Fluorine Pressure Research Articles

Experimental Study on Fluoride Volatility Process for Thorium Fuels

Selective removal of uranium from (Th/U)O2 by fluorination with fluorine was studied experimentally. The fluorination was performed both in a small boat and in a 2 inch inner diameter fluid-bed reactor. Fuel particles tend to agglomerate in the reactor due to the large amount of reaction heat and the comparatively low melting point of ThF4. The fluorinated fuels produced in the fluid-bed reactor were found to be partially agglomerated. Fractional retention of uranium was smaller in the agglomerated parts than in the un-agglomerated, and smaller in the outer layers of the cakes than in the core. On the other hand, it was also established beyond doubt from the results of the small boat fluorination experiment that heavy agglomeration inhibits the volatilization of uranium in the form of UF6. Inhibition of the violet exothermic reaction by lowering the fluorine pressure in the early stage of fluorination was found to be a very effective method of obtaining high uranium recovery. It was demonstrated that more than 99% of the uranium could be volatilized within 4 to 5 hr at a temperature of 580°C. The experimental results on the effects of temperature, particle size and fluorine concentration are presented. The variations of reaction rate observed in the course of fluorination are also discussed.

Experimental Study on Fluoride Volatility Process for Thorium Fuels

Selective removal of uranium from (Th/U)O2 by fluorination with fluorine was studied experimentally. The fluorination was performed both in a small boat and in a 2 inch inner diameter fluid-bed reactor. Fuel particles tend to agglomerate in the reactor due to the large amount of reaction heat and the comparatively low melting point of ThF4. The fluorinated fuels produced in the fluid-bed reactor were found to be partially agglomerated. Fractional retention of uranium was smaller in the agglomerated parts than in the un-agglomerated, and smaller in the outer layers of the cakes than in the core. On the other hand, it was also established beyond doubt from the results of the small boat fluorination experiment that heavy agglomeration inhibits the volatilization of uranium in the form of UF6. Inhibition of the violet exothermic reaction by lowering the fluorine pressure in the early stage of fluorination was found to be a very effective method of obtaining high uranium recovery. It was demonstrated that more than 99% of the uranium could be volatilized within 4 to 5 hr at a temperature of 580°C. The experimental results on the effects of temperature, particle size and fluorine concentration are presented. The variations of reaction rate observed in the course of fluorination are also discussed.

Fluorine Pressure Change Monitor for a Reacting System

Recent experimental results on the performance of a pulsed HF chemical laser have indicated that the presence of HF in the chemical reactants prior to laser initiation degrades the laser performance. In order to monitor the amount of HF produced when the chemical reactants are mixed, a device has been developed that measures the change in concentration of one of the reactants. This device, which relies on the absorption of light by molecular F2, has been shown to have an accuracy of better than 5% in the measurement of the F2 pressure.

The fluoridation kinetics of iron

The manner in which fluorine reacts with iron was investigated over a very broad range of temperatures and pressures. At medium pressures of fluorine it was observed that continuous films were formed. Where the pressure of fluorine was low and the temperature relatively high, there was found to be a process of nucleation and growth of fluorides. Traces of oxygen in the gaseous phase can have a distinct effect on the kinetics of the fluoridation reaction.

The kinetics of the cadmium-fluorine reaction

The kinetics of the cadmium-fluorine reaction have been investigated by the pressure drop method in the temperature range of 200 to 525°C and for fluorine pressures of 200 and 770 Torr. The reaction follows the parabolic rate law and the rate constants are independent of the fluorine pressure used. The reaction rate is sensitive to impurities in the lower part of the temperature range investigated. In the higher part of the temperature range the reaction rate constant is given by: k = 1·2 × 10 2 exp (−13·9 × 10 3/T)mm 2/sec. Plausible analyses are offered to explain temporary deviations of this reaction from the parabolic behavior.

Mass spectrometric and thermochemical studies of the manganese fluorides

Mass spectrometric, calorimetric, thermal analysis and X-ray diffraction studies have been performed on MnF 2, MnF 3 and MnF 4. The heat capacity of MnF 2 has been measured from 330°K to 770°K. D(MnF-F), D(MnF 2-F) and D(MnF 3-F) have been determined to be 126 ± 7, 79 ± 6 and 62.3 ± 2.4 kcal mole -1, respectively. The uncorrected electron impact ionization potentials of MnF, MnF 2, MnF 3, and MnF 4 are 8.41, 11.18, 12.25 and 13.15 eV, all ± 0.1 eV, respectively. Evidence for the phase Mn 2F 5(c) has been found. MnF 3 is far more volatile and stable than previously believed. The vapor pressure of MnF 3 (769-930°K) is given by ▪ MnF 4 exerts about 10 -9 atm for fluorine pressure at room temperature and about 10 -6 atm of sublimation pressure at 600°K. MnF 4(c) is 10.5 ± 2 kcal mole -1 more stable than MnF 3(c) at 298°K. Formation and atomization enthalpies for MnF, MnF 2, MnF 3 and MnF 4 have been derived from these new data and a critical review of existing data. No evidence was found for MnF 5, MnF 6 or MnF 7. A simple method of removing much of the ambiguity from the electron impact threshold measurements is reported.

Fluorination of polyhydrofluoroethylenes. I. Direct fluorination of poly(vinyl fluoride) film

AbstractIt has been demonstrated that the poly(vinyl fluoride) film can be fluorinated by exposing the polymer to an environment of fluorine under atmospheric pressure and at ambient temperature. Fluorine content, infrared spectra, thermal properties, and solubilities in the polar solvents were investigated for the fluorinated products and the following results were obtained. In the case of films less than 10 μ in thickness, the fluorination appeared to proceed homogeneously. Under any fluorinating conditions applied, i.e., fluorine pressure of up to 800 mm Hg and temperatures of up to 90°C, the fluorine content never exceeded 65% which corresponds to a composition of C2F2.5H1.5. The activation energy of the reaction was calculated to be 6.8 kcal/mole. The polymer reacted with a small amount of oxygen contained in the fluorine to form acyl fluoride groups. The fluorinated films became insoluble in boiling N,N‐dimethylformamide, N,N‐dimethylacetamide, and dimethyl sulfoxide, but colored gradually to a dark brown. The occurrence of some crosslinking in the products was revealed.

The mineralogy of the glaucophane schists and associated rocks from �le de Groix, Brittany, France

Ninety-seven mineral phases consisting of ten chloritoids, fifteen epidotes, sixteen garnets, four sphenes, seven rutiles, seven pyroxenes, thirteen blue amphiboles, two green amphiboles, eleven phengites, two paragonites, a mariposite, seven chlorites, and two specimens of albite were obtained from the metamorphic rocks of Ile de Groix, and their chemical, physical, optical and X-ray properties determined. The chloritoids are all optically positive, monoclinic polymorphs with large 2V, moderate refractive indices and characterized by high densities. Their fluorine contents have been used to propose a new upper limit for OH→F substitution in the chloritoid structure, suggesting that partial pressure of fluorine might modify the stability of chloritoids from that determined in pure H2O. The epidotes belong to the Al-Fe epidote series and are “epidote” sensu stricto. The almandine-rich garnets and the chloromelanites are metastable relics in the glaucophane schists. The grossular contents of the calcareous schist garnets are believed to have become depressed under high CO2 pressure and the low Tschermak's contents of the pyroxenes are to be explained by equilibria involving epidote at high \(P_{{\text{H}}_{\text{2}} {\text{O}}} \) and low temperature when the Tschermak's components will break down to epidote group minerals. The sphenes contain appreciable amounts of combined water, fluorine substituting for oxygen and aluminium substituting for silicon and titanium. The presence of H3O+ is suspected in a specimen of blue amphibole. The barroisite has a composition between glaucophane and hornblende. On account of its high Fe3+ content it is believed to have formed under higher PO2 than the blue amphiboles. The paragonites which occur in the ohloritoid veins are unstable in the potassium-rich aluminous schists. The phengites show a tendency towards sericitic composition due to post-glaucophanisation readjustments under the lower pressure conditions of the greenschist facies. Some of the Fe3+ contents of the chlorites are interpreted as due to oxidation of ferrous iron, e.g. 2 [Fe(OH)2]→2FeOOH + H2. The minerals show strong chemical control of the host rock and their Mn contents are directly related to those of the minerals from which they have evolved through retrogression.

The formation and fluorination of lithium fluoroplutonate(IV) compounds

At 300°C, the solid product of the reaction of PuF 6( g) with LiF( s) was found to be LiPuF 5. At 350–450°C, the solid product of the reaction of LiPuF 5( s) with F 2( g) was found to be Li 4PuF 8, and the solid product of the reaction of Li 4PuF 8( s) with F 2( g) was found to be LiF. These experimental observations were used to infer that the reaction of PuF 6 with LiF can be expected to produce a number of solid complexes that are analogues of the compounds known to exist in the condensed system LiF-UF 4. Activation energies for the rates of reaction of LiPuF 5 and Li 4PuF 8 with fluorine (1 atm) were found to be 12 and 10 kcal/mole PuF 4, respectively. Fluorinations of the complexes proceeded with a first-order dependence on fluorine pressure in the range from 0·3 to 1 atm. The fluorination results also limited the value of the equilibrium constant, p F 2 p PuF 6 , for the reaction 4LiF( s) + PuF 6( g) ⇄ Li 4PuF 8( s) + F 2( g) at 400°C between 1 × 10 3 and 16 × 10 3.

A Kinetic Study of the Fluorination of Silver

The effect of the variables, temperature, and pressure, on the kinetics of the reaction of fluorine with silver were studied. The temperature range of the investigation was from 25° to 300°C, and the reaction was measured at fluorine pressures of 50–600 Torr. The reaction was found to be pressure dependent. Three reaction products are identified: silver subfluqride, silver monofluoride, and silver difluoride. No simple rate law could describe the data over the entire time interval of the reaction.

Some aspects of the fluoridation of copper and iron

The reaction of fluorine with copper and iron was studied within a very wide temperature and pressure range. Under medium fluorine pressures the formation of continuous films is observed. With low fluorine pressures and at relatively high temperatures a process of nucleation and growth of fluorides takes place. The presence of traces of oxygen in the gas phase can have a strong influence on the nature of the products formed.

The catalytic formation of xenon difluoride

It is shown that heated filaments of palladium, nickel, copper, and aluminum catalyze the combination of xenon and fluorine. The principal reaction product was identified as xenon difluoride by infrared analysis. Other metals investigated; Ti, Zr, Mo, Ta, W, Re, Ir, Fe, Cr, V, Rh, and Pt, were ineffective as catalysts. Activation energies and reaction rates are presented for palladium at 50–160 °C and for nickel at 180–400 °C. For both metals the reaction is shown to be zero order in xenon and fluorine pressures for partial pressures >50 torr. The catalytically active metals were shown to be coated with an ionic fluoride layer under reaction conditions and it is suggested that xenon is chemically bound to fluorine at this fluoride surface.

Influence of the fluorine pressure on the rate of its interaction with silicon

1. The rate of interaction of silicon with fluorine at room temperature increases as a linear function of the pressure. 2. At fluorine pressures equal to 100 mm and above, a substantial increase in the reaction rate is observed, leading in certain cases even to fusion of the sample.

The Kinetics of the Fluorination of Beryllium

The kinetics of the reaction of sheet beryllium and gaseous fluorine to form beryllium fluoride were studied by means of the pressure drop method over the temperature range of 125°–775°C and at pressures from 20 to 700 Torr. The reaction followed the parabolic rate law. Parabolic rate constants were calculated, and activation energies are given. The pressure dependence is approximately first order with respect to the fluorine pressure. A change of slope in the plot of the rate constant against reciprocal temperature suggests a change in the nature of the reaction near 525°C. Above 525°C the crystal structure of the film changes from α‐quartz hexagonal to rhombic tridymite. Beryllium is identified as the diffusing species.

Mass-Spectrometric Investigation of the Nickel—Fluorine Surface Reaction

Mass-spectrometric measurements have been made of the reaction of polycrystalline nickel at temperatures between 900° and 1600°K with fluorine at pressures between 10−7 and 10−4 torr. Gaseous NiF, NiF2, and F are the major products, and are formed rapidly on the surface at rates linear with fluorine pressure. NiF is present on the surface over the entire temperature range and desorbs above 1100°C; the desorption step involves rupture of a Ni (substrate)—NiF bond and has an activation energy of 28 kcal mole−1. NiF2 formation and desorption are important between 900° and 1600°K with a maximum rate at 1250°—1300°K. The rate-limiting step in the formation of NiF2 has an activation energy of 39 kcal mole−1 and is probably dissociation of fluorine on the surface.

Kinetic studies of the fluorination of uranium oxides by fluorine—II: The fluorination of UO 2

A study has been made on the fluorination of UO 2 powder and pellet to UF 6 with gaseous fluorine over the temperature range from 300 to 430°C, using the same experimental method as reported in Part 1. As same as the reaction of U 3O 8 and UO 3, the overall reaction consists of two steps. In the first step, UO 2 is converted to UO 2F 2 and in the second the UO 2F 2 is further changed to UF 6. The first step reaction is very rapid in comparison with the second step which follows the linear law. The activation energies of the second step reaction were determined for the two types of powders, active and inactive UO 2, to be 33·1 and 29·4 kcal/mole respectively. The reaction rate were approximately proportional to the partial pressure of fluorine.

Kinetic studies of the fluorination of uranium oxides by fluorine—I: The fluorination of U 3O 8 and UO 3

The reactions of U 3O 8 and UO 3 with fluorine have been studied in the temperature range from 350 to 440°C with a thermobalance. The overall reaction consists of two steps. In the first step reaction, these oxides change to uranyl fluorides and in the second to UF 6. In the case of U 3O 8, the first step reaction influenced the rate of the second step, so that the formation of the UF 6 was slow at first, where an induction period was seen, and finally followed the linear law. The rate of the first step reaction of UO 3 was much faster than the second step, and the great part of the overall reaction followed the linear law. The activation energies of the second step reactions for U 3O 8 and UO 3 were 21·3 and 22·0 kcal/mole respectively. An almost linear relationship was found to exist between the reaction rate and the partial pressure of fluorine. For U 3O 8, the formation rate of UF 6 was nearly proportional to the surface area determined by gaseous adsorption.

Radiation-chemical effect of fast electrons on uranium fluorides

The effect of fast electrons on UF6, UF5, and UF4 is investigated. The radiation-chemical yield of the decomposition reaction of UF6 molecules is equal to 1.1 ·9 10−2 molecules per 100 eV. As a result.of long irradiation of UF6, the dynamic equilibrium UF6 ⇌ UF5 + 1/2F2 is established, The rate of radiation--fluorination of UF5 and UF4 is proportional to the fluorine pressure and to the square root of the radiation intensity.

The Fluorination of Plutonium Tetrafluoride and Plutonium Dioxide by Fluorinse

The conversion of plutonium tetrafluoride and plutonium dioxide to the hexafluoride by elemental fluorine was investigated in a flow system at temperatures between 100 and 600 C. The partial pressure of fluorine used was varied from 0.25 to 1.0 atmosphere. The rates of fluorination were dependent on the source of the starting material, probably due to differences in particle size. Activation energies of the reaction were between 10 and 12 kcal per mole. The reactions are believed to show promise for process application in the recovery of plutonium from nuclear reactor fuels.

The fluorides of uranium—III Kinetic studies of the fluorination of uranium tetrafluoride by flourine

The reaction between uranium tetrafluoride and fluorine has been studied between 265° and 348°C by following the change in weight of the solid phase, using a spring balance. Formation of uranium hexafluoride at the solid surface is accompanied by migration of fluorine ions into the UF 4 lattice. The rate of production of UF 6 is in agreement with the kinetics expected for reaction between a gas and a solid at a continuously diminishing spherical interface. The rate of reaction depends on the temperature; no reaction is detectable below 220°C. Within the limits of experimental accuracy the Arrhenius equation relates the reaction-rate constant and the temperature of reaction: the activation energies determined for three preparations of UF 4 were 15·5, 19·1 and 19·9 kcal per mole. A linear relationship is shown to exist between the reaction rate and partial pressure of fluorine, but within the range examined the reaction rate is not affected by the velocity of gaseous reactant past the solid. The rate of UF 6 production is dependent on an “effective” surface area of UF 4, rather than the surface area determined by gaseous adsorption.