Solid-phase zone

A schematic representation of the combustion wave structure of a typical energetic material is shown in Fig. 3.9 and the heat transfer process as a function of the burning distance and temperature is shown in Fig. 3.10. In zone I (solid-phase zone or condensed-phase zone), no chemical reactions occur and the temperature increases from the initial temperature (Tq) to the decomposition temperature (T ). In zone II (condensed-phase reaction zone), in which there is a phase change from solid to liquid and/or to gas and reactive gaseous species are formed in endothermic or exothermic reactions, the temperature increases from T to the burning surface temperature (Tf In zone III (gas-phase reaction zone), in which exothermic gas-phase reactions occur, the temperature increases rapidly from Tj to the flame temperature (Tg). 

The combustion wave of HMX is divided into three zones crystallized solid phase (zone 1), solid and/or liquid condensed phase (zone 11), and gas phase (zone 111). A schematic representation of the heat transfer process in the combustion wave is shown in Fig. 5.5. In zone 1, the temperature increases from the initial value Tq to the decomposition temperature T without reaction. In zone 11, the temperature increases from T to the burning surface temperature Tj (interface of the condensed phase and the gas phase). In zone 111, the temperature increases rapidly from to the luminous flame temperature (that of the flame sheet shown in Fig. 5.4). Since the condensed-phase reaction zone is very thin (-0.1 mm), is approximately equal to T . 

This sequence of reactions has led to the concept of biogeochemical zonation, with each zone named for the solute that serves as the principal electron acceptor or that is the principal product (Figure 1). The sequence of zones is determined by the chemical free energy yields released by possible reactants. The thickness of each zone is dependent on the rate of reaction consuming the electron acceptor, the rate of a reactant s transport through sediments, and the concentration of the acceptor in bottom waters or in solid phases. Zones may overlap, and tracer studies have shown that they need not be mutually exclusive. The existence of the deeper zones depends on the availability of sufficient reactive organic matter. 

Either low- or high-porosity-solids-phase concentrations can he formed in the purification and melting zones. End-fed units are characterized by low-porosity-solids packing in the purification and melting zones. 

J. H. Beattie, R. Self and M. P. Richards, The use of solid phase concenti ators for online pre-concentration of metallothionein prior to isofom separation by capillary zone electrophoresis , Electrophoresis 16 322-328 (1995). 

D. Eigeys, Y. Zhang and R. Aebersold, Optimization of solid phase microexti action-capillaiy zone electi ophoresis-mass specti ometi y for liigh sensitivity protein identification , Electrophoresis 19 2338-2347 (1998). 

D. Eigeys, A. Dua et, J. R. Yates-III and R. Aebersold, Protein identification by solid phase microextraaion-capillaiy zone electi ophoi esis-miaoelecti ospray-tandem mass specti ometi y , Nat. Biotechnol. 14 1579-1583 (1996). 

The easiest way to understand the SMB concept is to consider a true moving bed (TMB) as described in Eigure 10.1, in which a countercurrent contact is promoted between the solid and liquid phases. The solid phase moves down the column due to gravity and exits the system in Zone I. The liquid (eluent) stream follows exactly the opposite direction. It is recycled from Zone IV to Zone I. The feed, containing components A and B are injected at the middle of the column, and the fresh eluent is replenished in Zone I. 

Thus at = 10 the equilibrium pH will be 9-7 and the flpe2+ will be < 10 at any higher pH value it follows that the formation of a new solid phase Fe(OH)j at a sufficiently high pH must limit the zone of corrosion as defined by Pourbaix. 

A third alternative has been proposed by Anderson and Brown (A6, A9) as an outgrowth of their research on the ignition of composite propellants. Their ignition studies suggest significant contributions to the overall combustion process from the solid phase. Two exothermic reaction zones contributing to combustion are considered, as shown schematically in Fig. 19. 

Based on this approach, an approximate energy balance around the solid-phase reaction zone is given as... 

The most notable theoretical analysis of the instability problem has been presented by McClure and Hart (M5). These investigators postulated a generalized combustion zone that includes a temperature-dependent and pressure-independent solid-phase reaction zone, and a temperature- and pressure-dependent gas-phase reaction zone. From this general model, Hart... 

These studies have indicated that the independent parameters controlling the postulated solid-phase reactions significantly affect the resulting acoustic admittance of the combustion zone, even though these reactions were assumed to be independent of the pressure in the combustion zone. In this combustion model, the pressure oscillations cause the flame zone to move with respect to the solid surface. This effect, in turn, causes oscillations in the rate of heat transfer from the gaseous-combustion zone back to the solid surface, and hence produces oscillations in the temperature of the solid surface. The solid-phase reactions respond to these temperature oscillations, producing significant contributions to the acoustical response of the combustion zone. 

Williams (W2) has recently modified the analysis of Hart and McClure by considering in more detail the effect of diffusional processes on the gas-phase reaction zone. The results of his study show that the diffusional processes tend to stabilize the gas-phase combustion process, indicating that the postulated solid-phase reactions are probably the underlying cause of the instability. 

A reaction interface is the zone immediately adjoining the surface of contact between reactant and product and within which bond redistributions occur. Prevailing conditions are different from those characteristic of the reactant bulk as demonstrated by the enhanced reactivity, usually attributed to local strain, catalysis by products, etc. Considerable difficulties attend investigation of the mechanisms of interface reactions because this thin zone is interposed between two relatively much larger particles. Accordingly, many proposed reaction models are necessarily based on indirect evidence. Without wishing to appear unnecessarily pessimistic, we consider it appropriate to mention here some of the problems inherent in the provision of detailed mechanisms for solid phase rate processes. These difficulties are not always apparent in interpretations and proposals appearing in the literature. 

It is also possible to perform preparative TLC, developing the sample with AMD technique [36a]. After a solid-phase extraction of the waste water with C18-Empore discs, alkanesulfonate is isolated by using a specially dimensioned TLC plate and by scraping out the surfactant-containing zone. 

FIGURE 6.20 Sample application using preparative circular planar chromatographic device (the black zones symbolize the applied sample) (a) liquid phase sample application, (b) solid phase application into the center hole of the plate, (c) solid phase sample application into a scrapped channel. (From Botz, L., Nyiredy, Sz., and Sticher, O., J. Planar Chromatogr. 3, 401-406, 1990. With permission.)... 

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