Maximum Value Of Activation Energy Research Articles

Increasing the Service Life of Marine Transport Using Heat-Resistant Polymer Nanocomposites.

This paper presents the technological aspects of increasing the thermal stability of polymers, with epoxy binder used to form the polymer materials. Polyethylene polyamine was used to crosslink the epoxy binder. To ensure the thermal stability of the polymer, nanodispersed condensed carbon with a dispersion of 10-16 nm was used. The research into nanocomposites under the influence of elevated temperatures was carried out using the "Thermoscan-2" derivatograph. Complex studies of thermophysical properties were carried out, according to the results of which the optimal content of nanofiller (0.050 pts.wt.) was determined. At the same time, this particular polymer was characterized by the following properties: temperature of the beginning of mass loss-T0 = 624.9 K; final temperature of mass loss-Tf = 718.7 K; relative mass loss-εm = 60.3%. Research into the activation energy of thermal destruction was performed to determine the resistance to the destruction of chemical bonds. It was proved that the maximum value of activation energy (170.1 kJ/mol) is characterized by nanocomposites with a content of nanodispersed condensed carbon of 0.050 pts.wt., which indicates the thermal stability of the polymer.

Preparation and properties of Dy3+-Sm3+-Tb3+ co-doped Na0.98Sr0.02Y(MoO4)0.8(WO4)1.2 phosphors

In this paper, Dy3+ single-doped, Dy3+-Sm3+ double-doped and Dy3+-Sm3+-Tb3+ triple-doped Na0.98Sr0.02Y(MoO4)0.8(WO4)1.2 phosphors were synthesized using hydrothermal method and their structures, luminescent properties and thermal stability were investigated. The prepared single-doped, double-doped and triple-doped series of Na0.98Sr0.02Y(MoO4)0.8(WO4)1.2 phosphors all exhibited a tetragonal scheelite structure. Na0.98Sr0.02Y0.926(MoO4)0.8(WO4)1.2: 2%Dy3+, 5%Sm3+, 0.4%Tb3+ phosphor correlated with correlated color temperature of 5611 K and chromaticity coordinates of (0.33, 0.3284), achieving white light emission. Moreover, the Na0.98Sr0.02Y0.926(MoO4)0.8(WO4)1.2: 2%Dy3+, 5%Sm3+, 0.4%Tb3+ phosphor exhibited a maximum activation energy value of 0.17 eV, indicating excellent thermal stability.

Epoxy/Ionic Liquid-Modified Mica Nanocomposites: Network Formation-Network Degradation Correlation.

We synthesized pristine mica (Mica) and N-octadecyl-N’-octadecyl imidazolium iodide (IM) modified mica (Mica-IM), characterized it, and applied it at 0.1–5.0 wt.% loading to prepare epoxy nanocomposites. Dynamic differential scanning calorimetry (DSC) was carried out for the analysis of the cure potential and kinetics of epoxy/Mica and epoxy/Mica-IM curing reaction with amine curing agents at low loading of 0.1 wt.% to avoid particle aggregation. The dimensionless Cure Index (CI) was used for qualitative analysis of epoxy crosslinking in the presence of Mica and Mica-IM, while qualitative cure behavior and kinetics were studied by using isoconversional methods. The results indicated that both Mica and Mica-IM improved the curability of epoxy system from a Poor to Good state when varying the heating rate in the interval of 5–15 °C min−1. The isoconversional methods suggested a lower activation energy for epoxy nanocomposites with respect to the blank epoxy; thus, Mica and Mica-IM improved crosslinking of epoxy. The higher order of autocatalytic reaction for epoxy/Mica-IM was indicative of the role of liquid crystals in the epoxide ring opening. The glass transition temperature for nanocomposites containing Mica and Mica-IM was also lower than the neat epoxy. This means that nanoparticles participated the reaction because of being reactive, which decelerated segmental motion of the epoxy chains. The kinetics of the thermal decomposition were evaluated for the neat and mica incorporated epoxy nanocomposites epoxy with varying Mica and Mica-IM amounts in the system (0.5, 2.0 and 5.0 wt.%) and heating rates. The epoxy/Mica-IM at 2.0 wt.% of nanoparticle showed the highest thermal stability, featured by the maximum value of activation energy devoted to the assigned system. The kinetics of the network formation and network degradation were correlated to demonstrate how molecular-level transformations can be viewed semi-experimentally.

Effect of Surface Functionalization of SiO2 Nanoparticles on the Dynamic Mechanical, Thermal and Fire Properties of Wheat Straw/LDPE Composites

The scope of the present article is to study the effect of surface functionalization of SiO2 nanoparticles on the dynamic mechanical, thermal and fire properties of wheat straw flour (WSF) reinforced low-density polyethylene (LDPE) composites. Firstly, the SiO2 nanoparticles were modified by 3-aminopropyl-trimethoxysilane (APTMS), and then the WSF/LDPE composites containing different percentages of modified nano-SiO2 were prepared via a melt compounding using an internal mixer followed by injection molding. Changes in the chemical structure of treated SiO2 were tracked by Fourier transform infrared (FTIR). The appearance of N–H bond at 695 cm−1 and aliphatic C–H bonds at 2841 cm−1 and 2947 cm−1 were indications of successful grafting of APTMS on the SiO2 nanoparticles. Finally, the viscoelastic behavior, thermal stability and fire retardancy of the nanocomposites were evaluated by means of DMTA, TGA, DSC and CCT techniques. Results indicated that the dynamic modulus of the composites was greatly improved through the addition of functionalized SiO2 nanoparticles. In general, the specimens filled with 3 phr modified nano-SiO2 showed the highest values of storage and loss modulus compared with the other ones. Moreover, the tan δ peak signifying the glass transition temperature of nanocomposites shifted to higher temperature. The TGA results demonstrated that the introduction of APTMS grafted SiO2 nanoparticles can distinctly enhance thermal stability of the composites by increasing the thermo-oxidation decomposition temperature and char residues. The maximum activation energy value represents a higher thermal stability of the nanocomposites was obtained with modified nano-SiO2 at 5 phr content. In addition, the DSC data revealed that both the melting temperature and the degree of crystallinity of the specimens tended to substantially increase in presence of modified nano-SiO2. The surface functionalization of SiO2 particles produced remarkable evolution in the fire performance as indicated by reductions in the heat release rate, burning rate and mass loss rate. Furthermore, promoting the time to ignition and limiting oxygen index of the specimens equally to accommodate the addition of treated SiO2 nanoparticles.

Enhanced magneto-electric coupling and energy storage analysis in Mn-modified lead free BiFeO3-BaTiO3 solid solutions

The present study pertains to magnetoelectric coupling and energy storage analysis of (1 − x)BiFe0.95Mn0.05O3-xBaTiO3 (BFMO-BT) with x = 0.1, 0.2, 0.3 lead free solid solutions. BFMO-BT solid solutions possessed a cubic structure as confirmed from powder XRD and the Rietveld refinement. A maximum ferroelectric polarization of 0.82 μC/cm2 was observed in BFMO-0.3BT. BFMO-0.3BT exhibited a maximum energy storage density (WU) of 1.97 J/cm3 and an energy conversion efficiency of 81.7%. Enhanced bulk magnetization was associated with the lattice defects; however, it decreased with increased BT content. For BFMO-0.3BT, temperature dependent susceptibility, dielectric measurement, and differential scanning calorimetry measurement revealed the magnetic transition temperature to be 275 °C, 293 °C, and 223 °C, respectively. The linear magnetoelectric coupling coefficient was measured by quantifying change in maximum polarization with respect to the applied magnetic field and was found to be 28.55 mV cm−1 Oe for BFMO-0.3BT. Conductivity measurements of BFMO-0.3BT revealed a maximum value of activation energy, i.e., 0.21 eV at 1 kHz.

Effect of the Particle Size on Co-combustion of Municipal Solid Waste and Biomass Briquette under N2/O2 and CO2/O2 Atmospheres

The combustion characteristics and kinetics of municipal solid waste and biomass briquette blend were investigated at different particle sizes using thermogravimetric analysis. For the comparison between N2/O2 and CO2/O2 atmospheres, the mole fraction of oxygen was 20% and effects of the heating rate on the blend combustion behavior were also evaluated. Results showed that, in the range of less than 270 μm, the most vigorous combustion occurred at a particle size of 150–180 μm, regardless of the heating rate. With the increase of the heating rate, the combustion intensity of the blend could be improved and the reaction process was influenced to some extent. The replacement of N2 with CO2 reduced the combustion reactivity and had a significant effect at the particle sizes of less than 106 μm. The maximum values of activation energy (E) occurred at 150–180 μm, which corresponded to the maximum comprehensive combustion characteristic index S. The E values under an 80CO2/20O2 atmosphere were close to those un...

Flux Pinning in YBCO Single Crystal Grown on Y2O3 Layer

In this study, single-crystal Y123 samples were grown by a cold top-seeding method by using Nd123 seed, and the effect of Y2O3 buffer layer was investigated. The upper critical magnetic field and coherence length were established as 110 T and 17.3 Ǻ, respectively. The dependence of the effective activation energy U of the flux pinning on the magnetic field and temperature of the sample were determined using the Arrhenius activation energy law from the resistivity curves. It was found that the deduced value of the activation energy for a Y123 sample is in good agreement with the corresponding values in YBCO samples. The maximum activation energy value was approximately 0.9 eV in the zero magnetic field. In order to examine the homogeneity of the pinning properties of different layers, rectangular specimens were cut from the sample. AC susceptibility measurement was performed, and it was found that the shifting of the peak temperature (Tp) with an AC magnetic field is small, indicating good pinning properties. The normalized pinning force density versus the reduced field was examined at different temperatures to determine the pinning mechanism. It was found that normal core-type pinning was effective, and in low fields, pinning was only due to Y211 particles.

Effect of Yttrium Oxide on the Viscosity and Crystallization of Borosilicate Glass at High Temperature

Effect of Y2O3 on the viscosity and Crystallization of of borosilicate glass at high temperature was investigated at high temperature. Melt viscosity as a function of temperature was determined by using a rotating spindle viscometer. Liquidus temperature was determined by the Gradient Furnace Method. The results show that the viscosity decreased as a function of Y2O3 content. The activation energy of glass without Y2O3 is about 110.3 kJ·mol-1 and the activation energy increases with the Y2O3 addition up to the 2 wt%. At 2 wt% Y2O3, the specimen shows the maximum activation energy value of 112.6 kJ·mol-1. As Y2O3 content increase, the activation energy decreases. The fiber-forming temperature of glass without Y2O3 is about 1342 oC and the fiber-forming temperature increases with the Y2O3 addition up to the 2 wt%. At 2 wt% Y2O3, the sample shows the maximum activation energy value of 1370 °C. When Y2O3 content increase, the fiber-forming temperature decreases. The liquidus temperature of glass decreases from 1313 °C to 1023 °C when Y2O3 content increases from 0 wt% to 6 wt%. The difference between the fiber-forming and the liquidus temperatures of glass increases from 30 oC to 336 °C when Y2O3 content increases from 0 wt% to 6 wt%.

Preparation of n-type semiconductor SnO2 thin films

We studied fluorine-doped tin oxide on a glass substrate at 350°C using an ultrasonic spray technique. Tin (II) chloride dehydrate, ammonium fluoride dehydrate, ethanol and NaOH were used as the starting material, dopant source, solvent and stabilizer, respectively. The SnO2 : F thin films were deposited at 350°C and a pending time of 60 and 90 s. The as-grown films exhibit a hexagonal wurtzite structure and have (101) orientation. The G = 31.82 nm value of the grain size is attained from SnO2 : F film grown at 90 s, and the transmittance is greater than 80% in the visible region. The optical gap energy is found to measure 4.05 eV for the film prepared at 90 s, and the increase in the electrical conductivity of the film with the temperature of the sample is up to a maximum value of 265.58 (Ω·cm)−1, with the maximum activation energy value of the films being found to measure 22.85 meV, indicating that the films exhibit an n-type semiconducting nature.

Effect of substrate temperature on the stability of transparent conducting cobalt doped ZnO thin films

Transparent conducting Co doped ZnO thin films have been fabricated by Ultrasonic spray. The thin films were deposited at three different substrate temperatures of 300, 350 and 400 °C. The obtained films had a hexagonal wurtzite structure with a strong (002) preferred orientation. The maximum crystallite size value of the film deposited at 350 °C is 55.46 run. Spectrophotometer (UV-vis) of a Co doped ZnO film deposited at 350 °C shows an average transmittance of about 90%. The band gap energy increased from 3.351 to 3.362 eV when the substrate temperature increased from 300 to 350 °C. The electrical conductivity of the films deposited at 300, 350 and 400 °C were 7.424, 7.547 and 6.743 (Ω·cm)−1 respectively. The maximum activation energy value of the films at 350 °C was 1.28 eV, indicating that the films exhibit a n-type semiconducting nature.

Effect of annealing temperature on magnetoresistivity, activation energy, irreversibility and upper critical field of the Cu-diffused MgB2 bulk superconductors

This study manifests the change of the pinning mechanism, superconducting and physical properties of Cu-diffused MgB2 superconductors prepared at different annealing temperature from 650 to 850 °C by means of the magnetoresistivity measurements conducted at several applied magnetic fields in a range of 0–7 T as a function of temperature from 15 to 50 K. The onset (T c onset ) and offset (T c offset ) critical temperatures, activation energies (U0), irreversibility fields (μ0Hirr), upper critical fields (μ0Hc2), residual resistivity ratios (RR), cross-sectional area fractions (AF), penetration depths (λ), coherence lengths (ξ) and electronic mean free path ( $$ \ell $$ ) of the samples are evaluated from the magnetoresistivity curves. Thermally activated flux creep (TAFC) model is used for the determination of the U0 values; likewise, the μ0Hirr and μ0Hc2 values are obtained by resistivity criteria of 10 and 90 % normal-state resistivity, respectively. At absolute zero temperature (T = 0 K), the extrapolation of the μ0Hirr(T) and μ0Hc2(T) curves is used to find the μ0Hirr(0) and μ0Hc2(0) values of the samples. Moreover, the ξ values are deduced from the μ0Hc2(0) values when the λ values are calculated from the Ginzburg–Landau parameter ( $$ \kappa $$ ). It is found that the superconducting and physical properties of the samples improve with the increment of the diffusion-annealing temperature; however, the presence of the magnetic field leading to the decrease of the flux pinning in the samples causes the reduction of these properties. Namely, the T c onset and T c offset values are found to increase from 38.4 to 39.3 K and 36.9 and 38.3 K with the enhancement in the diffusion-annealing temperature at zero filed. Similarly, the U0 values increase significantly with the increase of the annealing temperature. In fact, the U0 of 9,162 K belonging to the sample annealed at 850 °C is determined to be the maximum activation energy value. On the other hand, the minimum T c onset of 30.9 K, T c offset of 27.6 K and U0 of 1,365 K at 7 T applied magnetic field are obtained for the pure sample, indicating that the sample annealed at 850 °C obtains much stronger flux pinning, better crystallinity and connectivity between grains compared to the other samples prepared. Based on these results, the superconducting and physical properties of the MgB2 superconductors produced in this work are observed to enhance with the increase of the diffusion-annealing temperature as a result of the improvement of pinning abilities, crystallinity and connectivity between grains. The magnetic field and temperature dependence of the activation energy are also discussed.

Correlation between viscous-flow activation energy and phase diagram in four systems of Cu-based alloys

Activation energy is obtained from temperature dependence of viscosities by means of a fitting to the Arrhenius equation for liquid alloys of Cu–Sb, Cu–Te, Cu–Sn and Cu–Ag systems. We found that the changing trend of activation energy curves with concentration is similar to that of liquidus in the phase diagrams. Moreover, a maximum value of activation energy is in the composition range of the intermetallic phases and a minimum value of activation energy is located at the eutectic point. The correlation between the activation energy and the phase diagrams has been further discussed.

Convective Drying Kinetics of Red Chillies

The drying kinetics of four varieties of chillies (Pb-Lal, Pb-Guchhedar, Pb-Surkh, and CH-1) was studied. The chillies (pricked and unpricked) were pretreated in the dip sol solution. The treated chillies were dried in an automatic weighing experimental dryer at selected temperatures (45°, 50°, 55°, 60°, and 65°C). The results indicated that drying took place in the falling rate period. Out of three models considered, Page's model was found to be the most suitable for describing the drying behavior of chillies. The dependence of drying constant on temperature was analyzed using an Arrhenius equation. The variety Pb-Lal has the maximum value of activation energy (42.59 kJ/mol), which is also reflected in the reduced drying time for this variety. The results of quality studies of dried chillies in terms of capsaicin content and coloring matter indicated that the Pb-Lal variety had acceptable capsaicin content of 532.08 µg and coloring matter of 73.8 ASTA.

Proposed novel dynamic equations for direct determination of activation energy in non-isothermal isothermal systems

A new mathematical approach for the estimation of apparent activation energy is proposed for non-isothermal dynamic process in both weight loss and weight gain conditions and is tested in different organic and inorganic systems. Satisfactory agreement between the new approach and the classical Arrhenius equation is observed. The proposed equations are applicable to a particular change occurring at two specified reaction temperatures at a constant heating rate without recording the intermediate weight changes and the temperatures. The principal advantages of this model are that the knowledge of rate constant and the graphical work are not necessary for the determination of activation energy. Moreover, the order of the reaction course is the one which yields maximum value of activation energy. Direct determination feature further simplifies the new approach and is considered as a pragmatic achievement in academic and technological fields.