a 2t . ORNL-4257 g k- 41 UC-4 — Chemistry L) Ay AN EMF STUDY OF LiF—BeF2 SOLUTIONS B. F. Hitch C. F. Baes, Jr. OAK RIDGE NATIONAL LABORATORY operated by UNION CARBIDE CORPORATION for the - U.S5. ATOMIC ENERGY COMMISSION ¥ Printed in the United States of America. Availakle from Clearinghouse for Federal Scientific and Technical Information, National Bureau of Standards, U.S. Department of Commerce, Springfield, Virginia 22151 Price: Printed Copy $3.00; Microfiche $0.65 LEGAL NOTICE This report was prepared as an account of Government sponsored work. Naither the United States, nor the Commission, nor any person acting on behalf of the Commission: A, Makes any warranty or representation, expressed or irnplied, with respect to the accuracy, completeness, or usefulness of the information contoined in this report, or that the use of ony information, apparatus, method, or process disclosed in this report may not infringe privately owned rights; or 8. 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ORNL~4257 Contract No. W-~74Q5-eng-26 REACTOR CHEMISTRY DIVISION AN EMF STUDY OF LiF—BeF2 SOLUTIONS B. F. Hitch and C. F. Baes, Jr. LEGAL NOTICE This report was prepared as an account of Government sponsored work, Neither the United Siates, nor the Commission, nor any persen acting on behalf of the Commission: A, Makes any warranty or representation, expreased or implied, with respect to the sccu- racy, pl or H of the information contained in this report, or that the use of any information, apparsatus, method, or process disclosed in this report may not infringe privately owned rights; or B. Assumes any liabilities with respect to the iise of, or for damages resulting from the use of any information, apparetus, method, or process disclésed in this report, As used in the above, “‘person acting on behalf of the Commisston’” includes any em- ployes or contractor of the ¢ i or pl of such contractor, to the extent that such employee or contractor of the € or pl of such contractor prepares, disseminates, or provides acress 1o, any information pursuant to his employment or contract with the C n, OF Dis t with such contractor. JULY 1968 OAK RIDGE NATIONAL LABORATORY Oak Ridge, Tennessee operated by UNION CARBIDE CORPORATION for the U.S. ATOMIC ENERGY COMMISSION iii CONTENTS Abstract ...ccececccacnnans cecsescanca v Introduction e.sceoscosocesconososcnacsossce Experimental ....ccivevecrecocencsacananas Chemicals ..ccoceoscssososconsossacassesa GASES .vvesssesssoasssscsacan seassas Melt Components .....ceececensacs .o Reagents OOOOOOO & & & 2 & O & b F O ¢ & 9 ¢ ° 0 B O ® Apparatus ....... casesessecesscsne e . Cell Design .o.ceveecannsoosancasns HF-Ho Electrode ...cccveccneaconnss Beryllium Electrode ........ ceeennn Flow Control of Gases .......... coe Hydrogen Fluoride ............ ‘oo Hydrogen ...ccceececescsvscocssos Helium ....... ceece et et antonnusnee Titration Assembly ...ieeecccoascss Electronic Equipment .......... . Procedure ......c00c0000s00 csesenaoee MeasurementsS ...csscoscnsssscsnssass . Cell Potential .....ccee.. cesacas Hy and HF Partial Pressures ..... Melt TemperatuUre ....cocooooeneas Calculations ..ccceccos cesveseces Systematic EXrors ...ceceecaccooces Hydrogen Diffusion ......cc00ue.n Thermal Diffusion ........ ceneens Gas Cooling Effect on Electrodes Melt ComposSition ....eceeoocacsaecs Melt Impurities ....cccc.. cessana Oxide Contamination of Melt..... . SUMMATY s eecocesoscocansosasonnsascs Random ErrOorSeeeseceosssssoesas e ensee “ a % 2 3 Q¢ & 3 8T G ® 2 & % 0 2@ G > & 8 & O 6 -------------- b ® @ @ & * 6 6 & 5 8 6 B & 2 6 % o e & @ & 2 @ @ © ° B . 8 @ @ o * & @ % & o @ ®© 9 & 2 2 0 @ @ B 8 B o ------ e o & ¢ 8 8 & 3 % @ 8 ° 8 ® 0 © 9 F B8 8 ? 4 @ & ¢ e » 9 & B @ & * 4 @ ® 8 ¢ 6 3 8 % 3 ¥ 9 & O & O e ® & & 5 ° ¥ B 2 0 ® s 6 ® -------------- oooooooooooooo Precision of Potential Measurements ....ccecoeoa Melt Temperature ........ cesosnas Melt Composition ....ccevveccacns Titer Precision .eescecececocaseoa » Temperature of Bubble-0-Meter ... - Flow Rate Determination ....ecoee. Endpoint Precision .....cs0000cee . Hz and HF Flow Rates ......... e @ @ @ ¢ @ & @ O O B F “« 2 6 0 ¢ & 8 @ % o & @ ¢ © * & 2 a ¢ & 0 & P & © & O © -~ Oy OO 4 ~J 10 11 11 11 11 11 13 13 13 13 14 14 15 15 18 18 19 19 19 20 21 22 22 22 22 22 23 23 23 23 23 iv Statistical Error Analysis ....coen. ReSUltS @ & 6 F & & @ b O O C @ b € % £ O ¢t D P BB E Y O G & D D B B O O Ta—bulation ® & @ & B 6 & P T & O & S O 8 & O & G O S O B DO EXperimEBtS > & O * & L] o -] e @ @ ® @ e & 9 * @ ® 3 - (-] Corrected Cell Potentials ...ceeveas DiSCuSSiOn ® & & & & © &8 b o b & © & 3 ¥ G B 6 & & O F b B 6 O B € 8 & & ¥ YL AT DS S & 6 O G 6 & O Thermodynamics of LiF-BeFs ......... Reference Electrodes . .veeoceooocescss Beryllium Electrode .....coc0oceeeens HF-H7 Electrode ...icccerececccnnennncoacanoas cene REferenCeS ® & 4 6 8 & 4 & 6 F & 0 2 4 H 00 & T S 0 6B O B © O D OO ® 6 & & b ® & 5 O B Page 23 25 25 25 26 29 29 39 39 41 42 . AN EMF STUDY OF LiF~BeF2 SOLUTIONS B. F. Hitch and C. F. Baes, Jr. ABSTRACT The potential of the cell Be®|BeF,, LiF|HF,H 29 with the assumed cell reaction 23 Be(s) + 2HF(g) < Ber(d) + Hz(g) was measured over a composition range of 0.30 to 0.90 mole fraction BeF, and a temperature range of 500 to 900°C. Since this cell potential is related to the activity of BeFs in the solutions by P a o EO _.32 . H2 BeF2 2F PZ HF activity coefficients could be derived for BeFy (and by a Gibbs-Duhem integration for LiF). Usefully accurate measure- ments could not be made with pure BeFy in the cell, hence values of E° were calculated using values for aBeFoy derived from the phase diagram and previously reported heat of fusion (1.13 kcal/mole) giving EC = 2.4430 - 0.0007952T This comparison of the emf data with the LiF-BeFy phase dia- gram also indicated that the heat of fusion for BeFy is < 2.0 kcal/mole. A power series in xj4iF was assumed for log YBeF? and the coefficients determined by a least squares fit to the data. This gave log v, = (3.8780 - 2333 2323.3y 2+ (=40.7375 + ggz%g_g) 3 2 + (94.3997 - BBy (67,4178 + 222223y, 5 Formation free energies and heats for BeF, and Be( were also calculated by combining the results of the present study with available thermochemical data. The Be +|Be and HF,Hy|F~ electrodes performed acceptably for use as reference electrodes, both being stable and reproducible. I. INTRODUCTION Molten fluoride mixtures of LiF and BeF2 are of considerable interest at this Laboratory since they are the principal constituents in the molten-salt reactor (MSRE) fuel and coolant salts.l Although the molten LiFwBeF2 system has received considerable attention, only a limited number of emf investigations have been attempted. The development of reference electrode half-cells for molten fluorides in general would facilitate the determination of electrode potentials for various fluoride constituents and the detection of certain impurities contained in these mixtures. The purpose of this investigation was to study the cell reaction Be®(s) + 2HF(g) 2 BeF,(d) + H,(g) (1) + — in the molten LiF-BeF, system using Be2 lBeo and HF,H IF electrodes. 2 2 Emf data obtained in this study would hopefully extend and improve the thermodynamics of this molten fluoride system. At the same time emf measurements should demonstrate useful electrodes which may serve as reference electrodes in future emf studies in this important molten salt solvent system. Thus far activity data for the LiF-BeF, systems has been obtained 2 . . 2,3 . from mass spectroscopic studies of the vapor, from the phase dia- 4,5 6 . . gram, from emf measurements, and from transpiration data where gaseous HF-HZO mixtures were equilibrated with the molten fluoride mix- 7 : . . . . ture. The values derived from the phase data, besides being non-iso- thermal, have been limited in accuracy because the BeF, liquidus has 4,5,7,8,9 2 been difficult to determine. In addition, the reported wvalues for the heat of fusion for BeF, are not in agreement. Mass spectro- 2 scopic and emf values of the activity were determined for only a limit- ed number of compositions and temperatures. Probably the best activi- , 7 . . ty values are those determined by Mathews and Baes wusing a transpira- tion method to equilibrate gaseous HF—HZO mixtures with molten LiF—Ber mixtures. However, activities derived from these heterogeneous equi- libria are somewhat limited in accuracy (+ 6%) and the equilibrium quotients were measured in the presence of Be0 as a saturating solid which might have influenced the activity values. Direct determination of the activity of BeF, by emf measurements 2 should yield more accurate values over a greater composition range than . . — 1 any of the methods previously mentioned. Dirian, Romberger and Baes 0 measured the potential of the following cell as a function of tempera- ture. - 0.67 LiF|HF,H,,Pd Be®|0.33 BeF 5] 2 The cell reaction is that shown in eq. (1). The two electrodes - 2+ Be IBeO and HF,HZIF_ - were judged by Dirian et al, to be reversible from polarization measurements. In the present investigation these two electrodes were used to determine the cell potential over a composition range of 0.30 to (.90 mole fraction Ber and a temperature range of 500 to 900°C (Fig. 1). An attempt was made to obtain measurements in pure BeF,, but results 25 of useful accuracy could not be obtained presumably because of its high viscosity and/or high electrical resistivity. Even at 900°C, pure BeF, , . . 11 . is very viscous (about 180 poise 7). The reaction vessel was not heat- ed gbove 900°C because of the tendency of nickel to soften at such ‘elevated temperatures. The melting points of mixtures below 0.33 BeF 2 increase rapidly as the concentration approaches pure LiF as shown in the LiF—BeFZ phase diagram12 in Fig. 1. The lower BeF2 concentrations (below 0.30 Ber) were not investigated therefore since the accessible temperature range was so limited. According to the assumed cell reaction (eq. 1), the cell potential should be dependent on the activity of BeFZ, the activity of beryllium metal, and the‘partial pressures of HF and H . Py aReF E =g 2L, 2 7€ (2) 2F o2 HF 2Be® Previous-measurementslo with thé HF—HZ electrode, as well as the pre- sent ones, indicate the gases to be sufficiently ideal at the elevated temperatures and low pressure levels involved to allow the use of partial pressures in place of fugacities in this Nernst expression. In this study mixtures of HF-H, were bubbled through molten 2 LiF-—BeF2 and the partial pressures of the gases determined by alkali- metric titration and gas volume measurements. The measured cell po- tential (E) was then corrected for the effect of the gas pressure quotient. Pu E-E+%zn—2—% (3) Pur The corrected potential EC is related to the activity of BeF2 by 0 RT EC = E - oF A0 aBeFZ (4) L4 e a 0 - assuming the activity of Be to be unity. Notation The following notation will be used: X e ///////////\ €ogi7) L [(}] mmmmmmmmmmmmmmm 0.00 BeF,, The number preceding "BeFZ” denotes mole fraction. PT’PHF’PH LV, T Total pressure(atm), partial pressures(atm), 2 ' volume (£) per unit time, and temperature(°K) in the region where gas enters the melt. “ o 0 0 ,.0 . PT’PH sV ,T Corresponding measurements at the Bubble-0- 2 Meter. P ,PO Barometric pressure and vapor pressure of H,0 B’ H,0 : o 2 2 at T". ?SF The approximate partial pressure of HF at the titrator. (see Calculations section below.) AP Pressure drop required to maintain gas flow through the melt. E Cell potential measured experimentally for a fixed BeF2 concentration and temperature. Ec The observed cell potential corrected to a gas pressure quotient of unity (eq. 3). E° The standard cell potential with pure BeF, as i 2 the standard state. IT. EXPERIMENTAL Chemicals Gases Commercial HZ was purified by passage through a deoxo unit, a mag- nesium perchlorate drying tube and, finally, a liquid N, trap. An- 2 hydrous HF (99.97%) was used without further purification. Commercial He was purified by passage through an ascarite trap, a magnesium per- chlorate trap and, finally, a liquid N, trap. 2 Melt Components g Lithium fluoride (99.5%) was obtained from American Potash and Chemical Corporation. Beryllium fluoride was from three sources: | . Brush Beryllium Corporation, K and K Laboratories, Inc., and com- mercial BeF2 distilled by the Reactor Chemistry Division at Oak Ridge National Laboratory. Most of the commercial BeF2 contained impurities which ""poisoned" the electrodes (see p. 20). With the exception of one composition, the distilled BeF, was used throughout this investigation 2 since the purity was such that no electrode “poisoning' was encountered. Reagents Reagent grade 1IN NaOH from Fisher Chemical Company was standard- ized with potassium acid phthalate. Apparatus Experiments were carried out in the apparatus shown in Fig. 2. Cell Design A sketch of the nickel reaction vessel used to contain the LiF-BeF2 mixtures is shown in Fig. 3. This vessel was constructed of 2-1/2-in. schedule 40 nickel pipe and was separated into two compartments by a 1/16=in. nickel sheet which extended to within 1/2-in. of the vessel bottom. The nickel sheet was welded so that the only contact between the two compartments was through the 1/2-in. opening at the bottom. The vessel was 10-in. long. Each compartment was equipped with the following: a 3/4-in. Swagelok fitting through which melt components could be added or an electrode inserted, a 1/4-in. gas exit tube, and a thermocouple well. The Swageloks were equipped with Teflon seals when the electrodes were inserted. This provided an electrical insulator as well as a leak- tight fitting for the 1/8-in. nickel tubing. Cooling coils were wrap- ped around each Swagelok to provide cooling when the reaction vessel ORNL-DWG 67-13719 ANHYD HF He POTENTIOMETER AMPLIFIER RECORDER POTENTIAL MEASUREMENT I [._l Be ELECTRODE | EXHAUST | COMPART- I MENT HF-H, ELECTRODE : COMPARTMENT | i=2||~ ] T, 7 - , BUBBLE -0- ggeu COMPARTMENTED SO0N METER REACTION VESSE L Fig. 2. Schematic Diagram of Apparatus Used to Measure Cell Potentials in Molten LiF-BeF, Mixtures. '3 ORNL-DWG 67-13720 L S o L . VA Vd L Z Z = - SIS ISP I UL e SIS IIAIAIAS, SIS, Fig. 3. Compartmented Cell Used to Contain Molten LiF-BeF, Mixtures. 10 was at elevated temperatures. The reaction vessel was located inside an upright tube furnace, the temperature was controlled by an L & N Series 60 D.A.T. Control Unit. The temperature of the reaction vessel was checked with a cali- brated Chromel-Alumel thermocouple and an L & N K~3 potentiometer. A 4—in. diameter vessel, fitted with 1/2-in. diameter electrode compartments, was used for preliminary measurements. Electrodes used in the cylindrical compartments were insulated from the compartment walls with boron nitride spacers, but even then accidental electrical shorts were a problem. The large compartments of the reaction vessel used in the present investigation eliminated the need for insulating spacers except the Teflon seal at the top of the compartment, and no problems from electrical shorting were encountered. HF—H2 Electrode An HZ,HF,Pd electrode of the type used by Dirian and Rombergerlo was used in some of the preliminary measurements. This electrode produced stable potentials but was quite noisy (+ 1 mv). Platinum gauze was substituted for the palladium and was found to be just as responsive and capable of very low noise levels (0.1 mv). The platin- um gauze type (Fig. 4) was used for all measurements in this investi- gation. Electrodes were prepared by forming an egg-shaped bag with th- gauze and slipping the open end over 1/8-in. nickel tubing and tying it securely with small diameter nickel wire. The other end of the bag was crimped together so that the HF-H, mixture, passing down through 2 the nickel tubing had to pass through the gauze. The 1/8-in. nickel tubing transmitted the HF—H2 mixture and provided electrical contact. 11 Beryllium Electrode These electrodes (Fig. 4) were constructed by slipping a berylli- um metal cylinder (3/8-in. 0.D., 1/8-in. I.D., and 1/2-in. length) over a 1/8-in. nickel tube and crimping the nickel tube slightly on each side of the beryllium cylinder to hold it securely. The cylinder was positioned about 1/2-in. from the tip of the nickel tube. Lower- ing the beryllium metal closer to the tip of the nickel tube caused an increase in the potential noise. This was probably due to helium bubbles temporarily insulating the beryllium from the melt. The 1/8- in. nickel tube was used to bubble helium into the compartment and to provide electrical contact. Flow Control of Gases Hydrogen Fluoride.-- The HF manifold pressure was controlled by regulating the temperature of the HF supply cylinder. The flow of HF was controlled by a mass spectrometer leak valve.13 The gas flowed to a monel tee where it mixed with H2. The mixed gases were passed either directly to the HF-H, electrode or a portion was split off for in- 2 fluent gas analysis. Hydrogen.-- A pressure relief valve (Moore Products Company, dif- ferential type flow controller, Model 63 BD, modified form) was used to reduce the hydrogen manifold pressure to a constant value of 3.0 1b. gauge. The flow was then controlled by a brass needle valve obtained from Nuclear Products Company. The H2 was then mixed with the HF as described above. Helium.—-— Helium flow was controlled with the same type .needle valve used for the Hz; no attempt was made to control the manifold 12 ORNL-DWG 67-13721 BERYLLIUM ELECTRODE HF = H, ELECTRODE Fig. 4. HF-H, and Beryllium Electrodes. 13 pressure since a constant flow through the beryllium electrode was un- necessary. Titration Assembly i The NaOH titration vessel was a 200-ml test tube. A rubber stop- per was inserted into the test tube and was equipped with the following: Teflon (1/4-in. dia.) entrance and exit tubes for gas, a 5-ml Lab- Crest microburet, and Beckman No. 39166 (glass, Ag-AgCl) electrodes. A Beckman Zeromatic II pH meter was used to determine the endpoint. The pH was maintained on the alkaline side of the endpoint to avoid glass attack. Duplicate titration assemblies were used to measure in- fluent and effluent HF concentrations. Electronic Equipment An L & N K-3 potentiometer, calibrated with a standard cell from Eppley Laboratory, Inc., was used to buck out most of the cell voltage. When the cell voltage exceeded the range of the potentiometer, a mercury battery (Mallory Duracell No. RM 42R) was connected in series to extend the bucking voltage range. The voltage of the battery was checked daily with the potentiometer, and it proved to be an extremely stable voltage source (+ 0.02 mv/day). The remainder of the cell volt- age (< 100 mv) was coupled, through a Philbrick Model MP solid state operational manifold equipped with P65 AU amplifiers, to a Honeywell Brown Electronik recorder. Procedure Measurements The data obtained for each cell measurement were cell potential, cell temperature, and partial pressures of HF and H2. 14 Cell Potential.—— Cell potential measurements were always preced- ed by standardization of the potentiometer against a standard cell and a check of the amplifier zero on the recofder. During measurements of the cell potential, most of the voltage was bucked out by the potentio- meter (or potentiometer plus mercury battery), and the remainder read off the recorder. The noise level of the potential varied from + 0.2 mv to as high as + 1.0 mv for the high viscosity melts. Although the potential fluctuated as indicated, it did not show any drift toward a higher or lower potential, H2 and HF Partial Pressures.—— The determination of partial pressures was made as follows: (1) A measured volume of standardized NaOH was added to the titration vessel. (2) The time required for the HF to neutralize the base was determined. (3) H2 flow rates were determined by the use of a Bubble-0- Meter. (4) 1Influent partial pressures were checked simultaneously in experiments up to .60 Ber. (5) Partial pressure determinations were never begun until the cell potential had been steady for at least 30 minutes. (6) Six to ten successive titrations were carried out. (7) The barometric pressure, temperature of the titratica as- sembly, and pressure drop across the system were recorded. (8) Helium flowed through the beryllium electrode at a rate of 30 to 75 ml/min. This flow rate provided adequate sparging for this compartment and decreased the thermal gradients. Helium also protected the electrode from any HF which might 15 have entered the compartment. Melt Temperature.-- The temperature of the melt was determined by a calibrated Chromel-Alumel thermocouple positioned carefully to the exact depth of the electrode. Positioning was carried out as accurate- ly as possible to reduce any error in temperature readings caused by thermal gradients in the melt. Calculations.—— The required calculations to evaluate PHF’PH and 2 EC were carried out as follows: (1) The titration times were averaged for a series of titrations of a fixed increment of standard base. The gas volume passed was then calculated by (time of titration)/(time per 100 ml of gas) x 100 = ml of gas. (2) The number of millimoles of HF removed from the H2 stream by the titration was calculated by (m1l NaOH) (conc. of NaOH) = millimoles HF. (3) It was found convenient first to define an approximate partial pressure of HF (PEF) by introducing these measured quantities into the following simple gas law expression o _ f(mmoles HF)(0,08206) (abs.temp. of Bubble-0O-Meter) PHF ml of H2 passed The exact expression for the partial pressure of HF (PHF) at the e- lectrode includes the effect of the pressure drop (AP) caused by the pressure required to maintain bubbling through the melt and subsequent titrator, and the saturation of the H, stream with water prior to 2 measuring the flow rate. The relationship (eq. 11) between PEF and 16 PHF which is required was developed as follows: (3.1) The system may be visualized as consisting of three regions ~ the cell vessel (at PT,T), the titration assembly, and the Bubble-O-Meter (at P2, T°). (3.2) Assuming that the number of moles of HF passing through the cell assembly and into the titrator is the same for a given time interval, then nHF - o and "F T RT (Note that the first expression is merely a rearranged form of the o) y. previous equation which defines PHF Combining these two equatioms, PHF v _ PHF v RTo RT o o) v T P_ =P . (5) HF EF v To (3.3) Moles of H2 passing through the cell and through the Bubble-0-Meter may be treated in a like manner O O P \Y% P V o, - B o B 2 RT RTO P vo T i, S = o - (6) Vv T PH 2 (3.4) Combining equations (5) and (6) o P. Pur = Pup __Q_z_ (72 th 17 (3.5) The total pressure at the HF—H2 electrode is - PH2=PB+AP—PHF (8) and the total pressure of the gas at the Bubble~O-Meter is 0 o o P,.=P_ =P + P T B H2 HZO o o) P =P - P . (9 Hz B H20 (3.6) Substituting (8) and (9) into equation (7) , _ 50 PB 4+ AP - PHF (109 HF HF PB - PH 0 2 and solving equation (10) for PHF gives PB + AP P =P 5 (11) HF HF PB PHZO + PHF PHF can be evaluated since all the other quantities are known. The values for P then can be substituted into equation (8) and the P HF H 2 determined. (4) Using the measured cell potential (E) and the partial pres- sures of HF (PHF) and H (PH ) the corrected cell potential was then 2 2 calculated by PH RT 2 EC = B + 5F n P2 . (12) HF The cell potential E was recorded after gas equilibration with the melt was accomplished, and the melt temperature was constant. 18 Systematic Errors The preceding method of calculating partial pressures does not in- clude corrections for the diffusion of HZ through the walls of the nickel reaction vessel, nor does it consider the effect of thermal dif- fusion. Melt purity and composition should also be considered as sources of systematic errors. Hydrogen Diffusion.-— According to published diffusion coef- ficients,l4 the diffusion of H2 out of the nickel reaction vessel could be a few milliliters per minute at elevated temperatures. The rate of HZ diffusion was measured experimentally by Mathews and Baes7 in a vessel similar to the one used in the present experiment. They obtained the following rates: 700°C, 0.035 ml/sec; 650°C, 0.025 ml/sec; 600°C, 0.015 ml/sec. Extrapolatioh of these measurements to 800°C and 900°C yields diffusion rates of 0.055 ml/sec and 0.075 ml/sec, re- spectively. Typically emf experiments were conducted with a H, flow - y yP y P 9 rate of 2.5 ml/sec. This means that the measured volume of H2 would be in error by 0.67% at 600°C, 1.407%7 at 700°C, 2.20% at 800°C, and 3.00% at 900°C. These errors in partial pressures would cause the calculated potential to be about 1.0 mV lower at 700°C, 1.5 mV lower at 800°C, and 2.0 mV at 900°C. As mentioned previously, the HF-H, mixtures were 2 analyzed before and after entering the HF-H, electrode compartment, and 2 no discrepancy between the two could be detected. These analyses were performed periodically on all compositions up to .60 BeF, and tempera— 2 tures up to 700°C. Melts of higher BeF2 concentrations were not check- ed in this manner because difficulty was encountered in keeping the = flow rate constant through these high viscosity melts when the split . 19 flow technique was attempted. Since the H2 diffusion effect was not observed at temperatures up to 700°C, the errors calculated above seem to be somewhat high, Thermal Diffusion.-- Recognizing the possibility that H2 and HF might tend to separate along the thermal gradient in the reaction vessel, we carried out an experiment to see if this effect was signifi- cant. The total flow of HF-—-H2 passing through the HF—-H2 electrode was varied between 23 ml/min and 160 ml/min. The cell potential increased by about one millivolt over this range; the increase in cell potential over the range of flow rates where potential measurements were actually made (100-160 ml/min) was less than 0.3 millivolt. This is thought to be sufficient evidence that the thermal diffusion effect was not sig- nificant. Gas Cooling Effect on Electrodes.-- The experiment mentioned above also indicates that cooling of the electrodes by gas flow could not have caused more than a one millivolt error in the potential measure- ments. It was felt that although the possibility of a small error in potential might result from flow rates of 100-160 ml/min, vigorous agi- tation of the melt was necessary to reduce the effect of thermal gradients in the melt. Melt Composition.-- A composition error which was discovered at the end of run No. 4 was apparently caused by distillation of BeF2 to cooler regions of the apparatus. TIn this particular run, many attempts were made to measure the cell potential of pure BeF, over a temperature 2 range of 800°C to 900°C. At these elevated temperatures the vapor 20 15 pressure of BeF, is appreciable. Evidently loss of BeF, occurred 2 2 during the periods at high temperatures. Subsequent additions of LiF were made to bring the BeF, composition down to 0.9C BeF,, 0.80 BeF 2 2? 2° 0.70 Ber, and finally to 0.33 BeF The error was discovered at (.33 2 Ber since the potentials did not correspond to previous measurements. At this point enough BeF2 was added to bring the composition up to a book value of 0.40 BeF2 permitting thermal analysis of the liquidus temperature. Thermal analysis was carried out and compared with the . . . 16 . 14 A L1F~BeF2 liquidus data. Results indicated that the true composition was 0.388 Ber. Assuming that all or most of the Ber was lost before the LiF additions were begun, the compositions at 0.90, 0.80, and 0.70 BeF, were reduced to 0.896, 0.791, and 0.686 BeF 2 respectively. Changes 23 in Ec in the (.60 Ber to 0.80 BeF2 regions are small; thus, the compo- sition error at these concentrations should not be significant. How- ever, the values obtained for 0.33 BeF2 in this run were more seriously affected by the uncertainty in composition and were not used. Melt Impurities.-- Early in the experimental work it was found that commercial Ber which contained about 1000-2000 ppm sulfur and 1000 ppm total of Fe, Cr, Cu, and Ni caused "poisoning"™ of both elect- rodes. The cell potential would decay as much as 0.5 volts. Spectro- graphic examination of the Be electrode showed that Fe, Cr, and Ni had been reduced on the surface of the electrode; also metallic impurities originally in the beryllium metal were much higher in concentration on the electrode surface after exposure to the melt. These included Al, Mn, and Ti, the most abundant one being aluminum. 21 The platinum gauze on the HF-H, electrode was darkened by exposure 2 to these contaminated melts. This effect was not pursued since it was already evident that BeF, with the impurities mentioned above was not 2 suitable for use with the beryllium electrode. Distilled BeF containing only trace amounts of impurities, was 29 tested; and none of the problems mentioned above were encountered. This material was used for all measurements in this investigation. Oxide Contamination of Melt.-- The oxide chemistry of LiF-BeF 2 mixtures must be considered since the raw materials contain small a- mounts of moisture, and since beryllium oxide is an impurity in beryl- lium metal. Moisture contamination of the melt was kept to a minimum by freezing the mixtures prior to additions of raw materials. Beryl- lium fluoride was stored in a dry box prior to use. . o , . . 17 A standard purification procedure for removing oxides from fluo-— ride mixture is HF—~H2 sparging. This procedure was used throughout the present investigation to remove oxide impurities from the melts. Con- tinuous use of HF—H2 as one of the electrode materials undoubtedly kept the oxide concentration small. Typically, beryllium metal contains a- 18 ) . bout 1000 to 4000 ppm oxygen. Using the larger value for oxide con- tamination, the maximum concentration of oxide contributed by the beryl- L] —3 , L lium electrode would have been 1 x 10 ~ moles/kg, which is about one . . o 19 . order of magnitude below the solubility of BeO. Therefore, no sig- nificant error is expected due to oxide contamination of the melt by addition of raw materials or from the metal electrode. 22 Summary.-— The only known systematic errors that might be signifi- cant are those attributed to H2 diffusion and gas cooling of the electrodes. These are opposite in effect, and both are expected to be within the experimental scatter of the data. Random Errors In order to obtain a satisfactory estimate of the expected pre- cision of the experimental measurements, the various random errors and their probable magnitude were considered. Precision of Potential Measurements.-- Typically short term po- tential fluctuations were about + 0.2 mV for mixtures up to 0.60 Ber. These fluctuations increased to about + 1.0 mV for 0.90 BeFZ mixtures. However, even at the higher Ber concentrations, the average value of the potential did not change more than + 1.0 mV over a period of one to two hours. Melt Temperature.-— The temperature of the melt was controlled to + 0.2°C. The temperature gradient in the melt varied from about 2°C in melts up to 0.60 BeF,, to a maximum of 9°C in 0.90 BeF,. However, care 2’ 2 was taken during each potential measurement to position the thermo- couple in the melt so that it coincided within ob +<—+Q> gt 4 . ‘Applying this relation to P H E =E + Bz-fin 2 c nF P2 HF gives 02 BEC 2 O2 'aEc 2 02 EC = SEP E + 5—“~ T BEC 2 + oP BPEF HF (13) Differentiation of the above quantities may be carried out to obtain EE.C.__,]_ .?E_c_= 9E , R oE ’ oT aT 2F and oFE ] P P ) _c . Rry . f, OB CHF}|_ SPHF 2F P2 HF e BPHF — (It may be recalled that Py =Pp+ AP ~ P 2 AP may be neglected, thus, Py = PB PHF)' The expected uncertainty of EC HF® Hz 2 3 PHF E ZPB —' PHF F|2P (PB PHF) For the present analysis can now be calculated by 25 ~ n 2 - 12 . H 2P - P 2 2 JE R 2 2 RT ( B HF ) 2 o = g +l==+ = n— | o_ + |- — s . (14) E E T 2 2 - c b ¥ P b PN 2P (PpPypd/ | Pyg Evaluating the above equation numerically for the uncertainty in the calculated potential, using typical partial pressures of HF and H2 at a temperature of 1000°K and using the estimated uncertainties of + 0.5 mV, + 0.5°C, + 0.001 atm respectively in E, T, and P one obtains x HF’ 2 4.2 _ - _ of = (5% 107H% + (8.95 x 10 206 x 107092 + (2,102 x 10792 (o4 2 - - - 0f = (2.50 x 10 'y % (2,00 x 1077y + 4.42 x 1079 C 02 = 4,87 x 10_6 E C 8] - E. = + .0022 volts. The calculated standard deviation of + 2.2 mV is slightly larger than the standard deviation obtained from least squaring the actual data. The range of the standard deviation for the actual data was about 1.0 mV to 2.0 mV. The major uncertainty is in the PHF term and is due to the limited precision of HF flow. ITI. RESULTS Tabulation Table 1 contains the data obtained from each experiment, arranged according to melt compositiomn. Experiments . Four separate series of experiments were conducted during this in- . vestigation. The cell potential of each melt composition was determined 26 for a range of temperatures. In the first series the reaction vessel was initially loaded with 0.33 BEFZ" Subsequent additions of BeFZ were made to bring the concentrations up to 0.40 Ber, 0.50 Ber, and to 0.60 Ber. In the second series the reaction vessel was initially loaded with . ,» 0.80 BeF,, 0.70 Ber, 0.60 BeFZ, 0.50 Ber, 0.40 Ber, and finally 0.33 BeF pure BeF_, enough LiF was then added to give 0.90 BeF 9 Only omne or two determinations were made for 0.60 BeF2 and lower BeF2 compo- sitions since these were checks of previous measurements. Pure Ber was also the initial composition for the third series of measurements. Subsequent additions of LiF¥ were made to give 0.90, 0.80, 0.70, 0.60, and (.33 Ber. As previously mentioned the data for 0.33 BeF2 was considered to be in error and was not used. In the last series of measurements the reaction vessel was loaded initially with 0.33 BeF Enough LiF was added to give 0.30 BeF then 2" 23 BeF2 was added to bring the composition back to 0.33 BeF o Corrected Cell Potentials The corrected cell potentials (EC) for various compositions are plotted as a function of temperature and shown in Fig. 5. Ec is assumed to be a linear function of temperature, Ec = A+BT, over the temperature range investigated. The data points for each composition were least squared, and the calculated lines are also shown in Fig. 5. The para- meters from the least squaring treatment are listed in Table 2. ORNL-DWG 67-137234 £, {valis) B 1.60 \ - ™. / vald’4 / / /S /S S LSS 55 N 0.90 \\Q\;: . ) \ 0.30, 0.33, 040, 050, 0.60 BeF, 550 600 650 700 750 800 850 0.70 BeF, 600 650 700 750 800 850 900 0.80, 0.90 BeF, 850 700 ., 750 800 850 200 950 TEMPERATURE {*C) Fig. 5. Correlation of Pressure Corrected Cell Potentials for Various Compositions as a Function of Temperature. 238 OO OO0 C OO OO OO 0O Q- Table 1. Pressure Corrected Cell Potentials (Ec) Obtained from Measurements in Molten LiF—Ber X Temp. E (volts) X Temp. E (volts) X Temp. E (volts) BeF (°C) c BeF (°C) c BeF2 °C) c 0.30 585.1 1.8864 0.50 608.5 1.7671 0.90 804.1 1.5819 0.30 646.0 1.8447 0.50 613.1 1.7648 0.90 866.0 1.5307 0.30 696.2 1.8126 0.50 685, 2 1.7116 0.90 754.8 1.6208 0.30 732.0 1.7882 0.50 681.0 1.7163 0.90 706.2 1.6613 0.30 609.2 1.8680 0.90 778.0 1.5996 0.30 681.0 1.8213 0.60 637.0 1.7263 0.90 876.5 1.5277 o o 0.60 566.5 1.7856 0.90 802.5 1.5905 33 562.9 1.8812 0.60 735.0 1.6555 0.90 702.0 1.6620 33 514.0 1.9152 0.60 637.0 1.7283 33 601.0 1.8561 0.60 591.1 1.7656 33 649.5 1.8230 0.60 521.0 1.8160 33 698.0 1.7891 0.60 591.0 1.7672 33 624.1 1.8397 0.60 591.0 1.7667 33 565.0 1.8757 0.60 521.2 1.8170 .33 720.8 1.7653 0.60 710.0 1.6760 .33 529.0 1.9035 .60 709.0 1.6771 .33 617.2 1.8436 0.60 662.0 1.7128 .33 617.2 1.8396 .33 550.0 1.8857 0.70 760.0 1.6310 .33 624.5 1.8356 0.70 706.5 1.6736 33 671.0 1.8016 0.70 609.6 1.7477 .33 812.0 1.7081 0.70 562.0 1.7844 0.70 663.0 1.7085 0.40 597.5 1.8069 0.70 794.9 1.6079 0.40 609.5 1.8000 0.40 609.5 1.7991 0.80 800.4 1.6027 0.40 661.2 1.7623 0.80 751.0 1.6335 0.40 686.6 1.7430 0.80 656.5 1.7132 0.40 685.8 1.7478 0.80 632.5 1.7252 G.40 528.2 1.8578 0.80 704.9 1.6725 0.40 528.2 1.8578 0.80 754.0 1.6321 0.40 536.5 1.8540 0.80 681.0 1.6907 0.40 535.0 1.8522 0.80 633.5 1.7205 0.40 706.0 1.7337 0.80 611.5 1.7484 0.40 706.0 1.7316 0.80 639.7 1.7206 0.80 887.5 1.5304 0.50 632.8 1.7516 0.80 810.0 1.5967 0.50 561.5 1.8022 0.80 735.4 1.6482 0.50 728.0 1.6765 0.80 ° 663.0 1.7051 0.50 707.0 1.6972 0.80 616.0 1.7387 0.50 658.0 1.7340 0.80 814.1 1.5909 0.5 617.3 1.7629 0.50 568.3 1.7991 (.50 546.6 1.8127 0.50 503.3 1.8467 0.50 511.8 1.8387 29 Table 2. Parameters from Correlation of EC as a Function of Temperature at Specified Compositions (Ec = atbT) XBeF Intercept + o (Slope + o)x 1()“3 0Ecx103(volts) 2 (a) (b) 0.30 2.45212 0.0053 - 0.6607 0.0080 0.98 0.33 2.46021 0.0048 - 0.6944 0.0077 2.28 0.40 2.4258 0.0040 - 0.7091 0.0065 1.56 0.50 2.4179 0.0041 - 0.7369 0.0065 1.68 0.60 2.4162 0.0054 - 0.7537 0.0061 1.98 0.70 2.4226 0.0049 - 0.7643 0.0071 1.42 0.80 2.4149 0.0072 - 0.7595 0.0101 3.28 0.90 2.4296 0.0162 - 0.7861 0.0205 3.54 IV. DISCUSSION Thermodynamics of LiF—BeF2 The activity of BeF, may be calculated from eq. (4) using the emf data (Ec) obtained in this study if the appropriate values for the standard cell potential (E°) are known. As mentioned previously, sever-— al attempts were made to determine E° experimentally, but values of use- ful accuracy could not be obtained because of high melt viscosity and possibly because of high electrical resistivity. The values of EC obtained for various BeF, compositions do not lend 2 themselves to direct extrapolation to E, However, the standard cell potential may be calculated by relating data in this study with the BeF2 liquidus data in the following manner. 1If the assumption is made that the standard cell potential (EO) varies linearly with temperature 30 (E° = A+BT)#* then eq. (4) may be written RT EC = (A+BT) - T n aBeFZ 2F[ (A+BT) - EC] L tmag e = RT (15) It is then possible to equate eq. (15) to in a (BeF BeTF 5 sat'n) = - —(= - =) (16) 2 £ (where AHf is the heat of fusion of BeF,, and Tf is the melting point of pure Ber) to obtain a relationship between A, B, AH_ and EC calculated f at the BeF, liquidus temperatures and compositions. Combining eqs. (15) 2 and (16). 2F[(A+BT) - E_] - AHf(_l‘ 1 RT R T T f which simplifies to 2F Ec AHf 1 T = (2FB - "Egfi + (2FA + AHf'E . (17) This relationship permits correlation of the data (EC) obtained in the present investigation with the phase diagram data.12 A plot of the a- bove expression as ZFEC/T vs 1/T should be linear since the intercept and slope contain only constants. Using the least square parameters for each composition (Table 2), values for Ec were calculated for the liquidus temperatures at 0.515, 0.60, 0.70, 0.80 and 0.90 BeF., (see 2 footnote ) and then plotted according to eq. (17) (Fig. 6). The result- ing points follow the predicted linear relationship within their pre-— * Using the heat capacity data in the JANAF Tables (Ref. 21), the ACp effect over a temperature range of 450° - 900°C was evaluated and found to be negligible. 31 dicted uncertainties. Parameters for the least squared line are: AH Intercept = - 0.03805 + 0.0034,(Kcal/°K) = 2FB -7 (18) f Slope = 113.84 + 2.48 ,(Kcal) = 2FA + AHf (19) The point at 0.90 BeF, was not used because the uncertainty in EC is 2 relatively large. | Values for A and B were calculated using various literature values for the heat of fusion of BeF, and a melting point of 555°C for pure BeFZ. A tabulation of these wvalues is shown in Table 3. The values of A and B which are consistent with values obtained in the present in- vestigation are those for which the heat of fusion is assumed to be 2.0 kcal/mole or less as shown in Fig. 7. A heat of fusion for Ber >2.0 kcal/mole yields values of E® which are greater than corresponding values of Ec at the higher BeF2 concentration. This creates an impossible situation where the activity of BeF, in the mixture is greater than the 2 activity of pure liquid BeF Thus measurements in the present study 8,9 - 9° clearly support the lower values for the heat of fusion for BeF The emf data (EC) obtained in the present study were fitted by least squares to the expressions listed in Table 4, using the lowest literature value (1.13 kcal/mole) for the heat of fusion of Ber. A plot of the smoothed lines for EC at various BeF, concentrations is 2 shown in Fig. 8. The pressure corrected cell potentials (Ec) differed by 1.4097 standard deviations from the smoothed values given by eq. 4-1 (Table 4), and the average deviation of Ec from smoothed values was approxXimately + 2.5 mV. The average deviation is consistent with the value predicted by the error analysis for Ec' 32 ORNL-DWG 67-13722 0.515 Bef, 0440 — 0430 ////////J S 0120 080 Bef, ] ] - > u [19 od 0410 070 Bek, ] 0.80 Bef | / Q%fiféfi/4 0400 /f — Trm FOR Bef H 0.090 | 1.20 1.25 130 1.35 1.40 1.45 1.50 1.55 100 g Fig. 6. Correlation of Ec with BeF, Liquidus Data. 33 ORNL-DWG 68-230 1.825 1.800 1.775 ® £ 1750 Luo fa z A H¢=143 keal /mole < 1.725 — i OLu A H;=2.00 kcal/mole A H¢=5.80 kcal/mole 1.700 1.675 1.650 550 575 600 625 650 675 700 7 (°C) Fig. 7. Effect of the Heat of Fusion of BeF, in Determining E° (dashed lines). The solid lines represent Ec for various mole fraction of BeF;. 34 Table 3. Calculated Parameters for the Standard Cell Potential of Pure BeF (EO = A + BT) Assuming Various Values for the i Heat of Fusion of BeF2 Heat of Fusion (kzliiie) A3 8P} 3 No. x 10 ° 0.70 2.4525 - .8065 1.00 2.4460 - .7986 1.13 2.4432 - .7952 9 1.60 2.4330 - .7829 8 2.00 2.4241 - 71725 2.50 2.4135 - .7594 5.80 2.3420 - .6730 7 (a) From eq. (19). (b) From eq. (18). 35 Table 4. Expressions for Cell Potentials and Activity Coefficients in the LiF—BeF2 System Eq. No. o 2.3RT 2. 3RT 4-1 E.=E - =95 log XBeF2 - T oF 198 YBeF2 (a) T ] t it 2.4430 - 0.0007952T 2353.5)X2 T LiF 4-3 log YpeF (3.8780 - 2 +(-40.7375 + 202283 + (94,3997 - SRRy + (=67.4178 + égg%é;égxiiF 44 log v, = 0.9384 - 23208 14652.7, 2 T )XBer + (-36.9734 + 74588.5, 3 T XpeF 2 113592.3. 4 X T BeF2 + (126.0947 - + (-158.4173 + 52923.5,.5 T )XBeFZ + (67.4178 - (a) Calculated using a heat of fusion for BeF2 = 1.13 kcal/mole. 36 ORNL-DWG 67-13718 2.00 1.80 £, (volts) NN | .70 AN : x 160 \\ 0.80 0.80 PURE BefF, 2 N 1.50 | %\ 5G0 600 700 800 S00 7 (°C) Fig. 8. Correlation of Pressure Corrected Cell Potentials Ec as a Function of Temperature Using Smoothed Parameters. 37 A Gibbs-Duhem integration of the expression for Y peF Table 4) was . 2 carried out to give the corresponding expression for Y14F (eq. 4-4, Table 4). The integration constant for eq. 4-4 was determined by com-— parison with Y14iF values derived from the liquidus data12 and a heat of fusion of 6.47 kcal/mole for LiF. A more accurate evaluation of the integration constant should be possible when the heat of mixing measure- 22 ' ments of Holm and Kleppa =~ become available for the LiFmBer system. Smoothed values of Ypep are shown as a function of composition at 2 several temperatures in Fig. 9. These results are consistent with those obtained by Mathews and Baes7 over a composition range 0.30 to 0.60 Ber. However, at X > 0.60 the results are not in agreement. The values 2 obtained in the present study are thought to be the more reliable since they are consistent with both the phase data and with a low heat of fusion for BeF,. The previous measurements at compositions > 0.60 BeF 2 2 might be in error because of difficulties in mixing LiF-BeF, at high 2 BeF2 concentrations and because of the effects of BeO saturation. In the present study it was found that at 0.90 BeFZ, a well-mixed melt was not obtained until the temperature was raised above 850°C. This pro- cedure was followed for all high BeF, concentrations toc ensure proper 2 mixing of the LiF-BeF Another possible error in the previous measure- 20 ments could have been the presence of Be0 as a saturating solid. The solubility of Be0O might tend to influence the BeF, activity more at high 2 BeF2 concentrations. The free energy and heat of the cell reaction (eq. 1) were calcu- lated assuming a heat of fusion for BeF2 = 1.13 kcal/mole. These wvalues combined with the available thermochemical wvalues for HF21 were used ORNL-DWG 68- 231 O O 0.2 0.3 04 0.5 0.6 0.7 0.8 0.3 1.0 X, BeF2 Fig. 9. Activity Coefficients in Molten LiF-BeF, Mixtures. 39 to derive the free energy and heat of formation for liquid Ber at 900°K (Table 5). Mathews and Baes7 measured the equilibrium quotient for the reaction HZO(g) + Ber(d) Z 2HF(g) + Bel(s) (20) If eq. (20) is combined with the reaction in eq. (1) the resulting re- action is HZO(g) + Be(s) Z BeO(s) + Hz(g) (21) The free energy and heat of this last reaction thus could be obtained by combining the two sets of measurements, and, since the thermochemical data for H20 are accurately known, improved free energy and heats of formation for Be0 could be calculated. These are shown in Table 5. The preceding calculations for BeF, and Be0 were made for a temperature of 2 900°K. Values for other temperatures were generated using the heat capacity data in the JANAF Tables.21 Reference Electrodes Both electrode half-cells used in the present investigation per- formed acceptably for use as reference electrodes, both being stable and reproducible. Beryllium Electrode The BelBeZ+ electrode should work well in any melt containing beryl- lium ions and no reducible cations. Potential fluctuations due to this electrode were masked in the present study by the fluctuations due to the HF-H, electrode, but should be less than + 0.1 mV. Beryllium e~ lectrodes were fabricated from three different batches of beryllium metal and no discrepancies in potentials were noted when the electrodes Table 5. Formation Heats and Free Energies of BeF2 and Be( Compound Temp. State AHf AGf (°K) (kcal/mole) (kcal/mole) 22 22 Ber 298 Cryst. - 246.01 (=242.30 + 2) - 234.39 (~230.98 + 2) Ber 800 Cryst. - 244,75 - 215.50 Ber 900 Liquid - 243,12 (+ 1.1) - 211.90 (+ 1.1) Ber 1000 Liquid - 242,54 - 208.47 o~ o 22 22 BeO 298 Cryst. - 145,85 (-143.10 + 0.1) - 138.36 (=136.12 + 0.1) Bel 800 Cryst. - 145.68 - 125.70 BeQ 900 Cryst. - 145,57 (+ 1.5) - 123.20 (+ 1.5) BeO 1000 Cryst. - 145,46 - 120.73 41 were interchanged. Therefore, the electrode response does not appear to be a function of a particular batch of beryllium metal. The beryllium electrode does not appear to be suitable for small cell compartments since mass transfer causes the electrode to become en- larged due to spongy deposition of the Be metal, and eventually electri- cal shorts develop between the electrode and the cell compartment wall. HF~H2 Electrode The Pt, HF,Hle_ electrode should be a suitable reference electrode in any fluoride—containing melt where there is no possibility of oxida- tion by HF or reduction by H The solubility of HF in LiF-BeF, is 2° 2 low23 (about 0.0003 mole fraction for the partial pressures of HF used in this study), and no significant solubility of HZ is expected in this system. Potential fluctuations due to this electrode appear to be a function of the melt viscosity. Fluctuations are about + .1 mV in melts with a viscosity of one poise or less. The precision of this electrode was limited somewhat in the present study by the method of HF delivery, as previously mentioned. In future experiments the H,-HF mixture will be obtained by passing H, through a 2 2 thermostated NaHF2 bed. It is hoped that this will be a more precise method of producing mixtures of HF and H, of constant composition. 2 10. 11. 12. 13. 14. 15. 16. 42 REFERENCES W. R. Grimes, MSRP Semiann. Prog. Rept. July 31, 1964, ORNL-3708, p. 230. J. Berkowitz and W. A. Chupka, Ann. N. Y. Acad. Sci., 79, 1073 (1960) A. Buchler and J. L. Stauffer, "Vaporization in the Lithium Fluoride- Beryllium Fluoride System,” SM-66/26 in Thermodynamics, vol. 1, IAEA, Vienna, 1966. T. Férland, "Thermodynamics of Fused Salt Systems," p. 156 in Fused Salts, ed. by B. R. Sundheim, McGraw-Hill, New York, 1964, J. Lumsden, Thermodynamics of Molten Salt Mixtures, p. 227, Academic Press, London, 1966. A. Buchler, Study of High Temperature Thermodynamics of Light Metal Compounds, Army Research Office (Durham, N. C.) Progr. Rept. No. 9 (Contract DA-19-020-ORD-5584) Sept. 30, 1963. A. L. Mathews and C. F. Baes, Jr., J. Inor. Chem., 7, 373 (1968). J. A. Blauver et al., J. Phys. Chem., 69, 1069 (1965) A. R. Taylor and T. E. Gardner, Some Thermal Properties of Beryllium Fluoride from 8° to 1,200°K, U.S. Bureau of Mines, Rept. No. RI-6644 (1965). G. Dirian, K. A. Romberger, and C. F. Baes, Jr., Reactor Chem. Div. Ann. Progr. Rept. Jan. 31, 1965, ORNL-3789, pp. 76-79. C. T. Moynihan and S. Cantor, Reactor Chem. Div. Ann, Progr. Rept. Dec. 31, 1966, ORNL-4076, p. 25. R. E. Thoma et al., submitted for publication in J. Nucl. Mat. Diaphragm Type Adjustable Leak Valve (Ref. No. C-I 24492A) obtained from ORGDP, Oak Ridge, Tenn. S. Dushman, Scientific Foundations of Vacuum Technique, pp. 607-618, Wiley and Sons, N. Y., 1949. S. Cantor et al., Reactor Chem. Div. Ann. Progr. Rept. Dec. 31, 1965, ORNL-3913, p. 27. Temperature-Composition values used here for the BeF supplied by S. Cantor of this Laboratory. 2 liquidus were 17. 18. 19. 20. 21. 22. 23. 43 J. H. Shaffer, MSRP Semiann. Prog. Rept. July 31, 1964, ORNL-3708, p. 288. G. E. Darwin and J. H. Buddery, Beryllium, p. 85, Butterworths Scientific Publications, London, 1960. B. F. Hitch and C. F. Baes, Jr., Reactor Chem. Div. Ann. Progr. Rept. Dec. 31, 1966, ORNL-4076, p. 19. H. D. Young, Statistical Treatment of Experimental Data, p. 96, McGraw-Hill, New York, 1962. JANAF Thermochemical Tables, Clearing House for Federal Scientific and Technical Information, U.S. Dept. of Commerce, Aug., 1965. 0. J. Kleppa, private communication. P. E. Field and J. H. Shaffer, J. Phys. Chem., 71, 3320 (1967). 45 ORNL-4257 UC-4 — Chemistry INTERNAL DISTRIBUTION 1. A. L. Bacarella 43, T. B. Lindermer 2. C. F. Baes, Jr. 44, A. P. Litman 3. C. E. Bamberger 45. R. A. Lorenz 4, C. J. Barton 46. H., G. MacPherson 5. S. E. Beall 47. R. E. MacPherson 6. M. Bender 48. D. L. Manning 7. E. S. Bettis 49. H. E. McCoy 8. F. F. Blankenship : 50, H. F. McDhuffie 9. C. M. Blood 51. L. E. McNeese 10. E. G. Bohlmann 52. A. S. Meyer 11. C. J. Borkowski 53. 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Kasten 82, Biology Library 39. M. T. Kelley 83-85. Central Research Library 40, M. J. Kelly 86-87. ORNL — Y-12 Technical Library 41. S. S. Kirslis Document Reference Section 42. C. E. Larson 88-122. Laboratory Records Department 123. Laboratory Records, ORNL R.C. 124, 125. 126. 127. 128. 129, 130. 131. 132. 133. 134-386. 46 EXTERNAL DISTRIBUTION C. B. Deering, U.S. Atomic Energy Commission, Oak Ridge M. J. Blander, North American Aviation Science Center, 8437 Fallbrook Avenue, Canoga Park, California . G. Dirian, Commissariat A L'Energie Atomique, Centre D'Etudes Nucleaires De Saclay, France 0. J. Kleppa, The James Franck Institute, The University of Chicago, 5640 Ellis Avenue, Chicago, Illinois 60637 C. R. Masson, Atlantic Regional Laboratory, National Research Council of Canada, Halifax, Nova Scotia, Canada A. L. Mathews, Department of Chemistry, Western Carolina College Cullowhee, North Carolina J. A. Swartout, Union Carbide Corperation, New York, New York G. 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