Kinetics of thermal decomposition of the solid state

Garn, Paul D.

doi:10.1016/0040-6031(90)80254-v

Cited by 36 publications

(11 citation statements)

References 31 publications

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“…According to the heterogeneous nature of the glass transition, the traditional concept of a constant activation energy [which has already been criticized from a physical point of view (Garn, 1990)] is ill-suited for glass transition kinetics: Garn (1990) has pointed out that a constant activation energy is strictly applicable only to reactions that take place in homogeneous media. In the case of an extremely heterogeneous, hyperquenched CaO-MgO-SiO 2 glass, DSC showed the existence of two separate sub-T g relaxation peaks corresponding to two dynamically, structurally and energetically different domains (Zhang et al, 2013).…”

Section: Introductionmentioning

confidence: 99%

Structural Relaxation in Polyanionic Sodium Fluorophosphate Glasses

et al. 2019

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Structural heterogeneity is a common feature of all glasses, however, little is known about the underlying contributions of chemical fluctuations and modulations in free volume in concrete glass forming systems. In this investigation, we relate the dynamics of structural relaxation of (100-x)NaPO 3-xAlF 3 glasses to their heterogeneous structure as determined from multinuclear magnetic resonance spectroscopic analysis. For this, we evaluate differential scanning calorimetry (DSC) data using the integral isoconversional method to determine the variation in activation energy, E a , of the glass transition as a function of temperature and conversion progress. Specific heat measurements from DSC allow for the determination of the effective size of the cooperatively rearranging region (CRR). From 31 P, 19 F, and 27 Al NMR, we observe that the introduction of AlF 3 into the NaPO 3 network increases the average connectivity (i.e., the number of heteronuclear Al-O-P bonds), rationalizing the higher E a determined from the DSC measurements. We find highly constrained regions of Al(OP) 4 F 2 with Al-F-Al cross-linking (high E a) and, simultaneously, more flexible regions of phosphate chains containing P-F••(Na +) n bonds (low E a); this results in a topologically and dynamically heterogeneous structure as evidenced by the increased variability in E a with higher AlF 3 content. The decreasing size of the CRR reflects the increased heterogeneity: at low AlF 3 the CRR is large, while at high AlF 3 (high heterogeneity), the CRR is significantly smaller (by a factor of 10 3). Finally, we relate the heterogeneity to other macroscopic properties, such as T g and mechanical properties.

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Section: Introductionmentioning

confidence: 99%

Structural Relaxation in Polyanionic Sodium Fluorophosphate Glasses

et al. 2019

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“…Transfer of the strategy to heterogeneous kinetics should be promising, if the concentration is replaced by another adequate condition parameter, and if a general principle for the classification of solid-phase reactions [20][21][22][23], capable of including more than one basic process, will have been established. Indeed, a computer knows less than the experimenter and has, therefore, at least to be informed how the final consequences have to be displayed.…”

Section: Discussionmentioning

confidence: 99%

Experimentally available kinetic codes as a tool for promising data extraction in thermal analysis

Koch

1992

Journal of Thermal Analysis

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By the study of 3000 kinetic runs for all homogeneous two-step models under variation of activation and signal parameters, it has been stated that the generated Mechanistic Concentration Code ( = MCC) is the best vehicle for data extraction in Thermal Analysis. It summarises the rate-controlling steps and their molecularities, independently of their activation data and (to 80-90%) of their method-specific signal parameters. Hence, an optimum evaluation needs the internal (best-fitted) reference step, the initial concentration of a reference reactant, and equal weight of theoretical and experimental results, reached using the same algorithms. Thus, the MCC of any series measured in general allows for a reliable model determination via the distribution into all two-step models, using the tools of probability and decision theory. A transfer of the strategy to heterogeneous reactions is discussed.

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“…For the solid phase; the interpretation of kinetic studies (which are also very useful for the development of High-Tech components [6,47,48]) is much more difficult because of the influence of both transport processes and feedback effects of reactants moved into another phase [49]. An improvement of the usual kinetic strategies [12,50,51] could probably be reached using similar concepts based on standardized kinetic patterns, but using the heating rate or other transmitter parameters.…”

Section: Discussionmentioning

confidence: 99%

The ‘Theorem of common kinetic runs’ in homogeneous non-isothermal reaction kinetics

Koch¹

1992

Journal of Thermal Analysis

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The kinetic features of the fundamental homogeneous two-reaction models for linearly increasing temperature have been studied systematically by the analysis of 2500 signal curves (organized in 250 series), obtained from computer simulations and compared with numerous TA experiments.For methods based on a proportionality between the particular reaction rates and their contribution to the derivative overall signal, it has been found that characteristic behaviour sets of three order-dependent parameters which refer to definite intervals of the starting concentration in series, can be extracted from the halfwidth and shape index of the curves. Such thermoanalytical patterns agree with those obtained from the distribution lists of some thousand DTA-and UV-experiments. They are presented for the 21 most important two-step model and almost independent of the activation data and of the method-dependent proportionality factors. Therefore, they allow for the direct kinetic identification of the complex reaction involved.

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Kinetics of thermal decomposition of the solid state

Cited by 36 publications

References 31 publications

Structural Relaxation in Polyanionic Sodium Fluorophosphate Glasses

Structural Relaxation in Polyanionic Sodium Fluorophosphate Glasses

Experimentally available kinetic codes as a tool for promising data extraction in thermal analysis

The ‘Theorem of common kinetic runs’ in homogeneous non-isothermal reaction kinetics

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