Hydrothermal synthesis,thermal decomposition and optical properties of Fe2F5(H2O)(Htaz)(taz)(Hdma)

Crystal structure of Fe₂F₅(H₂O)(Htaz)(taz)(Hdma) which crystallizes in the triclinic system space group $\text{P}\overline{1}$ with unit cell parameters a = 8.8392(5) Å, b = 9.1948(5) Å, c = 9.5877(5) Å, α = 82.070(3)°, β = 63.699(3)°, γ = 89.202(3)°, Z = 2, and V = 690.91(7) ų, was synthesized under hydrothermal conditions at 393 K for 72 h, by a mixture of FeF₂/FeF₃, 1,2,4-triazole molecule (Htaz), and hydrofluoric acid solution (HF 4%) in dimethylformamide solvent (DMF). The main feature of this material is the coexistence of two oxidation states for iron atoms (Fe²⁺, Fe³⁺) in the unit cell, which associate by opposite fluorine corners of FeF₅N and FeF₂N₄ octahedra, and/or triazole molecule which originates the 2D produces material. The structure determination, performed from single crystal X-ray diffraction data, lead to the R₁/_WR₂ reliability factors 0.031/0.087. Thermal stability studies (TG/DTG/DTA) show that the decomposition provides in the temperature range 473–773 K and no mass loss was detected before 473 K. Mass spectrometry (MS) has been used. The optical absorption of the solid was measured at the corresponding λ_max using UV–vis diffuse-reflectance spectrum.     

Octadecylamine as chemical modifier for tuned hydrophobicity of surface modified cellulose: toward organophilic cellulose nanocrystals

Cellulose - A novel, environmentally friendly and simple method for chemical functionalization of microcrystalline cellulose (MCC) to produce organophilic cellulose nanocrystals (CNC-ODA) is herein...     

Use of thermal analysis to predict the conditions for thermal explosion to occur: application to a Ce triethanolamine complex

Journal of Thermal Analysis and Calorimetry - Thermal energy storage (TES) has been identified as a breakthrough concept in development of renewable technologies. However, the main challenges are...     

Number systems with negative bases

We study the expansion of real numbers with negative base (?β), and prove that if $\mathbb{Z^{-}}$ or $\mathbb{Z^{+}} \subset \mathop {\rm Fin}\nolimits \, (-\beta)$ , then β is a Pisot number.     

Singular limits for a 4-dimensional semilinear elliptic problem with exponential nonlinearity

Using some nonlinear domain decomposition method, we prove the existence of branches of solutions having singular limits for some 4-dimensional semilinear elliptic problem with exponential nonlinearity.     

Finite element method for the stress analysis of isotropic cylindrical helical spring

This paper presents an efficient two nodes finite element with six degrees of freedom per node, capable to model the total behaviour of a helical spring. The formulation, which includes the shear deformation effects, is based on the assumed forces hybrid approach. The resultant forces approximation verifies exactly the resultant equilibrium equations. The developed model proves its accuracy compared with other elements. This element permits to get the distribution of different stresses along the spring and through the wire surface by only one element.     

Structural,vibrational and thermal properties of a new inorganic compound: Tl0.92(NH4)0.08(SO4)0.65(SeO4)0.35Te(OH)6

Research on Chemical Intermediates - A new compound thallium ammonium sulfate selenate tellurate: Tl0.92(NH4)0.08(SO4)0.65(SeO4)0.35Te(OH)6 (TlNSSeTe) has been synthesized by slow evaporation at...     

Inclusion of the concentration dependence of the diffusion coefficient in the sand equation

The applications of the Sand equation in potentiometry of electrode and membrane systems for precise measurements of the transition time (τ) have been determined. An approach was suggested for choosing the diffusion coefficient of electrolyte (D) in the case when the concentration changes from its value in the agitated solution (where D = D_b) to the nearly zero value at the surface (D = D₀ corresponds to an infinitely dilute solution), D_b and D₀ being substantially different. The Nernst–Planck–Poisson nonstationary equations were numerically solved in a one-dimensional system including an ion-exchange membrane and two adjacent diffusion layers (for the electrode–solution system, the result is a particular case). An effective value D_ef was found, whose substitution in the Sand equation gave τ identical to that obtained by numerical solution. The neglect of the concentration dependence D(с) can lead to a nonadequate determination of the ion transport numbers in the membrane.     

Non-isothermal model-free predictions

Suitable thermal treatment of metal organic precursors is a key process to obtain oxide films. To this purpose, non-isothermal model-free predictions are specially suited. In this article we will explore the ability of these methods to provide an accurate prediction of the evolution of the decomposition of yttrium trifluoroacetate, a precursor used in the synthesis of YBaCuO superconducting thin-films. A good agreement has been obtained between the predicted and the measured reaction courses.     

Evolution of yttrium trifluoroacetate during thermal decomposition

A detailed analysis of the thermal decomposition of yttrium trifluoroacetate under different atmospheres is presented. Thermogravimetry, differential thermal analysis, and evolved gas analysis have been used for this in situ analysis. Solid residues at different stages have been characterized by means of X-ray diffraction, elemental analysis, Fourier transform infrared spectroscopy, and scanning electron microscopy. The first decomposition stage (310 °C) is exothermic and involves the complete removal of carbon (organic part) and the formation of yttrium fluoride. This process is characterized by a fast mass loss rate. Afterwards, yttria (Y₂O₃) is formed at 1200 °C through a slow process controlled by the out diffusion of fluorine that involves the formation of yttrium oxyfluoride as an intermediate. The evolution of the mass during the decomposition and the structure of the yttria particles is not affected by the presence of oxygen or water. However, when the oxygen (water) partial pressure is as low as 0.02% (<0.002%), the kinetics and final particle structure are strongly affected.