Kinetic decomposition

Diperoxyketals, and many other organic peroxides, are acid-sensitive, therefore removal of all traces of the acid catalysts must be accompHshed before attempting distillations or kinetic decomposition studies. The low molecular weight diperoxyketals can decompose with explosive force and commercial formulations are available only as mineral spirits or phthalate ester solutions. 

Equation (8.14) demonstrates once more that the cation flux caused by the oxygen potential gradient consists of two terms 1) the well known diffusional term, and 2) a drift term which is induced by the vacancy flux and weighted by the cation transference number. We note the equivalence of the formulations which led to Eqns. (8.2) and (8.14). Since vb = jv - Vm, we may express the drift term by the shift velocity vb of the crystal. Let us finally point out that this segregation and demixing effect is purely kinetic. Its magnitude depends on ft = bB/bA, the cation mobility ratio. It is in no way related to the thermodynamic stability (AC 0, AG go) of the component oxides AO and BO. This will become even clearer in the next section when we discuss the kinetic decomposition of stoichiometric compounds. 

Kinetic Decomposition of Compounds in Chemical Potential Gradients... 

We continue the discussion of multicomponent crystals placed in the potential chemical gradient of a component. Let us investigate what happens when a nearly stoichiometric compound crystal is brought between different potentials of its nonmetallic component (e.g., AO B203 between two different oxygen potentials). These two potentials are chosen to fall inside the stability field of the spinel phase so that the spinel will be neither reduced nor oxidized thermodynamically. We will demonstrate that the spinel can nevertheless decompose in the oxygen potential gradient. This decomposition is a purely kinetic effect and has therefore been named kinetic decomposition. 

Figure 8-4. Kinetic decomposition scheme of the stoichiometric compound AB,04 = AO-Bj03 Z3a>I.5Z b. AO and B203 are decomposition products.

The kinetic decomposition process is illustrated in Figure 8-4. In order to define the transport coefficients, we assume that the spinel is a semiconducting oxide with immobile oxygen ions. As before, the flux equations will then have the following forms... 

In combination with Eqn. (8.18), we can now calculate the oxygen potential difference across the sample at which kinetic decomposition of the spinel AB204 supposedly takes place... 

Here, p 0i and pq2 are the oxygen pressures at the opposite surfaces of the spinel sample. If bA>i bB, the decomposed binary reactant AO will be formed at the high oxygen potential side (Fig. 8-4), whereas if bA< -bB, AO will be formed at the low oxygen potential side, provided that A/Uo2> Mo2 (max)- B203 will be formed at the respective opposite sides. Experiments have been performed that confirm this mode of decomposition [W. Laqua, H. Schmalzried (1983)]. In concluding, we point out that, in principle, kinetic decomposition occurs in all semiconducting compounds for which bA = bB, independent of their anionic transference. 

Huang, C.-R. and Shu, H.-Y., The reaction kinetics, decomposition pathways and intermediate formations of phenol in ozonation, UV/03 and H202 processes, /. Hazardous Mater., 41, 47-64, 1995. 

Table HI. A. 1 - Comparison of the Equilibrium and Kinetic Decomposition of Hydrazine Monopropellant...

TITLE Kinetic decomposition of sodium acetate definition of Methane decouples C02 and CH4... 

Table 11.6. A phreeqc script for the kinetic decomposition of sodium acetate at 200°C.

Ewing, R.G., Kinetic decomposition of proton bound dimer ions with substituted amines in ion mobility spectrometry, dissertation. New Mexico State University, Las Cruces, December 1996. 

High temperature treatment requires consideration of reaction kinetics, decomposition kinetics and thermodynamics. These includes the rates of mass and heat transfer as well as chemical reaction rates [3]. 

Jacob KT, Shukla A (1987) Kinetic decomposition of Ni SiO in oxygen potential gradients. J Mater Res 2 338-342 Jamnik J, Meier J (1999) Defect chemistry and chemical transport involving interfaces. Solid State Ionics 119 191-198 Kida T, Shimanoe K, Miura N, Yamazoe N (2001) Stability of NASICON-based CO sensor imder humid conditions at low temperature. Sens Actuators B 75 179-187... 

Varying the kinetics of decomposition of the precursors was profitable for the controlled synthesis of RuPt NPs. Whilst the co-decomposition of [Ru(COD(COT)] and [Pt(dba)2] in the presence of polyvinylpyrrolidone as stabilizer led to a RuPt alloy with a fee structure, core-shell RuPt NPs were obtained in PVP, using [Pt(CH3)2(COD)] (i.e., [dimethyl(l,5-cyclooctadiene) platinum (II)]) instead of [Pt(dba)2] [91]. This is related to the slower rate of decomposition of [Pt(CH3)2(COD)]. In summary, the chemical order can be controlled via the choice of the precursor. The chemical segregation leading to core-shell RuPt results from kinetic (decomposition rate of the metal precursors) and thermodynamic (preferred location of each metal in the particle) parameters as well as from the steric... 

If eqn [5] is satisfied, the lifetime of RY is then drastically prolonged compared with a classical first-order kinetic decomposition occurring if a radical scavenger such as oxygen is present in the medium. When conditions for eqn [5] are not met (for instance, fec= 1-0 x lO instead of 1.0 x 10 M s ), the degradation of RY is very fast, that is, 10 s compared to 10 s if eqn [5] is fulfilled (Figure 13(b)). 

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