Hydrogen peroxide is used as both an oxidiser and a monopropellant. Relatively high density and non-toxic, it was abandoned after early use in British rockets, but recently revived as a propellant for the Black Horse spaceplane. Hydrogen peroxide solutions are clear, astringent, colorless liquids which are slightly more viscous than water. They are described by Military Specification MIL-H-16005. High-strength hydrogen peroxide solutions are very reactive oxidising agents. Hydrogen peroxide is miscible in all proportions in water; it is soluble in a large number of organic liquids which are also soluble in water. However, many of these mixtures form explosive mixtures. Hydrogen peroxide-water solutions are normally insensitive to detonation by shock or impact. Surfaces that come in contact with hydrogen peroxide must be specially treated (passivated) before use, to prevent the decomposition of the hydrogen peroxide. Hydrogen peroxide-water solutions and their vapours are considered non-toxic, but are characterised by their ability to produce local irritation.
Hydrogen peroxide is manufactured commercially by several processes. Inorganic processes employ the electrolysis of an aqueous solution of sulphuric acid or acidic ammonium bisulphate, followed by hydrolysis of the peroxydisulfate which is formed. For reasons of economy and flexibility of plant location, organic processing methods have become important in the production of hydrogen peroxide. These include (1) the autoxidation of hydroquinone or one of its homologues in a suitable solvent system and (2) the partial gas-phase oxidation of hydrocarbons.
Dilute aqueous hydrogen peroxide is concentrated to about 90 per cent by conventional distillation. Higher-strength solutions are prepared by fractional crystallisation of 90 per cent feed stock. Estimated United States production for 1959 was 50,000 tonnes based upon 100 per cent hydrogen peroxide. In large quantities, 95 per cent hydrogen peroxide then cost approximately $1.00 per kg. In small drum lots, 98 per cent solutions cost $ 2.00 per kg. Density varies: 2.44 g/cc for 100% H2O2, 2.43 for 98%, 2.42 for 96%, 2.33 for 75%.
Hydrazine (N2H4) found early use as a fuel, but it was quickly replaced by UDMH. It is still used as a monopropellant for satellite station-keeping motors. Hydrazine marketed for rocket propellant contains a minimum of 97 per cent N2H4, the other constituent being primarily water. Hydrazine is a clear, water-white, hygroscopic liquid. The solid is white. Hydrazine a toxic, flammable caustic liquid and a strong reducing agent. Its odour is similar that of ammonia, though less strong. It is slightly soluble in ammonia and methyl-amine. It is soluble in water, methanol, ethanol, UDMH, and ethylenediamine. Hydrazine is manufactured by the Raschig process, which involves the oxidation of ammonia to chloramine, either indirectly with aqueous sodium hypochlorite or directly with chlorine, and subsequent reaction of chloramine with excess ammonia. Raw materials include caustic, ammonia, and chlorine; these are high-tonnage, heavy chemicals. The cost of anhydrous hydrazine in drum quantities in 1959 was $ 7.00 per kg. The projected price, based on large-scale commercial production, was expected to be $ 1.00 per kg. Due to environmental regulations, by 1990 NASA was paying $ 17.00 per kg.