|Title of Invention||
A SLOW BURN PROPELLANT COMPOSITION WITH HIGH PERFORMANCE CHARACTERISTICS
|Abstract||A SLOW BURNING COMPOSITE SOLID PROPELLANT COMPOSITION AND A PROCESS OF MAKING THE SAME. The present invention relates to a slow burning solid propellant composition as binder with low burning rate comprising hydroxyl terminated polybutadiene (HTPB), ammonium perchlorate as oxidizer and aluminium powder as metallic fuel, oxamide as ballistic modifier and at least one aromatic/aliphatic isocyanate as curing agents.|
A slow burning composite solid propellant composition and a process of making
This invention relates to a slow burning composite solid propellant composition and a process of producing the same. This propellant composition is based on hydroxyl terminated polybutadiene.
Background and Prior art:
Slow burning propellant systems are used in gas generator propellants for generation of large volumes of gas, useful for performance of work, driving turbines etc and also for missions which have solid motors that burn at very low rates.
Survey of literature indicated existence of many slow burning propellant compositions in the prior art, but each of them has its own drawback. A patent US 19510205 titled 'Slow burning solid composite propellant' uses nitro guanidine as slow burning fuel, which is quite sensitive to friction and impact and is therefore unsafe. German patent DE 1446902 titled 'Solid propellant composition' also uses nitroguanidine or ammonium picrate as slow-burning fuel, which is quite unsafe to use. Another US Patent 19581114, titled 'Solid composite propellants containing oxamide dihydrazone' uses oxamide dihydrazone as fuel, which is not readily available in market. French patent FR 2803844 describes about 'Aliphatic polyol-based polyurethane combustion inhibitors for polyurethane-cross linked composite propellants' and the processing of these inhibitors is very complex and difficult. Another US Patent 2995430 describes about a 'Composite propellant reinforced with nitrogen compounds', but nitrogen rich compounds are highly sensitive and unsafe. European patent GB930540, 'Solid composite smokeless slow burning low flame temperature propellant' uses polyester based propellant,
whose performance in terms of Specific impulse (Isp) is lower. US 2974026, describes a solid composite, smokeless, low flame propellant with ammonium nitrate as oxidizer in conjunction with resinous condensation product of adipic acid, maleic anhydride and diethylene glycol as fuel. But, this is not a conventional fuel in use at present, which is only to be synthesized and is not available readily.
US 3031347, "Slow Burning Solid Composite Propellant' describes propellant composition with 1. ammonium perchlorate, cellulose nitrate, ammonium nitrate as oxidizers & diethylene glycol bis (allylcarbonate), methyl acrylate and methyl metha aery late as fuel. 2. ammonium perchlorate, cellulose nitrate, ammonium nitrate, guanidine nitrate as oxidizers with diethylene glycol bis (allylcarbonate), methyl acrylate and methyl metha acrylate as fuel. 3. ammonium perchlorate, cellulose nitrate, nitro guaidine as oxidizers diethylene glycol bis (allylcarbonate), methyl acrylate and methyl metha acrylate, n-butyl acrylate, glycol diacrylate etc as fuels. But the fuels used are not of conventional type and are to be synthesized.
From the above narration it is evident that the slow burn propellants in the prior art use fuels which are either non-conventional type and hence are not readily available in market or are highly dangerous and unsafe to use or are very complex and difficult to be processed.
The present invention is different from all the patents referred above. An object of the present invention is to provide a new propellant composition with hydroxyl-terminated polybutadiene as binder, ammonium perchlorate as oxidizer, aluminum as metallic fuel and oxamide as a burn rate retardant for developing a slow burning propellant, which is easy to produce, safe to handle and has high specific impulse.
The key ingredient oxamide doesn't seriously affect the energetics of the propellant. All the raw materials in the present composition are readily available. There is good reproducibility of propellant properties, mainly mechanical and ballistic properties and good compatibility of oxamide with other propellant ingredients. There are no corrosity or storage problems for the propellant. Ageing properties of the propellant are superior to the existing compositions.
Yet another object of this invention is to identify a suitable burn rate retardant, which can reduce the burn rate of propellant formulation without seriously affecting the energetics.
Description of the invention
This invention relates to a composite solid propellant composition based on hydroxyl-terminated polybutadiene as binder, ammonium perchlorate as oxidiser, aluminium as metallic fuel and oxamide as burn rate modifier.
The composite solid propellant of this invention exhibits very low burn rates. The bum rates are modified by addition of a critical ingredient oxamide. The viscosity build up, potlife and curing of the composite solid propellant are regulated by addition of isocyanates in the mixture.
Oxamide is an amide of oxalic acid derived by techniques such as vacuum dehydrogenation of ammonium oxalate. This amide of oxalic acid is cost effective and does not interact with propellant components. A further object of this invention is to identify a suitable bum rate retardant which can reduce the bum rate of propellant formulation without seriously affecting the energetics and oxamide does this job without much side reactions with other propellant components.
We have found that oxamide exhibits excellent bum rate retardant properties when added to solid propellants. Availability, reproducibility, good compatibility with other propellant components makes it a suitable choice as bum rate retardant. Ageing properties of composite propellant using oxamide are superior to that of other compositions.
The propellant composition consists of hydroxyl terminated polybutadiene (HTPB) which may be produced by free radical polymersation of butadiene using hydroxyl containing initiators. The said HTPB may preferably have a hydroxyl number of 40-50, molecular weight of 2000-5000 and bulk viscosity of 30-60 Poise. Ammonium perchlorate may have bimodal distribution of coarse to fine grade in weight ratio varied
from 6:1 to 2:1. Average particle size of ammonium perchlorate coarse grade is in the range 300-400 microns and ammonium perchlorate fine grade is in the range 50-100 microns.
In addition, the propellant may contain conventional additives like antioxidants, plasticizers, bonding agents and curing agents. Curing agents that show excellent results are toluene diisocyanate (TDI) and aliphatic isocyanate like isophorone diisocyanate (IPDI). Any known diol- triol mix comprising of diols such as ethylene glycol or 1,4 butane diol and triols such as 1,1,1-trimethylol propane or glycerol in ratios ranging from 3:1 to 1:3 may be added to the composition to control the chain extension and crosslinking of HTPB. The diol triol mix also acts as a bonding agent. The diol-triol mix must have a hydroxyl number of 1200-1225 measured as mgKOH/g, refractive index at 25°C of 1.453-1.457, moisture content less than 0.1%.
The composite solid propellant composition according to this invention comprises hydroxyl terminated polybutadiene, ammonium perchlorate and aluminium powder wherein said composite has oxamide as ballistic modifier and at least one aromatic and / aliphatic isocyanate as curing agents.
This invention also includes a process for preparing a composite solid propellant composition which comprises the steps of mixing hydroxyl terminated polybutadiene, ammonium perchlorate and aluminum powder and adding oxamide and at least one aromatic or aliphatic isocyanate to form a slurry and subsequently casting the said slurry.
Propellant mixing operations can be carried out in conventional horizontal sigma kneader or vertical change can mixer. Measuring the viscosity at regular intervals for a period of 5 to 10 hrs monitors castability of the resultant slurry. The slurry may then be subjected to de-aeration and cast into polyethene cartons at a residual pressure of 3 to 5 torr. The cast propellants are then cured at temperatures ranging from 40-60°C for duration of 5 to 10 days. The cured propellants are then evaluated for mechanical properties and bum rates.
Oxamide is used at concentration levels of 0.5 -6.0 % by weight to reduce the burn rate in the range of 17 to 30%. Propellant composition may have 80- 90% by weight of solid loading containing 16-20% by weight of aluminum powder with coarse and fine ammonium perchlorate in the weight ratio of 6:1 to 2:1.
Typical variation in vacuum specific impulse (V.lsp) with oxamide content of 5% at solid loadings of 80, 85 and 90% are 270.3, 283.4 and 286.3 s respectively. The sea level specific impulse (Isp) is of the order 247.4, 260.3 and 261.6 s respectively at a pressure of 70 kg/cm2'
Two different types of isocyanates namely toluene diisocyanate and isophorone diisocyanate are used either alone or in combination with each other. The viscosity build up of the propellant slurry, mechanical properties and burn rates are determined. It is seen that aromatic toluene diisocyanate is more reactive and as such the resultant propellant has shorter pot life. Primary and secondary isocyanate groups of alicyclic isophorone diisocyanate are slow reactive and give longer pot life.
Curing takes place when the composite propellant is kept for a period of time at the cure temperature. Mechanical properties such as tensile strength, elongation, modulus and hardness may be adjusted by varying NCO/ OH ratio of the composition in the range of 0.75 to 0.85.
Slow burning propellant composition can be used for specialized applications such as gas generators, in solid rocket motors for reusable launch vehicles etc.
1. A slow burning solid propellant composition as binder with low burning rate
comprising hydroxyl terminated polybutadiene (HTPB), ammonium perchlorate as oxidizer and aluminium powder as metallic fuel, oxamide as ballistic modifier and at least one aromatic/aliphatic isocyanate as curing agents.
2. The composite solid propellant composition as claimed in claim 1, wherein said HTPB
hae a hydroxyl number of 40-50, molecular weight of 2000-5000 and bulk viscosity of
3. The composite solid propellant composition as claimed in claim 1, wherein said
ammonium perchlorate is a mixture of coarse and fine grades in the weight ratio from
6:1 to 2:1.
4. The composite solid propellant composition as claimed in claim 1, wherein said oxarnide
is in the range of 0.5 to 6 % by weight of the total composition
5. The composite solid propellant composition as claimed in claims 1-4, wherein said
isocyanates are toluene diisocynate and isophorone diisocyanate or a combination thereof.
6. The composite solid propellant composition as claimed in claims 1-5, wherein said composition has conventional additives like antioxidants, bonding agents, plasticizers and curing agents.
7. The composite solid propellant composition as claimed in claims 1-6, wherein said composition optionally has a diol-triol mixture.
8. The composite solid propellant composition as claimed in claims 1-7, wherein said diol-triol mixture has a hydroxyl value of 1200-1225 measured as mgKOH/ g, a refractive index of 1.453 to 1.457 at 25°C, and a moisture content less that 0.1%.
9. A process for preparing a composite solid propellant composition comprising the steps of mixing hydroxyl terminated polybutadiene, ammonium perchlorate and aluminium
powder, and adding oxamide and at least one aromatic/aliphatic isocyanate to form a slurry and subsequently casting said slurry.
10. The process for preparing a composite solid propellant composition claimed in claim 9, wherein said oxamide is added in the range of 0.5 to 6% by weight of the total composition.Ammonium peroxide added is a mixture of coarse and fine grade in the weight ratio of 6:1 to 2:1, the isocyanates are selected from toluene diisocyanate, Iso phorone diisocyanate or a mixture thereof, and the HTPB has a hydroxy value of 40 to 50 mg KoH/g, molecular weight of 2000-5000 and bulk viscocity of 30 to 60 poise.
Dated this 7 day of March 2007
|Indian Patent Application Number||467/CHE/2007|
|PG Journal Number||03/2012|
|Date of Filing||07-Mar-2007|
|Name of Patentee||INDIAN SPACE RESEARCH ORGANISATION|
|Applicant Address||ISRO HEADQUATERS DEPARTMENT OF SPACE ,ANTARIKSH , NEW BEL ROAD , BANGALORE 560094|
|PCT International Classification Number||C04B 35/10|
|PCT International Application Number||N/A|
|PCT International Filing date|