Fluorine concentration

The ores of most importance are fluorspar, CaF2 fluorapatite, Ca (P0 2Fj cryoHte [15096-52-3], Na AlF. Fluorspar is the primary commercial source of fluoiine. Twenty-six percent of the world s high quaHty deposits of fluorspar are ia North America. Most of that is ia Mexico. United States production ia 1987—1991 was 314,500 metric tons, most of which occurred ia the Illinois-Kentucky area. Imported fluorspar ia 1990—1991 represented about 82% of U.S. consumption 31% of U.S. fluorspar imports were from Mexico and 29% from China compared to 66% from Mexico ia the 1973—1978 period. The majority of the fluorine ia the earth s cmst is ia phosphate rock ia the form of fluorapatite which has an average fluorine concentration of 3.5%. Recovery of these fluorine values as by-product fluorosiHcic acid from phosphate production has grown steadily, partially because of environmental requirements (see Phosphoric acid and THE phosphates). 

It can be seen from Table 1 that there are no individual steps that are exothermic enough to break carbon—carbon bonds except the termination of step 3a of —407.9 kJ/mol (—97.5 kcal/mol). Consequentiy, procedures or conditions that reduce the atomic fluorine concentration or decrease the mobiUty of hydrocarbon radical intermediates, and/or keep them in the soHd state during reaction, are desirable. It is necessary to reduce the reaction rate to the extent that these hydrocarbon radical intermediates have longer lifetimes permitting the advantages of fluorination in individual steps to be achieved experimentally. It has been demonstrated by electron paramagnetic resonance (epr) methods (26) that, with high fluorine dilution, various radicals do indeed have appreciable lifetimes. 

A simple equihbrium calculation reveals that, at 25°C and atmospheric pressure, fluorine is less than 1% dissociated, whereas at 325°C an estimated 4.6% dissociation of molecular fluorine is calculated. Obviously, less than 1% of the coUisions occurring at RT would result in reaction if step la were the only important initiation step. At 325°C the fluorine atom initiation step should become more important. From the viewpoint of energy control, as shown in Table 1, it would be advantageous to have step lb predominate over step 2a and promote attack by molecular rather than atomic fluorine. Ambient or lower temperatures keep the atomic fluorine concentration low. 

Reactant molecules are able to withstand more fluorine coUisions, as they become more highly fluorinated, without decomposition because some sites are stericaUy protected, ie, coUisions at carbon—fluorine sites are obviously nonreactive. The fluorine concentration may therefore be increased as the... 

To achieve the very low initial fluorine concentration in the LaMar fluorination process initially a helium or nitrogen atmosphere is used in the reactor and fluorine is bled slowly into the system. If pure fluorine is used as the incoming gas, a concentration of fluorine may be approached asymptotically over any time period (Fig. 3). It is possible to approach asymptotically any fluorine partial pressure in this manner. The very low initial concentrations of fluorine in the system greatiy decreases the probabiUty of simultaneous fluorine coUisions on the same molecules or on adjacent reaction sites. 

The opposite process, i.e. pouring the strip solution into the ammonia solution, significantly reduces the fluorine concentration in the hydroxides formed. Bludssus et al. [495] developed a process comprising the introduction of tantalum- or niobium-containing acid solution to an ammonia solution until achieving pH = 9. It is reported that this method enables the production of tantalum or niobium hydroxides with fluoride contents as low as 0.5% wt. with... 

The fluorine concentration in hydrofluorides of tantalum and niobium is an extremely important issue. Fluorine that separates into the gaseous phase interacts with the construction elements of the furnaces, leading to additional contamination of the final product by silicon, aluminum, etc. Thus, it is recommended to perform diying in crucibles made of Teflon or polypropylene with appropriate temperature limitations. Use of crucibles made of carbon-glass ensures high quality and a broad working temperature range, at least up to 300-350°C. 

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-... 

This method of low-temperature, direct fluorination involves very precise control of fluorine concentrations during the reaction, and initial high dilution of the fluorine with helium. The reaction of elemental fluorine with organometallic compounds is conducted (27) in a cryogenic-zone reactor (see Fig. 8) at temperatures in the range of - 78 to... 

Dynamar Polymer Processing Additive Technical Information, Parr Bomb Analytical Method for Determining Total Organic Fluorine Concentration in Polyethylene, Dyneon, Oakdale, MN (n.d.). 

Total surface fluorine concentration values (pg F/cm2) were determined using neutron activation analysis. 

To treat hollow dialysis fibers the fluorine gas was passed through the inside ofthe capillaries (Figure 17.3). By flow stream measurements the exact amount of gas that entered the capillaries could be determined. The treatment time and the fluorine concentration was measured to determine possible effects on the main biocompatibility properties.7,8... 

Fio. 15. Line width of F" NMR of fluorine-doped aluminum oxide versus fluorine concentration (116). 

Let (AHy)A denote the limiting second moment for zero fluorine concentration and (AHy) the second moment of F due to other F nuclei when the lattice under consideration is full. Then for any intermediate concentration of F the line width for a Gaussian shape is... 

The Aerosol Fluorination process [42] (Aerosol) is operated on the principle that the substrate is absorbed onto the surface of fine sodium fluoride particles in the fluorination apparatus in which the fluorine concentration and the temperature increases along the length of the reaction vessel. A U.V. photo-fluorination finishing stage completes the perfluorination process which has the advantage that it is a continuous flow method. 

The active carbon (C ), produced by the disproportionation reaction, reacts immediately with available fluorine producing more carbon tetrafluoride, which dilutes the fluorine concentration, thereby decreasing the rate of reaction.12 Formation of carbon tetrafluoride releases a large amount of heat (436 kJ moF ), thereby providing more energy to the product reactor to create more carbon tetrafluoride. This process can become uncontrolled when the entire reactor contents deflagrate and an explosive reaction can occur. 

Specific Gravity Fraction % Coal in Fraction Fluorine Concentration (w/g)... 

As shown in Table 1, the application of APS to the F-contaminated Si02 surface causes a significant drop in the fluorine concentration. This result led us to study the removal of fluorine from the surface with water, which is the primary component in the APS solution. The results are shown in Table 3. 

Goldhaber, M.B., Hatch, J.R., Pashin, J.C. et al. (1997) Anomalous arsenic and fluorine concentrations in Carboniferous coal, Black Warrior Basin, Alabama evidence for fluid expulsion during Alleghanian thrusting Abstracts with Programs. The Geological Society of America, 29(6), 51. 

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