Measurements of standard molar Gibbs energies of formation of NiO, CutO, and Co0 from solid and

A-032
J. Chem. Thermodynamics 1979,11,215-228
Measurements of standard molar Gibbs energies of formation of NiO, CutO, and Co0 from solid and liquid metals and oxygen gas by an e.m.f. method at high temperatures
(VI Pt~LaCrO~~Ni(s,l),NiO(s)~ZrO,+Ca0~Co(s,l),CoO(s)~LaCrOs~Pt.
The results were compared with previously reported values.
1. Introduction
Recently, thermodynamic properties of many metal + oxygen systems have been investigated by the use of galvanic cells employing solid oxide electrolytes. In the present work, the standard molar Gibbs energies of formation of NiO, Cu,O, and Co0 at high temperatures were determined by e.m.f. measurementsof galvanic cells with an air reference electrode. Each cell run was carried out over a wide temperature range in which melting temperatures of metal or metal oxide were included. The eutectic temperatures of the Ni + NiO, Cu + Cu,O, and Co + Co0 systems and the monotectic temperature of the Cu + Cu,O system,derived from the present work, were compared with those reported by other investigators. For the standard molar Gibbs energy of formation of NiO, many investigatorso-‘) have reported using the e.m.f. method in the lower temperature range from 973 to 1473 K. In the higher temperature range from 1473to 1726K (the melting temperature of Ni), the standard molar Gibbs energy of formation of NiO has been measured by a few researchers.(‘-‘) However, no values by the e.m.f. method have been reported hitherto at temperatures above 1726 K.
I. KATAYAMA,
AND Z. KOZUKA
For the standard molar Gibbs energy of formation of C&O, many investigator@ 3-5,*) have reported using the e.m.f. method at temperatures below 1356K(the melting temperature of Cu). In the temperature range from 1356to 1517 K (the melting temperature of Cu,O), the standard molar Gibbs energy of formation of Cu,O has been measured by a few researchers. (*-r’) Furthermore, at temperatures above 1517 K Osterwald(g’ has investigated this system. However, no systematic study has been carried out in the wide temperature range including the melting temperatures of both Cu and Cu,O. For the standard molar Gibbs energy of formation of COO, someinvestigators(‘,4* 5, have reported using the e.m.f. method at temperatures below 1473 K. In the temperature range from 1473 to 1766 K (the melting temperature of Co), only the results of Fischer and Pateisky(5)have been reported. No results by the e.m.f. method have been reported so far at temperatures above 1766 K.
t Throughout this paper atm = 101.325 kPa; cd, = 4.184 J; Torr = (101.325/760) kPa.
STANDARD
GIBBS ENERGIES
OF FORMATION
OF NiO, C&O, AND COO 217
If the mutual solubilities of M and M,O,, are negligibly small, A~G”(M,OJ is equal to AG. Consequently A@‘(M,O$ can be calculated from only the e.m.f. values of cell (VI) according to equations (I) and (5). However, if the mutual solubilities are relatively large, Acr can not be neglected compared with AG. Therefore, Acl must he evaluated for the accurate determination of A,G”(M,O,,). The evaluation of ALX will
N. KEMORI,a I. KATAYAMA, and Z. KOZUKA
Faculty of Engineering, Osaka Department of Metallurgical Engineering, University, Suita, Osaka 565, Japan
(Received 8 June 1977; in revised form II April 1978)
xM+ (y/2)0, = M,O,, (2)
by the equation:
UVLO,J = -RT ~~C~~~,~,>/~~~~~~“~~“~~~>/~“)y’21~ (3) Where p” is a standard pressure (101.325 kPa), and where a(M) and a(M,O,) denote the activities of M and of M,O, in equilibrium in the M + M,O, pseudobinary system. It is convenient for the evaluation of AfG”(M,O,,) that the right hand side of equation (3) is divided into two terms: A,G”(M,O,,) = AG+ Aa, (4) (5) AG = (Y/WT lnbeP2Yf~3 Au = RT In[{a(M))“/n(M,O,,)]. (6)
பைடு நூலகம்
E.m.f. measurements of the following galvanic cells with the solid oxide electrolyte (ZrOz + CaO) were carried out to determine the standard molar Gibbs energies of formation of NiO, C&O, and Co0 from solid and liquid metals and oxygen gas: (I) PtILaCrOsINi(s,l),NiO(s)lZrOz+CaO]airlPt, (II) Pt~LaCrO$u(s,l).CuzO(s,l)~ZrOa+CaO~air~Pt, (III) Pt~LaCrO~~Co(s,l),CoO(s)~Zr02+C?aO~air~Pt. The differences between the e.m.f.‘s of cells (I) and (II), and of cells (I) and (III) were compared with the e.m.f.‘s of the cells: (IV) PtINi(s),NiO(s)lZrO2+CaOICu(s,l),CuzO(s,l)lLaCrOBIPt,