Isothermal decomposition studies

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. 

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... 

Bel kova, Aleksenko, and Serebrennikov93 reported an isothermal decomposition study of several rare-earth perchlorates in which weight loss was measured under flowing nitrogen. The stoichiometry of all the salts could be represented by... 

Isothermal Decomposition Studies Following Rapid Heating... 

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. 

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)... 

Aryafar, M. and Zaera, F. (1998) Isothermal kinetic study of the decomposition of nitric oxide over Rh(lll) surfaces , J. Catal., 175, 316. 

Thirunavukkarasu, K., Thirumoorthy, K., Libuda, J. et al. (2005) Isothermal kinetic study of nitric oxide adsorption and decomposition on Pd(lll) surfaces Molecular beam experiments , J. Phys. Chem. B, 109, 13283. 

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. 

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. 

Following preliminary DSC studies, isothermal decompositions of small quantities (1-3 mg) of compound are performed at temperatures generally below the observed DSC exothermic maximum. Samples are usually thermolyzed in sealed Pyrex tubes. Use of Pyrex usually precludes reaction with the container that often occurs with metal reaction vessels. Sealed vessels also prevent corrosive decomposition products, e.g. NO2 or HF, from damaging laboratory instrumentation. Sealed reaction vessels confine the decomposition products where they can easily be identified and quantified. It is obvious that highly reactive decomposition products such as formaldehyde are not observed by this technique, but they would not be expected to survive over the time of these decomposition experiments (seconds to hours, depending on the temperature). Seal vessel thermoylses mimic real storage scenarios where the sample is self-confined. However, autocatalysis may occur in sealed vessels that would not be observed in open ones. On the other hand, in unsealed tubes sublimation of the sample may become competitive with decomposition. 

Non-isothermal kinetic studies [69] of the decomposition of samples of nickel oxalate dihydrate doped with Li and Cr showed no regular pattern of behaviour in the values of the Arrhenius parameters reported for the dehydration. There was evidence that lithium promoted the subsequent decomposition step, but no description of the role of the additive was given. 

In a thermogravimetric investigation of the products of reaction between NaHCOj and HjOj, Firsova et al. [158] concluded that NajCOj.l.SHjOj decomposed exothermically, 383 to 413 K, followed by the endothermic desorption of water. Firsova and Filatov [159] reported a gravimetric study of the isothermal decomposition of sodium and potassium peroxocarbonates (MjCjOg) within the temperature interval 373 to 413 K. These compounds are prepared by the reaction of carbon dioxide with hydrogen peroxide in the presence of alkali, e.g. ... 

Isothermal TG studies [33] of the thermal decompositions in Nj of BaOj (763 to 883 K) and SrOj (653 to 803 K) showed overall deceleratory kinetics described by the Ginstling-Brounshtein diffiision model (low a) and the first-order equation at higher nr values, is, values were 185 5 kJ mol for BaOj and 119 2 kJ mol for SrO. Non-isothermal kinetic analyses gave similar is, values for both decompositions (165 5 kJ mol ). It is suggested [33] that the rate of removal of oxygen from the peroxide by diffusion could be drastically altered by the formation of a crystalline layer of oxide on the reactant surface. 

Nakamori et al. [42] studied the isothermal decomposition of AgjO in vacuum (683 to 703 K), in ethene (409 to 418 K), in hydrogen (338 to 348 K) and in CO (265 to 283 K). All ar-time curves were sigmoid and a linear fi-ee energy relationship was found between values of ii, (403, 161, 103 and 68 kJ mol, respectively) and the enthalpy changes. The substantial influences of reactant gases on reaction temperatures unambiguously confirm the interactions of these additives with adsorbed intermediates in the oxide dissociation. 

Tanaka [45] used mass loss measurements to study the isothermal decomposition of NaHCOj between 383 and 397 K. Results fitted the Avrami-Erofeev equation, = 1.41. The value of , was 109 5 kJ mol, which was greater than the reaction enthalpy of 71.8 0.8 kJ mol. It was concluded that this is a nucleation and growth process. 

Mohamed et al. [42] have reported non-isothermal kinetic studies of the decompositions of nickel and lead acetate hydrates. They review previous studies and report analyses of reaction products. 

A kinetic study [69] of the isothermal decomposition of potassium trioxalatoferrate(III) ... 

An important effort in this investigation was the thermal decomposition study of the shales. Considerable effort has been made to find a simple kinetic model which will accurately describe the weight loss curves for non-isothermal pyrolysis at various heating rates. In the past, many researchers have proposed and tested theoretical kinetic models for this reaction Q-4), however, most attempts at finding a suitable model have been focused on finding a very accurate fit to experimental data. Successive studies have increasingly emphasized microscopic details (i.e., diffusion models, exact chemical composition, etc.) in an attempt to find a precise model to fit the weight loss curves. In this... 

In another investigation, Gallagher and Johnson (147) compared isothermal and nonisothermal methods to study the reaction kinetics of the thermal decomposition of CaC03. According to isothermal kinetics studies, the reaction... 

The second study to be described has somewhat more complexity. This study which is also due to Hofer and his associates at the U. S. Bureaii of Mines, concerns the isothermal decomposition of cobalt carbide in a Fischer-Tropscl catalyst. The carbide, CojC, had previously been reported (Hofer and Peebles, 49, 55). At moderately elevated temperatures it undergoes the reaction... 

Kinetic investigations of decomposition reactions can provide information about the reaction mechanisms and the influence of process variables such as temperature, particle size, mass of reactant, and the ambient atmosphere. They are conducted isothermally or at a fixed heating rate. In isothermal studies, the maintenance of a constant temperature represents an ideal that cannot be achieved in practice, since a finite time is required to heat the sample to the required temperature. However, isothermal decomposition kinetics are easier to analyze. The progress of the reaction is commonly measured by the weight loss and the data are plotted as the fraction of the reactant decomposed a versus time t with a defined as ... 

Vitamin C and Ion attachment mass spectrometry with a temperature-pro-grarmned direct probe allows the detection of irrtact pyrolysis products. It, therefore, offers the opportunity to monitor directly thermal byproducts on a real-time basis and potentially to detect thermally imstable products. EGA-IAMS is used to study the real-time, non-isothermal decomposition of vitamin C [30]. The results were compared with those obtained in a similar study on thermal decomposition of vitamin C using pyrolysis GC/MS. Significant differences were found between the two techniques, in terms of the nature and relative amoimts of products formed. A major difference between the two techniques was in the transportation time of the pyrolysis products out of the pyrolysis chamber (or hot zone). The time was significantly shorter in EGA-IAMS than in pyrolysis GC/MS, which reduces the occmrcnce of secondary reactions of the primary pyrolysis products. Some decomposition products formed in the EGA-IAMS system were not detected in the previous pyrolysis GC/MS study [38] and thus were detected for the first time. For instance, dehydro-L-ascorbic acid was observed as a decomposition product. This compoimd was the main degradation product detected by means of EGA-IAMS. While it is an important compoimd because it possesses some biological activity, dehydro-L-ascotbic acid is difficult to measure due to its chemical instabihty. 

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