysis of complex fluoride acids (shift to the right) and the fluorination of hydroxides (shift to the left). Near complete precipitation of hydroxides can be achieved by applying an excessive amount of ammonia. Typically, precipitation is performed by adding ammonia solution up to pH = 8-9. However, the precipitate that separates from the mother solution can be contaminated with as much as 20% wt. fluorine [490]. Analysis of niobium hydroxides obtained under different precipitation conditions showed that the most important parameter affecting the fluorine content of the resultant hydroxide is the amount of ammonia added [490]. Sheka et al. [491] found that increasing the pH to 9.6 toward the end of the precipitation process leads to a significant reduction in fluorine content of the niobium hydroxide. 

The subsequent steps in the production of tantalum and niobium are washing and thermal treatment of the precipitated hydroxides. For effective washing of precipitated hydroxides, Vaicenberg et al. [490] recommended the use of a 2% wt. ammonia solution that is added at a solid-liquid volumetric ratio of 1 15. It is reported that the above conditions ensure the preparation of dry hydroxides with fluorine contents of less than 2%. Sheka et al. [491] proposed precipitation with ammonia at pH = 8.7-9 (20-40°C) and the subsequent use of 0.5-10% NH4OH with a solid-liquid volumetric ratio of 1 5 for washing (re-pulping). This method enables to reduce the fluorine content in the dry hydroxides to 0.2% wt. 

Ammonia solutions are significantly more efficient than ammonium acetate as washing reagents. The process of fluorine content reduction is related to subsequent hydrolysis of fluoride and oxyfluoride contaminants by ammonia. 

The most efficient washing of the hydroxide was achieved applying a three-step process using an ammonium carbonate solution as the first step, followed by an ammonia solution, and water as the final step. This washing process brings about a ten-fold reduction in the concentration of fluorine compared with laboratory and industrial experience, in which a 2-4 fold reduction in the fluorine content of tantalum or niobium hydroxides following a one-step washing process was obtained. 

Ammonium hydrofluoride is relatively stable, even in the molten state. In addition to being in contact with tantalum or niobium oxide, the compound will initiate the fluorination process yielding complex tantalum or niobium fluoride compounds. There is no doubt that thermal treatment of the hydroxides at high temperatures and/or at a high temperature rate leads to the enhancement of the defluorination processes, which in turn results in an increase in fluorine content of the final oxides. 

Different procedures for the precipitation, washing and thermal treatment of hydroxides result in different fluorine contamination levels in the final products - tantalum and niobium oxides. Laboratory and industrial experience confirms some correlation between the initial concentration of fluorine in the dried hydroxides and the fluorine content in the final oxides obtained after appropriate thermal treatment. For instance, it is reported in [499] that if the initial concentration of fluorine in niobium hydroxide equals A%, then the fluorine content in the final niobium oxide can be estimated according to the thermal treatment temperature as follows ... 

Agulyanskaya et al. [507] investigated the impact of fluorine content on the particle size of niobium and tantalum oxides and powdered lithium niobate and tantalate prepared from the oxides. It was shown that fluorine concentrations lower than 10"2% wt. do not influence particle size and result in a set minimum particle size. This concentration range was referred to as being non-... 

To reduce fluorine content in (NFL MOg, the precipitate is washed. Use of water as a washing solution ensures a significant reduction of the fluorine content however, the process seems to be of low efficiency due to the relatively high solubility of ammonium peroxometalates. According to Belov et al. [512], solubility of the ammonium peroxometalates depends on the concentration of the ammonium salts. The solubility of ammonium peroxometalates (CM () ) in solutions of various ammonium salts can be... 

Additional confirmation of the approach can be found in the fact that mere thermal treatment of powder obtained from fluoride solutions by plasma chemical decomposition at 1000-1200K for 2-3 hours in air brings about a 100-300 fold reduction in fluorine content. Hence, the plasma chemical process and subsequent thermal treatment of the powder enables to obtain final products with fluorine contents as low as 10 2-10 3 % wt. 

Discussion. This method is based upon the precipitation of lead chlorofluoride, in which the chlorine is determined by Volhard s method, and from this result the fluorine content can be calculated. The advantages of the method are, the precipitate is granular, settles readily, and is easily filtered the factor for conversion to fluorine is low the procedure is carried out at pH 3.6-5.6, so that substances which might be co-predpitated, such as phosphates, sulphates, chromates, and carbonates, do not interfere. Aluminium must be entirely absent, since even very small quantities cause low results a similar effect is produced by boron ( >0.05 g), ammonium (>0.5 g), and sodium or potassium ( > 10g) in the presence of about 0.1 g of fluoride. Iron must be removed, but zinc is without effect. Silica does not vitiate the method, but causes difficulties in filtration. 

The last point has been studied more quantitatively for the electrolyte LiOjCCH Fy (x+y=3) / DMSO [97,105], Semiempirical quantum-mechanical calculations with the help of MOP AC [143] show that the mean electron density at the oxygen atoms q(0) decreases for these acetates by about 0.1 unit with increasing fluorine content of the anion [97]. As a consequence ... 

We recently prepared various types of differently fiuorinated alkyl sulfate ILs and discovered that the hydrophobicity was dependent on the content ratio of the fluorine on the alkyl sulfate anion and 2,2,3,3,4,4,5,5-octafiuoropentyl sulfate salts showed hydrophobic properties. Melting point and viscosity were also dependent on the fluorine contents of the anionic part, while conductivity was determined by the cationic part and not influenced by the fluorine contents. Efficient lipase-catalyzed transesterificafion was demonstrated using hydrophobic 1-butyl-3-methylimidazolium 2,2,3,3,4,4,5,5-octafiuoropentyl sulfate ([bmim][C5E8]) as solvent (Eig. 6). ... 

The temperature was set to -15 °C [38] (see also [3]). The molar ratio of fluorine to toluene spans the range from 0.20 to 0.83 hence under-stochiometric fluorine contents were employed. The concentration of toluene in the solvent was 1.1 mol As liquid volume flow always 13 ml h was applied. Acetonitrile was used as solvent for the aromatic compound. In the gas phase, 10% fluorine in nitrogen was used. The gas volume flow was varied from 12.1 ml min to 50.0 ml min . ... 

GL 1[ [R 1[ [R 3] [P la-d] When the fluorine-to-toluene ratio is increased, conversion increases in a linear fashion [38]. This basically means that transport resistance would most likely not prohibit using still higher fluorine contents, thereby further possibly increasing the productivity (space-time yield) of the reactor (Figure 5.19). 

GL 1[ [R 1[ [R 3[[P la-d[ The fluorine content in the gas phase of a falling film micro reactor was varied at 10, 25 and 50% [38]. A nearly linear increase in conversion results at constant selectivity. The substitution pattern, i.e. the ratio of ortho-to para-isomers, is strongly affected by this. 

Attempts to perform hydrodefluorination on other polyfluoroarenes using 9c met with mixed success (Table 8.4). Pentafluoropyridine proved to be highly active with a turnover number of 13.6, although the distribution of products revealed up to three hydrodefluorination reactions (Table 8.4, entry 4). Substrates with a lower fluorine content, such as CF.CH, and 1,2- or 1,4-CF,H were unreactive. 

Poly(Fluoroalkoxyphosphazene) Elastomers. When I is substituted with a mixture of trifluoroethoxide and telomer fluoroalkoxides, an elastomer II is obtained having a fluorine content of approximately 55 percent. A small amount of an unsaturated cure site may also be Incorporated into the polymer to promote vulcanization. 

The fluorine content of II gives it excellent resistance to fuels, oils, most hydraulic fluids and chemicals. Since there are no C-C and C-H bonds along the polymer backbone, II displays excellent resistance to degradation by atmospheric oxygen and ozone. Tn addition, the Inherently flexible nature of the P-N backbone allows this elastomer to be used at temperatures down to -65°C, and gives the polymer excellent flex fatigue resistance over a broad temperature range (-65 to 175°C). 

Above 400°C in hydrogen, deflagration and flaming of the polymer occurs, the vigour depending on the fluorine content. Rapid heating to 500°C in an inert atmosphere causes explosive deflagration. 

The heat resistance and chemical resistance of the fluoropolymers is mainly dependent on the extent of fluorination and stability of the crosslinks. For example, most fluorocarbons have fluorine contents of 50-70%, more chemically resistant types 65-69%. For comparison, fluorosilicones contain about 36% fluorine. 

The commercially available materials are copolymers of vinylidene fluoride and hexafluoropropylene, and generally have a fluorine content in the range of 65-69% fluorine. 

Terpolymers generally have an increased fluorine content of 66-71%. Several different types can be identified, depending on the termonomer used. 

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