Chlorine trifluoride was another of the extremely reactive and toxic oxidisers tested in the United States in the late 1950's. As in the other cases, it was found that the handling problems and safety risks outweighed the performance benefits. ClF3 is available commercially in purities of 99+ per cent ClF3. The most likely impurity is hydrogen fluoride. Chlorine trifluoride is a colorless gas at atmospheric pressure and temperature. The liquid has a pale green colour, while the solid is white. The odour of ClF3 has been described as both sweet and pungent, similar to chlorine or mustard. ClF3 is a toxic and corrosive oxidising agent similar to elemental fluorine in nature. It reacts with water. ClF3 is non-flammable with air, but will support combustion with almost all organic vapours and liquids. ClF3 reacts with every element except the rare gases, nitrogen, and possibly platinum and palladium. However, at low or intermediate temperatures, a protective fluoride film is formed on certain metal surfaces, which halts further reaction. Thus, metals such as mild steel, copper, brass, steel, Monel, and nickel may be used as materials of construction.
Chlorine trifluoride is prepared by direct combination of the elements. The 1959 ClF3 production capacity was 12 to 25 tonnes/year; this could be increased in six to eight months to 50 to 100 tonnes per year by enlarging halogen fluoride reactor capacity without incurring a shortage of fluorine. Quantities in excess of this amount would require a lead time of one year, and would involve construction of new fluorine facilities. The projected price of ClF3 $ 6.00 per kg at the existing rate.
Unsymmetrical Dimethylhydrazine ((CH3)2NNH2) became the storable liquid fuel of choice by the mid-1950's. Development of UDMH in the Soviet Union began in 1949. It is used in virtually all storable liquid rocket engines except for some orbital manoeuvring engines in the United States, where MMH has been preferred due to a slightly higher density and performance. Unsymmetrical dimethylhydrazine (UDMH) is 98 to 99 per cent pure and is described by Military Specification MIL-D-25604. The normally expected impurities are dimethylamine and water. UDMH is a clear, hygroscopic liquid which yellows on exposure to air. It absorbs oxygen and carbon dioxide. UDMH is a toxic volatile liquid. It exhibits the sharp ammoniacal or fishy odour which is characteristic of organic amines. It is completely miscible with water, ethanol, and most petroleum fuels. It is not shock sensitive. The vapours are flammable in air over 2.5 to 95 per cent concentration range. UDMH can be produced commercially by nitrosation of dimethylamine, to N-nitro-sodimethylrtmine, followed by reduction of the intermediate to UDMH and subsequent purification. UDMH can be prepared, also, by a modification of the Raschig process (see discussion of hydrazine), in which the chloramine intermediate is with dimethylamine rather than with ammonia. The price in 1959 for tank-car quantities was under $ 1.00 per kg. Engineering studies indicated a price of $ 1.00 per kg with large scale sustained production. But due to its toxic nature, production and transport costs soared in response to environmental regulations. By the 1980's NASA was paying $ 24.00 per kg.