Americium

At americium, dihalides become isolable for the first time. 

They are black solids with the PbCH (X = Cl) EuBr2 (X = Br) and Euh (X = I) structures. As with plutonium, only fluorides occur in the higher ( 3) oxidation states. The trihalides are important they have the usual pastel colours, pink in the case of the fluoride and chloride, white-pale yellow (bromide), and pale yellow (iodide). 

AmOa + 4HE (aq) (with HNO3) Amp4.xH20 Amp4.xH20 AmE3 (NH2HE2 125°C) 

There is an unsubstantiated report of the isolation of AmPe (lu. V. Drobyshevshii et al., Radiokhimiya, 1980,22, 591)  

The product was a volatile dark brown solid, with an IR absorption at 604 cm (compare V U-F at 624 cm i in UFe). 

The longest-lived isotope of americium is Am with a half-life of about 7370 years. Other relatively long-lived isotopes are Am and Am. Americium can also form four oxidation states in aqueous solution trivalent, tetravalent, pentavalent and hexavalent. No data are available for the tetravalent and hex-avalent oxidation states and only a relatively small amount for both the trivalent and pentavalent states. The behaviour of all oxidation states should be reasonably similar to those of uranium, neptunium and plutonium. 

Rai et al. (1983), Edelstein et al. (1983) and Nitsche and Edelstein (1985) studied the solubility of amorphous americium hydroxide. GuUlaumont etal. (2003) reviewed these data and determined a solubility constant at zero ionic strength of 

For zero ionic strength, Guillaumont et al. (2003) determined a solubility constant of 15.6 0.6 for Am(OH)3(s) at zero ionic strength in their review of the thermochemistry of americium, and this value was later accepted by Neck et al. (2009). This value is also accepted in the present review but is coupled with the data of Stadler and Kim (1988) and Runde and Kim (1994) to determine the ionic strength dependence of the solubility constant in NaCl media using 

The value obtained for the solubility constant is in very good agreement with the value selected by Guillaumont et al. (2003) and accepted by Neck et al. (2009) but with a much reduced uncertainty. This lower uncertainty may be expected from use of the extended specific ion interaction theory since the data used are in reasonable agreement. The uncertainty is retained, but it is recognised that it could be as much as an order of magnitude too low. The value obtained at zero ionic strength is also consistent with those values determined for Am(OH)3(s) in 0.1 moir sodium perchlorate (Silva, 1982 Stadler and Kim, 1988). 

The data given in Table 9.20 are in good agreement with the values selected by Guillaumont et al. (2003) and accepted by Neck et al. (2009) and are within the obtained uncertainty values for all three stability constants. The accepted 

The vast majority of electrochemical data on americium ions has heen obtained in aqueous solutions. Americium can exist in aqueous solutions in the oxidation states III, IV, V, and VI. The divalent state is difficult to attain in aqueous solutions because of the proximity of the standard potential of the Am(III)/Am(II) couple to the solvent/supporting electrolyte breakdown potential. Previous reviews have presented the formal and standard potentials for the various americium couples and these reviews should be consulted by the interested reader for more detailed discussion [133, 134]. Table 3 contains a summary of selected formal potentials Ef from these reviews in 1 M HCIO4 for convenience. AU values are calculated from various measurement techniques except for the Am(VI)/Am(V) couple (Am02 /Am02 ), which was determined directly. 

More recent experimental reports have focused on detailed electrochemical studies to characterize the different americium ions in solution in relation to their stability and molecular composition. The electrochemical behavior of americium in carbonate media has been studied by several different authors because of the tendency 

Another strong complexing agent sodium tripolyphosphate, NasPsOio, was employed during the electrolysis of Am(III) inadilute (2 mM) H2SO4 solution to attempt stabilization of Am(IV) [142]. The concentration of NasPsOio was 0.17-0.8 M at pH 1-3 with 0.9 mM Am(III). The reported results indicate that a mixture of Am(IV) and Am(VI) was produced in solution during the electrolysis at 1.9 V versus SHE. 

The Am species decays by a first-order process (A =9.7 x 10 s ) which may be a reaction with water. Americium(iv) disproportionates [A = (5 1) x 10 M s ] at a rate which is qualitatively consistent with the decreasing stability of quadrivalent actinides observed in going from U to Pu.  

Compared with which has similar radius, charge, and formal potential, Am is 100 times less reactive with eaq. This is probably a reflection of the greater overlap of 5/orbitals, compared with 4/ orbitals, with ligands in the first co-ordination shell of Am, resulting in a larger rearrangement free energy of formation of the activated complex. 

Reaction with ammonium phosphate yields AIPO4 (see Aluminum phosphate, preparation) 

Elemental analysis A1 15.77% O 56.12% S 28.11%. A1 may he determined hy colorimetric method or hy atomic absorption or emission spectrophotometry sulfate may he determined by BaCb precipitation method in the aqueous solution of the salt. 

Synonyms alum, cake alum (the term alum also refers to aqueous solutions of this substance, as well as other hydrate salts containing varying number of waters of crystaUization also the term alum apphes to a whole class of sulfate double salts, such as potassium aluminum sulfate or ammonium aluminum 

White crystal sweet taste density 1.62 g/cm ble in water. 

Prepared from bauxite, kaolin or aluminum compounds on reaction with H2SO4. The insoluble silicic acid is filtered out the hydrate salt forms on crystallization. 

SYMBOL Am PERIOD 7 SERIES NAME Actinide ATOMIC NO 95 

ATOMIC MASS 243 amu VALENCE 3, 4, 5, and 6 OXIDATION STATE +3, +4, +5 and +6 NATURAL STATE Solid 

ORIGIN OF NAME Named after the continent America because Europium was named after the European continent. 

ISOTOPES There are 24 isotopes of americium. All are radioactive with half-lives ranging from 72 microseconds to over 7,000 years. Five of americium s isotopes are fissionable with spontaneous alpha decay. 

AH the isotopes of americium belonging to the transuranic subseries of the actinide series are radioactive and are artificially produced. Americium has similar chemical and physical characteristics and is hofflologous to europium, located just above it in the rare-earth (lanthanide) series on the periodic table. It is a bright-white malleable heavy metal that is somewhat similar to lead. Americiums melting point is 1,176°C, its boiling point is 2,607°C, and its density is 13.68g/cm.  

T0463 Klean Earth Environmental Company (KEECO, Inc.), KB-SEA 

T0669 Rocky Mountain Remediation Services, L.L.C., Envirobond and Envirobric T0686 Sanexen Environmental Services, Inc., Ultrasorption T0692 see Environmental, Micro-Flo 

T0709 Sevenson Environmental Services, Inc., MAECTITE Chemical Treatment Process T0726 S olidific ation/S tabilization—General 

T0727 Soliditech, Inc., Soliditech Solidification and Stabilization Process 

Altenpohl, Dietrich G., and Kaufman, J. G. (1998). ALUMINUM Technology, Applications, and Environment (A Profile of a Modem Metal, Sixth edition). Washington, DC Minerals, Metals and Materials Society. 

Farndon, John (2001). Aluminum. Tarrytown, NY Benchmark Books. 

Metallic americium has a face-centered cubic structure at its melting point and a double hexagonal closed-packed structure at temperatures below its melting point. The isotope americium-241 emits a-particles and y-rays in its radioactive decay, and is a source of y-radiation, used to measure the thickness of metals, coatings, degree of soil compaction, sediment concentration, and so on. The same isotope, mixed with beryllium, is used as a neutron source in oilwell logging and other applications. Americium-241 

Manhattan Project government project dedicated to creation of an atomic weapon directed by General Leslie Groves 

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In the actinides, the element curium, Cm, is probably the one which has its inner sub-shell half-filled and in the great majority of its compounds curium is tripositive, whereas the preceding elements up to americium, exhibit many oxidation states, for example -1-2, -1-3. -1-4, -1-5 and + 6, and berkelium, after curium, exhibits states of -1- 3 and -E 4. Here then is another resemblance of the two series. 

The many possible oxidation states of the actinides up to americium make the chemistry of their compounds rather extensive and complicated. Taking plutonium as an example, it exhibits oxidation states of -E 3, -E 4, +5 and -E 6, four being the most stable oxidation state. These states are all known in solution, for example Pu" as Pu ", and Pu as PuOj. PuOl" is analogous to UO , which is the stable uranium ion in solution. Each oxidation state is characterised by a different colour, for example PuOj is pink, but change of oxidation state and disproportionation can occur very readily between the various states. The chemistry in solution is also complicated by the ease of complex formation. However, plutonium can also form compounds such as oxides, carbides, nitrides and anhydrous halides which do not involve reactions in solution. Hence for example, it forms a violet fluoride, PuFj. and a brown fluoride. Pup4 a monoxide, PuO (probably an interstitial compound), and a stable dioxide, PUO2. The dioxide was the first compound of an artificial element to be separated in a weighable amount and the first to be identified by X-ray diffraction methods. 

Each of the elements has a number of isotopes (2,4), all radioactive and some of which can be obtained in isotopicaHy pure form. More than 200 in number and mosdy synthetic in origin, they are produced by neutron or charged-particle induced transmutations (2,4). The known radioactive isotopes are distributed among the 15 elements approximately as follows actinium and thorium, 25 each protactinium, 20 uranium, neptunium, plutonium, americium, curium, californium, einsteinium, and fermium, 15 each herkelium, mendelevium, nobehum, and lawrencium, 10 each. There is frequently a need for values to be assigned for the atomic weights of the actinide elements. Any precise experimental work would require a value for the isotope or isotopic mixture being used, but where there is a purely formal demand for atomic weights, mass numbers that are chosen on the basis of half-life and availabiUty have customarily been used. A Hst of these is provided in Table 1. 

Kilogram quantities of americium as Am can be obtained by the processing of reactor-produced plutonium. Much of this material contains an appreciable proportion of Pu, which is the parent of Am. Separation of the americium is effected by precipitation, ion exchange, or solvent extraction. 

Most chemical iavestigations with plutonium to date have been performed with Pu, but the isotopes Pu and Pu (produced by iatensive neutron irradiation of plutonium) are more suitable for such work because of their longer half-Hves and consequendy lower specific activities. Much work on the chemical properties of americium has been carried out with Am, which is also difficult to handle because of its relatively high specific alpha radioactivity, about 7 x 10 alpha particles/(mg-min). The isotope Am has a specific alpha activity about twenty times less than Am and is thus a more attractive isotope for chemical iavestigations. Much of the earher work with curium used the isotopes and Cm, but the heavier isotopes... 

In general, the absorption bands of the actinide ions are some ten times more intense than those of the lanthanide ions. Fluorescence, for example, is observed in the trichlorides of uranium, neptunium, americium, and curium, diluted with lanthanum chloride (15). 

Actinide Peroxides. Many peroxo compounds of thorium, protactinium, uranium, neptunium, plutonium, and americium are known (82,89). The crystal stmctures of a number of these have been deterrnined. Perhaps the best known are uranium peroxide dihydrate [1344-60-1/, UO 2H20, and, the uranium peroxide tetrahydrate [15737-4-5] UO 4H2O, which are formed when hydrogen peroxide is added to an acid solution of a uranyl salt. 

AH of the 15 plutonium isotopes Hsted in Table 3 are synthetic and radioactive (see Radioisotopes). The lighter isotopes decay mainly by K-electron capture, thereby forming neptunium isotopes. With the exception of mass numbers 237 [15411-93-5] 241 [14119-32-5] and 243, the nine intermediate isotopes, ie, 236—244, are transformed into uranium isotopes by a-decay. The heaviest plutonium isotopes tend to undergo P-decay, thereby forming americium. Detailed reviews of the nuclear properties have been pubUshed (18). 

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