Isothermal decomposition

Fig. 1. Generalized a—time plot summarizing characteristic kinetic behaviour observed for isothermal decompositions of solids. There are wide variations in the relative significance of the various stages (distinguished by letter in the diagram). Some stages may be negligible or absent, many reactions of solids are deceleratory throughout. A, initial reaction (often deceleratory) B, induction period C, acceleratory period D, point of inflection at maximum rate (in some reactions there is an appreciable period of constant rate) E, deceleratory (or decay) period and F, completion of reaction.

A particle size effect has been detected by Chou and Olson [486] in the isothermal decomposition of isothiocyanatopentammine cobalt(III) perchlorate. Below a = 0.09, the larger crystals decompose relatively more rapidly than the smaller, whereas for a > 0.09, the reverse is true. This behaviour was attributed to enhanced nucleation in the larger particles due to strain, but this favourable factor was later offset by the inhibiting influence of the product ammonia which accumulated in the larger crystals. 

Fig. 4. Reduced time plots, fr = (f/fo.s), for the isothermal decomposition of ammonium vanadyl oxalate using master data for the Avrami—Erofe ev equation [eqn. (6), n = 2], by the application of a method of analysis [73] described in the text. The circles are experimental measurements and the lines correspond to exact agreement with the equation. (Reproduced, with permission, from Thermochimica Acta.)...

Reference to the decomposition of KMn04 has already been made in the discussion of chain branching reactions (Chap. 3, Sect. 3.2) in which the participation of a highly reactive intermediate was postulated. This work provided a theoretical explanation of the Prout—Tompkins rate equation [eqn. (9)]. Isothermal decomposition in vacuum of freshly prepared crystals at 473—498 K gives symmetrical sigmoid a time curves which are described by the expression... 

The predominant gaseous products of the decomposition [1108] of copper maleate at 443—613 K and copper fumarate at 443—653 K were C02 and ethylene. The very rapid temperature rise resulting from laser heating [1108] is thought to result in simultaneous decarboxylation to form acetylene via the intermediate —CH=CH—. Preliminary isothermal measurements [487] for both these solid reactants (and including also copper malonate) found the occurrence of an initial acceleratory process, ascribed to a nucleation and growth reaction. Thereafter, there was a discontinuous diminution in rate (a 0.4), ascribed to the deposition of carbon at the active surfaces of growing copper nuclei. Bassi and Kalsi [1282] report that the isothermal decomposition of copper(II) adipate at 483—503 K obeyed the Prout—Tompkins equation [eqn. (9)] with E = 191 kJ mole-1. Studies of the isothermal decompositions of the copper(II) salts of benzoic, salicylic and malonic acids are also cited in this article. 

Isothermal Decomposition Studies. An exotherm was not detected in any of the isothermal experiments that were conducted at various isotherms ranging from 100 to 225 °C. This was true even after extended periods of time and at a temperature only 21 C below the onset of the exothermic reaction as determined by the standard ARC experiments (see Table I). However, significant pressure accumulations were detected at Isotherms as low as 140 °C. In fact. 

Figure 2. Pressure profile of isothermal decomposition of 4,4 -methylene diphenyl diisocyanate.

Figure 3. Carbon Dioxide Evolution from Isothermal Decomposition of MDI at 225 °C.

Table III. Summary of Zero-order Rate Constants for the Isothermal Decomposition of MDI in terms of CO2 Evolution...

ABAQUS, description, 123 Accelerating-rate calorimetry advantages and disadvantages, 428-429 experimental procedure, 429-430 hazard evaluation on MDl, 43lr isothermal decomposition studies, 431-432,433/ use in assessment of hamrds of chemicals, 428... 

In dynamic systems we may have the situation where a series of runs have been conducted and we wish to estimate the parameters using all the data simultaneously. For example in a study of isothermal decomposition kinetics, measurements are often taken over time for each run which is carried out at a fixed temperature. 

These surface kinetics studies initially focused on the dissociation of NO. For instance, Comelli and co-workers reported on the kinetics of the isothermal decomposition of NO on Rh(110) at temperatures ranging from 198 to 240 K and NO coverages below 0NO 0.3 ML [45], Auger electron spectroscopy (AES) lineshape analysis was used to measure the amount of undissociated NO as a function of time, and the resulting 0NO(t)... 

Hofer, L. J. E., Cohn, E. M., and Peebles, W. C. 1949. Isothermal decomposition of the carbide in a carburized cobalt Fischer-Tropsch catalyst. J. Phys. Coll. Chem. 53 661-69. 

The effect of catalytic metal chloride additives on the kinetics of isothermal decomposition of LiAlH in a Sieverts-type apparatus has been studied by a few research groups and the results seem to be rather contradictory. 

D. Blanchard, H.W. Brinks, B.C. Hauback, P. Norby, J. Muller, Isothermal decomposition of LiAlD with and without additives , J. Alloys Compd. 404 06 (2005) 743-747. 

Alternatively, the decomposition can be followed isothermally (at a controlled temperature), again by measuring the rate of gas production. Figure 2.4 shows a typical result for isothermal decomposition. 

Fig. 14.4 Isothermal decomposition of lepidocrocite (specific surface area 14 m g ) in vacuum. (Giovanoli. Brutsch, 1975 with permission)...

Kinetics of isothermal decompn of K perchlorate) 3) Inst of Study of Rate Processes, Univ of Utah, "The Isothermal Decomposition of Tetryl and Hydrazine Nitrate , TechRept No XL111 (Dec 1954) Contract N7-onr-45107 4) R.M. 

No other expl examined by Cook et al (up to 1958) exhibited the "autostabilization effect, as did EDNA (Ref 1, pp 175-78). Fig 8.3, p 176 of Ref 1 shows the curves of first-order followed by autostabilization isothermal decomposition in EDNA at different temperatures and Fig 8.4, p 177 shows the curves autocatalyzed isothermal decomposition of PETN at different temperatures Refs 1) Cook (1958), 175-78 2) Dunkle s... 

Under isothermal decomposition, he states that it is difficult to maintain isothermal conditions in such strongly exothermic reactions as are involved in the thermal decomposition of explosives owing to their tendency for selfheating. One is also concerned with. the elimination (or minimization) of temperature transients in bringing the sample to the predetermined temp of the experiment. After a brief description of experiments of A.J.B. Robertson and of A.D. Yoffe, conducted in England, the quartz spring apparatus designed by M.A. Cook ... 

The (first-order) isothermal decomposition rate constant of expls can be expressed as ... 

Specific Rate Constants for Assumed First-Order Isothermal Decomposition... 

Decomposition reactions are solid-gas reactions which do not involve diffusional transport through the solid. Their reaction rates are determined by surface kinetics and possibly pore diffusion. The assumption of local equilibrium is not valid. The course of an isothermal decomposition is schematically illustrated in Figure 15-15. There is often an induction period followed by a rapid increase in relative yield until, after the inflection point, the reaction eventually ceases (the yield will not always be 100%). Since atomic transport in crystals is normally not involved in these decomposition reactions, we shall restrict ourselves to a few comments only. 

Fig. 3 illustrates the Na2B407 content of the samples containing about 2.50 wt.% Ca2+ taken from the batch calculator at different stages during isothermal decomposition conducted at various temperatures. The total Na2B4C>7 content of samples increased with increasing calcination tem-... 

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