Kinetics of transformation

Rapp P (2001) Multiphase kinetics of transformation of 1,2,4-trichlorobenzene at nano- and micromolar concentrations by Burkholderia sp. strain PS14. Appl Environ Microbiol 67 3496-3500. 

Sections 5.6.2 and 5.6.3 dealt with the deposition of metals from complexes these processes follow the simple laws dealt with in Sections 5.2 and 5.3, particularly if they take place at mercury electrodes. The deposition of metals at solid electrodes (electrocrystallization) and their oxidation is connected with the kinetics of transformation of the solid phase, which has a specific character. A total of five different cases can be distinguished in these processes ... 

Figure 5.6. Relationship between Co and Mn contents extracted from solid-phase of six Israeli arid-zone soils with sequential dissolution procedures (after Han et al., 2002b. Reprinted from J Environ Sci Health, Part A, 137, Han F.X., Banin A., Kingery W.L., Li Z.P., Pathways and kinetics of transformation of cobalt among solid-phase components in arid-zone soils, p 184, Copyright (2002), with permission from Taylor Francis)...

The kinetics of transformation of Mn and Fe among soil fractions is related to the redox potential (Eh changes) as well as the content of reductants or oxidants in the soil. Generally, a drop in Eh is observed within a few days of the waterlogging of a soil. In a coastal saline silty-clay soil, Eh was reduced to 210 mV after four days of submergence (Bandyopadhyay and Bandyopadhyay, 1984). The decrease in Eh mobilized Mn, and the maximal soluble Mn concentration was found after 14 days of submergence in a sandy-loam soil (Sadana and Takkar, 1988). 

Pathways and Kinetics of Transformation of Cobalt Among Solid-phase Components at Saturated Arid-zone Soils... 

Han F.X., Banin A., Kingery W.L., Li Z.P. Pathways and kinetics of transformation of cobalt among solid-phase components in arid-zone soils. J Environ Sci Health, Part A 2002b 137 175-194. 

Figure 6.30. Kinetics of transformation of Co in the ERO fraction in two Israeli soils according to the two-constant rate model (a) and the simple...

CALPHAD calculations were made for a number of binary systems including Au-Si, (Hf,Ti,Zr)-Be and Ni-Ti (Saunders and MiodoAvnik 1983) and a series of ternaries Hf-Ti-Be, Hf-Zr-Be and Hf-Ti-Be (Saunders et al. 1985). Figure 11.6 shows such a calculation for Ni-Ti. The results were encouraging in that they predicted with reasonable accuracy the limit to glass formation when the terminal solid solutions were considered. However, there was limited success when taking into account compoimd phases. To this end the approach was extended to include the kinetics of transformation more explicitly. Remarkably good results were then obtained for a wide variety of binary and ternary system and these are reported in Section 11.3.4. 

In cases where sorptive equilibrium is reached rapidly and transformation is much slower, the aqueous phase concentration of contaminant may show a rapid initial decrease due to adsorption followed by a slower decline due to transformation. Under these conditions, the kinetic model represented by Eq. (16) is sufficient to describe the kinetics of transformation after the initial data have been excluded. This approach has been taken for TCE [168], vinyl chloride [176], and probably in many other studies where the exclusion of initial rate data was not clearly documented. 

Irreversible transformations are those in which reactants do not reform from products upon cooling. Generally one of the reactants is in a metastable state, and only requires thermal agitation or the presence of a catalyst to initiate the transformation. Examples would be combustion of a fossil fuel or glass devitrification. Power-compensated DSC has a distinct advantage over heat-flux DSC in determining the kinetics of transformation from metastable phases. In these type of reactions,... 

Anatase with relatively large particle size was prepared by heating the freshly prepared oxide to 400°C anda sample of particle size 74> Pi > 53 microns was obtained by employing Tyler standard sieves (- 200 + 270 mesh). These particles were crushed to finer particles and sieved (mesh sizes -270 + 325 and -325) to provide anatase samples (P2and P3) with particle sizes 53>P2>43 and P3<43 microns respectively. Since the thermal history of all the three samples is the same, it was assumed that any changes in transformation characteristics can be attributed to particle-size effects. The kinetics of transformation of the three samples were studied at 700°C and the transformation curves shown in fig. 4a, clearly indicate that smaller particle size of... 

Handbooks. Tabulations of traditional properties of chemicals (Tb, Tm, p, Saq) are often available in publications by fine-chemical manufacturers (e.g., Fisher Scientific, Web page www.fishersci.com). Other collections of these parameters, surface tension, the specialized partition coefficient values, and kinetics of transformations include Winholz et al.,54 Howard et al.,55 Dean,56 Lide,57 Mackay et al.,58 Howard and Meylan,59 Tomlin,60 Yaws,61 and Verschueren.62... 

Wagh and Jeong [4] have reported that, once the metal ions are dissociated and screened in an acid solution that is rich with phosphate anions, the kinetics of transformation to a CBPC is very similar to that of the conventional sol-gel process of fabricating ceramics of nonsilicates [4] with the major difference here being that the acid-base reaction used in forming CBPCs carries the mixture all the way to the formation of ceramics, while in the sol-gel process the sols are ultimately sintered to form superior ceramics. Figure 5.1 illustrates the step-by-step kinetics of the formation of CBPCs. 

Zirconia also undergoes high pressure phase transitions from the monoclinic to two orthorhombic structures. A thermochemical study of these phases, combined with phase equilibrium observations (Ohtaka et al. 1991) suggests that surface energy changes the apparent position of phase boundaries, as well as enhances the kinetics of transformation. However Ohtaka et al. (1991) were unable to quantify these effects. 

---