Kinetic studies have been made of the thermal decomposition of precipitated calcium carbonate, powdered calcite, and regular fragments of calcite crystals. The powdered materials were examined in the form of pellets, which were prepared by compacting the powder to about 70% of its theoretical density. The work was done at one atmosphere of pressure in a flow of air containing various amounts of carbon dioxide. It was observed that the decomposition of the pellets, which were prepared in a variety of shapes, was characterized by the same advancing interface mechanism as that observed for single specimens of crystal fragments. When the rates of decomposition were normalized for the change in of interfacial area accompanying decomposition, it was possible to correlate the observed rates of decomposition for a variety of pellet shapes, and to relate these rates, as a function of particle size and pellet roughness, to the rates of decomposition of large fragments of calcite crystals. The activation energy for the decomposition reaction was found to be 40.6 kcal./mole. At a constant temperature, the decrease in reaction rate with increasing carbon dioxide pressure was found to be proportional to the difference between the equilibrium dissociation pressure and the back pressure of carbon dioxide. A reaction mechanism based on diffusion through a constant thickness of active calcium oxide is suggested.

A reversible silver − silver chloride reference electrode for use in melts at high temperatures has been developed. It was found that the solution of silver chloride in an equimolar mixture of KCl–NaCl melt is ideal for the range of concentrations studied, i.e. 1.0 × 10−3 to 6.0 × 10−2 mole fraction of AgCl.The electromotive force of the voltaic cell[Formula: see text]in which the half-cell to the right contains the above-mentioned reference electrode, was measured as a function of CoCl2 concentration. The applicability of the Nernst equation to this system was established. Deviation from ideality was observed in the case of the solution of CoCl2 in the melt solvent, and this was attributed to the formation of a complex. The dissociation constant of this complex was calculated as 4.50 × 10−2 at 710 °C.The effect of temperature on the electromotive force of this cell was also measured, and the heat of the cell reaction in the presence of solvent (Co + 2AgCl → CoCl2 + 2Ag) was calculated from the data as 22.8 ± 1.3 kcal.The thermodynamic significance of the standard electrode potential of the Co–Ag voltaic cell, derived experimentally as 0.324 volt, is discussed briefly.

PART 111. THE SYSTEM SILVER -SILVER CHLORIDE, CADMIUM -CADMIUM CHLORIDE'bsing a sil\.er-sil\.cr chloride reference electrode, the stantl.ird elrtctrocl-p-1tcnti:ll h-1s 11:-n establishetl for the eq~lilibriurn CdICd++ in melts containing ecl~rimolar cl~r~ntities of ICCI ancl NaCL. The csperirnerltally obtairietl stallclarcl potclitial \\.as greater than that calc~rlated from theoretical thermodynamic data. This difference was attributed to the formation of a cadmi~cm complex in the lnelt. A dissociation constant for thc co~nplex \\.as calc~rlatetl.The erfect of temperature on the electromotive force of the silver-caclrnium voltaic cell mas also mcas~rrecl, and the heat of the cell reactior~ mas calc~~lated from the data. To estcr~cl the ternperat~~re range of the cadnii~rm data, a catlrni~~m-lead alloy was ~~s e c l in the higher ternperatwe experiments. To correlate these data with those for the pure c a d m i~~r n systern, the act~vity coefficiel~ts of c a d m i~~n i in the alloy mere determined electromctrically using the silversilver chloride electrode as a reference. It was found that the activity coefficients were in agreement with previously publishecl data obtailled a t Iowrer temperatures usi~ig a purc cadmium reference electrode. The activity coefficients werc v i r t~~a l l y indepenclcnt of temperature but showed large positive deviations from unity whel~ thc mole fraction of c a t l m i~~n~ was decreased below about 0.8. INTIIODUCTIONParts I and I1 of this series (1, 2 ) described the development ancl use of a reversible silver -silver chloride reference electrode for determining the electromotive forces of voltaic cells in chloride melts a t high temperatures.In this paper, experiments will be clescribecl in nrhich the silver -silver chloride reference electrocle was used to study the cadmiunl -cadmium chloricle equilibria. An equi~nolar mixture of molten potassium and sodi~im chlorides was used as the colnlnoll solvent.These results are an additional contribution t o the current program of establishing electromotive series for metals in molten salts a t different temperatures.The technique used to studjr the Cd-Ag system was essentialll~ the same as that previously described (1). During the preliminary experimental a o r k it became apparent that because of the relatively high vapor pressure of moltell cadmium and the inflammability of cadmium vapor in air, a closed cell operating with an inert atmosphere ivould be required. The complete cell design is s h o n~i~ in Fig. I. The cell was constructed from silica tubing of 2 in. diameter and co~lsistecl of two sections connected by a ground silica joint. The upper section of the cell was closed with a cork stopper, into which were fitted the silver -silver chloride reference electrode, the thermocouple well, the feeding pipe with stirrer, and the gas inlet tube. The col-6 stopper was covered externally with Pyseal cement and then water-cooled to prevent the melting of the cement from the heat of the furnace. The inner surface of the cork stopper was ...

No abstract

The potentials of a series of metal‐metal chloride systems in an equimolar mixture of molten potassium and sodium chlorides have been measured against a silver‐silver chloride reference electrode. An electromotive force series of metals at different temperatures has been established for this particular solvent. Experiments with a chlorine electrode have shown that the solutions of silver chloride in the normalKCl‐normalNaCl solvent are ideal, and hence, deviations from ideality of the other chlorides in this solvent can be attributed directly to the formation of complexes in the melts. Three types of behavior have been observed for the salts studied in this solvent: ideality, and positive and negative deviations from ideality. The theoretical aspects of complex formation in melts are discussed.