The chemistry of FLiBe, and other
fluoride salts, is unique due to the high temperatures at which the reactions occur, the ionic nature of the salt, and the
reversibility of many of the reactions. At the most basic level, FLiBe melts and complexes itself through : This reaction occurs upon initial melting. However, if the components are exposed to air they will absorb moisture. This moisture plays a negative role at high temperature by converting , and to a lesser extent LiF, into an oxide or hydroxide through the reactions : and : While is a very stable chemical compound, the formation of oxides, hydroxides, and
hydrogen fluoride reduce the stability and inertness of the salt. This leads to
corrosion. It's important to understand that all dissolved species in these two reactions cause the corrosion—not just the hydrogen fluoride. This is because all dissolved components alter the
reduction potential or redox potential. The redox potential is an innate and measurable voltage in the salt which is the prime indicator of the corrosion potential in salt. Usually, the reaction : is set at zero volts. This reaction proves convenient in a laboratory setting and can be used to set the salt to zero through bubbling a 1:1 mixture of hydrogen fluoride and hydrogen through the salt. Occasionally the reaction: : is used as a reference. Regardless of where the zero is set, all other reactions which occur in the salt will occur at predictable, known voltages relative to the zero. Therefore, if the redox potential of the salt is close to a specific reaction's voltage, that reaction can be expected to be the predominant reaction. Therefore, it is important to keep a salt's redox potential far away from reactions which are undesirable. For example, in a container alloy of
nickel,
iron, and
chromium, the reactions of concern would be the fluorination of container and subsequent dissolution of these metal fluorides. The dissolution of the metal fluorides then alters the redox potential. This process continues until an equilibrium between metals and salt is reached. It is essential that a salt's redox potential be kept as far away from fluorination reactions as possible, and that metals in contact with salt be as far away from the salt's redox potential as possible in order to prevent excessive corrosion. The easiest method to prevent undesirable reactions is to pick materials whose reaction voltages are far from the redox potential of the salt in the salt's worst case. Some of these materials are
tungsten,
carbon,
molybdenum,
platinum,
iridium, and nickel. Of all these materials, only two are affordable and weldable: nickel and molybdenum. These two elements were chosen as the main portion of
Hastelloy-N, the material of the MSRE. Altering the redox potential of FLiBe can be done in two ways. First, the salt can be forced by physically applying a voltage to the salt with an inert electrode. The second, more common way, is to perform a chemical reaction in the salt which occurs at the desired voltage. For example, redox potential can be altered by
sparging hydrogen and hydrogen fluoride into the salt or by dipping a metal into the salt. ==Coolant==