Authors:J. Walczak, I. Rychlowska-Himmel, and P. Tabero
The reaction mechanism of the synthesis of Fe8V10W16O85 was studied by means of XRD, IR spectroscopy and DTA techniques. It was found that the intermediate in the reaction may be
either FeVO4 or FeVO4 admixed with an unidentified phase X, depending on the reaction temperature. The IR spectrum of the phase Fe8V10W16O85 is reported for the first time.
Two kinds of compensation mechanism are suggested: a genuine one due to thermodynamic factors and a pseudo one arising from
experimental or data-processing artifacts. It is computationally demonstrated that the choice of reaction mechanism strongly
influences the kinetic parameters determined in thermal analytical studies. It is further shown that the kinetic parameters
determined at different heating rates by using a pseudo reaction mechanism exhibit kinetic compensation that gives the temperature
of the experiment as the so-called isokinetic temperature. A rule of thumb relating to the magnitude of the isokinetic temperature
is suggested to differentiate genuine compensation from pseudo compensation.
Thermogravimetry is often used to study polymer degradation. Most often the information obtained may have some practical application
but is of limited value for the determination of fundamental processes which may be occurring. A kinetic expression or activation
parameters for a complex process which may involve consecutive or parallel reactions provides almost no information about
any of the reactions that might be occurring. However, for single, well-defined processes, thermogravimetry, in conjugation
with other analytical methods, can be effectively utilized in the determination of reaction mechanism. The thermal degradation
of vinylidene chloride barrier polymers corresponds to the elimination of hydrogen chloride initiated at an allylic dichloromethylene
unit in the mainchain. This process is uncomplicated by competing reactions.
Thermogravimetry may be utilized to obtain meaningful rate constants and activation parameters for the degradation. This in
conjunction with mass spectral analysis of evolved gas, characterization of both the polymer and degradation residue by ultraviolet,
infrared and 1H and 13C NMR spectroscopy, and the study of model compounds has permitted a detailed description of the degradation process. General
purpose poly(styrene) is a commodity polymer widely used in the food packaging industry as well as many others. If processed
at excessively high temperature, it undergoes thermal degradation to expel styrene monomer which can impart negative flavor
and aroma characteristics to packaged food items. The degradation reaction has been fully detailed using thermogravimetry
in conjugation with evolved gas analysis, size exclusion chromatography and NMR spectroscopy.
Authors:Zhong-Suo Liu, Qi Wang, Zong-Shu Zou, and Guang-Lei Tan
(O) is formed, while CO 2 is reduced to CO. Then, C f (O) is broken into CO. This is the slowest step of the reaction. Chen et al. [ 3 ] also proposed a reactionmechanism for carbon gasification. They considered that, in addition to C f , CO 2 is
Authors:Tugba Davran-Candan, Mehtap Demir, and Ramazan Yildirim
activity and selectivity at temperatures near the operating temperature of proton exchange membrane (PEM) fuel cells [ 1 – 5 ]. Despite the extensive research carried out in the field, controversies still remain related to the reactionmechanism and the
An established DTA/T/EGD/GC on-line coupled simultaneous technique and relevant equipment were applied to identify the micro
impurity minerals—pyrite and siderite in two kinds of dolomite in air and N2. The proportional five-component mixed minerals (siderite, kaolinite, dolomite, calcite and quartz) and the proportional
six-component mixed minerals (pyrite and the above five minerals) were detected in N2 and in air/CO2 (1∶1) separately by applying DTA/EGD/GC and DTA/GC. The experimental results provide the basis for demonstration of the reaction
mechanism of thermal decomposition of various gas—solid-phase minerals in N2 and air/CO2. The compositions of six-component mixed minerals can be distinguished individually from the DTA/GC curves; reliable results
There are two different opinions in the literature on the combustion mechanism of the Si-Pb3O4 system. Differential thermal analysis, X-ray diffraction and infra-red spectroscopy have been used to examine the thermal
behaviour of the mixture to characterize its combustion products and judge the validity of both proposed reaction paths.
It was concluded from the results that the Si-Pb3O4 system exhibits rather complicated reaction mechanism including both gas-solid and solid-solid (proceeding below oxidant
decomposition temperature) reactions whose importance depends on the fuel content of the mixture.
Various alkylammonium, dialkylammonium, trialkylammonium and tetraalkylammonium tetraphenylborates were prepared. The thermal
decomposition curves of RNH3BPh4, R2NH2BPh4, R3NHBPh4 and R4NBPh4 (whereR=Me, Et,n-Bu) in nitrogen atmosphere indicate that the elimination of volatile matter leads to the formation of both 1∶1 complex of
trialkylamino triphenylborane and dialkylamino diphenylborene. Further elimination of volatile matter leads to the formation
of borazine at 600–680°C. When borazine is further heated at 980–1090°C an exothermic change indicates the polycyclic condensation
of the borazine leading to the formation of boron nitride. The volatile matter evolved in these reactions was measured quantitatively
and reaction mechanisms were suggested.
A theoretical approach has been used to show that, except for certain types of reaction mechanism, the ease with which it
is possible to distinguish the form of the reaction mechanism by the reduced-time plot method depends particularly on the
rate of transfer of heat into the sample. The original reduced-time plots  were calculated from model equatioons which
assume that the sample is, from the outset, at a fixed temperature and remains under isothermal conditions throughout the
reaction. The variations produced in the appearance of reduced-time plots when the sample is programmed to rise to a given
fixed temperature through various temperature schedules have been investigated. It is shown that even relatively rapid temperature
rises can produce distortion of the reduced-time plots for various reaction equations. If the reaction mechanism is known,
however, fairly accurate values of the activation energy for the reaction can be determined, even when the furnace used has
relatively poor heat-transfer characteristics.