Powder Chemistry

[Danny]

Having found there's at least one chemist on the forum (Tom), can it be explained in words, rather than formulas, what exactly is going on when gnpowder is ignited in a firing cannon or musket barrel. Chemically, what does each component (nitre, sulphur, charcoal) bring to the party?

Adjuct questions would be what is the specific result of changing proportions of components for a particular use, and why is grain size a factor for each type of application?

I have seen occasional substitutions on the field and want to understand safety consequences, if significant.

Dan Wykes

[ScottWashburn]

I can't say much about the chemistry, but I seem to recall that the different grain sizes is an attempt to control the speed at which the powder burns. One of the drawbacks of Black Powder is that it burns TOO fast. In a gun or cannon what you want is the powder to burn relatively slowly and for the pressure of the gases to increase as the projectile is pushed down the barrel. Black powder tends to go BAM! and explode all at once. Since the projectile can only be accelerated so fast, this leads to a dangerously high level of pressure at the moment of ignition. This led to a lot of burst cannon barrels. Ideally, if you can slow down the rate of burn, you can keep the pressure in the barrel at a safe level.

[RJSamp]

I can't say much about the chemistry, but I seem to recall that the different grain sizes is an attempt to control the speed at which the powder burns. One of the drawbacks of Black Powder is that it burns TOO fast. In a gun or cannon what you want is the powder to burn relatively slowly and for the pressure of the gases to increase as the projectile is pushed down the barrel. Black powder tends to go BAM! and explode all at once. Since the projectile can only be accelerated so fast, this leads to a dangerously high level of pressure at the moment of ignition. This led to a lot of burst cannon barrels. Ideally, if you can slow down the rate of burn, you can keep the pressure in the barrel at a safe level.

The finer the grain, the faster it burns. The coarser the grain, the slower it burns. Pressure (confinement of gases from the reaction) causes black powder to explode.

found this on the internet and found it very readable (I'm not a chemist, but got an A in chemistry in High School 30+ years ago).

Historical Aspects and Black Powder Manufacturing
By

Michael A. Rosen, Ph.D., M.D.
Dade Behring Diagnostics™
Medical Products Division-DuPont Chemical®

Black powder was the original gunpowder and practically the only known propellant and explosive until the middle of the 19th century. Although it can explode (only when tightly compressed), its principal use is as a propellant. Gunpowder was invented by Chinese chemists in the 9th century. Originally, it was made by mixing elemental sulfur (S), charcoal (C), and “saltpeter” properly named potassium nitrate (KNO3). For the most powerful black powder "meal" a wood charcoal is used. The best wood for the purpose is pacific willow, however, grapevine, hazel, elder, laurel and even pine cones have been used. Charcoal is not the only carbon fuel that can be used. Sugar is used instead in many pyrotechnic applications.The ingredients are mixed as thoroughly as possible. This is achieved using a ball mill with non-sparking grinding apparatus (using lead balls), or similar device. The ingredients are mixed as thoroughly as possible.

When the ingredients were carefully ground together, the end result was a powder that was called 'serpentine.' The ingredients tended to require remixing prior to use, so making powder did involve significant of risk. Powder works realized that a large portion of the risk could be mitigated by making certain that the serpentine remained wet through out all but the last step of its manufacture.

Black powder was also “corned” as a simple but effective means by which its burn rate could be adjusted. The initial step of the corning process was to compress the fine black powder "meal" into wet cakes or blocks of a “standardized” density (1.7 g/cm³ or grams per cubic centimeter). The blocks, once allowed to dry would harden and become brittle, then broken up into granules. The granules would then sorted by size to yield the various “grain sizes” or grades of black powder. Standard grades of black powder run from the coarse and slower burning Fg grade used in large bore rifles and small cannon though FFg (medium and small-bore rifles), FFFg (pistols), and FFFFg the very fine and faster burning (small-bore, short pistols and priming flintlocks). Very coarse black powder was used in mining before the development of nitroglycerine and dynamite.



Chemistry, Composition and Combustion of Black Powder

The optimum proportions for gunpowder are: 74.64% saltpeter, 13.51% charcoal, and 11.85% sulfur (by mass). The current standard for black powder manufactured by pyrotechnicians today is 75% potassium nitrate, 15% softwood charcoal and 10% sulfur. A simple, commonly cited, chemical equation for the combustion of black powder is:

2 KNO3 + S + 3C → K2S + N2 + 3CO2



A more accurate, but still simplified, equation is:

10 KNO3 + 3S + 8C →2K2CO3 + 3K2SO4 + 6 CO2 + 5N2

The products of burning do not follow any simple equation. One study's results showed it produced (in order of descending quantities): 55.91% solid products: Potassium carbonate, Potassium sulfate, Potassium sulfide, Sulfur, Potassium nitrate, Potassium thiocyanate, Carbon, Ammonium carbonate. 42.98% gaseous products: Carbon dioxide, Nitrogen, Carbon monoxide, Hydrogen sulfide, Hydrogen, Methane. 1.11% water

Black powder is classified as a low explosive, that is, it deflagrates (burns) rapidly. High explosives detonate at a rate approximately 10 times faster than the burning of black powder. Although black powder is not a high explosive, the United States Department of Transportation classifies it as a "Class A High Explosive" for shipment because it is so easily ignited. Highly destructive explosions at fireworks manufacturing plants are rather common events, especially in Asia. Complete manufactured devices containing black powder are usually classified as "Class C Fireworks", "Class C Model Rocket Engines", etc. for shipment because they are harder to ignite than the loose powder.

To summarize, black powder consists of a fuel (charcoal or sugar) and an oxidizer that supplies oxygen to the reaction during combustion (saltpeter or niter), and sulfur, a “matrix constituent” that allows a more stable, hotter, even burning combustion reaction. The carbon from the charcoal plus oxygen forms carbon dioxide and energy. The reaction would be slow, like a wood fire, except for the oxidizing agent. In order to burn efficiently carbon (charcoal) must be able draw oxygen rapidly from the air. The saltpeter (potassium nitrate) provides that extra oxygen. Potassium nitrate, sulfur, and carbon react together to form large volumes of nitrogen and carbon dioxide gases and potassium sulfide. The large volume of expanding gases, nitrogen and carbon dioxide, provide the propelling force imparted to projectiles by black powder combustion.



Here are some questions regarding Civil War black powder:

1. What is the ignition temperature of Civil War black powder? Potassium nitrate black powder can be ignited with a low temperature flame, but ignites more readily with a hotter flame closer to the decomposition temperature of potassium nitrate which is about 400°C. It is ignited in firearms using concussion and friction/spark. Merely heating it up won't ignite the propellant.

2. What is the detonating temperature of Civil War black powder? It doesn't explode.

3. Is it highly sensitive to impact? No. Friction - if it leads to sparking, static electricity, spark, and flame. Static Electricity is a spark finer powder FFFG & FFFFG could be more susceptable; spark - yes by design; flame - yes by design

4. If you drop a Civil War shell could it explode? It could if it has a percussion, fulminate of mercury (mercury diisothiocyanate), detonator on its nose and if the slider is able to move freely. The percussion cap also has to be resting on the nipple in order for the slider to strike against the anvil cap. This is highly unlikely that a excavated percussion fuzed shell would explode when dropped.

5. Does the powder get stronger with age? No

6. Does the powder turn to Nitro Glycerin? No

[Slickrick214]

RJ pretty much covered everything in detail. To put it simply though and to add to (and repeat some of the things already said):

1)Potassium nitrate (KNO3)— Supplies oxygen for the reaction

2) Charcoal- Provides fuel for the reaction in the form of carbon

3) Sulfur- Also a fuel, lowers the temperature of ignition and increases the speed of combustion.

Potassium nitrate is the most important ingredient in terms of both bulk and function because the combustion process releases oxygen from the potassium nitrate, promoting the rapid burning of the other ingredients. To reduce the likelihood of accidental ignition by static electricity, the granules of modern black powder are typically coated with graphite, which prevents the build-up of electrostatic charge.

The current standard composition for black powder manufactured by pyrotechnicians was adopted as long ago as 1780. It is 75% potassium nitrate, 15% softwood charcoal, and 10% sulfur. These ratios have varied over the centuries and by country, and can be altered somewhat depending on the purpose of the powder.

The burn rate of black powder can be changed by corning. Corning first compresses the fine black powder meal into blocks with a fixed density (1.7 g/cm³). The blocks are then broken up into granules. These granules are then sorted by size to give the various grades of black powder. In the USA, standard grades of black powder run from the coarse Fg grade used in large bore rifles and small cannons, through FFg (medium and smallbore rifles), FFFg (pistols), and FFFFg (small bore, short pistols and priming flintlocks). In the United Kingdom, the gunpowder grains are categorised by mesh size: the BSS sieve mesh size, being the smallest mesh size on which no grains were retained. Recognised grain sizes are Gunpowder 'G 7', 'G 20', 'G 40', and 'G 90'.

A simple, commonly cited, chemical equation for the combustion of black powder is

2 KNO3 + S + 3 C → K2S + N2 + 3 CO2.
A more accurate, but still simplified, equation is[6]

10 KNO3 + 3 S + 8 C → 2 K2CO3 + 3 K2SO4 + 6 CO2 + 5 N2.
The products of burning do not follow any simple equation. One study's results showed that it produced (in order of descending quantities): 55.91% solid products: potassium carbonate, potassium sulfate, potassium sulfide, sulfur, potassium nitrate, potassium thiocyanate, carbon, ammonium carbonate. 42.98% gaseous products: carbon dioxide, nitrogen, carbon monoxide, hydrogen sulfide, hydrogen, methane, 1.11% water.

Black powder formulations where the nitrate used is sodium nitrate tend to be hygroscopic, unlike black powders where the nitrate used is saltpetre. Because of this, black powder which uses saltpetre can be stored unsealed and remain viable for centuries provided no liquid water is ever introduced. Muzzleloaders have been known to fire after hanging on a wall for decades in a loaded state, provided they remained dry. By contrast, powder that uses sodium nitrate, which is typically intended for blasting, must be sealed from moisture in the air to remain stable for long times.

[Curt-Heinrich Schmidt]

Hallo!

I would disagree on one small point...

Black Powder burns slowly compared to Smokeless "powder."
The finer the "grain," the faster it burns, because more of the surface area of the "grains" is exposed the smaller they are.

While smokeless burns really fast and develops peak breech pressure quickly, black powder burns slower and can continue to burn and push the projectile down the down the bore and out the muzzle.
At times, when the bore is over-charged for example, burning grains of black-powder are expelled from the muzzle (which makes for nice photographs in the dark...).

Others' mileage will vary...

CHS

[Craig L Barry]

...that converts only about 50% of its mass to energy and leaves behind copious amounts of fouling crud. Whatever the case, what is the nature of the discussion? Nobody is seriously contemplating making their own BP, I hope?

[thpritchett]

A very inefficient propellant...
...that converts only about 50% of its mass to energy

Technically, blackpowder does not convert 50% of its mass to energy (i.e., E=Mc2). That occurs in nuclear reactions. Rather black powder and explosives in general convert significant portions of their mass to gas, generating pressure. The heat of the reaction then heats the gases to generate additional pressure. It is the formation of the heated gas that is the energy that drives the projectile out of the barrel, not the direct converstion of mass to energy.

As far as the rest of the chemistry, I can not add any more than what has already been written except to say that the nitrates serve as the primary source of oxygen for the combustion reactions so that the reaction does not need oxygen from the air.

[Danny]

...that converts only about 50% of its mass to energy and leaves behind copious amounts of fouling crud. Whatever the case, what is the nature of the discussion? Nobody is seriously contemplating making their own BP, I hope?

Craig, no, thought it was quite clear I was only looking to understand those things which affect my safety -- enough working knowledge of the reaction to make the call for myself or those with me servicing the piece if asked to participate with subsititutions of grain, alternate round packaging material or process, alternate ignition methods or special primers, or even when occasionally some fireworks go down the barrel. I have an instance in mind for each of these.

Our armory sergeant inspects and makes the calls generally for our unit, and ours is well qualified to do that, but as artillerists we occasionally fall in with other units or participate in special event firing where there is no armory sergeant or an event range officer present.

Dan Wykes

[Dave Myrick]

Tom,
I beg to differ. Einstein's Theory states that the total energy of matter is equal to its mass times the speed of light squared. The theory is used to calculate the amount of stored energy that can be held or released by a mass.

Nuclear reactions do not alter the amount of energy contained within a mass. The first law of thermodynamics explains this.

What is happening in the explosive process is the conversion of solids to vapors (gasses). Pressure and heat (thermal) are forms of energy and have to be included in the total energy of the mass of powder. The mass of the solid propellant is exactly equal to the mass of the gasses as well and the residue left after combustion. The physics of this are explained by the 1st and 2nd laws of motion, 1st law of thermodynamics and Pascal's law.

Dave Myrick

[FloridaConfederate]

Tom,
I beg to differ. Einstein's Theory states that the total energy of matter is equal to its mass times the speed of light squared. The theory is used to calculate the amount of stored energy that can be held or released by a mass.


Ooh Oooh Nerd fight.

Gentlemen this fight is for three rounds, there will be no using your slide rule or periodic tables. Now touch pocket protectors and come out swinging.

[thpritchett]

I beg to differ. Einstein's Theory states that the total energy of matter is equal to its mass times the speed of light squared. The theory is used to calculate the amount of stored energy that can be held or released by a mass.

Nuclear reactions do not alter the amount of energy contained within a mass. The first law of thermodynamics explains this.

I would suggest that you reread first the post I was replying to and then my post. I was correcting the statement that 50% of the mass is converted to energy. As we both stated, when mass is "destroyed" in a nuclear reaction (i.e. the sum of the atomic masses of the products is less than the sum of the atomic masses of the reactants), the mass difference is converted into energy as stated by Einstein's famous law. (Similarly, when mass is "created" in accelerators and such, E=Mc2 also defines how much energy must be put into the collision for a given amount of mass to be created, even if for only a fleeting instance.) Also, as we both stated using different terminology (I was using chemistry terminology while you were using engineering terminology), what happens with black powder is that the solid carbon is converted to gaseous carbon dioxide and the solid sulfur is converted to gasous hydrogen sulfide. Since Avogradro's law states that P1V1/n1T1 = P2V2/n2T2, drastically increasing the number of moles of gas (i.e., generating the carbon dioxide and hydrogen sulfide) while probably doubling the temperature in degrees Kelvin, initially creates very large pressures that are then partially released as the volume of the hot gas expands down the barrel. As far as the energy of the reaction itself that can be harnessed for "work", you have the release of heat from the delta H, or change in enthalapy, of the reaction as well as the product of the temperature of the reaction times the positive change in ethropy due to the production of moles of gas from moles of solid. However, the initial reason that my description of the process may have seemed simplistic is that I wanted the average reader here to be able to follow the process and not get lost in the terminology (I am used to having to explain fairly complex chemical concepts to non-chemist laypeople).

[Dave Myrick]

Fair enough.
Dave