Electrolyte 3-alumina

For example, the structure of one of the best solid electrolytes, [3-alumina,... 

The molten salt (sodium aluminum chloride) fulfills two other tasks in the cell system. The ceramic electrolyte /3"-alumina is sensitive to high-current spots. The inner surface of the ceramic electrolyte tube is completely covered with molten salt, leading to uniform current distribution over the ceramic surface. This uniform current flow is one reason for the excellent cycle life of ZEBRA batteries. 

The electrolyte / " -alumina has already been described in Chapter III, Sec. 9. This section relates to additional information on the manufacture of / "-alumina and its application and behavior in high-tem-perature batteries (ZEBRA and Na /S). 

The results of development work on processes indicate that the two main methods of preventing the duplex microstructure from forming appear to be fast-firing, or increasing the amount of / "-alumina at low temperatures. Based on these results, Duncan et al. [20] and Zyl et al. [21] have described production processes starting from aluminum oxy-hydroxides or aluminum hydroxides as precursors for the synthesis of the solid electrolyte "-alumina. Duncan et al. described an alumina precursor which substitutes in part or wholly for or-alumina in an established... 

Primary electrolytic Alumina, carbon anodes, Fluoride, both gaseous Spent potliners... 

Fig. 6 Overvoltages in a Hall-Heroult cell versus electrolyte alumina content. From the work of Haupin [16].

Fig. 11 Dependence of exchange current density for the anodic reaction on electrolyte alumina content as reported by Kisza et al. [24].

The CTacks on the composite solid electrolyte-alumina interface usually appear when the composite solid electrolyte is rapidly quenching after the fusing temperature, which is normally over 1850°C, down to the temperature around 70Q-1000°C. Consequently, to avoid cracking, more gradual cooling should be provided around the whole interface area by various techniques. As a result, the... 

There are three groups of admixtures in raw Al nonmetallic, metallic, and gaseous. Nonmetallic admixtures are electrolyte, alumina, aluminium carbide, carbon particles, and oxide spots. They are taken from the reduction cell at tapping. Metallic admixtures are iron, silicon, titanium, sodium, and calcium. They come from raw materials. The gaseous admixture in raw Al is mostly hydrogen. 

Examples of similar processes are the decomposition of precipitated aluminum trHiydroxide to alumina, which is the feed for the electrolytic production of aluminum metal, and the drying of wet sulfide concentrates in preparation for flash roasting (see Aluminumand aluminum alloys). 

The electrolytic decomposition of alumina yields oxygen which reacts with the carbon anode for an overall cell reaction ... 

Purification actually starts with the precipitation of the hydrous oxides of iron, alumina, siUca, and tin which carry along arsenic, antimony, and, to some extent, germanium. Lead and silver sulfates coprecipitate but lead is reintroduced into the electrolyte by anode corrosion, as is aluminum from the cathodes and copper by bus-bar corrosion. 

Electrophoretic casting (38,59) is accompHshed by inducing controUed migration of charged particles under an appHed electric field to deposit on a mandrel. Thin tubular shapes and coatings of limited thickness are formed using this technique. Electrophoretic deposition (EPD) is also used to manufacture thin waU, soHd P -alumina [12005-16-2] NaAl Og, electrolytes for sodium—sulfur batteries. 

Electroplating. Aluminum can be electroplated by the electrolytic reduction of cryoHte, which is trisodium aluminum hexafluoride [13775-53-6] Na AlE, containing alumina. Brass (see COPPERALLOYS) can be electroplated from aqueous cyanide solutions which contain cyano complexes of zinc(II) and copper(I). The soft CN stabilizes the copper as copper(I) and the two cyano complexes have comparable potentials. Without CN the potentials of aqueous zinc(II) and copper(I), as weU as those of zinc(II) and copper(II), are over one volt apart thus only the copper plates out. Careful control of concentration and pH also enables brass to be deposited from solutions of citrate and tartrate. The noble metals are often plated from solutions in which coordination compounds help provide fine, even deposits (see Electroplating). 

Aluminum. Aluminum [7429-90-5] Al, is produced worldwide by the Bayer-HaH-Heroult process. This process involves the electrolysis of alumina [1344-28-1J, AI2O2, dissolved in molten cryoHte [15096-52-3] Na AIF (see Aluminumand aluminum alloys). The electrolytic cells or pots operate... 

Many metals are extracted from their compounds, as found in ores, by electrolytic processes. By far the most important is the Hall-Heroult process, invented in 1886, for producing aluminium from alumina, itself refined from bauxite ore. Alumina is dissolved in molten cryolite, Na3Alp6, and electrolysed, using carbon anodes and the aluminium itself as cathode. While various details are being steadily improved, the basic process is still the same today. 

Conventional batteries consist of a liquid electrolyte separating two solid electrodes. In the Na/S battery this is inverted a solid electrolyte separates two liquid electrodes a ceramic tube made from the solid electrolyte sodium /5-alumina (p. 249) separates an inner pool of molten. sodium (mp 98°) from an outer bath of molten sulfur (mp 119°) and allows Na" " ions to pass through. The whole system is sealed and is encased in a stainless steel canister which also serves as the sulfur-electrode current collector. Within the battery, the current is passed by Na+ ions which pass through the solid electrolyte and react with the sulfur. The cell reaction can be written formally as... 

Typical dimensions for the /5-alumina electrolyte tube are 380 mm long, with an outer diameter of 28 mm, and a wall thickness of 1.5 mm. A typical battery for automotive power might contain 980 of such cells (20 modules each of 49 cells) and have an open-circuit voltage of lOOV. Capacity exceeds. 50 kWh. The cells operate at an optimum temperature of 300-350°C (to ensure that the sodium polysulfides remain molten and that the /5-alumina solid electrolyte has an adequate Na" " ion conductivity). This means that the cells must be thermally insulated to reduce wasteful loss of heat atjd to maintain the electrodes molten even when not in operation. Such a system is about one-fifth of the weight of an equivalent lead-acid traction battery and has a similar life ( 1000 cycles). 

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