Influence of mechanical activation on decomposition of a chalcopyrite-pyrite mixture in an oxidizing atmosphere

The influence of the addition of pyrite and mechanical activation on an oxidative decomposition of chalcopyrite was studied. The course of the thermoanalytical curves and X-ray identification of the products showed that addition of pyrite affects mainly the endothermic processes taking place in region of low temperatures but does not significantly influence the temperature of CuSO₄ formation and its content in the products of decomposition. Changes in fine and superfine structure of chalcopyrite brought about by mechanical activation at grinding cause the complex of exothermic oxidative reactions to proceed at temperatures as much as 180 deg lower than for a non activated sample. The endothermic effect of these oxidation reactions become more marked and the proportion of CuSO₄ in the products of the oxidative decomposition increases significantly.

---

Zusammenfassung Am oxidativen Zerfall von Chalkopyrit wurde der Einfluss der Zugabe von Pyrit sowie der mechanischen Aktivierung untersucht. Der Verlauf der thermoanalytischen Kurven und Röntgendiffraktionsanalyse der Produkte zeigten, dass die Zugabe von Pyrit hauptsächlich die sich bei niedrigeren Temperaturen abspielenden endothermen Prozesse beeinflusst, nicht aber die Bildungstemperatur von CuSO₄ sowie dessen Gehalt in den Zersetzungsprodukten. Durch mechanisches Aktivieren mittels Feinmahlen hervorgerufene Veränderungen in der Fein- und Superfeinstruktur lassen die Gesamtheit der exothermen oxidativen Reaktionen bei Temperaturen ablaufen, die etwa 180 Grad unterhalb derer für unaktivierte Proben liegen. Die endotherme Färbung dieser Oxidation wird eindeutiger und der Anteil von CuSO₄ in den Produkten des oxidativen Zerfalles nimmt eindeutig zu.

---

. , . , , - , 180° , . - .

     

On the interpretation of differences in mechanisms, kinetics and dynamics of oxidation reactions on metal and oxide catalysts

Langmuir-Hinshelwood type mechanisms with competitive adsorption are suggested to be more typical for metal catalysts, since, unlike on oxide systems, oxidizable substance and molecular oxygen can be adsorbed on the same (reduced) active sites. Therefore, multiple steady states and critical phenomena are more characteristic for catalysis on metals.

---

, - , , () . .

     

Polyfunctional zeolite catalysts in the benzene-olefin-hydrogen system

Benzene alkylation by C₂–C₄ olefins in the presence of hydrogen over a steam-treated zeolite catalyst containing lanthanum and nickel, has been studied. The promoting action of hydrogen on benzene alkylation by propylene has been established.

---

C₂–C₄ , . .

     

Diffuse reflectance spectroscopic studies of supported molybdenum oxide catalysts for propene metathesis

Diffuse reflectance spectra of 10 wt.% MoO₃ supported on -Al₂O₃ and SiO₂ have been measured after various steps of treatment. -Al₂O₃ was pretreated by 0.05 and 1.0 wt.% KOH. The comparison of spectral data and catalytic properties allows to predict the optimal oxidation state of molybdenum ions in surface clusters (approximately Mo⁵⁺), necessary to obtain supported MoO₃ catalysts for propene metathesis with high activity and selectivity.

---

, -Al₂O₃ SiO₂ 10% . . -Al₂O₃ 0,05% 1,0% KOH. ( Mo⁵⁺), .

     

Kinetics and mechanism of reduction of thallium(III) by hydrogen peroxide in perchloric acid medium

The kinetics and mechanism of reduction of thallium(III) by hydrogen peroxide has been studied in 1.0 mol dm^–3 perchloric acid medium. The reaction is first order with respect to thallium(III) and second order with respect to hydrogen peroxide. A negative hydrogen ion and chloride ion catalysis is observed. Bromide ion is found to catalyze the reaction in low concentration. There is no effect of ionic strength on the rate of the reaction. A plausible mechanistic pathway for the reaction is suggested which leads to the following rate law: Rate=–d[T1(III)]/dt=kK[T1(III)][H₂O₂]²/[H⁺] where K is the formation constant of the complex between thallium(III) and hydrogen peroxide and k is the rate constant of the reaction between that complex and hydrogen peroxide. The computed values of E_a and S^# are 44.8±6.5 kJ mol^–1 and –107.8±22.2 JK^–1 mol^–1, respectively.

---

(III) - - . - (III) . - - . . -- . , - :=–[T1(III)]/dt=kK[T1(III)][H₂O₂]²/[H⁺], - (III) - . E_A S^# 44,8±6,5 / –107,8±22,1 /·, .

     

Synthesis and properties of hydrodesulfurization catalysts. IV. Thiophene hydrodesulfurization on molybdenum catalysts containing heteropoly compounds

Water soluble analogues of aluminium and cobalt heteropolymolybdates have been shown as possible precursors of active sites for thiophene hydrodesulfurization along with other molybdenum compounds. For the characterization of the catalysts Raman spectroscopy has been applied, and the catalytic activity of the samples is discussed.

---

. .

     

Catalytic properties of silica-molybdenum catalysts in propylene oxidation

The activity of silica-molybdenum catalyts in propylene oxidation is shown to be determined by the partially dehydrated silica-molybdenum heteropolyacid stabilized by the SiO₂ surface.

---

, , SiO₂.

     

Evaluation of quantum yields in the presence of an absorbing additive

A method is proposed for the evaluation of quantum yields of photochemical reactions studied in the presence of absorbing additives using cylindrical sample tubes.

---

.

     

The differential thermal analysis in the identification of cations through the Dowex 50W X12 resin

Starting from some satisfactory preliminary studies, the possibility of identifying single cations in solution has been investigated, by means of ionic exchange with a highly acidic resin (Dowex 50W) and a subsequent study by differential thermal analysis of the same resin. A catalogue of DTA curves has been prepared with 19 ionic forms of the said resin, and it has been found that the DTA curves are sufficiently distinguishable and reproducible to suggest an eventual analytical use in more complex cases of solutions containing more than one cationic species.

---

Zusammenfassung Ausgehend von befriedigenden Vorversuchen hat man die Möglichkeit der Identifizierung von einzelnen Kationen in Lösung mit Hilfe Ionenaustausches am hochsauren Austauscherharz (Dowex 50W) und darauffolgender differentialthermoanalytischer Prüfung des Harzes untersucht. Es wurde ein Katalog der DTA Kurven von 19 ionischen Formen des erwähnten Harzes aufgestellt. Die DTA Kurven sind genügend unterschiedlich und reproduzierbar, um eine analytische Anwendung von komplizierteren Fällen mit mehr als einem Kation in der Lösung vorzunehmen.

---

Résumé Après quelques essais préliminaires ayant donné satisfaction, on a recherché la possibilité d'identifier des cations présents seuls en solution par échange ionique sur une résine fortement acide (Dowex 50W et étude ultérieure de cette même résine par ATD. On a préparé un catalogue des courbes d'ATD de 19 formes ioniques de la dite résine. Les courbes se distinguent suffisamment les unes des autres et sont assez reproductibles pour suggérer leur emploi éventuel au cas plus complexe de solutions contenant plusieurs espèces cationiques.

---

- (Dowex 50W). - 19 . , .

     

Oxidizing properties of alumina towards alcohols. Possible reaction scheme

By chemical trapping, an acyl species has been evidenced in the oxidation of alcohols to carboxylate on an alumina surface. A possible reacton scheme is discussed.

---

. .

     

Reactivity and stability of monomeric forms of iron phthalocyanines

The effect of preparation methods of monomeric iron phthalocyanine on Mössbauer perameters and transformations was investigated. The form of iron phthalocyanine influences the reactivity and stability against oxidative destruction to iron oxides.

---

. .

     

Physico-chemical transformations during heating of phosphorites

The thermal behaviour of phosphorites in an oxygen or helium atmosphere was studied by means of simultaneous TG-DTG-DTA-gas titrimetric EGA. Thermal oxidation and/or decomposition steps of the contaminating organic materials, carbonate minerals and pyrite, and of the fluorocarbonate-apatite were identified. The evolution of CO₂ from the latter has its maximum at 750–850 °C and is accompanied by an increase in the lattice parametera ₀.

---

Zusammenfassung Das thermische Verhalten von Phosphoriten in Sauerstoff- oder Heliumatmosphäre wurde durch simultane TG-DTG-DTA-EGA (mittels Gastitrimetrie) untersucht. Thermische Oxidations- und/oder Zersetzungsschritte der Verunreinigungen (organische Materialien, Carbonatminerale und Pyrit) und des Calcium-fluoro-carbonat-apatit wurden identifziert. Die CO₂-Abspaltung aus dem letzteren hat ihr Maximum bei 750–850 °C, sie ist begleitet von einer Vergrösserung des Gitterparametersa ₀.

---

, , - . ( , , . 750–850° ₀.

     

Phase equilibria in the V2O5-Cr2O3 system

The phase equilibria in the total range of component concentrations in the V₂O₅-Cr₂O₃ system up to 1000 °C were studied by means of phase powder diffraction and DTA. Two compounds exist in the system: CrVO₄, melting incongruently at 860±5 °C, and Cr₂V₄O₁₃, which decomposes in the solid state at 640±5 °C to CrVO_4(s) and V₂O_5(s). At 645±5 °C, CrVO₄ and V₂O₅ form a eutectic mixture with the CrVO₄ content not exceeding 2% mol.

---

Zusammenfassung Mittels DTA und Pulverdiffraktionsaufnahmen wurde das Phasengleichgewicht des Systems V₂O₅-Cr₂O₃ bis 1000 °C im gesamten Konzentrationsbereich untersucht. Innerhalb des Systemes existieren zwei Verbindungen: CrVO₄ mit einem inkongruentem Schmelzpunkt bei 860±5 °C und Cr₂V₄O₁₃, das sich in festem Zustand bei 640±5 °C in CrVO_4(s) und V₂O_5(s) zersetzt. Bei 645±5 °C bilden CrVO₄ und V₂O₅ ein eutektisches Gemisch mit einem maximalen CrVO₄-Gehalt von 2 mol%.

---

DTA V₂₅-Cr₂₃ 1000° . : CrVO₄, 860±5° Cr₂V₄O₁₃, 640±5° CrVO₄ V₂O₅, 645±5° CrVO₄, 2 %.

     

Microcalorimetric and FT-IR spectroscopic study of benzene adsorption on α-Fe2O3 and γ-Al2O3

The adsorption of benzene at room temperature on-Fe₂O₃ and on-Al₂O₃ powders was investigated by heat-flow microcalorimetry and FT-IR spectroscopy.On iron oxide a chemisorption-combustion step is followed by a highly exothermic adsorption step, reversible at r.t.Few combustion centres exist on alumina if reducing pretreatment is not carried out. Two reversible adsorption steps are subsequently observed and were interpreted as due to interaction with two different types of surface hydroxy groups.

---

Zusammenfassung Die Adsorption von Benzol an-Fe₂O₃- und-Al₂O₃-Pulvern bei Raumtemperatur wurde mittels Wärmefluß-Kalorimetrie und FT-IR-Spektroskopie untersucht. Beim Eisenoxid folgt auf dem Chemisorptions-Verbrennungs-Schritt ein bei Raumtemperatur reversibler, stark exothermer Adsorptionsschritt. Aluminiumoxid besitzt einige Oxydationszentren, sofern keine reduzierende Vorbehandlung erfolgt. Zwei aufeinanderfolgende reversible Adsorptionsschritte treten auf und werden der Wechselwirkung mit zwei verschiedenen Typen von Oberflächenhydroxylgruppen zugeschrieben.

---

-Fe₂O₃ -l₂₃. - , . , , . , .

---

---

This work was supported by the CNR Progetto Finalizzato Chimica Fine e Secondaria. Prof. Vincenzo Lorenzelli is gratefully thanked for the kind loan of instrumental facilities and helpful discussions.     

Differential thermal analysis study of various oxalates in oxygen and nitrogen

Differential thermal analysis (DTA) of some 25 oxalates are reported in atmospheres of oxygen and nitrogen. It is shown that in some cases in nitrogen the metal is formed, in other cases the oxide of lowest valency state is produced, while a third group give the same oxide product in nitrogen and oxygen. The production in oxygen of the oxide for the first group, and of a higher oxide in the second group is a phenomenon which in the first case involves a further reaction of the metal with the oxygen atmosphere. Another group of oxalates produce characteristic DTA curves due to the formation of carbonate as the initial decomposition product. The dehydrations of these oxalates are marked by endothermic peaks.

---

Zusammenfassung Es wurden 25 verschiedene Oxalate durch DTA in Stickstoff- und Sauerstoffatmosphäre untersucht. In einigen Fällen wurde in Stickstoff das Metall gebildet, in anderen das Oxyd von niedrigster Wertigkeit. Es kommt auch vor, daß das gleiche Produkt in beiden Gasen entsteht. Beide erwähnten Produkte werden in Sauerstoff entsprechend oxydiert. Bei einigen Oxalaten erhielt man charakteristische Spitzen, die zeigten, daß das erste Zersetzungsprodukt Karbonat war. Die Dehydration dieser Oxalate zeigte sich durch endothermische Spitzen.

---

Résumé On communique les résultats de l'étude de 25 oxalates par analyse thermique différentielle, dans l'oxygène et dans l'azote. On montre que pour certains d'entre eux, dans l'azote, le métal se forme, et que pour d'autres l'oxyde correspondant à la valence la plus faible apparaît; d'autres encore donnent le même oxyde dans l'azote et dans l'oxygène. Dans l'oxygène, et pour le premier groupe, il se forme l'oxyde, tandis que l'oxyde supérieur apparaît pour le second groupe; dans le premier cas, une réaction ultérieure du métal avec l'oxygène de l'atmosphère est mise en jeu. Un autre groupe d'oxalates donne des enregistrements d'ATD caractéristiques en raison de la formation de carbonate comme produit de décomposition initial. Ces oxalates se déshydratent en donnant des pics endothermiques.

---

() 25 . , , , . , , , , , , . , , . .

     

Reaction kinetics of electron transfer between tungstovanadophosphoric heteropolyanions and Fe(II) ions

The reduction of PW_12–nV_nO₄₀ ^(3+n)– (n=1–4) heteropolyanions with Fe(II) ions occurs via intermediate complex formation. The rate constants of electron transfer in this complex tend to decrease in accord with the change of the oxidation potential of the heteropolyanions.

---

PW_12–nV_nO ₄₀ ^–(3+n) (n=1–4) Fe(II) . .

     

High-temperature phases of montmorillonite synthetized from the oxides SiO2-Al2O3-MgO-CaO

The high-temperature (950–1500°) changes in synthetic montmorillonite of relatively simple chemical composition, studied by X-ray diffraction analysis, infrared spectroscopy and electron microscopy, are described. It was found that this montmorillonite belongs to the Wyoming type and the high-temperature phases involve cristobalite, mullite, anorthite and spinel. Only mullite crystallized from this sample on heating for two hours at 1500°.

---

Zusammenfassung Die durch Röntgendiffraktionsanalyse, Infrarotspektroskopie und Elektronenmikroskopie untersuchten Hochtemperatur (950–1500°) — Änderungen in synthetischem Montmorillonit verhältnismässig einfacher chemischer Zusammensetzung werden beschrieben. Es wurde gefunden, daß dieser Montmorillonit dem Typ Wyoming angehört und, daß die Hochtemperaturphasen Cristobalit, Mullit, Anorthit und Spinell enthalten. Aus dieser Probe kristalliesierte bei zweistündigem Erhitzen auf 1500°C nur Mullit.

---

, (950–1500°) . , , , , . 2 1500° .

     

On the formation mechanism of hexafluoropropylene oxide in low-temperature liquid-phase oxidation of hexafluoropropylene by molecular oxygen

The effect of initiation rate (dose-rate of -radiation) on the formation rate of hexafluoropropylene oxide has been studied. Experimental data confirm that the epoxide forms in the reaction R–O–C₃F ₆ ^· R^·+C₃F₆O, as contrasted to the generally accepted fragmentation of -peroxyalkyl radicals R–O–O–C₃F ₆ ^· RO^·+C₃F₆O.

---

( -) . , , R–O–C₃F₆R+C₃F₆O R–O–O–C₃F₆RO+C₃F₆O.

     

Combinations of alkyl radicals with alkyl and substituted allyl radicals

In contrast with expectations based upon simple collision theory, reactions of alkyl radicals with substituted allyl radicals yield cross-combination ratios of =2. Reactions of CH ₃ ^\ with some C₅ radicals give >2, in accordance with theory.

---

, =2. CH₃ ^\ C₅ >2, .

     

The possible formation of surface ethylidyne on platinum black and its effect on some catalytic properties

Secondary Ion Mass Spectra of Pt-black exposed to ethylene at 633 K contain a PtC₂H₃ cluster identified tentatively with adsorbed ethylidyne like that reported for single crystal surfaces. The catalytic properties of Pt pretreated by ethylene are, to some respect, superior in hydrocarbon transformations to those containing other, less defined carbonaceous overlayers.

---

- Pt-, 633 , PtC₂H₃, , . Pt, , , , , .