Thermal characterization of iron oxide powders by emanation thermal analysis

Emanation thermal analysis (ETA) using a surface-impregnation method of Ra-226 nuclide was applied for the thermal characterization of near-surface of iron oxide powders with various preparation histories in the heating and grinding treatments. Peaks I and II appeared at the temperature regions lower and higher than 0.4 – 0.5 T_m, respectively, where T_m is a melting temperature (K) of powders. Further, peak I′ appeared at the temperature region of 0.4 – 0.5 T_m. The appearance of peak I was explained by the mechanochemical effects due to the grinding treatment, and it disappeared in the repeated run. The shift of peak II 900°C to 1000°C in the repeated run was explained by the orderingeffect of crystal lattice due to the heating treatment. The behavior of peak I′ was complicated.     

Investigation of the thermal decomposition of some periodates by means of emanation thermal analysis (ETA) and DTA

Thermal decomposition of Be₃(IO₅)₂ · 12H₂O, Mg₂I₂O₉ · 11H₂O, Ca₂I₂O₉ · 9H₂O and Ba₂I₂O₉ · 9H₂O in the temperature interval of 20 to 600° was studied by means of emanation thermal analysis (ETA) and differential thermal analysis (DTA). The magnetic properties of decomposition intermediates of periodates studied are discussed.     

A study of thermal preparation of iron (III) pigments by means of thermal analysis methods

The decomposition of hydronium jarosite occurs in two temperature ranges: first a loss of 8 moles of H₂O from 2 moles of jarosite, then in the second step one mole of H₂O and 4 moles of SO₃ are simultaneously evolved. Fe(OH)(SO₄)₂ and Fe₂O(SO₄)₂ are assumed intermediates. During the thermal treatment of Na or K jarosits, only Fe2(SO₄)₃ appears as intermediate. The decomposition temperatures are significantly influenced by the type of crucible used (determination of partial pressure of gaseous decomposition products). The particle size distribution of the starting jarosite has no effect upon the temperature of the decomposition steps and of the reaction with ZnO.The results of TG measurements were evaluated via calculations of the steps of the experimental activation energies for these partial decomposition jarosites and for their reaction with ZnO.

---

Zusammenfassung Die Zersetzung von Hydronium-jarosit verläuft in zwei Stufen: (1) Abgabe von 8 Mol Wasser, (2) simultane Abspaltung von 1 Mol Wasser + 4 Mol SO₃/2 Mol Jarosit. Als Zwischenprodukte werden Fe(OH)(SO₄) und Fe₂O(SO₄)₂ vermutet. Bei der thermischen Zersetzung von Na- und K-Jarosit tritt nur Fe₂(SO₄)₃ als Zwischenprodukt auf.Die Zersetzungstemperaturen werden durch die Tiegelform erheblich beeinflusst (über den Partialdruck der gasförmigen Zersetzungsprodukte). Die Teilchengrössenverteilung des Ausgangs-Jarosits hat keinen Einfluss auf die Temperaturen der Zersetzungsschritte des Jarosits und der Reaktion mit ZnO. Aus den Ergebnissen der TG-Messungen werden experimentelle Aktivierungsenergien für die Zersetzungsreaktionen der Jarosite und ihre Umsetzung mit ZnO berechnet.

---

- . 8 , — 4 . Fe(OH)SO₄ Fe₂O(SO₄)₂. Fe₂(SO₄)₃. , , . . .

     

Mössbauer study of the thermal decomposition of some iron(III) dicarboxylates

The thermal decomposition of iron(III) succinate, Fe₂(C₄H₄O₄)₂(OH)₂ and iron(III) adipate pentahydrate, Fe₂(C₆H₈O₄)₃·5 H₂O, has been investigated at different temperatures for different time intervals in static air atmosphere using Mössbauer spectroscopy and nonisothermal techniques (DTG-DTA-TG). The reduction of iron(III) to iron(II) species has been observed at 533 K and 563 K in the case of iron(III) succinate and iron(III) adipate, respectively. At higher temperatures, α-Fe₂O₃ is formed as the final thermolysis product.     

Characterization of high-technology materials by emanation thermal analysis

The principles of the emanation thermal analysis, based on the measurement of inert gas release from solids, are given. Results of the computer modelling of inert gas release curves during heating of porous and dispersed samples are demonstrated.Examples of the characterization of high-tech ceramic materials and raw materials for their preparation by means of emanation thermal analysis are given, such as the evaluation of reactivity and sinterability of ceramics powders, quality testing of intermediate and final products of advanced technology materials (such as thoria, urania, ferrites, superconducting oxide ceramics, etc.).

---

Zusammenfassung Es werden Grundlagen für die Emanationsthermoanalyse /ETA/ auf der Basis der Messung der Inertgasfreisetzung bei Feststoffen gegeben. Ergebnisse von computermodellierten Inertgasfreisetzungskurven bei Erhitzen von porösen und dispersen Proben werden angeführt.Weiterhin werden Beispiele für die mittels ETA durchgeführte Charakterisierung von Spitzentechnologiekeramikmaterialien und den Rohstoffen zu deren Herstellung gegeben: Auswertung von Reaktivität und Sinterbarkeit von Keramikpulver, Qualitätskontrolle der Zwischen- und Endprodukte aus modernen Rohstoffen /wie z. B. Thorerde, Uranerde, Ferrit, supraleitende Oxidkeramiken usw./.

---

, , . . - , , - /, , , . /.

     

Some reactions of iron (III) and chromium (III) fluorides with oxides

Reactions of FeF₃ with several oxides at elevated temperatures are described. Reaction products were usually Fe₂O₃ and the fluoride of the other element. With higher valency elements complete fluorine exchange did not always occur and oxyfluorides were formed. Intermediates in the reactions include oxyfluorides and mixed oxides, again only found with higher valency elements. Some shorter studies on the reaction of CrF₃ with oxides are included for comparisons, the reactions observed being generally similar.     

Hydration of tricalciumsilicate (Ca3SiO5) investigated by emanation thermal analysis

The method of emanation thermal analysis (ETA), based on the measurement of radon release from samples, has been used in the investigation of the tricalcium-silicate (Ca₃SiO₅) to characterize the microstructure development during the sample hydration. Results of the ETA made it possible to obtain the diffusion structural diagnostics of the material under in situ conditions of it is hydration. The influence of temperature and surface area of the tricalcium-silicate sample on kinetics of the sample hydration was characterized. Computer modeling of time dependences of radon release rate during hydration of tricalcium-silicate was carried out. A good agreement of the numerical model with the experimental results of the radon release was found.     

Application potential of emanation thermal analysis

The application potential of the emanation thermal analysis with respect to the actual needs of chemical technology and material science is given.

---

Zusammenfassung Im Hinblick auf die praktischen Erfordernisse der chemischen Verfahrenstechnik und Materialkunde werden die Anwendungsmöglichkeiten der Emanationsthermoanalyse beschrieben.

     

Identification of iron(III) oxides and hydroxy-oxides by voltammetry of immobilised microparticles

In this paper, we propose the use of an electroanalytical technique based on the direct oxidation or reduction of the electroactive components of the sample on the surface of the working electrode, called voltammetry of immobilised microparticles (VMPs). The sample is easily deposited on the electrode by abrasion and then the electrode is transferred to the electrochemical cell where the square wave potential scan is performed. Electroactive species showed peaks whose peak potential is related to the standard formal potentials. We applied this technique to the identification of iron oxides and hydroxy-oxides in cosmetics. To characterise and identify the iron(III) oxides and hydroxy-oxides VMP was performed in two different media: oxalic acid and hydrochloric acid, that is, a complexing and a slightly complexing media. Two electrode processes were observed. They were influenced by the media and the synthesis procedure of the oxides. The reduction peak at negative potentials (−0.50 V in hydrochloric acid and −0.60 V in oxalic acid) is related to the direct reduction of the iron(III) oxide and it does not appear in the case of the more reactive phases (hydroxy-oxides). The peak at positive potentials (0.90 V in hydrochloric acid and 0.60 V in oxalic acid) involves the reduction of iron(III) in solution. The same electrode process were observed for binary mixtures but the peak potentials are shifted from the pure components peak potentials. This allowed us to distinguish between their mixtures. Finally, VMP was used to characterise iron oxides in cosmetic powders.     

Mössbauer study of the thermal decomposition of iron(III) benzoate and iron(III) fumarate

The thermal decomposition of iron(III) benzoate, Fe(C₇H₅O₂)₃, and iron(III) fumarate pentahydrate, Fe₂(C₄H₂O₄)₃ 5 H₂O, containing uni- and bidentate ligands, respectively, has been investigated at various temperatures for different intervals of time in a static air atmosphere. Thermolysis of these compounds leads directly to the formation of α-Fe₂O₃ in the case of iron(III) benzoate and Fe₃O₄ in the case of iron(III) fumarate as the ultimate products, thus without undergoing reduction to the iron(II) state.     

Spectral and thermal features of some novel iron(III) chelates with substituted 2-hydroxyaryloximes

The reaction products of five substituted 2-hydroxyaryloximes with Fe(III) ion were obtained and characterized by means of elemental analysis, conductometric measurements, magnetic moment determinations and spectroscopic data (IR and electronic absorption).The thermal stability and mode of decomposition were studied in air atmosphere by using TG-DTA. Kinetic analysis of the TG data was performed with the Coats-Redfern method to determine the apparent activation energies and the pre-exponential factor of the Arrhenius equation. Mass spectrometry was also used, and possible fragmentation patterns are given and discussed.Thanks are due to Tekkosha Hellas, Thessaloniki, for making available the thermogravimetric analysis facilities.     

Synthesis and the thermal decomposition of iron(III) tris(oxalato) ferrate(III) tetrahydrate

The paper describes the synthesis and thermal decomposition of Fe[Fe(C₂O₄)₃]4H₂O in air. The compound is completely dehydrated at 170°C and some reduction in the inner sphere iron(III) occurs. At 290°C, a mixture of ferric oxide and ferrous oxalate is obtained. Beyond 420°C, the decomposition is complete and final residue is ferric oxide. A probable reaction mechanism is proposed.     

Simultaneous differential rate determination of iron(II) and iron(III) by flow-injection analysis

Flow-injection procedures for the simultaneous spectrophotometric determination iron(II) and iron(III), relying on the different kinetic-catalytic behaviour of iron(II) and iron(III) in the redox reaction between leucomalachite green and peroxodisulphate with and without the presence of the activator 1,10-phenanthroline, are described. Exploiting the fact that one of the chemical reactions is very rapid whereas the other one is comparatively slower, two experimental procedures are presented. In the first, two individual zones of sample solution are injected simultaneously into separate carrier streams of reagent in a two-line system. Taking advantage of the different residence times of the samples in the manifold lines, the resulting colour formation is measured by a single optical detector with two separate flow cells aligned within the same optical path. The second approach is based on the use of a single-line flow-injection system, exploiting the formation of a double peak as a result of injecting a large sample zone, sandwiched between reagent zones of appropriate composition. In this manner two time-resolved signals for the kinetically governed processes can be obtained and thus used for quantification of the individual species.     

Use of emanation thermal analysis and evolved gas analysis in thermal study of zinc(II) benzoate complex compounds

Volatile organic compounds (VOCs) are the main factors involved in pollution control and global warming in industrialized nations. Various treatment methods involving incineration, adsorption, etc., were employed to reduce VOCs concentration. Various absorbents, such as activated carbon, zeolite, silica gel or alumina, and so on were broadly used to adsorb VOCs in various industrial applications. Differential scanning calorimetry (DSC) was handled to analyze the thermal characteristics of absorbents. Typically, a scanning electron microscope (SEM) has been used to evaluate the structure variation of absorbents under high temperature situations. In view of pollution control and loss prevention, versatility and analysis of recycled adsorbents are necessary and useful for various industrial applications.     

Physico-chemical studies on the thermal decompositions of iron(III) phthalates

The thermal decompositions of basic salts of iron(III)o-phthalate sesquihydrate, Fe(C₈H₄O₄)(OH)·1.5H₂O, iron(III)m-phthalate trihydrate, Fe(C₈H₄O₄)(OH)·3H₂O, and iron(III)p-phthalate monhydrate, Fe(C₈H₄O₄)(OH)·H₂O, have been investigated from ambient temperature up to 973 K in air using Mössbauer and infrared spectroscopy, derivatography (DTG-DTA-TG) and X-ray diffraction. The thermal decomposition proceeds without reduction to Iron(II) species in the cases of iron(III)o-phthalate and iron(III)p-phthalate, whereas iron(II) species have been detected in the case of basic iron(III)m-phthalate.-Fe₂O₃ is formed as the end-product. Increase in the particle size of the-Fe₂O₃ with increasing decomposition temperature has also been observed.

---

Zusammenfassung Die thermische Zersetzung basischer Salze von Eisen(III)-o-phthalat-Sesquihydrat, Fe(C₈H₄O₄)(OH) · 1,5H₂O, Eisen(III)-m-phthalat-Trihydrat, Fe(C₈H₄O₄)(OH)·3H₂O, und Eisen(III)-p-phthalat-Monohydrat, Fe(C₈H₄O₄)(OH)·H₂O, wurden im Temperaturbereich von Raumtemperatur bis 973 K in Luft mittels Mössbauer- und IR-Spektroskopie, Derivatographie (DTG-DTA-TG) und Röntgendiffraktometrie untersucht. Im Gegensatz zu basischem Eisen(III)-m-phthalat erfolgt bei den entsprechendeno- undp-Phthalatverbindungen im Verlaufe der Zersetzung keine Reduktion zu Eisen(II)-Species.-Fe₂O₃ wird als Endprodukt erhalten. Mit steigender Zersetzungstemperatur nimmt die Größe der-Fe₂O₃-Partikel zu.

---

c Fe(C₈H₄O₄)(OH)·vH₂O, x = 1.5,3 1, , -, - n-, 973 . , , ë . - n- , m- . -Fe₂O₃. -Fe₂O₃.

     

Formation of uniform colloidal iron (III) oxides in ethylene glycol-water solutions

The aging of ferric chloride in ethylene glycol-water mixtures in the presence of chloride and phosphate ions has been carried out at 100 °C. The morphology and the structure of the resulting ferric (hydrous) oxide colloidal particles obtained under various conditions were evaluated by scanning and transmission electron microscopy and by X-ray diffraction analysis.Supported by the NSF Grant CHE 83-18196.Part of a M. S. thesis.     

The thermal decomposition of some Cr(III) complexes

The thermal decomposition reactions of the following chromium(III) complexes were investigated: Cr(CH₃COO)₃·2 H₂O, [C_r3O(CH₃COO)₆(H₂O)₃]Cl·2 H₂O and [Cr₃O(CH₂ClCOO)₆(H₂O)₃]Cl·6H₂O. Simultaneous TG/DTG/DTA were applied nonisothermal conditions. From the recorded curves, the activation energiesE _a were calculated for all the thermal decomposition steps. Appropriate chemical reactions were attributed to the thermal effects, with consideration to the X-ray diffraction and IR spectra results.

---

Zusammenfassung Für die Untersuchung der thermischen Zersetzungsreaktion der Chrom(III)-Komplexe Cr(CH₃COO)₃·2H₂O [C_r3O(CH₃COO)₆·(H₂O)₃]Cl2H₂O und [C_r3O(CH₂ClCOO)₆·(H₂O)₃]C₁₆H₂O wurde simultane TG/DTG/DTA unter nichtisothermen Bedingungen eingesetzt. Ausgehend von den aufgezeichneten Kurven wurden für alle Schritte der Zersetzungsreaktion die E_a-Werte berechnet. In Übereinstimmung mit röntgenographischen und IR-spektroskopischen Ergebnissen wurden den thermischen Effekten passende chemische Reaktionen zugeordnet.

     

Exchange interactions in some binuclear iron(III)complexes studied by EPR

The binuclear iron(III) complexes have been the subject of widespread study^1–8, mainly by use of magnetic susceptibility measurements, because of their unusual magnetic properties. Among dimeric iron compounds, especially interesting features are exhibited by complexes containing an Fe-O-Fe bridge.The oxygen bridge is not confined only to dimeric iron compounds^8–10, and thus EPR has been applied to the problem of recognizing such structures and the role of iron in bridge systems. One example of this is the attempt¹¹ to recognize complexes of Fe^III with HEDTA¹, and the quintet state spectrum was obtained. The spin Hamiltonian parameter values D and E were not calculated precisely, because of the lack of data relating to resonance field angular dependence.     

Kinetics of thermal decomposition of iron(III) dicarboxylate complexes

Summary Tris(dicarboxylate) complexes of iron(III) with oxalate, maleate, malonate and phthalate viz. K₃[Fe(C₂O₄)₃]×3H₂O (1), K₃[Fe(OOCCH₂COO)₃]×3H₂O (2), K₃[Fe(OOCCH=CHCOO)₃]×3H₂O (3), K₃[Fe(OOC-1,2-(C₆H₄)-COO)₃]×3H₂O (4) have been synthesized and characterized using a combination of physicochemical techniques. The thermal decomposition behaviour of these complexes have been investigated under dynamic air atmosphere upto 800 K. All these complexes undergo a three-step dehydration/decomposition process for which the kinetic parameters have been calculated using Freeman-Carrol model as well as using different mechanistic models of the solid-state reactions. The trisoxalato and trismalonato ferrate(III) complexes undergo rapid dehydration at lower temperature below 470 K. At moderately higher temperatures (i.e. >600 and 500 K, respectively) they formed bis chelate iron(III) complexes. The trismalonato and trismaleato complexes dehydrate with almost equal ease but the latter is much less stable to decomposition and yields FeCO₃ below 760 K. The cis-dicarboxylate complexes particularly with maleate(2-) and phthalate(2-) ligands are highly prone to the loss of cyclic anhydrides at moderately raised temperatures. The thermal decomposition of the tris(dicarboxylato)iron(II) to iron oxide was not observed in the investigated temperature range up to 800 K. The dehydration processes generally followed the first or second order mechanism while the third decomposition steps followed either three-dimensional diffusion or contracting volume mechanism.     

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.