Atmospheric methane

Ohtake, N., and Yashikawa, M., Diamond Film Preparation by Arc Discharge Plasma Jet Chemical Vapor Deposition in the Methane Atmosphere, / Electrochem. Soc., 137(2) 717-722(1990)... 

Many years later, Schwartz (Schwartz and Goverde, 1982 Voet and Schwartz, 1983) discovered that the synthesis of adenine via polymerisation of HCN can be accelerated by adding formaldehyde and other aldehydes. Reactions in the gas phase (nitrogen/methane atmosphere) promoted by electrical discharges led to the formation of cyanoacetylene in relatively good yields the latter reacts with urea to give various products, including cytosine (Sanchez et al., 1968). 

For gases, at pressures that are not too far from atmospheric, the space occupied by one molecule of methane is equal to that occupied by one molecule of nitrogen or oxygen gas. We can therefore use the ideal gas law to convert ppm(v) to atmospheres of methane/atmosphere of total pressure. 

Figure 6.1. The Jovian moon lo deep ultraviolet (UV) photolysis of its methane atmosphere proceeds with electron ejection, generating the molecular ion of methane (see color insert). NASA JPL Galileo program image from Voyager 1, http //www.jpl.nasa.gov/galileo/io/...

The transmission of the detonation figure for the complete cartridge is 4-7 cm. Pobedit P-8 is tested not only in a steel mortar in a gallery, but also suspended free in methane atmosphere and in the presence of coal-dust. 

By 2.7 Ga ago, the modern carbon cycle was in operation the oxygen production must have been considerable. Did it build up in the air For contrasting views on this vexed problem, see Holland (1999) and Ohmoto (1997). Catling et al (2001) argue persuasively for a high-methane atmosphere, or Earth would have frozen over. 

Methane in the present atmosphere, molecule for molecule, is a much more powerful greenhouse gas than carbon dioxide (Hansen Sato 2001). Today small changes in methane can have large climatic results. In a high-methane atmosphere, however, the incremental impact of emissions would be much less. 

Pure and NaP-modified MnOx-catalysts were used in our study. Due to easy visualization by AFM, the MnOx layer was placed on a Si-wafer substrate (1 cm x 1 cm plate), by a reactive deposition technique. The sample preparation was carried out in a vacuum installation equipped with an resistance evaporator. Metallic manganese (99.8%) as a source and a Si wafer with a surface orientation (111) and resistivity of 7.5 ohm/cm as support, were used. During MnOx deposition, an oxygen partial pressure of ca 10 torr, in dynamic mode, was maintained. Before used for the catalytic purpose, MnOx samples were calcined in air at 700°C for 60min. In order to prepare the NaP-modified catalyst, the MnOx samples were impregnated in a diluted Na4P20 solution (5 wt %), dried and finally calcined at 500° C, in air during 30 min. The interaction with methane was performed in a quartz reactor in a methane atmosphere at 700° 5° C. 

Figure 5. AMF images of NaP-MnOx catalyst surface before (a) and after different exposure to methane 15 min., 700°C, 300 ton (b, c, d) 5 s, 700°C, 10 ton (e) and 30 s, 700°C, 170 ton (f) Structure of the catalyst surface covered partially by carbon coke deposits visualized after cooling in the methane atmosphere (g, h). Image size 6pm x 6pm (a) 17pm x 17pm (b) 3 pm X 3pm (c, h) 4pm x 4pm (d) 1 75pm x 1,75pm (e, f) 12pm x 12pm (g).

The CVD reactor consists of a vitreous silica tube of about 20 cm in diameter (8") and a height of 30.5 cm (1 ft). The filament was made from tantalum wire with 0.5 mm diameter and attached to water-cooled copper electrodes. Heat treatment in a methane atmosphere produces a thin layer of tantalum carbide that protects the sample from contamination with metallic tantalum. A gas-leaking unit allows the introduction of various gases and their mixtures into the reaction chamber under controlled pressure. Before introducing or changing the gas the unit s internal pressure was reduced by a mechanical pump to about 0.1 Pa. 

To avoid the contamination of the samples with tungsten atoms emitted from the hot filament the latter was carbonized in situ in the vacuum chamber in a methane atmosphere for 20 min. The layer of tungsten carbide formed has a much lower vapour pressure compared to metallic tungsten within the temperature range of the filament chosen (1800-2500°C). Figure 3.6 shows an SEM micrograph of a carbonized filament. 

Atmospheric pressure CVD of NbCi-yN, using NbCl, NH3, and CH4 has been employed in three separate approaches toward the optimization of reaction characteristics [69]. These were (i) simultaneous deposition of niobium, carbon, and nitrogen by hydrogen reduction of NbCls with decomposition of methane and ammonia at a temperature of 900-1000°C (ii) deposition of a niobium amide complex derived from NbCl.s/NHi in nitrogen as a carrier gas at 250-350 °C, and subsequent conversion in ammonia/methane at 1 000-1 100 °C (iii) separate deposition of elemental niobium or NbCl.3 by hydrogen reduction at 500-1000°C and subsequent conversion to NbCi yNy in an ammonia/methane atmosphere at 1000-1 100°C. The results of these three approaches are given below. 

The tube is usually coated with pyrolytic graphite, which is made by heating the tube in a methane atmosphere. Pyrolytic graphite exhibits a low gas permeability and good resistance to chemical attack and this lengthens the lifetime (i.e., the number of successful firings) of the tube. There is, however, a finite lifetime for each tube in GFAA. 

Decay of °Pb(CH3)4 in the gas and in the liquid phase has been studied under different conditions. Bi(CH3)3 [1, 5] and also Po(CH3)2 [1] are assumed as decay products, and evidence of molecular survival, i.e., failure of bond rupture in the primary p- and internal conversion process was obtained [5, 6] see also [7, 10]. [Bi(CH3)4]+ is presumed to be the initial ionic species of the decay process [9,10]. A very detailed study revealed that at low pressures no Bi(CH3)3 is obtained, the primary ion [Bi(CH3)4]+ disproportionates and gives depositions on the wall however, at higher pressures, production of Bi(CH3)3 becomes the dominant process since the primary ion undergoes many collisions before reaching the wall [10]. A volatile organolead compound was produced in a methane atmosphere by Pb recoiling from... 

Solid oxide Ceramic oxide Flydrogen, reformed methane Atmospheric oxygen 800-1000°C (1500-1800°F) 45-60%... 

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