Thermodynamic measurements in liquid tin-tellurium alloys
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THE
present work was c a r r i e d out as a continuation of the investigation of systems showing strong interactions in the liquid state. Thermodynamic data for molten Sn, T e alloys are limited. Although s e v e r a l authors have reported measurements of the heats of solution,1~ only P r e d e l et a l6 have published values concerning the activities at 1281 K. 2.
EXPERIMENTAL
Ill
Tin activity in liquid Sn, T e alloys was determined by electromotive force measurements involving the following c e l l : Sn(l) ISn÷2ISn, We(l).
=RT I n a s n = - 2 E F ;
~Sn = 2F
~
/
The apparatus and experimental techniques were ident i c a l with those used in previous studies and full details may be found in an e a r l i e r publication,7 so that a b r i e f account will suffice h e r e . The P y r e x galvanic cell used in this work is shown in Fig. 1. It consisted of three tin reference electrodes and five tin-tellurium alloy electrodes of different composition. The p u r i t y of tin and tellurium used in the experiment was better than 99.980 and 99.999 mass pct respectively. The liquid electrolyte was made of the eutectic mixture of potassium and lithium chlorides containing about two mass pct of stannous chloride. The electrical junctions were tungsten wires. After transfer of the liquid electrolyte into the cell which contained the electrodes, the assembly was evacuated, then filled with a r g o n and sealed. Temperatures were controlled t o +1 K and measured M. LeBOUTEILLER, R. FARHI, and C. PETOT are all with the Universit6 de Paris-Nord, A. M.MARTRE is CNRS, Laboratoire d'Etudes des Propri6t6s M6caniques et Thermodynamiques des Mat6riaux, Universit6 Paris-Nord, 93430 Villetaneuse, France. Manuscript submitted August 9, 1976. METALLURGICAL
i
I
TRANSACTIONS B
electrolyte; 2) electrolyte; 3) Pyrex cell; 4) Pyrex sheath for thermocouple; 5) Pyrex crucible; 6) alloy or reference cell, Sn(1); and 7) tungsten leads.
;
/oE/r'
---2F \0
®
F i g . 1--Cell a s s e m b l y : 1) i n t r o d u c t i o n h o l e for a l l o y s and
The partial thermodynamic properties of tin were found from the relations: ~Sn
-.
with a chromel-alumel thermocouple placed in the middle of the cell (Fig. 1). The alloys were homogenized by maintaining the temperature of the cell a p proximately 40 K above the melting point of the more refractory alloy for about 12 h. The reversibility of the c e l l s was checked during the recording of the emf. Indeed, in seeking the null point at which the r e c o r d e r potential balanced the potential of the c e l l , a s m a l l current from the recorder passed in either direction through the cell without disrupting the null p o i n t . The measurements were c a r r i e d out at constant temperature at approximately 10 to 20 K intervals. For each isotherm the stability is verified for 30 t o 45 min. Moreover the temperature r a n g e is investigated many times to verify the reproducibility of the obtained results. 3. RESULTS 3.1. Thermodynamic Properties Fig. 2 shows the variation E = f ( T ) for 16
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