THE VAPOUR PRESSURE OF Th(g) ABOVE ThC$sub 2$ AS DETERMINED BY EMISSION SPECTROSCOPY

Abstract

E m i s s i o n s p e c t r a offer a useful but relatively unexplored technique I for detection of species in high t e m p e r a t u r e s y s t e m s . In t h i s work the Y \ ' ? .' , ' /'. emission intensity of atomic Th above carbon s~t u r a t e d ThC was used a s a 2 m e a s u r e of Th vapour, p r e s s u r e .by applying the second and t h i r d laws of thermodynamics. A King igraphite t u b e ) ' f u r n a c e operated a t 2100 t o 2500 ".C was. used f o r . t h e e m i s s i o n s o u r c e . The inner b o r e of a graphite h e a t e r tube was coated with p r e r e a c t e d ThC t o .provide a region of equilibrated vapour. 2 ' 1 . Spectra w e r e detected by focusing the vapour e m i s s i o n ontb the ' s l i t of a scanning grating s p e c t r o m e t e r . Intensities w e f e measured. w i t h . a photomultiplier . Intensity m e a s u r e m e n t s w e r e made a t s e v e r a l t e m p e r a t u r e s , . f o r Th e m i s s i o n t o the ground s t a t e a t wavelength:s of 4 4 9 3 . 3 3 and 5760.55A, and fdr the C2 ( 0 -1) band head in t h e Swan s y s t e m a t 5 6 3 5 . 5 A . The second law . . ... of thermodynamics w a s applied to the data by using.the relation p a ,IT.. , Enthalpies of r e a c t i o n obtained w e r e : ' -iii-ThC2 ( s ) = 2C (graph)' ,. v + Th(g); AHo = 165 k c a l . .. . . 298 ThC2 ( s ) = C2 ( g ) + Th(g); = 361 k c a l 2C ( g r a p h ) = C2 (g); AH;98 = 199 kcal. By using, 137.7 . k~a l /~. . a t o m f o r the AH0 of sublimation of Th, the data . 298 . r e s u l t in -26.9* 5 kcal/mole for the AH0 f ,298 of. ThC2. The value for the of sublimation of C2 i s in a g r e e m e n t with previous work and lends confidence .to. the se'cond law t r e a t m e n t . In o r d e r t o use the t h i r d law method a' Th p r e s s u r e calibration was n e c e s s a r y . According1.y a W-foil tube lined on the inside with Th I-~ietal was supported within a graphite heater tube. The e m i s sion intensity was observed a t 1950 "C and c o m p a r e d with the known vapour p r e s s u r e of Th to obtain -" ..the calibration f a c t o r . C o r r e c t i o n s w e r e applied f o r solubility, of W i n .the Th, and f 0 r . a difference in. emitting pathlength of g a s in the two types of U e x p e r i m e n t s . A value of < -24.9 k c a l w a s obtained f o r AH" f ,298 of ThC2. Absolute e r r o r s in the determinations a r e difficult to evaluate. An uncertainty in the stoichiometry of the ThC phase and lack of sufficient 2 heat capacity information complicate the situation. P r e c i s i o n of intensity . m e a s u r e m e n t s i s good, however, with standard deviations ranging f r o m 0.1 t o 67'. . The technique c a n potentially provide rapid and a c c u r a t e determinations of thermodynamic data. It i s well suited for actinide work.in that it i s o l a t e s radioactive m a t e r i a l s f r o m . t h e detection s y s t e m .

International conference on large meteorite impacts and planetary evolution

“…The main conclusion to be drawn from our results is that (I) the 55 is the erosional remnantofa peak-ormultiring impactbasin with an original diameter in the 200-to 240-km range and (2) the SIC is no endogenic intrusion but rather the main part of an impact melt sheet that occupies the central depression of the basin and has been produced by shock-induced total meltinS of crustal rocks (8)(9)(10)(11)(12). Independently, R. A. F. Grieve of the Geological Survey ofCanada has come to quite identical conclusions [9].…”

“…It comprises from bottom to top (I) the sublayer, including the offsetdikes, anoritic to quartz-dioritic, clast-rich melt breccia that covers the floor of what is considered the transient cavity of the impact basin; (2) the norite, quartz gabbro, and granophyre units that are interpreted as clast-free, differentiated impact melt; and (3) the Basal Member of the Onaping Formation, a clast-rich melt breccia. The complete melt sequence has the chemical and isotope signatures of a mixture of upper and lower crustal rocks [12,14,15).…”

“…The Footwall rocks [6][7][8][9][10][11][12] exhibit shock metamorphic phenomena ofshock stage I, which is characteristicofan impactcrater floor. Shock metamorphism, including especially planar elements in LPI Contribution No.…”

“…790 7 quartz and shatter cones, can be observed up to a radial distance of 9 km from the lower SIC contact or up to 17 km (shattercones). The Footwall rocks were subjected to a thennal overprint by the SIC up to a distance of 1 km [8,12].…”

“…The FB [3,6,10,12,13) is the remnant of a clastic matrix crater floor breccia. It occurs u irregularly or lenticularly shaped bodies at thecontactbetween the Footwall and the SIC.…”