Title:
ELECTROPHILLIC GAS GENERATING COMPOSITIONS AND PROCESS
United States Patent 3779008


Abstract:
Gas-generating, combustion-sustaining compositions, which produce electrophillic combustion products in amounts effective to attach free electrons in the atmospheric wake of a rapidly moving vehicle, consisting essentially of a metallic component selected from the group consisting of molybdenum, tungsten, molybdenum oxide, tungsten oxide, and mixtures thereof, an oxidizing agent, and an organic fuel binder as required or desired. Process for removing free electrons from the atmospheric wake of a rapidly moving vehicle comprising injecting into said wake the combustion products of the aforedescribed gas-generating, combustion-sustaining compositions.



Inventors:
Henderson, Charles B. (Alexandria, VA)
Hoglund, Richard F. (Reston, VA)
Application Number:
05/098453
Publication Date:
12/18/1973
Filing Date:
12/15/1970
Assignee:
ATLANTIC RES CORP,US
Primary Class:
Other Classes:
60/219, 60/220, 149/19.1, 149/20
International Classes:
C06B23/04; C06B33/02; C06D5/06; (IPC1-7): C06D5/06
Field of Search:
149/19,20 60
View Patent Images:



Primary Examiner:
Padgett, Benjamin R.
Claims:
We claim

1. Gas-generating, combustion-sustaining compositions which generate electrophillic combustion products in amounts effective to attach free electrons in the atmospheric wake of a rapdily moving separately powered vehicle, said compositions consisting essentially of a metallic component selected from the group consisting of molybdenum, tungsten, molybdenum oxide, tungsten oxide, and mixtures thereof, an oxidizing agent other than molybdenum oxide or tungsten oxide, and an organic fuel binder,

2. The compositions of claim 1 wherein the oxidizing agent or the organic fuel binder contains molecularly combined hydrogen.

3. The compositions of claim 1 wherein the oxidizing agent is an inorganic oxidizer salt.

4. The compositions of claim 2 wherein the oxidizing agent is an inorganic oxidizer salt.

5. The compositions of claim 3 wherein the oxidizing agent is ammonium perchlorate.

6. The compositions of claim 4 wherein the oxidizing agent is ammonium perchlorate.

7. The compositions of claim 1 wherein the metallic component is tungsten metal.

8. The compositions of claim 2 wherein the metallic component is tungsten metal.

9. The compositions of claim 3 wherein the metallic component is tungsten metal.

10. The compositions of claim 4 wherein the metallic component is tungsten metal.

11. The compositions of claim 5 wherein the metallic component is tungsten metal.

12. The compositions of claim 6 wherein the metallic component is tungsten metal.

13. The compositions of claim 7 which additionally contain tungsten oxide.

14. The compositions of claim 8 which additionally contain tungsten oxide.

15. The composition of claim 9 which additionally contain tungsten oxide.

16. The compositions of claim 10 which additionally contain tungsten oxide.

17. The compositions of claim 11 which additionally contain tungsten oxide.

18. The compositions of claim 12 which additionally contain tungsten oxide.

19. The compositions of claim 1 wherein the metallic component is molybdenum metal.

20. The compositions of claim 2 wherein the metallic component is molybdenum metal.

21. The compositions of claim 3 wherein the metallic component is molybdenum metal.

22. The compositions of claim 4 wherein the metallic component is molybdenum metal.

23. The compositions of claim 5 wherein the metallic component is molybdenum metal.

24. The compositions of claim 6 wherein the metallic component is molybdenum metal.

25. The compositions of claim 7 which additionally contain molybdenum oxide.

26. The compositions of claim 8 which additionally contain molybdenum oxide.

27. The compositions of claim 9 which additionally contain molybdenum oxide.

28. The compositions of claim 10 which additionally contain molybdenum oxide.

29. The compositions of claim 11 which additionally contain molybdenum oxide.

30. The compositions of claim 12 which additionally contain molybdenum oxide.

31. A process for removing free electrons from the flowfield of a vehicle moving rapidly through the atmosphere which comprises injecting into said flowfield through a restricted orifice the products produced by the combustion of an auxiliary gas-generating composition consisting essentially of a metallic component selected from the group consisting of molybdenum, tungsten, molybdenum oxide, tungsten oxide, and mixtures thereof, an oxidizing agent other than molybdenum oxide or tungsten oxide, and an organic fuel binder,

32. The process of claim 31 wherein the oxidizing agent or the organic fuel binder contains molecularly combined hydrogen.

33. The process of claim 32 wherein the oxidizing agent is an inorganic oxidizer salt.

34. The process of claim 33 wherein the oxidizing agent is ammonium perchlorate.

35. The process of claim 34 wherein the metallic component is tungsten metal.

36. The process of claim 35 wherein said composition additionally contains tungsten oxide.

37. The process of claim 34 wherein the metallic component is molybdenum metal.

38. The process of claim 35 wherein said composition additionally contains molybdenum oxide.

Description:
BACKGROUND OF THE INVENTION

Vehicles such as aircraft or rockets which move at high speeds through the atmosphere frictionally ionize the air, thus producing free electrons in their wake. Since such a wake is radar-reflective and/or -absorptive, it provides a signature which is readily detected. Quenching of the absorptive or reflective wake by removal of the free electrons may, therefore, be highly desirable, as, for example, in the case of re-entry vehicles.

The feasibility of quenching the wake has been demonstrated by injecting into the base region of the vehicle flowfield a liquid compound which has the capability of attaching free electrons. Use of the particular compound suffers, however, from several serious disadvantages. In high temperature regions of the flowfield, the compound loses electron-attachment effectiveness, apparently because of dissociation into lower species and oxidation into particular oxides which have inadequate electron-attaching capability. It is also reduced to compounds of substantially reduced electrophillic properties by hydrogen which may be present in the wake, as, for example, hydrogen evolved by an organic polymer heat shield. Liquid injectants additionally require a controlled mechanical pumping and ejection system which adds considerable weight and operational complexity.

Solid combustion-sustaining compositions which are capable of generating electrophillic species, which maintain their electrophillic properties in the presence of hydrogen and oxygen and under different temperature conditions, and which reduce the weight and mechanical complexity problems associated with liquid injectants, provide an important advance in the art.

Small amounts, e.g., about 1 to 2 percent, of molybdenum and tungsten compounds have been incorporated into high performance solid rocket propellants to reduce free electrons generated by combustion of the propellant and thereby to reduce the radar attenuation caused by the rocket exhaust plume, which interferes, for example, with guidance systems. However, such additives to high performance propellants reduce thrust performance and must, therefore, be held to a minimum.

U.S. Pat. Reissue No. 26,468 discloses the use of small amounts of molybdenum oxide as combustion catalyst in gas-generating compositions containing a coolant. U.S. Pat. No. 2,988,438 discloses incendiary mixtures comprising zirconium and molybdenum dioxide wherein the molybdenum dioxide functions as the oxidizer for the zirconium and is thereby reduced to free molybdenum metal.

None of the known art discloses solid combustion-sustaining compositions designed to or capable of quenching the free electrons in the wake generated by a high speed vehicle or which include free metal tungsten or molybdenum or these metals in combination with their oxides.

The object of this invention is to provide solid gas-generating, combustion-sustaining compositions which generate electrophillic species capable of attaching free electrons present in the wake of a vehicle moving through a gaseous medium.

Another object is to provide solid combustion-sustaining compositions which generate electrophillic species that are substantially insensitive to hydrogen and oxygen.

Still another object is to provide electrophillic-species-producing compositions capable of providing a quenching system for a free-electron-containing wake which is simple, versatile, and relatively low weight.

Another object is to provide an improved process for removing free electrons from the wake of a vehicle moving rapidly through the atmosphere.

Still other objects will become obvious from the following detailed description.

SUMMARY OF THE INVENTION

Broadly speaking, the invention comprises solid, gas-generating, combustion-sustaining compositions which are capable of generating electrophillic combustion products in amounts sufficient to remove free electrons from the wake of a rapidly moving vehicle and which consist essentially of a metallic component selected from the group consisting of molybdenum, tungsten, molybdenum oxide, tungsten oxide, and mixtures thereof, an oxidizing agent other than molybdenum oxide or tungsten oxide, and an organic fuel binder as required.

Molybdenum oxide and tungsten oxide occur in the form of several oxide species, e.g., Mo2 O3, MoO2, MoO3, W2 O5, WO2, WO3, as well as in the form of hydrates and acids, e.g. H2 MoO4, H2 MoO3, H2 WO3, and H2 WO4. The terms molybdenum oxide and tungsten oxide as employed in this specification and claims will be understood to include all of the above identified species, namely the free oxides, their hydrates, and the acids such as molybdic and tungstic acids. The stable oxides and their hydrates and acids are electrophillic, namely capable of attaching free electrons and are, therefore, the species desired in the combustion products. The hexavalent metal compounds are most electrophillic and are, therefore, preferred.

The combustion products of the composition include molybdenum trioxide or tungsten trioxide (as well as some lower oxides) which are provided by combustion of the metals, by the ejection of these oxides originally incorporated in the compositions, or by oxidation of incorporated lower oxides by the oxidizing agent. Preferably, the products include the hydrates or acids in addition to the free hexavalent metal oxides. This can be accomplished by including a source of molecularly combined hydrogen in the compositions. The hydrogen source can be either the particular oxidizing agent employed or an organic, hydrogen-containing binder.

The oxidizing agent is essential for combustion of the molybdenum or tungsten to their oxides, if either or both are present, and/or oxidation of any lower molybdenum or tungsten oxides present, and/or combustion of the organic fuel binder if present. The oxidizer should be present in sufficient amount to sustain combustion of the organic fuel binder and/or a major proportion of the free metal molybdenum or tungsten or their lower oxides to their hexavalent metal oxides.

The organic fuel binder is essential only if the molybdenum or tungsten is not present in free metal or lower oxide form to sustain combustion of the composition. In such case the organic binder must be present in amount sufficient to maintain sustained combustion of the composition and thus provide for ejection of the molybdenum and/or tungsten oxides, including their hydrate or acid forms. An organic fuel binder is also desirable as a source of additional gaseous combustion products to improve ejection efficiency of the electrophillic components into and mixing with the free-electron-containing wake. It can also provide a source of molecularly combined hydrogen to provide for hydrated molybdenum or tungsten oxide species.

To provide an adequate amount of electrophillic species in the combustion products to effect quenching of the vehicle wake, the compositions should contain at least about 1 × 10-3 gm atoms of molybdenum per gram of composition or at least about 6.5 × 10-4 gm atom of tungsten per gram of composition, the molybdenum or tungsten being in the form of either free metal or oxide. In the case of a mixture of molybdenum and tungsten (either as free metal or oxide), the compositions should contain at least about 8.5 × 10-4 gm atom of the mixture per gm of composition.

DETAILED DESCRIPTION

The molybdenum or tungsten additives can be incorporated as free metals, or any of their oxides including the hydrates and acids. Although all of the additives can be in the form of oxide, preferably at least a portion of the additive is in the form of free metal to provide high combustion temperatures and, thereby, more effective ejection of the electrophillic species into and mixing with the wake. The addition of at least a portion in oxide form is also desirable since it increases the amount of hexavalent oxide in the combustion products without excessive requirements of oxidizing agent. The added oxide can be hexavalent or in the form of lower oxides, e.g., MoO2, Mo2 O3, WO2. The lower oxides are oxidized to the hexavalent state by the oxidizing agent and perform as combustion-sustaining and heat-producing components.

Although mixed molybdenum and tungsten additives can be employed in the same composition, it is generally preferred that a single one of these metal species be used, e.g., molybdenum and/or molybdenum oxide or tungsten and/or tungsten oxide.

Sufficient electrophillic species must be ejected into and mixed with the wake effectively to attach the free electrons in the wake. In general this requires at least about 1 × 10-3 gm atoms of molybdenum (based on metal) per gm of composition, preferably at least about 1.4 × 10-3 or at least about 6.5 × 10-4 gm atoms of tungsten (based on metal) per gm of composition, preferably at least about 7.8 × 10-4, the molbdenum or tungsten being in the form of either free metal or oxide. Thus the tungsten comprises at least about 12 percent by weight of total composition and molybdenum comprises at least about 9.6 percent. In the case of a mixture of molybdenum and tungsten (either as free metal or oxide), the compositions should contain at least about 8.5 × 10-4 gm atoms of the mixture per gm of composition, preferably at least about 1.1 × 10-3.

A small proportion of the generated electrophillic species may be utilized to attach free electrons produced in the combustion process. However, this normally utilizes only about 1 to 2 percent (by weight of total composition) of the electrophillic precursor additives.

Maximum concentration of the molybdenum and/or tungsten additives is limited only by oxidizing agent requirements and/or processibility of the mixture.

The oxidizing agent can be any active oxidizer, inorganic or organic, such as the inorganic oxidizing salts, e.g., ammonium, alkali metal (Na, K, Li), or alkaline earth metal (Ca, Ba) chlorates, perchlorates, nitrates, and the like; nitronium perchlorate; organic oxidizers, such as cyclotrimethylene trinitramine, cyclotetramethylene tetranitramine, pentaerythritol tetranitrate, hexanitroethane, mannitol hexanitrate and the like. The inorganic oxidizing salts, especially ammonium perchlorate, are generally preferred.

Preferably the oxidizing agent is capable of forming gases during the combustion process. Gases are produced, for example, by such molecularly combined elements as hydrogen, chlorine, nitrogen, oxygen, and carbon. Chlorine is particularly desirable since it can combine with hydrogen available from the oxidizer or organic fuel binder in the composition to produce hydrogen chloride, which is itself electrophillic at certain high temperature regimes.

The amount of oxidizer required is primarily determined by the other components of the composition. It must be present in amount sufficient to oxidize a substantial, preferably a major proportion of any free molybdenum or tungsten metal and/or their lower oxides to the hexavalent oxide and to sustain combustion of any organic fuel binder present. The amount required for any given composition and application is readily calculated by anyone skilled in the art.

An organic fuel binder is essential only if the composition does not contain free molybdenum or tungsten metal, or their lower oxides, or a non-gas-forming oxidizing agent. In such case the organic fuel binder is required to sustain combustion of the composition and/or to provide gases, such as CO, CO2, H2, H2 O, HCl, for ejection of the molybdenum or tungsten oxides into the vehicle wake and for effective mixing with and attachment of the free electrons in the wake. Inclusion of some organic fuel binder is desirable even if not essential since the additional combustion gases produced improve injection into and mixing action with the wake and, therefore, the electron-quenching action of the electrophillic species.

The organic fuel binder can be any conventional polymeric binder used in gas-generating or propellant compositions. It can be, for example, polyvinyl chloride; polyamide, polyester; carboxy- or hydroxy-terminated polyester; polybutadiene; hydroxy- or carboxy-terminated polybutadiene; polyacrylate or polymethacrylate ester; polyurethane; cellulose acetate; polybutadiene-acrylic acid; double base, e.g. nitrocellulose plasticized with nitroglycerin, triethylene glycol dinitrate, and the like.

Plasticizers known to the art may be used as required or desired. Examples include, but are not limited to, inert plasticizers such as alkyl (e.g., ethyl, butyl, octyl) phthalates, sebacates, and adipates, triacetin, polyethylene glycol, and active plasticizers, namely plasticizers which contain molecularly-combined oxidizer elements, e.g., oxygen or fluorine, available for self-sustaining combustion, such as trimethylol ethane trinitrate, diethylene glycol dinitrate, triethylene glycol dinitrate, nitroglycerin, and the like.

The use of an active polymer and/or plasticizer in the organic fuel binder is advantageous since they increase the amount of oxidizing agent available for oxidation of the free molybdenum or tungsten metal or their lower oxides, increase combustion temperatures, and improve composition processing.

The organic fuel binders also provide a desirable source of molecularly combined hydrogen which, together with oxygen contributed by the oxidizing agent or molecularly combined oxygen in the binder, provides for the formation of desired electrophillic hydrate or acid species of the molybdenum or tungsten oxides in the combustion products.

The amount of binder is not critical other than to provide for sustained combustion and/or gaseous combustion products as required by the particular composition. Beyond that, the amount can be tailored for characteristics such as particular gas-forming properties desired, acceptable ease of composition processing, physical properties, and the like.

Other conventional additives may be incorporated in the usual small amounts. These include, for example, burning rate catalysts, stabilizers for the polymeric fuel binder, and the like.

Although the compositions are relatively low-performance in terms of specific impulse, this is not an important criterion since primary application is free electron quenching of the wake.

A precise identification of the electron-attaching mechanisms has not been established. However, the compounds are believed to attach electrons in the combustion chamber by the following typical reactions:

e- + HA WOB ⇋ HA-1 WOB - + H

e.g., e- + H2 WO4 ⇋ HWO4 - + H

e- + HA MoOB ⇋ HA-1 MoO4 - + H

e.g., e- + H2 MoO4 ⇋ HMoO4 - + H

e- + MoOB ⇋ MoOB -

e.g., e- + MoO3 ⇋ MoO3 -

e- + WoOB ⇋ WOB -

e.g., e- + WO3 ⇋ WO3 -

Although the electron affinity of the hydrated or acid form of the oxide is somewhat higher than that of the free oxide, both forms are effective in attaching electrons.

They also have the important advantage of maintaining this high electron affinity over a wide temperature regime. Although other compounds, such as HOBO and HCl are effective electron attachers at combustion chamber temperatures, e.g., 2500°K, they rapidly decrease in efficiency with decreasing temperatures, whereas the electrophillic properties of tungsten and molybdenum oxide compounds actually increase somewhat with decreasing temperature. This maintenance of electrophillic capacity is very important for free-electron wake quenching since temperature of the combustion products drops rapidly as they are injected into and mix with the wake. Additionally the tungsten and molybdenum oxide compounds are not adversely effected by the presence of hydrogen or oxygen in the wake.

The compositions may be formed into shaped, combustion-sustaining grains in any well-known manner. The free tungsten or molybdenum metal-oxidizing agent mixtures can be compacted to the desired shape and size under high pressures. Although not essential, such compression molding is facilitated by the addition of a small amount of organic binder, e.g., up to about 3 percent by weight of composition. The small amount of binder also improves the physical integrity of the shaped grain.

Where a substantial amount of organic binder is employed, e.g., at least about 8 percent, and preferably at least about 12 percent, the composition can be conventionally processed by mixing the solid components with the binder in liquid form, casting into a mold of the desired size and shape, and heat curing into a solid grain.

The electrophillic-species-generating compositions are preferably burned under pressure in combustion chambers having restricted orifices or nozzles, namely in rocket motors, so that the combustion products can be injected at high velocity into the flowfield or wake of the vehicle. The electrophillic rocket motor can be strategically attached and its nozzle or nozzles so canted as to provide maximum wake quenching. Since the electrophillic species are produced by gas-generating solid grains, no pumping or metering systems are required with resultant reduction in weight, complexity, maintenance, and cost.

EXAMPLE 1

A composition comprising 20 percent by weight tungsten, 67 percent ammonium perchlorate, and 13 percent carboxy-terminated polybutadiene was prepared, molded, and cured into a shaped grain. The grain was ignited and burned stably and completely at atmospheric pressure. No unburned tungsten was ejected and no residue remained.

EXAMPLE 2

A grain was prepared from the following compositions:

% by Weight Triethylene glycol dinitrate 16.5 Nitrocellulose 8.0 Ammonium perchlorate 25.0 WO3 40.0 Polyethylene glycol400 0.5 Tungsten 10.0

The composition burned cleanly and completely. Burning rate at 1,000 psia was 0.23 in./sec.

EXAMPLE 3

A grain was prepared from the following compositions:

Tungsten 15.0 Ammonium perchlorate 28.0 WO3 40.0 Carboxy-terminated polyester binder 11.0 Trimethylol ethane trinitrate 6.0

The composition burned cleanly and completely. Burning rate at 1,000 psia was 0.23 in./sec.

Although this invention has been described with reference to illustrative embodiments thereof, it will be apparent to those skilled in the art that the principles of this invention can be embodied in other forms but within the scope of the claims.