Spirocyclohexadienones: XII. Dienone-phenol rearrangement of 1-substituted 2-azaspiro[4.5]undeca-1,6,9-trienes and their analogs

Hydrolytic cleavage of 1-substituted 2-azaspiro[4.5]undeca-1,6,9-trienes in acid medium is accompanied by dienone-phenole rearrangement with formation of substituted N-[2-(p-hydroxyphenyl)ethyl] carboxylic acid amides. 1,2-Dimethoxy-3-oxo-15-phenyl-14-azadispiro[5.1.5.2]pentadeca-1,4,14-triene and 2′-R-7a′-methyl-3a′,4′,5′,6′,7′,7a′-hexahydrospiro[cyclohexa[2,5]diene-1,3′-indol]-4-ones undergo analogous cleavage.     

Synthesis of the Zn1.9Cu0.1SiO4 pigment via the sol–gel and coprecipitation methods

Journal of Sol-Gel Science and Technology - The Zn1.9Cu0.1SiO4 pigment was obtained by two variants of “soft” chemistry methods: using sol–gel synthesis in ethanol from TEOS and...     

Stabilizing the triclinic structure of Mn2V2O7 via isovalent cationic substitution

The thermal expansion of Mn₂V₂O₇ in the temperature range of ?190 to 1030°C is studied. The volumetric thermal expansion coefficients for triclinic (α) and monoclinic (β) modifications are 2.57 × 10^?5 and 3.86 × 10^?5 1/deg, respectively. It is shown that as the Ni²⁺ concentration in Mn_2?2x Ni_2x V₂O₇ rises, the point of the α → β phase transition point moves from room temperature for Mn₂V₂O₇ to 155 ° 5°C for Mn_1.46Ni_0.54V₂O₇ (27 mol % Ni₂V₂O₇).     

Synthesis,sintering, and conductivity of Mn<Subscript>2</Subscript>V<Subscript>2</Subscript>O<Subscript>7</Subscript>

Studies on the sintering of manganese pyrovanadate depending on the temperature and the crystallite size show that we are prevented from obtaining a bulk ceramic sample by the anisotropic growth of grains. Investigation of the electrical properties of Mn₂V₂O₇ in the temperature range of 250–800°C reveals the activation energy at which bulk conductivity is 0.62 eV.     

Stabilizing the associated non-autonomous phase upon thermal expansion of Zn<Subscript>2</Subscript>V<Subscript>2</Subscript>O<Subscript>7</Subscript>

The previously unknown effect of emergence of an associated non-autonomous phase upon heating of zinc pyrovanadate Zn₂V₂O₇ within the region of negative volume expansion is detected. Comparison of the data of high-temperature X-ray diffraction of the Zn₂V₂O₇ samples synthesized via solution and solid-phase routes shows that the grain size affects the stabilization of the non-autonomous phase. The presence of a non-autonomous phase results in self-dispersion of the substance upon phase transition in heating–cooling cycles.     

Phase equilibria in the Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>–CdO system and the thermal stability of Cd<Subscript>2</Subscript>Nb<Subscript>2</Subscript>O<Subscript>7</Subscript> and CdNb<Subscript>2</Subscript>O<Subscript>6</Subscript>

Phase equilibria were studied in the Nb₂O₅–CdO system in the Nb₂O₅-rich region including CdNb₂O₆ and Cd₂Nb₂O₇. It was determined that CdNb₂O₆ and Cd₂Nb₂O₇ in air are stable to 1150 and 1120°C, respectively, and that, above these temperatures, there is solid-phase decomposition of niobates with CdO release in the gas phase. Along with the cadmium oxide evaporation, the Cd₂Nb₂O₇ decomposition is accompanied by the formation of cadmium metaniobate CdNb₂O₆ and the CdNb₂O₆ decomposition results in the formation of niobium oxide Nb₂O₅. No thermal events were observed in the differential thermal analysis curve for a 1: 1 CdNb₂O₆–Cd₂Nb₂O₇ mixture heated to 1100°C in air, which suggests that there are neither phase transformations in cadmium niobates, nor a eutectic within this temperature and concentration ranges. A study of the morphology of compacted samples of niobates determined specific conditions for producing dense composite ceramics, a mixture of niobates, that is suitable for using as a dielectric material.     

Phase equilibria in the V2O5-NaVO3-Ca(VO3)2-Mn2V2O7 system and interactions of phases with H2SO4 and NaOH solutions

Phase composition of the V₂O₅-NaVO₃-Ca(VO₃)₂-Mn₂V₂O₇ system was studied, and a subsolidus phase diagram constructed. The tetrahedration of the diagram is determined by the fact that the end-member of Ca_1–x Mn _x (VO₃)₂ solid solution is in equilibrium with all compounds of the system (V₂O₅, NaVO₃, Ca(VO₃)₂), vanadium β-bronzes Na _x V₂O₅ (0.22 ≤ x ≤ 0.40) and κ-bronzes (0.25 ≤ x ≤ 0.45, 0 ≤ y ≤ 0.16), Mn₂V₂O₇, and Na₂Mn₃(V₂O₇)₂ and with the end-members of reciprocal solid solutions based on calcium and sodium metavanadates. At 20°C, the degree of vanadium dissolution α for Na₂Ca(VO₃)₄ is 100% for 0.5 ≤ pH ≤ 10; for the other phases of the system, vanadium dissolution ranges from 100 to 10% for pH below 3.5; in the alkaline pH range, ≤ 10%. Sodium for calcium substitution in Ca(VO₃)₂ increases α in aqueous NaOH to 20%. For Na₂Mn₃(V₂O₇)₂, α decreases from 92 to 80% as pH changes from 0.5 to 2.5; at pH above 4, α = 30%.     

Structural modification of Mn2V2O7: Thermal expansion and solid solutions

Thermally activated structural change of Mn₂V₂O₇ has been studied at ?180 to 1000°C. The patterns of the solid solutions based on magnesium pyrovanadate stability upon isovalence substitution have been induced.     

Origin of the Concentration Quenching of Luminescence in Zn2SiO4:Mn Phosphors

Physics of the Solid State - The analysis of the unified series of single-phase Zn2&nbsp;–&nbsp;2xMn2xSiO4 samples (x ≤ 0.2) has provided the possibility to determine the...