Title of Invention

"A PYROTECHNIC COMPOSITION FOR ENERGY RICH PROPELLANT AND PROCESS THEREOF"

Abstract

This invention relates to a pyrotechnic composition for energy rich propellant comprising boron powder as metal fuel present in an amount of 5 to 50% by weight preferably 25 to 40% by weight, potassium nitrate as an oxidiser present in an amount of 95 to 50% by weight preferably 75 to 60% by weight, remainder being a binder as solution of plasticised ethyl cellulose n toluene which is 10% to 12% by weight comprises of ethyl cellulose with diethyl phthalate taking 70 to 80% preferably 75 to 77.5% by weight of ethyl cellulose and 30 to 20% preferably 25 to 22.5% by weight of diethyl phthalate.

Full Text

FIELD OF INVENTION This invention relates to a formulation of boron based pyrotechnic composition for energy rich composite propellants. and to a process for the preparation thereof. PRIOR ART: The conventional double based propellants posess very high mechanical properties and relatively low ignition temperature (170°C). However, modern propellants like composite and composite modified double base propellants posess relatively low mechanical properties, high ignition temperatures (240°C, 185°C respectively) and generally have to be operated at high altitudes. Conventionally gun powder having high gas to solid ratio has been used as an efficient igniter for ignition of double based propellants at ground level. The disadvantage of using gun powder as igniter is that it fails to ignite at high altitude. Another disadvantage of using gun powder as igniter is that it is not a reliable igniter for composite and composite modified double based propellants. Yet another disadvantage of using gun powder as igniter is that it does not give satisfactory ignition for composite propellants which have high auto ignition temperature and poor mechanical properties Further disadvantage of using gun powder as igniter is that it is not very efficient for propellants which have low structural integrity and require low critical pressure for steady state of combustion. A pyrotechnic composition usually contains a small percentage of binder which may be of natural origin or man made organic polymer, which holds fuel (metal) and oxidiser components in homogenous blend. Some other pyrotechnic compositions with metal powders such as Al, Mg, B as fuel and KNO3 as oxidiser, with or without binder have also been used as igniter for the propellants. However, disadvantage of using these pyrotechnic compositions without binder is that on storage the ingredients of constituent composition are likely to segregate. Another disadvantage of using these pyrotechnic compositions without binder is that the composition becomes sensitive to mechanical impulse. Yet another disadvantage of using these pyrotechnic compositions without binder is that the composition is susceptible to ingress of moisture which affects the final performance. Still another disadvantage of using these pyrotechnic compositions without binder is that the composition does not have pelleting property and thus are unsafe. Further disadvantage of using these pyrotechnic compositions without binder is that such compositions does not give reproducible and reliable results. Still further disadvantage of using these pyrotechnic compositions without binder is that such compositions do not have high compressive strength. The disadvantage of using pyrotechnic composition with organic polymer binder viz Ethyl cellulose without plasticisation, the composition is prone to oxidation in presence of light and temperature above the softening point (150°C). Another disadvantage of using pyrotechnic composition with ethyl cellulose without plasticisation as binder is that on storage the composition deteriorates and pellet becomes brittle in nature OBJECTS OF THE INVENTION The primary object of the present invention is to propose a formulation of a boron based pyrotechnic composition for energy rich propellants. Another object of the present invention is to propose a boron based pyrotechnic composition with satisfactory ignition delay. Still another object of the present invention is to propose a boron based pyrotechnic composition which has minimum burning time to reach pressure maximum i.e. mass consumption rate is high. Another object of the present invention is to propose a boron based pyrotechnic composition which has lower softening point due to use of plasticised ethyl cellulose. Yet another object of the present invention is to propose a boron based pyrotechnic composition which is pelleteable to give desired pellet densities and crushing strength. Further object of the present invention is to propose a boron based pyrotechnic composition with sufficiently long shelf life. Yet further object of the present invention is to propose a boron based pyrotechnic composition which is reasonably insensitive and easy to process. Still further object of the present invention is to propose a boron based pyrotechnic composition that gives desired ignition to various classes of propellants. DESCRIPTION OF INVENTION According to this invention there is provided a pyrotechnic composition for energy rich propellant, comprising (a) boron powder as metal fuel present in an amount of 5 to 50Z by weight preferably 25 to 40% by weight, (b) potassium nitrate as an oxidiser present, in an amount of 95 to 50% by weight preferably 75 to 60% by weight,, (c) remainder being a binder as solution of plasticised ethyl eellalose in toluene which is around 10Z by weight. Further according to this invention there is provided a process for the preparation of boron based pyrotechnic composition comprising in the steps of (a) preparing a solution of plasticised ethyl cellulose, (b) preparing a mixture of boron and potassium nitrate powders, (c) mixing said nitrate powders with PEC solution. In accordance with the present invention, the preparation of boron based pyrotechnic composition comprises of the steps of :- a) Preparation of Plasticiised Ethyl Cellulose Plasticised ethyl cellulose (PEC) is prepared by plasticisstion of ethyl cellulose with diethyl phthalate taking 70 to 80% preferably 75 to 77.5% by weight of ethyl cellulose and 30 to 20% preferably 25 to 22.5% by weight of d i e t h yl p h t h a l a t e . b) Preparation of solution of Plasticised Ethyl Cellulose 10% to 12% solution of 10% by weight dried plasticised ethyl cellulose (PEC) is prepared by dissolving PEC in toluene in a suitable vessel with constant stirring to get uniform solution. c) Preparation of Mixture of Boron and Potassium Nitrate Powders 5 to 50% preferably 25 to 40% by weight of boron amorphous (Gr.1) powder with purity higher than 95% is mixed with 95 to 50% preferably 75 to 60% by weight of potassium nitrate. The mixture is sieved 3-4 times to get homogeneity. d) Mixing of Boron and Potassium nitrate Powder mixture with PEC solution. The composition of the present invention is prepared by mixing around 50% of PEC solution with the mixture of boron powder and potassium nitrate as prepared above. The remaininq 50% PEC solution is poured over mix and is throughly mixed to get homogenous mix. This mix is allowed to become semi-solid which is then granulated by passing through a sieve. These granules are dried in a water jacketed oven at 60+5oC for about 2 to 6 hours to reduce to volatile matter to around 1%. The invention will now be illustrated with an example which is intended to illustrate the working of the invention and is not intended to be taken restrictively to imply any limitation on the scope of the present invention. Example 1 The plasticised ethyl cellulose (PEC) was prepared by 29% plasticisation of ethyl cellulose N-200 with diethyl phthalate. A 10% solution of dried plasticised ethyl cellulose was prepared using 50g of dried plasticised ethyl cellulose and 500 cm3 of distilled toluene as solvent in a suitable vesel wth constant stirring to get uniform solution. 25.0g of boron amorphous Gr. 1 powder with purity more than 95% & 475.0g of potassium nitrate with particle size between 90 & 53 micrometer were weighed accurately and mixed on a wax paper using hom spatula. This mix was then sieved 3 times through 600 micrometer sieve for better mixing. In a mixing vessel 50% of plasticised ethyl cellulose (PEC) solution was taken in which the above mix of boron & potassium nitrate was added carefully avoiding the spillage of material. The remaining 50% of PEC solution was poured over mix and was thoroughly mixed using horn spatula to get homogeneous mix. The mix was poured on conducting polythene sheet kept in a tray and allowed to become semisolid The semisolid mass/dough was then granulated by passing through 25 BSS (600 micrometer) sieve. The sieved granules were then retained on 52 BSS (300 micrometer) sieve and retained material was dried in water jacketed oven at 60 + 5° C for 2 to 6 hours to reduce the volatile matter to Example No 2 to 10 In these examples the procedure for preparation is identical to that of example 1 except that boron was increased from 10 to 50 parts while Potassium Nitrate was reduced from 90 to 50 parts by weight keeping binder (PEC) constant at 10%. These formulations are given in Table 1 TABLE -1 Boron Based Pyrotechnic Compositions Results (Table Removed) (*DNI: Did not ignite) The calorimetric Value of each composition was determined in the Julius Peters' bomb having 300 cc volume. The results indicates that, except example 1 which did not ignite, all other compositions have Cal-value in between 690-1814 cal/g. The ignition temperature evaluated by Micro DTA for all compositions. Except example 1, all compositions were found be in the range of 502°C to 563°C The composition at example 4 which is Stoichiometric composition, revealed that it was more sensitive to impact as compared to other compositions for impact test. For the friction test it was observed that all compositions are insensitive to friction upto 36 kg dead load. The formulated compositions were evaluated at loading density 0.01 g/cc in a simple closed vessel (free volume 700 cc) designed for this purpose. The results are given in Table-1. The compositions at example 1 to 3 gave considerable ignition delay and rate of rise of pressure was sluggish in nature. For the example 4, the pressure maximum (Pmax) recorded was higher while example 4 onwards there was downfall of pressure maximum with same level of ignition delay. The plasticised ethyl cellulose binder 10% by parts by weight gave satisfactory structural integrity for the compositions except example 1, and 2. On the basis of these findings, it was established that compositions at example 5 to 8 gave highly encouraging results as igniter compositions. The compositions at example no.6 was selected as igniter composition on the basis of results obtained and successfully used for the ignition of solid rocket propellants, which delivered smooth pressure-time (p-t) profile with minimum ignition delay The example 6 composition in pellet form was subjected to environmental trials, after trials it gave results which are within the specified limits Also the composition at example 6 in granular and pellets form undergone ISAT "B" trials for 12 months, with periodic withdrawal of igniters, gave repeatable performance for required parameters On the basis of ISAT "B" trials the composition has been allotted life of 10 years from the date of preparation. It is to be understood that the formulation of the present invention is susceptible to modifications, adaptations, changes by those skilled in art. Such modifications, adaptations, changes are intended to be within the scope of the present invention, which is further set forth under the following claims:- WE CLAIM; 1. A boron based pyrotechnic composition for energy rich propellant composition comprising: - a) boron powder as metal fuel present in an amount of 5 to 50% by weight preferably 25 to 40% by weight, b) potassium nitrate as an oxidiser present in an amount of 95 to 50% by weight preferably 75 to 60% by weight, c) remainder being a binder as solution of plasticised ethyl cellulose in toluene which is 10% to 12% by weight and comprises of ethyl cellulose with diethyl phthalate taking 70 to 80% preferably 75 to 77.5% by weight of ethyl cellulose and 30 to 20% preferably 25 to 22.5% by weight of diethyl phthalate. 2. A boron based pyrotechnic composition for energy rich composite propellants as substantially described herein. 3. A process for the preparation of boron based pyrotechnic composition as claimed in claim 1 comprising the steps of mixing a) a 10 to 12% solution of plasticized ethyl cellulose (PEC) in toluene; and b) a mixture of 5 to 50% by weight of boron and potassium nitrate powders, and forming the mixture into granules. 4. A process as claimed in claim 3 wherein granules are dried at 50±5°C for 2 to 6 hours to reduce the volatile matter to 5. A process as claimed in claim 3 wherein 10% to 12% solution of 10% by weight dried plasticised ethyl cellulose (PEC) is prepared by dissolving PEC in toluene in a suitable vessel with constant stirring to get uniform solution. 6. A process as claimed in claim 3 wherein preferably 25 to 40% by weight of boron amorphous (Gr 1) powder with purity higher than 95% is mixed with preferably 75 to 60% by weight of potassium nitrate. 7. A process for the preparation of a boron based pyrotechnic composition substantially as herein described and illustrated in the example.

Documents:

893-del-2000-abstract.pdf

893-del-2000-claims.pdf

893-del-2000-correspondence-others.pdf

893-del-2000-correspondence-po.pdf

893-del-2000-description (complete).pdf

893-del-2000-form-1.pdf

893-del-2000-form-19.pdf

893-del-2000-form-2.pdf

893-del-2000-gpa.pdf