Jadwiga Walczak

The CrVO4-MoO3 system

Abstract The phase equilibria in the CrVO 4 -MoO 3 system were studied up to 1000°C over the entire range of concentration of components using differential thermal analysis and X-ray powder diffraction. The compound CrVMoO 7 exists in this system and melts incongruently at 820 ± 5°C. This system appears to be a real two-component system up to the solidus line. All the results are shown in the form of a phase diagram.

The FeVO4-MoO3 system

A phase diagram of the FeVO4-MoO3 system has been constructed from the results of DTA and X-ray analysis. The components of the system form a compound FeVMoO7. This compound melts incongruently at 680±5 °C, with separation of the solid Fe4V2Mo3O20.ZusammenfassungDas Phasendiagramm des Systems FeVO4-MoO3 wurde basierend auf Ergebnissen der DTA und Röntgenanalyse aufgestellt. Die Komponenten des Systems bilden die Verbindung FeVMoO7,. Diese Verbindung schmilzt inkongruent bei 680±5° unter Abscheidung von festem Fe4V2Mo3O20.РезюмеФазовая диаIрамма сис темы FeVO4-МоО3 была установлена на основ е измерений ДТА и фазивого анализ а. Компоненты системы образуют соединение FeVMoO7, которое плавилось инконгруэ нтно при 680 ±5 °? с выделен ием твердого вещества Fe4V2Mo3O20.

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 CrVO4(s) and V2O5(s). At 645±5 °C, CrVO4 and V2O5 form a eutectic mixture with the CrVO4 content not exceeding 2% mol.ZusammenfassungMittels 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 CrVO4(s) und V2O5(s) zersetzt. Bei 645±5 °C bilden CrVO4 und V2O5 ein eutektisches Gemisch mit einem maximalen CrVO4-Gehalt von 2 mol%.РезюмеМетодом DTA и порошкого р ентгенофазового анализа изучено фазо вое равновесие системы V2О5-Cr2О3 до темп ературы 1000° и во всей области концентраци й компонентов. Установлено наличие двух соединений: CrVO4, пла вящегося инконгруэнтно при 860±5° и Cr2V4O13, разлагающегося в твердом состоянии пр и 640±5° до твердых CrVO4 и V2O5, которые при температуре 645±5° об разуют эвтектическу ю смесь с содержанием CrVO4, не превышающим 2 мольных %.

Iron(III) tungstate and its modifications

The conditions for the synthesis of Fe2WO6 in the solid state have been studied. It has been found that, at 750-840°C, a new polymorphic modification can be obtained. Its X-ray diffraction characteristics are given and some of its properties determined.

Studies on the system Al2O3-V2O5-MoO3

Studies on the three-component system Al2O3-V2O5-MoO3 have shown the existence of a new compound with molecular formula AlVMoO7. The synthesis conditions and X-ray characteristics of this compound and its melting temperature, 690±10°C, are reported.ZusammenfassungEinleitende Untersuchungen am Dreikomponentensystem Al2O3-V2 O5-MoO3 zeigten die Existenz einer neuen, noch nicht publizierten Verbindung der Formel AlVMoO7. Die Synthese der Verbindung sowie ihre röntgenographischen Eigenschaften wurden beschrieben. Ihr Schmelzpunkt beträgt 690±10°C.

Synthesis and some properties of the phase Cr2V4O13

Abstract A compound Cr 2 V 4 O 13 existing beside the hitherto known CrVO 4 in a two-component system, Cr 2 O 3 –V 2 O 5 , has been prepared by two methods, that is, by a reaction taking place in the solid state between the oxides and by co-precipitation made using solutions containing chromium(III) nitrate and ammonium metavanadate. The compound Cr 2 V 4 O 13 has been found to crystallise in a monoclinic system, parameters of its unit cell have been calculated and the infra-red spectrum of the compound shown.

Phase equilibria in the systems Fe2O3-WO3 and FeVO4-WO3

Abstract Diagrams of phase equilibria of the systems Fe 2 O 3 -WO 3 and FeVO 4 -WO 3 have been constructed based on the results of DTA and X-ray phase powder diffraction. It was found that Fe 2 WO 6 melts incongruently at 1100 ± 10°C yielding solid α-Fe 2 O 3 , and that the FeVO 4 -WO 3 system is not a two-component system, even below the solidus line.

Study of the solid solution of MoO3 in Fe2V4O13

Differential thermal and phase X-ray analyses have shown that MoO3 and Fe2V4O13 form a solid substitution solution, in which Mo6+ ions are incorporate into the crystal lattice of Fe2V4O13 in place of V5+ ions. The solubility limit of MoO3 in Fe2V4O13 at ambient temperature is 18 mole % of MoO3. The phase equilibria in the system Fe2V4O13-FeVMoO7, were also studied. Results are presented in the form of a phase diagram.ZusammenfassungDurch DTA und Röntgenphasenanalyse wurde gezeigt, daß MoO3 und Fe2V4O13 Substitutionsmischkristalle bilden, in denen Mo6+-Ionen anstelle von V5+-Ionen in das Kristallgitter von Fe2V4O13 eingebaut sind. Die Löslichkeitsgrenze von MoO3 in Fe2V4O13 beträgt bei Umgebungstemperatur 18 Mol-% MoO3. Ebenfalls wurden die Phasengleichgewichte im System Fe2V4O13-FeVMoO7 untersucht. Die Ergebnisse sind in Form eines Phasendiagramms dargestellt.РезюмеДифференциальный те рмический и рентгено-фазовый ана лизы показали, что МоО3 и Fe2V4O13 образуют твердый р аствор замещения, в ко тором ионы Мo6+ замешают ионы V5− в кристаллической реш етке Fe2V4O13. Предел растворимости МоО3 в Fe2V4O13 при обычной температуре составл яет 18 мольных %. Изучено также фазовое равновесие с истемы Fe2V4O13-FeVMoO7 и результаты предста влены в форме фазовой диаграммы.

Reactivity of Sb2O3 with Fe2O3 in ambient air

The use of X-ray phase diffraction and DTA methods has allowed studies on the interaction of the oxides Sb 2 O 3 and Fe 2 O 3 , taking place in the solid state and in the medium of ambient air. The experimental results have shown that the reaction yields the FeSbO 4 phase - recently produced by other workers using only co-precipitation methods. The compound has also been obtained from a reaction of α-Sb 2 O 4 with Fe 2 O 3 .

Studies on chromium(III) molybdate and equilibria in the CrVO4-Cr2(MoO4)3 system

Abstract The behaviour of Cr 2 (MoO 4 ) 3 towards CrVO 4 up to 1000 °C over the entire range of component concentrations was investigated using differential thermal analysis and X-ray powder diffraction. The results are shown in the form of a phase diagram. Chromium(III) molybdate decomposes to Cr 2 O 3 and MoO 3 before reaching its melting point. The decomposition of Cr 2 (MoO 4 )3 takes place at 810°C accompanied by the sublimation of MoO 3 .