Analysis of temperature profiles

As discussed earlier, analysis of temperature profiles obtained by microthermocouple measurements have elucidated the unique conditions associated with the combustion synthesis process. However, this approach does not directly identify the composition or microstructure of the phases formed. It is important to recognize that most published investigations in the field of combustion synthesis only address the final product structure. Considerably less has been reported about the structure formation processes leading to the final product. Most results that describe the evolution from the initial reactants to the final product are inferred by the effects of processing variables (e.g., density, dilution, particle size) on the final microstructure (see Section V). To date, only a few investigations have directly identified initial product structure. As discussed earlier, identification of this structure is important since the initial structure represents the starting point for all subsequent material structure formation processes. Thus, the focus of this section is on the initial stages of the structure formation mechanisms in combustion synthesis and novel methods developed especially for this purpose. 

As indicated above, determination of the kinetic parameters of the SHS process can be made through a mathematical analysis of temperature profiles [14]. Integration of an adiabatic form of Eq. (1) along with appropriate substitutions gives the following expression for the conversion parameter [9],... 

T. Boddington, P. G. Laye, J. Tipping, and D. Whalley, Kinetic analysis of temperature profiles for pyrotechnic systems. Combust. Flame, 1986, 24, 359-368. 

For the above reasons, temperature of the monomer far from the incoming front is a more significant parameter to be checked. Indeed, if a temperature increase happens in regions distant from the hot travelling zone, SP is probably taking place. A convenient method to verify the occurrence of that is given by the analysis of temperature profiles (Figure 1). 

Previous studies (1-3) have shown that manganese redox chemistry in the oxygen evolving center (OEC) can be probed by flash-induced enhancements of the nmr relaxation rate of solvent protons (nmr-PRE). We report here an analysis of temperature profiles of the 1 and 2 flash nmr-PRE amplitudes at two field strengths, 0.48 and 1.08 Tesla. Results on model Mn complexes are also reported. 

Ramirez I, Jayaram S, Chemey EA (2010) Analysis of temperature profiles and protective mechanism against dry-band arcing in silicone rubber nanocomposites. TEF.E Trans Diel Electr Insul 17 597-606... 

A considerable amount of experimental information has been obtained for difiusion-reaction-deactivation in pellets by the use of so-called "single pellet difiiision reactors". These come in two forms the first, origiiMy developed by Balder and Petersen [11] ("Petersen s Pellet Poisoner"), relies upon the analysis of concentrations of reactants and their variation with time the second, fi om Kehoe and Butt [12] ("Kehoe s Katalyst Killer") involves measurement of temperature profiles within the pellet and their variation with time. The first is usefiil for deactivation in isothermal systems the second, at the expense of more complexity, can be used for both isothermal and nonisothermal systems. It is not possible to go into a long discussion of these systems here, but some discussion of the more simple reactor, for isothermal systems, will be useful as an example. 

A picture of the infrared emission profile for the dissociation of hydrogen chloride, highly dilute in argon, is shown in Fig. 2. The proportionality of emission signal to concentration has to be demonstrated before kinetic analysis of the profile. The sweep speed of the oscilloscope for this particular experiment was set at 10 psec cm . The first 26 /isec of the recorded time depicts the unshocked gas at its initial pressure at room temperature. The sudden increase in the emission signal is caused by shock arrival at the observation window and is followed by the disappearance of the emitting species as it decomposes. The total reaction time is of the order of 70 jusec. 

An analysis of the profiles of present-day temperatures and paleotemperatures in the Paleozoic sediments has indicated favorable conditions for the hydrocarbon generation mostly in the south and south-west of the region. As to the hydrocarbon generation in the central and northern areas, it might have taken place mainly in the Mesozoic. 

Numerical simulations of granular flow and heat transfer in an agitated filler dryer are presented using TPD. The effects of operating parameters (wall tonperature and impeller speed) and batch size on drying behavior have been systematically stedied and compared with experimental data. Detailed analysis of temporal profiles of temperature and solvent content in the bed was performed. Under constant fill, both... 

Curve analysis by multidifferentiation is primarily employed in spectroscopic applications (notably UVWIS, IR, F, ESR, AAS, NMR) for the enhancement of spectroscopic quantitative analysis (1 to 3 orders of magnitude more sensitive), identification by fingerprints, purity tests, signal sharpening (for separation in multicomponent analysis), etc. However, also various non-spectroscopic applications benefit from derivative spectroscopy, such as GC, HPLC, TLC (quantitative analysis, resolution of shoulders and inflection points) and DTA (fine resolution of temperature profiles) [136]. 

Mossbauer spectroscopy provides microscopic information on the electronic state of atoms. The method applied here to Fe nuclei gives direct evidence that Fe has two charged states in RFe204. At the same time, the analysis of the profile of the spectrum by a stochastic theory of the motional narrowing of resonances gives a frequency of the fluctuation of these state as a function of temperature. 

Temperature profiles along the different sections of the MREF, at various radial positions, (a) Along the total length of the reactor for reforming section and hot gas section at different radial positions and (b) detailed analysis of the profiles in the reformer inlet region, where the feed inlet is subjected to a steep temperature drop (HG, hot gas Ref, reformer Perm, permeate). 

Seam correlations, measurements of rank and geologic history, interpretation of petroleum (qv) formation with coal deposits, prediction of coke properties, and detection of coal oxidation can be deterrnined from petrographic analysis. Constituents of seams can be observed over considerable distances, permitting the correlation of seam profiles in coal basins. Measurements of vitrinite reflectance within a seam permit mapping of variations in thermal and tectonic histories. Figure 2 indicates the relationship of vitrinite reflectance to maximum temperatures and effective heating time in the seam (11,15). 

Phase transitions in overlayers or surfaces. The structure of surface layers may undergo a transition with temperature or coverage. Observation of changes in the diffraction pattern gives a qualitative analysis of a phase transition. Measurement of the intensity and the shape of the profile gives a quantitative analysis of phase boundaries and the influence of finite sizes on the transition. ... 

More recently, Rosen (R3), Spalding (S5), and Johnson and Nachbar (J4) have considered a simplified approach using the analysis of laminar-flame propagation velocities. According to these investigators, the principal exothermic reactions occur in the gas phase. Some of the heat liberated by these reactions is then transferred back to the solid surface to sustain the endothermic surface-gasification processes. Thus, the temperature profile within the reactive zone is quite similar to that of Rice and Crawford. However, gasification of the solid surface is assumed to be endothermic, while exothermic reactions were considered in the studies discussed previously. 

To illustrate this case, consider the parallel reactions of Eq. (7-30). Suppose Af/ = 60.0 kJmol-1 and A= 110.0 kJmol-1. There must exist a temperature (the isokinetic temperature) where the separate straight lines intersect. At this temperature, k(, = k i. Figure 7-2 shows the temperature profile for this case over the range 5-55 °C. The values of AS = -70.0 and ASf = 98.4 J mol-1 K l were chosen. The analysis of this situation yields an isokinetic temperature of 23.8 °C. The plot also shows k(, and k7 separately, to aid the appreciation of the nature of the summation. 

---