High-test peroxide (HTP) is a highly concentrated (85 to 98 percent) solution of hydrogen peroxide, with the remainder predominantly made up of water. In contact with a catalyst, it decomposes into a high-temperature mixture of steam and oxygen, with no remaining liquid water. It was used as a propellant of HTP rockets and torpedoes, and has been used for high-performance vernier engines.
Hydrogen peroxide works best as a propellant in extremely high concentrations (roughly over 70%). Although any concentration of peroxide will generate some hot gas (oxygen plus some steam), at concentrations above approximately 67%, the heat of decomposing hydrogen peroxide becomes large enough to completely vaporize all the liquid at standard pressure. This represents a safety and utilization turning point, since decomposition of any concentration above this amount is capable of transforming the liquid entirely to heated gas (the higher the concentration, the hotter the resulting gas). This very hot steam/oxygen mixture can then be used to generate maximal thrust, power, or work, but it also makes explosive decomposition of the material far more hazardous.
Normal propellant-grade concentrations, therefore, vary from 70 to 98%, with common grades of 70, 85, 90, and 98%.
The volume change of peroxide due to freezing varies with percentage. Lower concentrations of peroxide (45% or less) will expand when frozen, while higher concentrations (65% or greater) will contract.:4–39
Hydrogen peroxide becomes more stable with higher peroxide content. For example, 98% hydrogen peroxide is more stable than 70% hydrogen peroxide. Water acts as a contaminant, and the higher the water concentration the less stable the peroxide is. The storability of peroxide is dependent on the surface-to-volume ratio of the materials the fluid is in contact with. To increase storability, the ratio should be minimized.
HTP has been used safely and successfully in many applications, beginning with German usage during World War II, and continues to the present day. During World War II, high-test peroxide was used as an oxidizer in some German bipropellant rocket designs, such as the Walter HWK 509A rocket engine that powered the Messerschmitt Me 163 point defense interceptor fighter late in World War II, comprising 80% of the standardized mixture T-Stoff, and also in the German Type XVII submarine.
Some significant United States programs include the reaction control thrusters on the X-15 program, and the Bell Rocket Belt. The NASA Lunar Lander Research Vehicle used it for rocket thrust to simulate a lunar lander.
The first Russian HTP torpedo was known by the strictly functional name of 53-57, the 53 referring to the diameter in centimeters of the torpedo tube, the 57 to the year it was introduced. Driven by the Cold War competition, they ordered the development of a larger HTP torpedo, to be fired from the 65-centimeter (26-inch) tubes. HTP in one of the 65–76 torpedoes on August 12, 2000 exploded on board and sank the K-141 Kursk submarine.
British experiments with HTP as a torpedo fuel were discontinued after a peroxide fire resulted in the loss of the submarine HMS Sidon (P259) in 1956.
British experimentation with HTP continued in rocketry research, ending with the Black Arrow launch vehicles in 1971. Black Arrow rockets successfully launched the Prospero X-3 satellite from Woomera, South Australia using HTP and kerosene fuel.
The Blue Flame rocket-powered vehicle achieved the world land speed record of 622.407 mph (1,001.667 km/h) on October 23, 1970, using a combination of high-test peroxide and liquified natural gas (LNG), pressurized by helium gas.
Propellant-grade hydrogen peroxide is being used on current military systems and is in numerous defense and aerospace research and development programs. Many privately funded rocket companies are using hydrogen peroxide, such as Armadillo Aerospace and Blue Origin, and some amateur groups have expressed interest in manufacturing their own peroxide, for their use and for sale in small quantities to others.
HTP will be used again in an attempt to break the land speed record with the Bloodhound SSC car, aiming to reach over 1000 mph. It will be the oxidiser for the hybrid fuel rocket, reacting with the solid fuel hydroxyl-terminated polybutadiene.
The available suppliers of high-concentration propellant-grade hydrogen peroxide are, in general, one of the large commercial companies that make other grades of hydrogen peroxide, including Solvay Interox, PeroxyChem (formerly FMC Global Peroxygens, a division of FMC Corporation), and Evonik. X-L Space Systems upgrades technical-grade hydrogen peroxide to HTP. Other companies that have made propellant-grade hydrogen peroxide in the recent past include Air Liquide and DuPont. DuPont recently sold its hydrogen peroxide manufacturing business to Evonik.
Propellant-grade hydrogen peroxide is available to qualified buyers. In typical circumstances, this chemical is sold only to companies or government institutions that have the ability to properly handle and utilize the material. Non-professionals have purchased hydrogen peroxide of 70% or lower concentration (the remaining 30% is water with traces of impurities and stabilizing materials, such as tin salts, phosphates, nitrates, and other chemical additives), and increased its concentration themselves. Distillation is extremely dangerous with hydrogen peroxide; peroxide vapor can ignite or detonate depending on specific combinations of temperature and pressure. In general, any boiling mass of high-concentration hydrogen peroxide at ambient pressure will produce vapor-phase hydrogen peroxide, which can detonate. This hazard is mitigated, but not entirely eliminated, with vacuum distillation. Other approaches for concentrating hydrogen peroxide are sparging and fractional crystallization. High-concentration hydrogen peroxide was formerly available in 70, 90, and 98% concentrations in sizes of 1-gallon, 30-gallon, and bulk-tanker truck volumes. Hydrogen peroxide in concentrations of at least 35% appear on the US Department of Homeland Security's Chemicals of Interest list.
Since many common substances catalyze peroxide's exothermic decomposition into steam and oxygen, handling of HTP requires special care and equipment. It is noted that the common materials iron and copper are incompatible with peroxide, but the reaction can be delayed for seconds or minutes, depending on the grade of peroxide used.
Small hydrogen peroxide spills are easily dealt with by flooding the area with water. Not only does this cool any reacting peroxide but it also dilutes it thoroughly. Therefore, sites that handle hydrogen peroxide are often equipped with emergency showers, and have hoses and people on safety duty.
Contact with skin causes immediate whitening due to the production of oxygen below the skin. Extensive burns occur unless washed off in seconds. Contact with eyes can cause blindness, and so eye protection is usually used.
The Kursk submarine disaster involved the accidental release of HTP in a torpedo which reacted with the torpedo's fuel.
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