High Temperature Activation Energy Research Articles

Electric current stressing enhanced damping properties in Sn5Sb solder

PurposeThe purpose of this paper is to investigate the effects of electric current stressing on damping properties of Sn5Sb solder.Design/methodology/approachUniformly shaped Sn5Sb solders were prepared as samples. The length, width and thickness of the samples were 60.0, 5.0 and 0.5 mm, respectively. The damping properties of the samples were tested by dynamic mechanical analyzer with a cooling system to control the test temperature in the range of −100 to 100°C. Simultaneously, electric current was imposed to the tested samples using a direct current supply. After tests, the samples were characterized using scanning electron microscope, electron backscatter diffraction and transmission electron microscope, which was aimed to figure out the damping mechanism in terms of electric current stressing induced microstructure evolution.FindingsIt is confirmed experimentally that the increase in damping properties is due to Joule heating and athermal effects of current stressing, in which Joule heating should make a higher contribution. G–L theory can be used to explain the damping properties of strain amplitude under current stressing by quantitative description of geometrically necessary dislocation density. While the critical strain amplitude and high temperature activation energy decrease with increasing electric current.Originality/valueThese results provide a new method for vibration reliability evaluation of high-temperature lead-free solders in serving electronics. Notably, this method should be also inspiring for the mechanical performance evaluation and reliability assessment of conductive materials and structures serving under electric current stressing.

Electrical and gamma ray shielding properties of phospho-tellurite glasses doped with alkali and transition metal oxides

This article presents investigated results on physical, electrical and gamma radiation shielding properties of glasses of composition, (P2O5)0.25-(TeO2)0.5-x-(Na2O)0.1- (ZnO)0.15-(CoO)x (x= 0.10, 0.15, 0.20, 0.25, 030 and 0.35) were synthesized by melt quenching procedure. After confirming non-crystallinity, density was measured and found it to be decreased with increase of CoO concentration in the range 4.0370 gm/cm3 - 3.5673 gm/cm3. Molar volume, mean distance between TMIs, small polaron radius, oxygen packing density and field strength were estimated. Conductivity was measured in the temperature range 303K -663K. High temperature conductivity is found to be varied as per Mott’s (SPH) model. High temperature activation energy is found to be increased with CoO content. Low temperature conductivity variation has been analyzed using Mott’s (VRH) model. Gamma ray shielding parameters were evaluated using Phy-X/PSD software for the energy range 0.005 MeV-15 MeV. The mass and linear attenuation coefficients were found to decrease with CoO content and photon energy. Half and tenth value layers increased with increase of mole fractions of CoO. All the observed shielding parameters are superior to those reported previously for other glasses. The glass with x=0.10 is best suited for the utility of gamma shielding at low energy.

Comprehensive electrical characterization and theoretical analysis of Mn and As doped β-FeSi2 through DFT: A promise to rectification and photovoltaic applications

The effects of Mn and As doping in β-FeSi2 have been studied by theoretical simulations and electrical characterizations by analyzing Hall parameters within the temperature range of 20–300 K using mobility and the dual band model. The Hall resistivity ρ of doped samples increases linearly from a negative to a positive magnetic field (B), demonstrating the normal Hall effect at room temperature. High temperature Hall concentration increases significantly with the gradual increase in both Mn and As doping due to more and more ionization of the deep donor level. High temperature activation energies of Mn doped β-FeSi2 are considerably greater than that of low temperature energies, which demonstrates clear evidence of the dual band model. From density functional theory calculations, the origin of the dual band model has been validated from the electronic structure of β-FeSi2. Both density of states and charge transfer to the system upon doping have been investigated through the density functional theory, which demonstrates the Mn and As doped systems to be p-type and n-type, respectively. Both Mn and As doped β-FeSi2 exhibit p-type and n-type conductivities for spin down and spin up channels, respectively, in the presence of an external magnetic field, which will encourage its applications in novel spintronic devices. In addition, a β-FeSi2 based homo-junction diode fabricated from the Mn and As doped β-FeSi2 exhibits a cut-in voltage of 0.82 V, a reverse breakdown voltage of −10 V, and an ideality factor of 3.87. Thus, doped β-FeSi2 will be very much useful for fabricating an efficient and cost-effective solar cell if fabricated physically.

Physical and electrical studies of tellurite-lead-vanadate glasses doped with CoO

This article presents structural, physical and conductivity results on tellurite-lead-vanadate glasses, (PbO)0.3 – (TeO2)0.1 – (V2O5)0.6-x – (CoO)x, (x = 0.05, 0.1, 0.15, 0.20, 0.25, 0.30). XRD spectra indicated non-crystallinity of the samples. Density is found in the range 4.401 g/cm3 – 5.092 g/cm3. Density increased as well as molar volume decreased with respect to increase of CoO content. This reveals shows that the glass network is becoming increasingly congested due to an increase in CoO content. Conductivity variation with temperature in the range 300 K – 523 K inferred semi conductivity behavior. High temperature conductivity is obeyed Mott’s small polaron happing mechanism and low temperature data obeyed Mott’s/Greaves VRH model. High temperature activation energy increased with CoO content in the glasses. Number of states at Fermi level derived from VRH model fits are well within the range quoted for similar glasses.

On the origin of carrier localization in AlInAsSb digital alloy

We compared the photoluminescence (PL) properties of AlInAsSb digital alloy samples with different periods grown on GaSb (001) substrates by molecular beam epitaxy. Temperature-dependent S-shape behavior is observed and explained using a thermally activated redistribution model within a Gaussian distribution of localized states. There are two different mechanisms for the origin of the PL intensity quenching for the AlInAsSb digital alloy. The high-temperature activation energy E 1 is positively correlated with the interface thickness, whereas the low-temperature activation energy E 2 is negatively correlated with the interface thickness. A quantitative high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) study shows that the interface quality improves as the interface thickness increases. Our results confirm that E 1 comes from carrier trapping at a state in the InSb interface layer, while E 2 originates from the exciton binding energy due to the roughness of the AlAs interface layer.

Comparison of Acidity Test Method of Nickel Phosphate Silica Catalyst for Production Levulinic Acid from Glucose

The reaction of levulinic acid production from glucose has a reaction stage that requires a high temperature and high activation energy so that in this levulinic acid production reaction a catalyst is needed. The required catalyst must have a lewis acid site and a bronsted acid site so that the acidity of the catalyst is very influential for the successful production of levulonic acid. Silica nickel phosphate catalysts have lewis acid sites from Ni metal and bronsted acid sites from phosphoric and silica groups. The acidity of the catalyst was measured using the pyridine and ammonia adsorption method and the acidity center strength method using the TGA-DTA base adsorption-desorption. The adsorption of ammonia and pyridine uses the gravimetric method so that it can easily obtain the amount of total acidity of the catalyst and the acidity of the catalyst surface while the TGA-DTA method shows the acid strength of the actual catalyst, which is the real state of the catalyst when catalyzing a reaction and shows the catalyst's resistance to high temperatures. These two methods of measuring acidity have the same disadvantage that they cannot show and know the number of lewis acid sites and bronsted acid sites.

Strain Relaxation in Metal Alloy Catalysts Steers the Product Selectivity of Electrocatalytic CO2 Reduction.

Strain engineering in bimetallic alloy structures is of great interest in electrochemical CO2 reduction reactions (CO2RR), in which it simultaneously improves electrocatalytic activity and product selectivity by optimizing the binding properties of intermediates. However, a reliable synthetic strategy and systematic understanding of the strain effects in the CO2RR are still lacking. Herein, we report a strain relaxation strategy used to determine lattice strains in bimetal MNi alloys (M = Pd, Ag, and Au) and realize an outstanding CO2-to-CO Faradaic efficiency of 96.6% and show the outstanding activity and durability toward a Zn-CO2 battery. Molecular dynamics (MD) simulations predict that the relaxation of strained PdNi alloys (s-PdNi) is correlated with increases in synthesis temperature, and the high temperature activation energy drives complete atomic mixing of multiple metal atoms to allow for regulation of lattice strains. Density functional theory (DFT) calculations reveal that strain relaxation effectively improves CO2RR activity and selectivity by optimizing the formation energies of *COOH and *CO intermediates on s-PdNi alloy surfaces, as also verified by in situ spectroscopic investigations. This approach provides a promising approach for catalyst design, enabling independent optimization of formation energies of reaction intermediates to improve catalytic activity and selectivity simultaneously.

Studies of Anomalies in Mixed Conduction of Na<sub>2</sub>O and V<sub>2</sub>O<sub>5</sub> Doped Boro-Phosphate Glasses

A set of borophosphate glasses doped with alkali and transition metal (TM) ions have been synthesized. The glasses were carried through; annealing, XRD, density, DC conductivity studies. Molar volume and density varied nonlinearly. High temperature activation energy is analysed taking into consideration of Mott’s SPH model. The low temperature electrical conductivity was analysed by Mott and Greaves VRH. Several polaron hopping related parameters at high temperature region and density of states at low temperature region were computed. The high temperature DC activation energy measured by conductivity, calculated numerous pertained parameters varied nonlinearly with mole fraction of vanadium content. The Study exhibits DC electrical conduction is due to both alkali and transition metal ions and thus confirms the mixed conductivity. A crossover conduction mechanism from the ionic dominant region to polaronic predominant region has been also observed. Studies revealed the single transition effect at 0.4 mol fraction of V2O5 content.

Viscosity of silica and doped silica melts: evidence for a crossover temperature

AbstractSilica is known as the archetypal strong liquid, exhibiting an Arrhenius viscosity curve with a high glass transition temperature and constant activation energy. However, given the ideally isostatic nature of the silica network, the presence of even a small concentration of defects can lead to a significant decrease in both the glass transition temperature and activation energy for viscous flow. To understand the impact of trace level dopants on the viscosity of silica, we measure the viscosity‐temperature curves for seven silica glass samples having different impurities, including four natural and three synthetic samples. Depending on the type of dopant, the glass transition temperature can vary by nearly 300 K. A common crossover is found for all viscosity curves around ~2200–2500 K, which we attribute to a change of the transport mechanism in the melt from being dominated by intrinsic defects at high temperature to dopant‐induced defects at low temperatures.

Flux-assisted low-temperature synthesis of Mn4+-doped unusual broadband deep-red phosphors toward warm w-LEDs

Abstract Rare-earth free ions, especially Mn4+, doped phosphors with red emission have become a research hotspot. To achieve high-performance phosphor-converted warm w-LEDs, blue light activable Mn4+-doped phosphors with broadband red emission rather than the commonly sharp ones are highly desired. In this work, we report a novel Mn4+-doped Li2Mg3TiO6 phosphor prepared by the conventional solid-state reaction and the synthesis temperature is remarkably lowered from 1300 °C to 950 °C with the addition of LiF flux. The fluorescence properties were well characterized by steady and transient state spectroscopies. The occupation of Mn4+ ions for the center of octahedral sites leads to a blue light excitable phosphor showing unusual broadband deep-red emission. The addition of LiF enhances the Mn4+ emission intensity and 0.1 mol% Mn4+-doped phosphor attains the highest red emission intensity with the maximum PLQY = 35.1%. The Mn4+ emission presents good thermal resistance demonstrated by high-temperature dependent fluorescence and activation energy ΔE = 0.369 eV. The as-obtained red phosphor enables the fabrication of a warm w-LED device by the combination of commercial YAG yellow phosphor and blue LED (BLED) chip, giving CIE(x, y) = (0.307, 0.337), CRI = 83.9 and CCT = 5258 K. This work provides a promising candidate Li2Mg3TiO6:Mn4+ as broadband deep-red phosphor for warm w-LEDs as well as a method to effectively lower the preparation temperature.

Spent fluid catalytic cracking (FCC) catalyst enhances pyrolysis of refinery waste activated sludge

Catalytic pyrolysis is an effective innocuity, volume reduction and resource recovery technology for petroleum refinery waste activated sludge (rWAS). However, the high cost of catalysts hinders its application. In the present study, the spent fluid catalytic cracking catalyst (sFCCc) was reused to catalytically pyrolyze rWAS for the first time. The pyrolytic kinetics, yields and characteristics of pyrolytic products were investigated. sFCCc reduced the low-temperature (139–390 °C) and high-temperature (390–540 °C) average activation energy by 12.9% and 6.6% compared to rWAS alone. sFCCc and metallic oxides in rWAS jointly catalyzed the decomposition of rWAS and primary vapor via a series of thermochemical reactions. sFCCc promoted the conversion of rWAS into bio-oil and non-condensable gases. The lowest yield of biochar was 40.6 wt % and the highest content of H2 in non-condensable gases was up to 38.4 vol %. sFCCc significantly improved the quality of bio-oil. The content of saturated hydrocarbons increased from 37.3 wt % to 45.7 wt % and H/C molar ratios increased from 1.4 to 1.6. The O mobility from rWAS to bio-oil decreased from 22.1 wt % to 14.9 wt %. The pyrolytic residue presented a low environmental risk and showed a catalytic potential in ozonation treatment of refractory refinery wastewater. This study provides a new “wastes-treat-wastes” method for petroleum refinery waste management with the advantages of value-added energy recovery and resources reuse.

MD simulations of charged binary mixtures reveal a generic relation between high- and low-temperature behavior.

Experimental studies of the glassy slowdown in molecular liquids indicate that the high-temperature activation energy E∞ of glass-forming liquids is directly related to their glass transition temperature Tg. To further investigate such a possible relation between high- and low-temperature dynamics in glass-forming liquids, we analyze the glassy dynamics of binary mixtures using molecular dynamics simulations. We consider a binary mixture of charged Lennard-Jones particles and vary the partial charges of the particles and, thus, the high-temperature activation energy and the glass transition temperature of the system. Based on previous results, we introduce a phenomenological model describing relaxation times over the whole temperature regime from high temperatures to temperatures well inside the supercooled regime. By investigating the dynamics of both particle species on molecular and diffusive length scales along isochoric and isobaric pathways, we find a quadratic charge dependence of both E∞ and Tg, resulting in an approximately constant ratio of both quantities independent of the underlying observable, the thermodynamic ensemble, and the particle species, and this result is robust against the actual definition of Tg. This generic relation between the activation energy and the glass transition temperature indicates that high-temperature dynamics and the glassy slowdown are related phenomena, and the knowledge of E∞ may allow us to approximately predict Tg.

Investigating the high-temperature performance and activation energy of carbon black-modified asphalt binder

This study set out to evaluate the influence of carbon black (CB) on the rheological properties and activation energy of asphalt binder at high service temperatures. The rheological performance of virgin and modified asphalt binders are investigated using three evaluation approaches: (1) Superpave specification parameter (G*/sinδ), (2) multiple stress creep recovery (MSCR) test, and (3) interaction model for computing zero shear viscosity (ZSV). Moreover, the Arrhenius model was used to quantify the activation energy (Ef) of virgin and CB-modified asphalt binders. The result of this study reveals that modifying asphalt binder with up to 10% of CB, by weight of the total asphalt binder, enhances the elastic behavior (R%) and decreases the non-recoverable creep compliance (Jnr) of asphalt binder at high temperatures. Moreover, according to this study, the ZSV index can describe successfully rutting resistance of asphalt binder when compared with MSCR and Superpave rutting specification parameter. Besides, it was indicated that CB-modified asphalt binder has a high fluid resistance as more thermal energy was required for overcoming intermolecular force between molecules.

Synthesis, characterization and catalytic behavior of MFe2O4 (M = Ni, Zn and Co) nanoparticles on the thermal decomposition of TKX-50

Bimetallic iron oxides (NiFe2O4, ZnFe2O4 and CoFe2O4) were prepared via the facile solvothermal method and characterized using SEM, TEM, XRD, FTIR, XPS and BET instruments. The catalytic behavior of the bimetallic iron oxides on the thermal decomposition of 5, 5′-bistetrazole-1, 1′-diolate (TKX-50) was studied using DSC and TG-DTG methods. Besides, the corresponding kinetic parameters of TKX-50 thermal decomposition were calculated by multi-kinetics methods including traditional, iso-conversional and iteration methods. The thermal decomposition peak temperature (Tp) and the activation energy (Ea) reduced obviously after the addition of bimetallic iron oxides. Among different bimetallic iron oxides, the ZnFe2O4 has the best catalytic activity for TKX-50 thermal decomposition. The high thermal decomposition peak temperature (THDP) and average apparent activation energy (Ea) of TKX-50 were decreased by 47.0 °C and 34.34 kJ mol−1 in the presence of ZnFe2O4 sample. The excellent catalytic activity of ZnFe2O4 for thermal decomposition of TKX-50 makes it a promising combustion catalyst of insensitive solid propellants containing TKX-50.

Catalytic Activity of Ferrates (NiFe2O4, ZnFe2O4 and CoFe2O4) on the Thermal Decomposition of Ammonium Perchlorate

AbstractThree kinds of ferrates (NiFe2O4, ZnFe2O4 and CoFe2O4) were prepared via the facile solvothermal method and characterized using SEM, TEM, XRD, XPS, FT‐IR and BET instruments. The NiFe2O4, CoFe2O4 and ZnFe2O4 particles possess hollow structure with average particle size of 70, 220 and 360 nm, respectively. The catalytic performance of the ferrates for AP thermal decomposition were studied using DSC and TG‐DTG methods, and the decomposition mechanism of AP were suggested. The catalytic effects of different ferrates for AP thermal decomposition were significantly different. The CoFe2O4 has the best catalytic activity, and the high thermal decomposition peak temperature (THDP) and apparent activation energy (Ea) of AP were decreased by 108.99 °C and 37.38 kJ mol−1 in the presence of CoFe2O4 sample. Adding ferrates has no obvious influence on the gas‐phase decomposition products of AP, but has a great influence on the energy barrier of high temperature decomposition of AP. The excellent catalytic activity of CoFe2O4 is mainly attributed to the synergistic interaction between Fe and Co, which is conducive to the thermal decomposition of AP.

Examining the thermal degradation behaviour of a series of cyanate ester homopolymers

AbstractA series of thermally stable dicyanate monomers was prepared containing different thermally stable structural units, namely 2,2′‐bis(4‐cyanatophenyl)propane, bis‐4‐cyanato‐biphenyl, bis‐4‐cyanato naphthalene, 3,3′‐bis(4‐cyanatophenyl)sulfide and 3,3′‐bis(4‐cyanatophenyl)sulfone, was prepared and the identity of the products was confirmed by Fourier transform infrared and NMR spectral methods. The corresponding cyanate homopolymers were prepared and their properties were evaluated and compared. The composites were analysed for their thermal stability and thermal degradation kinetics. The series of homopolymers exhibit excellent thermal characteristics, e.g. relatively high glass transition temperatures of at least 215 °C, which were inversely proportional to the molecular weight between the crosslinks, high thermal decomposition temperature and high activation energies for the decomposition of cured resins. Determination of their limiting oxygen indices indicates that all the homopolymers are characterized as ‘self‐extinguishing’ materials. © 2019 Society of Chemical Industry

Towards understanding the morphological, magnetic, optical and electrical properties of MnO2 nanowires for magneto-and optoelectronic applications

Mixed solutions of manganese sulfate and potassium permanganate were hydrothermally used to synthesis α-MnO2 nanowires. Energy dispersive analysis of X-ray revealed the formation of stoichiometric MnO2 and X-ray diffraction revealed the formation of single crystalline α-MnO2. Examinations using both SEM and TEM yielded nanowires with diameters ranged from 40 to 50 nm and lengths ranged from 5 to 6 µm. The magnetic properties revealed that the α-MnO2 NWs exhibit ferromagnetic/antiferromagnetic characteristics at liquid nitrogen and room temperatures. This kind of materials may be find usage in electromagnetic shielding applications. Direct optical band gap of 2.6 eV, that was blue shifted from the bulk value, was reported. Photoluminescence examinations displayed a strong emission peak around 395 nm and broad peak around 477 nm. The α-MnO2 NWs showed a semiconducting behavior where the resistivity decreased with increasing temperature. Two activation energies were reported; the low temperature activation energy was 0.089 eV and the high temperature activation energy was 0.782 eV. Based on the observed high intensity UV emission peak, the obtained α-MnO2 NWs may find applications in UV light emitting diodes.

Radiation defect dynamics in GaAs studied by pulsed ion beams

Gallium arsenide under ion bombardment at room temperature and above exhibits pronounced dynamic annealing that remains poorly understood. Here, we use a pulsed beam method to study radiation defect dynamics in GaAs in the temperature range of 20–100 °C irradiated with 500 keV Xe ions. Results show that, with increasing temperature, the defect relaxation time constant monotonically decreases from ∼5.2 to ∼0.4 ms. A change in the dominant dynamic annealing process occurs at a critical temperature of ∼60 °C, as evidenced by a change in the activation energy. A comparison with the other semiconductors studied by the pulsed beam method (Si, Ge, and 4H-SiC) reveals that both the high-temperature activation energy and the temperature below which dynamic annealing becomes negligible scale with the melting point.Gallium arsenide under ion bombardment at room temperature and above exhibits pronounced dynamic annealing that remains poorly understood. Here, we use a pulsed beam method to study radiation defect dynamics in GaAs in the temperature range of 20–100 °C irradiated with 500 keV Xe ions. Results show that, with increasing temperature, the defect relaxation time constant monotonically decreases from ∼5.2 to ∼0.4 ms. A change in the dominant dynamic annealing process occurs at a critical temperature of ∼60 °C, as evidenced by a change in the activation energy. A comparison with the other semiconductors studied by the pulsed beam method (Si, Ge, and 4H-SiC) reveals that both the high-temperature activation energy and the temperature below which dynamic annealing becomes negligible scale with the melting point.

Non-isothermal thermogravimetric analysis of heavy oil in an O2/CO2 atmosphere

Abstract Although heavy oil is an abundant and promising energy source, its processing and utilization are complicated due to its high density, low hydrogen/carbon ratio, and high asphaltene content. Fortunately, these problems can be mitigated by the application of oxy-fuel combustion. To gain deeper insights into the above technology, the characteristics of heavy oil combustion in an O2/CO2 atmosphere was investigated using non-isothermal thermogravimetric analysis. We demonstrate that the combustion process consisted of four stages. Low-molecular-weight hydrocarbons reacted at low temperature, whereas heavy ones required a higher temperature. Increasing the concentration of oxygen resulted in increased TGA and DSC peak intensities and decreased peak widths, and these peaks were shifted to lower temperatures. Coat-Redfern and Flynn-Wall-Ozzawa methods were used to evaluate the kinetic parameters (E, A) of the oxidation process, showing that the high-temperature activation energy was much higher than the low-temperature one due to the different molecular weights of the oxidized substrates in each region. The reaction was demonstrated to be diffusion-controlled, as reflected by the lower activation energy at high oxygen concentration and high temperature, with the influence of oxygen concentration on QO processes being much more obvious than that on SO ones.

Disorder-induced f-electron localization in Nb and Y co-doped CeO2

We report the effect of the charge compensation on the electronic transport and optical properties of CeO2 co-doped with donor, Nb, and acceptor, Y, ions. As expected, the concentration of Ce3+ decreases with an increase in the Y content in Ce0.992−xNb0.008YxO2, where 0 ≤ x ≤ 0.008. More importantly, random electric fields generated by the Y ions bring additional disorder into the system. As a result, the high-temperature activation energy of conductivity increases significantly from 189 to 430 meV. A similar energy shift in the optical absorption peak centered at 1.3–1.5 eV is attributed to an increase in the energy gap separating the localized f-electrons from the empty Ce 4f band. The results underline the paramount importance of the disorder-induced Anderson localization of the f-electrons in ceria.