Thermochemische Untersuchungen im System V/Nb/O. II Zum chemischen Transportverhalten im Bereich V2O5/Nb2O5/VO2/NbO2

Thermochemical Investigations in the System V/Nb/O. II. Chemical Transport in the Region V₂O₅/Nb₂O₅/VO₂/NbO₂ Transport experiments were used to support the phase relationships of the V₂O₅/Nb₂O₅/VO₂/NbO₂ system, which were established by annealing experiments of powder mixtures. The phase relations were studied in the NbO₂-rich region of the system by means of X-ray and ESMA methods. The NbO₂-rich section is characterized by the following two phase and three phase regions: Two phase region: V₃Nb₉O₂₉/rutile mixed crystal V_1?xNb_xO₂ Two phase region: BI-mixed crystal/V_xNb_1?xO₂ Three phase region: V₃Nb₉O₂₉/solubility limit LG1 (V_1?xNb_xO₂)/BI-mixed crystal Three phase region: solubility limit LG1 (V_1?xNb_xO₂)/BI-mixed crystal/solubility limit LG2 (V_xNb_1?xO₂). The composition of the solubility limits LG1 and LG2 was ascertained by means of ESMA-investigation: LG1: 57.5 ± 5 mol% NbO₂/43.5 ± 5 mol% VO₂ LG2: 22.5 ± 5 mol% NbO₂/78.5 ± 5 mol% VO_2?     

Untersuchungen zum chemischen Transport der Vanadiumoxide V2O5, V3O7 und V6O13

Chemical transport of the vanadium oxides V₂O₅, V₃O₇, and V₆O₁₃ The suitability of water and some halogenating transport agents (NH₄Cl, NH₄Br, I₂) for the chemical transport (temperature gradient 850/750 K) of V₂O₅, V₃O₇, and V₆O₁₃ has been investigated. Transport rates for V₂O₅ and V₆O₁₃ could be measured and reproduced. The best transport agent for V₂O₅ is NH₄Cl or H₂O. For V₃O₇ a combination of the transport agents I₂/H₂O give the best results and for V₆O₁₃ the combination of NH₄Br/H₂O was most appropriate.     

Zu den Phasenverhältnissen im System V/Nb/O. I. Koexistenzbeziehungen im Bereich V2O5/Nb2O5/VO2/NbO2

The Phase Relations in the System V/Nb/O. I. Coexistence Relations in the Section V₂O₅/Nb₂O₅/VO₂/NbO₂ . Phase relations in the section Nb₂O₅/V₂O₅/VO₂/NbO₂ of the ternary system V/Nb/O have been studied by X-ray diffraction. The investigated samples were prepared by high temperature synthesis at 900°C–1000°C. The section Nb₂O₅/V₂O₅/VO₂/NbO₂ is charakterized by fife three phase regions: The limits of solubility of the pseudobinary system were ascertained by determination of lattic parameters of powder samples:      

Untersuchungen zum ternären System V/Mo/O

Investigation on the Ternary System V/Mo/O During chemical transport reactions mixtures of pseudo-binary line of intersection V₂O₅/MoO₃ are separated into two phases, the V₂O₅-(α) phase, which MoO₃-content depends on the oxygen partial pressure during the deposition and the MoO₃ phase which contains no more than 1% (n/n) V₂O₅. Ternary compounds do not exist on the pseudo-binary line. V₉Mo₆O₄₀ is formed by the reaction of V₂O₅ and MoO₃ (3:2) under exclusion of oxygen. The compound may be chemically transported under the own oxygen coexistence pressure. It was shown by total pressure measurements of V₂O₅/MoO₃ starting mixtures that the insertion of MoO₃ in the α-phase and the formation of the V₉Mo₆O₄₀ phase respectively is connected with elimination of oxygen and the reduction of V^V to V^IV in equivalence of the quantity of incorporated MoO₃.     

Zum Chemischen Transport im System Mg/Mo/O ‐ Experimente und Modellrechnungen

On the Chemical Vapour Transport in the Mg/Mo/O System ‐ Experiments and Model Calculations Single crystals of MgMoO₄ and Mg₂Mo₃O₈ have been obtained via chemical vapour transport in a temperature gradient 1273 to 1173 K using Cl₂ and Br₂ as transport agents. Pure powders of the ternary compounds have been used as starting materials as well as mixtures of three coexisting phases. The observed transport behaviour is compared with results of thermodynamical model calculations. The influence of source composition, transport agent and the moisture contents is described in detail.     

Untersuchungen zum System Bi2O3/BiI3

Investigations on the System Bi₂O₃/BiI₃ The temperature functions of decomposition pressures of the ternary compounds on the quasibinary line Bi₂O₃/BiI₃ were determined by total pressure measurements and mass spectrometry. The barogram of the system was constructed and the melting diagram precised. The enthalpies of formation and the standard entropies of the solid phases were derived from the decomposition functions: (Values see Inhaltsübersicht).     

Untersuchungen zum System Bi2O3/BiBr3

Investigation on the System Bi₂O₃/BiBr₃ The temperature functions of decomposition pressures of the ternary compounds on the quasibinary line Bi₂O₃/BiBr₃ were determined by total pressure measurements. The barogram of the system was constructed and the melting diagram precised. The enthalpies of formation and the standard entropies of the solid phases were derived from the decomposition functions (Values see “Inhaltsübersicht”).     

Untersuchungen zum System Bi2O3/BiCl3

Investigation on the System Bi₂O₃/BiCl₃ The temperature functions of decomposition pressures of the ternary compounds on the quasibinary line Bi₂O₃/BiCl₃ were determined by total pressure measurements and mass spectroscopy. The barogram of the system was constructed and the melting diagram precised. The enthalpies of formation and the standard entropies of the solid phases were derived from the decomposition functions: (Values see Inhaltsübersicht).     

Untersuchungen zum System BiOCl/SeO2

Investigations on the System BiOCl/SeO₂ The section BiOCl/SeO₂ was shown to be quasibinary one and include only one intermediate phase BiOCl · SeO₂ = BiSeO₃Cl. The phase barogram and the phase diagram were determined by total pressure measurements and DTA. BiSeO₃Cl shows on heating two transitions in crystal phase, (α → β) at 400 ± 2 °C and (β → γ) at 410 ± 3 °C. The compound melts peritectically at 417 ± 3 °C. The experiments on sublimation of BiSeO₃Cl in the temperature gradient and chemical vapour transport with SeO₂ allowed to make the conclusion on the existence of BiSeO₃Cl molecules in the vapour. Some standard thermodynamic data were determined by solution calorimetry and evaluated from the vapour pressure and chemical vapour transport rate data. (Data see Inhaltsübersicht)     

Untersuchungen zum System BiOBr/SeO2

Investigations on the System BiOBr/SeO₂ The section BiOBr/SeO₂ was shown to be quasibinary and include only one intermediate phase BiOBr · SeO₂ = BiSeO₃Br. The phase barogram and the phase diagram were determined by total pressure measurements and DTA. BiSeO₃Br melts peritectically at 490 ± 3 °C and forms an eutectic mixture with SeO₂ at 70 Mol.‐% SeO₂ and 210 ± 10 °C. From the chemical vapour transport of BiOBr_s with SeO_2,g and the sublimation of BiSeO₃Br_s followed the existence of BiSeO₃Br_g molecules in the vapour. The thermodynamic data of the solid and the vapour phase were derived. (Data see Inhaltsübersicht)     

Cadmium in tetragonal pyramidaler Koordination im Barium-Cadmium-Oxovanadat: Ba2Cd3(VO4)2(V2O7)

Cadmium in Square Pyramids of Oxygen in the Barium Cadmium Oxovanadate: Ba₂Cd₃(VO₄)₂(V₂O₇) Single crystals of Ba₂Cd₃(VO₄)₂(V₂O₇) have been prepared by crystallization of a melt of BaCO₃, CdO and V₂O₅. It shows orthorhombic symmetry, space group D? P2₁2₁2₁, a = 7.206(2), b = 9.978(1), c = 19.617(3) Å, Z = 4. The crystal structure is characterized by (VO₄)^3? and (V₂O₇)^4? groups, CdO₆ octahedra, BaO₁₂ and BaO₉ polyhedra and with respect to Cd containing oxides unusual square pyramids of O^2? around Cd²⁺. The observed [CdO₄] zickzack chains are connected by VO₄ tetrahedra, V₂O₇ double tetrahedra and CdO₅ pyramids, forming a tunnel structure along [100]. The tunnels are filled by barium.     

Neues zum chemischen Transport von CuO und Cu2O

New Results on the Chemical Transport of CuO and Cu₂O The preparation of CuO crystals by chemical transport reactions with HCl is already well known, a comparison with other transport agents based on the principal of thermodynamic equilibrium and also the rate of transport was missing up to now. We report about experiments with the transport agents HgCl₂, Cl₂, I₂, Nh₄Cl, or CuCl; the quantitative evaluation was made by means of the cooperative transport model on the basis of the free energy function. By this way it is possible to find favourable experimental conditions for the suitable transport agents at the outset. It turned out that HgCl₂ is an appropriate transport agent which can easily be weighed. Also I₂ is useful, whereas the effect fo transport with Cl₂ (1 atm/298 K), CuCl, or NH₄Cl is very small. We investigated the chemical transport of Cu₂o and the conditions for the change of its direction of transport.     

Experimente und Modellrechnungen zum chemischen Transport von V2O5 mit NH4Cl

Experiments and Calculations for the Chemical Transport of V₂O₅ with NH₄Cl For the chemical transport of V₂O₅ in a temperature gradient (T₂ – T₁ = ΔT = 100 K) the influence of temperature (T₂ = 770 K to 970 K) on the transport rate n′(V₂O₅) using an admixture of 2 to 8 mg NH₄Cl (2,3 to 9,2 × 10^?3 mmol/cm³) has been investigated. Also the dependence of n′ on the admixture of the transport agent has been examined from 2 to 52 mg NH₄Cl (T₂ = 850 K, T₁ = 750 K). We observed that n′ increases with increasing temperature and increasing admixture of NH₄Cl. The model calculations show the opposite tendency of the dependence on temperature; for all experiments the value of n′ was lower by a factor of 10 to 320 than the calculated one. These deviations indicate, that our knowledge on the gas phase of this system is incomplete.     

Zum Chemischen Transport im System Mn/Mo/O

Chemical Transport Reactions in the System Mn/Mo/O For the ternary system Mn/Mo/O the phasepure preparation of the compounds MnMoO₄ and Mn₂Mo₃O₈ by chemical transport is reported. The deposition from a source of coexisting threephase mixtures give the possibility to prepare single crystals under defined oxygen partial pressure. The influence of different startmixtures and the agents Cl₂, HCl, I₂, HI, TeCl₄ and SeCl₄ on the transport behaviour are described. Results hitherto existing for the single crystals give hints of only very small homogeneity ranges for both phases.     

Beiträge zum thermischen Verhalten von Sulfaten. XV [1]. Zum chemischen Transport von Al2(SO4)3 mit SOCl2. Experimente und Modellrechnungen

Contributions on the Thermal Behaviour of Sulfates. XV. The Chemical Vapour Transport of Al₂(SO₄)₃ with SOCl₂. Experiments and Calculations Well shaped crystals (cubical or rectangular parallelepiped respectively) of rhombohedral Al₂(SO₄)₃ can be grown in the less hot zone of a closed silica ampoule by means of chemical (vapour) transport using SOCl₂ as transport agent in endothermal transport reactions. The influence of the mean transport temperature as well as the concentration of the transport agent on the deposition rates was investigated. We also tried to describe this transport system on the basis of thermochemical calculations.     

Beiträge zum thermischen Verhalten von Sulfaten. XIII. Zum chemischen Transport von Cr2(SO4)3 mit Cl2 und mit HCl. Experimente und Modellrechnungen

Contributions on the Thermal Behaviour of Sulfates. XIII. The Chemical Vapour Transport of Cr₂(SO₄)₃ with Cl₂ and with HCl. Experiments and Calculations Well shaped crystals (cubical or rectangular parallel-epiped respectively, edge length up to 1 mm) of rhombohedral Cr₂(SO₄)₃ can be grown in the less hot zone of a closed silica ampoule by means of CVT using Cl₂ or HCl as transport agents in endothermal transport reactions. The influence of the mean transport temperature as well as the concentration of the transport agents on the deposition rates was investigated. On the basis of thermochemical calculations an explanation of the transport mechanism is given in the present paper.     

Chemischer Transport und Sauerstoffionenleitfähigkeit von Mischkristallen im System In2O3/SnO2

Chemical Transport of Solid Solutions. 8. Transport Phenomena and Ionic Conductivity in the In₂O₃/SnO₂ System Chemical transport reactions are a suitable pathway to the preparation of In₂O₃‐rich and SnO₂‐rich mixed crystals coexisting in the In₂O₃/SnO₂ system (Cl₂ as transport agent, 1050 → 900 °C). Experiments are consistent with thermodynamic calculations. The existence of other phases in the system In₂O₃/SnO₂ could not be confirmed. The ionic conductivity of In₂O₃(SnO₂) was investigated.