THE PREPARATION OF METALLIC LANTHANUM BY ROGER GREENLEAF STEVENS B.S. University of Illinois, 1920 THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN CHEMISTRY IN THE GRADUATE SCHOOL OF THE UNIVERSITY OF ILLINOIS, 1922 URBANA, ILLINOIS \ c 5 6 * 6 - UNIVERSITY OF ILLINOIS THE GRADUATE SCHOOL May_ 2.5. —1922— I HEREBY RECOMMEND THAT THE THESIS PREPARED UNDER MY SUPERVISION BY_ . Roger- Qreenle-a f S t e v ens ENTITLED__Ilie— Preparation of - Me ta 11 ic - Lanthannm- BE ACCEPTED AS FULFILLING THIS PART OF THE REQUIREMENTS FOR THE DEGREE OF ¥ aatflu of ? o . I PnR fi- In Charge of Thesis Head of Department Recommendation concurred in’* Committee on Final Examination* ^Required for doctor’s degree but not for master s A OQ/M Q Digitized by the Internet Archive in 2016 https://archive.org/details/preparationofmetOOstev TABLE OF CONTENT? I. ACKNOWLEDGMENT Page No. II. INTRODUCTION 1 Object 1 Occurrence 1 Historical 1 III. THEORETICAL IV. EXPERIMENTAL Source of material Preparation of anhydrous LaCl^ Factors in electrolysis Discussion of difficulties encountered and suggested remedies Result of run 3 V. CONCLUSION 3 3 3 5 10 15 18 24 Summary 34 Bibliography 35 ACKNOWLEDGEMENT Til 3 writer desires to express his appre- ciation to Dr. H. 0. Kreraers for the U3e of apparatus and for many helpful suggestions. Appreciation is also due Dr. 3. S. Hopkins for valuable suggestions and in- terest shown throughout the work. INTRODUCTION The object of the present work was to prepare metallic lanthanum in such amounts and form aG to be able to study the physical and chemical properties in a later investigation. Lanthanum is one of the elements included in the cerium group of rare earths and is found in a large number of widely distributed minerals which include orthite, cerite, lan- thanite, monazite, fluocerite, yttrocerite, bastn&site, tysonite, parisite and melanocerite^. Of these, mcnazite is by far the most important and because of the thorium content finds wide use in the gas mantle industry. Consequently, the residues from this industry form a prolific source for the rare earths. 3 Lanthanum wa3 discovered in 18 33 by Mosander . After the discovery of lanthanum, attention of investigators was direct- ed to obtaining pure lanthanum . As a result it was found that lanthanum compounds are most easily obtained by: 1. The fractional crystallization of the double magnesium 3 nitrates of the cerium earths after the cerium has been removed . 3. The double carbonate method after the separation of 4 cerium . The first method has been used in thi3 laboratory with good results. Most of the previous work on the rare earth metals has been concerned with the preparation of misch metal, (a mixture of the metals of the cerium group rare earths) and the preparation of metallic cerium . However, Muthmann and his associates, in - • • 'i " , ' - 3 - 1803, began an. investigation of the preparation of the individual metals of the cerium group and obtained lanthanum in an impure and finely divided state which necessitated subsequent fusion under 3 B aCl 3 for pur i f i c at ion , THEORETICAL In the preparation of metals, two general methods are used: (1) Reduction of the oxides or chlorides by one of the very electropositive metals. (2) Electrolysis of a fused salt or an aqueous solution of the salt . The first method was discarded because of the very strong electropositive nature of metallic lanthanum itself and also because of the unsuccessful attempt of Alcan Hirsch to even obtain metallic cerium (which is less electropositive than lanthanum) by 7 this method . Consequently, attention was directed to the second method. The use of aqueous solutions was out of the .question be- cause of the reason stated above and thus the problem resolved it- self into the study of the electrolysis of a fused salt. It wa3 necessary to prepare some anhydrous salt of lanthanum and because the electrolysis of the fused chlorides is a more general procedure, study was made of the preparation and electrolysis of fused lan- thanum chloride. . ■ . . ' . . - 3 - SOURCE OF MATERIAL. The double magnesium nitrates of lanthanum were used as the source of material. The nitrates were prepared and frac- tionated by Dr. L. F. Yntema and showed no traces of the two most likely impurities to be present, praseodymium and neodymium, when the absorption spectrum was examined. In order to replace the above material, fractionation of the double magnesium nitrates of lanthanum, praseodymium and 3 neodymium, was undertaken". This material had already been frac- tionated by other workers in this laboratory until it was rich in lanthanum, praseodymium end neodymium. After 30 crystallizations the following results were noted: Fr action Nd. Pr. 1 none none 3 t! trace 3 Less than .01% NdgOj More than 0.1% PrgOs 4 Hd #2 line faint Fractions which were shown to be free from praseodymium and neodymium according to the absorption spectra were set out from time to time. After 70 fractionations about one-half of the ori- ginal showed no absorption spectrum., thus indicating the absence of praseodymium and neodymium. In connection with the separation of lanthanum from praseodymium and neodymium, it might be mentioned that the method of Prandtl and Rauchenberger was tried using a small amount of I 4 material . The theory is "based on the following reversible re- action: III MeCl 3 “f 3NH 3 + 3H S ° — III Me (OH) 3NH 4 C1. They give experimental data on the solubilities of lanthanum, praseodymium, neodymium and samarium chlorides, nitrates, double magnesium nitrates, and double zinc nitrates in solutions contain- ing varying amounts of NH^Cl in the case of the chlorides and NE 4 N0 3 in the case of the nitrates. Because the material was al- ready in the form of double magnesium nitrates, the purification of lanthanum was undertaken according to the following equation: III III 2Me (W0 3 ) 3Mg(N03) g-j-SNHg-j-SHgO ~ — * 2Me(0H) 3 3Mg(H03 ) 2 6NH 4 T?0 3 . It is claimed that the most rapid separation occurs in a 5-normal HH 4 H0 3 solution at 50°0. At this concent ration and temperature, the following solubilities in 100 grams of solution are given: L 3 ^ r 3 C 3 Nd 2 0 3 Thus, upon continued fractionation, the lanthanum would tend to concentrate in the soluble end and the praseodymium and neodymium in the insoluble end, A sufficient amount of material containing lanthanum and praseodymium ’was taken so that all the praseodymium which was present would be theoretically precipitated according to the above figures, Eighty grains of crystals of the double magnesium nitrates were weighed out and dissolved in 2 liters of a 5 U - 5 - NH 4 NO 3 solution. Twenty-six cc. of NHqOH (sp. gr. .90) were added for each precipitation. This amount was calculated from the above equation. The lanthanum double magnesium nitrate tended to remain in solution while the praseodymium double magnesium nitrate was precipitated as the hydroxide. The precipitates were dissolved in HC1 and the colors noted. Fraction Color 1 Green 3 « 4 Faintly green. 5 Very " " The material left in solution was precipitated as the oxalate, ignited and dissolved in HC1. No green color was visible and the absorption spectrum showed the absence of praseodymium. THF PREPARATION OF ANHYDROUS LaCl 3 There have been a good many methods proposed for the preparation of the anhydrous chlorides of the cerium group of rare earths. Hirsch has tried out a number of the methods and found 7 only one of these successful'. Consequently, this method, namely, the heating of the hydrated chlorides in dry HC1 gas, wa 3 studied with the point in view of making improvements in the apparatus or devising an entirely different form of dehydrating apparatus. Since the chloride crystallizes with 3-? molecules of water^~, it was found necessary to heat very cautiously until the monohydrate was formed and then the final heating could be carried . . * . . . . . ' . .. | '• | - 6 - out at a higher temperature and without much care. If the initial heating were carried out at tec high a. temperature, the basic chloride was easily formed and the material would not fuse to a clear melt. Hermann states that hydrated lanthanum chloride loses both HgO and HC1 when strongly heated and forms the basic chloride 11 of the composition: 2LaClg. SLagOg . The chief difficulty with the method of Hirsch was the time required for the conversion of the nitrates to chlorides. The following method was found to be more rapid and convenient. Since the pure material used consisted of the double magnesium nitrates of lanthanum, it was necessary to remove the magnesium. To the water solution of the nitrates was added a sufficient amount of NH^Cl to prevent the precipit at ion of Mg(OH)g. It was determined that sufficient NH^Cl should be added until the amount was equal to appr oxirnately one-half the theoretical amount of NH^OH needed to insure complete precipitation. It was found necessary to repeat the precipitation 6 times, adding the required amount of NH^Ol each time and washing the precipitate by decanta- tion several times with water. The filtrate from the last precipi- tation showed a trace of magnesium upon the addition of UagHPOq. However, a small portion of the precipitate was dissolved in HC1 and a large excess of NH^Cl and NH^OH added to precipitate the lan- thanum. Magnesium was 3hown to be absent when N agHPO 4 was added to the filtrate. In separating magnesium from lanthanum in this way, an appreciable amount of lanthanum material is lost. mis is probably due to the reversible reaction which has been discussed above under the method of Prandtl and Rauch enberger . Other workers . . ' . . . . 1 m i 7 in this laboratory have since found that magnesium and lanthanum may be completely separated with two precipitations of the rare earth oxalate in dilute nitric acid solution with a minimum less of lanthanum material. The balk of the material was then dissolved in dilute HC1 and evaporated down as far as possible cn the steam bath. Heat- ing was continued with a ga.s flame until a small amount of the material which was removed and placed on a marble slab solidified to a moderately hard mas 3 . The rest of the material was then pour- ed out and allowed to cool. The marble slab was previously par- affined by dissolving paraffine in ether and pouring the solution over the marble. At first, paraffine was simply rubbed on, but difficulty was experienced in the sticking of the solidified mater- ial to the slab. It 3eems that the solution containing the par- affine penetrates the pore3 in the marble, preventing sticking. No basic chloride was formed, although it was found if the heating were carried too far, this difficulty would arise. The mass was then ground as finely as possible and placed in a drying oven at ?G°-8C° for several days. Under no circumstances was it possible 0 to raise the temperature above 80 ^without the basic salt being formed. It was thought that if dried air were circulated above the material, more rapid drying could be obtained. However, basic chloride was formed in all cases and the conclusion was reached that it is impossible to raise the temperature above 80°C in the presence of air without basic salt being formed. The chlorides were then further dried in an atmosphere of dry HC1 gas. The waste ga3 was passed into a bottle in which a . . . . . * i - 8 - small jet cf water was constantly being sprayed. The excess water after dissolving the HC1 passed out of the bottom of the bottle. The chlorides were heated in the following manner. Two electric furnaces 18" long, 8" outside diameter, si" inside diameter, which were constructed by Dr. H. C. Xremers, were placed in series. A pyrex glass tube 3" in diameter was placed in and through the furnaces sc that about 8" of the tube extended from one end of each of the furnaces. When the first runs were carried out, the chloride was placed directly in the tube and the furnaces connected in 3erie3 with the electric current. In drying the material by raising the temperature gradually, several tubes broke for some unknown reason. The material was then placed in a smaller tube of lj" in diameter and this tube and contents placed inside the larger tube. No further difficulty was experienced with broken tubes. In order to save time, the furnaces were kept at different temperatures oy connecting them to different sources of electric current. It was found that if the material were kept at a temperature of 125°-150 c for 7-3 hours, the temperature could be raised rapidly to 3CC c without basic chloride being formed. Con- sequently, the furnaces were kept a.t these two temperatures. The tube containing the material was placed in the cooler furnace for the required length of time and then pushed forward into the hotter furnace where the dehydration was completed in 2 or 3 hours. In this connection it might be mentioned that a final temperature of at least 3C0°C was found to be necessary to drive off all traces of water. If a small amount of basic chloride were present before the material was placed in the furnace, the HC1 gas reconverted it * . . ■ . - . / - 9 - to the normal chloride. After each electrolytic ru.n, the undecomposed material was recovered. The melt was dissolved in dilute KC1 and filtered. Oxalic acid was added to the acid solution and the lanthanum oxa- late precipitate washed several times by decantation. The oxalate was calcined in an electric muffle at about ?OC°C, and the oxide dissolved in dilute HC1. The anhydrous chloride was again ob- tained as described above. . . . . . ■ - 10 - FACTORS IN ELECTROLYSIS There are numerous factors which enter into the electrolysis of the fused anhydrous chlorides and upon which the quantity of metal produced is dependent. The Cell The first in importance is concerned with the cell, the material composing it, the size, and shape. 6 Mathmann used a copper cell hut this type was not considered because of the difficulty in constructing it. The choice of material was limited by the fact that the rare earth- metals alloy more or les3 easily with other metals. In the case of carbon or graphite, carbides are formed and in the case of iron, alloys of iron are formed. Since the corrosion of a graphite cell is stated to be less than if; of the corrosion of a carbon cell 12 graphite was used instead of carbon . The cell should be sufficiently large so as to be un- affected by slight changes in external conditions but small enough to conserve material. The most suitable size which met these re- quirements wa,s found to be a cell whose inside diameter was about 2 inches and about 4-5 inches in height. A cylindrical shaped cell is more efficient than a square shaped cell because of the more uniform heating. Best re- sults are obtained when the inside of the cell tapers to the bottom. In this way, the bottom tends to become hotter than it otherwise would, which is very necessary in order tc obtain a regulus of metal r . ■■ . : . .... . 7 . . - 11 - Electrodes The electrodes come next into consideration. The cell itself may act as the cathode or an insulated cathode may project upward through the cell. The cathode should be sufficient- ly small so that a large quantity of heat i3 produced within a small area, as a cell of this design is used with that end in view. The anode may be composed of either carbon or graphite. Carbon is probably the least desirable of the two materials be- cause the greater resistance produces excessive heating. Further- 13 more, car con is more easily attacked by the chlorine , thereby introducing carbon into the bath. For these reasons, graphite' anodes were used in the later experiments. The anode should be sufficiently large so as to obtain a reasonable current density. However, the anode should not be 3C large that electrolysis takes place between the walls of the cell and the anode rather than from the bottom of the cell and the anode. Also, the larger the anode, the greater the current density required to supply sufficient heat to keep the bath molten. In addition, chlorine i3 more easily evolved with a smaller anode. However, the use of a very small anode i3 limited by the fact that excessive heating of the anode takes place, thereby aiding the re- action between the liberated metal and the anode forming a carbide. The ratio of the diameter of the cell to the diameter of the anode as 4 is to 1-2 was found the most suitable. Composition of Electrolyte In the choice of materials to compose the electrolyte. - 12 - the melting point and specific gravity of various mixtures should he taken into consideration as well as the probable reaction of the melt on the metal. The specific gravity of the mixture of fused salts was approximately 3, while that of the metal i3 3.15, The difference between the two specific gravities is sufficient to allow the liberated metal to fall to the bottom of the cell. The melting point of lanthanum i3 claimed to be 810° w while that is the melt was about 300°. Sodium chloride was used to the extent of about 15 $ of the total amount of rare earth chloride added. The conductivity 13 is relatively high, thereby raising the temperature of the bath . Even though there is a possibility of double chlorides of sodium and lanthanum being formed, sodium chloride is used because it in- creases the current efficiency by reducing metal fog formation and vaporization of the lanthanum chloride and metal. However, when used in large amounts, sodium chloride actually reduces the effi- ciency. Oettel found in the electrolysis of magnesium chloride, 14 that powder formation was obviated by the use of calcium fluoride . His explanation was that the surface tension effect and the dis- solving of traces of oxide from the surface of the globules aided the powdered metal to coalesce. The solubility of metallic alum- 15 inum in the melt is increased by the addition of sodium fluoride and because the same effect probably occurs to a less or greater extent in the electrolysis of lanthanum chloride, the amount of potassium fluoride added should be as am all as possible. . . . - J . . . - 13 - Radi at ion Several runs "became viscous shortly after starting the electrolysis due to excessive radiation even though the cell was imbedded in silocel. Consequently, in the later runs an external heating element was used to obtain a finer control of the temperature. Temperature For economical production, the temperature in the neighborhood of the cathode 3hould just exceed the melting point of the metal and the rest of the electrolyte should be as much as possible below this temperature but above the point of fusion of the electrolyte. Faraday’s law is valid for the electrolysis of fused salts -and hence the current efficiency may be calculated from the ampere hours and quantity of metal formed. Causes which lower the current efficiency are far more active at higher temper- atures than at lower temperatures. In the electrolysis of fused lead chloride and also fused caustic soda, no metal is obtained if the temperature is high Furthermore, a low temperature allows a solid layer of salt to form on the walls of the cell, protecting the cell from corrosion. Amperage The amperage should be sufficiently high to supply heat to the melt bat at the same time should be low enough to prevent metal fog formation. Between 30 and 50 amperes were used in the mo3t successful runs. . ' ♦ . . - 14 - Decomposition Voltage The decomposition voltage depends upon the nature of the electrolyte, the nature of the electrodes, and the temperature. The voltage necessary for decomposition diminishes as the tempera- ture rises, due to the greater tendency of LaClj to dissociate. From the point of view of voltage alone, it would be advisable to use a high voltage out this is more than neutralized by increased wear and tear of the apparatus and by the heat expenditure necessary to compensate for radiation losses. At the same time, the current efficiency is decreased. *: • ' ' ’ ' ' • . < - 15 - ELECTROLYSIS OF THE FUSED CHLORIDES The chief difficulties involved in the electrolysis were : A. The bath ’'freezing" or becoming thick, thereby producing metallic conduction of the bath; B. Formation of carbide; C. Presence of "anode effect" which lowers the currect effi- ciency; D. Loss of metal in other ways than the formation of carbide. All of the above difficulties were studied in the hope of finding the cause 3 and the proper remedies. A. Excessive radiation caused the bath to "freeze" very easily. This could not be obviated even by well insulating the cell with silocel. It was not deemed advisable to use a larger anode for the reasons stated under a discussion of the electrodes. Consequently, heating elements were made to fit each cell. The elements were constructed according to directions given by Dr. H. 1 7 C. Kremers and proved very suitable. Unless potassium fluoride is present, the addition of a large amount of basic chloride tends to make the bath viscous, thus preventing the easy evolution of chlorine gas. However, the normal anhydrous chloride was readily obtained, and ths chloride added to the bath contained little, if any, basic chloride. The formation of a higher melting salt such a3 the oxide or carbide necessitates a higher temperature in order to keep the bath molten. The oxide is dissolved by the potassium -15- fluoride "out the carbide is not 3c easily removed. In the runs where the hath became viscous because of the formation of carbide, the electrolysis had to be stopped. A small amount of barium chloride increased the resis- tance of the bath and kept the electrolyte well fused. The conductivity of fused salts increases considerably with rise of temperature. Hence, the conductivity of the melt may be increased by temporarily raising the temperature of the external unit and then allowing the Joule heating effect to maintain the temperature. B. The formation of carbide was aided materially by the deterioration of the graphite anode due to a high current density. o 15 Aluminum and carbon form the carbide at 1000 C Hence, it is reasonable to suppose that a high temperature favors the formation of lanthanum carbide. A large quantity of carbide was formed when a graphite cell was U3ed. It was found impossible to prevent the formation of carbide with such a cell and in the later runs, an iron cell was used. C. "Anode effect", that is, sparking at the anode, is undesirable because it results in a low current efficiency and a disintegration of the anode. It is probably due to the electrode becoming covered with a film cf chlorine gas through which the current can only pass as an arc. This film may be removed by stir- ring or raising the anode from the melt for a moment. The removal may also be accomplished by reversing the current for a moment or « . - 17 by increasing the temperature at constant current density, or in other words, by increasing the current through the external heat- ing unit. A high current density causes rapid electrolysis attended by the evolution of a large amount of chlorine. The "anode effect" was more noticeable at the beginning of the elec- trolysis when a copious evolution of gas was taking place. It is estimated that the anode effect is likely to occur when the current O density exceeds 4-5 amps./cmf in the case of hard carbon and 7-8 3 IS amps./c ml in the case of graphite J . Since NaCl has a smaller conductance than LaCl^, the current density ma 3 r be lowered by the addition of NaCl, thereby preventing the "anode effect". If the voltage exceeded 8-10 volts the "anode effect" made its appearance. In all of the runs, the voltage seldom ex- ceeded 7 volt 3. D. Even after the metal is formed, it may become dis- sipated in several ways. Volatilization may occur if the temperature is too high and the proper procedure in this case is to lower the voltage. Metal fog or the distribution of finely powdered metal throughout the melt is a source of considerable annoyance. In the case of the electrolysis of caustic soda, the yield of metal at a temperature above 535° was practically zero due to the increased 19 diffu 3 ivity of the metal in the electrolyte'". Metal in a finely divided state is produced also by a high current density. The addition of a neutral salt such as NaCl prevents, largely, metal fog formation. It wa 3 found advisable to raise the temperature - 18 - of the cell near the end of the ran' by raising; the temperature of the heating element and by ’’shorting” the cell every few minutes. At the same time the temperature was raised, the melt was stirred with a tungsten rod so as to coagulate the finel 3 r disseminated metal. The use of potassium fluoride in obtaining a regulus of metal has been stated above. Oxidation of the metal by the air may form another source of loss. This difficulty may be remedied by keeping the cell partially covered during electrolysis. The metal may react with the melt forming sub-salts and other compounds. If perfectly anhydrous LaClg is not used, the introduction cf water causes a rapid reaction to take place according to the equation: SLa+SHgO - 3La(0Hh-h3H 2 . When a graphite cell was used, a considerable amount of metal united with the cell forming a carbide; in fact, some runs produced carbide only and no metal. In the case cf an iron cell, there is a tendency for FeClg to form. The current efficiency is lowered because of the alternate reduction and oxidation of the FeClg at the cathode and anode respectively. In fact, it is stated that less than 0.1$ FeClg reduces the current efficiency more than 30^?° The formation cf FaClg i3 largely prevented by allowing a solid layer cf salt to form on the inside of the cell. The metal may react with the chlorine which is liber- ated at the anode. Allowing the chlorine to escape rapidly by frequent stirring inhibits this reaction. . - . . . . . . . ■ . . - 19 EXPEEIMEN TAL RE SUL TS In the first few experiments, the cerium group chlor- ides were used to work out a general procedure without running the risk of losing lanthanum material, a3 these salts are more easily prepared than lanthanum salts. The anhydrous chlorides were pre- pared in the same way as the anhydrous lanthanum chloride. In cases where the finely divided metal was obtained, it was found that the metal was in a very impure form. Attempts to fuse it under UaCl resulted in the oxide. Other attempts were made to obtain it in a pure state so that it might be pressed into a rod and the particles sintered together as in the case of tungsten. The powder was mixed with anhydrous bromofcrm in hopes that the bromoform which has a specific gravity between that of the metal and carbon would effect a separation, but this method failed as the particles of carbon held too tenaciously to the metal. This explains the effort made to obtain the metal in a pure coherent mass. In all the runs, graphite anodes were used of various size3. 1. A graphite crucible was used, the average diameter / being S n . The diameter of the anode in this case was 5/6”. The electrolyte was composed of ITaCl, KF, and cerium chloride. A regulus of metal weighing 5 grains was obtained, together with a large amount cf carbide and finely divided metal. The melt was dissolved from the crucible with cold water, the water decomposing the carbide and having little effect on the metal. Hydrogen wa3 evolved upon the addition of acid to the powder and the residue consisted mainly of powdered graphite. The current was 7 volts . , * 1 . . - 30 - and 20 amperes for 3i hours . The temperature of the bath was a cherry red and an auxiliary heating element maintained this temper- ature. 3. An attempt was made to duplicate this run by re- producing the same conditions; however, it resulted in finely divided metal being formed and also metallic sodium, which upon rising to the surface burned with a yellow flame, sometimes with explosive violence. It was found that upon lowering the voltage, the formation of sodium and the "anode effect" ceased, 3. Because of the difficulty in maintaining a suffi- ciently high temperature in the previous rim, a -J" anode was used in this case. Instead of KF, KOI was used as it was thought that the lowered specific gravity of the bath and the lowered tempera- ture (sp. gr. KC1 = 1.984; KF = 2.481; — rn.p. KC1 * 773°; KF = 830°) would result in the aivided metal settling rapidly to the bottom of the cell and forming a coherent mass. However, the re- sults obtained were similar to those of the previous run. -4. In this run an anode of diameter was used ’’cut only powdered metal and carbide were obtained. The voltage and the amperage were the same a3 in the preceding experiments, but the electrolysis had to be stopped at the end of 2i hours because of the "freezing" cf the bath. 5. It was thought that the formation of carbide might be obviated by coating the inside of the cell to within about of the bottom with alundum cement. The anode was in diameter, the voltage 14 and the amperage 10, A very small amount cf KF was used in this case and consequently after the run, the alundum . ' •' • - r. ■ ■ . w 1 • • v/ y . . ; ' *’ ■ . ; - 31 - cement lining was found to be fairly intact. LaClj was used in- stead of C 3 CI 3 and carbide and no coherent metal were obtained. 8 , At this point it was decided to abandon the idea of carrying on the electrolysis in a graphite cell because of the formation of large amounts of carbide. It was decided to use a soft steel crucible, 4" in depth and 3” in diameter. The cell formed the cathode and the anode was a 7/8” graphite rod. In order to obtain a higher temperature, 0 , greater conductance was needed and so only the chlorides and oxides of cerium were added. It was • 1 thought that the oxide would oxidize any free carbon present in the bath. The voltage was 7 and the amperage 300. At the end of 3 hours, the electrolysis was stopped as the high current density produced a hole in the crucible allowing the melt to flow out into the external heating unit. 7. A new type of cell wa 3 then devised. A 4” length of a 3" pipe with a -J” reduced coupling screwed into the end formed the cell. A tungsten rod of 3/8” diameter projected upward for a distance of about 1” through the bottom of the cell and was well insulated with asbestos string. The rod projected outside of the bottom of the cell for about 3” and in order to protect it from oxidation was brazed with copper. Chloride and oxide of lanthanum were used and an amperage of between 100-150 was obtained at 8 volt 3 , Very little carbide was formed and the metal obtained was in a finely divided state. In this run, an external heating ele- ment was not used because the high conductivity cf the bath kept the temperature sufficiently high. 8 . Since the metal fog formation was evidently due to . - 33 - the high temperature 3nd high current density, and in order to re- duce vaporization of the chloride, it was decided to U3Q an elec- trolyte consisting of NaCl, KF and LaClg. No external heat was applied and difficulty was experienced in keeping the hath molten. It was necessary to "short" the cell frequently 30 as to keep the bath fluid. This run gave the first indication of success and aboul 3 grams of coherent metal were obtained lying close to the cathode and showing that the high temperature of the cathode was necessary to melt and coagulate the metal. 30-50 amperes and 7-3 volts were 1 used. 9. In order to be more conserving of material, a smaller cell whose diameter was 1 -J” was constructed similar to the cell used in the previous experiment. A heating element was made to fit this cell. Because of the success obtained, this run will be described in some detail. A 5/8 " anode was U 3 ed and the elec- trolyte consisted of: 150 3 . LaClj, 30 g, KF, and 35 g, NaCl, A small amount of NaCl and KF was melted by "shorting" the cell with a i" short carbon rod. When the temperature was sufficiently high to keep the bath molten, the plug was removed and the electrolysis begun. The electrolysis was carried on for 4 hours at ? volts and 30-40 amperes. During the last \ hour of electrolysis the temper- ature was raised by adding BaCl^ in small amounts and raising the voltage. The melt was stirred from time to time with a tungsten rod. 12.3 grams of metal in coherent globules were obtained, the largest globule weighing 3.2 grams. This weight of metal repre- sented a current efficiency of about 6 per cent, Upon analysis, 0.77 per cent of iron was found to be present and not a trace of tungsten. - 33 - 10. It was than decided to carry out an electrolysis in an iron cell. The cell was identical to that containing the insulated tungsten cathode except for the fact that the iron cell in this case was the cathode. The anode was 5/8” and the elec- trolyte was composed of LaCl^, KF and NaCl as before. Thirty amperes at 5 volts were used. The electrolysis was carried on for 4 hours and 9.1 grams of metal in coherent particles were obtained, the largest particle weighing 3 grams. The metal showed about 15$ iron upon analysis. 11. Because of the contamination of the metal with iron when an iron cell was used, it was decided to attempt the use of a graphite cell again. The cell was identical to that used in the first run 'out this run yielded better results. 21.4 grams of metal in coherent particles were obtained, the largest particle weighing 6.3 grams. This represented a current efficiency of 10 per cent. The electrolyte wa3 composed of 335 grams of LaCl^, 50 grams of KF and 40 grams of NaCl. The metal thus obtained is in a high state of purity although the efficiency cannot be made to equal the efficiency which could be obtained with an iron cell, due to the formation of carbide. 12 . In hopes of raising the current efficiency, another run was made using the same graphite cell and a 3/4” anode. The electrolyte consisted of 335 grams LaCl^ 30 grams KF, and 30 grams NaCl. This run was very successful and resulted in the obtaining of 68 .4 grams oi metal, most of tne metal .cin~ in three large pieces and the largest particle weighing 33 grams* The electrolysis was carried on for 3 hours at 50 amperes and 7-8 — 3«3a— volts. The amperage represented a lowering of about 30 amperes from that of the previous run. At the end of the run, the tempera- j ture of the melt was raised by "shorting" the cell for intervals of a minute or two. Very little carbide was formed and the current efficiency was 37.2 percent. The increase in efficiency over the | previous run was probaoly due to the use of smaller amounts of KF and NaCl and the lowered current density. . . . - 34 - SUMMARY . 1, The new method of Prandtl and Rauchenberger in the separation of lanthanum from neodymium and praseodymium was tried with encouraging results, 2, A 3tudy was made of the various methods of obtain- ing anhydrous LaCl^ and the dehydration of the partially dried LaClg in a pyrex glass tube in a current of dry HOI gas met ’with success, 3, An exhaustive study was made of the electrolysis of fused anhydrous LaOl^ and it was found that: A. Electrolysis in an iron cell containing an insulated tungsten cathode produced metal of a fair degree of purity; B. Then an iron cell acting as a cathode wa3 used, metal con- taminated with iron resulted; C. Metal in a high state of purity may be obtained by elec- trolysis in a graphite cell. , . , . . . 25 BIBLIOGRAPHY 1. J. F. Spencer, The? Metals of the Rare Earths, (1919). 2. Mo Sander, Pogg. Ann., 46 . 64S (1339); i old. , 47 . 207, (1839); Corapt. rend., 3, 358-57, (1839). 3. Demarcay, Corapt. Rend., 130, 1019-33 (1900); Brauner and Pavlicek, Proc. Chem. Soc., 17 . 63-64 (1901). Brauner and Pavlicek, Trans. Chem. Soc., j31, 1343-39 (1903). , Demarcay, Corapt. rend., 130 . 1185-1183 (1900). 4. 'Jrbain and Lacorabe, Corapt. rend., 137 . 793-24 (1903); ibid., 133 . 84-85 (1904). Brauner, Proc. Chem. Soc., 14 . 71-72 (1893), 5. Hillabrand and Norton, Pogg. Ann., 158 . 486 (1375). 6. Mathmann and Kraft, Lieb. Ann., 325 . 381-78 (1902). 7. Alcan Hirsch, Trans. Am. Electr. Soc., 30 . 57-104 (1911). 8. Drossbach, Ber, 35 . 3826-31 (1303). 9. Prandtl and Rauchenberger, Zeit. fflr Anorg. Chemie, 1 30 . ISO- 128 (1931). 10. Ley, Zeit. physikal. Chemie, _3C, 193-357 (1899). 11. Hermann, J. pr. Chem. 82, 385-408 (1861). 12. Keramerer, Trans. Amer. Electr. Soc., 9, 117 (1308). 13. Arndt, Zeit. Elektroch. 12, 337 (1908). 14. Osttel, Dissertation, Dresden (1908). 15. Fedot is ff and II jin sky, J.S.C.I., 337 (1913). 16. Trans. Amer. Electr. Soc., 19, 167-188 (1911) Discussion. 17. H.C.Kremers, Jour.Ind. and Eng. Chem. , 13 . 561 (1921). 13. Allmand, A.J., The Principles of Applied Electrochemistry, 134 (1220). - 33 - IS. Rideal, E.K., Industrial Electrometallurgy, 110 (1918), 30, Appel berg, Zeit. Anorg. Chew . , 36, 36 (1903).