The Lux-Flood definition

Reactions with the transfer of oxide ions in ionic media are mainly considered as oxoacidity or acid-base equilibria by Lux-Flood  

The addition of acids (bases) in a melt as it follows from [10.4.6] leads to changes of the oxide ion activity, for the characterization of melt acidities (basicities) Lux proposed the oxygen index, or pO, which was similar to pOH (i.e., basicity index) in aqueous solutions  

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Hie base (GaO) is an oxide donor and (be add (SiO,) is an oxide acceptor The usefulness of the Lux-Flood definition is mostly limited lo systems such as molten oxides. 

Effects of Additives. Selected additives to molten nitrate systems offer possibilities of specific acid-base reactions or formation of specific complexes with the various chemical species. Acids and bases are conveniently denoted in oxyanionic molten salt systems by the Lux-Flood definition (18, 19). Acids are defined as compounds capable of removing oxide ions from the melt, while bases are defined as compounds capable of donating oxide ions to the melt. Examples of various acidic and basic species may be found in the general review articles (14, 15,... 

It should be noted that there are some curious interpretations in the literature concerning oxoacidity, which distort to a greater or lesser degree the original definition. For example, Delimarskii and Barchuk [3] give as the Lux definition where a base is a donor of oxide or halide ions. Moreover, at least in the Russian translation of a book [21], the Lux-Flood definition is where an acid is a donor of oxide ions and a base is an acceptor of O2-. Certainly, these definitions are erroneous, as may be seen by reading the original Lux paper [17]. 

Find out about the Lux-Flood definition of acids and bases. 

From this scheme it follows that the Lux-Flood definition is a particular case of more common Lewis definition described above. For the quantitative interpretation of interactions with the transfer of, Lux introduces the pO index serving as a measure of basic (acidic) properties of a melt ... 

The data on solubility of CaO and ZnO in the chloride melts permit to follow the effect of the acidic properties of the melt constituent cation on the metal oxide solubilities. The ratio of solubilities in K, Na and Lf-based melts is as follows 1 1.5 15. The total solubilities are discussed and the obtained data are distorted by contribntion of appreciable concentrations of non-dissociated oxide, which is not sensitive to the melt acidity changes. It should be emphasized that, since we do not know the ratios of the ionized fraction to the non-dissociated fraction in the melts studied, we cannot quantitatively estimate the oxoac-idic properties of these melts. The metal oxide dissociation was neglected because studies were conducted in 1923, whereas the Lux-Flood definition was formulated only in 1939. 

Since Arrhenius, definitions have extended the scope of what we mean by acids and bases. These theories include the proton transfer definition of Bronsted-Lowry (Bronsted, 1923 Lowry, 1923a,b), the solvent system concept (Day Selbin, 1969), the Lux-Flood theory for oxide melts, the electron pair donor and acceptor definition of Lewis (1923, 1938) and the broad theory of Usanovich (1939). These theories are described in more detail below. 

In silicate melts and other nonprotonated solvents, the Bronsted-Lowry equation is not applicable and is conveniently replaced by the Lux-Flood acid-base definition (Lux, 1939 Flood and Forland, 1947), according to which free oxygen 0 replaces A basic oxide is one capable of furnishing oxygen ions, and an acidic oxide is one that associates oxygen ions ... 

Lux—Flood Definition In contrast to the BrpnstedLowry theory, which emphasizes the proton as the principal species in acid-base reactions, the definition proposed by Lux and extended by Flood describes add-base behavior in terms of the oxide ion. This add-base concept was advanced to treat non protonic systems which were not amenable to the Bipnsted-Lowry definition. For example, in high-temperature inorganic melts, reactions such as the following take place ... 

Molten carbonates display variable acid-base behavior according to the Lux-Flood modification of the Lewis definition of acidity,... 

Lux—Flood Definition In contrast to the Brpnsted-Lowiy theory, which emphasizes the proton as the... 

Donor-acceptor interactions in ionic media are often deseribed as acid-base interactions according to Lewis and Lux-Flood " definitions. The elassie variant of the former definition considers acids as acceptors of electron pairs and bases as their donors. In modem variant of this definition, acids are the electron pair (or anion) acceptors or cation (proton) donors, bases are the electron pair (anion) donors or cation (proton) acceptors. 

In non-protonic solvents like molten oxides and silicates, such a definition is clearly unsuitable, and in the case of molten oxides or oxy-acids the Lux-Flood acid-base definition is frequently used. In this, oxide-ion, 02, takes the place of protons in the Bronsted-Lowry scheme. Thus, a basic oxide is a substance capable of fiurnishing pxide ions, and an acidic oxide is one which reacts with 02 ... 

The various acid-base definitions are summarized in the Venn diagram (Fig. 2.1). From this it can be seen that the Usanovich definition subsumes the Lewis definition, which in turn subsumes all other definitions (i.e. Arrhenius, Bronsted-Lowry, Germann-Cady-Elsey, Lux-Flood). 

Use the Lewis definition of acids and truces to explain the examples given tor the Br0nsted-Lowry, Lux-Flood, and solvent system definitions (Eqs 9.1-9.4, 9.S-9.8, 9 9-9.361. 

Use the generalized deHnilion of acids and buses to explum the examples given for the Br0nsicd-Lowry, Lux-Flood, solvent system, and Lewis definitions (Eqs. 9.I-9.4. 9 5-9 8. 9.9-9 36 9.37-9.40). 

Systems defined by the Arrhenius description, solvent system, Lux-Flood and proton acid-base definitions... 

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