Thermal and electrical properties of CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> synthesized by soft chemistry route

The non-isothermal sintering process of cerium dioxide containing gadolinium sesquioxide powders within a wide range of specific surface area was investigated by dilatometry. Linear shrinkage data of powder compacts were recorded under several constant rates of heating. Dilatometry data were analyzed by two methodologies enabling to preview the relative density for any temperature/time profile, and determination of the apparent activation energy for sintering. Correlation of dilatometry results with microstructure evolution was also carried out. Remarkable differences in sintering powders with different specific surface areas were found. The apparent activation energy for sintering increases with decreasing specific surface area and, in most cases, it does not change significantly in the approximately 70–85% range of relative density.     

Investigation of catalytic activity of ZnAl<Subscript>2</Subscript>O<Subscript>4</Subscript> and ZnMn<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles in the thermal decomposition of ammonium perchlorate

A new powder metallurgy technique was developed in order to increase the reinforcement proportion of aluminum with two different fractions of Al₂O₃. Aluminum powders were mixed with 20 % vol of alumina particles as primarily reinforcement, and additional alumina was produced in situ as a result of reaction between Al and additional 7.5 % vol of Fe₂O₃ powder. The three grades of powders were milled and hot-pressed into small preforms, and differential scanning analysis (DSC) was performed to determine the kinetics of microstructural transformations produced on heating. DSC curves were mathematically processed to separate the superposing effects of thermal reactions. Transformation points on resulting theoretical curves evidenced two distinct exothermal reaction peaks close to the melting point of aluminum that were correlated with formation of Fe–Al compounds and oxidation of aluminum. Microstructural investigations by means of SEM-EDX and XRD suggested that these exothermal reactions produced complete decomposition of iron (III) oxide and formation of Fe–Al compounds during sintering at 700 °C, and therefore, heating at higher temperatures would not be necessary. These results, along with calculation of activation energies, based on Kissinger’s method, could be used to optimize the fabrication of Al-Al₂O₃ composites by means of reactive sintering at moderate temperatures.     

Phase transition of YBO<Subscript>3</Subscript>

Yttrium orthoborate crystallizes in the vaterite-type structure and has two polymorphous forms, viz. a low- und a high temperature one. DTA measurements of YBO₃ confirmed a reversible phase transition with a large thermal hysteresis. The phase transition has been accurately characterized by the application of different heating and cooling rates (β). Consequently, the extrapolation of the experimental data to zero β yields the transition points at 986.9°C for the heating up and at 596.5°C for the cooling down cycle. These values correspond to samples just after treatment at 1350°C. For samples with a different ‘thermal history’ other phase transition temperatures are observed, (e.g. after having performed several heating and cooling cycles). The linear relationship between the associated DTA signal ΔT=T _onset–T _offset and the square root of the heating rate β was confirmed, but the relation between T _onset and square root of β is not found here. From the empirical data a good linear fitting between T _onset and ln(β+1) can be derived. From the kinetic analysis (Kissinger method) of the phase transformation of YBO₃ an apparent activation energy of about 1386 kJ mol^–1 for heating and of about 568 kJ mol^–1 for cooling can be determined     

Synthesis of Na<Subscript>2</Subscript>Ti<Subscript>3</Subscript>O<Subscript>7</Subscript> nanoparticles by sonochemical method for solid state electrolyte applications

Na₂Ti₃O₇ ceramic materials have been widely used in sodium-ion battery applications with relative good results; however, there are still several studies that might be carried out in the improvement of the Na₂Ti₃O₇ properties and the overall batteries’ performance. In this direction, we used sonochemical method following a thermal treatment in order to synthetized pure phase Na₂Ti₃O₇ nanopowders. X-ray diffraction characterization revealed that Na₂Ti₃O₇ is the primary phase in nanopowders and ceramic sample; although, a high level of amorphization was observed in the sonicated nanopowder without heat treatment process. Nanopowder-prepared ceramic sample showed a crystallite size of 50 nm after sintering at 900 °C for 1 h. The specific surface area, pore volume, and pore size were obtained from the B.E.T. measurements, being 51 m² g^?1, 0.07 cm³ g^?1, and 55 Å, respectively. The capacitance values of the nanopowder-prepared ceramic sample were in the order of microfarad. The total energy of the system was used to determine relaxation time of the sample (τ ₀ = 31 ms).     

Synthesis of Gd<Subscript>0.5</Subscript>Sr<Subscript>0.5</Subscript>FeO<Subscript>3</Subscript> perovskite-type nanopowders for adsorptive removal of MB dye from water

In the present study, nanoparticles of perovskite-type Gd_0.5Sr_0.5FeO₃ (GSFO) were fabricated by a sol–gel method. A series of analytical techniques were used to characterize the crystallinity, morphology, specific surface area and grain size of GSFO powders. The thermal decomposition process of the complex precursor was examined by means of differential thermal analysis–thermal gravimetric analysis. X-ray diffraction results showed that a single perovskite phase was completely formed after calcination at 700 °C. In addition, transmission electron microscopy images revealed that the average size of the particles is approximately 35.23 nm in diameter. The surface morphology and composition of these nanopowders were also investigated using a scanning electron microscope and an energy dispersive X-ray spectrometer. GSFO nanoparticles showed excellent adsorption efficiency towards methylene blue dye in aqueous solution. The adsorption studies were carried out at different pH values, initial dye concentrations, various adsorbent doses and contact time in batch experiments. The dye removal efficiency was found to be increased with increasing the initial pH of the dye solution, and GSFO exhibited good dye removal efficiency at a basic pH, especially at a pH of 12. Experimental results indicated that the adsorption kinetic data follow a pseudo-second-order rate for the tested dye. The isotherm evaluations revealed that the Redlich–Peterson model attained better fits to the experiment's equilibrium data than the Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich models.     

Surface and bulk conduction and thermodynamic properties of ionic salt CsH<Subscript>5</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript>

Transport properties of ionic salt CsH₅(PO₄)₂ are studied by the impedance method. The salt’s bulk conductivity ranges from 10^?8 to 10^?4 S cm^?1 in the temperature interval 90 to 145°C. The apparent activation energy is high (1.6–2.0 eV). The conductivity is slightly anisotropic: it is maximum in the [001] direction and minimum in the [100] direction (～5.6 and 1 times × 10^?6 S cm^?1, respectively, at 130°C). The conductivity of polycrystalline samples is higher by 1–2 orders of magnitude, and the activation energy drops to 1.05 eV due to the formation of a pseudoliquid layer with a high proton mobility at the intercrystallite boundary. The salt’s thermodynamic properties are examined by differential scanning calorimetry and thermogravimetry. No phase transitions are discovered in the salt up to the melting point (151.6°C), with the melting enthalpy equal to ～34 kJ mol^?1. The crystallization occurs at lower temperatures (107°C) and the crystallization enthalpy (?18 kJ mol^?1) is lower than the melting enthalpy. The melting is accompanied by slow decomposition of the salt. Factors affecting the proton transport in the salt are analyzed.     

Study of non-isothermal crystallization of amorphous Cu<Subscript>50</Subscript>Ti<Subscript>50</Subscript> alloy

The crystallization kinetics of amorphous Cu₅₀Ti₅₀ has been studied using differential scanning calorimetry (DSC) under non-isothermal conditions. The curves at different linear heating rates (2, 4, 8 and 16 K min^–1) show sharp crystallization peaks. The crystallization peak shifts to higher temperatures with increasing heating rate. The Kissingers method of analysis of the shift in the transformation peak is applied to evaluate the activation energy (E _c). The KJMA formalism, which is basically developed for isothermal experiments, is also used to obtain E _c and the Avrami parameter (n).The DSC data have been analysed in terms of kinetic parameters, viz. activation energy (E _c), Avrami exponent (n) and frequency factor K ₀ using three different theoretical models. It is observed that the activation energy values derived from KJMA approach and modified Kissinger equation agree fairly well with each other. The activation energy values obtained from normal Kissinger method, and Gao and Wang expression underestimate the activation energy.The financial support provided by All India Council for Technical Education (AICTE), New Delhi (Govt. of India) is gratefully acknowledged.     

Thermal analysis on C<Subscript>6</Subscript>H<Subscript>10</Subscript>Ge<Subscript>2</Subscript>O<Subscript>7</Subscript>-doped MgB<Subscript>2</Subscript>

Additives to MgB₂ can improve the superconducting functional characteristics, such as critical current density (J _c) and irreversibility field (H _irr). Recently, we have shown that repagermanium (C₆H₁₀Ge₂O₇) is an effective additive, enhancing both J _c and H _irr. To look into details of the processes taking place during the reactive sintering, a thermal analysis study (0.167 K s^?1, in Ar) is reported. We used differential scanning calorimetry between 298 and 863 K and simultaneous thermogravimetric—differential thermal analysis between 298 and 1233 K. Samples were mixtures of powders with composition 97 mol% MgB₂ and 3 mol% C₆H₁₀Ge₂O₇. Up to 863 K, repagermanium decomposes by multiple steps and forms amorphous phases. A reaction with MgB₂ is not observed. Above this temperature, partial decomposition of MgB₂ occurs. Crystalline Ge and MgO are detected before formation of Mg₂Ge and MgB₄, when temperature approaches the melting point of Ge (1211 K). Carbon substitution for boron in the crystal lattice of MgB₂ is observed for samples heated above 863 K. The amount of substitutional C does not significantly change with temperature.     

Thermal decomposition of the carbon nanotube/SiO<Subscript>2</Subscript>precursor powders

Summary TG-DSC-MS (thermogravimetry-differential scanning calorimetry-mass spectrometry) coupling techniques were used to make a simultaneous characterizing study for the thermal decomposition process of the carbon nanotube (CNT)/SiO₂precursor powders prepared by rapid sol-gel method. The thermal stability of the CNT and the SiO₂pure gel were investigated by TG-DSC. The results showed that the oxidation of CNT began from 530 and combusted at about 678°C at the heating rate of 10°C min^-1in air. Moreover, the faster the heating rate, the higher the temperature of CNT combustion. The appropriate calcinations temperature of the CNT/SiO₂precursor powders should be held for 1 h at 500°C.     

Thermal properties,phase transitions,vibrational and reorientational dynamics of [Mn(NH<Subscript>3</Subscript>)<Subscript>6</Subscript>](NO<Subscript>3</Subscript>)<Subscript>2</Subscript>

[Mn(NH₃)₆](NO₃)₂ crystallizes in the cubic, fluorite (C1) type crystal lattice structure (Fm \( \overline{3} \) m) with a = 11.0056 Å and Z = 4. Two phase transitions of the first-order type were detected. The first registered on DSC curves as a large anomaly at T _C1 ^h  = 207.8 K and T _C1 ^c  = 207.2 K, and the second registered as a smaller anomaly at T _C2 ^h  = 184.4 K and T _C2 ^c  = 160.8 K (where the upper indexes h and c denote heating and cooling of the sample, respectively). The temperature dependence of the full width at half maximum of the band associated with the δ_s(HNH)F_1u mode suggests that the NH₃ ligands in the high temperature and intermediate phase reorientate quickly with correlation times in the order of several picoseconds and with activation energy of 9.9 kJ mol^?1. In the phase transition at T _C2 ^c probably only a some of the NH₃ ligands stop their reorientation, while the remainders continue to reorientate quickly with activation energy of 7.7 kJ mol^?1. Thermal decomposition of the investigated compound starts at 305 K and continues up to 525 K in four main stages (I–IV). In stage I, ²/₆ of all NH₃ ligands were seceded. Stages II and III are connected with an abruption of the next ²/₆ and ¹/₆ of total NH₃, respectively, and [Mn(NH₃)](NO₃)₂ is formed. The last molecule of NH₃ per formula unit is freed at stage IV together with the simultaneous thermal decomposition of the resulting Mn(NO₃)₂ leading to the formation of gaseous products (O₂, H₂O, N₂ and nitrogen oxides) and solid MnO₂.     

Fabrication and characterisation of a mixed oxide-covered mesh electrode composed of NiCo<Subscript>2</Subscript>O<Subscript>4</Subscript> and its capability of generating hydroxyl radicals during the oxygen evolution reaction in electrolyte-free water

A mixed oxide-covered mesh electrode composed of NiCo₂O₄ (MOME-NiCo₂O₄) was prepared on a stainless-steel substrate using thermal decomposition (slow-cooling rate method). Surface, bulk and electrochemical properties of MOME were studied using different techniques, namely scanning electron microscopy (SEM), X-ray diffraction (XRD), cyclic voltammetry (CV) with determination of the electrochemical porosity (?) and morphology factor (φ) parameters, quasi-stationary polarisation curves (PC) and electrochemical impedance spectroscopy (EIS). SEM images revealed a good coverage of the metallic wires by a compact oxide layer (absence of cracks). XRD analysis confirmed the formation of the spinel NiCo₂O₄ with the presence of NiO. The ‘in situ’ surface parameters denoted as ? and φ exhibited values of 0.39 and 0.33, respectively, revealing that the electrochemically active surface area is mainly confined to the ‘outer/external’ surface regions of the oxide layer. The PC was characterised by two Tafel slopes distributed in the low (b ₁ = 46 mV dec^?1) and high (b ₂ = 59 mV dec^?1) overpotential domains. The corresponding apparent exchange current densities were j ₀₍₁₎ = (3.43 ± 0.11) × 10^?6 A cm^?2 and j ₀₍₂₎ = (6.70 ± 0.08) × 10^?6 A cm^?2, respectively. The EIS study accomplished in the low-overpotential domain revealed a Tafel slope (b ₁) of 51 mV dec^?1. According to the spin-trapping reaction using N,N-dimethyl-p-nitrosoaniline (RNO), the MOME-NiCo₂O₄ electrode exhibited good performance for the generation of weakly adsorbed hydroxyl radicals (HO^?) during the OER in electrolyte-free water.     

Thermodynamic investigations of BaUF<Subscript>6</Subscript>(s)

The calcium fluoride solid electrolyte Galvanic cell: (-) Pt, U₃O₈(s) + UO₂F₂(s) + BaUF₆(s) + BaF₂(s) | CaF₂(s) | NiO(s) + NiF₂(s), Pt (+) was used to measure the standard molar Gibbs energy of formation of BaUF₆(s). From the measured emf values of the cell and required Gibbs energy values from the literature, Δ_f G _m° (T) of BaUF₆(s) has been calculated. The pseudo-binary phase diagram of BaF₂–UF₄ system was calculated by minimization of Gibbs energies of the phases present in the system. The stability domain of BaUF₆(s) has been calculated from the chemical potential diagram of Ba–U–F–O system at 800 K.     

Study on the hydration products of C<Subscript>3</Subscript>S prepared by sol–gel method

Fly ash from coal combusting thermal power plants is a serious problem from the point of view of its storing and pollution of the environment. Currently, thermal power plants change the combustion technology from pulverized firing to fluidized bed combustion. A promising reutilization of the fly ash from fluidized bed combustion (FFA) shows itself in the ceramic industry. In this paper, the influence of the FFA content in illite-based ceramics on its thermophysical and elastic properties was investigated during heating and cooling stages of firing. The samples are made from a mixture of the illitic clay (60 mass%), various portion of FFA (0–40 mass%) and grog (40–0 mass%). The impulse excitation technique is used for the determination of Young’s modulus and the internal friction. Analyses that included DTA, TG, thermodilatometry, XRD and SEM are used to obtain the better understanding of the development of the phase transformations in the samples. It is found that a higher amount of FFA in the sample leads to a higher mass loss at low temperatures, a higher mass loss due to the decomposition of calcite, a less intensive shrinkage after firing, a lower bulk density and lower Young’s modulus during firing above 800 °C and after cooling. After firing of the samples at 1100 °C, the mechanical strength and Young’s modulus decrease with the FFA content. A linear relationship between Young’s modulus and the mechanical strength is observed.     

The effect of melt flow index, melt flow rate, and particle size on the thermal degradation of commercial high density polyethylene powder

The powder of EX5 grade of high density polyethylene—without any additives—manufactured by Amirkabir petrochemical company was separated by shaker equipment. The separated powder of average diameter ~25, ~62.5, ~87.5, ~112.5, ~137.5, ~175 and the particles >200 μm was tested by a thermogravimetric (TG) analysis instrument in nitrogen atmosphere and heating rates of 10, 20, and 30 °C min^?1. In addition, the separated powders were analyzed by a melt flow index (MFI) instrument, and the viscosity average molecular mass (M _v) of the powders was tested by a viscometer. Kinetic evaluations were performed by Friedman and Kissinger analysis methods and apparent activation energy for the overall degradation of the powders was determined. The effects of molecular mass, MFI, MFR, and particle size on the degradation TG curve, derivative thermogravimetry curve breadth, and activation energy of thermal degradation were considered. The results showed that the M _v of EX5 pipe grade produced by two serial reactors is increased by increasing of the particle size and, MFI is decreased with a little deviation by particle size increasing. The particle size has no obvious effect on the melt flow rate (MFR), and MFR as function of molecular mass distribution does not change very much. The results showed that the powder with bigger particles and higher molecular mass moderately increases the activation energy and shifts the degradation curve to the higher temperatures.     

Viscosity and shrinkage of porous and quartzoid glasses of the Na<Subscript>2</Subscript>O-B<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> system

Shrinkage of porous glasses on heating from 20 to 800°C was studied and temperature dependences of the viscosity in the range of 10¹¹–10¹³ P were determined for quartzoid (sintered) glasses based on five glasses with different compositions in the Na₂O-B₂O₃-SiO₂ system. The shrinkage of porous glasses and the viscosity of quartzoid glasses were analyzed in relation to their composition and temperature of preliminary thermal treatment.     

Red water treatment by photodegradation process in presence of modified TiO<Subscript>2</Subscript> nanoparticles and validation of treatment efficiency by MLR technique

An active photocatalyst under sunlight irradiation was proposed for treatment of red water of TNT production process. The nanoparticles of TiO₂/S_0.05,Zn_0.05 were prepared by the sol–gel method and were verified by XRD pattern, TEM image, EDXS analysis, BET analysis and DRS spectra. The proposed photocatalyst showed the surface area of 146 m² g^?1, anatase and rutile phases and band-gap energy of 2.92 eV. The prepared nanoparticles were used as photocatalyst in treatment of red water under UV lamp and sun irradiations. The photodegradation process was optimized in conditions of 5 g L^?1 of photocatalyst, irradiation time of 4 h and dilution times of 1000 of real samples. The treatment efficiency of 76 and 69 % and rate constants of 0.368 and 0.319 h^?1 were obtained under UV and sun irradiations, respectively. The multiple linear regression as a statistic technique was used for study of validation and verification of four factors of mole fraction of S dopant, the irradiation intensity of UV lamp, the dose of photocatalyst and dilution times on samples as predictor’s on the treatment efficiency of red water as the response variable. The output of MLR showed the obtained P values <0.05 in confidence level of 95 % for all of the variables. Thus, the null hypothesis is rejected, and a meaningful addition is observed in the model because changes in the predictor’s value are related to changes in the response variable.     

Non-isothermal crystallization kinetics of Ti<Subscript>20</Subscript>Zr<Subscript>20</Subscript>Hf<Subscript>20</Subscript>Be<Subscript>20</Subscript>(Cu<Subscript>50</Subscript>Ni<Subscript>50</Subscript>)<Subscript>20</Subscript> high-entropy bulk metallic glass

The crystallization transformation kinetics of Ti₂₀Zr₂₀Hf₂₀Be₂₀(Cu₅₀Ni₅₀)₂₀ high-entropy bulk metallic glass under non-isothermal conditions are investigated using differential scanning calorimetry. The alloy shows two distinct crystallization events. The activation energies of the crystallization events are determined using Kissinger, Ozawa and Augis–Bennett methodologies. Further, we observe that similar values are obtained using the three equations. The activation energy of the initial crystallization event is observed to be slightly small as compared to that of the second event. This implies that the initial crystallization event may have been easier to be occurred. The local activation energy (E(x)) maximizes in the initial stage of crystallization and keeps dropping in subsequent crystallization process. The non-isothermal crystallization kinetics are further analyzed using the modified Johnson–Mehl–Avrami (JMA) equation. Further, the Avrami exponent values are observed to be 1.5 < n(x) < 2.5 for approximately the entire period of the initial crystallization event and for most instances (0.1 < x < 0.6) of the second crystallization event, which implies that the mechanism of crystallization is significantly controlled by diffusion-controlled two- and three-dimensional growth along with a decreasing nucleation rate.     

MnCo<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles with excellent catalytic activity in thermal decomposition of ammonium perchlorate

MnCo₂O₄ spinel nanoparticles (NPs) have been prepared using Aloe vera gel solution. The characterization of prepared spinel was performed applying Fourier transform infrared spectroscopy, X-ray diffraction, Raman spectroscopy, transmission electron spectroscope, scanning electron microscope and dynamic light scattering. The results manifested that the prepared nanoparticles were mainly spherical plus minor agglomeration with average size distribution between 35 and 60 nm. The catalytic activity of the prepared nanoparticles upon thermal degradation of ammonium perchlorate (AP) was evaluated applying differential scanning calorimetry and thermogravimetry instruments. MnCo₂O₄ nanoparticles increased the released heat of AP from 450 to 1480 J g^?1 and decreased the decomposition temperature from 420 to 293 °C. The kinetic parameters obtained from Kissinger methods showed that the activation energy of AP thermal decomposition in the presence of MnCo₂O₄ NPs considerably decreased. Also, a mechanism has been proposed in the presence of catalyst for the process of thermal decomposition of AP.     

Preparation and methane adsorption of two-dimensional carbide Ti<Subscript>2</Subscript>C

Here a novel material for methane adsorption was synthesized and studied, which is a graphene-like two-dimensional (2D) carbide (Ti₂C, a member of MXenes), formed by exfoliating Ti₂AlC powders in a solution of lithium fluoride (LiF) and hydrochloric acid (HCl) at 40 °C for 48 h. Based on first-principles calculation, theoretically perfect Ti₂C with O termination has a specific surface area (SSA) of 671 m² g^?1 and methane storage capacity is 22.9 wt%. Experimentally, 2.85 % exfoliated Ti₂C with mesopores shown methane capacity of 11.58 cm³ (STP: 0 °C, 1 bar) g^?1 (0.82 wt%) under 5 MPa and the SSA was 19.1 m² g^?1. For Ti₂C sample intercalated with NH₃·H₂O, the adsorbed amount was increased to 16.81 cm³ (STP) g^?1 at same temperature. At the temperature of 323 K, the adsorbed amount of as-prepared Ti₂C was increased to 52.76 cm³ (STP) g^?1. For fully exfoliated Ti₂C, the methane capacity was supposed to be 28.8 wt% or 1148 V (STP)v^?1. Ti₂C theoretically has much larger volume methane capacity than current methane storage materials, though its SSA is not very high.     

The use of methylcellulose for the synthesis of Li<Subscript>2</Subscript>FeSiO<Subscript>4</Subscript>/C composites

The key parameters related to cathode materials for commercial use are a high specific capacity, good cycling stability, capacity retention at high current rates, as well as the simplicity of the synthesis process. This study presents a facile synthesis of a composite cathode material, Li₂FeSiO₄ with carbon, under extreme conditions: rapid heating, short dwell at 750 °C and subsequent quenching. The water-soluble polymer methylcellulose was used both as an excellent dispersing agent and a carbon source that pyrolytically degrades to carbon, thereby enabling the homogeneous deployment of the precursor compounds and the control of the Li₂FeSiO₄ particle growth from the earliest stage of processing. X-ray powder diffraction reveals the formation of Li₂FeSiO₄ nanocrystallites with a monoclinic structure in the P2₁/n space group (#14). The composite’s electrochemical performance as a cathode material in Li-ion batteries was examined. The influence of the amount of methylcellulose on the microstructural, morphological, conductive, and electrochemical properties of the obtained powders has been discussed. It has been shown that the overall electrochemical performance is improved with an increase of carbon content, through both the decrease of the mean particle diameter and the increase of electrical conductivity.