US3099132A - Propulsion method using organic thiophosphites with hydrogen peroxide - Google Patents

Description

United States Patent 3,099,132 PROPULSION METHOD USH'JG (NRGANIC THIG- PHOSPHlTES WITH i-IYDRUGFJN PEROE Paul C. Condit, Berkeley, Calif., assignor to California Research Corporation, San Francisco, Calif, a corporation of Delaware N0 Drawing. Filed June 20, 1952, Ser. No. 294,727

1 Claim. (Cl. 60-354) This invention relates to self-igniting propellant fuel compositions.

Self-igniting compositions of various kinds have for many years found use in the construction ofassorted tools of war for use against personnel and property. More recently, it has been recognized that self-igniting compositions are useful as propellants for rockets, guided missiles, -'and aircraft powered by jet or thrust engines.

In the development of fuels for rockets, thrust engines, etc., it has been recognized that the property of selfignition in the propellant fuel, while not absolutely essential, constitutes a major convenience in the construction and operation of these devices. In the development of rocket fuels, two types have been recognized: Monergolic fuels, or monergols, i.e., unitary compositions which require ignition by spark, pyrotechnic charge or otherwise and, once started, they continue to burn on being sprayed into the hot zone; and hypergolic fuels, or hypergols, which comprise two or more components which are separately stored and which spontaneously ignite upon proper mixing in a combustion chamber. The individual components of the hypergolic mixture are not selfigniting.

Monogols so far developed have proved unreliable in that they have all shown a tendency to backfire from the combustion chamber to storage tanks. This diffi culty is not encountered with hypergolic fuels since selfignition occurs only upon mixing of the individual components which are not themselves self-igniting and neither of which alone has the property of undergoing selfsustained combustion after ignition.

l-lypergolic propellants may be generally described as mixtures of a reducing component and an oxidizing component. When the two components are mixed, there is a short period during which the mixture exists as a composition of matter. During this short period relatively slow reaction of the two components is apparently initiated and this relatively slow reaction is followed by spontaneous ignition of the fuel. The ignition delay period is quite short, being substantially less than one second and being preferably not more than about fifty milliseconds.

The reducing component of a hypergolic propellant should have certain properties as follows: It should ignite spontaneously upon being combined with the selected oxidizing agent; the ignition delay period should be short, preferably not exceeding 50 milliseconds; it should have a low freezing point so that it can be pumped to the combustion chamber at the low temperatures prevailing at high altitudes; it should have a high boiling point to facilitate handling and increase its safety in use; it should be chemically stable in storage; it should have a relatively low viscosity at low temperatures; it should form gaseous oxidation products and the average molecular weight of these products should be as low as possible in order that the specific impulse (pounds thrust/ pounds propellant/ second) be high. In addition to the foregoing properties, it is desirable that self-ignition of the mixture of the reducing component and the oxidizing agent be rapid over a wide temperature range; that the reducing component have a high density so that the volume of fuel tanks may be reduced; that the material ,inafter.

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be non-toxic and easy to handle; that it have a high heat of combustion; and that it be non-corrosive.

It has now been found that the foregoing property requirements of the reducing component are remarkably well satisfied by trialkyl trithiophosphites containing 1 to 4 carbon atoms in each alkyl group and by trialkenyl trithiophosphites containing 2 to 4 carbon atoms in each alkenyl group. Mixtures of these trithiophosphites with an oxidizing agent of the group consisting of concentrated nitric acid and concentrated hydrogen peroxide are selfigniting over a wide range of temperatures and are characterized by short ignition delay periods.

The reducing component of these hypergolic propellants may be prepared either by reacting a mercaptan with phosphorous trichloride or by oxidizing a mercaptan to a disulfide and then reacting the disulfide with elemental phosphorous as iudicated in the following equations:

(2) (a) 3RSH V 02 RSSR H20 R is an alkyl group containing 1 to 4 carbon atoms or an alkenyl group containing 2 to 4 carbon atoms.

The boiling point, melting point and density of some of the trithiophosphites are tabulated below:

Alkyl Groups B.P., I Press, M.P., F. (14

mm. Hg Met yl .t 208-210 5 below 100- 284-289 18 0 1.1883 327-336 15 to -83 1.1277 n-butyl 345-356 15 150 to -148. 1 .0773

Trimethyl trithiophosphite, triethyl trithiophosphite, tripropyl trithiophosphites, tributyl trithiophosphites, trivinyl trithiophosphite, triallyl trithiophosphite and tributenyl trithiophosphites are all characterized by high boiling points, low melting points and relatively high densities, and all of them ignite spontaneously and rapidly when mixed with either concentrated nitric acid or concentrated hydrogen peroxide.

The term concentrated nitric acid as employed above and in the appended claims is intended to include several readily available nitric acid compositions described here- Ordinary white fuming n'tric acid, i.e., nitric acid having a purity in the range from to by weight HNO particularly commercial fuming nitric acid composed of 98.5% by weight of HNO and 1.5% by weight of water are satisfactory. A small amount of N 0 may desirably be added to commercial fuming nitric acid to render it anhydrous. A. nitric acid composition containin-g 92-98 parts by weight of HNO 1 to 4 parts by weight of water, and 1 to 4 parts by weight of sodium nitrite, which is characterized by a very low freezing point and high storage stability, is effective. Red fuming nitric acid, i.e., fuming nitric acid containing 2 to 20% by weight, ordinarily about 7 /2% by weight of nitrogen dioxide, is effective. Burning nitric acid containing from 2 to 20% by weight of sulfuric acid is also effective. Ordinarily, from 12 to 15% by weight of sulfuric acid will be employed. Fuming nitric acid containing from 2 to 20% by weight of nitrosyl sulfuric acid is also an effective oxidizing agent. The nitrogen dioxide, sulfuric acid, and nitrosyl sulfuric acid are added to fuming nitric acid as ignition accelerators. While they have the effect of shortening the ignition delay period of the hypergolic fuel mixture, their inclu- 10.5 milliseconds; at 80 was 6 nu lliseconds; at 20 F. the

sion in the nitric acid introduces problems of sludging and decomposition on storage. The trithiophosphite reducing components of the hypergolic fuels of this invention are especially attractive in that they ignite very rapidly with white fuming nitric acid and the storage examples illustrate the propellant of Example 1 1 volume of triethyl trithiophosphite and 3 volumes of nitric acid composed of 92.16 parts by weight of HNO 3.84 parts by weight of water, and 4 parts by weight of sodium nitrite were mixed at 75 F. 12 milliseconds after mixing spontaneous ignition of the mixture occurred. The triethyl trithiophosphite was very rapidly oxidized, forming water vapor, carbon dioxide, carbon monoxide, sulfur dioxide and oxides of phosphorus. acid was reduced forming water vapor, nitrogen nitrogen oxides. The ignition delay was measured by mixing the triethyl trithiophosphite and the acid in an especially constructed oxidizer cylinder so arranged that mixing the trithiophosphite and the acid, an electrode was grounded initiating a pulse to an electhe measurement of the delay. Soon after the acid contacted the trithiophosphite, ignition occurred. Ionization caused by the flame grounded a tubular electrode to the walls of the oxidizer cylinder, pulse to the electronic timer delay measurement. Ignition delays as measured by this device are accurate within one millisecond.

'Ignition delays of triethyl trithiophosphite and the acid above described were made at several temperatures and the following results were obtained: At 20 F. the ignition delay was milliseconds; at 40 F. the ignition delay was 8 milliseconds; at -70 F. the ignition delay was F. the ignition delay was 37 F. the ignition delay was 55 and milliseconds; and at 90 milliseconds.

Example 2 One volume of trisecondarybutyl trithiophosphite was mixed with 3 volumes of white fuming nitric acid containing 98.5% of HNO and 1.5% of water at -40 F. The ignition delay, measured as in Example 1, was 49 milliseconds. Trisecondarybutyl trithiophosphite is a very viscous liquid at -40 F. and a part of the length of the ignition delay may be attributed to poor mixing with the nitric acid.

Example 3 One volume of triallyl trithiophosphite was mixed with 3 volumes of commercial fuming nitric acid at 40 F. The ignition delay, measured as in Example 1, was 49 milliseconds. Triallyl trithiophosphite is very vicous at low temperatures and a part of this delay may be attributed to poor mixing with the nitric acid.

Example 4 periods were measured at several temperatures for trimethyl trithiophosphite with 3 volumes of white turning nitric acid containing 4% by weight of sodium nitrite. The following results were obtained: At 75 F. the ignition delay ignition delay was 3 milliseconds; at 40 F. the ignition delay was 4.5 milliseconds; at 70 F. the ignition delay was 6 milliseconds; at F. the ignition delay was 19.5 milliseconds; and at 9-0 F. the ignition delay was 71 milliseconds.

Example 5 One volume of trimethyl trithiophosphite and 3 volumes of 80% hydrogen peroxide were mixed. The ignition delay period was not measured, but visual observation indicated that the delay period was short, the materials appearing to burst into flame immediately upon mixing.

Example 6 A mixture of trivinyl trithiophosphite and white fuming nitric acid ignites immediately upon mixing.

Example 7 A mixture of tributenyl trithiophosphite and white fuming nitric acid ignites immediately upon mixing.

In the foregoing examples the trithiophosphites of the invention are shown to ignite spontaneously when mixed with white fuming nitric acid which is the least active of the nitric acids above described. Red fuming nitric acid, i.e., nitric acid containing dissolved N0 mixed acid, i.e., nitric acid containing l2l5% H SO nitric acid containing nitrosyl sulfuric acid and the mixed oxides of nitrogen all give ignition required for the complex oxidation of the trithiophosphite component.

trialkyl trithiophosphites to ignite The capacity of the spontaneously upon mixing with the described oxidizing which do not ignite spontaneously, to produce blends exhibiting ignition delay periods below 50 milliseconds at temperatures about 40 F. and higher.

I claim:

A rocket propulsion method, which method comprises injecting separately and simultaneously into the combustion chamber of a rocket motor a fuel consisting of a trithiophosphite selected from the group consisting of trialkyl trithiophosphites containing from 1 to 4 carbon atoms in each alkyl group and a trilower alkenyl trithiophosphite and an oxidizing agent consisting of concentrated hydrogen peroxide, in an amount and at a rate sufiioient to initiate a hypergolic reaction with and to support combustion of the fuel.

References Cited in the file of this patent OTHER REFERENCES Journal of the American Rocket Society, cember 1947, pages 17, 33, and 35. Copy Library.

No. 72, Dein Scientific