Graphite baths

Graphite Baths.—These are sometimes used in place of oil baths. 

Fig. 28. Apparatus for preparation of phthalic anhy

Aluminum industry uses molten fluoride salts in graphite baths to produce aluminum (100+ years of experience)... 

Only one type of nuclear fuel has been fully demonstrated for use in high-temperature reactors for commercial applications the graphite-matrix coated-particle fuel. Although helium has historically been the coolant used in high-temperature reactors, graphite-based fuel is also compatible with one other type of coolant molten fluoride salts. For example, for over a century the aluminum industry has produced aluminum by electrolytic methods in graphite baths filled with molten fluoride salts at 1000°C. The AHTR uses a low-pressure molten fluoride salt with a boiling point of 1400°C. 

Molten Fluoride Salts Have Been Used for a Century to Make Aluminum in Graphite Baths at 1000°C... 

For high-temperature operations, materials, and fuels are key technologies. There is a century of large-scale experience in the use of fluoride molten salts. Aluminum is made by electrolysis of a mixture of bauxite and sodium aluminum fluoride salts at 1000 C in large graphite baths. Fluoride salts are compatible with graphite fuels. A smaller nuclear experience base exists with molten fluoride salts in molten salt reactors. Nickel alloys such as modified Hastelloy-N have been qualified for service to 750 C. A number of metals and carbon-carbon composites have been identified for use at much higher temperatures however, these materials have not yet been fully developed or tested for such applications. 

The pure oxide is dissolved in molten cryolite in an iron bath lined with graphite which acts as the cathode (see Figure 7.1). The anode... 

The most common fused salt baths are complex mixtures of alkah chlorides, rigorously purified and dried. Fused salt plating must be done under an inert atmosphere. Often argon is used because nitrogen can react with some metals. Inert anodes, eg, Pt-coated titanium or graphite, are used and the plating metal is suppHed by additions of an appropriate metal salt. 

Fig. 2. Downs cell A, the steel shell, contains the fused bath B is the fire-brick lining C, four cylindrical graphite anodes project upward from the base of the cell, each surrounded by D, a diaphragm of iron gau2e, and E, a steel cathode. The four cathode cylinders are joined to form a single unit supported on cathode arms projecting through the cell walls and connected to F, the cathode bus bar. The diaphragms are suspended from G, the collector assembly, which is supported from steel beams spanning the cell top. For descriptions of H—M, see text.

T. D. Burchcll. Studies of Fracture in Nuclear Graphite, Ph.D Thesis, University of Bath, UK, 1986. 

The electrolyte is made by in situ chlorination of vanadium to vanadium dichloride in a molten salt bath. Higher valent chlorides are difficult to retain in the bath and thus are not preferred. The molten bath, which is formed by sodium chloride or an equimolar mixture of potassium chloride-sodium chloride or of potassium chloride-lithium chloride or of sodium chloride-calcium chloride, is contained in a graphite crucible. The crucible also serves as an anode. Electrolysis is conducted at a temperature about 50 °C above the melting point of the salt bath, using an iron or a molybdenum cathode and a cathode current density of 25 to 75 A dnT2. The overall electrochemical deposition reaction involves the formation and the discharge of the divalent ionic species, V2+ ... 

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