(NF.sub.4).sub.2 NiF.sub.6 High energy solid propellant oxidizer and method of producing the same

The combination of the strongly oxidizing NF.sub.4.sup.+ cation with the strongly oxidizing NiF.sub.6.sup.-- anion in the form of the stable salt (NF.sub.4).sub.2 NiF.sub.6 produces a powerful oxidizer, useful for solid propellant formulations and NF.sub.3 -F.sub.2 gas generators. A process for its production is described.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a high energy oxidizer and a method of producing 
the same. The composition of the present invention is particularly useful 
for applications, such as solid propellants and NF.sub.3 -F.sub.2 gas 
generators. 
2. Description of the Prior Art 
For oxygen-containing oxidizers, the combination of an oxidizing cation 
with an oxidizing anion in the form of a stable solid has previously been 
achieved, as demonstrated by the well known existence of nitronium 
perchlorate NO.sub.2 .sup.+ ClO.sub.4.sup.-. Whereas fluorine compounds 
are generally stronger oxidizers than the corresponding oxygen compounds, 
the synthesis of very powerful, solid, ionic, fluorine containing 
oxidizers had previously not been possible owing to the incompatibility 
between energetic anions and the cations. Attempts to combine oxidizing 
highly fluorinated cations and anions had always resulted in 
decomposition, accompanied by elimination of elemental fluorine. 
Consequently, all the previously known solid highly fluorinated oxidizers 
consisted of the combination of an energetic ion with an non-energetic 
counter ion. The only progress made in this area consisted of minimizing 
the relative weight of the non-energetic counter ion. Obviously, the 
performance of such oxidizers could be significantly improved if the 
combination of an energetic anion with an energetic cation in the form of 
a stable solid were possible. 
BRIEF SUMMARY AND OBJECTS OF THE INVENTION 
The above-described problem of preparing fluorine containing high energy 
solid oxidizers is overcome by the present invention. We have found two 
highly energetic ions which can be combined to form a stable ionic solid. 
These ions are the NF.sub.4.sup.+ cation and the NiF.sub.6.sup.-- anion, 
and the resulting stable solid is the powerful oxidizer (NF.sub.4).sub.2 
NiF.sub.6. The oxidizing power of the NF.sub.4.sup.+ cation is well 
established. The oxidizing power of the NiF.sub.6.sup.-- anion is due to 
the fact that the parent compound NiF.sub.4 is unstable and decomposes to 
NiF.sub.2 and F.sub.2. Thus, the thermal decomposition of (NF.sub.4).sub.2 
NiF.sub.6 proceeds according to: 
##STR1## 
This high oxidizing power of (NF.sub.4).sub.2 NiF.sub.6 renders it 
extremely useful for high energy solid propellant formulations. Of 
particular interest is its application to solid propellant NF.sub.3 
-F.sub. 2 gas generators for chemical HF-DF lasers. For the latter 
application, (NF.sub.4).sub.2 NiF.sub.6 possesses, in addition to an 
energetic counter ion, the desirable properties of being self-clinkering, 
and of containing a multiply charged counter ion, as disclosed in our 
copending application Ser. No. 731,197, filed Oct. 12, 1976. Consequently, 
it is not surprising that its theoretical performance in an NF.sub.3 
-F.sub.2 gas generator is superior to those of the best previously known 
systems, as becomes obvious from an inspection of Table I. 
TABLE I 
______________________________________ 
A Comparison of the Theoretical Performance of 
Various NF.sub.4.sup.+ Based NF.sub.3 --F.sub.2 Gas Generator 
______________________________________ 
Ingredients 
System Performance (weight % usable F) 
______________________________________ 
NF.sub.4 SbF.sub.6 . 1.2KF 
24.0 
NF.sub.4 BF.sub.4 . 1.2KF 
38.5 
(NF.sub.4).sub.2 SnF.sub.6 
46.0 
(NF.sub.4).sub.2 TiF.sub.6 
55.6 
(NF.sub.4).sub.2 NiF.sub.6 
64.6 
______________________________________ 
Since NiF.sub.4 is only stable in the form of its NiF.sub.6.sup.-- anion, 
the (NF.sub.4).sub.2 NiF.sub.6 salt cannot be prepared directly from 
NF.sub.3, F.sub.2, and NiF.sub.4, but was prepared by the following 
indirect synthesis in anhydrous HF solution: 
##STR2## 
It resulted in the precipitation of the rather insoluble salt CsSbF.sub.6, 
while the soluble (NF.sub.4).sub.2 NiF.sub.6 remained in solution. The two 
products were separated by a simple filtration step. The composition of 
the crude product was: (mol %) (NF.sub.4).sub.2 NiF.sub.6, 81.7; NF.sub.4 
SbF.sub.6, 14.4; CsSbF.sub.6, 3.9. The purity of this product can be 
easily increased by following the procedures outlined for NF.sub.4 
BF.sub.4 in our copending application Ser. No. 731,198, filed Oct. 12, 
1976. 
Accordingly, it is an object of the present invention to provide an 
improved fluorine containing high energy oxidizer derived from the 
combination of an energetic cation with an energetic anion in the form of 
a stable solid. 
Another object of the present invention is to provide an improved high 
energy oxidizer for solid propellants. 
Another object of the present invention is to provide an improved solid 
propellant NF.sub.3 -F.sub.2 gas generator for chemical HF-DF lasers. 
Another object of the present invention is to provide a novel composition 
of a matter consisting of (NF.sub.4).sub.2 NiF.sub.6. 
Another object of the present invention is to provide a process for the 
production of (NF.sub.4).sub.2 NiF.sub.6. 
These and other objects and features of the present invention will be 
apparent from the following example. It is understood, however, that this 
example is merely illustrative of the invention and should not be 
considered as limiting the invention in any sense. For example, the 
oxidizing anion is not limited to NiF.sub. 6.sup.--, but could be replaced 
by other suitable energetic transition metal fluoride anions.

EXAMPLE 
In a typical example, Cs.sub.2 NiF.sub.6 (13.45 mmol) and NF.sub.4 
SbF.sub.6 (27.9 mmol) were combined in a Teflon FEP U-trap containing a 
magnetic stirrer. The U-trap was closed off on one side by a valve and was 
connected on the other side through a Teflon filter containing union to a 
second U-trap. Anhydrous HF (10 ml liquid) was added to the first U-trap 
and the resulting mixture was stirred for 30 minutes at 25.degree. C. The 
trap was cooled to -78.degree. C and its contents were passed through the 
filter. The solid retained by the filter consisted of 10.0 g of 
CsSbF.sub.6 (weight calcd for 27 mmol of CsSbF.sub.6 = 9.95 g), whereas 
the solid (4.4 g) obtained after evaporation of the HF from the filtrate 
consisted of a mixture (mol %) of (NF.sub.4).sub.2 NiF.sub.6 (81.7), 
NF.sub.4 SbF.sub.6 (14.4), and CsSbF.sub.6 (3.9). The composition of the 
product was established by chemical analyses for NF.sub.3, Ni, Cs, and Sb. 
The ionic nature of the adduct was established by infrared spectroscopy 
which showed the strong bands at 1157 and 607 cm.sup.-1, characteristic 
for NF.sub.4.sup.+, and a strong band at 640 cm.sup.-1, characteristic for 
NiF.sub.6.sup.--. The (NF.sub.4).sub.2 NiF.sub.6 salt is a dark red, 
crystalline, hygroscopic solid which is stable at room temperature. 
Obviously, numerous variations and modifications may be made without 
departing from the present invention. Accordingly, it should be clearly 
understood that the forms of the present invention described above are 
illustrative only and are not intended to limit the scope of the present 
invention.