Thermal and structure analysis of FeSO4·H2O-BaO2 mixtures

Investigations on the thermal decomposition of FeSO₄·H₂O-BaO₂ mixtures were carried out under isothermal conditions by using simultaneously solid electrolyte cell (EMF-method). Evoked interactions producing oxygen in the temperature range 553-673 K were established by means of a solid electrolyte oxygen analyzer. Based on Mössbauer spectroscopy data and X-ray analysis it was proved that these reactions were associated with the release of oxygen from barium peroxide, oxidation of ferrosulphate-monohydrate to FeOHSO₄, and formation of barium ferrites such as BaFe₂O₄ and BaFe₁₂O₁₉.     

Effect of P2O5 content in phosphogypsum on its thermal decomposition to CaCO and SO2

The effect of P₂O₅ on the thermal decomposition of phosphogypsum to phospholime and sulphur dioxide has been studied.

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Zusammenfassung Es wurde der Einfluß von P₂O₅ auf die thermische Zersetzung von Phosphogips zu Phospholim und Schwefeldioxid untersucht.

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Modification of asbestos by siliconates

The ability of some siliconates to hydrophobize and modify the surface of different kinds of asbestos was studied. A 6 wt% aqueous solution of potassium methylsiliconate was used in various quantities. After treatment, the asbestos samples were analysed by IR-spectroscopy, TG-DTA and electron microscopy. Structural changes were found on the asbestos surface, including the appearance of chemical bonds. The studies revealed that the sorption and lyophilic properties of asbestos are lowered, these being the basic preconditions for its injurious action on health.     

Thermal Analysis for Control of the Properties of Mineral Fertilizers

The development of equipment for thermal analysis has opened up new areas for applications in science, industrial practice and environment studies. On the basis of the literature and information from equipment producers, the directions for the use of thermal analysis in research and practice are classified. Special attention is paid to the possibilities of controlling environmental pollution, and the stability and other properties of intermediate and final industrial products. It is stressed that DSC and DTA systems can be successfully applied to determine enthalpy changes in raw materials and products as control tests for their application. The advantages of coupled thermal systems for complex studies and the control of raw materials, products and wastes are described. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermochemical investigations of natural phosphate with ammonium sulfate additive

Summary The free energy of the acidic ammonium sulfate is a good precondition its use as an additive or reagent for decomposition of natural phosphates on the way to obtain NPS or NPKS complex fertilizers. During our previous studies it was confirmed that as a result of thermo-mechanical treatment new solid phases are formed as a result of the phosphates decomposition. The aim of this study is to find out appropriate conditions for thermal treatment of Tunisia phosphorite with ammonium sulfate where the content of P₂O₅ soluble forms has its maximum. The process was investigated under dynamic thermal conditions. Structure and phase transformations of the mixtures to intermediate and final solid products are confirmed by different techniques. X-ray powder diffraction, infrared spectroscopy and electron microscopy have been applied successfully and relationship found between phase structure and thermal treatment applied. As a result of the complex studies optimal temperatures are determined. The solid products under optimal conditions contain phosphorous in soluble forms available for plants in the soil. As a final it is concluded that the final products could be used as complex mineral fertilizers.     

Mechanism and kinetics of inorganic sulphates decomposition

Thermal decomposition of different inorganic sulphates are presented. A number of techniques, but mainly TG and DTA, are used to prove the mechanism and kinetics of CaSO₄, BaSO₄, FeSO₄·xH₂O, Al₂(SO₄)₃·xH₂O under various gas atmospheres. It is shown how the partial pressure of gas components and heating rate may effect the mechanism and kinetic parameters. There are also examples on the effects of some additives and initial treatment on the thermal processes. On the base of the results obtained some recommendations are given concerning the precautions to be taken into account in the thermal decomposition studies and the sulphur recovering.     

Evolved gas analysis at thermal treatment of some solid fossil fuels

Coupled TG-FTIR technique was used for identification of gaseous compounds evolved at thermal treatment of six coal samples from different deposits (Bulgaria, Russia, Ukraine). The experiments were carried out under dynamic heating conditions up to 900°C at heating rates of 5, 10 or 50 K min^–1 in a stream of dry air. The emission of CO₂, H₂O, CO, SO₂, COS, methane, methanol, formic acid, formaldehyde, acetaldehyde, chlorobenzene was clearly identified in FTIR spectra of the samples studied. The formation of ethanol, ethane, ethylene and p-xylene, at least on the level of traces, was also identified. At the heating rate of 5°C min^–1 the temperature of maximum intensities of the characteristic peaks of COS was 270°C, of formaldehyde, formic acid, ethane and methanol 330°C, of SO₂, CO, acetic acid, ethylene and p-xylene 400°C and of chlorobenzene 500°C. At 10°C min^–1 and 50°C min^–1 these temperatures were shifted, respectively, by 70–300°C and 150–450°C towards higher temperatures and the respective absorption bands in FTIR spectra were, as a rule, more intensive.     

Comparative DSC study on thermal decomposition of iron sulphates

The objects for the studies of this paper are iron sulfates where the iron has second or third valences and where coordination between iron, sulfur and oxygen is different. DSC technique is used to investigate thermal stability and enthalpy changes when iron compounds are treated in different gas medium. The main objective is to compare thermal stability and enthalpy of iron oxy-sulphate, often detected as an intermediate, with commonly known iron sulphates. DSC curves of samples with equal mass under different gas medium, determining different partial pressure of oxygen in the gas phase, are the base for comparative study of the sample’s thermal properties. Obtained different values of the enthalpy and mass losses and kinetic parameters demonstrate that the stability of oxy-sulphate strongly depended on the value of oxygen partial pressure in the gas phase. The new evidences from the experimental study help to propose the mechanism of the decomposition and to compare some of the iron sulphates properties.     

Influence of gas media on the thermal decomposition of second valence iron sulphates

FeSO₄·H₂O and FeSO₄ represent the second valence of iron sulphates. Number of studies has been done to understand formation of intermediate sulphates like FeOHSO₄ and Fe₂O(SO₄)₂, representing the oxidation of Fe²⁺ to Fe³⁺. At selected temperatures, both the thermo-dynamical equilibrium in the Fe–S–O system and the formation of the crystal structures in the solid phase are controlled by the partial pressure of water vapour and oxygen in the gas phase. The effects of the temperature and the partial pressure of gas components on the solid-phase content are demonstrated by phase diagrams. The study puts the accent on the influence of oxygen content in gas environment on processes of thermal decomposition of FeSO₄·H₂O and FeSO₄. At three quantities of oxygen content—0% (100% Ar), 21% (dry air) and 100% (pure O₂) the processes of oxidation and formatting metastable iron sulphates were examined by several experimental techniques. The thermal decomposition of samples was investigated by TG–DTG–DTA method in the temperature range 293–1400 K. Partial pressure of water vapour was determined by the quantity of water released from dehydration process of FeSO₄·H₂O. Infrared spectroscopy, Mössbauer spectroscopy and X-Ray powder diffraction method were used for identification of the new formed solid structures and for characterization of the content of the iron sulphates with different valencies of iron. The experimental data and their analyses give the possibility to determine the different stages of decomposition, related to the formation of intermediates. Depending on gas environment, the basic relationships for reaction kinetics is drawn. It is demonstrated on that correlation exists between the kinetic’s parameters and the content of oxygen in the gas phase.     

Thermal Analysis of Polymer-silicate Nanocomposites

The thermal behavior of epoxy-smectite nanocomposites (hybrids) is examined by non-isothermal thermogravimetry (TG, DTG and DTA) in air atmosphere. It has been shown that the thermal stability of hybrids is much greater than that of epoxy resin and strongly depends on both the smectite loading and the type of the gallery cations of organically modified smectites. The kinetics of degradation of nanocomposites is significantly influenced by the presence of smectites and proceeds in three stages. Stage I is attributed to the effect of quaternized ammonium ion exchanged smectite, as stages II and III are associated with the decomposition of the bulk epoxy resin. Because of the interfacial interactions and thesilicate-polymer multilayered nanoscale organization, the nanocomposites act as excellent heat insulator and mass transport barrier, which shift the thermal decomposition peaks towards much higher temperatures. This revised version was published online in July 2006 with corrections to the Cover Date.