103 504 EQU’EMERMM STUQEES 63%: “SEE LEEi‘fiRifia’ifl QEQXESE-fl: £5.35! AND NEQQYéfiifiifii SESQUSQXEEE $13.3 322‘s EYETEMS 3114332 (“311’ fire Beam 5-? M. 5.. MICHQGAN ETAY‘E fiflé‘é‘ERSTiW Garaficfi i Eucé‘wi $963 HESIS 3-9», M!CHIGAE‘~! STATE UE‘HVERSITY EAST LANSING, MICHIGAN MlCHIGJ‘N STAT? 'BN'VERSITY EQUILIEIIUM STUDIES OF T213 LR‘LIJIUH DIOXIE - CARBCN AND NBODYT‘ELW SESQUIOYIDS - GREEN SYSTEMS by Gerald L. Buchcl The equilibriun pressure for the reaction of uranium dioxide end carbon, as e function of torpemture, was recorded over the tempere- ture range of 131140 to 1891", end for the reaction of neoflmiun ses- quioxide and carbon over the temperature range of 1L26° to 2OL3°. A graph of the logarithm of the presume versus tenpereture for both systems was best deecribed by e straight line; the entraipy end entropy of motion calculated from the slope and intercept were found to be: max - 16h.h8 * 5.15 ital/mole, 58sz - 76.20 t 2.65 eel/deg-noie for the vol-c system) “53x - 15o.9h t 7.h1 ken/mote, 55$ - 6351‘ t 3.68 cal/deg-mole for the naps-c system. The composition of the equilibrium gas phase was determined by was spectrometric emlyeie. X~ray powder diffraction photographs were taken efter eech run to determine the phases present in the products. The 114,034 system pro- duced an unlmown pneee which we: enelynd grevinetriceliy in an effort to determine its composition. The mknoun phase we: hydrolyzed with dilute hydrochloric acid and the products of this reaction were found by gas chromtography to be etham, ethylene, and acetylene. The com- position of the phase was found to be approximately Nd1.34O3OZ7C1 00. 50111113111138 STUDIES OF TH". ' MILE DICKIDE - GEM Al‘z'D NECDYE’IIUM SESQUIOXIIE - C31? 11%")! SY‘STBE‘ES 87’ Gerald L. Buchcl A THESIS Submitted to Noni-fin State University in partial fulfillment of the requirements for the degree of MJKSTER CF SCIEKCE Department of Chemistry 1963 acmoemmz “ The euthor expresses his sincere gratitude to Dr. Harry A. Eick for his advice, essistance, and patience during the course of this investigation. I would also like to thank the other members of the Chemistry Department for their essistance, especially, Dr. H. 12. Russell for the use of his instruments. Ry gratitude is extended to the Atomic Energy Commission for their finencisl eid. Finely, I so most indebted to my wife, Judi, for her umierstand- ing and perm while this work was being cos-plead. ii I. 11. IV. TABLE OF WTS PIEFm . O . C C . C O C O O O O C O O O O O 0 12mm ICii A. BPE’EHEIJTAL A. B. C. D. E. F. A. B. O O O O O O I O O I O I O O O O l UoerS’Otm.............. BeRdIOS'CSYStmeeeeeeoeeeeee mmiax80eeeeeee 00000000000000... Apparatus................. ExperimentelProcedure .......... Amlyticelnethods ............ 1eX‘“Yee0e-eeeocoeeoees 2. MassSpectromtry........... 3.6asChromtogrephy.......... h. Grevimetric.............. mz-CSCriC. IOOOOOOOOUOOIO. Hd203-Cseries see-eooeeeeee RESULTSANDDISCIBSION ............ Milwimmu IOOOOOOIOODCO 1e mz-Csysum eeeeeeeeeee 2e Ndzog“C$3th eeeeeseees “Micalmtl.............. 1e [Dz‘CSyStcll eeeeeeeeeee 2. Ndfig-Csysten eeeeeeeeee e. X~ray Diffraction. ...... . bem’le'S‘leeeeeeeeee c. Deposit Formed During Reactor. . d. Investigation of the HdeC Phase e. Results of Gravimetric Amliysis . f. Determination of Total (hrbon . . g. CamositionodeOC ...... suggestions for Future Reseai‘cx. . . . . . C. mum Appendices A. B. O O O U O O I C O I O I I O C eeeeeeeeeeeeeeee Summary of All Runs Made During This Study Temperature Corrections . . . . . . . . . . C. Observed 'd-velues' for the NdeC Phase . 3’ iii 0 I O I O O O I O U C O O O O O O O C C O O O 0 I I I O O O O O O O U Q C O O 27 36 LIST OF TABLES TABLE PAGE 1.8mmryofthemz-Cruns............... 17 II. Equilibrium pressure—temreture data for the 1101-0 system 18 III. Sumryofthelidzos-Crms'.............. 19 IV. Equi libriun pressure-tementure «to for the NdIOS‘C‘y'uneeeeeeeeeseeeeeeeee 20 V. Approximte composition of gas mixture from hydrolysis . 23 MM LIST OF'FIGURES FIGURE PAGE 1. Apparatus for the equilibrium . . . . . . . . . . . 7 2. Apparatus for the hydrolysis runs . . . . . . . . . . . 13 3. Graph of the equilibrium dete for the UOl—C system . . . 23 h. Greph of the equilibrium date for the mazes-c system . . 26 I. PRU-TEE The first section of this stucbr, which was solely concerned with the reaction between uranium dioxide and carbon, was initially under- taken because of the recent widespread interest in uranium and plu- toniim carbides es potentially veltable fuel materials for nuclear reectorsy uranium nonocerbide, for emmple, has been reported to com-- bine e high melting point end high thermi conductivity with good resistance to irradiation «tinge. Carbides can be used for both fast ' end therml reactors; the lover cerbides ere usually considered for that reactor fuels, while the higher carbides dispersed in graphite have Men considered es mels for various designs of high-tevsaereture, ws-cooled theml reactors.‘ Since the reaction beta-veer: uranium dioxide end carbon is believed to involve en equilibrium, en etteopt Hes mde to firmly establish the position of this equilibrium over the relevant range of “mi-stuns. This espect of the work use undertaken beam of the relative absence of reports in the litereture concern- ing eeesumnts of the equilibrium. Sinileriy, the reaction between neodymims sesquioxide end carbon was investigated because there had been no previous equilibrium studies of this reaction. It was elso desirable to determine whether or not the procedure epplied to the uranium dioxide - carbon system could be applied toenother system. As e result of this letter investigation, some quite surprising and interesting results were observed. II. WWDW A. Q, - C System A. considerable amount or work has been performed on various as- pects of the uranium - carbon system. One of the pioneers in this field 'was Roisoan, who in 1896 prepared a uranium carbide compound by heating U30. and graphite in an electric Inmate.t In 1925, the noted German scientist, Otto Heusler’, reported the results of his investigations of the reactions "02m “ ”in ' ”Cam ’ 20%) ‘1’ He was the first to record the carbon monoxide equilibriun pressure of this reaction which was performed in e vacma furnace in the towereture range of moo to 15010. Hamlet ascribed the ferrule cc, to the carbide fortned. However, Lita, Garrett, and Croxton“, in 191.8, reported the preparation of uranium eonocarbide from 0,0. and carbon at temper- atures up to 18000 and indicated that pure dicarbide can be formed only if the mixture is tested to 21:00": the proportion of the dicerbide in the product decreasing as lower temperatures are used. The phase diagram of the uraniue - carbon system indicates that both the nonocarbide end the dicerbide exist as distinct phases in the tamer-attire range or 16000 to 1850°.5 It is now widely accepted that U163 exists in the uranium - carbon system, although there is some dis- agreement remi'ding its range of stability. ballot, at 21.,“ report trust it is formed readily and rapidly at 16000, chi le others claim that it is stable above 21400°, but has not been successfully quenched) 3 There is widespread agreement among investigators regarding the structure of the mnimn carbides. A representative mmie is that reported by Austin. (1959), who determined the carbon atom positions by mutton diffraction. He reported the following structures end lattice pat-ammo: uc, face-centered cubic, no - b.9598 t 0.00033; 0103, body-centered enable, ea In 8.0885 x 0.000533 11c” face-centered tetragomi, e9 - 3.509 : 0.0033, c. - 5.980 1 0.0053. A more recent study of the phase equilibrie of the mnim - aogygen ~ carbon system was performed by Plum“ (1962). In the temper- eture range of W ~ 17oo°, Pun postulated that the two following mimiant equiiihrie exist: ”0%) ‘ “m ' ”Cam * mm ‘1’ mm) ’ 3mm) " ”Cm ‘ 20%) ‘2’ the first being the same reaction u reported by iieusier. Pim natured the carbon monoxide equilibrima pressure with a mercury mour- etet end emlyud the equi iibriun gas mixture with I use spectrometer. may aspects of the experimental investimtions reported in this die- uruuon ere eimiiar to those performed by Piem with the exceptioe! that this work extended the temperatm end pressure range well above that reported by Plum. He studied the equilibrium below 17000 end at I pressure of 03 torr, whereas, this etucv extended measurements to epprmcinntely 19500 end 650 tor-r. B. E53393 - C §xstem Utilizing the same apparetue end procedure that were used for the no, - C eyetem, mammnts were mde of the carbon monoxide equilibrium 1. meme es e mnction of teapernture for the reaction: "4203(3) e 7cm . zundcg'm 0300(3) (3) between Him" and 2000", end X-rey diffraction techniques were employed to determine the phases present in the product from each run. Apmx‘ently, there has been no previous equilibrium study of the 3:50; - C system, although Vickery, Sedincek, end Ruben” report the preparation of neodymium dicerbide by the heating of e nixture of neodymium semiootide end graphite in en ergon atmosphere. These in~ vestigetore, erroneously report thet carbon dioxide rather than carbon Wide is the genomes species produced by the reaction even et temperatures of 1900". In contrast to the ureniun - carbon system, there is no eveileble evidence to mart the aristence of e neodymium nonocerbide end there ere conflicting reports concerning the existence of e sesquicerbide menu’s“ The dicerbide does exist end its structure is reported by Spedding, 35 3.“, to be body-centered tetregoml, with lattice peranetersc e0 - 3.823 : 0.001X, co - 6.105 3 0.0033. Therefore, ell products of the reactions included in this section were thoroughly mined for the existence of both e dimrbide end sesquicerbide phase, end for the possible ccistence of other concurrent high-tetwereture compounds of methionine. III. E?" ifiil‘JTAL A. itterials 1. Graphite. The graphite used in this study was ground from ultrvhigh purity spectroscopic electrodes obtained from national Gel-- ban Products, my City, Elohim. 2. Uraml Acetate. The uml eoetete, iD,(C,H,0,),o2H,O, was obtained tm hliinckrodt Omicel Horns end enehrsed es follows: Alluslies end elkeline eerths es sulfates 0.05 Chlorides 0.00 Heavy netele es lend 0.C02$ Insoluble utter 0.01 % Substances redming low. as mnium IV 0.06 ii Sulfete 0.01 S Urenyi acetate 99.86% 3. Uranus: Biggie. U30. used for the preparation of uranium dioxide was obtained by the eir azimtion of the urenyl ecetete. The amiss were heated in pletinun crucibles over it Faker homer to e constant weight. The urenim dioxide was then prepared by the reduction of 0,0. with hydrogen et 10000. Smll qusrte boats cmteining the black U30. were pieced in e tube (tarmac end e steady stream of purified end dried hydrogen was pessed over the samples es the temereture was ninteined et 10000, for twenty-fair hours. The cessposition of the brown uranium dioxide wes determined by heating it over e Husker burner to the Constant weight of the U50. phase. The composition was "Wt fund to 23. 9mm? than 1302.01. 5 6 h. Hemline eeeqxiqide. Bieociymitm seequioocide oi‘ 99.% purity was obtained from the Michim Chemical Company, St. Louis, hichimn. The eeequioxide we: not celeinedpbefore use because it was believed that the carbon oxides driven off would not effect the equilibrium mmnte e B e fitizig‘ Mtg: The existing “cum system used tirmghout this inveetigetion is shown in Figure l. The emratue is constructed almost entirely of glass except for the ems adjacent to the absolute present-c guy and the difmsion m, which are node of copper. Using e maimed mm. Corporation moo oil diffusion we. booked by e Cenco Hmcfl forcepwp, e resithal pressure of l x 10'" torr we umlly obtained by evacuating the system for at least twelve ham prior to heating. A cylindrioelly striped motion crucible me mchined from teo'rmi- eel grade graphite. It: totel length was 2 9/16 inchee end it me en outside diameter of i 1/8 inches, e 3/1. inch hole we drilled into its center which utended to within 1/16 inch of the bottom A graphite lid wee machined to fit snugly around the 1/3 inch lip of the crucible. The lid had e 1 1/6 inch outside diameter end we 3/3 inch high; e 1/32 inch hole drilled through its center as used to determine «our-- etely the “mes-emu insidethe crucible. The graphite etend which W the crucible wee 3/1. inch high and 1 1/8 inchee in diameter. Three 1/8 inch diameter graphite legs were made to fit tightly into holes drilled into the batten of the stand. The crucible and stand were placed on e mart: table of 1 inch diameter which v31; set upon e 6 1;. 15130616211121: 38903119533. Reodymium sesquiwidc of 99.9% writ}; was obtained from the Hichigan Chemical (Emmy, St. ionic, Michigan. The eeequiaxide me not calcinedbefore use because it was believed that the when oxides driven of! would not effect the equilibrium mmnte. B. Bra-13] Pi‘atiis “In“ The existing vacuum system used throughmit this inveatigation is sham in Figure l. The apparatue is constructed almost entirely of glue except for the ems adjacent to the absclute pressure gauge and the diffusion pm, which are made of copper. Using e Coneolichted Vam Corporation mace oil diffusion pump, backed by e Cenco Mo? form, e residini pressure of i x 10" tore we usually cbtained by evacuating the system {or et least twelve houre prior to heating. A cylindricelly amped reaction cmcible was mchined from techni- cel gredc graphite. lte totel length was 1 9/16 inchee end it had en euteide diameter of i 1/8 inches, e 3/2. inch hole was drilled into its center which extended to within 1/16 inch of the bottom. A graphite lid me nechined to fit snugly around the 1/8 inch lip of the crucible. The lid hed e 1 1/3 inch «iteide diamter and as 3/3 inch high: e 1/32 inch hole drilled through its center as used to determine eccur- etely the taper-tun inside.the crucible. The graphite etend which We! the crucible was 3/1; inch high and 1 1/8 inchee in diameter. mm 1/8 inch diameter graphite iega mu m to fit tightly into holes drilled into the bottm of the stand. The crucible and stand were placed on e qmrte table of 1 inch diameter which was set upon e imczp Esmpnwfimsvm pom magnumaa< ,H cnzmwm Y— QESQ - aerg impom sancmb , \IIIIII), “QHCH .. fl . i mmcrfls J ‘l Qfism M _ mfiasmm mmo xoooQOQm rli_ nu nu Envom> \\MM Qma Npcmzo nu Hwou CowpUUUCHxi nu .1 MP. ®HQHUSpo 1 n U 3 gamma xuooQOpm pmwi w , pm; QSH uou>> mm>Hm> EQUCHB mxo: awowpao Nppmso A mu mnsc cowpmNWCOH ocumo wflou '— conmsncwm cmsmo Eswfim whammmpm ./kllbllv\\ $// 7 HMO _ iflHHVHHW!!. . mmsmo Endom> //k //\ . / . i QES MV\\ umHCH m /. :0 C 8 tubular vycor poet. The legs of the cz'izible stand fitted neatly into three mil notches in the quart: table. h’i‘ien all we properly posiu- tiomd, the crucible was in the approximate center of the wear heat- ing cell. This reaction crucible was heated uith a twenty kl louatt, variable output, Thcnmic induction furnace. Tmratures were measured by 51 gluing into the hole in the crucn ible lid with e Leeds and Northrup, disappearing filament type, optical pyroneter (serial mmber 1521:3353), calibrated at the Natimai Bureau of Standards. Temeratures contained herein have been corrected {or eh- ecrption due to the optical window and prism“ which were masonry for sighting directly into the reaction crucible. It was {curd desirable to place some aluminum foil between the top of the heating cell and the top of the water lacket to prewnt the'ccoling water from splashing onto the qmrte optical window. The equilibriim gee pressure within the system was mmred with e Bullece and Tim, le FA 1L5, absolute presnire mnoiaeter, (rectory calibrated from zero to 800 ton), which enabled the observer to read the pressure directly to the nearest torr. The gauge ie ennu- mctured with the toilet-ring specifications: Accuracy -- 1 part in 1,000 of full scale flange. Sensitivity «- 1 part in 10,000 of mu ecele range Watereeis -- 1.5 parts in 1,000 of mu pressure range. it was possible to circulate the cooling enter in e steady flow crowd the heating cell by continually removing the enter uith e Fisher leientii‘ic water pump, model number Vii-l. Samples of the equilibrium gee were taken for analysis in e 200 nl glee: bulb comected to the vuwun system by means of e Pyrex to Rover “See Appendix B. 9 metal graded seal, a 12/30 standard taper glass joint and a vacuum stopcock. The residual pressure within the system was measured with a cold cathode waCuum gauge, model number loo-A, obtained from the Miller laboratories, Letham, New York. A Consolimted Electrodynamics Corporation leak detector was used to find minute leaks in the metallic Joints of the apparatus. A Tesla coil was employed to check for leaks in the glass sections of the vacuum system. C. wrimntel Procedure The sea experimental procedure was used in obtaining the equilib- rium pressure-teupereture data for both the 002-0 and Ndzoa-C systems. Finely ground graphite was sized using a number 60 wire mesh. The graphite and oxide were weighed out to the molar ratio indicated by eqmtions (1) and (3) with a slight excess of graphite, and then mixed thoroughly by grinding in en agate mortar and pestle. The mixture was placed in the reaction crucible, either as a’powder or in the form of 3 mil comressed pellet. The pellets were formed under a pressure of 2100 psi by improvising e KBr pellet die and press. The loaded crucible was placed in the vacuum line and the system was evacuated until the residuel pressure was approximately 1 x 10" torr. Just before heating was initiated, the stopcock lending to the vacuum source was closed, and the system was opened to the absolute pressure unclear. One side of the absolute pressure nanometer is connected to a vacuum pump and it is necessary to completely evacuate the case and capsule of the nanometer before admitting the unknown pres- sure. The temreture was increased slowly. When reaction had begun lo and carbon monoxidc was being liberated, the system was allowed to equilibrate by waiting until there no longer was a change in pressure with tim. The temperature of the reaction was not recorded until the change in pressure with time was zero. It should be mentioned that, in some instances, it was necessary to pump off an initial amount of gas at temperatures below that of the reaction. This initial gas pressure was belier to be due to the outgassing of the oxide and graphite mixture. During each equilibration, the temperature was carefully measured with the pyrometer. For statistical reasons, the temperature was measured not more than seven times, nor less than four times; the aver- age or the several readings was taken as the apparent temperature. The length of time required for equilibration was inversely pro- portional to the temperature, with web more time required at the lower temperatures than at the higher temperatures. In some cases, when readings were taken at decreasing pressures and at relatively low temper- atures, up to three days were required for the pressure to completely stop changing. When at least ten equilibration masurements had been completed, the power was shut off and the system reopened to the forepump. The minim number of points required to adequately represent the data graphically was considered to be ten. After the reaction crucible had cooled sufficiently, the system was returned to atmospheric pressure by slowly bleeding helium into the vacuum system. The crucible, together with the sanple, were removed and placed into a vacuum desiccator. ll D. Ammical Methods 1. 352531. X-ray powderiphotographs of the products from all the m were taken with a Debye-Scherrer 1114.59 m diameter camera using Cu Ra radiation “on II 1.51118 2). In some instances, a Sie‘nné Counter- Tube Diffractoneter was also used to obtain the position and relative intensity of the diffraction lines. with this information, the observed 'd values' could be calculated for each line and the phases present could be identified by comparison of these observed values with the values listed in the American Society for Testing Materials File on X~rey powder diffraction data. Prior to this procedure, positive ident- ification of the phases was attempted by visually comparing the lines on the Xv‘ray file of the unknown with the lines on films of known sub- stances. 2. Pass Sgctmter. Because of the unique nature of the results obtained from the reaction of neothmiun sesquioxide and carbon, it was found advantageous to employ other techniques in conjunction with X-rey diffraction. It was desirable to determine the composition of the gas phase present in the system at equilibrium since the presence of cone stituents other than carbon nonoxide would considerably alter the inter- pretation of the results. lherefore, gas armies were taken during each run and analysed by bleeding the ms into a Consolidated Electro- mmamics Corporation electronngnetimfocusing mass spectrometer (type 214036). 3. Gas Chromtography. The product of the reaction between neo- dymium sesquioxide and carbon was hydrolysed with all hydrochloric acid 12 using the apparatus sham in Figure 2. The system was first flushed with helium, than approximtely 20-30 ml of hydrochloric acid was added to the reaction flask and the system was'again flushed with helium. About 0.1 g of the product was weighed in an inert atmosphere and placed in the sample holder. The cold trap was inserted in liquid nitrogen, the sample holder was inserted and then inverted spilling the sample into the hydrolyeing Indium. With a steady flow of helium the products of the hydrolysis were swept into the cold trap where thou mses which are condensed by liquid nitrogen were collected. This pseous mixture was analyzed with an F and H Scientific Corporation, Flame-Ionization Gas Chromatograph (Model 609). Several macs of known identity were injected into the chromatographic column and the unlmown components of the mixture were identified by compar- ison with these stanchrds. The qualitative results were obtained by conquering the teuzperaturu at which the unknown components volatilieed with those at which the standards volatiliaed. A rough quantitative determination could be rude by measuring the contribution of each peak to the sun of the peak heights of all the components. 14. gravimtric. a. Total modyniutg gravimetric analysis was made on the pro- duct obtained by the reaction of neodymium sesquioxide and carbon to determine the total per cent modyniun and the total per cent of free or machined carbon. Approximtely a 0.1 to 0.2 9 sample of the product was weighed into a 250 nl beaker. The weighing had to be performed quickly because the sample would hydrolyze in air upon prolonged standing. About 50 ml 13 [I'll ... fl... HflflE omcsu mmmzqouvxn pom mapmumaa< .m wudmwm 1/1 gang cfloo ,Illdwmoupmz 1 mmmmO mammcwuaoo \\\\X\\\\1 Uwsvmq pom manpub Aflumv mumnam089< oh Edmvmz mcmuxHouuzm mxoooaopm acumumam¢ oh wommo mcMchpmmm wash cw Es..\ esmflmm ¥ ' r umUHom mHgEmm 1b of l N hydrochloric acid was added and the beaker was placed on the hot plate at 70° to dissolve all the neodymium and combined carbon, leaving the free carbon undissolved. The free carbon was removed from the solution by filtration through an.alundum crucible. The car- bon was then dried at 101° for at least two hours before weighing. The filtrate was transferred to a 600 m1 beaker, the pH adjusted to 3, and then an excess of a saturated solution of oxalic acid was added to precipitate neodymium oxalate. The precipitate was allowed to digest for at least six hours at 70°. Aqueous ammonia was also used as the precipitant in this analysis scheme because it was thought that the hydroxide precipitate required less time for digestion; however, it was found that the gelatinous hydroxide precipitate could not be com- pletely filtered with an.alundum crucible, so its use was abandoned. After digestion was complete, the oxalate was filtered, more oxalic acid was added to the filtrate, it was redigested, the rest of the pre- cipitate was added to the first, and then the oxalate was ignited at 1000. in a muffle furnace and weighed as the oxide. b. Total carbon. The method used to determine the total percent carbon in the products of the Ndzos-C system.was a modification of the gravimetric method for obtaining the total carbon in iron.and steel.u Essentially, the method involves the burning of the sample in oxygen; the carbon monoxide produced is then oxidised to carbon dioxide with an appropriate catalyaer and is absorbed in ascarite. The change in weight of the ascarite before and after reaction is equal to the amount of carbon dioxide produced. The percent total carbon is then calculated from the weight of the carbon dioxide absorbed. The apparatus lS , consisted of the following parts listed in the order of their position: a cylinder of oxygen, a drying u-tube containing ascarite and anhydror..e, a tower of concentrated sulfuric acid, a resistance furnace with a quarts tube containing the sample and the catalyzer, a gas scrubbing tower filled with alum/dram, and, finally, the escarite tower. Two separate determinations were node. In the first attemt, powdered copper oxide was used as the catalyur and was placed in the qmrts tube out to the satanic; but during the reaction it fused with the qmrta and cracked it mdly. This remilted in a loss of an waterw- mined amount of carbon dioxide. mpric oxide wire was used for the next attemt and it was placed in porcelain boats before inserting it into the reaction tube next to the ample. The procedm-e followed was simple: the system was thormghly flushed with dry oxygen) the variac was tweed on to 130 volts; the reaction was allowed to proceed for about one hour, at which time the voltage was turned off, and the system al- lowed to cool . E. 00rd Series A series of experiments was performed in en attewt to correctly measure the carbon monoxide equilibrium pressure according to the reactions I102(8) . he“) ' "my“, ' ”0(9) (1) In addition to overcoming the inherent problem of leakage in the vacuum system, the major difficulty encountered in the experimental work we allowing sufficient time for equilibrium to be attained. This was an extreuly slow process in the lower temperature range. Although it was mentioned previously that equilibrium was considered to be attained 16 when the change in pressure with tits ms zero, it was difficult to deterudne the pressure exactly, in some instances, because the indica~ tor on the gauge began to fluctuate es the pressure in the system ex- ceeded 200 torr. As the temperature and congruentty the pressure were increased, the degree of fluctuation increased until it reached e maximum deviation of t S torr in the high.pre3oure range. ‘The carbon. eonoxide present in the mazes-c system appeared to be very sensitive to slight danger in tenpereture heause, (luring en equilibration et low temperature; the pressure would slowly increase and decreese if the crucible temperature was not being held constant at ell times by the luster. The error involved in seeming the equilibrium pressure was thought to he reduced by taking e series of readings over e period of epprmtieetely 30 minutes while closely observing eny slight oranges in pressure. At tines, the presoure would remain constant for severei nimtes erd then slowly chenge slightly to a new value, where it mid rennin constant for severel more minutes. Therefore, it was believed thet the pressure which corresponded to e particular temperature ues recorded.eccurately in spite of’ony uonentsry changes which occurred in the system. The use of en optic-i pyrooeter elso introduces e pos- sible experimental error since its eccurecy would he in the vicinity of t 5 degrees in the temperature range of these reactions. Equilibrations were node at both increasinglsnd decreasing carbon monoxide pressures (or increasing and decreasing temperatures) to check for hysteresis of the pressure mugs end the system and to more edequ- etely establish e set of equilibrium presmre-tenpereture values. A summary of'two of the successful runs is presented in.Teble I. A run was considered successful when sufficient time was allowed for 17 the system to reach equilibrium before the pressure and temperatum were recorded, and man no procedure! difficulties were encountered. Table I. Sumry of the int-C runs. .4 .4 A M A h... Mole Ratio Tote! Heating Temperature Pressure Int/C Time (hours) Range (96) Range (torr) 9A 135 265.25 Bib-1351i 061;? 1111 135.7 1914.5 1369—1891 O~SGO w v—V— v—v The residuu pressure in the system was We!!! for Run “A because the cold cathode vecmm gauge was inoperetive et thet tin. However, before Run 9A was started e mm of 2 x 10“ torr was obteined tmder the some conditions. This residmi pressure mid certainly be con- sidered es en edoquate evaluation of the system. Also, our the end 01‘ Run 11A e leek which developed in the system terminated the run sooner tint: desired. Because of this leek, the reactants were heated for minutely 2h hours with the system unknouingly open to the et- eosphere. The equilibriua presme-temereture at: for both runs are listed in Table II. The date ere listed in the some order in which they were recorded during the rms. Temperatures ere corrected for both absorp- tion end Wu:- scale errors. I". Edég-‘C Series Studies similar to those of the preceding section were per- fanned with modymium sesquioxide according; to the expected ecaxaticm mp3“) 9 70(3) - waxy“) 1» 300(9) (3) 18 Table II. Pusm-Mmmture date for the uorc system. fie; 9A Run 111 l‘enpereture (“0) Pressure (torr) Temperature (9C) Pressure (tort) 1329.1 81 1368.5 0.2 1776.2 290 1525.0 25.0 1708.7 165 1696.2 11.7.6 1667.9 8).. 1 1'53. 5 169. 1 1536.5 to 1856.5 1.61. 11.56.: 12.3 1890.? 5130 1137.7 7.1. 1811.. 1 303 1656.3 7i..1 1603.8 53.5 l7211.9 151. 1699.5 127 1709 139.1 1173.8 211 1786.8 2911.1 18511.2 61.9 1615.1 1.5.1. 11.1.7.1 6.2 1313.9 0.1. 10 a“, Using the methods outlined previously, the carbon monoxide equilibrium pressure Hes measured es e function of temperature. In the hope of attaining e tester equilibrium, the ammo momma. end cerbon mixture were compressed into snail pellets, then loaded into the crucible. Them pellets were on average height of 1!); inch end about 1/2 inch in diameter. However, it is questionable if the use of pellets reduced the tin required for equilibrium since there was no significant orange in the total length of time required for e run. Table 111 lists the pertinent date for tuo successful runs in the 116,034: series. The reactants were weighed to the mole ratio required for the fmtion or the dicarbide according to mum (3). Table 111. Sumry of the “303-6 Series. Run this Ratio Totel Heetin Tempereture Pressure 8.110310 Time (hours Range (°C) Range (torr) m 117.? 115.33 1607~2CD1 23-4178 1.8 117.2 190.67 11.264011) 15-623 During run 123 e deposit formed on the exterior of the reaction crucible, apparently es e result of the diffusion or neodymium monoxide through the crucible well. An unsuccessful ettewt to stop this diffu- sion involved the use of e high density graphite crucible; out the dif- . fusion of the oxide was still observed in subsequmt runs. The observed equilibrium pressures end temperatures ere listed in Table IV. Fear equilibrations were recorded at decreeoing temperetures tron in the previous rum because of the excessive time involved. ft) (3 Table IV.. Equilibrium pram-temperature data {or the l1d203~c system. Run 12A Run LB Mature (06) Pressure (torr) Temmtm (0C) Pressure (torr) 1606.8 28.9 11:25.8 15.0 1710.1; 711.6 1569.9 22.2 1783.1 1615.7 1736.1 8b.! 1871..) 22.1.? 2831.3 212.3 1914.6 31:3 1921.2 375.1. 1730.8 96.8 1985.0 i=9? 2 5 1662 50.? 20142.9 625' t 5 1839.6 193 18?8.5 320 s S 1.391;.11 252.7 17813.3 173.7 2001 1.78 1691.1 68.2 161.05! mus 1510.6 23.8 11.6512 21.8 17%.3 11.9.5 w _.___ _._v Since the product or run 12A as observed to hydrolyse in air, the prodmts oi‘ later rum were handled in en inert etmaphers. In like fashion, capillaries for the X-roy powder diffraction owners end the ample holder used for the hydrolysis runs were loaded under an etnosphere of dry helium. IV. RESULTS AND DISCUSSION A- Wigwam. For the following reaction at T 0K: H(9 or I) 1"(g) H (h) the free energy of motion is glwn by the expression: a o .. . O .. 36,: . 5”? msT - mum“ (5) tumor. 1! - PM’ tho only gaseous species in the equation. When AC9“: 0, 1°? Pu " ‘mfn‘ . WAS” (6) which is In the form of the expression for a straight. line: A ,4 log P O - T '0' B (I) man A it tho slop. and B to tho won't-mph.1 Thereforo, from the plot of 109 PM vs 1/1' bath AHT" tad :61." my be obtained. If ACp I O, tho graph 13 a straight. line) if ACP J O, tho plot will dorm: Idight m. 1. The 991“: Sigma. From the above example, it Is apfiamnt that. for tho motion: 003(8) . 1‘ C(3) ' 'mz'h) . 2 00(9) (1) K " Péo v (7) thorofon, - m In 950 . AH?" - TAST°, (8) EM 0 0 log P I ' A"? '0 AS? (9) 0° W m 21 22 Since Acpfis 0 for the reaction to form "U02" at high temperatures,1 a plot of log Pm versus 1/! should result in a straight line. Piazza’ performed experiments to assesa the activity of the solid phases involved in the above equilibrium; these experiments include precision lattice parameter determinations of the monocsrbide and diox~ ide phases in the solid residue at room temperature. As a result of this study, he estimated the activity of the dicarbide phase to be 0.95 t 0.05. He assumes that the activities of the graphite and the diox- ide are equal to unity since the solubility of oxygen and uranium in graphite are negligible. Thus, the equilibrium constant for equation (1) could be expressed as: x - 930 ave: - 0.95 P50 (10) which indicates that the errors in carbon monoxide equilibrium pressures may be considered essentially non-existent, or within the limits of the leasurenents. The graph of the logarithm of the pressure (atmospheres) versus the reciprocal teaperature (01(4) and the straight line equation which describes the points for runs 911 and 11A are shown in Figure 111. The data for both runs were fit by a two parameter least squares method to obtain both the slope and the intercept. Figure 111 indicates that the observed equilibrium pressure—teap- erature data give a fairly linear plot. The slight deviation of a few points from linearity is possibly a result of experimental error invol- ved in reading either the pyrometer or the pressure gauge, which fluct- uated during equilibrations at high temperatures. Also, the extent of the initial outgassing of the reaction mixture and crucible for Run 11A Lilihi‘rit anuL e DLL“: L n L Li IF“ «V -~[‘Pi| \. . .. o 23 .Eobmxm o-~o: opp How womb muapmquEobumusmmmua easubsflw:oo one no sumac .m mnammm Afluxovfi\¢ofl ousbmanEme Hmooumsoom - m6 0.0 m.m o.m mg s m _,J_ _ 4,‘n — s _ _ _ _ A_\o 4,1H4 b, ~ ~ _ a _ _ _ _ ~,4, s a}. s a _ _ _ 1 I1 N.Ml I 19m- T l I.