Volatile evolution

Phenylquinoxalines - Polyphenylquinoxalines (PPQ) prepared from the reaction of aromatic bi s (o-di amines) and aromatic bis (phenyl-ot-diketones) are high temperature thermoplastics. They are process-able with little or no volatile evolution at relatively high temperatures (> 316°C) and pressure (-1.38 MPa) by virtue of their thermoplasticity. Like other thermoplastics, the processability is governed primarily by the chemical structure, molecular weight and molecular weight distribution. 

Fig. 9. Volatiles evolution profile of PMDA/ODA based polyfamic acids) compared to polyfamic ethyl ester). ( ) mass 18-water, ( ) mass 99-NMP, ( ) mass 46-ethanol...

A novel and very attractive approach to cure imide oligomers via benzocyclobutene endgroups was first published in 1985 (17). Benzocyclobutene endgroups are particularly attractive because they are neat hydrocarbons (provide low dielectrics), cure thermally around 200-250 °C with no volatile evolution and copolymerize with other functional groups, for instance, male-imide. 

The idea of synthesizing imide oligomers which carry acetylenic terminations appeared attractive because homopolymerization through acetylenic endgroups occurs without any volatile evolution and provides materials with good properties. Landis et. al (8,9) published the synthesis of such acetylene terminated imide oligomers from benzophenone tetracarboxylic anhydride, aromatic diamine and 3-ethynylaniline via the classical route. As usual, the amide acid is formed as an intermediate which, after chemical cyclodehydration, provides the polymide. Since ethynyl-terminated polyimide is used as a matrix resin for fiber composites, processing is possible via the amide acid, which is soluble in acetone, or via the fully imidized prepolymer, which is soluble in NMP. The chemical structure of the fully imidized ethynyl-terminated polyimide is provided in Fig. 44. 

Most models of fluidized-bed combustors have been developed for chars on cokes with negligible volatile content or, if addressing coals, have treated the volatile evolution as being either instantaneous or uniformly distributed throughout the fluidized bed. The coal devolatilization step is, however, of major importance to the operation of AFBC s since the coal must be distributed throughout a bed in a manner that ensures that the volatiles will have access to sufficient air for their complete oxidation. 

Condensed-phase cross-linking occurred as the copolymer-containing phosphorus decomposed, facilitating char formation and reducing flammable volatile evolution. 

Jakosky B. M. (1991) Mars volatile evolution evidence from stable isotopes. Icarus 94, 14. 

Van Keken P. E. and Ballentine C. J. (1998) Whole-mantle versus layered mantle convection and the role of a high-viscosity lower mantle in terrestrial volatile evolution. Earth Planet. Sci. Lett. 156, 19-32. 

Mars. The combination of Viking in situ measurements and SNC meteorite data has provided a much more quantitative view of the present state and possible history of martian volatiles. Further progress requires greater precision for the atmospheric composition, more data on possible near-surface and mantle reservoirs, and further constraints on the conditions that affect the volatile evolution of all the terrestrial planets. 

Combustion of coal particles included volatile evolution and char combustion to simulate pulverized coal combustion. 

Bumard PG (1999a) The bubble-by-bubble volatile evolution of two mid-ocean ridge basalts. Earth Planet Sci Lett 174 199-211... 

Crushing. Byrskii et al. (8) used a vibration ball mill to study the volatile compounds released from a series of crushed polymers. They chose this method to intensify the mechanical degradation process and thus to increase the rate of volatile evolution from the polymer. For polymers such as polyethylene (PE) and polytetrafluoroethylene (FIFE), compound evolution rates are low from other methods of mechanical deformation hence, it is difficult to obtain mass spectra. Byl skii et al. used this technique to successfully obtain mass spectra of compounds from PE and PTFE and demonstrated the feasibility of the vibration ball mill for performing kinetic studies of mechanical degradation as a function of the amplitude of the vibration and duration of the grinding. 

The role of heating rate on the onset of volatile evolution, volatile yield, product composition, and, to a lesser extent, coal type and particle size were found to be well established. As heating becomes more rapid, the onset of devolatilization shifts to much smaller timescales and to much higher surface temperatures (Maloney et al., 1991 Sunol and Sunol, 1994 Sampath et al., 1996). However, the role of heating rate on coal thermal properties was not found to be well understood. Previous results clearly demonstrated that particle temperature-dependent thermal property assumptions routinely applied in coal combustion models result in large errors (up to 100%) in calculated temperature histories (Maloney et al., 1991 Sampath et al., 1996). 

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