Thermodynamic evaluation

3 Removal of Hf from Zr with molten salt extraction 6.1.3.1 Thermodynamic evaluation 

The molten salt extraction of hafnium from the Zr-Hf alloy phase is based on the fact that the reaction between hafnium and CUCI2 is more favorable thermodynamically than that between zirconium and CUCI2. Since Zr and Hf can exist in a valence of either four or two, a thermodynamic evaluation of both valences for the equilibrium constant is shown below as at 850 °C  

Hf[metal] b uCl2[salt] CUjmgjaj] + HfCl2[salt] [metal] b 2CuCl2[salt] CUjmgjaj] + ZrC jgalt] 

---

Equations X-12 and X-13 thus provide a thermodynamic evaluation of the change in interfacial free energy accompanying adsorption. As discussed further in Section X-5C, typical values of v for adsorbed films on solids range up to 100 ergs/cm. ... 

A thermodynamic evaluation of this equation indicated that the reaction could proceed with SO2 levels as low as 100ppm. 

Dremlyuzhenko SG, Voloshchuk AG, Zakharuk Zl, Yurijchuk IN (2008) Thermodynamic evaluation and potentiometric study of Cdi xMnxTe and Cdi xZnx Te dissolution in acid and alkaline solutions. Inorg Mater 44 21-29... 

Wohl, K. Trans. Amer. Inst. Chem. Eng. 42 (1946) 215. Thermodynamic evaluation of binary and ternary liquid systems. 

Herzberg C. T. (1978b). Pyroxene geothermometry and geobarometry Experimental and thermodynamic evaluation of some subsolidus phase relations involving pyroxenes in the system CaO-MgO-AljOj-SiOj. Geochim. Cosmochim. Acta, 42 945-957. 

The first step is relevant to the start-up phase, which in this particular case we chose to extend for up to 1 h in order to verify the reactor stability also in these conditions, where water is not present and while there is a higher oxygen concentration in the feed gas with respect to the ATR conditions. By lowering the 02 CH4 ratio, the H2 concentration at the reactor outlet increases, approaching the value expected by thermodynamic evaluation and CH4 conversion is still complete. A further decrease in the 02 CH4 feed ratio to values lower than 1.16 corresponds to an abrupt decrease in temperature in the lower section and a simultaneous temperature increase in the catalytic reforming section. 

From the point of view of thermodynamics —which is oblivious to details at the molecular level-the dividing boundary may be placed at any value of x in the range r. The actual placement of a 0 is governed by consideration of which properties of the system are most amenable to thermodynamic evaluation. More accurately, that property that is least convenient to handle mathematically may be eliminated by choosing x0 so that the difficult quantity has a surface excess of zero. 

Taylor, J. D., Gilbert, P J., Williams, M. A., Pitt, W. R., and Ladbury, J. E. (2007). Identification of novel fragment compounds targeted against the pY pocket of v-Src SH2 by computational and NMR screening and thermodynamic evaluation. Proteins Structure Function and Bioinformatics 67, 981-990. 

Meltser, L. H., "Method of Thermodynamic Evaluation of Theoretical and Actual Cycles of Cooling Machines,"... 

Kato, K., "Energy Savings in Grain Drying - A Thermodynamic Evaluation," Energy Dev. Japan, j4, 153, Oct. (1981). 

A characteristic feature of some of these reactions is the dependence of their efficiency on the basicity of the radical anion [108], The differences are especially manifested in non-polar solvents, where the CIP are expected to dominate. Some of these cleavage processes are more efficient than expected, based on the thermodynamic evaluations of the unassisted fragmentation (Sect. 3.2). Also a stereochemical preference for cleavage is observed for erythro isomers as compared to the threo isomers (Scheme 6). In benzene erythro/threo selectivity is high, being highest for the relatively basic radical anion of dicyanonaphthalene and lowest for the relatively nonbasic radical anion of thioindigo. The stereochemical preference disappears in acetonitrile if biphenyl is used as a co-sensitizer [108]. 

It is essential to realize that any thermodynamic evaluation of this solubility "maximum" with standard reference conditions in the form of the three pure components in liquid form is a futile exercise. The complete phase diagram. Fig. 2, shows the "maximum" of the solubility area to mark only a change in the structure of the phase in equilibrium with the solubility region. The maximum of the solubility is a reflection of the fact that the water as equilibrium body is replaced by a lamellar liquid crystalline phase. Since this phase.transition obviously is more. related to packing constraints — than enthalpy of formation — a view of the different phases as one continuous region such as in the short chain compounds water/ethanol/ethyl acetate. Fig. 3, is realistic. The three phases in the complete diagram. Fig. 2, may be perceived as a continuous solubility area with different packing conditions in different parts (Fig. 4). 

Table II. Thermodynamic evaluation of the heat of sublimation of gold and the dissociation energy of AU2...

This is a severe drawback in the case of equilibrium studies of metal molecules since, as a rule, such molecules are minor vapor components and maximum sensitivity is required for their thermodynamic evaluation. However, very precise ionization potentials can be measured using photoionization spectroscopy (5,28). Berkowltz (28) reviewed early work concerning alkali metal dimers. Herrmann et al. ( ) have measured the ionization potentials of numerous sodium, potassium and mixed sodium-potassium clusters. For most of these clusters the atomization energies of the neutral molecules are not known. Therefore, the dissociation energies of the corresponding positive ions cannot be calculated. 

Johnson, A.R., O Sullivan, B., and Raymond, K.N. (2000) Synthesis of a ligand based upon a new entry into the 3-hydroxy-N-alkyl-2(lH)-pyridinone ring system and thermodynamic evaluation of its gadolinium complex. Inorganic Chemistry, 39, 2652-2660. 

It is apparent that in order to use our rate model, a thermodynamic evaluation of the bulk fluid and surface speciation is... 

Physical Properties of 02" AF Salts. The physical properties of the 02 AF (c) salts A = BF3, PF5 and ASF5 fit the expectations based on these simple thermodynamic evaluations. At least the relative stabilities of the salts are accounted for. Because of inherent imprecision (particularly in lattice energy evaluation (6)), the AG values for process (2) and (3) are not accurate to more than 5 kcal mol". As we have already seen the lattice enthalpy advantage of about 11 kcal mol" for 02 BF4 over 02 PF6 approximately balances the difference in the F affinities of PF5 and BF3. The thermodynamic stability of 02 BF4 should only be slightly better than 02+PF6". 

Gerlach T. M. (1993) Thermodynamic evaluation and restoration of volcanic gas analyses an example based on modem collection and analytical methods. Geochem. J. 21, 305-322. 

Another example of aqueous speciation that includes redox can be shown with the arsenic pe-pH diagram shown in Figure 1. Arsenic can exist in several oxidation states including As(-lll) as in arsine gas (ASH3), As(0) as in elemental arsenic, As(ll) as in realgar (AsS), As(lll) as in orpiment (AS2S3) and dissolved arsenite, and As(V) as in dissolved arsenate. Figure 1 shows the dominant dissolved species, arsenate and arsenite, and their hydrolysis products as a function of redox potential and pH based on the thermodynamic evaluation of Nordstrom and Archer (2003). These results show the dominance of hydrolysis for arsenate species, but it is of minor consequence for the arsenite species. 

Casolaro M and Barbucci R. An insuhn-releasing system responsive to glucose—thermodynamic evaluation of permeabihty properties. International Journal of Artificial Organs 1991 14 732-738. 

Numerous determinations of differential heats of adsorption have been made, both by direct calorimetric and by indirect thermodynamical evaluations. Generally speaking, these determinations cannot be regarded as highly accurate. For the calorimetric measurement, difflculties are encountered due to the frequently low heat conductivity of the adsorbent at a low pressure, leading to abnormal heat curves as shown frequently in the earlier literature. 

---