Phase equilibria in the oxide system Nd2O3–K2O–P2O5

A phase equilibria diagram of the partial system NdPO₄–K₃PO₄–KPO₃ has been developed as part of the research aimed at determining the phase equilibrium relationships in the oxide system Nd₂O₃–K₂O–P₂O₅. The investigations were conducted using thermoanalytical techniques, X-ray powder diffraction analysis and reflected-light microscopy. Three isopleths existing between: K₃Nd(PO₄)₂–K₄P₂O₇, NdPO₄–K₅P₃O₁₀ and NdPO₄–K₄P₂O₇ have been identified in the partial NdPO₄–K₃PO₄–KPO₃ system. Previously unknown potassium-neodymium phosphate “K₄Nd₂P₄O₁₅” has been discovered in the latter isopleth section. This phosphate exists in the solid phase up to a temperature of 890 °C at which it decomposes into the parent phosphates NdPO₄ and K₄P₂O₇. Four invariant points: two quasi-ternary eutectics, E₁ (1057 °C) and E₂ (580 °C) and two quasi-ternary peritectics, P₁ (1078 °C) and P₂ (610 °C), occur in the NdPO₄–K₃PO₄–KPO₃ region.     

New Phase in the Bi–Sr–Ca–Cu–O System

Cooling a melt of a Bi–Sr–Ca–Cu–O system (Bi:Sr:Ca:Cu = 4:3:3:4 or 2:2:2:4) from 1000°C-1050°C yielded crystals of a new red-colored nonsuperconducting phase, accompanying the superconducting 2212 and 2201 phases. Based on the EPR spectra, it was concluded that copper is univalent in this compound. The new phase has a composition Bi_2.2Sr_1.6Ca_1.3Cu₂Ox. The X-ray diffraction pattern has been indexed, and the unit cell parameters of the phase have been determined: space group P2/m, a = 12.93, b = 4.55, c = 10.94 ; = 102.72°.     

Phase Equilibria in the System Fe2O3–V2O5 –WO3 in the Solid State

DTA and X-ray phase diffraction methods were used to construct a solidus area projection onto the component concentration triangle plane of the system Fe₂ O₃-V₂ O₅-WO₃. This revised version was published online in August 2006 with corrections to the Cover Date.     

Electrotransfer in nonstoichiometric lanthanum scandate LaSc1 ? x O3 ? �� (x = 0?0.1)

The phase composition and the total and partial conductivities of ceramic samples LaSc_{1 ? x} O_{3 ? ??} (x = 0?0.1) are studied as a function of the air humidity (pH₂O = 0.04?2.35 kPa) and the oxygen partial pressure (?15 ?? logpO₂ ?? ?0.68) in a wide temperature range from 100 to 900??C as well as their thermal expansion.     

Phase Transformations in the Mn–Ga–O System Depending on the Preparation Conditions

Manganese-gallium samples with cation ratios Mn:Ga = 1:2, 1.5:1.5, and 2:1 are synthesized by coprecipitation with subsequent annealing in air in a temperature range 600–1200 °C. Powder XRD, TEM, and BET methods are used to study the physicochemical characteristics of the samples. It is found that in the air at the annealing temperature of 600 °C finely dispersed low-temperature Mn_3–xGa_xO₄ spinels primarily form in all series, but in the whole temperature range (600–1200 °C) the system is multiphase. Annealing at 800–1200 °C leads to an increase in the concentration of simple oxides (β-Mn₃O₄ and β-Ga₂O₃). Only simple α-Mn₂O₃ and β-Ga₂O₃ oxides exist in a Mn:Ga = 2:1 series at 800 °C. In the sample with a cation ratio Mn:Ga = 1.5:1.5 annealed in air at 1000 °C, the formation of a superstructure based on the spinel structure is found.     

Ionic Lewis superacids in the gas phase. Part 5. Competing ligand displacements in the adducts between SiF3−x(OH)+x (x = 0–3) ions and H218O1

The actual nature of the ionic intermediates involved in the gas-phase reaction of SiF⁺₃ with water has been ascertained using a Fourier-transform ion cyclotron resonance (FT-ICR) instrument equipped with an external ion source. The complete kinetic pattern following attack of SiF_3−x(OH)⁺_x (x = 0–3) on H₂¹⁸O has been investigated, revealing the occurrence of competing H₂¹⁸O-to-HF and H₂¹⁸O-to-H₂¹⁶O displacement processes, whenx = 1 or 2. The factors governing the relative extent of such competing reactions and the overall reactivity of SiF_3−x(OH)⁺_x (x = 0–3) toward H₂¹⁸O are discussed. Occurrence of a relatively fast displacement in the tetracoordinated adducts of SiF_3−x(OH)⁺_x (x = 1–3) with H₂¹⁸O prevents their FT-ICR structural characterization.     

Phase Relations in The System Al2(MoO4)3–V2O5

The phase equilibria established in the system Al₂ (MoO₄ )₃ –V₂ O₅ throughout the whole component concentration range up to 1000°C were investigated by DTA and XRD methods. The results are presented in the form of a phase diagram. This revised version was published online in August 2006 with corrections to the Cover Date.     

Hydrogen content in proton-conducting perovskites CaZr1 − x Sc x O3 − x /2 (x = 0.0–0.2)

The hydrogen content in CaZr_{1 ? x} Sc _x O_{3 ? x/2} (x = 0.00–0.20) and BaZr_0.9Y_0.1O_3-α (for comparison) was studied by powder nuclear microanalysis. The samples were saturated with heavy water (D₂O) vapors at 350 and 400°C in air. The chemical expansion of the CaZr_0.95Sc_0.05O_3-α and BaZr_0.95Y_0.05O_3-α samples at 700°C was measured at different water vapor pressures. A model was suggested to explain the lowered hydrogen content in oxides based on CaZrO₃.     

Phase Equilibria in The System La2O3–K2O–P2O5

The ternary system La₂O₃–K₂O–P₂O₅ has been examined by thermal, X-ray, IR and microscopic methods. The existence of three double potassium-lanthanum phosphates, K₃La(PO₄)₂, KLa(PO₃)₄ and K₂La(PO₃)₅ has been confirmed, and the phase diagram of the ternary system La₂O₃–K₂O–P₂O₅ over the composition range LaPO₄–K₃PO₄–P₂O₅ has been determined. This revised version was published online in August 2006 with corrections to the Cover Date.     

LaMn1 – xFexO3 (x = 0–1) Perovskites in Methane and Carbon Monoxide Oxidation Reactions

Kinetics and Catalysis - The LaMn1 – xFexO3 (х = 0–1) perovskites were prepared by the Pechini route and characterized by X-ray diffraction analysis, HR TEM, XPS, and BET. Their...     

Reinvestigation of Phase Equilibria in the V2O5–ZnO System

A diagram of phase equilibria established in a two-component oxide system V_{2 5}–ZnO has been worked out applying differential thermal analysis and X-ray phase analysis as well as depending on investigations carried out with the aid of high-temperature X-ray attachment and scanning electron microscope linked to an X-ray microanalyser. This revised version was published online in July 2006 with corrections to the Cover Date.     

Phase Diagram of the AgNO3–CsNO3 System

The phase diagram of the binary AgNO₃–CsNO₃ system was constructed using differential thermal analysis (DTA) technique in the range 300–700 K. The apparatus is described briefly. The results exhibit a congruently melting compound CsNO₃·AgNO₃ (m.p.=453 K) characterized by two allotropic varieties and , an incongruently melting compound AgNO₃·CsNO₃ (m.p.=450 K) with three forms , and , two eutectics (16 mol% CsNO₃, 442 K and 32.5 mol% CsNO₃, 445 K) and a peritectic (38mol% CsNO₃, 450 K). The occurrence of the transitions of intermediates was confirmed by X-ray diffraction at variable temperatures. The phase diagram exhibits also two plateaus at 429 K and 435 K corresponding to the phase transitions of CsNO₃ and AgNO₃, respectively.This revised version was published online in November 2005 with corrections to the Cover Date.     

Formation of (C x H2x+1)4NBr·nH2O (x = 1–3) hydrate

The phase diagram of the binary system tetramethylammonium bromide-water was studied by the differential thermal analysis. In the stable region two phases, ice and the salt itself, were detected, and in the metastable region, three tetramethylammonium bromide hydrates (bromide-water, 1 : 4, mp 68.8°C, 1 : 5, mp 36.0°C, 1 : 7.5, mp ?19.5°C) were found. Formation of (C _x H_2x+1)₄NBr·nH₂O (x = 1–3, n = 4, 5, 7.5) hydrates was revealed.     

Forms of oxygen in La1 − x Ca x MnO3 + δ (x = 0–1) perovskites and their reactivities in oxidation reactions

The effects of substitution in the cationic sublattice and of the synthesis procedure on the reactivity of different forms of oxygen in La_{1 ? x} Ca _x MnO_{3 + δ} perovskites synthesized by mechanochemical and ceramic processing was studied by temperature-programmed reduction (TPR) with hydrogen. As the calcium content of the perovskite is raised, the maxima of the TPR peaks shift to lower temperatures and the extent of reduction of the perovskite increase, implying an increase in the reactivity of the system. Conversely, raising the calcination temperature or extending the calcination time shifts the maxima of the peaks to higher temperatures and diminishes the extent of reduction of the sample. TPR data for the intermediate-composition samples can be explained in terms of the dependence of microstructure on the synthesis procedure (near-surface calcium segregation in the mechanochemically synthesized samples and the microheterogeneous structure of the ceramic samples). The reduction process Mn⁴⁺ → Mn²⁺ takes place in the low- and medium-temperature regions. According to the literature, the bulk reduction process Mn³⁺ → Mn²⁺ occurs at high temperatures. The activity of the system in CO oxidation is correlated with the amount of the most reactive surface oxygen, which is eliminated in hydrogen TPR runs below 250–300°C.     

Phase Relationships in the U – Np – O System

U – Np – O phase equilibria was experimentally studied by X-ray diffraction in reducing and oxidizing conditions. Both (U1yNpy)O2 stoichiometric and hyper-stoichiometric compounds were characterized after a heating treatment and resulting lattice parameters were compared to that of previous studies. Synthesized stoichiometric compounds are monophasic and their lattice parameters as a function of Np content are in nice agreement with the Vegard's law between UO2 and NpO2 end-member. Resulting compounds after an oxidizing heat treatment of the stoichiometric samples confirm previous reported U – Np – O relationship. For low Np content, a biphasic hyper-stoichiometric compound is observed: a (U1-y’Npy’)O2+x phase (space group fm-3m) and a (U1-y”,Npy”)3O8 phase (space group C2 mm). For higher Np content (with starting material y = 0.7), only one monophasic hyper-stoichiometric phase (U1-y’Npy’)O2+x appears. Lattice parameters of the (U1-y”,Npy”)3O8 phase differ from the ones of pure U3O8, indicating some Np solubility in this compound. Although Np might remain tetravalent in the (U1y”,Npy”)3O8 phase, this result is in conflict with the assumption of Yamashita et al. (1994).     

Phase Equilibria in the System YPO4–K3PO4–KMgPO4

The phase equilibria in the part of the ternary system YPO₄–K₃PO₄–Mg₃(PO₄)₂ over the composition range YPO₄–K₃PO₄–KMgPO₄ were examined and determined by differential thermal analysis, X-ray powder diffraction and microscopic analysis in reflected light. This revised version was published online in August 2006 with corrections to the Cover Date.     

Phase Equilibria in the System NH4Al(SO4)2–H2SO4–H2O

Equilibrium solubility curves of the ammonium aluminium sulphate in aqueous solutions of sulphuric acid have been calculated using checked literature data and our own measurements. The concentration of sulphuric acid ranged from 0 to 23 mass%, temperature range between 20 and 60°C has been extrapolated up to 75°C by means of a thermodynamically based correlation method. The solubility correlation as well as the hydration analysis implied a possible destructuralization of solutions at higher acid concentrations. This revised version was published online in August 2006 with corrections to the Cover Date.