|Title of Invention||
"AN IMPROVED GAS-GENERATING COMPOSITION"
|Abstract||This invention relates to an improved gas generating composition comprising a mixture of 10 to 40% of the weight of the mixture of epoxy binder such as novolac epoxy binder resin, 10 to 30% by weight of mixture of energetic plasticizer such as azide polymer like glycidyl azide polymer, 2 parts per 100 parts of the weight of mixture of ballistic modifier such as ferrocene derivative, an oxidizer such as ammonium perchlorate and a hardener such as polyamide.|
|Full Text||FIELD OF INVENTION
The present invention relates to an improved gas-generating composition having superior burn rates and low flame temperature.
During recent years, gas generators have gained tremendous importance in view of their wide applications as source of power for a relatively short duration. Gas generators are used for seve ral applications such as driving of turbines of auxiliary power devices, air bag systems, etc which demand clean burning with pollution free exhaust products. The ballistic requirements of these gas generators are low flame temperature (Tf) in the range of 750-2200°C and sustained combustion in the pressure zone of 2-7MPa. The gas-generating compositions used for these applications are generally based on Ammonium nitrate (AN) or Triamino guanidine nitrate (TAGN) as oxidiser.
Gas generator devices also find wide applications for augmenting the range of gun projectile by overcoming base drag. Such devices are referred to as base bleed units (BBU). These units are required to undergo sustained combustion under atmospheric/subatmospheric conditions and have flame temperature (Tf) in the range of 1300 to 3000°C with burn rates of l-5mm/s at atmospheric pressure. The gas-generating compositions used for these applications are generally based on Ammonium Perchlorate (AP) as oxidizer in addition to binder and plasticiser.
Ammonium nitrate based gas-generating composition has the disadvantage that due to thermal cycling during storage and exposure in the field, the grains of ammonium nitrate undergo crystal phase transition at 32°C leading to volume changes which are undesirable as these căuşe dimensional changes of propellant in temperature range of practicai importance as well as căuşe development of cracks.
Ammonium perchlorate based gas generating compositions known in the art for base bleed units (BBU) use various binders such as cellulose acetate, polyesters, polyethers, hydroxy/carboxy terminated polybutadienes (HTPB/CTPB). Out of these binders, HTPB is preferred in view of its clean cross-linking reaction with isocyanate curative and superior low temperature străin capability.
The disadvantage of the above gas generating compositions using ammonium perchlorate and HTPB is that these have low burn rates and combustion inefficiency in actual operating conditions in base bleed units (BBU), particularly under sub-atmospheric conditions.
Another type of ammonium perchlorate based gas generating compositions known in the art, which are recently recommended for BBU, use azido-polymers like glycidyl azide polymer (GAP) as energetic binder/plasticiser which result in improvement of combustion efficiency due to exothermic cleavage of azide bonds near deflagrating surface.
The above type of gas generating compositions incorporating azide polymers like GAP as binder have inferior mechanical properties as azide polymers like GAP have relatively higher glass transition temperature (-40°C) and lower load bearing capability as compared to HTPB which result in poor structural integrity of propellant grains.
Still another type of ammonium perchlorate based gas generating composition known in the art, use HTPB as binder and GAP which has a low molecular weight, as a plasticiser.
The above type of gas generating compositions have the drawback that GAP interacts with isocyanates used as curative for curing of HTPB, resulting in brittle structura.
Another disadvantage of the above gas generating composition is gasification due to fast reaction of low molecular weight GAP with the curative s.
Further disadvantage of the above type of gas generating compositions is that the different rates of reaction of low molecular weight GAP and high molecular weight HTPB with isocyanate result in inferior rnechanical properties. NEED FOR INVENTION
Thus, there i s a need for ammonium perchlorate based gas generating composition which uses such a binder that GAP does not interfare with the curing process of the binder so as to lead to a gas generating composition without physical defects like voids and cracks. OBJECTS OF THE PRESENT INVENTION
The primary object of the present invention is to provide a process for the preparation of an improved gas-generating composition with super burn rate.
Another object of the present invention is to provide a process for the preparation of an improved gas-generating composition which is relatively more combustion efficient.
Still another object of the present invention is to propose a process for the preparation of an improved gas-generating composition which incorporates an epoxy polymer as binder which eliminates interference of GAP with curing process of the binder.
Yet another object of the present invention is to provide a process for the preparation of an improved gas-generating composition which incorporates a ballistic modifier which enables preparation of composition with super burn rates.
Additional object of the present invention is to provide a process for preparation of gas generating composition with wide range of burning rates by varying GAP content.
Further object of the present invention is to provide a process for the preparation of an improved gas-generating composition which is slurry castable.
Still further object of the present invention is to provide a process for the preparation of an improved gas-generating composition which overcomes the problems of gasification experienced in known processes clue to fast interaction of low molecular weight glacidyl azide polymer (GAP) with curatives (isocyanates) used for HTPB.
Yet further object of the present invention is to provide a process which provides a gas generating composition free from physical defect (void/crack).
Other objects, features and advantages of the present invention will become apparent from the description and working example that follow.
60g of novolac epoxy resin, 300g of glycidyl azide polymer and 20g of ferrocene derivative were mixed in a planetary mixer and deaerated by constant agitation for l hour. 600g ammonium perchlorate in fine partide of 4 microns were then added and mixing continued for 30 minutes without vacuum and for l hour under vacuum of lOmm of Hg. 40g of polyamide were added and mixing continued for 20 minutes keeping temperature of about 25°C. The slurry
obtained was cast in the mould under vacuum. After casting was over, vacuum released and mould was transferred to a water jacketed oven for curing at 40°C for 5 days.
The burn rates of cured gas generator formulations were determined in the pressure range of 1-6. 9Mpa by employing Acoustic Emission (AE) technique. The formulation prepared as per above example containing 60% AP, 10% epoxy binder, 30% GAP and 2 parts of ballistic modifier exhibited burn rates varying from 34 to 56 mm/s in the pressure range of 1-6. as per table below:-
By varying the content of plasticiser like glycidyl azide polymer (GAP) the process of the present invention provides compositions with wide range of burning rates. The burn rates evaluated for different compositions with varying amounts of GAP are tabulated in the following table:-
Burn Rates for compositions with different amounts of GAP
The calorimetric value and flame temperature of different composition obtained by varying amounts of GAP are tabulated in Table-III.
As is evident from Table-II and Table-III, the composition with 60% AP, 10% Epoxy binder, 30% GAP and 2 Parts/ 100 of Ferrocene derivative has significantly superior burn rates and low flame temperature. The composition as prepared by the working example has burning rates between 33 to 55mm/s at l to 1.69 MPa and flame temperature of 2100°C. The compositions prepared by this invention give stable combustion at as low pressure as l MPa.
11 is to be understood that the process of the present invention is susceptible to modifications, changes and adaptations by those skilled in the art. Such variations, spirit and scope of the present invention which is set forth by the following claims:-
1. An improved gas generating composition comprising a mixture of 10 to 40% of the weight of the mixture of epoxy binder such as novolac epoxy binder resin, 10 to 30% by weight of mixture of energetic plasticizer such as azide polymer like glycidyl azide polymer, 2 parts per 100 parts of the weight of mixture of ballistic modifier such as ferrocene derivative, an oxidizer such as ammonium perchlorate and a hardener such as polyamide.
2. An improved gas generating as claimed in claim 1 wherein oxidizer ammonium perechlorate (AP) is used in the preferred oxidizer to binder ratio of 60:4p.
3. An improved gas generating as claimed in claim 1 wherein the slurry casting of the composition is carried out in a mould kept under vacuum.
4. An improved gas generating composition substantially as herein described and exemplified in the example.
|Indian Patent Application Number||2474/DEL/2005|
|PG Journal Number||15/2010|
|Date of Filing||13-Sep-2005|
|Name of Patentee||THE CHIEF CONTROLLER,RESEARCH & DEVELOPMENT ORGANISATION,|
|Applicant Address||MINISTRY OF DEFENCE, GOVT.OF INDIA,TECHNICAL COORDINATION DTE.,B-341,SENA BHAWAN, DHQ P.O. NEW DELHI-110011. AN INDIAN NATIONAL.|
|PCT International Classification Number||C06B 31/12|
|PCT International Application Number||N/A|
|PCT International Filing date|