GB2184719A

GB2184719A - Nitrogen sources

Info

Publication number: GB2184719A
Application number: GB08625794A
Authority: GB
Inventors: Amnon Yogev
Original assignee: Yeda Research and Development Co Ltd
Current assignee: Yeda Research and Development Co Ltd
Priority date: 1985-10-29
Filing date: 1986-10-29
Publication date: 1987-07-01
Also published as: GB8625794D0; IL76874A0

Abstract

The invention relates to a source of practically pure gaseous nitrogen which is a composition comprising a solid alkali metal azide or alkaline earth metal azide in self-supporting unit dosage form. Amongst the uses there may be mentioned the firing of e.g. arrows in underwater sport and for other purposes such as pneumatics or guidance systems. The azide is preferably lithium azide, suitably in the form of tablets.

Description

SPECIFICATION Nitrogen sources There are provided novel sources of nitrogen. These are of value where nitrogen is required for Joule-Thomson cooling, for pneumatic control actuation or for propulsion. The novel sources are based on chemical compounds adapted to release nitrogen in a controlled manner. The sources are azides of alkali metals and alkaline earth metals.

They are characterized by a considerable saving of weight and volume compared with compressed nitrogen.

Various detection means require cooling down to very lowtemperatures. For this purpose there are in extensive use portable flasks of compressed nitrogen with valve means. In these, nitrogen compressed to about 400 atmospheres (atm.) is provided which is used at a pressure down to about 100 atm. For prolonged use, a supply of sources of this type is required, which constitutes a logistic problem. Such containers of pressurized nitrogen are in use in aircraft, missiles, also in hand held systems and the like where weight is a considerable problern. They are also in use in guidance systems of missiles where weight and volume are problematic.

The present invention provides a source of nitrogen for the above uses which is of considerably reduced weight and volume of system per mission, which can be stored and transported without serious problems and which is adapted to replace existing vessels of compressed nitrogen. The sources with reduced weight and volume ofthe present invention are useful in the various pneumatically controlled systemswhich are of importance in guidance systems of missiles and which have to perform rapid changes of direction. (Pneumatic control has advantages over electric control where rapid development ofan impulse is required within a short period oftime). Conventionally pressurized gases are used in such systems, but the nitrogen sources according to the present invention overcome some ofthe more serious drawbacks of conventional ones.

The present invention provides a composition comprising a solid alkali metal azide or alkaline earth metal azide in self-supporting unit dosage form. The composition may provide a controlled and predetermined release of nitrogen. The invention is based on the storage of nitrogen in the form of suitable decomposable compounds, alkali metal azides or alkaline earth metal azides, and especially lithium azide, and on the thermal decomposition of predeterminea quantities of such compounds, resulting in the desired quantity of nitrogen and in the free metal, which in the case of lithium azideis metallic lithium. The lithium is capable of reacting with residual oxygen, carbon dioxide and water which are thus scavenged, resulting in essentially dry and pure nitrogen.Lithium azide, for example, contains about 85.7 weight-% of nitrogen, and thus is advantageous compared with other azides which contain a lowerweigl1t-percentage. The decomposition is an exothermai one and thus a delicate initiation suffices for initiating such decomposition. This can be effected by chemical or electrical means, as is customary with detonators.

The azide has adequate stabilityforsafe transportation and handling during prolonged periods of time. The specific gravity of this material is about 1 g/ml, compared with about 0.35 g/ml of compressed nitrogen. The weight of the pressure vessel is also saved, as the azide can be provided and transported in tablet form or other unit dosage form.

One of the methods of use is by way of initiation by a chemical or electric detonator, or by a mechanical shock. This system resembles that used for launching rifle grenades or of initiating a propellant artillery charge.

Lithium azide is the material of choice, but also azidesofotheralkali metals orofalkaline earth metals may be used. For example, tablets of about 1 g each were prepared by compaction of pure lithium azide. Each such tablet is capable of evolving a volume of about 0.85 g of nitrogen. Initiation was effected by means of heating, pyrotechnic or by electrical initiation. Such tablets were used for effecting cooling by means of the Joule-Thomson effect. Such tablets were also used for actuating pneumatic control means.

Tablets can be produced of various sizes and weight: for example, there were tried out tablets of from 0.1 g to about 5 g each. Storage tests showed that no deterioration took place during a period of time of about 6 years.

The lithium azide can also be provided in unit dosage forms of lithium azide in a suitable iight-weight enveiope.

The present invention also provides a source of gaseous nitrogen which comprises a composition comprising solid alkali metal azide or alkaline earth azide in unit dosage form, provided with mechanical, electrical, pyrotechnical or chemical means for initiating the formation of the nitrogen.

Gaseous nitrogen may be produced by thermally decomposing a composition according to the invention or initiating nitrogen formation from a nitrogen source according to the invention.

The nitrogen sources of the present invention provide means forthe firing of objects e.g. arrows and other projectiles, for use in underwater sport and for other purposes. These are propelled by nitrogen which is evolved from solid alkali metal azide or alkaline earth metal azide.

The actuation of a predetermined charge of such azide by suitable actuation means, such as mechanical, electrical, pyrotechnical or chemical means, results in a sudden release of nitrogen, which propels the desired projectile (e.g. an arrow or flachette),to its target. The release of the nitrogen is nearly without sound and this is advantageous for various purposes. The specific charge of nitrogen obtainable from lithium azide is a very high one, as lithium azide contains about 85.7 weight-% of pure nitrogen.

Experiments indicate that there can be obtained a high acceleration of the projectile and that it can be targeted with ease.

The present invention further provides propulsion means and pneumatic control means each comprising a composition or nitrogen source as described above.

Claims

1. A composition comprising a solid alkali metal azide or alkaline earth metal azide in self-supporting unit dosage form.

2. A composition as claimed in claim 1 in the form of a tablet.

3. A composition as claimed in claim 1 or 2 in which the amount of azide present is in a form capable of producing a predetermined amount of gaseous nitrogen.

4. A composition according to any one of the preceding claims in which the azide is an alkali metal azide.

5. A composition according to claim 4 in which the azide is lithium azide.

6. Acomposition according to any one of claims 1 to 3, in which the azide is an alkaline earth metal azide.

7. Acomposition comprising a solid alkali metal azide or alkaline earth metal azide substantially as herein described.

8. A source of gaseous nitrogen which comprises a composition as claimed in any one of claims 1 to 7, provided with mechanical, electrical, pyrotechnical or chemical means for initiating the formation of the nitrogen.

9. A source of gaseous nitrogen which comprises in a suitable container a composition as claimed in any one of claims 1 to 7, and lead azide in powder form to initiate the formation ofthe nitrogen.

10. Asource of gaseous nitrogen which comprises a solid alkali metal azide or alkaline earth metal azide and is substantially as herein described.

11. Amethodofproducing gaseous nitrogen which comprises thermally decomposing a composition as claimed in any one of claims 1 to 7.

12. A method of producing gaseous nitrogen which comprises initiating nitrogen formation from a sourceasclaimed in any one of claims 8to 10.

13. A method of producing gaseous nitrogen from an alkali metal azide or alkaline earth metal azide which method is substantiaily as herein described.

14. Propulsion means comprising a source of nitrogen as claimed in any one of claims8to 10.

15. Pneumaticcontrol meanscomprisinga source of nitrogen as claimed in any one of claims 8 toll.

16. A method of propelling objects comprising generating nitrogen from a composition as claimed in any one of claims 1 to 7 orfrom a source as claimed in any one of claims 8 to 10.