Eutectic carbonate melt

In the case of the ternary eutectic Li2C03-Na2C03-K2C03 at 605°C saturated with pure C02 (p02 = 6), the anodic limit is about 0.27 V vs. the oxygen electrode however, when saturated with Li20 (pO2- = 0) this melt is reported to exhibit an anodic limit of only -0.23 V [5]. The cathodic limit of ternary eutectic carbonate melts with p02 = 2 to 6 is about -1.9 to -2.1 V [5]. The reduction process produces elemental carbon according to the reaction... 

The carbonate ions are transported towards the anode electrode through the electrolyte, which is an eutectic carbonate melt The cathodic exhaust gas leaves the fuel cell and, due to its high temperature of about 500 °C, it can be used for subsequent steam generation, for additional production of electric energy via a micro turbine or for other purposes. 

Zhang, X.G. Capobianco, P. Torazza, A. Passalacqua, B. A solubility study of prelithiated NiO and prelithiated cobaltite as cathode materials for MCFC in 62 Li-38 K eutectic carbonate melts. Electrochemistry 1999, 61 (6), 603-607. 

Many electrochemical devices and plants (chemical power sources, electrolyzers, and others) contain electrolytes which are melts of various metal halides (particularly chlorides), also nitrates, carbonates, and certain other salts with melting points between 150 and 1500°C. The salt melts can be single- (neat) or multicomponent (i.e., consist of mixtures of several salts, for their lower melting points in the eutectic region). Melts are highly valuable as electrolytes, since processes can be realized in them at high temperatures that would be too slow at ordinary temperatures or which yield products that are unstable in aqueous solutions (e.g., electrolytic production of the alkali metals). 

In the molten carbonate process, a molten eutectic mixture of lithium, sodium, and potassium carbonates is used to scrub the power plant gas stream. The sulfur oxides in the gas stream react with the carbonates to form sulfites and sulfates which remain dissolved in excess unreacted carbonate melt. The molten carbonate-sulfite-sulfate mixture is then... 

Carbon activities in alkali metals are also estimated by electrochemical meters. These are based on the activity differences between two carbon bearing electrodes separated by a carbon ions conducting electrolyte. The electrolyte is a molten salt mixture, consisting of the eutectic of lithium and sodium carbonate, melting at approximately 500 °C. The molten salt mixture has to be kept free from any impurities or humidity. The mixture, acting as liquid electrolyte is kept in an iron cup. The iron wall is in contact with both the liquid electrolyte and the liquid metal. Thus, it exchanges carbon with both up to the equilibrium. Iron, with the same carbon potential as the liquid metal, acts as one electrode. The reference electrode of graphite or any other material with a well defined and stable carbon activity is immersed in the molten electrolyte. The Nernst equation defines the potential of the electrochemical chain ... 

The working temperature of molten carbonate fuel cells is around 600-650°C. Mixed carbonate melts containing 62-70 mol% of lithium carbonate and 30-38 mol% of potassium carbonate, with compositions close to the eutectic point, are used in molten carbonate fuel cells as an electrolyte. Sometimes, sodium carbonate and other salts are added to the melts. This liquid melt is immobilized in the pores of a ceramic fine-pore matrix, made of sintered magnesium oxide or lithium aluminate powders. 

O ] decreases if the carbon dioxide partial pressure increases therefore, the carbonate melt changes to acidic. The solubility of NiO then increases according to the equilibrium of Eqs. 6 and 7. Therefore, the durability of the pressurized system is more severe than the ambient pressure system. The cation species also affects the basicity. A higher charge density, which is smaller ion diameter and higher valence, produces more basic property. The Li/Na eutectic carbonate is more basic than the Li/K eutectic therefore, the solubility in the Li/Na eutectic carbonate is lower than that in the Li/K eutectic carbonate. An alkaline earth metal or rear earth metal additive to the electrolyte decreases the NiO solubility by the control of basicity [2-6]. 

In view of their importance, corrosion of non-oxide ceramics were studied in chloride, sulphate and carbonate melts. Tressler etal. have studied the corrosion resistance at 1(XX)°C of commercially available SiC and Si N4 ceramics against pure Na2S04 and NaCl and their eutectic mixture. The corrosiveness of these salts decreases in the following sequence Na2S04 > Na2S04 -F NaCl NaCl, showing the dependence of the corrosion effects on the free-oxide ion activity. Si3N4 is much less reactive than SiC. It was... 

The MCFC is an electrochemical reaction system where the anode oxidizes Ha to HaO and the cathode reduces Oa to CO as shown in Eqs. 8.1a and 8.1b. Thus carbonate materials serve as the electrolyte, which is generally a mixture of various alkali metal carbonates of LiaCOs, NaaCOa, and KaCOa. Table 8.1 shows the melting points (m.p.), surface tension (y), density (p), electric conductivity (k), and Henry s Law constant of Oa dissolution (/toz) for various eutectic carbonates. 

The diagram for the system nickel-ternary eutectic at 600 °C is shown in Fig. 84 as an example. It is divided into three regions in which only one nickel phase may be present at unit activity. The boundary between the Ni" and NiO areas is the value of PCO2 at which solid NiO precipitates from a pure nickel carbonate melt. When the oxygen pressure is reduced beyond the dissociation pressure of NiO atni), nickel metal... 

Lithium carbonate addition to HaH-Heroult aluminum ceU electrolyte lowers the melting point of the eutectic electrolyte. The lower operating temperatures decrease the solubiHty of elemental metals in the melt, allowing higher current efficiencies and lower energy consumption (55). The presence of Hthium also decreases the vapor pressure of fluoride salts. 

Lithium Chloride. Lithium chloride [7447- 1-8], LiCl, is produced from the reaction of Hthium carbonate or hydroxide with hydrochloric acid. The salt melts at 608°C and bods at 1382°C. The 41-mol % LiCl—59-mol % KCl eutectic (melting point, 352°C) is employed as the electrolyte in the molten salt electrolysis production of Hthium metal. It is also used, often with other alkaH haHdes, in brazing flux eutectics and other molten salt appHcations such as electrolytes for high temperature Hthium batteries. 

Lithium Bromide. Lithium biomide [7550-35-8] LiBi, is piepaied from hydiobiomic acid and lithium carbonate oi lithium hydroxide. The anhydrous salt melts at 550°C and bods at 1310°C. Lithium bromide is a component of the low melting eutectic electrolytes ia high temperature lithium batteries. 

The reaction of chlorine gas with a mixture of ore and carbon at 500—1000°C yields volatile chlorides of niobium and other metals. These can be separated by fractional condensation (21—23). This method, used on columbites, is less suited to the chlorination of pyrochlore because of the formation of nonvolatile alkaU and alkaline-earth chlorides which remain in the reaction 2one as a residue. The chlorination of ferroniobium, however, is used commercially. The product mixture of niobium pentachloride, iron chlorides, and chlorides of other impurities is passed through a heated column of sodium chloride pellets at 400°C to remove iron and aluminum by formation of a low melting eutectic compound which drains from the bottom of the column. The niobium pentachloride passes through the column and is selectively condensed the more volatile chlorides pass through the condenser in the off-gas. The niobium pentachloride then can be processed further. 

Electrolytic aluminum production is the most important process in both volume and significance. World production is about 15 megatons per year, consuming about 240 billion kilowatthours of electrical energy. Aluminum oxide (alumina), AI2O3, is subjected to electrolysis at a temperature of 950°C to this end it is dissolved in molten cryolite NujAlFg, with which it forms a eutectic melting at about 940°C. Carbon anodes that are anodically oxidized to CO2 in the process are employed. The overall electrolysis reaction can be written as... 

The carbon monoxide prevents reoxidation of the hot copper. A further temperature rise to about 900°C results in the copper and gold (or silver) at the surface of the parts interacting to form a eutectic. The eutectic melts and runs freely, wetting the surface as well as the attached wires or granules. When the assemblage is finally cooled, the eutectic solidifies, firmly joining the wires or granules to the now decorated surface. 

---