ORNL-1816 - the Molten Salt Energy Technologies Web Site

ANP QUARTERLY PROGRESS REPORT
If a meta-oxysalt rather than an oxide is used as
the starting material, in some instances, the meta-
oxysalt may be converted into the ortho-oxysalt.
Fourth, oxides of atoms having very low ioni-
zation energy should not undergo solvolysis at
all. For example, the inert behavior of magnesium
oxide toward sodium hydroxide is no doubt due to
the low ionization energy of magnesium.
There still remain a large number of potential
solutes not treated above. Of these, the only ones
which the writer has considered are the relatively
tallic salts. These substances will
bably be separated into ions by the highly
dipolar hydroxyl ions, and the solvolysis of the
cation and the anion can be considered separately.
The cation should tend to form oxides and oxy-
salts. This reaction should go virtually to com-
pletion except for metals of very small polarization
tential. The anionic-solvolytic reaction can
ry from very complex to nil, and an adequate
treatment will require the development of a some-
what more generali zed acid-base theory.
As an example of the reaction of a metal salt
with a fused hydroxide, a small amount of nickel
chloride was added to fused sodium hydroxide at
4OOOC. The reaction proceeded rapidly with the
evolution of gaseous water and the formation of
a fine black precipitate. The precipitate was
separated from the hydroxide and found by x-ray
analysis to consist largely of nickel(l1) oxide,
together with a small amount of an unidentified
compou nd.
This reaction can probably be represented, in
large measure, as
(23) NiCI, + 20H-s NiO + HOH + 2CI-
Previous experiments indicate that at higher
temperatures the reaction represented by Eq. 22
would have followed that represented by Eq. 23.
Oxidic-Neutralization-Type Reactions. The neu-
tralization reactions of nonprotonic, oxidic solutes
can be divided into two classes. First, the
neutralization of a base by water takes place
according to the reaction
This reaction will only occur for nonprotonic
acids, Bt+, which are stronger than water.
Second, reactions of the following type, which
occur in pure oxide melts, would represent a
special type of pseudoneutralization in which no
solvent would be produced.
(25) Acid + O-----+ Base
The reaction shown in Eq. 25 includes the entire
host of reactions treated in the original Lux
theory.
When reactions of the type given in Eq. 25 occur
in fused hydroxides, the oxide ion concentration
can be varied over a wide range of values. This
is not possible with the pure oxide melts to which
the Lux theory has previously been applied. Ex-
amples of the classes of reactions which are of
the type represented by Eq. 25 may be obtained
by substituting 0-- for 20H- and deleting H,O
in Eqs. 20 through 23. The essential difference
between reactions of the type of Eq. 25 and those
given in Eqs. 20 through 23 is that water is
present in the latter reactions but not in the
former. The presence of the acid of medium
strength should shift the equilibrium considerably
for much weaker acids, that is, those derived from
atoms of low ionization energy, but only slightly
for stronger acids, those derived from atoms of
high ionization energy.
Mixed-Type Reactions. Finally, reactions of
substances of what may be called “mixed” types
should be mentioned. These mixed reactions
might involve protonic-oxidic salts of alkali
metals, and protonic or oxidic salts of nonalkali
metals, or combinations of both. The resulting
reactions should be capable of analysis in terms
of the same considerations used in arriving at
the conclusions already stated.
The Brijnsted protonic theory was originally de-
veloped to treat the more useful low-temperature
solvents, such as water and liquid ammonia, while
the Lux theory was originally developed to treat
the metallurgically important, high-temperature,
fused-oxide systems. It is of some theoretical
interest that both theories may be rigorously
applied to reactions in fused hydroxides, although
the types of reactions for which these applications
are useful form two sets of almost mutually ex-
clusive reactions - one set for each theory. This
is symptomatic of the need to develop a more
general acid-base theory along the lines proposed
by Audrieth.” For many solvent systems, such a
theory would be a luxury; for fused hydroxides,
such a theory is a necessity.
”L. F. Audrieth and J. Kleinberg, Non-Aqueous Sol-
vents, Wiley, New Yark, 1953, p 272-3.
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