Solids’ conversion

The complete chemistry of plutonium 1 iquid-to-solid conversion processes, especially peroxide and oxalate precipitation, should be further studied. Research and development of direct thermal denitration methods should also be pursued. 

Total solids conversion reached almost 90% when a two-stage process was employed. 15 refs. 

High MWs tend to indicate solids. Conversely, low MWs tend to indicate gases. Agents easily broken down by heat often have very high MWs. These very high MWs may indicate that decontamination by fire is practical. 

Fig. 4.22. Complementary thermogravimetric and DSC thermograms, showing loss of a volatile component and solid-solid conversion of some of the sample from the amorphous to the crystalline phase.

This result is very interesting because whilst we have shown that G(0) has been excluded from the relaxation spectrum H at all finite times (Section 4.4.5), it is intrinsically related to the retardation spectrum L through Jc. Thus the retardation spectrum is a convenient description of the temporal processes of a viscoelastic solid. Conversely it has little to say about the viscous processes in a viscoelastic liquid. In the high frequency limit where co->oo the relationship becomes... 

Solid conversion not determined due to the absence of an organic layer. 

The electron formed as a product of equation (2.5) will usually be received (or collected ) by an electrode. It is quite common to see the electrode described as a sink of electrons. We need to note, though, that there are two classes of electron-transfer reaction we could have considered. We say that a reaction is heterogeneous when the electroactive material is in solution and is electro-modified at an electrode which exists as a separate phase (it is usually a solid). Conversely, if the electron-transfer reaction occurs between two species, both of which are in solution, as occurs during a potentiometric titration (see Chapter 4), then we say that the electron-transfer reaction is homogeneous. It is not possible to measure the current during a homogeneous reaction since no electrode is involved. The vast majority of examples studied here will, by necessity, involve a heterogeneous electron transfer, usually at a solid electrode. 

We need to describe the conversion of the sohd from reactant to product. We can use concentrations in the solid to describe the solid transformations. However, the concentrations are varying within each particle, while we want the overall conversion to describe the transformation. Therefore, we wiU use a variable describing the solid conversion to describe the conversion of a sohd, in analogy with the conversion X of homogeneous fluids used previously, so that Xj goes from 0 to 1 as the reaction proceeds. 

Another simplifying assumption we wiU make in soUd-gas reactions is that the gas composition profile around and through the sohd remains in steady state as the solid conversion increases. This is obviously not precisely true because the composition of the solid is varying with time. 

Another important example of a solid transformation where growth requires diffusion through the product film is the transformation of solid spheres. The principles of this process are similar to those for planar films, but now the concentration profile is not linear, and the expression one obtains for the transformation and the solid conversion is more complex. 

Hailing, P. J., Eichhorn, U., Kuhl, R, and Jakubke, H.-D. (1995). Thermodynamics of solid-to-solid conversion and application to enzymic peptide synthesis. Enzyme Microb. TechnoL, 17, 601-6. 

Provided that the same reference standard state (for example the pure solid) is used in Kth and Z for each reactant, we can combine these to give the free energy of the solid-to-solid conversion according to Equation 4 ... 

It has been theoretically derived that the favorability of solid-to-solid conversion is solvent independent [30]. Practical evidence was presented that the mass action ratio and equilibrium constant varied in the same proportions as the solvent was changed (Figure 12.4) [45]. 

Boskey, A. L., Posner, A. S. Conversion of amorphous calcium phosphate to microcrystalline hydroxyapatite pH-dependent, solution-mediated, solid-solid conversion. J. Phys. 

Under ordinary laboratory conditions (at lower temperatures than shown in Fig. 7.5), it is seen that only the red a-sulfur form is stable. The yellow /3-sulfur needles are the most stable phase only in a narrow temperature range around 96-120°C, but they persist as a supercooled metastable phase well below this range (surviving, for example, on a stock-room shelf for indefinite periods). Given a sample of yellow /3-sulfur, it is easy to detect the melting point near 120°C, but is far from easy to detect the enantiomorphic a/13 solid-solid conversion near 96°C, unless a nucleating crystallite or catalyst is introduced. Once produced, the /3-phase tends to persist as a supercooled (undercooled) metastable extension... 

Results and Discussion. Some experimental results on H2/CO mixtures with no added CO2 or H2O, were available from previous work (12) using a high purity pelletised ore (Carol Lake). A comparison of the experimental and predicted results using the water gas shift reaction at a solid conversion of 50% is given in Table X below. 

Figure 1 shows the effect of gas flow rate predicted by the model on the solid conversion for a CO rich gas mixture. Three gas flow rates of 9,7 and 5 m/s are shown. Also illustrated is the predicted conversion for the model which does not include the... 

Ug,Us gas solids velocity, respectively y dimensionless concentration X solids conversion in bed... 

Figures 4, 5, and 6 show the solid conversion efficiencies of the three SRC and the reference coals in air in the DTFS at three temperatures (furnace wall temperatures of 2500, 2700, and 2800 F). The CSD and PFD SRC and WSB reference coal achieved a high solid conversion efficiency (>75%) in less than 50 milliseconds, while the ASD SRC and the KHB reference coal resulted in lower initial conversion efficiencies, less than 60%. The initial high degree of conversion of the CSD and PFD SRC results in relatively low amounts of residual char to be burned in the latter stages of combustion.

The CSD SRC showed the highest initial and overall solid conversion efficiency of all the fuels studied. 

The results further show that the solid conversion efficiencies increase more dramatically with temperature than with residence time increases. For the CSD SRC solid conversion efficiencies increased from 91 to 95% at a furnace temperature of 2500 F, as the residence time increased from 0.05 second to 0.3 second. The corresponding efficiencies at 2800 F were 97% and 99% respectively indicating the pronounced effect of higher temperatures. 

Figure 4. DTFS solid conversion efficiencies of fuels in air at TW = 2500°F.

Varying the primary stage residence time (Figure 8) showed the importance of providing a sufficient time in the substoichio-metric primary stage for achieving low N0X. The overall solid conversion efficiencies were unaffected by changes in this parameter. 

In order to extrapolate the laboratory results to the field and to make semiquantitative predictions, an in-house computer model was used. Chemical reaction rate constants were derived by matching the data from the Controlled Mixing History Furnace to the model predictions. The devolatilization phase was not modeled since volatile matter release and subsequent combustion occurs very rapidly and would not significantly impact the accuracy of the mathematical model predictions. The "overall" solid conversion efficiency at a given residence time was obtained by adding both the simulated char combustion efficiency and the average pyrolysis efficiency (found in the primary stage of the CMHF). 

The model predictions indicate that at typical commercial coal firing conditions, the carbon in the fly ash for the CSD SRC would lie between 1.9 and 12.2%, whereas that for the PFD SRC would lie between 26.9 and 46.4%. These results show that the high overall solid conversion efficiency of the CSD SRC is due to its higher pyrolysis/initial solid conversion efficiency. 

Rapid pyrolysis is most pronounced in the CSD SRC and is predominantly responsible for achieving high overall solid conversion efficiencies despite the lower char reactivity of the CSD SRC relative to the PFD SRC. The ASD SRC exhibits a markedly lower pyrolysis rate than the other two SRC solids which renders it overall less reactive. 

Reactions proceed faster and more smoothly when the reactants are dissolved, because of diffusion. Although reactions in the solid state are known [1] they are often condensations in which a molecule of water is formed and reaction takes place in a thin film of water at the boundary of the two solid surfaces. Other examples include the formation of a liquid product from two solids, e.g. dimethylimidazolium chloride reacts with aluminum chloride to produce the ionic liquid, dimethylimidazolium tetrachloroaluminate [2]. It is worth noting, however, that not all of the reactant(s) have to be dissolved and reactions can often be readily performed with suspensions. Indeed, so-called sol-id-to-solid conversions, whereby a reactant is suspended in a solvent and the product precipitates, replacing the reactant, have become popular in enzymatic transformations [3]. In some cases, the solvent may be an excess of one of the reactants. In this case the reaction is often referred to as a solvolysis, or, when the reactant is water, hydrolysis. 

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