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Thread: Ulrich Bretscher's SMOKELESS BLACK POWDER & HANDGONNE web page. Re-found!

  1. #76
    Member Cordite's Avatar
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    Ullrich Bretscher's page discusses one of the inventive ways of improving on Black Powder at the end of its era while Nitrocellulose based powders replaced it. One such powder was "brown powder", or "prismatic powder" or "cocoa powder" made with brown charcoal. Brown charcoal is charcoal charred at a lower temperature. Brown powder was more powerful than black powder. But there were anecdotes of it being less stable and more prone to go off by itself. One theory is that the magazine explosion which sank the USS Maine in Havana Harbour (triggering the Spanish American War of 1898) was caused by brown powder, but the cause is still debated.

    USS Maine blows up, this may be a screenshot of contemporary cellphone footage but I cannot confirm that:
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    Brown powder was made with 1%-3% sulphur instead of 10% sulphur as the brown charcoal itself made up for the lack of sulphur, both by lowering ignition temperature and also by acting as a binder, it having some tar left in it. The powder was made by charring straw with hot steam at a desired temperature. (This is the modern method of making "activated charcoal" as the hot steam causes the charcoal to be more porous and have a larger, reactive surface area).

    Image of prism powder, click on image to see article on victorianshipmodels.com
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    Interesting enough, the coastal batteries at Oamaru had similar rifled muzzle loading cannons as depicted in the link.

    I came across some interesting Wikipedia information on the charcoal component which somewhat explains the behaviour of brown powder:

    The question of the temperature of the carbonization of wood is important:
    220 C (428 F) Brown charcoal.
    280 C (536 F) Deep brown-black, after some time.
    300 C (572 F) Brown, soft and friable, and readily inflames at 380 C (716 F).
    310 C (590 F) An easily powdered mass.
    Higher temperatures: Hard and brittle charcoal which does not fire until heated to about 700 C (1,292 F).

    I note Ulrich Bretscher made his BP with charcoal charred to 350C (the temperature at which smoke stops being given off) and he found that the ignition temperature of his sulfur-free smokeless black powder was 440C, while his sulfur-containing black powder ignited at 300C. He determined his sulphur-free smokeless black powder was some 10% less powerful than the traditional recipe (but NB, this was sulfur free powder made with black charcoal, not brown charcoal).

    For the historical brown powder, the the ignition temperature was artificially increased and burn rate reduced by reducing sulphur content. The brown charcoal, being slightly tarry, took over the role of sulphur as a binder and for cannon use it was hydraulically pressed into prismatic powder to further slow the burn rate. Brown powder provided higher impulse power than black powder as it combusted into carbon monoxide and carbon dioxide which were both of a lower molecular weight compared to hydrogen sulphide from burning sulphur - i.e., more gas volume for same powder weight.

    So, if one makes black powder it's worth looking into smokeless, not-so-black, powder.
    zimmer and Micky Duck like this.
    "I find television very educating. Every time somebody turns on the set, I go into the other room and read a book." Groucho Marx

  2. #77
    Member Cordite's Avatar
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    For my fellows in the forum nerd herd interested in BP chemistry, I gleaned this from a youtube greenie lecture on bio char (the sensitive souls can't bring themselves to say "charCOAL").

    Biochar has value in remineralising soil, and works synergistically with chemical fertiliser in increasing crop yields. This slide looks at the persistence in soil of different types of charcoal, grouped according to the temperature it's made at.

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    "Brown", less hot pyrolysed charcoal consists of smaller molecules, whereas in charcoal cooked at hot temps the carbon has polymerised into larger and more stable molecules (hence it's tinkly, glassy sound!). The lighter cooked charcoal is more easily broken down in soil than the hotter cooked charcoal with its larger, more stable molecules.

    The traditional explanation for brown charcoal/gunpowder's easy ignition and higher power is that its brown charcoal has not had all the wood tars cooked off. Brown charcoal's smaller, more reactive carbon molecules seems to be another reason.
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    "I find television very educating. Every time somebody turns on the set, I go into the other room and read a book." Groucho Marx

  3. #78
    Member Cordite's Avatar
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    And table giving an idea of how charring temperature affects carbon to tar/volatiles ratio. Burnt at 300C a third of its weight is volatiles, but at 800C it's no volatiles and about 95% carbon. The chemical formula for the reaction of burning different colour BP would seem quite different for this reason alone.

    Source: Chapter 4 - Carbonisation processes

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    Brown charcoal is more hygroscopic, so for heating purposes it means a lot of heat is lost up the chimney in the steam.

    In gunpowder, it higher water content would be a negative in regard to keeping one's powder dry. Water-to-steam usually means more pressure generated, and heat loss is no problem as you don't want efficient barrel heating.
    Last edited by Cordite; 18-04-2021 at 02:35 PM.
    "I find television very educating. Every time somebody turns on the set, I go into the other room and read a book." Groucho Marx

 

 

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