Authors:Y. Hui-Mei, L. Chang-Wei, Q. Ling-Jun, X. Hua-Qing, X. Tong-Geng and L. Lan
We studied the removal process of excessive free
carbon in the nano-SiC powder by TG-DTA-MS, XRD and TEM three methods. The
studies showed that the temperature of removing excessive free carbon in the
nano-SiC powder should be about 750°C in air.
The thermal decomposition of cadmium acetate dihydrate in helium and in air atmosphere has been investigated by means of a
coupled TG-DTA-MS method combined with X-ray diffraction analysis. Dehydration of Cd(CH3COO)2·2H2O is a two-stage process with Cd(CH3COO)2·H2O as intermediate. The way of Cd(CH3COO)2 decomposition strongly depends on the surrounding gas atmosphere and the rate of heating. CdO, acetone and CO2 are the primary products of decomposition in air. In helium decomposition goes by two parallel and consecutive reactions
in which intermediates, Cd and CdCO3, are formed. Metallic cadmium oxidizes and cadmium carbonate decomposes giving CdO. Some of the metallic cadmium, depending
on the heating rate and the concentration of oxygen, evaporates. Acetone is partially oxidized in secondary reactions with
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:János Madarász, Ana Brăileanu, Maria Crişan, Malina Răileanu and György Pokol
Thermal decomposition of an amorphous precursor for S-doped titania (TiO2) nanopowders, prepared by controlled sol–gel hydrolysis–condensation of titanium(IV) tetraethoxide and thiourea in aqueous
ethanol, has been studied up to 800 °C in flowing air. Simultaneous thermogravimetric and differential thermal analysis coupled
online with quadrupole mass spectrometer (TG/DTA-MS) and FTIR spectrometric gas cell (TG-FTIR) have been applied for analysis
of released gases (EGA) and their evolution dynamics in order to explore and simulate thermal annealing processes of fabrication
techniques of the aimed S:TiO2 photocatalysts with photocatalytic activities under visible light. The precursor sample prepared with thiourea, released
first water endothermically from room temperature to 190 °C, carbonyl sulfide (COS) from 120 to 240 °C in two stages, ammonia
(NH3) from 170 to 350 °C in three steps, and organic mater (probably ether and ethylene) between 140 and 230 °C. The evolution
of CO2, H2O and SO2, as oxidation products, occurs between 180 and 240 °C, accompanied by exothermic DTA peaks at 190 and 235 °C. Some small
mass gain occurs before the following exothermic heat effect at 500 °C, which is probably due to the simultaneous burning
out of residual carbonaceous and sulphureous species, and transformation of amorphous titania into anatase. The oxidative
process is accompanied by evolution of CO2 and SO2. Anatase, which formed also in the exothermic peak at 500 °C, mainly keeps its structure, since only 10% of rutile formation
is detected below or at 800 °C by XRD. Meanwhile, from 500 °C, a final burning off organics is also indicated by continuous
CO2 evolution and small exothermic effects.
Authors:Kairi Otto, Petra Bombicz, János Madarász, Ilona Oja Acik, Malle Krunks and György Pokol
atmospheres by simultaneous thermogravimetric and differential thermal analysis coupled online with quadrupole mass spectrometer (TG/DTA-MS) or FTIR spectrometric gas cell (TG-FTIR).
Preparation of samples
Degradation of relatively large particle size, 0.5 mm of Type-G PMMA (Rohm and Haas) were conducted with thermogravimetric
analysis and evolved gas measurements using quadrupole mass spectrometer under conditions of mass transport limitation. In
addition, differential thermal analysis was performed in order to furnish information with regards to exothermic or endothermic
reactions associated with the degradation. The tests were conducted in an inert environment of pure N2 and oxygenated environment. The results indicated one step degradation process in pure N2 and the degradation process is endothermic. As the O2 fraction increases the degradation process is transformed to exothermic.
Thermogravimetric analysis in conjunction with evolved gas analysis are discussed for powder PMMA, particle diameter of 0.1
mm. Furthermore, differential thermal analysis measurements were performed in both pure nitrogen and oxidative environment.
These measurements are conducted to assess major differences associated with particle size. The results indicated for powder
PMMA, in pure nitrogen the degradation can be described as three-step reactions, while in oxidative environment it is two-step
reactions. Furthermore the reaction in both environments are mainly endothermic. This in contrast to results reported for
industrial-grade PMMA with relatively larger particle size of 0.5 mm.
The thermal decomposition of FeSO46H2O
was studied by mass spectroscopy coupled with DTA/TG thermal analysis under
inert atmosphere. On the ground of TG measurements, the mechanism of decomposition
of FeSO46H2O is:
i) three dehydration steps
ii) two decomposition
The intermediate compound was identified as Fe2(SO4)3 and the final product as the hematite Fe2O3.
Analytically pure nickel(II)- and cobalt(II)-acetylacetonate were used to prepare several addition compounds with Lewis-bases (2-picoline-N-oxide, 4-picoline-N-oxide, pyridine-N-oxide) in order to investigate their thermal stability in oxidative atmospheres. Comparison of the thermoanalytical TG-DTA data of the chelates with those on the adducts showed similarities in thermal degradation. A fragmentation pattern observed on simultaneous mass spectrometric investigation is discussed. Elimination of ligand or base molecules corresponding quantitatively to the estimated mass loss values from the TG-curves has been demonstrated.