Dynamic atmosphere

It must be also considered that the reaction rates of different thermal processes which can occur simultaneously are influenced by the treatment conditions (temperature, heating rate, pressure, static or dynamic atmosphere). This will affect the relative quantities of the products formed and in some cases also their nature, when recombination reactions give rise to secondary degradation products. On account of its sensitivity and resolution power Py-GC/MS will also provide useful information on minor components present in a material, including low molecular weight additives and pigments. 

Geankoplis CJ (1993) Transport Processes and Unit Operations. Third edition, PTR Prentice Hall International Editions, Englewood Cliffs Ghil M, Childress S (1987) Topics in geophysical fluid dynamics Atmospheric dynamics, dynamo theory, and climate dynamics. Volume 60 of Applied mathematical sciences. Springer-Verlag, New-York... 

When the thermal decomposition reaction was carried out in a dynamic atmosphere of nitrogen, both the loss of water and the loss of carbon dioxide were affected by the geometry of the container. Likewise, the decomposition of CaC204 was unaffected. The marked effect of the geometry of the sample holder provides evidence that a significant pressure of water vapor and carbon... 

All the mechanical part of the balance, with the beam, set of weights, beam position sensor and compensation electromagnet, is enclosed in a thick-walled metallic chamber, which allows evacuation of the balance and beam cavity (of total volume of about 40 L) to a pressure of 4 x 10 bar with a mechanical rotary pump and to 4 x 10 bar with an additional diffusion pump. The evacuation can be performed either before starting the heating or during the course of the measurements. The gas distribution system allows the furnace space to be filled with various gases. Both static and dynamic atmospheres can be provided in the furnace, and two gases can be introduced in a preset ratio. 

Conducting the normal Kratschmer-Muffman arc fullerene preparation, with graphite rods doped with SC2O3 in a dynamic atmosphere that contains dinitrogen in addition... 

To a flame-dried round-bottomed flask under nitrogen, was added 8 mg bis(acetonitrile)dichloropalladium(II) (5 mol %) and 0.67 mmol iminodiazophospholidine in 5 mL CH2CI2 the resulting solution was stirred for 16 h under a dynamic atmosphere of nitrogen and then checked for completion by NMR. The solution was then concentrated in vacuo. The residue was dissolved in a minimum amount CH2CI2 and purified by flash column chromatography (EtOAc/hexanes, 2 1) to afford 91% A-(l,3-dimethyl-2-oxo-2A -[l,3,2]diazaphospholidin-2-yl)-4-methyl-A-(l-vinyl-butyl)-benzenesulfonamide as a clear oil, R/ = 0.36 (EtOAc/hexanes, 2 1). 

The reaction equilibria for the CO2 - calcite system have been determined by several scientists. Hougen et. al, (10) obtained a value of 0.6x10" for the equilibrium constant from thermodynamic calculations. Carrels and McKenzie (9, p. 146) reported a value of 1.58xl0 . Gauri et. al. (8, Table 1), reacting Green Vermont Marble in dynamic atmospheres with variable partial pressures of... 

Australian Oil Shales in Inert Dynamic Atmospheres," Thermochim. Acta 58 271 (1982). 

A) Static or dynamic atmosphere. Under static conditions, gaseous products cannot be removed rapidly from the vicinity of the sample. This leads to a partial pressure of the products and the reaction temperature is increased. Under dynamic or flowing conditions, evolved gases can be removed from the vicinity of the sample, and the partial pressure of the products decreases. 

Molecular chemistry, which includes particulate matter dynamics, atmospheric chemistry, and combustion chemistry. 

The experiment was performed inside a UHV chamber with a dynamic atmosphere of 8 X 10" mbar hydrogen. The result is shown in Fig. 2.17, in which the water evolution detected by a QMS is compared to the evolution of the metallic character of the surface, as expressed by the intensity at the Fermi edge monitored by He I UPS (for the shape of the whole spectra, see Section 2.7). The water evolution curve indicates two steps in the reduction process, but only the second step leads to the formation of metallic iron in the region near the surface. This evidence provides further strong support for the suggested two-step nucleation mechanism found for the reduction of magnetite in its modified form, which is now suggested as a model for the activation of the ammonia synthesis catalyst. 

The sample can be heated in a furnace equipped with a programmed tenqterature regulator. One works either in a dynamic atmosphere, that is, under gas current, the composition of the entering gas being fixed by mass flowmeters, or in a static atmosphere, the gas being introduced into the enclosure at the beginning of the reaction (the volume of the enclosure is very large compared with the volume of gas or product consumed by the reaction, which makes it possible to consider that the partial pressures remain constant) (see Chapter 11). 

The device thus makes it possible to maintain a water partial pressure ranging between 3.3 x lO " and 0.08 atm. It can be seen that the higher value is relatively low, so we could increase it by raising the temperature of the devices intended to heat the whole of the conduits but we are generally limited by the cooling water of the external walls of the furnaces, which, to play its part of cooling, must be at a low temperature and which, often, is the cause of condensation in the neighborhood of the upper part of the furnace, ft is obvious that the method is appropriate to create static atmospheres. To create dynamic atmospheres, we can get across the water container by inert carrier gas with sufficiently low flows to allow liquid water equilibrium to be established. 

The sample environment may influence behaviour in various ways. Degradation in air will usually be more complex than in nitrogen due to additional oxidation reactions. An inert atmosphere is preferred to simplify interpretation of the basic processes induced by heat, but behaviour may differ greatly between a static and a dynamic atmosphere, since if products are not quickly removed from the degrading sample, secondary reactions may occur. The most efficient removal is under continuous evacuation. 

Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) experiments were performed in a simultaneous DTA-TGA apparatus (Shimadzu DTG 60). Throughout the experiment, the sample temperature and weight-heat flow changes were continuously monitored. The conditions of measurement were heat flow 10 °C/ min and dynamic atmosphere of nitrogen (50 ml/min). The range of temperature measurement was from 40 to 500 °C. 

Fig. 3.14 Jupiter structures in its dynamic atmosphere. At the lower right the great red spot is seen composed of 4 images taken by NASA s Cassini spacecraft on December 7, 2000. Courtesy NASA/JPL...

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