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Mössbauer spectroscopy on 237Np-doped borosilicate glasses
654
Structural aspects, physical properties and X-ray photoelectron spectra of valence bands of new pseudo-binary thorium silicides: a-ThSi, _,T, (O
de Chimie du Solide du CNRS, 33405 Talence Cddex (France)
Universite’ de Bordeaux
1, 351 Cours de la
P. LEJAY Centre de Recherches sur les Tres Basses B.P. 166, 38402 Grenoble Ckdex (France)
Temperatures,
CNRS,
Avenue
des Martyrs,
L. PORTE and TRAN MINH DUC Znstitut de Physique Nucleaire de Lyon (IN 2P3), Universite 43 Bdl du 11-Novembre 1918, 69622 Villeurbanne (France)
Claude Bernard,
Lyon
I,
J. P. KAPPLER and M. J. BESNUS LMSES, Znstitut de Physique,
3 rue de I’Universite,
67084 Strasbourg
Cedex (France)
Thorium disilicide is dimorphic and both forms are superconducting @ThSiz, AlBztype, T, = 2.41 K and o-ThSiz, tetragonal, Tcr = 3.16 K). New materials have been obtained by substitution of silicon by transition elements such as rhodium and iridium in a-ThSiz. The superconducting behaviour of the silicides has been shown by electrical, magnetic and specific heat measurements. The variation in the superconducting transition temperature T, versus x is similar for both o-ThSiz_,Rh, and a-ThSiz_,Ir, systems. With increasing x, T, decreases for 0 < x < 0.25 and increases sharply for x > 0.75 reaching 6.50 K for the equiatomic compounds (x = 1). The maximum TcI value is a little higher than twice that of o-ThSiz. In the intermediate composition range 0.25 / x < 0.75 the corresponding compounds have not been found to be superconducting above 1.7 K. X-ray photoelectron measurements carried out on ThSiz _,Ir, silicides show that electrons are transfered towards silicon and iridium atoms since the bonding energy of the Si( 2p) and Ir( 4f “‘) core electrons decrease with increasing x. The spectra of the valence bonds of o-ThSi, and a-ThSiz_,Ir, show a dominant character of the thorium 6d states at the Fermi level. A band centred at around 3.2 eV below the Fermi level appears in a-ThSiz_,Ir, compounds. It is attributed to the iridium 5d states and its intensity increases with x.
MSssbauer spectroscopy on 237Np-doped borosilicate glasses* I. POIROT and M. BEAUVY Commissariat ci 1’Energie Atomique, Centre d%tudes Nucleaires de Cadarache, DMECN/DECPu/SEFCA, 13108 St-Paul-lez-Durance Ckdex (France)
ZRDZ/
M. BOGE, D. BONNISSEAU, A. BLAISE, J. M. FOURNIER and P. G. THEROND C.E.N./Grenoble, *Abstract 1985.
ZRF/DRF/SPh,
85 X, 38041
Grenoble
of paper presented at Actinides
Cedex (France)
35, Aix en Provence, September 2 - 6,
655 Mossbauer measurements have been carried out on borosilicate glasses containing less than 5 weight % of neptunium [l]. Using the 59.5 keV MSssbauer resonance in 237Np we have characterized the valency states of neptunium ions in glasses and studied the hyperfine interactions. After this study it is possible to define the typical MSssbauer spectra for these compounds. The absorption spectra show two sites above 50 K easily differentiated by two lines. One very well resolved, with an isomer shift of +32.5 (f0.5) mm s-l (relative to NpAlz), is characteristic of Np3+. The second very broad, with an isomer shift of -10.0 (fl.O) mm s-l must be assigned to Np4+. This result had been checked by optical spectroscopy [2]. At 4.2 K, Np4+ ions exhibit an hyperfine splitting arising from paramagnetic relaxation phenomena. Magnetization measurements do not show any magnetic ordering. The effect of the neptunium concentration had been analysed. 1 I. Poirot, M. Beauvy and M. Boge, J. Less-Common Met., 121 (1986). 2 I. Poirot and M. Beauvy, J. Less-Common Met., 121 (1986).
The reaction of PuH, and Pu + PuH, mixtures with air* J. M. HASCHKE and A. E. HODGES, III Rockwell
International,
Rocky
Flats Plant, Golden,
CO (U.S.A.)
The Pu + H2 reaction is used in recovery for separating plutonium from other materials that do not readily form hydrides and in preparing finely divided plutonium for powder metallurgy. Conflicting reports in the literature describe the hydride both as “stable” and as “pyrophoric” in air. During hydriding and dehydriding operations, the hydride (PuH,, 2 4 x Q 3) is typically contained in a pressure-vacuum system to protect the PuH, from the atmosphere. A study was initiated to investigate the possible consequences of accidentally venting a system containing PuH, or a Pu + PuH, mixture to air. The reaction between PuH, and air is a complex process in which 02 and Nz react and H2 forms. At various conditions, three types of reaction occur. (1) If the hydride is cubic PuH, (2.G < x < 3.0) obtained by slow reaction of the elements at low P and 2’ (less than 100 “), a rapid pyrophoric reaction ensues if the system containing the hydride is vented to 1 bar of air at ambient or elevated temperatures. During this reaction, all the O2 entering the system and 1.6 + 0.5 times that amount of Nz are consumed with the formation of PuO, (y = 1.5/2.0), PUN and Ha, but no HzO. (2) If the hydride is hexagonal PuH, (2.88 < x < 3.00) formed by rapid reaction of the elements at high P and T (greater than 300 “C), reaction with air does not initiate on venting. On heating under 1 bar of air, this hydride ignites as 377 f 13 “C in a pro’cess similar to that for cubic PuH,. (3) If the system contains a mixture of plutonium and cubic PuH,, a violent reaction frequently ensues on air venting. The reaction initiates as in (1) but does not stop until the entire sample is converted to oxide and nitride. The difference between cases (1) and (2) and conflicting literature reports are consistent with the properties of cubic and hexagonal PuH,. In comparison with the hexagonal phase, the cubic hydride has a high surface area (0.20 m* g-‘) and low activation dehydriding energy (E, = 0 for PuHz.8). Formation of hydrogen at the surface of hexagonal
1985.
*Abstract
of paper presented at Actinides 85, Aix en Provence,
September 2 - 6,
Structural aspects, physical properties and X-ray photoelectron spectra of valence bands of new pseudo-binary thorium silicides: a-ThSi, _,T, (O
de Chimie du Solide du CNRS, 33405 Talence Cddex (France)
Universite’ de Bordeaux
1, 351 Cours de la
P. LEJAY Centre de Recherches sur les Tres Basses B.P. 166, 38402 Grenoble Ckdex (France)
Temperatures,
CNRS,
Avenue
des Martyrs,
L. PORTE and TRAN MINH DUC Znstitut de Physique Nucleaire de Lyon (IN 2P3), Universite 43 Bdl du 11-Novembre 1918, 69622 Villeurbanne (France)
Claude Bernard,
Lyon
I,
J. P. KAPPLER and M. J. BESNUS LMSES, Znstitut de Physique,
3 rue de I’Universite,
67084 Strasbourg
Cedex (France)
Thorium disilicide is dimorphic and both forms are superconducting @ThSiz, AlBztype, T, = 2.41 K and o-ThSiz, tetragonal, Tcr = 3.16 K). New materials have been obtained by substitution of silicon by transition elements such as rhodium and iridium in a-ThSiz. The superconducting behaviour of the silicides has been shown by electrical, magnetic and specific heat measurements. The variation in the superconducting transition temperature T, versus x is similar for both o-ThSiz_,Rh, and a-ThSiz_,Ir, systems. With increasing x, T, decreases for 0 < x < 0.25 and increases sharply for x > 0.75 reaching 6.50 K for the equiatomic compounds (x = 1). The maximum TcI value is a little higher than twice that of o-ThSiz. In the intermediate composition range 0.25 / x < 0.75 the corresponding compounds have not been found to be superconducting above 1.7 K. X-ray photoelectron measurements carried out on ThSiz _,Ir, silicides show that electrons are transfered towards silicon and iridium atoms since the bonding energy of the Si( 2p) and Ir( 4f “‘) core electrons decrease with increasing x. The spectra of the valence bonds of o-ThSi, and a-ThSiz_,Ir, show a dominant character of the thorium 6d states at the Fermi level. A band centred at around 3.2 eV below the Fermi level appears in a-ThSiz_,Ir, compounds. It is attributed to the iridium 5d states and its intensity increases with x.
MSssbauer spectroscopy on 237Np-doped borosilicate glasses* I. POIROT and M. BEAUVY Commissariat ci 1’Energie Atomique, Centre d%tudes Nucleaires de Cadarache, DMECN/DECPu/SEFCA, 13108 St-Paul-lez-Durance Ckdex (France)
ZRDZ/
M. BOGE, D. BONNISSEAU, A. BLAISE, J. M. FOURNIER and P. G. THEROND C.E.N./Grenoble, *Abstract 1985.
ZRF/DRF/SPh,
85 X, 38041
Grenoble
of paper presented at Actinides
Cedex (France)
35, Aix en Provence, September 2 - 6,
655 Mossbauer measurements have been carried out on borosilicate glasses containing less than 5 weight % of neptunium [l]. Using the 59.5 keV MSssbauer resonance in 237Np we have characterized the valency states of neptunium ions in glasses and studied the hyperfine interactions. After this study it is possible to define the typical MSssbauer spectra for these compounds. The absorption spectra show two sites above 50 K easily differentiated by two lines. One very well resolved, with an isomer shift of +32.5 (f0.5) mm s-l (relative to NpAlz), is characteristic of Np3+. The second very broad, with an isomer shift of -10.0 (fl.O) mm s-l must be assigned to Np4+. This result had been checked by optical spectroscopy [2]. At 4.2 K, Np4+ ions exhibit an hyperfine splitting arising from paramagnetic relaxation phenomena. Magnetization measurements do not show any magnetic ordering. The effect of the neptunium concentration had been analysed. 1 I. Poirot, M. Beauvy and M. Boge, J. Less-Common Met., 121 (1986). 2 I. Poirot and M. Beauvy, J. Less-Common Met., 121 (1986).
The reaction of PuH, and Pu + PuH, mixtures with air* J. M. HASCHKE and A. E. HODGES, III Rockwell
International,
Rocky
Flats Plant, Golden,
CO (U.S.A.)
The Pu + H2 reaction is used in recovery for separating plutonium from other materials that do not readily form hydrides and in preparing finely divided plutonium for powder metallurgy. Conflicting reports in the literature describe the hydride both as “stable” and as “pyrophoric” in air. During hydriding and dehydriding operations, the hydride (PuH,, 2 4 x Q 3) is typically contained in a pressure-vacuum system to protect the PuH, from the atmosphere. A study was initiated to investigate the possible consequences of accidentally venting a system containing PuH, or a Pu + PuH, mixture to air. The reaction between PuH, and air is a complex process in which 02 and Nz react and H2 forms. At various conditions, three types of reaction occur. (1) If the hydride is cubic PuH, (2.G < x < 3.0) obtained by slow reaction of the elements at low P and 2’ (less than 100 “), a rapid pyrophoric reaction ensues if the system containing the hydride is vented to 1 bar of air at ambient or elevated temperatures. During this reaction, all the O2 entering the system and 1.6 + 0.5 times that amount of Nz are consumed with the formation of PuO, (y = 1.5/2.0), PUN and Ha, but no HzO. (2) If the hydride is hexagonal PuH, (2.88 < x < 3.00) formed by rapid reaction of the elements at high P and T (greater than 300 “C), reaction with air does not initiate on venting. On heating under 1 bar of air, this hydride ignites as 377 f 13 “C in a pro’cess similar to that for cubic PuH,. (3) If the system contains a mixture of plutonium and cubic PuH,, a violent reaction frequently ensues on air venting. The reaction initiates as in (1) but does not stop until the entire sample is converted to oxide and nitride. The difference between cases (1) and (2) and conflicting literature reports are consistent with the properties of cubic and hexagonal PuH,. In comparison with the hexagonal phase, the cubic hydride has a high surface area (0.20 m* g-‘) and low activation dehydriding energy (E, = 0 for PuHz.8). Formation of hydrogen at the surface of hexagonal
1985.
*Abstract
of paper presented at Actinides 85, Aix en Provence,
September 2 - 6,