Here is information from an elderly manuscript of mine. While I believe these data are accurate, I haven't looked at the material in more than a decade. It may be nonsense intermixed with fact. While none of the products of black powder combustion are chlorides, salts at temperature must be significantly corrosive??
What I'm unclear on is why black powder substitutes' corrosive compounds are [apparently] significantly more corrosive than black powder's cocktail of salts and corrosive gases.
***Follows is elderly manuscript text***
This is a generally accepted formula for black powder combustion:
Ignition temperature is about 315° C (600° F), and burning temperature is as high as 2200° C (4000° F) for a few milliseconds.
Slightly less than 56% (55.91%) of the powder charge is residue. The solids, all of which I believe are salts except the last three, are composed of the following compounds:
Potassium carbonate (K2CO3).
Potassium sulfate (K2SO4).
Potassium sulfide (K2S).
Potassium thiosulfate (K2S2O3).
Potassium thiocynate (KSCN).
Ammonium carbonate [(NH4)2CO3].
Carbon (C).
Sulfur (S).
Gases include:
Carbon dioxide (CO2).
Carbon monoxide (CO).
Methane (CH4).
Hydrogen sulfide (H2S).
Hydrogen (H2).
Nitrogen (N2).
***
The accepted chemical equation for combustion is:
KNO2 + 96 C + 30 S + 16 H2O Ζ 35 N2 + 56 CO2 + 14 CO + 3 CH4 + 2 H2S + 4 H2 + 19 K2CO3 + 7 K2SO4 + 8 K2S2O3 + 2 K2S + 2 KSCN + (NH4)2CO3 + C + S.
Combustion liberates about 680 kg-cal of heat per kilogram and forms 600 grams of solids and 278 liters of gas.
Black and smokeless propellants store energy that can be measured as British Thermal Units. Smokeless powders store more energy per unit of weight. Generally, double-base smokeless powders — that is, ones that contain nitrocellulose and nitroglycerine — store more energy than single-base powders, ones containing only nitrocellulose. Cordite, used for many years by Great Britain in .303 British rifle ammunition, is a double-base smokeless powder. Its stored energy is 2295 BTUs. Du Pont IMR 4198 is a single-base powder intended for use in .30-06 rifle ammunition. It stores 1815 BTUs.
Du Pont FFg black powder stores 1420 BTUs; FFFg stores 1470. Smokeless powders store between 120 and 156 percent of black powders. What does this mean? For black powder to achieve like amounts of energy acting upon the bullet, you must use significantly larger quantities of it. But wait, there’s more. You will need still more powder because black powder residue becomes additional ejecta to be propelled from the muzzle. Smokeless powder has essentially no residue.
***End manuscript text***
What cpompounds result from combustion of potassium perchlorate?
When potassium perchlorate is used in a propellant composition the end product is potassium chloride. When the powder is burning the potassium perchlorate simply gives up the oxygen atoms to support combustion leaving potassium chloride.
Whenever we think of chloride corrosion around here we think of all of the common salt, sodium chloride, used in the winter on our streets and roads. I think back to some of the 1950's and 1960's hot rods. How fast the road salt corroded the bodies of these cars. Then here in eastern PA you were to avoid buying used cars that came out of New Jersey where they spent a lot of time along the coast getting salt spray from the ocean.
Chlorides, be they sodium or potassium are rather corrosive.
Bill K.
