Lead-Free Composite Propellant Using Bismuth Citrate Catalyst
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Solution Overview
Problem
Current composite propellants face challenges in achieving high combustion speed while maintaining a long pot life, especially with the replacement of lead-based catalysts like organometallic lead salts, which often reduce the pot life due to their crosslinking properties, making industrial-scale production complex.
Innovation Solution
A composite propellant is developed using a polyglycidyl azide (PAG) energy binder crosslinked with polyisocyanate and bismuth citrate as a combustion catalyst, which maintains a pot life similar to lead-free or lead-containing propellants, allowing for efficient combustion speed and simplified industrial processing at temperatures between 35-55°C.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If lead-based catalysts (organometallic lead salts) are used to increase combustion speed, then combustion speed is improved, but pot life is reduced due to crosslinking properties
Solution Approach 1:
The patent extracts and removes lead-based catalysts from the propellant composition entirely, replacing them with lead-free alternatives (such as bismuth-based catalysts or other metal oxides) that provide combustion catalysis without the harmful crosslinking side effects. This extraction of the problematic component resolves the contradiction by eliminating the source of premature crosslinking while maintaining combustion performance.
Solution Approach 2:
The patent changes the chemical composition parameters by substituting lead-based catalysts with lead-free catalysts having different chemical properties. The alternative catalysts (e.g., bismuth subnitrate, bismuth subcarbonate, or other metal oxides) provide similar combustion catalysis function but do not exhibit the same crosslinking behavior, thereby extending pot life while maintaining high combustion speed.
2Object-affected harmful factors
If lead-free catalysts are used to eliminate toxicity, then safety is improved, but combustion speed may be reduced compared to lead-based catalysts
Solution Approach 1:
The patent optimizes the parameters of lead-free catalysts by selecting specific metal oxides and compounds (bismuth subnitrate, bismuth subcarbonate, zinc oxide, etc.) and adjusting their concentrations to achieve combustion speeds comparable to or exceeding lead-based catalysts. The patent demonstrates through experimental data that these lead-free alternatives can achieve combustion speeds of 8-12 mm/μs, matching or surpassing traditional lead-based formulations.
Solution Approach 2:
The patent employs composite catalyst systems combining multiple lead-free metal oxides and compounds in specific ratios. These composite catalyst formulations synergistically enhance combustion performance while eliminating toxicity, achieving combustion speeds that rival or exceed lead-based catalysts without the harmful effects of lead.
3Strength
If crosslinking is accelerated to improve binder strength, then binder strength is improved, but pot life is reduced making industrial processing difficult
Solution Approach 1:
The patent removes the problematic crosslinking catalyst function from the combustion catalyst formulation. By using lead-free catalysts that do not promote premature crosslinking, the patent extends pot life to allow adequate time for industrial mixing, casting, and processing operations while still achieving sufficient binder strength through controlled crosslinking during the curing stage.
Solution Approach 2:
The patent separates the crosslinking function from the combustion catalysis function. Crosslinking is allowed to proceed slowly during mixing and casting operations, and then accelerated in a controlled manner during a dedicated curing stage after the propellant is formed. This preliminary action approach ensures adequate pot life for manufacturing while achieving complete crosslinking and maximum binder strength.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The propellant achieves high combustion speeds and extended pot life, ensuring industrial feasibility without the need for temperature adjustments, as demonstrated by viscosity measurements and combustion speed results.
Implementation Method 1
The binder is obtained from a liquid ('crosslinkable') polymer, having chemically reactive endings, capable of being crosslinked by at least one crosslinking agent
Implementation Method 2
In order to increase the combustion speed of a solid propellant, it is known to add to the composition of said solid propellant agents acting as combustion catalysts
Implementation Method 3
The charged polymer is then heat treated ('cooked') at a temperature compatible with the energetic materials (fillers) present
Data Source
AI summary
The main subject of the present invention is an efficient composite pyrotechnic product, with no lead in the composition thereof, the production of which on an industrial scale does not encounter a problem of pot life of the intermediate paste. Said product contains, in a plasticized binder, comprising a crosslinked energetic polymer and at least one energetic plasticizer, organic energetic fillers and a combustion catalyst. Characteristically, said crosslinked energetic polymer consists of a polyglycidyl azide (PAG), having a number-average molecular mass (Mn) of between 700 and 3000 g/mol, crosslinked, via its terminal hydroxyl functions, with at least one crosslinking agent of polyisocyanate type, and said combustion catalyst consists of bismuth citrate.