Fluorine temperature

Standard commercial iastmmentation and control devices are used ia fluorine systems. Pressure is measured usiag Bourdon-type gauges or pressure transducers. Stainless steel or Monel constmction is recommended for parts ia contact with fluoriae. Standard thermocouples are used for all fluorine temperature-measuriag equipment, such as the stainless-steel shielded type, iaserted through a threaded compression fitting welded iato the line. For high temperature service, nickel-shielded thermocouples should be used. 

Fig. 10.1.17 Cls XPS spectra of (a) the fluorinated carbon deposited film and (b) the carbon nanotubes from the film (fluorination temperature 175°C). (From Ref. 42.)...

A procedure for the fluorination of 1 mm thick wafers of rutile has been developed by Wold and co-workers.161 The products are Ti02 JtFJt, and the value of x is an essentially linear function of the fluorination temperature over the range 575-700 °C. For example, x = 0.002 for the preparation at 700 °C. Samples with the smallest value of x exhibit the largest photocurrent on irradiation despite having the highest resistance. Under irradiation from a xenon arc source, rutile wafers fluorinated at 575 °C produced almost twice the photocurrent of rutile reduced at the optimum temperature (600 °C). 

Increase in fluorination temperature would enhance the covalency of C—F bond and destruction of the layered carbon skeleton by C—C bond rupture as indicated by X-ray diffraction profiles shown in Fig. 9. The C—C bond rupture leads to... 

However, the addition and displacement of fluorine are such exothermic reactions that they are accompanied by the ring-opening reaction and cleavage of methylene bridges, of which relative amounts are affected by the fluorination temperature. Therefore, in order to restrict the ring-opening reaction, the fluorination must be carried out at relatively low temperatures, for instance, 50°C and 70°C. On... 

Fig. 2. F/C atomic ratio of solid type fluorinated pitch as a function of the fluorination temperature.

In general, the refractive index decreases with the increment of the fluorine content in a polymer because of the small polarizability of fluorine. Column 6 in Table 1 shows refractive indexes of S-type fluorides. As the reaction temperature increases, the refractive index tends to decrease. This tendency is in good agreement with that of F/C atomic ratio. On the basis of the Maxwell s theory of electro-magnetism, the dielectric constant, e is equal to the square of refractive index, n under a fixed frequency. The dielectric constants of the S-type fluoride calculated based on the relation are also shown in Table 1, Column 7. The dielectric constant slightly decreased with increasing the fluorination temperature. 

Properties investigated so far are summarized in Table 4 together with those of (CF) and PTFE. The properties such as composition, molecular weight, specific gravity, interlayer spacing, which reflect the characteristics of the bulk, changes as a function of the fluorination temperature and there is no inconsistency with the proposed structure shown in Fig. 7. On the other hand, surface energy, water-... 

Any kind of carbon, such as natural graphite, petroleum coke, carbon black, carbon fiber, exfoliated graphite, natural or synthetic graphite and fullerenes can be fluorinated under controlled conditions. Each carbon has unique crystalline properties. To achieve a desired degree of fluorination — or carbon fluorine ratio — numerous experiments are conducted in specialized TGFA reactors to determine the operating conditions such as fluorination temperature, fluorine flow rate, and fluorination duration. 

In a typical experiment, once the fluorination temperature and flow rate is determined, a finely divided carbon powder is loaded into the reactor. The tempera-... 

Figure 1. Interlayer spacing dooi as a function of fluorination temperature (after ref. 13).

An apparatus similar to that described for the preparation of SFs (p. 169) is used for the fluorination of pulverized electrolytic Cr or CrClg contained in a fluorspar or small alumina vessel. The fluorination temperature is 350-500°C. Some CrF, as well as most of the CrFs, migrates into the receiver. The main portion of the CrF4 is deposited in the reaction tube beyond the boat in varnish-like, glittering brown beads. When the fluorination is complete, the apparatus is flushed out with Ng or CO and the CrF4 is immediately sealed o in glass ampoules. 

One of the most efficient and simplest routes for the fabrication of these perfluorodioxolane monomers and polymers is shown in Scheme 4.3 [26-30]. Commercially available methyl pyruvate and diols are used as the starting materials. The condensation product is then directly fluorinated in a fluorinated solvent such as Fluorinert FC-75 (3M) with a F2/N2 mixture. After flushing the system with nitrogen gas for 1 h, fluorine gas diluted to 20% with nitrogen is blown into the reaction mixture at a flow rate of 2401/h. The reaction is carried out at approximately 25 C for over 20 h. After the reaction is complete, the mixture is neutralized with aqueous potassium hydroxide. The crude monomer is isolated upon decarboxylation of the potassium salt and then purified by fractional distillation. The fluorination process is the key step in the synthesis. The yield is as high as 75% with careful control of the fluorination temperature, and it depends on the structure of the hydrocarbon precursor. Recently, over 90% yield of the fluorination of similar compounds has been reported [31]. The polymerization of these monomers is generally carried out in bulk at 60 - 80 °C for 24-35 h using perfluorodibenzoyl peroxide as the initiator [32]. The conversion yields are 70-80%, and the polymers obtained are colorless and transparent. 

Melt Viscosity, 10 poise PPVE Content, wt% Pressure, atmospheres Fluorination Temperature, C/Time, hours Fluorine Concentration, mole% Total Fluorine Recycled, g/l polymer... 

Table 17.1 Synthesis conditions and elemental analysis offluorinated silica. Influence of the F2 dilution and fluorination temperature on chemical compositions of surface (XPS) and bulk (F titration by specific electrode). The fluorination duration is two hours for all samples...

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