Studies of fly ash using thermal analysis techniques

Improved thermoanalytical methods have been developed that are capable of quantitative identification of various components of fly ash from a laboratory-scale fluidized bed combustion system. The thermogravimetric procedure developed can determine quantities of H₂O, Ca(OH)₂, CaCO₃, CaSO₄ and carbonaceous matter in fly ash with accuracy comparable to more time-consuming ASTM methods. This procedure is a modification of the Mikhail-Turcotte methods that can accurately analyze bed ash, with higher accuracy regarding the greater amount of carbonaceous matter in fly ash. In addition, in conjunction with FTIR and SEM/EDS analyses, the reduction mechanism of CaSO₄ as CaSO₄+4H₂ CaS + 4H₂O has been confirmed in this study. This mechanism is important in analyzing and evaluating sulfur capture in fluidized-bed combustion systems.     

Thermal analysis of agricultural residues with application to production fuels

An important application of agricultural residues is as fuels for combustion processes. This paper shows how thermal analysis can be used for characterization of different kinds of cereals with a view to increasing efficiency in combustion processes. Results are in good agreement with those derived from standard ASTM methods.     

Characterization of FDR fly ash and brick/lime mixtures

The present research is concerning the characterization of FDR (fuel derived from residues) fly ash and mixtures with lime/brick hydraulic binder by DTA/TG/DTG thermo-analysis, X-ray diffractometry and chemical analysis. The use of hydraulic binder obtained from building brick rejects, which is less expensive than the usual solidifiers such as cementitious binder and silicates, allows us to reutilize, in the meantime, this wreckage material, to the advantage of environmental sustainability. Fly ash samples investigated in the present study were separated in a thermo-incineration plant. Mineralogical DTA/TG/DTG and XRD investigations reveal the presence of different phases as well as chemical analysis shows a moderate concentration of heavy metals and high content of chloride and sulphate. Results obtained from leaching tests with water carried out on hardened pastes containing fly ash lead to interesting results, which highlight behaviour to the release of contaminants. The whole of the results obtained in the present study make it possible to regard the objective of disposing such hardened materials in inert waste landfill sites as achievable.     

Evaluation of pozzolanic activity of natural and artificial pozzolans by thermal analysis

In this research, the pozzolanic activity of natural and artificial pozzolan used for preparation of restoration mortars was evaluated. For this purpose, several pastes were prepared, by mixing two artificial pozzolans and a natural one with commercial hydrated lime, in different ratios. The pastes were cured in standard conditions (RH = 98%, T = 25 °C). The pozzolanic activity was evaluated by using simultaneous differential thermal and thermogravimetric analysis (DTA/TG) after curing for 3, 7, 14, 28 days. The obtained results revealed that the various lime/pozzolan pastes displayed different reaction kinetics and therefore the various pozzolans present different reactivity, in proportion to its mineralogical, physical and chemical characteristics.     

The application of thermal analysis and conduction calorimetry on the formation and hydration of calcium aluminoferrite

DTA was used to study the formation of calcium aluminoferrite from CaO, Al₂O₃ and Fe₂O₃ (proportion=2 x 1–x),x=0-3/4) and the effects of C4A₃ C₁₁ A₇·CacF₂, -C₂S and MgO on that process. The fusion of CF and the eutectic of CaO-Fe₂O₃, CA-C₁₂A₇, CA-C₃A, C₁₂A₇-CA-C₃A and CA-C₂A_xF_(1–x) will be favourable for the formation. The presence of -C₂S and MgO will decrease its formation temperature by an extra eutectic while C₄A₃ . and C₁₁A₇·CaF₂ will not.The early heat evolution during the hydration of C₂A_xF_(1–x) were measured by the conduction calorimeter made by ourselves and the products after 1 day hydration were examined by TG and DTA. The results revealed that the peak of heat evolution rise, the amount of the hydrating product iron hydrate gel decreases, CAH₁₀ and C₃(A, F)H₆ increase with the increase of the value x. The more MgO (up to 5%) soluted in C₆AF₂, the higher the hydration heat for this solid solution is, when TiO₂ soluted in C₆AF₂ is 2%, the hydration heat for the system reaches the highest.This project is supported by National Natural Science Fundation of China and by the National Science and Technology Developing Fundation in Building Materials Field.     

Hydration behaviour of a lime-pozzolan cement containing MSW incinerator fly ash

A lime-pozzolan cement was used to make pastes containing different quantities of MSW fly ash. After setting, the pastes were cured in water at room temperature from 1 h to 260 days. The hydration characteristics and the nature of the hydration products of the various pastes were studied by simultaneous TG/DSC thermal analysis and X-ray diffractometry. The MSW fly ash was found to induce a slowing of the hydration process in lime-pozzolan pastes, and after some days an evident acceleration of hydration reactions occurred. Sulphate and chloride in the MSW fly ash yield hydration products forming a cementitious matrix.The author is grateful to D. Calabrese for assistance with the thermal and XRD analyses.     

The study of the dehydration and dehydroxylation of smectites by emanation thermal analysis

The dehydration and dehydroxylation of the smectites, beidellite and montmorillonite (dioctahedral) and saponite and laponite (trioctahedral), were investigated by ETA, DTA, TG and X-ray diffractions. There are differences between the behaviors of di- and trioctahedral clays which are due to the differences in the ability of the exchangeable cations to migrate into hexagonal holes of the SiO₄ network and due to the fact that the dehydroxylation and recrystallization of dehydroxylated trioctahedral smectites occur simultaneously, whereas there is a temperature gap of about 300°C between the dehydroxylation and the recrystallization of dioctahedral smectites.Dedicated to Dr. Robert Mackenzie on the occasion of his 75th birthdayThe authors wish to thank Laporte Industries, Inc. UK for the laponite sample.This research was supported under Project No. C12-219, Grant No. HRN5544 G002069, U.S.-IsraelCooperative Development Research Program, Office of the Science Advisor, U.S. Agency for International Development.     

A study on the thermal decomposition of iron-cobalt mixed hydroxides

Thermal decomposition of pure Fe(OH)₃ and mixed with Co(OH)₂ were studied using TG, DTA, kinetics of isothermal decomposition and electrical conductivity measurements. The thermal products were characterized by X-ray diffraction and IR spectroscopy. The TG and DTA analysis revealed the presence of Co²⁺ retards the decomposition of ferric hydroxide and the formation of -Fe₂O₃. The kinetics of decomposition showed that the mixed samples need higher energy to achieve thermolysis. The investigation of thermal products of mixed samples indicated the formation of cobalt ferrite on addition ofx=1 or 1.5 cobalt hydroxide. The electrical conductivity accompanying the thermal decomposition decreases in presence of low ratio of Co²⁺ (x=0.2) via the consumption of holes created during thermal analysis. The continuous increase in values on increasing of Co²⁺ concentration corresponded to the electron hopping between Fe²⁺ and Co³⁺.

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Zusammenfassung Mittels TG, DTA und der Kinetik von Messungen der isothermen Zersetzung und der elektrischen Leitfähigkeit wurde die Zersetzung von Fe(OH)₃ in reinem Zustand und vermengt mit Co(OH)₂ untersucht. Die thermischen Produkte wurden mittels Röntgendiffraktion und IR-Spektroskopie charakterisiert. TG und DTA zeigen, daß die Zersetzung von Eisen(III)-hydroxid und die Bildung von -Fe₂O₃ durch Gegenwart von Co²⁺ verzögert wird. Die Zersetzungskinetik zeigt, daß die Mischproben mehr Energie für die Thermolyse benötigen. Die Untersuchung der thermischen Produkte zeigt die Bildung von Cobaltferrit bei Zusatz vonx=1 oder 1,5 Cobalthydroxid. Die elektrische Leitfähigkeit nimmt bei der thermischen Zersetzung in Gegenwart von niedrigen Co²⁺-Konzentrationen (x=0.2) durch Verbrauch der bei der Thermoanalyse geschaffenen Löcher ab. Das monotone Ansteigen der -Werte bei steigender Co²⁺-Konzentration stimmt mit dem Überspringen von Elektronen zwischen Fe²⁺ und Co³⁺ überein.

     

Remediation of textile effluent using agricultural residues

The sorption of artificial dye effluent made from two different dyes, Solar orange 7 GLL and Solar Jade Green FFB from Clariant, onto three different agricultural residues—barley husk, sugarcane bagasse, and wheat straw—was studied. Twenty percent of 600-μm particle size of these agricultural residues was used as substrates and studied individually. The percentage of dye removal was observed in concentrations of dye varying from 50 to 200 mg/L. The effect of temperature ranging from 25 to 50°C and pH from 6.0 to 12.0 on the dye removal by the substrates was also studied. The effective adsorption of the substrates was calculated.     

Characterization of fatty acid methyl esters by thermal analysis

The thermal stability of selected straight-chain (C₆-C₁₄) esters of fatty acids has been studied by TG-DTG and DTA analysis. In DTG, a peak is detected between 84° and 125° C followed by a main effect in the range 105°–215°C, whereas in DTA only an exothermic peak appears in the range of 126.5° to 187°C (onset temperatures). The temperatures of these effects have been related with ignition points, molecular weights and boiling points. The characteristics of melting and recrystallization of the above fatty acid methyl esters and those with carbon numbers between C₁₄ and C₂₄ have been established by DSC along the melting range between ?83° and 50°C. Polymorphism appears in caproic, heptanoic, palmitic and stearic acid methyl esters.     

Study of a Brazilian spent catalyst as cement aggregate by thermal and mechanical analysis

Fluidized catalytic cracking units of refineries normally use zeolite catalysts to treat heavy oil fractions. This catalyst is regenerated continuously, but due to the reduction of its activity during the process, it is partially substituted by a new catalyst make-up. The spent residue has a high content of silicon and aluminum oxides and usually presents pozzolanic properties. This paper presents the study of a Brazilian spent catalyst, which is being tested as a pozzolanic aggregate in partial substitution to cement. Pastes were prepared with 15, 20 and 25% in substitution to cement mass and analyzed after 28 days of hydration. Hydrated paste samples were analyzed by simultaneous thermogravimetry and differential thermal analysis, to quantify the calcium hydroxide consumption, as well as the content of other main hydrated cement phases. Compressive strength analysis was also performed after 28 days of hydration. Although, as spent catalyst content is increased, the pozzolanic activity is confirmed by the increase of calcium hydroxide consumption on cement mass basis, unlikely to other studied spent FCC catalysts, tested for the same purpose, the compressive strength of respective paste specimens decreases, due to the increase of other hydrated phases formation.     

Combining thermal analysis with other techniques to monitor the decomposition of poly(m-phenylene isophthalamide)

The pyrolysis behaviour of Nomex, poly(m-phenylene isophthalamide) fibres under argon has been investigated up to a temperature of 1173 K with different methods to get direct information on the progressive changes taking place in the solid material and its carbon fibre residues. The main stages of the pyrolytic degradation of the fibres were determined by thermal analysis (TG and DTA) and their chemical and morphological evolution through the different steps was subsequently followed by Fourier transform infrared spectroscopy (FTIR) and atomic force microscopy (AFM) measurements, respectively, on samples treated to various temperatures. This revised version was published online in July 2006 with corrections to the Cover Date.     

Application of thermal analysis to study of the synthesis of K0.5Bi0.5Tio3 ferroelectric

Synthesis of potassium bismuth titanate ferroelectric by heating of mixtures prepared using oxide precursors, i.e. Bi₂O₃, TiO₂ and K₂CO₃ was investigated. DTA, TG, XRD and SEM methods were used to study the formation of intermediate compounds and the final product. Usage of associated homogenization and grinding of precursors mixture permits to decrease the temperature of formation of K_0.5Bi_0.5TiO₃. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis and thermal decomposition of mixed Gd-Nd oxalates

Several (Gd_1−xNd_x)₂[C₂O₄]₃·nH₂O samples (0≤x≤1) were prepared by a coprecipitation method: the precipitation is quantitative and all the samples are homogeneous in stoichiometry. XRD analyses have shown that a complete solid solution is formed over the whole range of compositions. The dried Gd rich oxalates have initially a low water content which gradually increases with the Nd content. All the oxalates decompose in O₂ around 700°C either into a single mixed oxide or in a mixture of oxides through several steps, which can be ascribed to the loss of water and CO₂.     

Evaluation of the combustion behaviour of perhydrous coals by thermal analysis

Summary Perhydrous coals are characterized by a high hydrogen content and exhibit a modified composition and physico-chemical properties in comparison with normal coals. These modifications affect the behaviour of perhydrous coals during pyrolysis and, therefore, may have an influence on the subsequent combustion process. In this work the combustibility behaviour of a series of perhydrous coals was evaluated in order to study the effect of hydrogen enrichment during the thermal treatment of the coals in an oxidant atmosphere. To this end temperature programmed combustion tests for the coals, and air isothermal (500°C) reactivity tests for their chars, were carried out in a thermogravimetric analyser. A clear relationship between the combustion behaviour of the perhydrous coals, and the aromatic to aliphatic hydrogen ratio was found.     

Application of thermal analysis in a phase composition study on by-product from semi-dry flue gas desulfurization system

DTA, TG and XRD methods were used for the determination of by-product - obtained during flue gas desulfurization by means of introduction of dehydration - resisting sludge from water decarbonization system. Analysis results enabled the development and application of sludge utilization technology by means of semi-dry flue gas desulfurization in 'Siersza' power plant. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal analysis of renal stones

The chemical composition of 200 renal stones, collected from Taxila, Rawalpindi and Islamabad regions in Pakistan, was determined by thermogravimetric (TG) and differential thermal analysis (DTA) techniques. The thermal curves show weight losses at various temperatures indicating dehydration and decomposition phenomena of renal stones. Results were compared with qualitative data obtained by IR analysis which confirmed the chemical composition of various stones in the solid state. The thermal curves helped in the differentiation of various kinds of water held by stones and their chemical composition was obtained by weight loss during pyrolysis. It was found that 26.5% of the stones were pure whewellite, 3% weddellite, 13% uric acid anhydrous, 7.5% struvite, 2.5% ammonium acid urate, 0.5% cystine and 47% stones had mixed composition. In the mixed state the most frequent combinations were those of calcium oxalate with uric acid (14.5%) and with phosphates (27.5%).

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Zusammenfassung Mittels TG und DTA wurde die chemische Zusammensetzung von 200 Nierensteinen untersucht, die in den Gebieten Taxila, Rawalpindi und Islamabad in Indien gesammelt wurden. Die Thermogramme zeigen Masseverluste bei verschiedenen Temperaturen, die auf Dehydratation und Zersetzung der Nierensteine hinweisen. Die Ergebnisse wurden mit den qualitativen Resultaten aus der IR-Analyse verglichen, welche die chemische Zusammensetzung der verschiedenen Steine im festen Zustand bekräftigte. Die Thermogramme halfen bei der Unterscheidung von verschieden gebundenem Wasser, ihre chemische Zusammensetzung wurde durch Gewichtsverlust bei der Pyrolyse bestimmt. Man fand, daß 26.5 % der Steine aus reinem Whewellit bestanden, 3 % aus Weddellit, 13 % aus anhydrierter Harnsäure, 7.5 % aus Struvit, 2.5 % aus Ammmoniumhydrogenurat, 0.5 % aus Cystin und 47 % der Steine hatten eine gemischte Zusammensetzung. Die häufigsten Kombinationen der Mischzusammensetzungen waren Calciumoxalat mit Harnsäure (14.5 %) und mit Phosphaten (27.5 %).

     

Thermal behaviour of gypsum based composites

DTA/TG and X-ray investigations were carried out on different building composites in order to examine their relative hydration processes. The presence of lime, hemihydrate gypsum, ferosilicate, and some other wastes as leaner and hydrophobic additive in different proportions into composites provokes hydration reactions, leading to calcium silicate hydrate (CSH), ettringite and an intermediate phase formation with varying chemical composition of calcium, aluminum, silicon and sulfur. DTA curves indicate several transformations taking place between composites components, related to hydration of some phases. The content of ettringite component corresponds to the properties and it is used as an indicator for the possibility of industrial application. It is found out that gypsum based cementitious binders could be used as building material in the industry. The same time it is confirmed that the selected wastes could be considered as secondary raw materials.     

A TG/DTA study on the effect of coal blending on ignition behaviour

Understanding the ignition behaviour of coal is of utmost importance for the design of boilers and control of the combustion process. In recent years there has been an increasing utilisation of coal blends for combustion, but information on the possible interactive effects during ignition of the individual components is scarce. In this work the ignition behaviour of a series of coal blends, made up from three coals of different rank, sub-bituminous, high volatile and low volatile bituminous, was studied. To this end a thermogravimetric analyser linked to a mass spectrometer for evolved gas analysis was used. Different ignition behaviour was observed for the coals studied; the sub-bituminous and low volatile bituminous coals ignited heterogeneously, while homogeneous ignition occurred for the high volatile bituminous coal. In the case of blends of the low and high volatile bituminous coals, different mechanisms of ignition were observed depending on the blends composition. This revised version was published online in July 2006 with corrections to the Cover Date.     

The thermal behaviour of compounds in the Ca-S-O system

Simultaneous thermogravimetry and differential thermal analysis up to ca. 1400C of the thermal stability of CaSO₃, CaS, CaSO₄ and physical mixture of CaS and CaSO₄ (molar ratio = 13) both in air and nitrogen atmosphere has allowed overlapping reactions to be defined. The thermal decomposition of CaSO₃ in air does not result in CaO and SO₂ either, but after disproportionation reaction they are formed via the system: 3CaSO₄ + CaS 4CaO + 4SO₂. The oxidation reactions of CaSO₃ and CaS should also be taken into account. The data from the X-ray diffraction analysis of the stable solid intermediates and from the polythermal X-ray diffraction studies provide supporting evidence for the proposed reaction mechanisms.The author thanks Prof. Dr. D. Knöfel of the Universität Gesamthochschule in Siegen and Prof. Dr. W. H. Hoffmann of the Westfälische Wilhelms-Universität in Münster for making the facilities of their laboratories available to her. This work was performed under a UN-Fellowship.