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Mixed Oxides of Nitrogen - Nitric oxide (NO) is a low-boiling cryogenic gas. Both the liquid and the solid are blue. Solutions of NO in nitrogen tetroxide sharply depress the freezing point of the high-melting oxidiser. The mechanism of depression is believed to involve the formation of N2O3, which is soluble in nitrogen tetroxide. Solutions are called mixed oxides of nitrogen (MON), and have been used as oxidisers for liquid-rocket engines. Various concentrations have been considered. However, the high vapour pressure of MON limits the concentration of NO in N2O4 to about 30 per cent. Aside from the high vapour pressure of MON, the material is quite similar to nitrogen tetroxide.
Hydyne was a propellant blend pushed rather vigorously by the Redstone arsenal in the late 1950's, but it found little application. Hydyne, which is also known as MAF-4, is a 60 per cent, by weight, mixture of UDMH and 40 weight percent diethyltrianine (DETA). The normally occurring impurities are dimethylamine, beta-aminoethyl-N-piperazine, and water. Hydyne is a clear, colourless liquid which may become discoloured on exposure to air during storage. Both UDMH and DETA have an ammoniacal odour; the odour is not so sharp or fishy as that of UDMH. Hydyne is a hygroscopic liquid which will absorb carbon dioxide and oxygen from air. It is completely miscible with water and ethanol; the solubility of gasoline and JP-4 in Hydyne are somewhat limited. It forms flammable explosive mixtures with air. Amines generally yellow during storage due to oxidation followed by polymerisation induced by air (O2)· reaction is believed to form an intermediate amine oxide which undergoes polymerisation. The cost of Hydyne in 1959 was $ 0.80 per kg.