Authors:J. Madarász, M. Krunks, L. Niinistö, and G. Pokol
Identification and monitoring of gaseous species released during thermal decomposition of the title compound 1, Zn(tu)2Cl2, (tu=thiourea, (NH2)2C=S) have been carried out in flowing air atmosphere up to 800°C by both online coupled TG-EGA-FTIR and simultaneous TG/DTA-EGA-MS.
The first gaseous products of 1, between 200 and 240°C, are carbon disulfide (CS2) and ammonia (NH3). At 240°C, an exothermic oxidation of CS2 vapors occurs resulting in a sudden release of sulphur dioxide (SO2) and carbonyl sulphide (COS). An intense evolution of hydrogen cyanide (HCN) and beginning of the evolution of cyanamide
(H2NCN) and isothiocyanic acid (HNCS) are also observed just above 240°C. Probably because of condensation and/or polymerization
of cyanamide vapors on the windows and mirrors of the FTIR gas cell optics, some strange baseline shape changes are also occurring
above 330°C. Above 500°C the oxidation process of organic residues appears to accelerate which is indicated by the increasing
concentration of CO2, while above 600°C zinc sulfide starts to oxidize resulting in the evolution of SO2. All species identified by FTIR gas cell were also confirmed by mass spectrometry, except for HNCS.
Identification and monitoring of gaseous
species released during thermal decomposition of pure thiourea, (NH2)2C=S
in argon, helium and air atmosphere have been carried out by both online coupled
TG-FTIR and simultaneous TG/DTA-MS apparatuses manufactured by TA Instruments
(USA). In both inert atmospheres and air between 182 and 240°C the main
gaseous products of thiourea are ammonia (NH3) and
carbon disulfide (CS2), whilst in flowing air sulphur
dioxide (SO2) and carbonyl sulphide (COS) as gas phase
oxidation products of CS2, and in addition hydrogen
cyanide (HCN) also occur, which are detected by both FTIR spectroscopic and
mass spectrometric EGA methods. Some evolution of isothiocyanic acid (HNCS)
and cyanamide (NH2CN) vapours have also observed mainly
by EGA-FTIR, and largely depending on the experimental conditions. HNCS is
hardly identified by mass spectrometry. Any evolution of H2S
has not been detected at any stage of thiourea degradation by either of the
two methods. The exothermic heat effect of gas phase oxidation process of
CS2 partially compensates the endothermicity of the
corresponding degradation step producing CS2.
Authors:T. Vlase, Gabriela Vlase, N. Doca, G. Ilia, and Adriana Fulias
The thermal behavior of Cd2+ and Co2+ vinyl-phosphonates was studied using two different experimental strategies: the coupled TG–EGA (FTIR) technique by decomposition
in nitrogen, respectively, air, and the kinetic analysis of TG data obtained in dynamic air atmosphere at four heating rates.
The both compounds exhibited a good thermal stability: in nitrogen, only an endothermic dehydration step was observed. In
air the Cd2+ salt presents the same dehydration step whereas by the Co2+ salt two simultaneous processes take place dehydration, respectively, thermooxidative destruction of the vinyl group. The
kinetic analysis of the TG data was performed with the Flynn–Wall–Ozawa, Friedman’s, and modified non-parametric kinetic methods.
By means of the coupled techniques, some spectroscopic arguments on the reaction mechanism were obtained. The values of the
activation energy by the three methods are in good agreement and support the two different suggested mechanism.
Authors:N. Doca, G. Vlase, T. Vlase, M. Perţa, G. Ilia, and N. Plesu
Polyaniline was obtained by oxidizing aniline in hydrochloric acid media with ammonium peroxidisulfate as oxidizing agent.
Molar ratio aniline/oxidant was 1 and aniline/acid ratio: ½, at −5 and 400 °C, respectively, 800 mL water. The both compounds
were studied using two different experimental strategies: the coupled TG-EGA (FTIR) technique by decomposition in dynamic
air atmosphere and the kinetic analysis of TG data obtained at four heating rates (5, 7, 10 and 15 K min−1). The kinetic analysis of the TG non-isothermal data was performed with the Flynn–Wall–Ozawa, Friedman’s, and modified non-parametric
kinetic (NPK) methods. By means of the coupled techniques spectroscopic arguments on the reaction mechanism were obtained,
i.e. the oxidative degradation of the quinoine ring as the first step. The values of the activation energy by the three used
methods are in good agreements. According to the NPK method, the termodegradation process consist in physical (diffusion)
and chemical steps.
Authors:N. Doca, Gabriela Vlase, T. Vlase, and G. Ilia
The thermal behavior of Cd2+ and Co2+ phenyl-vinyl-phosphonates was studied using two different experimental strategies: the coupled TG-EGA (FTIR) technique by
decomposition in nitrogen respectively air, and the kinetic analysis of TG data obtained in dynamic air atmosphere at four
heating rates. In nitrogen two decomposition steps were observed: the loss of crystallization water, respectively the decomposition
of the phenyl-vinyl radical. In air, the same dehydration was observed as the first step, but the second one is a thermooxidation
of the organic radical with formation of the pyrophosphoric anion.
The kinetic analysis of the TG non-isothermal data was performed by the isoconversional methods suggested by Friedman and
Flynn, Wall and Ozawa, as well as by the non-parametric (Sempere-Nomen) method. All processes put in evidence in TG curves
exhibit strong changes of the activation energy values with the conversion degree, which mean that these processes are complex
ones. Assuming that each of these processes consists in two steps, the application of non-parametric method leads to average
values of the activation energy close to the average values of this parameter obtained by isoconversional methods.