R.D. Baybarz

Electron-transfer and f → d absorption bands of some lanthanide and actinide complexes and the standard (III–IV) oxidation potentials for each member of the lanthanide and actinide series

Abstract Best values for the standard (III–IV) oxidation potentials for each member of the lanthanide series and for each member of the actinide series are obtained from a variety of sources, namely, from the direct electrode measurements reported in the literature, from linear plots of electron-transfer absorption band energy for various Ln(IV) and An(IV) complexes versus the respective (III–IV) potentials, from linear plots of f → d absorption band energy for various Ln(III) and An(III) complexes vs. the respective (III–IV) potentials, and from theoretical correlations using Jorgensens refined-electron-spin-pairing-energy theory. Two major results of this work are; (1) the M(III–IV) potentials for M ≐ Cm, Cf, Pr, and Tb are all within −3·2±0·3 V, and (2) the indication that the unknown oxidation states Cf(IV), Es(IV), Pm(IV), Sm(IV), Fm(IV), and possibly Md(IV), listed in the order of decreasing stability, may be stabilized in various media. Altogether, the results are in excellent accord with the actinide hypothesis.

Dissociation constants of the transplutonium element chelates of diethylenetriaminepenta-acetic acid (DTPA) and the application of DTPA chelates to solvent extraction separations of transplutonium elements from the lanthanide elements

Abstract The dissociation constants of the DTPA complexes with Am, Cm, Bk, Cf, Es and Fm have been determined by an ion exchange technique, and the values obtained are: Americium 10 −22·92 , Curium 10 −22·99 , Berkelium 10 −22·79 , Californium 10 −22·57 , Einsteinium 10 −22·62 and Fermium 10 −22·70 . A solvent extraction system has been developed to completely separated the transplutonium elements from the lanthanide fission products by extracting the lanthanide elements into an organophosphonate from a carboxylic acid-buffered solution of DTPA. The separation factor between americium and the lanthanide elements is about fifty.

A spectrophotometric study of the complexing of Am3+ with aminopolyacetic acids☆

Abstract Eight aminopolyacetic acids, varying in size from iminodiacetic to tetraethylenepenta-amineheptaacetic, were studied with respect to their complexation with trivalent americium. The compositions and pH ranges of stability of 22 complexes were determined by using an absorption spectrophotometric technique. Instability constants were calculated for 13 of these complexes. The data obtained in this study were compared with published data for americium and for the lanthanides.

On the californium oxide system

Abstract Californium dioxide was prepared by oxidation with high pressure molecular oxygen and by atomic oxygen. The CfO2 has a fcc structure with an expansion corrected lattice parameter of 5·310 ± 0·002 A. Several areas of oxide stability in the range CfOχ(2·00 > χ > 1·50) are reported and these phases have a rhombohedral structure. The phase transition temperature between the body-centered cubic Cf2O3 and monoclinic Cf2O3 is ∼ 1400°C.

Hexagonal and orthorhombic crystal structures of californium trichloride

Abstract Californium trichloride has been prepared in two crystalline modifications and single-crystal specimens of each have been studied by X-ray diffraction. The hexagonal UCl3-type crystal has unit-cell dimensions of a = 7·379(1) A and c = 4·0900(5) A and the orthorhombic PuBr3-type, a = 3·869(2) A , b = 11·748(7) A and c = 8·561(4) A . Structural parameters including anisotropic thermal motion have been refined by the method of least squares. In the hexagonal form the Cf atom is 9-coordinated by six Cl atoms at 2·815(3) A and three at 2·924(4) A, while in the orthorhombic form the coordination is 8-fold with two Cf-Cl distances of 2·690(7) A; four of 2·806(4) A and two of 2·940(6) A. An ionic radius of 0·932(3) A was derived for the 6-coordinated Cf3+ ion.

The crystal structures and lattice parameters of berkelium metal

Abstract The first bulk samples of berkelium metal have been prepared by the reduction at ∼1000°C of BkF3 with lithium metal in a tantalum crucible system. Berkelium metal has been found to exhibit two stable crystallographic modifications—face centered cubic (fcc) and double hexagonal closest packed (dhcp). The cubic lattice parameter, derived from the averaged values of 10 independent metal samples, is 4·997±0·004 A. The dhcp lattice parameters, derived from the averaged values of 6 independent samples, are a o = 3·416±0·003 A and c o = 11·069±0·007 A . The error limits given in all three cases represent the 95 per cent confidence level calculated using the standard statistical method for the average of independent determinations.

Divalent americium: The crystal structure and magnetic susceptibility of AmI2☆

Abstract The preparation and identification of divalent americium, as AmI2, are reported. Lattice constants for the monoclinic AmI2 are a 0 = 7·677 ± 0·003 A , b = 8·31 ± 0·004 A , c = 7·925 ± 0·003 A and β = 98·46±0·03°. The effective magnetic moment for AmI2 is μeff = 6·7±0·7 BM. AmOI was also prepared, and the lattice constants for the tetragonal cell are a 0 = 4·011±0·002 A and c = 9·204±0·007 A .

Identification and analysis of einsteinium sesquioxide by electron diffraction

Abstract Einsteinium sesquioxide was prepared by calcining submicrogram quantities of the metal nitrate, and the resulting oxide was analyzed by electron diffraction. The lattice parameter of the body-centered cubic Es 2 O 3 was found to be 10·766±0.006 A for a hydrogen-reduced oxide sample. The ionic radius of Es 3+ calculated from this lattice parameter was 0·928 A, which is approximately midway between the values calculated for Gd 3+ and Tb 3+ from their sesquioxides.

High-temperature phases, crystal structures and the melting points for several of the transplutonium sesquioxides☆☆☆

The monoclinic form of Bk2O3 and the hexagonal forms of Bk2O3 and Cf2O3 have been prepared. The monoclinic structure of Bk2O3 was obtained in the range 1200–1700°C and was found to have lattice parameters of a0 = 14·197 ± 0·007 A, b0 = 3·606 ± 0·003 A, c0 = 8·846 ± 0·005 A and β = 100·23 ± 0·09°. At temperatures above 1750°C the monoclinic form of Bk2O3 transformed to a hexagonal structure having room-temperature lattice parameters of a0 = 3·754 ± 0·002 A and c0 = 5·958 ± 0·002 A. The hexagonal form of Cf2O3 was also prepared and the lattice parameters determined to be a0 = 3·72 ± 0·01 A and c0 = 5·96 ± 0·01 A. The m.p. of Cm2O3, Bk2O3 and Cf2O3 were measured and the values observed to be 2260, 1920 and 1750°C, respectively. A stability diagram for several of the actinide sesquioxides, which includes the above data, was constructed.

Preparation of the high temperature form of curium metal

Abstract The high temperature form of curium metal was prepared by reduction of curium oxide with thorium metal and volatilizing the curium at 1650°C. The high temperature form of curium metal is fcc with a lattice parameter of 5·039 ± 0·002 A which gives a metallic radius of 1·78 A and a metallic valence of + 3·0.