Rate-limiting mechanisms

I don t think we know what the rate-limiting mechanisms are for most of the behaviors that we think we are concerned with. 

Axe,L. Anderson, P.R. (1995) Sr diffusion and reaction within Fe oxides. Evaluation of the rate limiting mechanism for sorption J. Coll. Interf. Sd. 175 157—168 Axe,L. Anderson, P.R. (1997) Experimental and theoretical diffusivities of Cd and Sr in hydrous ferric oxide. J. Coll. Interface Sci. 

The key feature of the model of Nicollian and Reisman (73) is that the surface-reaction-limited oxidation process has viscous oxide flow as the rate-limiting mechanism. During oxidation, volume expansion occurs when silicon is oxidized, and the viscous flow of oxide accompanies this expansion. The rate of growth at the interface is given by... 

There are basically three, rate-limiting mechanisms for mineral dissolution assuming a fixed degree of undersaturation. They are (1) transport of solute away from the dissolved crystal or transport-controlled kinetics. 

The third type of rate-limiting mechanism for mineral dissolution— mixed or partial surface reaction-controlled kinetics—exists when the surface detachment is fast enough that the surface concentration builds up to levels greater than the surrounding solution concentration but lower than that expected for saturation (Berner, 1978). 

Li T, Farrell J. Rate-limiting mechanisms for carbon tetrachloride and trichloroethylene reactions at iron surfaces. 221st National Meeting, San Diego, CA, American Chemical Society 2001 41 (1) 1154—1159. 

For uptake of solute from solution by porous solids the rate will be endothermic rather than exothermic if intraparticle transport is the rate-limiting mechanism. Because diffusion is an endothermic process while adsorption is exothermic, rate of uptake of solute by porous solids will often increase with increasing temperature while for the same system the equilibrium position of adsorption or adsorption capacity will decrease with increasing temperature. 

Assuming Fickian diffusion in the film, the time to reach equilibrium is proportional to the square of film thickness, so thinner films respond more rapidly at the expense of lower sensitivity and limit of detection. Regardless of the rate-limiting mechanism, response time invariably improves with increasing temperature. 

Importance of Rate-Limiting Mechanisms in Different Pressure Regimes"... 

The experimentally determined reaction rate equation is fourth-order and dependent on [Fe " ], [O2], and [OH ] (Table 9.3b). The rate dependence on [Fe and [O2] was determined by measuring the rate of disappearance of Fe(II) (Roman numerals are used to indicate the oxidation state without specifying the actual species in solution) at various pHs while O2 remained constant (and vice versa for the O2 dependency) (Stumm and Lee, 1961). We loiow from previous discussion that the fourth-order reaction mechanism in Table 9.3b would be nearly impossible. Millero et al. (1987a) suggested a rate-limiting mechanism that is a second-order reaction between... 

Mullis, A.M. 1993. Determination of the rate limiting mechanism for quartz pressure solution. Geochim. Cosmochim. Acta, 57 1499-1503. 

Intrasorbent diffusion involves the mass transfer of sorbate within the matrix of the sorbent. Given organic matter as the predominant sorbent for HOC, intrasorbent diffusion is usually considered to involve diffusive mass transfer within the matrix of organic matter (intraorganic matter diffusion, or lOMD). Intraorganic matter diffusion was proposed as the rate-limiting mechanism for sorption of organic chemicals as early as 1966 by Hamaker... 

Under some conditions there may be two rate-limiting mechanisms. The solution to the combined pore and film diffusion problem (R=0) is (7)... 

Kelly, Robert G. The Determination of the Rate Limiting Mechanism in Lithium/Iodine (PZZP) Batteries. M.S. thesis. Johns Hopkins... 

A review of the literature suggests that different mechanisms may play important roles in different systems. For example, results from pressure-jump studies of sorption reactions at nonporous surfaces have shown that the chemical reactions themseleve are very fast [13-16], so that in most cases a slow chemical reaction rate is not likely a rate-limiting step. Spectroscopic evidence indicates that in some systems surface precipitation or solid solution formation does not occur even at high adsorbate loadings [17-20]. We believe, however, that intraparticle diffusion can be an important rate-limiting mechanism for all porous oxides. 

In summary, although intraparticle diffusion is a rate-limiting mechanism for sorption in porous minerals, implications in using the diffusion model include accounting for such effects as coprecipitation, adsorbate type, potential exchange reactions, sorbent and solution chemistry, and the stability of the particle size distribution. 

Kelly RG, Moran PJ (1987) The rate limiting mechanism of Li/l2 (PV2P) batteries. J Electrochem Soc 134 25-30... 

McLeod L S, Degertekin F L and Fedorov A G (2009), Determination of the rate-limiting mechanism for permeation of hydrogen through microfabricated palladium-silver alloy membranes , J Membrane Sci, 341,225-232. 

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