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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 .

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The s ilic id e s of T i, Z r, Ce and Nb were Investigated to determine the phases present a t tem peratures around 2000*K* The m o tio n s o f s ilic id e s of T i, Z r, Ce, Nb, Ta, Ho and V with earbon were studied a t these tempera tu re s * Also a U n ited amount of work was dons on the reactions o f some of the s ilic id e s with nitrogen* The data have been used to estab lish tern ary phase diagrams for the systems and to obtain upper and lower lim its fo r the heats o f formation of the silic id e s * The till* on natal m s obtained fra ths J. T. Baker Chesdeal Company 1a the form of lumps. It was ground to finsr than H O math with a steal mortar I and pestle. Spsctroenalyeia showed the main Impurities to bat T1 lass than 1#» Cr 0.1-1# and A1 and fa approximately 0,1#. X-ray analysis showed a ray weak unidentified second phase* The Zr natal was obtained in the font of high parity eposes and of rather impure powder* The main inpurities in the powder tsars dissolved oxygen and nitrogen. X-ray diffraction showed two Zr phases-on# set of lines corre sponding to purs Zr and the other to Zr with dissolved 0 or M. The phase with the emended lattioe (a • 3.26 A, o • 5.19A) corresponds to 22 atomict oxygen assuming that all of ths dissolved gas le oxygen.Î gnition experiments showed that tha Zr contains 214 atomic % (4*54 wt. t) oxygen. The value fra tha ignition experiments is taken to be correct.X-ray analysis of the Ti mstal showed that it also contained dissolved oxygen and nitrogen. Assuming that all of ths d iaaolved gas is oxygen ths lattice constants (a • 2.95 A, c ■ 4*69 A) indicats 4*5 atonic percent oxygen.^ Ths main imparity in ths Ct metal was 5 atomic % carbon.All of ths other ns tala were of 99*91 or greater purity* *• *