G. E. Boyd Oak Ridge National Loboratory
Oak
Ridge, Tennessee
Technetium and Promethium
T h e synthetic elements of nuclear charge 43 and 61, now known as technetium (Tc) and promethium (Pm), respectively, occupy a special place in the history of the discovery of the elements. Technetium was the first artificial element to he synthesized (I), whereas promethium was identified chemically for the first time during war-time researches on the rareearth uranium fission products (2). These elements, which are the only elements lighter than uranium which have not yet been found on the earth's crust, are, of course, quite different chemically. This difference was anticipated as early as 1869 in Mendeleev's Periodic Chart of the Elements (3) wherein ekamanganese (Tc) and dwi-manganese (Re) appear in the seventh subgroup together with manganese, while the then known rare earths were placed in the third and fourth groups. Because of the great similarities in chemical properties betweenzirconium and hafnium, niobium and tantalum, and molybdenum and tungsten, there was some reason to believe that the properties of eka- and dwi-manganese, likewise, would resemble one another closely. It was not unexpected, then, that when the Noddacks announced the discovery of rhenium in 1925 they also claimed to have found element 43 in the same minerals (4).I n spite of a number of reports by the Noddacks on the isolation of element 43 in the period from 1925 t o 1927, however, their observations were not confirmed by other investigators and their claim was not generally accepted. I n contrast, small quantities (i.e., 120 mg) of rhenium were separated in 1927 by these workers and in 1928 they isolated the first gram. The number of rare-earth elements has proved to be much larger than was suspected in Mendeleev's time, and they could not be accommodated logically in his Periodic Chart of the Elements. The position of element 61, accordingly, remained obscure until Mosley derived his rules for determining atomic numbers (Z). It was then realized that one rare earth, that with Z = 61, lying between neodymium and samarium, remained undiscovered. I n 1926, Harris and Hopkins (5) separated a rare-earth concentrate from monazite sands which possessed the properties they believed to be characteristic of element 61, and on this basis they announced the discovery of the element. At the same time, the isolation of element 61 was also claimed by Rolla and Fernandes (6). Again, partly because of the extreme difficulty in separating the rare earths cleanly from one another, the work of Harris and Hopkins was Presented as part of the Symposium on the New Elements before the Division of Chemical Education at the 133rd Meeting of the American Chemical Society, San Francisco, April, 1958. Based on work ~erformedunder the auspices of the U. S. Atomic Energy Commission.
not confirmed. I n 1945 the question of the natural occurrence of element 61 was reviewed by Yost, Russell, and Garner (7), who have stated "The evidence for the existence in nature of element 61 is somewhat circumstantial rather than conclusive, and the isolation of this element cannot be regarded as having been effected." The date of the beginning of a knowledge of the chemistry of element 43 based on experiment is now regarded as coinciding with that of the first reports by Perrier and Segr6 in 1937 and 1939 (8). The discovery of element 43 was a direct consequence of the invention of the cyclotron. Following the successful operation of the Berkeley cyclotron in 1935, it became possible for the first time to transmute molybdenum atoms into element 43 by bombarding molybdenum metal with energetic protons or deuterons. Observations on the chemical behavior of the element were made with quantities not greatly exceeding 10-l2 g, that is to say, with unweighable amounts. The properties observed were unlike those of any other element, although they resembled those of rhenium fairly closely as had been anticipated. I n 1947, Perrier and Segr6 proposed that element 43 be named "technetium" (symbol Tc) after the Greek word " ~ e x v ~ 7s"o (signifying "artificial") in keeping with the mode of production of the element. This claim of the discovery of element 43 and the proposed name has been accepted officially (3). It was soon recognized that element 61, like terhnetium, might also be produced by a nuclear transmutation reaction. In 1941, Law, Pool, Kurbatov, and Quill (10) working a t the Ohio State University produced several new activities which presumably were those of element 61 by irradiating neodymium and praseodymium with neutrons, deuterons, and alpha particles, respectively. The formation of these radioactivities was confirmed in 1942 by Wu and Segr6 (11) and by Bothe (18). Chemical proof of the production of element 61 was lacking in all this work, however, primarily because of the extreme difficulty a t that time in effecting a separation of the rare earths from each other. It was not until in researches on the fission-product rare earths in 1945 that Marinsky, Glendenin, and Coryell (IS) supplied the first positive chemical identification of element 61 using the newly developed techniques of ion-exchange chromatography. Their work consisted in first establishing the rare-earth character of an unidentified fission-product activity, and then in demonstrating that this tracer preceded Nd in the chromatographic spectrum for the elution of the rare earths from a cation exchanger. An additional and stronger argument was supplied by the data (14) given in Figure 1 wherein it is seen that element 61 is bracketed in the elution sequence by Sm and Nd. The name "proVolume 36, Number
I, January 1959
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. E
1o4
u
f ro3
-
2
+ ro2 r O t ~1500 ~ ~ 2000
2500 3000
3500 4000 4500 5000 TIME irninl
Figure 1. Elution sequence in the ion-exchange chromatographic reparation of buffer elvonfr a t 100°C 1141.
methium" (symbol Pm) was proposed in 1948 by Marinsky and Glendenin (2) for element 61, aud this has been accepted officially (9). Searches for technetium (15-18) and promethium (19) in terrestrial materials have continued in the post-war period. The reported occurrence in 1951 (20) of several lines of Tc-I1 in the spectrum of the sun, and particularly the dramatic discovery by P. W. Merrill (21) of many lines of Tc-I, in absorption, in the spectra from S-type (Fig. 2) and more recently (22) in N-type stars greatly stimulated these searches which have used powerful new and sensitive methods. The results to date have indicated that the concentration of primordial technetium on the earth's crust must be exceedingly low. ks yet there is no independently confirmed report of its occurrence. The evidence for technetium in the sun has been re-examined (39, 241, and i t has been concluded that the case for its existence here is not proved. One search for promethium among rare-earth materials has been reported (19). This, too, yieldedanegative result, which, when coupled with the fact that in recent years very large quantities of rare earths have been processed without any indications of this element suggests that primordial promethium is also missing from the earth's surface. The discovery of technetium in a number of stars of spectral classes S, M, and N has been of great significance. Its presence has led to new theories of the production of heavy elements by neutron capture in the stellar interior (24, 25) or by nuclear transmutations caused by magnetically accelerated charged particles a t the stellar surface (26).
are emittedinits decaymake it particularly convenient to use. It may he prepared in good yield by proton bombardment of molybdenum metal from which it is easily separated. The metastable 90 d TcS7" activity has been of interest because it has been shown to decay to a ground state, Tcg", 5500 6000 6500 7000 of extremely long half life 0.4 (90). A value of 2.6 t h e cerium earths uring citrate x 106 years for its decay by orbital electron capture (K-capture) has been determined recently (91). Tc9" is therefore the longestlived technetium isotope known. The 6.0 h Tc99" first studied by Seaborg and Segr6 in 1939 (92) occupies an important place in the development of the nuclear chemistry of technetium. These investigators showed that this isomeric activity decayed with the emission of a line of electrons and Tc K, X-rays to ground state, Tc9", whose radiations were undetected. It was concluded that Tcgg' possessed a half life greater than 40 years. In 1940, following the discovery of uranium fission, Segrt5 and Wu (99) found 6.0 h Tcg9" among the fission products; hence, this isotope was the first of technetium to have been thus observed. In 194647 the radiations of the longlived Tcg99were finally detected in technetium fractions isolated from the fission products (94, 95) and from molybdenum metal irradiated for one year with neutrons in a nuclear reactor (96). Painstaking specific activity measurements using weighable amounts of technetium isolated from the fission products have yielded a half life of 2.12 X lo6 years for the beta decay of Tcsg9
*
Nuclear Chemistry of Technetium and Promethium
All of our knowledge of the properties of technetium and promethium has been gained using their unstable isotopes, so that i t may he of interest to review briefly some of the information available on the nuclear chemistry of these two elements. Technetium
The oldest known technetium isotopes are, of course, those of 60- and 90-day half life used by Perrier and Segrt5 in their chemical studies. Researches performed since 1946 have shown that these periods are associated with mass numbers 95 and 97, respectively (27, 28,29). The most useful isotope for tracer work with tecbnetium unquestionably is the 60 d Tcg6'. Its relatively long half life and the fact that energetic gamma rays
LINES OF T c I IN THE SPECTRUM OF R ANDROMEDAE MOUNT WILSON OBSERVATORY
Figure 2.
Plate;
Lines of Tc-1 in t h e spectrum of R Andrornedoe.
(57). The recent development of the macrochemistry of technetium hasbeen based on the use of this isotope which has been isolated in gram quantities. Finally, the unique featuresof thedecay of 6.0 h Tcggm have made possible another test as t o whether the half life of a nucleus can be altered either by the state of the chemical bindingoftheatomsinwhich it iscontained,orbylowtemperatures. Since the classic experiments of Rutherford, it had been assumed that nuclear properties could not he altered by a change in &aal environment. Extremely precise half-life measurements (58), however, have now revealed that decay relative to its metal becomes more rapid when 6.0 h TcQ9" is combined into KTcOa or Tc2S7. The most recent and possibly the last long-lived technetium isotope to be Figure 3. Flow plan for the isolation of technetium a n d other flrsion-product ocid-insoluble sulfides from discovered is Tcg8. This pile-irradiated uranium metal 1441. activity has been produced by prolonged and intense irradiations of molybdenum metal with protons (59) or levels of radioactivity also involved, such operations by a long irradiation of ruthenium with neutrons in a must be conducted using remote handling techniques high intensity neutron reactor (40). A preliminary and extensive gamma-ray shielding as afforded by hot half life of approximately 2 X lo6 years has been cells. I n the absence of such facilities it is possible to estimated for TcsB. It may be concluded that the exproduce and isolate small amounts of technetium and istence of three very long-lived technetium isotopes is promethium by prolonged neutrou irradiations of now well established. However, none possesses a highly purified molybdenum and neodymium, reshalf life sufficiently long to allow technetium to occur pectively, in a chain reacting pile. After a time suffinaturally. cient for the complete decay of the 2.8 d Mog9or 11.1 d Nd'" also formed, conventional laboratory bench-top Promethium chemical operations may be employed to separate the technetium or promethium. Two reports (56, 43) have Four long-lived isotopes of promethium have been appeared describing the separation of fractional millicharacterized (41), but none shows a half life of greater gram quantities of Tcggofrom Mo. than 18 years. Thus, by comparison with technetium, The concentration of technetium produced in natural promethium is a highly transitory element. The most uranium metal irradiated in the identical neutron flux generally useful isotope of promethium is the 2.64 y is approximately six times larger than that obtaiued in l'rn14' which occurs in good yield among the uranium the irradiation of an equal volume of molybdenum metal fission products. Other long-lived isotopes of promefor an equal period. Accordingly, in 1948 Parker, thium of possible interest are 270 d Pm143,300 d Pm'44, Reed, and Ruch (44) separated milligrams of fissiou18 y Pm145,1 y Pml", 42 d PI^"^, and 5.3 d Pml". product technetium from several kilograms of uranium The last activity may be produced by neutron capture metal irradiated in the ORNL Graphite Moderated in Pm'"', and was observed soon after the isolation of Neutron Reactor (Fig. 3). After dissolution of the milligram quantities of the latter in 1948 (48). It uranium in hydrochloric acid and oxidation of the decays with energetic gamma rays and is useful as a uranous chloride to uranyl chloride with bromine water, promethium tracer. the technetium was separated from the solution by The Isolation of Weighable Amounts of Technetium coprecipitating it with platinum sulfide. Subsequently, and Promethium the technetium was separated from the platinum by oxidizing the sulfide with ammoniacal hydrogen perThe best method for obtaining the relatively large oxide, placing the resulting solution in concentrated quantities of technetium needed for chemical and physical researches is to isolate it from uranium fissionsulfuric acid and distilling off the Tc. Reprecipitaproduct mixtures. Because of the extremely high tions were performed until technetium sulfide could be Volume 36, Number I , January 1959
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precipit~ted by itself without the use of "carrier." Sufficient quantities of pure technetium were isolated to permit the X-ray emission spectrum of the element to be recorded for the first time, and to allow preliminary measurements of other physical properties. The amount of promethium recoverable from irradiated uranium is usually considerably less than that of technetium, partly because of the lower fission yield of the former and partly because of losses by decay of the relatively short-lived I'm14' before chemical processing. Nevertheless, milligram quantities of promethium were isolated successfully in 1948 by Parker and Lmtz (45). In this separation the uranium was removed by solvent extraction, and all of the cationic fission products were absorbed from the remaining dilute acid solution onto a cylindrical bed of strong acid-type cation exchanger. The fission products zirconium and niobium were then preferentially removed by elution with a dilute oxalic acid solution. This step was followed by a chromatographic fractionation of the rare earths from one another, using ammonium citrate buffer solutions. The promethium fraction was purified by several additional ion-exchange absorption-elution cycles, and, after concentration by evaporation, Pm(OH)3 was precipitated with 4 M NH40H. Almost all the information on the chemical behavior of promethium now in hand was obtained with the element isolated in this operation. This isolation of weighable quantities of Pm for the first t i e was of importance in establishing the discovery of element 61. Appreciable quantities of technetium and promethium are found, and hence are potentially available in the waste products i e , solvent extraction raffinates) from radiochemical processing plants, as may be seen on inspection of Table 1. The first gram of technetium, in fact, was isolated in 1952 from a "Redox" process waste following the flow diagram shown in Figure 4 (46). Insoluble acid sulfides could not be used to coprecipitate and separate the technetium from these solutions because of the high concentrations of nitrate ion
-r 1 0 0 GALLONS FISSION PRODUCT WASTE ( I gm To) (ACIDIC1
(I) ADD ilqms. HClO, (CARRIER) (21 HEAT
131 @,As Cl (4) W O L AND FILTER
FILTRATE
D &
&As TcO. ,CI04
Sr, atc.
I l l ADD CONC. H2S04
in them. Good use, however, was made of the organic base, tetraphenylarsonium chloride, which forms a slightly soluble precipitate with perchlorate ion added to the waste, and in turn coprecipitates the structurally similar pertechnetate anion. The impure "crude" technetium-containing precipitate was processed (47) by dissolving it in concentrated sulfuric acid and electrolyzing this solution for 24 hours using large bright platinum electrodes. The black solid (TcOJ which was deposited was then purified by distillation with perchloric acid followed by sulfide precipitation, conversion to ammonium pertechnetate and reduction to technetium metal using hydrogen gas. The electrolysis procedure has the disadvantage that the expensive organometallic reagent, tetraphenylarsonium chloride, is destroyed. A simple procedure wherein this reagent is recovered has been developed meanwhile: the "crude" is dissolved in ethyl alcohol and the solution is passed through a bed of the chloride-salt of a strong-base anion exchanger. Pertechnetate ion is strongly absorbed and soluble tetraphenylarsonium chloride is formed which appears in the effluentand may be recovered and purified by recrystallization. Technetium may be eluted quantitatively from the anion exchanger with 2 N perchloric acid and refined additionally as required. Table
I.
Compositions of Typical Metal Recovery Waste Solutions (Based on Analysis) Purex process ...
AKNOdr NH4NOa HdNOa)? HNOJ
...
Cs'" Srao Ru'oe Cd4' Pm"' 6 . 5 mg/liter Small, variable
TcQe Fe, Ni, Cr
Multigram amounts of technetium and promethium are destined to become available in the near future as a consequence of the initiation of operations in the recently constructed Fission Product Recovery Pilot Plant a t the Oak Ridge National Laboratory (48). The design production rates for this plant indicate (Table 2) that approximately 650 g of promethium and 1200 g of technetium will be isolated per year! Promethium is being produced a t a rate of about one gram per month a t the present time, using a process which utilizes solvent extraction to separate the element partially from large quantities of other fission-product rare earths, followed by anion-exchange chromatography to purify the promethium and to remove the small quantities of the difficultly separable americium usually present in process waste solutions (49). Table 2.
Design Production Rates for the ORNL Fission Product Recovery Pilot Plant Production
Cs'='
Flow sheet for edroction of gram amouds of process waste (46).
Figure 4.
6
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Journal of Chemical Educotion
Tc from redox
Sra Ce"' Rulo8 Pml*' T-90
per year
200,000 c u r i e s 240,000 c u r i e s 2,400,000 curies 200,000 curies 625,000 curies 12ke
Precaufions to Be Observed
I n view of probable laboratory experimentation with gram and milligram quantities of technetium and promethium, respectively, within the next few years, some mention should he made of the potential hazards involved. Both synthetic elements decay with relatively long half lives emitting only beta particles of relatively low average energy. Because of its two hundred thousand year half life, the specific activity of fissionproduct technetium is only about 20 microcuries per milligram. The walls of ordinary laboratory glassware, therefore, should give adequate radiation protection. Promethium, in contrast, possesses a specific activity of nearly one curie per milligram, and, although no gamma rays are emitted, appreciable quantities of hremsstrahlung or "white" X-radiation are generated. Moderate thicknesses of glass or plastic, however, are sufficient to allow chemical experimentation with quantities of less than 10 mg. Care must he taken in working with both elements to avoid contaminating the laboratory. This is especially true for measurements with promethium where, it is emphasized, special arrangements must be made for its containment in the event of an accident. Complications may also arise in work with promethium because of the radiation decomposition of the solvents in which it is dissolved, or of the constituents of compounds into which it is formed. Comparatively few reports have appeared describing investigations of the chemical toxicity and metabolic behavior of technetium and promethium. I n experimentation with small animals, it has been found that ingested teohnetium is excreted with extraordinary speed (50). More recently, however, it has been reported (61) that injected technetium is selectively filtered from the blood and concentrated by the thyroid gland. The affinity of the thyroid for teohnetium, ruthenium, and iodine was found to be roughly equal. The deposition of promethium in tissue of the rat has been measured (5f), and some of its metabolic history has been determined (53). The incompleteness of the available evidence on the biological effects of technetium and promethium should be kept in mind in the conduct of laboratory work with these elements. Chemistry of Elemental Technetium
Preparation. Metallic technetium has been prepared by several reduction reactions. I n the first preparation (54) hydrogen gas was passed a t 1100' over Tc& to form a dark sintered mass which was identified as technetium metal by X-ray diffraction. This metal usually contaius variable amounts of sulfur, however, unless the reaction is prolonged a t a high temperature. Alternatively (47), the heptasulfide may be dissolved in ammoniacal hydrogen peroxide and evaporated to dryness to give a mixture of ammonium pertechnetate and ammoninm sulfat,e. This mixture when heated in hydrogen gas a t 500-600' gives an exceptionally pure metallic product. A bright, cathodic deposit of technetium metal on platinum is obtained on the electrolysis of solutions of ammonium pertechnetate in 2 N sulfuric acid solutions containing a trace of fluoride ion (55, 56). Electrolysis of neutral, unbuffered solutions, however, yields a black deposit of Tc02. Physical Properties of Elemental Technetium. The
metal obtained by the hydrogeu reduction of ammonium pertechnetate is a silver-gray spongy mass which tarnishes slowly in moist air. The atomic weight of the element, determined by burning this metal in oxygen to technetium heptoxide and weighing the latter, was 98.8 + 0.1 (47). The directly measured mass spectrometer value is 98.913 (67) which agrees well with a value of 98.911 obtained using the mass spectrometrically determined mass of RuQQ (58) and the beta decay energy of TcQe. The structure of technetium metal (59) is quite similar to that of rhenium metal. Both crystallize in a hexagonal close-packed arrangement with metallic radii for twelve coordination of 1.358 for technetium and 1.373 A for rhenium. These radii may he compared with values (60) of 1.306 or 1.261, 1.386, and 1.336 Afar manganese, molybdenum, and ruthenium, respectively. The calculated density of technetium metal based on the X-ray measurements and an atomic weight of 99 is 11.50 gm/cm3 which value is intermediate betweeu that for molybdenum (10.2) and ruthenium (12.06), and for manganese (7.20) and rhenium (20.53). Electrical resistance measurements on technetium metal over a range of pressures up to 30,000 kg/cm2 give no evidence for a transition in the metallic state, nor do shearing measurements indicate any transition below 60,000 kg/cm2 (61). Preliminary determinations of the melting point of metallic technetium have been conducted (62). A value of 2140 1 20°C was found, which may be compared with values of 1260' for manganese, 3180" for rhenium, 2620" for molybdenum, and 2450" for ruthenium. Technetium metal is like manganese and different from rhenium metal in that its melting point is lower than that of the metal of the next heavier element in its period. Atomic magnetic susceptibility measurements (65) on metallic technetium show the element to he weakly paramagnetic, x = 270 X c g s (Mn, Re, x = 69 X 10-8). x = 527 X The optical emission spectrum of technetium is uniquely characteristic of the element (64, 65) with a few strong lines relatively widely spaced as in the spectra of manganese, molybdenum, and rhenium. The wavelengths and relative intensities of about 2300 lines characteristic of Tc atoms and ions have been determined (66). Twenty-five such lines are observed in the arc and spark spectra between 2200 and 9000 A. Many of these lines are free from ruthenium or rhenium interferences and are therefore useful analytically. The ionization potentials for Tc(g) and for Tc+(g) have been given as 7.28 and 15.26 ev, respectively (67), and the ionization potential for Tc++(g) has been estimated as 31.9 ev (68). Analysis of the data of the first spectrum of Tc shows that in the normal unexcited state the atoms of this element (like Mn atoms) have five d-type and two s-type valence electrons (i.e., 4d55s26Sa,J. In recent years several measurements of the X-ray emission spectrum of technetium have been reported (69-71). The wavelengths of these lines, of course, fall between those for ruthenium and molybdenum, and the most recent measurements (1955) show excellent agreement with calculated values. An estimate of 4.4 volts for the work function for metallic technetium has been published, based upon considerations of the variation of this quantity with Z (72). Measured values for molybdenum, ruthenium, manganese, and rhenium are Volume 36, Number I , January 1959
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4.27, 4.52, 3.95, and 5.1 volts, respectively. Technetium metal, like rhenium but unlike manganese, has been found to become superconducting a t low temperatures (73). The exceptionally high transition temperature (11.2'K) exhibited by technetium has been of interest. Chemical Properties of Elemental Technetium. Metallic technetium dissolves in dilute or concentrated nitric acid, in aqua regia and in concentrated sulfuric acid, but, interestingly, it is not soluble in hydrochloric acid of any strength (54). It is not soluble in ammoniacal hydrogen peroxide, and in this respect contrasts with rhenium metal which does dissolve (47). Metallic technetium, like rhenium, will burn in oxygen to form a volatile oxide (74) with a heat of combustion of 266.1 =t 2.6 kcal/mole to form Tc207(c) a t 298.16"K (75). Chlorine gas reacts slowly or not a t all with technetium (63), whereas rhenium reacts to form a volatile chloride. KO alloys of technetium have been prepared, although there is evidence for the solution of Tc in nickel (38). I n analogy with rhenium, alloys with molybdenum, nickel, cobalt, iron, palladium, and platinum should exist. Xone of the thermodynamic properties of gaseous technetium has been determined experimentally; however, the entropy of the species Tc(g) has been estimated as 43.3 =t 0.1 esu. a t 25" (75). In mass spectrometric studies Tc+ (g) ion has been formed by thermal ionization and by electron bombardment (39). Chemistry of Technetium Compounds
Heptaualent Osidation State. The anhydrous heptoxide of technetium, TczOi,is readily prepared by hurning the metal with oxygen gas a t 500" (74). The compound so formed may he purified by resublimation. At room temperature it is a highly hygroscopic, crystalline, light-yellow compound. The compound is highly soluble in water and also dissolves in dioxane. The measured melting point is 119.5', and the estimated boiling point, 311 i ZO, compared with values for RepO7of 300 and 360°, respectively. Technetium heptoxide thus possesses a much longer liquid range than RelO7, apparently because of the low melting point for Tcz07. At its melting point Tcz07exhibits a vapor pressure of about 1.0 mm which is much higher than that for Re,07 a t the same temperature (76). Vapor pressure measurements on crystalline and melted Tc& have led to an unexpectedly large entropy of fusion (i.e., 42.3 eu, compared with 27.6 eu, for RezOi). The value for Tcz07may not be correct, and, in the absence of a calorimetric determination, the derived heat of fusion (16.6 * 0.5 kcal/mole) must be regarded as provisional. Interestingly, electric conductivity is observed in solid TcnOibut not in the melt, whereas, with RezOr the reverse holds. X-ray diffraction powder patterns have been measured on TclOr; the crystal is one of low symmetry and is not isomorphous with Re207 (77). Magnetic susceptibility measurements (63) show TclOi to be very weakly paramagnetic as might he expected for technetium when it has no d electrons. Technetium heptoxide is stable on heating up to 260'. It shows a strong oxidizing character and is reduced by organic vapors (i.e., stopcock grease) quite readily. Its heat of formation, AH,", has been measured as -266.1 i 2.6 kcal/mole, and, from the estimated entropy value
of 45.8 eu, the free energy of formation, AF,", is -224.1 kcal/mole (77). Technetium heptoxide on dissolving in water forms a colorless solution which upon evaporation yields long, red-black crystals of the anhydrous pertechnetic acid, HTcOn (74). This acid is extremely strong and its concentrated solutions are dark red. Vapor pressures of it,s aqueous solutions have been measured (78). Information on the thermodynamic properties of the crystalline compound is summarized in Table 3. Toble 3.
Compound
Te (c)
Te
(9)
To02 [c) ToOx(e)
Thermodynamic Properties of Technetium and Some of Its Com~oundsot 298.16OK. -AH,(koal/mole) 0.0
1 0 3 7 % 2.0 129.0+5.0
Te,Oi (o) 266.1 + 2 . 6 HToOd(o) 107.4 + 1 . 3 TeO,-(&q) 173.0 f 1 . 3 KTeOl(e) 242.551.5 K I T c C (o) ~
...
So -ds0 (oal/mole deal
+ + * 0.5 +
7.4 0.2 43.26 0.01 14.9 17.3*0.6 45.8 2.0 33.3 f 46.0 -t 0 . 1 39.74+0.10 7 9 . 5 3= 1 . 0
2.0
0.0 35.9 0.2 41.5 & 0 . 5
*
63.1*0.6
140.9 f 2 . 0 8 7 . 7 5 2.0 75.0 0.1 78.9*1.0 117.6 1.0
*
*
- aF,
(Ichl/mole)
0.0 91.4'&2.0 110.23=5.0 224.1 2.6 141.3 1.3 1 3 0 . 6 2 ~1.3 219.0+1.5
**
...
A number of salts of pertechnetic acid have been prepared, among which are ammonium pertechnetate, NH4Tc04,potassium pertechnetate, KTcOl, cesium pertechnetate, CsTcOl, silver pertechnetate, AgTcO4, tetraphenylarsonium pertechnetate, and nitron pertechnetate. The latter two salts are insoluble and may be utilized as gravimetric forms. Potassium pertechnetate is considerably more soluble a t 25' than potassium perrhenate (46) and, likewise, (CsHs)nAsTc04is more soluble than (CsHs)AsReOl. The crystalline forms of the alkali metal and ammonium salts are colorless and are isomorphous with the corresponding salts of rhenium. X-ray diffraction measurements (79) have shown that NH,Tc04, KTcOI, and AgTcO4 have the CaWOrstructure. The density of NH4Tc04is2.73. Ammonium pertechnetate on heating in vacuo to 550' decomposes to form TcOz (80). The fragmentation of NHI TcOaunder electron bombardment a t 80' to 160°C has been studied in a mass spectrometer (81). The cracking patterns revealed the following ions: Tc107+,TcOn+,Tc08+, Tc02+, TcO+, and Tc+ in this order of abundance a t 80'. Other fragments such as Tc206+,Tc206+and TczOl+ were also noted. KTcO4, in contrast to NHpTcOa, may be fused a t ea. 540°C and sublimed a t ca. 1000°C without apparent decomposition (82). The most stable species of the element in aqueous solution is pertechnetate ion, TcOa-. Pertechnetate, like perrhenate, ion is stable over a very wide range of pH, in contrast to permanganate ion. The ionic radius of Tc+?has been estimated as 0.56 A (83), a value identical with that also estimated for Re+' but larger than that for Mn+' (0.46 A). The estimated (83) ionization potential for Tc+' is 95 electron volts, a value intermediate between that for Mn+' (122 ev) and Re+' (79 ev). The Tc-Q spearation in the tetrahedral TcOl- ion is about 1.75 A (79) which may be compared with a value (84) of 1.97 A for Re04-. I t is not unexpected, therefore, that the pertechnetate ion should possess a stability intermediate between that for Re04- and MnOl- ions. The oxidation-reduction diagrams sholvn in Figure 5 hear out this expectation. I t is seen that the oxidation potential for the TcOz/ Tc04- couple in acid aqueous solutions is intermediate between those for the corresponding couples of man-
ACID SOLUTIONS
Figure 5. Oxidation-reduction diagrams for the elements in the subgroup of the periodic table.
7th
ganese and rhenium. Pertechnetate ion is a weak oxidizing agent although somewhat stronger than perrhenate ion. Aqueous solutions of pertechnetate and perrhenate ions display a strong absorption of light in the ultraviolet (Fig. 6). Accurate measurements of the molar absor~ancyindices for the Tc04- peaks a t 2440 and 2875 A have given values of 6220 and 2360, respectively (85). It may be seen that the spectrum of TcOn- in aqueous solution bears a considerable resemblance to the spectrum of the isoelectronic species ReOa-. The spectra of Mn04-and RuOa are also quite similar. The relative sharpness of the electronic bands and the existence of vibrational structure which arises presumably from the metal-oxygen vibrations in the ions suggests that the electrons giving rise to the transitions responsible for the absorption are protected. However, there are no electrons remaining in the d-orbitals of Tc and Re because these are in their maximum oxidation state. Information on the solubility of Tc04- ion in organic liquids may be inferred from its solvent extraction behavior. The earliest work on the solvent extraction of pertechnetate ion showed that it did not extract into diethylether (8). However, subsequent work (86-89) has revealed that heptavalent technetium extracts well into a wide variety of organic solvents containing oxygen, phosphorus, or nitrogen. The behavior of pertechnetate ion in concentrated hydrochloric acid solutions is of interest. Spectrophotometric studies have shown that a change in the species begins when the concentration reaches 6 N a n d that this change is complete when the concentration rises to 9 N. I n this respect, pertechnetate ion is strikingly different from perrhenate which does not show this behavior except a t the highest concentrations of HC1. Small amounts of the sulfide, Tc&, cannot be precipitated from 9 N hydrochloric acid solutions, even though this sulfide is quite insoluble in 3 N acid (8,90). The brown-black heptasulfide of technetium is best prepared by precipitation from 2 to 4 N HC1 or HpS04 solutions using hydrogen sulfide (91). Usually the precipitate contains free sulfur which must be removed by careful washing with carbon disulfide. On heating, the heptasulfide decomposes to form a n amorphous disulfide, TcSz (80). One of the oxyhalides of heptava-
lent technetium has been prepared recently (82). Pertechnetyl chloride, TcOZCI,may be formed by the simple procedure of adding 12 M HC1 to a solution of KTcOl dissolved in 18 M H2S04. On shaking the acid with carbon tetrachloride, chloroform, or hexane the compound is extracted into the organic phase. The optical absorption spectrum measured on this compound shows a vibrational characteristic superimposed on the electronic band quite reminiscent of that for pertechnetate ion. Mass spectrometric data have been ohtained (81) which suggest the formation of T c O S by the reaction of KH4TcOlwith UF, in the mass spectrometer. Hexavalent State. KO compound of Tc(V1) has been prepared, although several unsuccessful efforts to synthesize TcOa have been made (77). The thermodynamic properties of this compound have been estimated from observations on TczO, and the difference between Rek07and ReOa (75). These estimates suggest that Tc(V1) will be unstable with respect to Tc(1V) and Tc(VI1) and that it will disproportionate to the latter in aqueous solution. It has been predicted (92) that the technetate ion, Tc04-, may be stable enough in basic media and even in very dilute acids to permit cell emf measurements to be made. Pentavalent State. There is no record of the successful preparation of any solid compound of Tc(V). The preparation of TcCISby heating AgzTcCls, the procedure that is successful in the case of the preparation of ReC15 when AgZReCl6is heated, is not1feasible hecause, owing
Figure 6. Optical absorption spectra observed with dilute aqueous solutions of KTcO. and KReO+
to the hydrolysis of the ion TcC16-, AgXeCl, cannot he isolated. Several products have been obtained in the reaction of chlorine gas with TcOr (63). A light-brown product, which may be TcOCl,, was formed which could be sublimed a t 900'. This compound was paramagnetic. As might be expected, Tc(V) may be prepared in aqueous solution when stabilized as a complex ion. Recently evidence for the formation of a thiocyanate complex ion in aqueous solutions has been ohtained (93). This thiocyanate complex may be extracted quantitatively into a solution of trioctylphosphine oxide or of trioctylamine hydrochloride in cyclohexane or 1,2dichloroethane. The very large molar absorbance index (52,200 + 500) a t 5100 A (see Fig. 7) of the complex makes it useful for the detection and estimation of trace amounts of technetium. Quadrivalent State. A variety of solid compounds of Tc(1V) has been prepared and characterized. In Volume 36, Number
I, Jonuory 1959
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n 3500
T c x (SCN), IN 40-'MCYCLOHEXANE SOLUTION OF TOA
4500 5500 WAVE LENGTH IN
6500
Figure 7.
Optical mbrorption spectrum of technetiumN) thiccyanate complex dissolved in syclohexone.
aqueous solution, however, quadrivalent technetium does not appear to exist as TC(OH)+~, TcO++, or TcOr (OH)+ ion, but only as a complex anion. The estimated ionic radius for the Tc+&cation is 0.70 A which value is very close to that for Mo+&and W+4. Black TcOz.2HZOmay be synthesized by the reduction of pertechnetate ion in hydrochloric acid with metallic zinc (69). Relatively pure deposits of TcOz.2Hz0 may be formed by the electrolysis of neutral or alkaline pertechnetate solutions between platinum electrodes (77). Anhydrous TcOz may be produced by the thermal decomposition of ammonium pertechnetate. Anhydrous black TcOz (density = 6.9) like Re02 (11.2) has the Moo2 structure (79, 94). Technetium dioxide dihydrate shows a very small magnetic susceptibility which does not obey the Curie-Weiss equation (69). The dioxide is readily oxidized to Tc20; with oxygen and reacts readily a t 300" with dry chlorine. In acid aqueous solutions TcOz may be oxidized readily to Tc04- using Ce(1V) or, in alkaline solutions, using hydrogen peroxide. Technetium disulfide, TcSz, is another important solid compound of Tc(1V). The crystalline compound is best prepared by heating precipitated Tc& with excess sulfur in a bomb for 24 hours a t 1000°C., and afterwards removing the unreacted sulfur by sublimation i n vacuo (80). The X-ray diffraction pattern for this ~ ~ o m p ~.41ows ~ t n ~it~111 l 1 1 1 1 \ ~a disord~red>truvturc rrI:~ttrlto t h e \IoSr.;tru(.turr :ind r o hc iso~n(~rnh~~u.; with ReS, (79). he- true unit cell is not knoLwn. I t is pseudohexagonal and may be either orthorhombic or monoclinic. When technetium sulfide is heated in a stream of HpSa t 1000' technetium metal is produced. The only halide of Tc(1V) thus far prepared is TcCl4 which may he synthesized by heating Tc207 with CCL in a closed bomb (95). Small, blood-red crystals are formed which are paramagnetic. The temperature variations of the vapor pressure of TcC19 have also been ~
10
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Journal of Chemical Educofion
measured. If the highest chloride of technetium is truly TcCla, then technetium is more like manganese which forms MnC14 than like rhenium where the pentachloride, ReCb, is known. Several of the complex salts of Tc(1V) have been prepared, the best studied of which is potassium hexachlorotechnetate (IV), K2TcCls. This compound may be formed by the reduction of ammonium pertechnetate with potassium iodide in concentrated hydrochloric acid (63) or, alternatively, better by the reduction of KTcO4 with hypophosphorus acid in concentrated HCI. The golden-colored, needle-like crystals of KTcCL display a strong paramagnetism which obeys the Curie-Weiss law (69). The effective magnetic moment is 4.3 Bohr magnetons, which wlue may be compared wit,h the theoretical estimate of 3.88 for three unpaired electrons. The compound K2TcCle differs from KzReC16 most importantly in its instability toward hydrolysis in aqueous solutions. The former compound decomposes completely to give TcOz in neutral solutions; even in 3 N hydrochloric acid solutions changes in its optical absorption spectrum occur upon standing 24 hours. Measurements of the optical absorption spectrum in aqueous solution have revealed KzTcC16 absorbs strongly in the visible with bands having maxima a t 2400 and a t 3380 A (Fig. 8). X-ray diffraction measurements (79, 96) on K3cCle demonstrate that this compound possesses the K2PtCls-structure and is isomorphous with KzReCls. The compound may be extracted quantitatively from aqueous acid solutions by a number of organic liquids including alcohols and by trioctylamine hydrochloride dissolved in cyclohexane. The compounds KzTcBrband KJcIs have also been prepared and the optical absorption spectra of these in aqueous solution have been measured (88).
0
2000
i
2500
i
3000 WAVE-LENGTH IN
3500
4000
I
Figure 8. Opticol absorption spectra observed with dilute aqueous roiutions of K%TcC16and KnReCi&
Trivalent State. Unsuccessful efforts have been made to prepare the lower oxides of technetium, including the sesquioxide TczOa(65). On heating TcOz to 900' in a high vacuum a black deposit was observed to deposit upon the walls of the containing vessel, and, after heating one hour a t 110O0,approximately 50% of the initial material had sublimed and condensed. However, Xray diffraction analysis of the deposit showed that Tc02 had sublimed unchanged. I n this respect Tc(1V) differs from both Mil and Re. When MnOp is heated
Mn2O8and lower oxides are formed, whereas when Re02 is heated a t 750°C it disproportionates to rhenium metal and Rez07. Recently evidence has been obtained for the formation of Tc(II1) in aqueous solution (97). Controlled potential electrolysis of pertechnetate ion a t pH 7.0 in a phosphate buffer appears to give Tc(II1). This valence state is highly unstable and is easily oxidized by air to Tc(1V). The optical absorption spectrum of the green Tc(II1) formed in aqueous solution by electro-reduction has been measured. Comparisons of the Chemistry of Technetium with T h d for Manganese and Rhenium
From what is known a t present concerning the chemistry of technetium, it is clear that the properties of this element are much more like those of rhenium than of any other element in the periodic table. The expectations based on the periodic table and on the lanthanide contraction are amply confirmed. I t should be emphasized however, that quantitative differences do exist between the chemistries of technetium and rhenium. In the lower oxidation states there are suggestions that technetium may he like manganese, while in the upper oxidation states the element is unmistakably most like rhenium. The data summarized in Table 4 may serve to give quantitative comparisons between manganese, technetium, and rhenium. Table 4.
Chemical and Physical Properties of Some of the Group VII Elements and Compounds C1
Mn
Te
Re
-31.4 keal/mole
- 1.34 volts
-129.7 -0.786
-173.0 -0.477 -242.5 1.358
-190.3 -0.367 -263 0 1.373
13.01 volts
7.43 7.20
Property AH,',
XOd- (aq)
E s , X/XO,c AH,', KXO. (el Covhle"t rsdius 1onizatmn ~otentid
Density Melting
wint XzO? ("I
-103.6 koal/mole (OSYI d
.. .
-92'
-194.4
1.306
< -20"
7.28 11.50
120D
7.87 20.53 300'
Analytical Chemistry of Technetium
General Considerations. The analytical behavior of technetium is very similar to that of rhenium. The heptavalent form of technetium, however, is more easily reducible than Re(VI1) and, in a non-complexing form medium, forms a slightly soluble dioxide. Technetium dioxide may he oxidized quantitatively with ceric sulfate to give Tc(VII), although the reaction may be slow if the compound has been heated. Acid solutions of Tc(VI1) may not be evaporated to dryness without some loss of the element because of the volatility of the acid HTcOa and of the oxide Tcz07. Tc(VI1) may be distilled quantitatively from concentrated sulfuric or perchloric acid. In the presence of hydrobromic or hydrochloric acid, however, technetium may be heated without loss, probably because of the fact that these two acids form lower oxidation states which are not volatile. Heptavalent technetium forms an acid insoluble sulfide which is slightly more soluble than the corresponding rhenium compound, Re&. Several insoluble organic pertechnetate salts are formed such as those with nitron and with tetraphenylarsonium or phosphonium compounds. These are more soluble than the corresponding perrhenates, and may be extracted into organic liquids such as chloroform, etc.
The organic reagent tetron forms an insoluble precipitate with the anion, TcCls=. Separation of Technetium. In radiochemical analyses for technetium it is frequently necessary to separate the element from uranium and/or the fission products. Two procedures have found application: The first, which is employed when irradiated uranium metal is analyzed, involves the dissolution of the metal in hydrochloric acid, oxidation of the uranium to uranyl chloride and precipitation of an acid-insoluble sulfide slwh >I*pl:~tinumor copper sulfide 1r.hir.h copreripiratethe ttdlllrtium. Thia ~)rwiuirnwis (:ontxninated w i t h fission-product molyhdenum, ruthenium, palladium, and antimony. A decontamination of the technetium is effected by dissolving the sulfide in ammoniacal hydrogen peroxide, and distilling i t with sulfuric acid to which inactive fission products ("hold-hack carriers") have been added. Finally pertechnetate is coprecipitated with tetraphenylarsonium perrhenate. In an alternative procedure (87) use is made of the solvent, extraction of tetraphenylarsonium pertechnetate after a preliminary removal of radioactive fission product iodine. The latter is effected by heating the uranium with a mixture of sulfuric acid and sodium peroxydisulfate. The solution is then neutralized with ammonium carbonate, tetraphenylarsonium chloride is added and an extraction with chloroform is performed. Technetium goes quantitatively and preferentially into the organic phase. The separation of technetium from molybdenum when the former occurs as a radioactive daughter-product of the latter has been performed by a variety of procedures: molyhdenum may he precipitated away from Tc(VI1) using 8-hydroxyquinolie or or-henzoinoxime. Alternatively, pertechnetate ion may be separated from an alkaline molybdate solution by coprecipitation with tetraphenylarsonium perrheuate. Distillation techniques using sulfuric plus phosphoric acid mixtures have been found to work quite well. The addition of phosphoric acid drastically reduces the volatilization of molybdenum by forming a phosphomolybdate complex. Yet another method is that of ion-exchange chromatography, with which a very efficient separation can he achieved. Finally, it is possible to separate molyhdenum from technetium by an ether extraction from hydrochloric acid solutions. I n this separation molyhdenum is extracted and technetium remains in the aqueous layer. Technetium may sometimes he associated with ruthenium which may occur either as a fission-product ruthenium activity, or as a bulk constituent as in neutron irradiations to produce Tcg". A separation from small amounts of ruthenium may be carried out after the distillation of technetium and ruthenium (as h o d ) with perchloric acid by reducing the latter in dilute acid with alcohol. Minor quantities of ruthenium are separated almost completely from weighable quantities of technetium in the recrystallization of KTc04. The separation of technetium from rhenium is the most difficult of all, as might be expected. A variety of procedures have been employed: One is a volatility method involving the distillation of the chlorides of the two elements. A mixture of rhenium and technetium metals or of rhenium and technetium heptasulfides is heated a t 300' in a stream of gaseous chlorine (8). The
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rhenium chloride formed is stable and volatilizes, whereas the technetium chloride decomposes and remains behind. A second method is based upon differences in the solubilities of the sulfides of technetium and rhenium in concentrated hydrochloric acid solutions (8, 90). A complete separation of weighable amounts of rhenium from trace amounts of technetium can be effected. Another method for the removal of technetium from rhenium consists in the selective reduction of Tc(VI1) from Re(VI1) by an electrolysis in an alkaline solution a t a controlled potential (98). A good deposit of technetium dioxide is obtained, and perrhenate remains in solution. Finally, efficient ion-exchange chromatographic methods (99, loo), (17) have beenemployed in obtaining excellent separations of rhenium and technetium using thiocyanate and perchlorate solutions as eluting agents. Assay Methods. Fission-product Tcg9may be determined readily by means of a radioactivity assay. Its specific activity is 37,800 d/m/pg, so that a practical sensitivity of detection of about 0.1 pg is attainable. There are a number of difficulties, however, with the assay because the beta particles emitted in the decay of Tcg9are of very low energy. Care must be taken in source preparation for beta counting to minimize errors caused by anomalous back-scattering, sample selfabsorption, etc. Another sensitive method for the estimation of minute quantities of technetium is that of spectrochemical analysis. Using the resonance lines in Tc and Tc-I a t 42977.6, 4262.26, 4238.19, and 4031.63 A, respectively, as little as 0.1 pg can be determined reliably. Several spectrophotometric methods for the determination of small amounts of technetium are available. Quantities of Tc(V1I) in aqueous solutions as small as 1 pg may be determined by using the ultraviolet absorption bands a t 2470 and 2890 A in the spectrum of pertechnetate ion. Somewhat smaller quantities (i.e., 0.2 pg) of technetium may be estimated using the absorption of technetium(V) thiocyanate at 5150 A (93). Perhaps the most sensitive chemical method is that employing the polarographic half-wave observed in the reduction of Tc(VI1) to Tc(IV) in a phosphate buffer a t pH 7.0. As little as 0.05 wg of technetium may be estimated using the ORNL high sensitivity polarograph. Of all the methods for the determination of trace quantities of technetium, the neutron activation analysis procedure is the most sensitive by far. Use is made here of the 15.8 s Tc'O0 formed by neutron capture in TcS9. The capture cross section for thermal neutrons by TcB9is sufficiently large (20 5 X cm2/atom) as to permit the detection of 20 micrograms of the element (17). However, special arrangements t o use this method are needed because of the very short half life of the activity induced. Weighable quantities of technetium are easily determined by the precipitation of tetraphenylarsonium pertechnetate which may be filtered, dried, and weighed with excellent precision.
*
Chemistry of Promethium
Many fewer studies have been performed on the chemistry of promethium and its compounds than has been the case with technetium. This may he partly because Pm possesses but one valence state, namely, the 12 / Journal of Chemical Education
typical rare-earth trivalent state, so that its chemistry is not of especial interest, and partly because of the large amounts of activity that must be contained in working with this fission-product element. As yet, promethium metal has not been prepared. Promethium hydroxide, Pm(OH)8,which is a light-brown gelatinous precipitate, is readily formed with ammonia by neutralization of acid promethium solutions. Promethium chloride, PmCI,, is produced by treating Pm(OH)3 with HCI. I t forms yellow crystals in appearance not unlike those of samarium trichloride. Promethium nitrate, Pm(NO&, prepared by neutralizing the hydroxide with nitric acid, forms pink crystals resembling those of neodymium nitrate. The atomic weight of promethium has not been determined either chemically or mass spectrometrically. Preliminary observations on the optical emission spectrum of Pm have been reported (64), and subsequently arc and spark emission spectra have been recorded photographically using a large diffraction grating (101). The wavelengths and intensities of more than 2300 lines were determined betn.een the ultraviolet (2300 A) and the red (6900 A). I t has not yet been possible t o identify which lines are associated with neutral and/or ionized Pm, however. The strongest lines, probably arising from Pm+, have wavelengths and intensities as follows: 3998.96 (loo), 3957.74 (loo), 3919.09 (loo), 3910.26 (loo), and 3892.16 (100). No ionization potentials have been deduced; the proposed electron structure for the gaseous atom is 4f56s2('H.,J. Measurements of the K- and I, X-ray emission spectra of promethium have been reported (1Of&lO$). The absorption spectrum of PmCI3 in an aqueous solution has been measured (104, 101) in the visible wavelength ranges. The rare-e'rth character of promethium is demonstrated unmistakably by the narrow, strong bands which occur a t wavelengths of 494.5,548.5, 568.0, 685.5, and 735.5 mp. The band at 548.5 mp is free of interferences with either Nd or Sm and shows a molar absorbance index of 2300. Radiochemical analyses for promethium in fissionproduct mixtures require first an isolation of a rareearth fraction, usually by the precipitation of LaFa, followed by an ion-exchange chromatographic separation of the Pm. After removal of the organic acid used to elute the promethium, an aliquot of solution is evaporated and counted with a flow-type beta proportional counter. Care in source preparation is essential because of the low energy of the beta particles emitted in the decay of Pm14'. Promethium may be determined spectrochemically using the aforementioned lines with a sensitivity of about one microgram (66). Precaution to reduce errors caused by interferences from lines of other rare earths, especially Nd and Sm, is essential. Uses for Fission-Product Technetium and Promethium
It seems likely that practical applications of the synthetic elements technetium and promethium ill be based, in the first case, on the unique chemical properties and, in the second, on the unique nuclear properties of the element. Technetium is a lomenergy, pure beta emitter of very low specific activity. The nuclear energy it possesses
is not released a t a rate sufficient to make the element attractive for the conventional applications of radioactivity (i.e., thickness gauges, phosphors, etc.). Hoaever, already one unique chemical property of technetium has been discovered which may ultimately prove directly, or indirectly, to be of widespread usefulness. This is the discovery of the remarkable inhibition of the corrosion of soft iron in neutral aqueous solutions by minute quantities of TcOa- ion (105). Mild carbon steels may be protected effectively by as little as 5 ppm of technetium (5 X lO-=M KTcO*) in aerated distilled 7%-atera t temperatures up to at least 250'. Specimens of steel have now been observed a t room temperature for over five years with no evidence of attack. Interestingly, and of importance to theories of the mechanisms of corrosion inhibitors, perrhenate ion does not inhibit. Promethium, although chemically unnotemorthy, is rapidly becoming widely used in applications where its unique nuclear characteristics are employed. Because of its quite high specific activity, Pm is useful as a beta source for thickness gauges (106, 107). Possibly of more importance are uses in which the nuclear decay energy of promethium is converted either into light or beat. Its use in the preparation of self-luminous compounds has been described (108), and a report of its employment in the construction of miniature "atomic" batteries has appeared (109). The advantage of such a battery is its relative temperature independence. It will operate with increased efficiencyat temperatures to -200°F and with about 70% of room temperature efficiency a t the boiling point of water. Literature Cited
(1) PERRIER,C., AND SEGRE,E., Nature, 159, 24 (1947). (2) MARINSKY, 5. .4., AND GLENDENIN, L. E., Chem. Engr. News, 26, 2346 (1918). of (3) Spe, far example: MARYELVIRAWEEKS,"Di~~overy the Elements," J. CHEM.EDUC.,6th ed., 1956, p. 652; MENDELEEV, D. I., J. Ru8s. Chem. Soe., 1, 60 (1869). ., (4) XODDACK, W., TACKE,I., A N D BERG,O., N a l w w i ~ ~13, 567 (1925). (5) H A R R I ~ , J. A., A N D HOPKINS,B. S., J . Am. Chem. Soc., 48, 1585 (1926). L., Gasz. chim. ital., 56, 435 (6) ROLLA,L., AND FERNANDES, 114%)
(7) YOST,D. M., RTTSSELL, H., JR., A N D GARNER, C. S., "The Rare Earth Elements and Their Compounds," Chap. 4, John Wilev & Sons. Inc.. New York. 1947. (8) PERRIER,c:, AND sEGR*,' E., J. ~ h k m .Phys., 5, 712 (1937); ibid., 7, 155 (1939). (9) Committee on New Elements, Internationd Union of Pure and Applied Chemistry, Chem. Engr. N m s , 27, 2996 110461 - - - - ,. (10) LAN, H. B., POOL,M. L., KUBRATOV, J.II.,ANDQuILL, I,. L., Phys. Rev., 59, 936 (1941). ~ , Phys Rev., 61,203 (1942). (11) Wu, C. S., AND S E G R E., (12) BOTHE,W., 2.Natu~fomh.,1, 179 (1946). C. D., (13) AIARINSKY, J . A,, GLENDENIR, L. E., A N D CORYELL, J. Am. Chem. Soe., 69, 2781 (1947). (14) KETELLE,B. H., AND BOYD,G. E., J. Am. Chem. Soe., 69, 2800 (19471,(15) w., Z. Naturjomeh., 9A, 907 (1954). E., A N D MILLER,J . M., Nature, 176, 299 (16) ALPEROVITCH, (1955). (17) BOYD,G. E., A N D LARSON,Q. V., J . Phw. Chem., 60, 707 (1956). (18) ANDERS, E., SENSARMA, R. X., AND KATO,P. H., J. Chem. Phys., 24, 622 (1956). de. Chim. Anal., 11, 113 (1945). (19) T ~ x v o n r S., ~ ~Ann. , (20) MOORE,C. E., Science, 114, 59 (1951). \
HERR;
\---.
MERRILL,P. W., Astrophys. J., 116, 21 (1952). MEREILL,P. W., Publs. Astvon. Soc. Pacffi, 68, 70 (1956;. GREENSTEIN,J. L., AND DE JAGER, C., Bull. Astron. Instit. ojthe Netherlands, 19, 13 (1957). GREENSTEIN, J . L., Mem. soe. roy. sci. Likge, 14, 307 O*?> \'i.l,"",.
CAMERON, A. W., Ast~ophys.J., 121, 144 (1955). G. R., AND BURBIDGE, E. M., FOWLER,W. A,, BURBIDGE, Anl~oohm. , . , ~.J.., 122. ~ 271 , -119551. ~ -. ~ ..,.MOTTA,E. E., AND BOYD,G. E., P h w Rev., 74,344 (1948). EGGEN,D. T., A N D POOL,M. I,., Phyz Rev., 74, 57, 1248 OAR) I1 ,-" -",. MOTTA,E. E., BOYD,G. E., A N D BROSI,A. R., P h y ~Rec., 71, 210 (1947). BOYD,G. E., Phya. Rev., 95, 113 (1954). . 111, 575 (1958). KATCOFF, S., P h y ~Rev., ~ ~ Phrls. Reu., 55, 808 SEABORG,G. T., AND S E G R E., (193Ri. SE&, E., AND WU, C. S., Phys. Rev., 57, 552 (1940). N , H., "National Nuclear LINCOLN, D. C., A N D S ~ L I V A W. Energy Series-IV," McGraw-Hill Rook Co. ., Inc., New York, 1951, Vol. 9, p. 778. SULLIVAN, R. P., "National Nuclear Energy Series-IV," McGraw-Hill Book Co.. Inc.. New York. 1951. Vol. 9. p. 783. Q. V., Phw. MOTTA,E. E., BOYD,G. E., A N D LARSON, Rm.., 72. - , 1270 - (1847). ~ - - , FRIED,S., JAFFEY, A. H., HALL,N. F , AND GLENDERIN, L. E., Phys. Rev., 81, 741 (1951). BAINBRIDGE, K. T., GOLDAABER, M., AND WILSON,E., Phw. Rev., 90, 430 (1953). Q. V., AND BALDOCK, BOYD,G. E., SITES,J. R., LARSON, C. R., Phys. Rev., 99, 1030 (1955). KATCOFP, S., Phys. Rev., 99,1618 (1955). D.. HOLLANDER. J. M.. AND SEABORG. G. T.. STROMINGER. Reu. ~od.'PhPh$s., 30, [2], 585 (1958). PARKER,G. W., ET AL.,Rev. Mod. Phys., 72, 85 (1947). HAL^ N. F., AND JOHNS,D. H., J. Am. Chem. Soe., 75, 5787 (1953). PARKER,G. W., REED,J., AND RUCH,J. W., U.S.A.E.C. Declassified Document, AECD-2043, June 4, 1948. P ~ K E RG., W., A N D LANTZ,P. M., U.S.A.E.C. Declassified Document, AECD-2160, July 19, 1948. PARKER,G. W., AND MARTIN,W. J., "Results of the First Large-scale Separation of Technetium," Oak Ridge Nstional Laboratory Declassified Report ORNL-1116 (Jan. 29, 1952), pp. 26-30. J. W., ET AL.,J. Am. Chem. Soe., 74, 1852 (1952). COBBLE, For a description of some of the features of this plant see: (a) BOD, G. E., "Production, Availability and Economics of Reactor By-Products," Proceedings of the Conference on the Peaceful Uses of Atomic Energy, May 13-17, 1957, Tokyo, Japan, U. S. Atomic Industrial Forum, Inc., pp. 161-66. ( b ) LAMB,E., SEAGREN, H. E., A N D BEAUCHAMP, E. E., "Fission Product Pilot Plant and Other Developments in the Radioisotope Program at the Oak Ridge National Laboratory," Proceedings of the 2nd International Conference on the Peaceful Uses of Atomic Energy, Geneva, Switzerland, September 1-13, 1958 (to be published b>the United Nations). PRESSLEY, R. S., "Preparation of Fission Product Rare Earth Isotopes," Oak Ridge National Laboratory Unclassified Report, ORNL-2252 (1957). J. G., Univewityof California. Radiation LabHAMILTON, oratory Declassified Report, UCRL-98 (May 24, 1948), pp. 5-9. BAUMAN, E. J., ET AL.,Am. J. Physiol., 185, 71 (1956). ASLING.C. W.. ET AL.. Anat. Record.. 113.. 285 11952). DURBI&,P. w., ET A;., Pmc. Soe. Ezpt. BioL'and ~ e d . , 91, 78 (1956). FRIED. . S... J . Am. Chem. Soc.., 70.. 442 (1948). MOTTA,E. E., LARSON, Q. V.,AND BOYD,G. E., "Stlldie~ on the Tracer Chemistry of Element 43," Oak Ridge National Laboratory Declassifiod Report, MonC-$19, April, 1947, p. 22. PARKER,G. W., Private Communication. R. J., Phys. INGHRAM, M. G., HESS, D. C., A N D HAYDEN, Rev., 72, 1269 (1947). ~
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(74) BOYD,G. E., ET AL., J . Am. Chem. Soe., 74, 556 (1952). J. W., SMITH,W. T., JR., A N D BOYD,G. E., J. Am. (75) COBBLE, Chem. Soe., 75. 5777 (1953). (76) SMITH,W. T., JR., LINE,L. E., AND BELL,W. A,, J . Am. Chem. Soc., 74, 4964 (1952). J. W., "The Thermodynamics of Technetium and (77) . . COBBLE. Its ~ b m ~ o u h d s ,Doctoral " Dissertation, University of Tennessee (June. 1952). o. 98. G. E., J . Am. (78) SMITH,W. T.; JR., COBBLE;J. W., ANDBOYD, Chem. Soc., 75, 5773 (1953). W., H., Private communication, April 25, (79) Z A C ~ A S E N 1952. (80) FFSED, S., Private communication, May 23, 1950. C. R., AND GILPATRICK, L. O., (81) SITES, J. R., BALDOCK, Oak Ridge National Laboratory Unclassified Report, ORNL-1327 (August, 1952). (82) BUSEY,R. H., AND LIUISON,Q. V., Oak Ridge National Laboratory Unclassified Report, ORNL2584 (September, 1958), p. 6. (83) AHRENS,L. H., Geochim. Cosmchim. Acta, 2, 155 (1952).
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