Talk:Golden Powder
From PyroGuide
U.S. Patent #4,497,676, February 5, 1985.
Laboratory Process
A typical laboratory recipe is as follows: Weigh 105.7 g of potassium nitrate, 65.2 g of ascorbic acid, 3.7 g of potassium bicarbonate, and 128.5 g of deionized water into a 250 ml Erylemenmer flask. (2) Potassium bicarbonate is added as a precaution to prevent the formation of nitric acid due to acidic impurities present in the raw materials. Agitate the slurry using a magnetic stirring bar. The temperature falls several degrees during the solid dissolution process. Heat the solution to 600C to completely dissolve the solids. When the solids are dissolved, the solution will be pale yellow.
Pour the solution into a 45 cm x 37L cm pyrex dish. Some material will crystallize out in the coo- dish but will re- dissolve Later. The solution will form a Layer 2-3 m-thick. Place the dish into an oven preheated to 7-200C. During the first 1 1/2 hr. of heat treatment, the majority of the water is removed. The dried solid will rise to a thickness of 5-10 mm and turn from yellow to brown in color. The best performing material is heated for 3 hr. The tray is removed from the oven, covered with aluminum foil and allowed to cool to room temperature.
The heat-treated material is a brittle sponge like solid which breaks up easily when touched. As soon as cool, the solid is removed from the tray and ground into a powder using a mortar and pestle. At this point, we have Golden Powder in its crude state. The powder is hygroscopic and care should be taken to minimize exposure to water or humid atmosphere to avoid caking.
2. Potassium nitrate and potassium bicarbonate are reagent,-- grade material. The ascorbic acid is Hoffmann-La Roche, U.S.P. grade material.
-Heat Treatment
While the water is vaporized, crystals of potassium nitrate 10-50 microns in size are formed. These crystals are visible in the final product under a scanning electron microscope (Figure 1). The photograph shows the cross-section of a typical particle. The lighter particles seem to be crystals of potassium nitrate surrounded by a matrix of ascorbic acid "polymer". Golden powder is similar to other composite propellants where the oxidizer is coated by the fuel. In this case, the oxidizer is potassium nitrate and the fuel is ascorbic acid polymer.
Figure 1 Scanning Electron Micrograph of Golden Powder (20OX)
Although we do not know the reactions which take place during the heat treatment, several observations have been made. The potassium nitrate is essentially unaffected by the heating so the reacting component is ascorbic acid. During the treatment, gaseous products are given off which causes the powder to rise. These products have been identified as carbon dioxide and water and account for a weight loss of 10-12% during the heating (Figure 2). This loss is in addition to the water used to dissolve the ascorbic acid and potassium nitrate. The reaction progress can be followed by monitoring the ascorbic acid content of the powder.
Several temperatures have been used for the heat treatment ranging from 105oC to 140oC (Figure 3). As we would expect, the degradation is more rapid at higher temperatures.For convenience on a laboratory scale, we chose 120oC asour working temperature. The best powder contains 2-5% residua ascorbic acid which is produced after about 3 hr at 1200C. Higher temperatures are possible with good control on the heating time and temperature. Overheating of the powder results in the formation of carbon and a decrease in performance and safety.
The physical properties of golden powder are summarized below in Table I. Golden Powder has several advantageous properties as a propellant. It can be molded without any binders into a solid fuel for use as consumable cartridges. The heat of combustion is 5% higher and the gas volume produced is 10% greater than an equivalent amount of black powder. The residue on ignition is only 28% compared to about 50% using black powder. In addition, the residue from burning golden powder is water soluble, unlike many other propellants.
Table I
Physical Properties of Golden Powder and Black Powder
Golden Powder Black Powder
Color Golden to medium Black brown Bulk Density (20-50 mesh) .88-.90 gm/cc --- Heat of Combustion 718 cal/gm 684 cal/gm) Gas Volume on Combustion 298 cc/gm 271 cal/gm Residue on Combustion 28% (H2O soluble) 50% Ignition Temperature 333o C 313oC (4)
4.Initiation temperature from differential calorimentry on Gearhart-Owen Industries Superfine, FFFG Black Powder.
Using differential scanning calorimetry, the ignition temperature of golden powder was determined to be 333oC (Figure 4). The ignition temperature is 200C higher than that measured for black powder in the same equipment. Scanning calorimetric studies show a two-stage exotherm over a temperature range of 333oC to 455oC.
Ballistic Performance
Although Golden Powder offers a wide spectrum of applications, one area which has attracted the attention of end users is its use as a black powder substitute. Golden Powder can be easily granulated to any grade of gun powder. The crude powder can be compacted to pellets or sheets which can be milled to appropriate grain sizes. We have made granulation's of golden powder which pass through a 20-mesh screen but are retained on a 40-mesh screen. This material was tested ballistically in a .45 caliber, 32 inch rifled test barrel. Muzzle velocities where measured using lumiIine screens and the peak pressures measured using lead crushers. The balIistic data from three separate lots or golden powder are summarized in Table 2.
Table 2
Ballistic Performance of Golden Powder
60 Grain loading in 32 inch, 45 caliber, 138, grain, Hornady
- 6060 lead balls and Connecticut Valley Arms #11 percussion
Golden Powder Lot 5 Shot Average
Muzzle Velocity Peak Chamber Pressure
(ft./sec) (LUP,)
1 1,363 5,300 2 1,375 5,000 3 1,383 5,400
Range (3 Lots) 1,330-1,410 4,600-5,500 SD 20.2 230 (3 Lots)
These muzzle velocities are comparable to black powder at significantly lower chamber pressures. The ballistic results are extremely reproducible from shot to shot and from lot to lot. The standard deviation of velocities over the fifteen shots was only 20.2 ft./sec. and the standard deviation of peak pressures was 230 LUP.
As we stated earlier, the best performing material was powder in which the ascorbic acid has been reacted to a residual level of 2-5%. The ballistic performance of golden powder has been measured as a function of the ascorbic assay (Figure 5). The muzzle velocity of the powder, which has a residual ascorbic acid assay -less than 5%, is double that of powder which has an ascorbic acid assay greater than 30%.
Safety
One of the advantageous properties of golden powder is its safety. Unlike black powder, golden powder can be shipped as a flammable so-'Lid following the recommendation of the Bureau of Mines. They recommend a DOT classification as a Class B Explosive. The Bureau of Mines testing included thermal stability at 75oC for 48 hours during which golden powder was stable. No detonation of golden powder occurred during the blasting cap sensitivity test, the package burn test, and the squib test. Golden powder did not ignite on the Association of American Railroads Bureau of Explosives strip friction test in 10 out of 7-0 trials under 500 psig, which is equivalent to 100 pounds of friction force.
Summary
Golden Powder is a new explosive product based on ascorbic acid. Its combustion characteristics are comparable to black powder but with several other distinct advantages. Golden powder is safer to handle and transport. It forms about half the residue as black powder when burned. The residue formed is non-corrosive and is water-soluble. Golden powder is easily molded into solid fuel elements which burn at a well controlled rate. When used as gunpowder, the performance is comparable to black powder but is significantly more reproducible. The inherent safety of' the powder allows its shipment as a flammable solid by common carrier. With these characteristics, golden powder is a product with many potential applications.
