The relationship between properties of fluorinated graphite intercalates and matrix composition 7

Inclusion compounds (intercalates) of fluorinated graphite matrix with ethyl acetate (C₂F_xBr_z·yCH₃COOC₂H₅, x = 0.49, 0.69, 0.87, 0.92, z = 0.01) were prepared by guest substitution from acetonitrile to ethyl acetate. The kinetics of the thermal decomposition (the first stage of filling → the second stage of filling) was studied under isothermal conditions at 291–307 K. The relationship of the host matrices’ structure with inclusion compounds’ thermal properties and kinetic parameters is discussed.     

The relationship between properties of fluorinated graphite intercalates and matrix composition

Inclusion compounds (intercalates) of fluorinated graphite matrix with butanone (C₂F_xBr_z·yCH₃COC₂H₅, x = 0.49, 0.69, 0.87, 0.92, z ≈ 0.01) were prepared by guest substitution from acetonitrile to butanone. The kinetics of the thermal decomposition (the 1st stage of filling → the 2nd stage of filling) was studied under isothermal conditions at 294–313 K. The relationship of the host matrices structure with inclusion compounds’ thermal properties and kinetic parameters is discussed.     

Thermophysical properties of thorium–praseodymium mixed oxides

Thorium–Praseodymium mixed oxide solid solutions (Th_1?yPr_y)O_2?x (y = 0.15, 0.25, 0.4, 0.55) were prepared by co-precipitation method. These mixed oxides form single-phase fluorite solid solutions (fm3m). Heat capacity (C _p) measurements and lattice thermal expansion characteristics of these solid solutions were determined with differential scanning calorimeter in the temperature range of 298–800 K and high temperature X-ray diffractometer in the temperature range of 298–2,000 K, respectively. The C _p,₂₉₈ of (Th _1?yPr_y)O_2?x pertaining to the solid solutions with the compositions, y = 0.15, 0.25, 0.4, and 0.55, were found to be 65.2, 62.4, 60.1, and 57.1 J K^?1 mol^?1, respectively. The coefficients of lattice thermal expansion in the temperature range of 298–2,000 K of (Th_1?yPr_y)O_2?x for these solid solutions with the compositions y = 0.15, 0.25, 0.4, and 0.55 were found to be 16.97, 20.43, 25.63 and 30.82 × 10^?6 K^?1, respectively.     

The influence of concentration of doping elements on anatase–rutile transformation at the synthesis of rutile pigments (Ti,Cr,Nb)O2 and their pigmentary properties

An analysis of the effects of dopants concentration and different starting titanium compounds on the anatase to rutile phase transformation at the synthesis of rutile pigments Ti_1?3xCr_xNb_2xO_2±δ is presented in this study. The main goal was to analyze reaction mixtures for x = 0.05 (previous study) and 0.30 by simultaneous TG–DTA analysis and to determine the temperature of anatase–rutile transition. For x = 0.05, initial temperatures 760–830 °C are needful for a formation of rutile structure. The temperature is the lowest for the hydrated Na₂Ti₄O₉ paste (760 °C) and similar for other starting compounds of titanium. But for x = 0.30, the anatase–rutile transition begins at higher temperatures 910–1,030 °C because of high-Nb content, which is the inhibitor of this modification change. In addition, we found the influence of calcination temperatures (850, 900, 950, 1000, 1050, 1100, and 1150 °C) on color properties and particle size distribution of these materials prepared from anatase TiO₂ and with x = 0.30. Selected pigments were also analyzed by X-ray powder diffraction.     

Molecular structure and conformation of nitrobenzene reinvestigated by combined analysis of gas-phase electron diffraction,rotational constants,and theoretical calculations

The molecular structure and conformation of nitrobenzene has been reinvestigated by gas-phase electron diffraction (GED), combined analysis of GED and microwave (MW) spectroscopic data, and quantum chemical calculations. The equilibrium r _e structure of nitrobenzene was determined by a joint analysis of the GED data and rotational constants taken from the literature. The necessary anharmonic vibrational corrections to the internuclear distances (r _e ? r _a) and to rotational constants (B _e ⁽ⁱ⁾  ? B ₀ ⁽ⁱ⁾ ) were calculated from the B3LYP/cc-pVTZ quadratic and cubic force fields. A combined analysis of GED and MW data led to following structural parameters (r _e) of planar nitrobenzene (the total estimated uncertainties are in parentheses): r(C–C)_av = 1.391(3) Å, r(C–N) = 1.468(4) Å, r(N–O) = 1.223(2) Å, r(C–H)_av = 1.071(3) Å, \({\angle}\)C2–C1–C6 = 123.5(6)°, \({\angle}\)C1–C2–C3 = 117.8(3)°, \({\angle}\)C2–C3–C4 = 120.3(3)°, \({\angle}\)C3–C4–C5 = 120.5(6)°, \({\angle}\)C–C–N = 118.2(3)°, \({\angle}\)C–N–O = 117.9(2)°, \({\angle}\)O–N–O = 124.2(4)°, \({\angle}\)(C–C–H)_av = 120.6(20)°. These structural parameters reproduce the experimental B ₀ ⁽ⁱ⁾ values within 0.05 MHz. The experimental results are in good agreement with the theoretical calculations. The barrier height to internal rotation of nitro group, 4.1±1.0 kcal/mol, was estimated from the GED analysis using a dynamic model. The equilibrium structure was also calculated using the experimental rotational constants for nitrobenzene isotopomers and theoretical rotation–vibration interaction constants.     

Anatase–rutile transformation at the synthesis of rutile pigments (Ti,Cr,Nb)O2 and their color properties

Synthesis of rutile pigments is based on solid state reaction and on Hedvall effect, i.e., phase transformation from anatase to rutile. Therefore, it is important to know the thermal behavior of these compounds (the temperature of this change). The goal was to prepare rutile pigments of type Ti_1?3xCr_xNb_2xO_2+x/2 by conventional solid state method from titanium dioxide TiO₂ (AV-01, anatase), to determine an influence of composition (x = 0, 0.05, 0.10, 0.20, 0.30, 0.50) and calcination temperature (850; 900; 950; 1,000; 1,050; 1,100; 1,150 °C) on color properties of these compounds and to analyze other starting compounds of titanium (hydrated anatase paste TiO₂·nH₂O, titanyl sulfate dihydrate TiOSO₄·2H₂O (VKR 611), hydrated sodium titanium oxide paste Na₂Ti₄O₉·nH₂O) and their reaction mixtures for x = 0.05 by simultaneous TG–DTA analysis. According to the highest chroma C of color, the optimal conditions for synthesis of these pigments are concentration x = 0.05 and calcination temperature 1,050 °C and higher. It was observed that initial temperature 760–830 °C is needful for a formation of rutile structure. This temperature is the lowest for hydrated Na₂Ti₄O₉ paste (760 °C) and similar for other starting compounds of titanium.     

Phase equilibriums, oxygen exchange kinetics and diffusion in oxides CaZr1 ? x Sc x O3 ? x/2 ? δ

Oxides CaZr_{1 ? x} Sc _x O_{3 ? x/2 - ??} (x = 0.00?C0.20) were synthesized according to the ceramic technology. The solubility boundary of scandium with formation of solid solutions on the basis of calcium zirconate CaZrO_{3 ? ??} corresponds to x = 0.07?C0.08. The second phase of CaSc₂O₄ is present in the samples with scandium content of x = 0.10, 0.15, 0.20. Its fraction grows at an increase in x. The method of full-profile Rietveld analysis was used to calculate the structure parameters for oxides CaZr_0.99Sc_0.01O_{2.995 ? ??} and CaZr_0.95Sc_0.05O_{2.975 ? ??}. The method of isotopic exchange with gas phase analysis was used to study the kinetics of gas-phase oxygen interaction with the CaZr_0.95Sc_0.05O_{2.975 ? ??} oxide in the temperature range of 700?C850°C and at oxygen pressures of 0.13?C6.67 kPa. The values of effective activation energies of the oxygen exchange and diffusion processes were 1.36 ± 0.32 and 1.92 ± 0.21 eV, accordingly. The dependence of the interphase exchange rate on the pressure of oxygen corresponds to the power law with the exponent of 0.31 ± 0.04 at the temperature of 750°C.     

Electrophysical and electrochemical properties of Y1 − x Ca x Cr1 − y Me y O3 (Me = Mg, Cu)

Structure, thermal elongation coefficient, and conductivity of Y_{1 ? x} Ca _x Cr_{1 ? y} Me _y O₃ (Me = Mg, Cu) in air are studied at 100–1000°C. Electrochemical activity of electrodes made of most conducting compositions Y_{1 ? x} Ca _x Cr_{1 ? y} Me _y O₃ (Me = Mg, Cu), contacting solid electrolyte 0.9ZrO₂ + 0.1Y₂O₃, is studied over a wide range of polarizations, in air, at 700–900°C.     

Synthesis, electrical and thermal properties of Bi4V2−xMexO11 (x = 0.0 and 0.02) ceramics

Polycrystalline ceramic samples of Bi₄V_2?xMe_xO₁₁ (Me = Nb, Zr, Y and Cu and x = 0.0 and 0.02) have been synthesized by standard solid state reaction method using high purity oxides. The formation of the compounds have been analysed by X-ray diffraction method. The dielectric constant, dielectric loss and AC conductivity as a function of frequency and temperature have been measured. The dielectric studies indicate that the material is highly lossy and hence its AC conductivity increases with the increase of temperature. The DC conductivity of material has been measured as a function of temperature from room temperature to 380 °C and its activation energy was calculated using the relation σ = σ ₀exp (?E _a/kT). The modulated differential scanning calorimetry has been used to investigate the effect of substitution on the heat capacity and heat flow of the compounds. The results are discussed in detail.     

Estimation of the heat capacity of some uranium-rare earth mixed oxides from thermal expansion and vice versa

Estimation of the high temperature heat capacity (C _p) data from experimental high temperature thermal expansion (α _v) data and vice versa from the known values of the ratio (α_v/C _p) at low temperatures were carried out by assuming linear relationship of the ratio α _v /C _p with temperature (at T > θ _D). The assumption was examined using the known α _v and C _p values of single phase fluorite systems such as UO₂, ThO₂ and PuO₂. It was also examined using the known α _v and C _p of the mixed oxides (U_1?y La_y) O_2±x (y = 0.2, 0.4, 0.6 and 0.8). The estimated values of α _v and C _p are in good agreement with the experimental values within ±3%. Using the assumption the high temperature heat capacity data of (U_1?y Ce _y ) O₂ (y = 0.2, 0.8) and (U_1?y Gd _y ) O_2±x (y = 0.2, 0.5) were computed from the experimental high temperature α _v data.     

Heat treatment of rapidly solidified Fe−Cr−Zr−B alloys

The crystallization behaviour of amorphous melt spun Fe_82?x?yCr₁₈Zr_xB_y (x=0–8, y=10–20) ribbons have been investigated using differential scanning calorimetry. The crystallization temperature and crystallization behaviour change with varzing Zr and B content. The microstructural development during annealing of amorphous Fe₆₄Cr₁₈Zr₈B₁₀ has been investigated by a combination of transmission electron microscopy and energy dispersive X-ray microanalysis. Isothermal annealing for 2 h at temperatures in the range 600–1000°C produces a variety of different microstructures depending on the annealing temperature. At 600°C, the amorphous alloy partially crystallizes to a form a microstructure consisting of 9 nm sized bee ferrite grains embedded in an amorphous matrix. At temperatures in the range 700–900°C, the alloy microstructure transforms into a mixture of bee ferrite, faulted fcc MB₁₂ boride particles and tetragonal M₃B boride particles. At 1000°C, the faulted fcc MB₁₂ boride particles are replaced by orthorhombic M₄B boride particles.     

Influence of Ca2+ substitution on thermal,structural, and conductivity behavior of Bi1−xCaxFeO3−y (0.40 ≤ x ≤ 0.55)

Bi_1?xCa_xFeO_3?y (0.40 ≤ x ≤ 0.55) perovskite oxides have been synthesized by solid-state reaction method to study their properties as a cathode material for intermediate temperature solid oxide fuel cells. The as prepared samples were characterized by X-ray diffraction, differential thermal analyzer/thermogravimetry, dilatometer, and impedance spectroscopy to study their structural, thermal, and electrical properties. The Rietveld refinement results confirmed that all the samples exhibit tetragonal structure with P4mm space group. In addition to this, sample x = 0.55 exhibits Ca₂Fe₂O₅ as a secondary phase. It has been observed that lattice parameters decrease with increase in calcium content. The thermal expansion coefficient and ionic conductivity increases with increase in calcium content up to x = 0.50. The highest ionic conductivity is observed for Bi_0.5Ca_0.5FeO_3?y i.e. 1.71 × 10^?2 S cm^?1.     

Study of ceramic pigments based on Er2Ce2?x Mo x O7

This contribution is focused on the synthesis, characterization and optical properties of new inorganic pigments which are environment friendly and can substitute some toxic metals in interesting colour compounds. Pyrochlores belong to the group of high-temperature pigments, and are a variety of actual and potential applications for several materials. Examples include catalysts, thermal barrier coatings, solid electrolytes, nuclear waste forms and host materials for luminescence centers. The pigments were prepared by the solid state reaction and also by method of suspension mixing of materials in the series with increasing content of molybdenum. The pigments were applied into organic matrix and ceramic glaze. The colour properties of these applications were investigated depending on content of Mo, method of preparation and temperature of calcination (1350?C1550?°C after step 50?°C). The optimum conditions for their synthesis were determined. The pigments were evaluated from standpoint of their structure, colour and particle sizes. Characterization of Er₂Ce_2?x Mo _x O₇ pigments (x?=?0.1, 0.3, 0.5 and 0.7) suggests that they have a potential to be alternative yellow or orange colourants for paints, plastics, ceramics and building materials.     

The Ba1−ySryMnO3−x system

Subsolidus phase relations at ambient atmospheric pressure and elevated temperatures in the Ba_1?ySr_yMnO_3?x system were investigated by quenching, gravimetric, and X-ray diffraction methods. The system is not binary above ～1035°C because of reactions with atmospheric oxygen. The air isolar, P_O2 = 0.2 atm, was characterized at 1225, 1375, 1490, and 1610°C. Seven oxygen-deficient phases including a perovskite phase characterize the system. Their stability depends on the values of y and x in Ba_1?ySr_yMnO_3?x. The cell dimensions of these phases expand as x increases at fixed y. These seven modifications can be retained in stoichiometric form by oxidation at lower temperatures.     

Thermal analysis and calorimetry in the study of materials and processes for fundamental sciences and various applications in Central and Eastern Europe

We investigated the influence of B substitution for Al₂W₃O₁₂ on thermal changes of UV–Vis and Raman spectra, and colors. First, B-substituted Al₂W₃O₁₂ powder was synthesized by a solid-state reaction method. Single-phase Al_2?xB_xW₃O₁₂ powders with x = 0, 0.10 and 0.20 were successively prepared. B substitution promoted thermal changes of the UV–Vis spectra, resulting in a more pronounced color change of Al₂W₃O₁₂ in the range of 30–150 °C. Raman spectra of the Al_2?xB_xW₃O₁₂ powders with x = 0 and 0.20 indicated that the lattice vibrations of Al_2?xB_xW₃O₁₂ with x = 0.20 were larger than those of Al₂W₃O₁₂. The thermal change of the color phase (ΔE) in the range 30–150 °C of Al₂W₃O₁₂ was increased by B substitution. The color of the B-substituted Al₂W₃O₁₂ powders changed reversibly from pale white at 30 °C to light yellowish green at 150 °C.     

Chelating behavior, thermal studies and biocidal efficiency of tioconazole and its complexes with some transition metal ions

New seven metal complexes of tioconazole drug with the general formulae [MCl₂(L)₂(H₂O)_x].yH₂O (where, x = 0 and y = 1 for M = Mn(II) or x = 2, y = 2 for M = Co(II)), and x = 0, y = 3 for M = Cu(II), Ni(II), Zn(II)) and [MCl₂(L)₂(H₂O)₂]Cl.3H₂O (where M = Cr(III) and Fe(III)) have been prepared and characterized based on elemental analyses, IR, magnetic moment, molar conductance, and thermal analyses techniques. From molar conductance data bivalent metal chelates are non-electrolytes while Cr(III) and Fe(III) chelates are electrolytes and of 1:1 type. According to the IR spectral data, TCNZ is coordinated to the metal ions in a neutral unidentate manner with N donor site of the imidazole–N. All the complexes are octahedral except Mn(II) complex has tetrahedral structure. TCNZ drug and its metal complexes were also screened for their biological activity.     

Studies regarding the formation from metal nitrates and diol of NiM 2 III O4 spinels, inside a silica matrix

The present study deals with preparation and characterization of spinel mixed oxide systems NiM ₂ ^III O₄, where M^III?=?Fe^III, Cr^III. In order to obtain 50% NiFe₂O₄/50% SiO₂ and 50% NiCr₂O₄/50% SiO₂ nanocomposite, we have used a versatile route based on the thermal decomposition inside the SiO₂ matrix, of some particular precursors, coordination compounds of the involved M^II and M^III cations with dicarboxylate ligands. The ligands form in the redox reaction between metal nitrates mixture and 1,3-propanediol at the heating around 140?°C of the gels (tetraethylorthosilicate?Cmetal nitrates?C1,3-propanediol?Cwater). The as-obtained precursors, embedded in silica gels, have been characterized by FT-IR spectrometry and thermal analysis. Both precursors thermally decompose up to 350?°C leading to the formation of the corresponding metal oxides inside the silica matrix. X-ray diffraction of the annealed powders have evidenced the formation of NiFe₂O₄ starting with 600?°C, and NiCr₂O₄ starting with 400?°C. This behavior can be explained by the fact that, by thermal decomposition of the Fe(III) carboxylate at 300?°C, the spinelic phase ??-Fe₂O₃ is formed, which interacts with the NiO, forming the ferrite nuclei. By thermal decomposition of chromium carboxylate, a nonstoichiometric chromium oxide (Cr₂O_3+x ) is formed. In the range 380?C400?°C, Cr₂O_3+x turns into Cr₂O₃ which immediately interacts with NiO leading to the formation of nickel chromites nuclei inside the pores of silica matrix. Both spinels have been obtained as nanocrystalites homogenously dispersed as resulted from XRD and TEM data.     

Phase separation characteristics of (U,Nd)O2 solid solutions by high temperature oxidation

The phase separation characteristics of the Nd element from SIMFUEL (simulated spent fuel) by high temperature oxidation was investigated in terms of the temperature range between 1,150 and 1,300 °C and the initial concentration of Nd (x) in the pellets of (U_1?x Nd _x )O₂ with x = 0.03, 0.037 and 0.09. The XRD and SEM results indicate that an increase of the heat treatment temperature increases the amount of the Nd-rich (U_1?y Nd _y )O_2+v phase, while decreasing that of the Nd-poor (U_1?z Nd _z )₃O_8?w phase after heat treatment. Since the solubility of Nd in the (U_1?z Nd _z )₃O_8?w phase was almost constant regardless of the heat treatment temperature, the decrease of the Nd concentration in the Nd-rich (U_1?y Nd _y )O_2+v phase with increasing heat treatment temperature seems to be due to a diffusion of the U ions from the Nd-poor (U_1?z Nd _z )₃O_8?w phase to the Nd-rich (U_1?y Nd _y )O_2+v phase. The phase separation ratio of Nd was not nearly affected by the heat treatment temperature, but was increased with an increase in the initial concentration of Nd (x) in the pellets of (U_1?x Nd _x )O_2.00. However, the phase separation ratio of U was slightly decreased with an increase in the heat treatment temperature and was strongly decreased with an increase in the initial concentration of Nd (x) in the pellets of (U_1?x Nd _x )O_2.00.     

Thermal stability of the manganese-nickel mixed ferrite and iron phases in the Mn0.5Ni0.5Fe2O4/Fe composite/nanocomposite powder

The composite/nanocomposite powders of Mn_0.5Ni_0.5Fe₂O₄/Fe type were synthesized starting from nanocrystalline Mn_0.5Ni_0.5Fe₂O₄ (D = 7 nm) (obtained by ceramic method and mechanical milling) and commercial Fe powders. The composites, Mn_0.5Ni_0.5Fe₂O₄/Fe, were milled for up to 120 min and subjected to heat treatment at 600 °C and 800 °C for 2 h. The manganese-nickel ferrite/iron composite samples were subjected to differential scanning calorimetry (DSC) up to 900 °C for thermal stability investigations. The composite component phases evolution during mechanical milling and heat treatments were investigated by X-ray diffraction technique. The present phases in Mn_0.5Ni_0.5Fe₂O₄/Fe composite are stable up to 400–450 °C. In the temperature range of 450-600 °C, the interdiffusion phenomena occurs leading to the formation of Fe_1?xMn_xFe₂O₄/Ni–Fe composite type. The new formed ferrite of Fe_1?xMn_xFe₂O₄ type presents an increased lattice parameter as a result of the substitution of nickel cations into the spinel structure by iron ones. Further increases of the temperature lead to the ferrite phase partial reduction and the formation of wustite-FeO type phase. The spinel structure presents incipient recrystallization phenomena after both heat treatments (600 °C and 800 °C). The mean crystallites size of the ferrite after heat treatment at 800 °C is about 75 nm. After DSC treatment at 900 °C, the composite material consists in Fe_1?xMn_xFe₂O₄, Ni structure, FeO, and (NiO)_0.25(MnO)_0.75 phases.     

Microstructure and dielectric properties of Nd doped CaCu3Ti4O12 synthesized by sol–gel method

Ca_(1?3x/2)Nd _x Cu₃Ti₄O₁₂ (x = 0, 0.1, 0.2 and 0.3) powders and ceramics were prepared by sol–gel method. Effect of Nd on microstructure and dielectric properties were investigated. XRD patterns suggest that pure perovskite-like CCTO phase were obtained after calcining at 800 °C for 2 h. SEM pictures reveal that particle size monotonously decreases from 250 to 120 nm with increase of Nd concentration. The lattice parameters show an increasing trend with the enhancing amount of Nd³⁺ substitution. The average grain size of CCTO ceramics decrease from 2.0 to 0.8 μm with increase in Nd doping, which indicates that high concentration of Nd inhibits grain growth of CaCu₃Ti₄O₁₂. Both of the dielectric constant and dielectric loss decrease with increase in Nd concentrations. Ca_(1?3x/2)Nd _x Cu₃Ti₄O₁₂ ceramics with x = 0.3 shows the lowest dielectric constant of 1.12 × 10⁴ as well as the lowest dielectric loss value of 0.12 at 20 °C(10 kHz).