Thermal behaviour of arsenic oxides (As2O5 and As2O3) and the influence of reducing agents (glucose and activated carbon)

In this paper the thermal behaviour of pure arsenic oxides (As₂O₅.aq and As₂O₃) and the influence of the presence of reducing agents (glucose or activated carbon) on the thermal behaviour of the arsenic oxides are studied through thermogravimetric (TG) analysis.The TG experiments with pure As₂O₅.aq reveal that the reduction reaction As₂O₅→As₂O₃+O₂ does not take place at temperatures lower than 500 °C. At higher temperatures decomposition is observed. Pure As₂O₃, however, is already released at temperatures as low as 200 °C. This release is driven by temperature dependent vapour pressures.Comparing these results with earlier observations concerning the thermal behaviour of chromated copper arsenate (CCA) treated wood, suggests that wood, char and pyrolysis vapours form a reducing environment that influences the thermal behaviour of arsenic oxides. Therefore, the influence of the presence of reducing agents on the thermal behaviour of As₂O₅.aq is studied. First, TG experiments are carried out with mixtures of As₂O₅ and glucose. The TG and DTG curves of the mixture are not a simple superposition of the curves of the two pure constituents. The interaction between As₂O₅.aq and glucose results in a faster decomposition of arsenic pentoxide. This effect is more pronounced if the purge gas nitrogen is mixed with oxygen. Second, TG experiments are performed with mixtures of As₂O₅ and activated carbon. The presence of activated carbon also promotes the volatilisation of arsenic for temperatures higher than 300 °C, probably through its reducing action.Extrapolation of the thermal behaviour of these model compounds to the real situation of pyrolysis of CCA treated wood confirms the statement that the reduction of pentavalent arsenic to trivalent arsenic is favoured by the reducing environment, created by the presence of wood, char and pyrolysis vapours.     

Thermal stability of several polyaniline/rare earth oxide composites III

Polyaniline/Nd₂O₃ (PANI/Nd₂O₃) composites were synthesized by in situ polymerization at the presence of sulfosalicylic acid (as dopant). The composites obtained were characterized by Fourier transform infrared spectra (FTIR) and X-ray diffraction (XRD). The thermal stability of the composites was investigated by thermogravimetry (TG) and derivative thermogravimetry (DTG). The electrochemical performance of the composites was investigated by cyclic voltammetry (CV). The results of FTIR, XRD, and CV show that the structure of composite has changed greatly when Nd₂O₃ content is ≥0.7 g and the PANI in the composite has transformed into pernigraniline base (non-conducting state) from emeraldine base (conducting state). TG–DTG analysis indicates that the thermal stability of PANI/Nd₂O₃ composites was higher than the pure PANI.     

Effect of accelerated thermal ageing on the thermal behaviour of the recently made parchments

To reveal the fire injuring of parchment, the changes in the thermal behaviour of some goat parchments, obtained from skins originating from different animals, as a result of thermal aging were determined by thermal analysis methods (DSC; simultaneous TG/DTG, DSC; micro hot table (MHT)). Thermal aging of parchments was revealed to bring about the decrease in shrinkage temperature, absolute value of enthalpy of denaturation in water and some changes in non-isothermal parameters characteristic for dehydration process in static air atmosphere. The results obtained by DSC analysis performed in N₂ and O₂ flows as well as those obtained by simultaneous TG/DTG, DSC analyses have shown that both softening (melting) process parameters and parameters of thermo-oxidative processes have not been changed by thermal ageing. The results obtained by thermal analysis methods were correlated with those obtained by microscopic investigation of parchment samples immersed in water and scanning electron microscopy (SEM). The application of these microscopic techniques has revealed the morphology changes in the investigated parchments as a result of thermal degradation.     

A study of the compounds present in the three-component system Dy2O3-SeO2-H2O at 100°C

The solubility isotherm of the system Dy₂O₃-SeO₂-H₂O at 100°C was studied and drawn. The selenites present in the system were identified and isolated. A thorough TG, DTG and DTA analysis was made. By modelling the conditions of TG, DTG and DTA analysis, the phases of the thermal decomposition were isolated and identified. The chemistry of the reaction was described.     

Potassium Ferrites Formation in Promoted Hematite Catalysts for Dehydrogenation. Thermal and structural analyses

K-promoted hematite catalysts for ethylbenzene dehydrogenation were studied by thermal analysis (TG/DTG) and high-temperature XRD. The formation of potassium ferrite (K₂Fe₂O₄), considered to be a catalytically active phase, was observed during calcination of the Ce-promoted catalysts. A linear correlation of the catalytic activity and the temperature of potassium ferrites formation was found. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal decomposition of lanthanide(III) complexes of bis-(salicylaldehyde)-1,3-propylenediimine Schiff base ligand

The thermal decomposition of lanthanide complexes, with a general formula: [LnL(NO₃)₂](NO₃), where Ln = La, Pr, Nd, Sm, Gd, Tb, Dy, and Er; and L = bis-(salicyladehyde)-1,3-propylenediimine Schiff base ligand, was studied by thermogravimetric (TG) and derivative thermogravimetric (DTG) techniques. The TG and DTG data indicated that all complexes are thermostable up to 398 K. The thermal decomposition of all Ln(III) complexes was a two-stage process and the final residues were Ln₂O₃ (Ln = La, Nd, Sm, Gd, Dy, Er), Tb₄O₇, and Pr₆ O₁₁. The activation energies of thermal decomposition of the complexes were calculated from analysis of the TG-DTG curves using the Kissinger, Friedman, and Flynn-Well-Ozawa methods.     

Thermal behavior of some new complexes bearing ligands with polymerisable groups

This paper reports the investigation of the thermal stability of a series of new complexes with mixed ligands of the type M(dipy)(C₃H₃O₂)₂(H₂O)_y ((1) M: Mn, y=1; (2) M: Ni, y=2; (3) M: Cu, y=1; (4) M: Zn, y=2; dipy: 2,2’-dipyridine and C₃H₃O₂ is acrylate anion). The thermal behaviour steps were investigated. The thermal transformations are complex processes according to TG and DTG curves including dehydration, oxidative condensation of acrylate and thermolysis processes. The final products of decomposition are the most stable metal oxides.     

Preparation of Mixed Co and Cu Oxides via Thermal Decomposition of Their Oxalates,and Study of Their Catalytic Properties

Mixed oxides were prepared by the thermal decomposition of the oxalates of cobalt(II) and copper(II) coprecipitated from aqueous solution or made by mechanical mixing. The compositions and structures of the oxides were confirmed by means of TG and X-ray powder diffraction spectroscopy. The catalytic behaviour of the oxides obtained was studied by using the decomposition of H₂O₂ as a model reaction. The results were compared with those on the oxides produced from the thermal decomposition of mechanically mixed oxalates. The catalytic activities of the mixed oxides were found to be lower than that of pure cobalt oxide, but higher than that of copper oxide. This result was interpreted in terms of the relative standard reduction potential of the catalyst as compared with that of H₂O₂. The catalytic activity of the mixed oxides obtained from the coprecipitate was found to be lower than that of the oxides obtained from the mechanical mixture at the same temperature. As the temperature of preparation was increased, the catalytic activities of the oxides obtained decreased. This was attributed to the solid-solid interactions, which gave a new phase with lower catalytic activity than those of the interacting phases. This revised version was published online in July 2006 with corrections to the Cover Date.     

Some new acrylate complexes as a criterion in their selection for further co-polymerization reaction

Summary This paper reports the investigation of the thermal stability of a series of new complexes with mixed ligands of the type M(phen)(C₃H₃O₂)₂(H₂O)_y ((1) M=Mn, y=0; (2) M=Ni, y=2; (3) M=Cu, y=1; (4) M=Zn, y=2; phen=phenanthroline and C₃H₃O₂ is acrylate anion). The thermal behaviour steps were investigated. The thermal transformations are complex processes according to TG and DTG curves including dehydration, oxidative condensation of acrylate and thermolysis processes. The final products of decomposition are the most stable metal oxides.     

Thermal behaviour of fumaric acid, sodium fumarate and its compounds with light trivalent lanthanides in air atmosphere

Characterization, thermal stability and thermal decomposition of light trivalent lanthanide fumarates, as well as, the thermal behaviour of fumaric acid and its sodium salt were investigated employing simultaneous thermogravimetry and differential thermal analysis, differential scanning calorimetry, Fourier transform infrared spectroscopy (FTIR), TG?CFTIR techniques, elemental analysis and complexometry. On heating, sublimation of fumaric acid is observed, while the thermal decomposition of the sodium fumarate occurs with the formation of a mixture of sodium carbonate and carbonaceous residue. The thermal decomposition of light trivalent lanthanide fumarates occurs in consecutive and/or overlapping steps with the formation of the respective oxides: CeO₂, Pr₆O₁₁, and Ln₂O₃ (Ln?=?La, Nd, Sm, Eu, Gd).     

Use of Methods of Thermal Analysis in Studying Ceramic Materials on the Basis of Al2O3, ZrO2, Si3N4, SiC and Inorganic Binder

By thermoanalytical methods TG, DTG, DTA there have been investigated the processes occurring during the formation of ceramic materials on the basis of Al₂O₃, ZrO₂, Si₃N₄, SiC,and inorganic binder. IR spectroscopy has been an additional research method. It's been determined that with the use of H₃PO₄ as the binder for ceramic materials, the mechanisms of thermal decomposition are connected with the following processes: 1. removal of weakly tied and crystallized water in the temperature range of120–230°C, the removal being characterized by the endothermic effect, 2. interaction of the initial powder components of the ceramic materials with orthophosphoric acid conditioned by a strong exothermic effect on the DTA curve in the range of 230–530°C, 3. overlapping of endo- and exo-effects, testifying to a complex mechanism of thermal transformations, 4.oxidizing of the non-reacted silicon at the temperature of 720(760)°C, an increase of mass is observed on the TG curve as a result of the formation of SiO₂ – crystoballite. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal decomposition kinetics of Schiff base complexes of copper(II) and palladium(II)

Thermogravimetric (TG), derivative thermogravimetric (DTG) and differential thermal analysis (DTA) curves of CuL₂ and Pd(LH)₂Cl₂ (LH=salicylidene-2-aminofluorene and 2-hydroxy-1-naphthalidene-2-aminofluorene) in air are studied. Mass loss considerations at the main decomposition stages indicate conversion of the complex to oxides. Mathematical analysis of TG data shows that first order kinetics are applicable in all cases. Kinetic parameters (energy and entropy of activation and preexponential factor) are reported.     

Electrical conductivity measurements during the thermal decomposition reaction of ammonium metavanadate

Electrical conductivity vs. temperature curve shows all characteristic peaks due to individual stages of the thermal decomposition reaction of NH₄VO₃, including the stage of formation of the anhydrous ammonium divanadate at ～150°, obtainable only under special experimental conditions on TG, DTG, and DTA curves. It is suggested that such measurements can be used for detecting and/or confirming the existence of intermediate solid products of decomposition in case they are difficult to be identified.     

Thermal decomposition of the biguanide complexes of the 3d-transition metals

The thermal decomposition (TG, DTG and DTA) of the complexes of biguanide with the following metals was studied: V, Cr, Mn, Co, Ni, Cu and Zn. Structural water, when present, is first eliminated at ～100–150°C; this is followed by a main decomposition state at ～300–350°C. Pyrolytic residues are analysed and characterised by their x-ray powder diffraction patterns and are found to be the oxides V₂O₅, Cr₂O₃, Mn₃O₄, Co₃O₄, NiO, CuO and ZnO, respectively. The decomposition curves of the free ligand (biguanide) and biguanide sulphate are also given. The decomposition characteristics are discussed.     

Study of thermal behaviour of some edible mushrooms

This paper is aimed to analyse the thermal behaviour in air of edible mushrooms through nonisothermal (TG, DTG, DTA) and calorimetric (Berthelot calorimeter) methods. The studied mushrooms were Pleurotus ostreatus spontaneously grown and from culture and Agaricus bisporus from culture, currently used in alimentation but insufficiently investigated from this point of view. The analysis of TG–DTG–DTA curves has indicated that the degradation mechanism is complex and characteristic to every species and major differences between the cap and the stipe of investigated mushrooms have not been recorded. These species are thermally stable in the range of 30–160 °C. The thermal stability in terms of initial degradation temperature (T _i °C) and the temperature corresponding to the conversion grade (T _α=0.03 °C) indicate that the stipe has a thermal stability close to the cap one and that the cultivated mushrooms are more thermally stable than those spontaneously grown. The obtained results concerning the combustion of the sample using Berthelot calorimeter are in accordance with the TG–DTG–DTA analysis. The residue obtained is a measure of the mineral content and is quantitatively close.     

Thermal behaviour of synthetic pyroaurite-like anionic clay

Thermal behaviour of synthetic pyroaurite-like anionic clay with molar ratio Mg/Fe=2 was studied in the range of 60-1100°C during heating in air. TG/DTA coupled with evolved gas analysis, emanation thermal analysis (ETA), surface area measurements, XRD, IR and Mössbauer spectroscopy were used. Microstructure changes characterized by ETA were in a good agreement with the results of surface area measurements and other methods. After the thermal decomposition of the pyroaurite-like anionic clay, which took place mainly up to 400°C, a predominantly amorphous mixture of oxides is formed. A gradual crystallization of MgO (periclase) and Fe₂O₃ (maghemite) was observed at 400-700°C by XRD. The MgFe₂O₄ spinel and periclase were detected at 800-1100°C. The spinel formation was also confirmed by Mössbauer spectroscopy.     

Thermal decomposition of rare-earth trioxalatocobaltates

The thermal decomposition of rare-earth trioxalatocobaltates LnCo(C₂O₄)₃ · x H₂O, where Ln  La, Pr, Nd, has been studied in flowing atmospheres of air/oxygen, argon/ nitrogen, carbon dioxide and a vacuum. The compounds decompose through three major steps, viz. dehydration, decomposition of the oxalate to an intermediate carbonate, which further decomposes to yield rare-earth cobaltite as the final product. The formation of the final product is influenced by the surrounding gas atmosphere. Studies on the thermal decomposition of photodecomposed lanthanum trioxalatocobaltate and a mechanical mixture of lanthanum oxalate and cobalt oxalate in 1 : 2 molar ratio reveal that the decomposition behaviour of the two samples is different. The drawbacks of the decomposition scheme proposed earlier have been pointed out, and logical schemes based on results obtained by TG, DTA, DTG, supplemented by various physico-chemical techniques such as gas and chemical analyses, IR and mass spectroscopy, surface area and magnetic susceptibility measurements and X-ray powder diffraction methods, have been proposed for the decomposition in air of rare-earth trioxalatocobaltates as well as for the photoreduced lanthanum salt and a mechanical mixture of lanthanum and cobalt oxalates.     

Dependence of lithium–zinc ferrospinel phase composition on the duration of synthesis in an accelerated electron beam

Kinetic changes in the phase composition of the Li₂CO₃?CFe₂O₃?CZnO system are investigated by the methods of X-ray phase and TG/DTG analysis. The powder mixture components were in the ratio corresponding to Li_0.4Fe_2.4Zn_0.2O₄ ferrite. The synthesis was performed by thermal heating of mixture reagents in a furnace and heating of the mixture upon exposure to high-power beam of accelerated electrons with energy of 2.4?MeV. It is demonstrated that the sequence of phase formation is independent of the heating method. The radiative effect of synthesis intensification is most strongly manifested in the initial stage of forming lithium monoferrite phases. The rate of diffusion interaction of intermediate phases also increases upon exposure to the electron beam in the stage of end-product formation.     

Thermal behaviour of new N,N-dimethylbiguanide complexes having selective and effective antibacterial activity

The complexes of the type M(HDMBG)₂(CH₃COO)₂·nH₂O ((1) M:Mn, n=1.5; (2) M:Ni, n=0; (3) M:Cu, n=2; (4) M:Zn, n=2; DMBG: N,N-dimethylbiguanide) present in vitro antimicrobial activity. The thermal analysis has evidenced the thermal intervals of stability and also the thermodynamics effects that accompany them. The different nature of the ligands generates a different thermal behaviour for the complexes. The thermal transformations are complex processes according to TG and DTG curves including dehydration, oxidative condensation of –C=N– units as well as thermolysis processes. The final products of decomposition are the most stable metal oxides.     

Sol–gel combustion synthesis and characterization of nanostructure copper chromite spinel

Nanocomposite copper chromite spinel was fabricated by sol–gel process using copper nitrate trihydrate, chromium nitrate nonahydrate, ethylene glycol, diethyl ether, and citric acid. The thermoanalytical measurements (TG–DTG), X-ray powder diffractometry (XRD), field emission scanning electron microscopy (FESEM), and energy dispersive X-ray analysis were used to characterize the structural and the chemical features of the nanocomposites. TG–DTG results showed that the major mass loss for copper(II) nitrate, chromium(III) nitrate as precursors occur at 258 and 140 °C, respectively. The major mass loss for dried gel of copper chromite occurs at 310 °C. XRD data revealed the formation of pure copper chromite after thermal decomposition at 1,000 °C for 2 h. The observation of XRD patterns reveals the presence of single-phase tetragonal spinel CuCr₂O₄. FESEM analysis of calcined composite was found to be in the range of 20–30 nm.