Ammonia sulfur hexafluoride

Chemica.1 Properties. With few exceptions, SF is chemically inert at ambient temperature and atmospheric pressure. Thermodynamically SF is unstable and should react with many materials, including water, but these reactions are kineticaHy impeded by the fluorine shielding the sulfur. Sulfur hexafluoride does not react with alkah hydroxides, ammonia, or strong acids. 

The first use of supercritical fluid extraction (SFE) as an extraction technique was reported by Zosel [379]. Since then there have been many reports on the use of SFE to extract PCBs, phenols, PAHs, and other organic compounds from particulate matter, soils and sediments [362, 363, 380-389]. The attraction of SFE as an extraction technique is directly related to the unique properties of the supercritical fluid [390]. Supercritical fluids, which have been used, have low viscosities, high diffusion coefficients, and low flammabilities, which are all clearly superior to the organic solvents normally used. Carbon dioxide (C02, [362,363]) is the most common supercritical fluid used for SFE, since it is inexpensive and has a low critical temperature (31.3 °C) and pressure (72.2 bar). Other less commonly used fluids include nitrous oxide (N20), ammonia, fluoro-form, methane, pentane, methanol, ethanol, sulfur hexafluoride (SF6), and dichlorofluoromethane [362, 363, 391]. Most of these fluids are clearly less attractive as solvents in terms of toxicity or as environmentally benign chemicals. Commercial SFE systems are available, but some workers have also made inexpensive modular systems [390]. 

In sulfur hexafluoride, the sulfur atom is shielded by six fluorine atoms which impede kinetically any reaction with water, alkali hydroxides, ammonia or strong acids as a result it remains inert to these reagents. 

Maiwald and Schneider134 studied the probe pair 8/7 in order to examine the EPD/HBA abilities of supercritical chlorotrifluoromethane, sulfur hexafluoride, dinitrogen oxide and SCCD and found, as expected, that none of these had such abilities (i.e. fi 0). On the contrary, supercritical ammonia had appreciable fi values (0.70 at 293 K and 100 MPa), being moderately temperature dependent but with little change on lowering the pressure. 

Sulfur hexafluoride. The hexafluoride is normally very resistant to attack and extreme conditions are often required. Thus SF6 resists molten KOH and steam at 500°. It reacts with 02 when a platinum wire is exploded electrically,34 also with some red-hot metals and with alkali metals in liquid ammonia.35 Because of its inertness, high dielectric strength and molecular weight, it is used as a gaseous insulator in high-voltage generators and other electrical equipment.---------------------------------------------------------... 

Sulfur hexafluoride accelerates the pyrolysis of paraffin hydrocarbons (164), lowers the octane number of gasoline containing lead tetraethyl (189), removes silicon from a platinum catalyst when heated to 800 to 1000° (206) and catalyzes the reaction of ammonia with a ketone and aldehyde to give a substituted pyridine (196). It may be used at high pressure to fill a fuse. When the fuse blows an arc is prevented (210). 

Systematic changes of the shapes of the critical curves are also found for other families, where a fixed component 1 (like methane, ethane, ethene, nitrogen, tetra-fluoromethane, helium, argon, xenon, sulfur hexafluoride, methanol, ammonia, etc.) is combined with a second component 2, which is systematically varied. For reviews and references see [2-6,10-12]. A compilation of the literature concerning experimental methods and systems investigated (1978-1987) is given in [31], and of gas-liquid critical data for mixtures in [32]. 

Fluorine is used to make sulfur hexafluoride, a gas with high dielectric strength used in electrical equipment. As previously noted, anhydrous ammonia is used to fertilize crop-... 

Tellurium Halides. Tellurium forms the dihalides TeCl and TeBi, but not Tel2. However, it forms tetrahalides with all four halogens. Tellurium decafluoride [53214-07-6] and hexafluoride can also be prepared. No monohalide, Te2X2, is believed to exist. Tellurium does not form well-defined oxyhalides as do sulfur and selenium. The tellurium halides show varying tendencies to form complexes and addition compounds with nitrogen compounds such as ammonia, pyridine, simple and substituted thioureas and anilines, and ethylenediamine, as well as sulfur trioxide and the chlorides of other elements. 

Derivation (pure oxide) Powdered uranium ore is digested with hot nitric-sulfuric acid mixture and filtered to remove the insoluble portion. Sulfate is precipitated from the solution with barium carbonate, and uranyl nitrate is extracted with ether. After re-extraction into water, it is heated to drive off nitric acid, leaving uranium trioxide. The latter is reduced with hydrogen to the dioxide. Can be prepared from uranium hexafluoride by treating with ammonia and subsequent heating of the ammonium diuranate. It is also recovered from phosphoric acid. 

URANIUM HEXAFLUORIDE (7783-81-5) FjU Radioactive. Violent reaction with water, steam, ethanol, producing hydrogen fluoride gas. Violent reaction with alcohols, aromatic hydrocarbons (benzene, toluene, xylenes, etc.), bromine trifluoride. Aqueous solution increases the explosive sensitivity of nitromethane and is incompatible with sulfuric acid, alkalis, alcohols, ammonia, aliphatic amines, alkanolamines, alkylene oxides, amides, epichlorohydrin, ethers. 

ANTIBULIT (7681-49-4) Reacts with acids, forming hydrogen fluoride. Aqueous solution attacks glass, and reacts violently with xenon hexafluoride. Aqueous solution is incompatible with sulfuric acid, caustics, ammonia, aliphatic amines, alkanolamines, amides, organic anhydrides, isocyanates, vinyl acetate, alkylene oxides, epichlorohydrin,... 

The mined uranium ore is crushed and ground into a fine powder. After ore dressing, the concentrate is leached with sulfuric acid. The solution is treated in a Hq-uid-Hquid extraction, in which uranium is transferred to an organic phase. It is extracted from that with ammonia, and ammonium uranate is precipitated. At 1000°C it is decomposed to yellow uranium oxide UOj. Uranium hexafluoride is prepared by treating the oxide with hydrogen fluoride to make uranium tetrafluoride. This in turn is treated with elemental fluorine to prepare the gaseous hexafluoride UF (sub-Hmation point 56°C). 

---