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Fire Hazards and Associated Terminology
Published in Asim Kumar Roy Choudhury, Flame Retardants for Textile Materials, 2020
A flame is a mixture of reacting gases and solids emitting visible, infrared, and sometimes ultraviolet light, the frequency spectrum of which depends on the chemical composition of the burning material and intermediate reaction products. In many cases, such as the burning of organic matter, for example wood, or the incomplete combustion of gas, incandescent solid particles called soot produce the familiar red-orange glow of fire. This light has a continuous spectrum. Complete combustion of gas has a dim blue color due to the emission of single-wavelength radiation from various electron transitions in the excited molecules formed in the flame. Usually oxygen is involved, but hydrogen burning in chlorine also produces a flame, producing hydrogen chloride (HCl). Among many other possible combinations producing flames are fluorine and hydrogen, and hydrazine and nitrogen tetroxide. Hydrogen and hydrazine/unsymmetrical dimethylhydrazine (UDMH) flames are similarly pale blue, while burning boron and its compounds, evaluated in the mid-20th century as a high-energy fuel for jet and rocket engines, emits intense green flame, leading to its informal nickname of “Green Dragon”.
Launch Vehicles, Propulsion Systems, and Payloads
Published in Janet K. Tinoco, Chunyan Yu, Diane Howard, Ruth E. Stilwell, An Introduction to the Spaceport Industry, 2020
Janet K. Tinoco, Chunyan Yu, Diane Howard, Ruth E. Stilwell
Based on research to date, nation-states use a variety of propellants. Table 3.8 compares countries with their most prevalent propellant type, while Figures 3.16, 3.17, and 3.18 highlight the propellant of choice used by the U.S., Russia, and China, respectively. Most LVs in the U.S. today use solid propellant and LOX/kerosene. Russian rockets largely use N2O4/Unsymmetrical dimethylhydrazine (UDMH) and LOX/kerosene, while China favors N2O4/UDMH, followed by solid. This, of course, depends on the number of rocket stages and boosters needed for the mission at hand. Finally, once LV manufacturers lock into a reliable design that meets their requirements, they typically create scalable versions of the same design. Hence, SpaceX uses LOX/kerosene with its Merlin-1D rocket engines. It builds larger rockets and fulfills increased propulsion needs by adding more Merlin-1D engines. This standardization leads to increased savings in time and money.
The Apollo command and service modules
Published in Jonathan Allday, Apollo in Perspective, 2019
The service propulsion engine was just over 1 m long and its engine bell extended 2.7 m from the base of the service module and opened to a maximum diameter of 2 m. This crucial engine had to be ultra-reliable, with the fewest number of parts possible. If it did not ‘light’ at the appropriate moment, the spacecraft could not enter lunar orbit, or worse, break free of orbit to return to Earth. To ensure reliability, pumps were not used to transfer fuel and oxidiser to the thrust chamber. Instead, pressurised nitrogen from the two tanks mounted in the central core was used to force fuel and oxidiser from their storage tanks into their respective sump tanks and from there to the thrust chamber, a process that simply required valves to open. A hypergolic propellant mixture (fuel: 50% hydrazine and 50% unsymmetrical dimethylhydrazine (UDMH) oxidiser: nitrogen tetroxide) was used and 75% of the fully deployed module's mass was propellant.
Aqueous N-nitrosamines: Precursors, occurrence, oxidation processes, and role of inorganic ions
Published in Critical Reviews in Environmental Science and Technology, 2021
Tahereh Jasemizad, Peizhe Sun, Lokesh P. Padhye
Aqueous NDMA formation pathway was first suggested (Choi & Valentine, 2002b; Mitch & Sedlak, 2002) for chlorination of waters containing DMA and in the presence of ammonia. The proposed mechanism involved the generation of unsymmetrical dimethylhydrazine (UDMH) intermediate, with its subsequent oxidation to NDMA. Later, this pathway was revised by Schreiber and Mitch (2006), suggesting a nucleophilic substitution reaction between secondary amines and NHCl2, formed via disproportionation of NH2Cl, forming chlorinated UDMH (Cl-UDMH) and subsequent NDMA formation from oxidation of Cl-UDMH with dissolved oxygen. Although dichloramine is not intentionally applied for disinfection, it has been reported that the presence of NHCl2 could significantly enhance NDMA formation from DMA (Schreiber & Mitch, 2006) and tertiary amines, regardless of its relatively minor fraction (Mitch et al., 2005). At pH less than 8, dichloramine can be formed due to the self-decomposition of monochloramine (Valentine & Jafvert, 1988).
Preparation and characterization of graphene oxide/O-carboxymethyl chitosan (GO/CMC) composite and its unsymmetrical dimethylhydrazine (UDMH) adsorption performance from wastewater
Published in Environmental Technology, 2023
Jun Su, Ying Jia, Ruomeng Hou, Yuanzheng Huang, Keke Shen, Zhaowen Hao
Unsymmetrical dimethylhydrazine (UDMH, (CH3)2NNH3) is a high-energy liquid rocket propellant with good performance [1]. The large amount of UDMH wastewater generated by its leakage and emergency disposal poses a major threat to the environment and humans. UDMH can lead to carcinogenic, mutagenic, convulsive, teratogenic, embryotoxic, and other adverse consequences [2]. Hence, UDMH is known as a highly dangerous toxic substance with the maximum permissible concentration in ambient water as low as 0.02 mg · L−1 [3]. Therefore, the removal of UDMH is highly significant and desirable.
A novel CWPO/H2O2/VUV synergistic treatment for the degradation of unsymmetrical dimethylhydrazine in wastewater
Published in Environmental Technology, 2021
Xu Meng, Pingchuan Zeng, Junru Wang, Yamin Shao, Min Wu, Henmei Ni, Yingping Zheng, Yueming Sun
As one of the liquid fuels widely used as a high energy propellant in present various strategic missiles and spacecraft launches due to its good thermal stability, large combustion heat and high specific impulse, unsymmetrical dimethylhydrazine (UDMH, (CH3)2NNH3) is planned to stay in use for the next 25–50 years [1–4]. Despite the fact inclining the use of greener and more ecological rocket fuels in space and defense programmes, the consumption of UDMH is estimated to continuously increase in the future decades owing to its unique physicochemical characteristics in contrast to the solid propellants [1,5,6]. What’s more, in some developing countries, UDMH/Trioxide system is still used as the major liquid fuel for rockets and missiles because of the high heat of combustion and specific pressure of UDMH [7], and a large amount of polluted wastewater will be produced after launching rockets and missiles. In addition, UDMH is now a common contaminant in wastewater [8] and is also a primary eco-toxicant which can accumulate in natural ecosystems and evolve into other highly toxic products while decomposing. For example, exposed to natural conditions, UDMH is spontaneously oxidized to some toxic substances. An important one of them is called as NDMA, a refractory toxic compound with acute carcinogenic and mutagenic properties [9]. It has been declared by the U.S. Environmental Protection Agency (USEPA) [10] that NDMA is a probable human carcinogen posing a cancer risk associated with a concentration of 0.7 ng L–1 in drinking water determined during the UDMH treatment process without UV or VUV irradiation [11–13]. It is commonly produced in the process of catalytic wet peroxide oxidation with hydrogen peroxide as an oxidant in the presence of Cu, Fe, Co salts supported on carriers as catalysts [14,15]. Therefore, the maximum permissible concentration for UDMH in ambient water is as low as 10–5 g L–1 [9].