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Concept
Minol (explosive)
Summary
Minol (pronounced mine-ol) is a military explosive developed by the Admiralty early in the Second World War to augment supplies of trinitrotoluene (TNT) and RDX, which were in short supply. The aluminium component in Minol significantly prolongs the explosive pulse, making it ideal for use in underwater naval weapons (e.g. naval mines, for which it was developed, depth charges and torpedoes) where munitions with a longer explosive pulse are more destructive than those with high brisance. Minol cannot be used in weapons fired from gun barrels (e.g. artillery shells) because there is a risk of detonation when subjected to over 250 gs of acceleration. Initially, three Minol formulas were used. All percentages shown are by weight:
Minol-1: 48% TNT, 42% ammonium nitrate (AN) and 10% powdered aluminium
Minol-2: 40% TNT, 40% ammonium nitrate and 20% powdered aluminium
Minol-3: 42% TNT, 38% ammonium nitrate and 20% powdered aluminium
These three Minols suffered from expansion, spewing and gassing due to the reaction of fine aluminium powder with moisture and structural phase transitions in ammonium nitrate. To improve stability of Minol and increase production, more coarse aluminium powder was introduced. Later it was found that aluminium chips, such as filings, flakes and shavings, also gives good performance and improved stability.
To solve the problem with dimensional instability, pure ammonium nitrate was replaced by a solid solution of 10% of potassium nitrate in AN. Thus, a new formula was adopted:
Minol-4: 40% TNT, 36% ammonium nitrate, 4% potassium nitrate and 20% powdered aluminium
The addition of potassium nitrate minimized expansion of Minol, making it more stable to temperature changes than TNT, but didn't solve the problem. Minol IV could still expand and develop cracks after prolonged thermal cycling. A new composition, with 20% of potassium nitrate in solid solution, was developed. It didn't expand or crack even when cycled for months, but wasn't adopted for production and service.
Official source
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