Thermal Stability Criteria Research Articles

First-principles calculations of ScMC2 (M = Fe, Co, Ni, Cu) ternary carbides: A suitable candidate for shielding purpose

Physical properties of scandium-based ternary ScMC2 (M = Fe, Co, Ni, Cu) carbides have been investigated using first-principles calculations. The Wien2k code based on Density Functional Theory (DFT) is employed for these calculations. The study validates that all examined carbides satisfy the criteria for structural, mechanical, thermal, and thermodynamic stability. Among the four studied carbides, ScCuC2 is found to exhibit the most stable structure. The lengths of carbon-carbon (C-C) bonds differ across the compounds under study. Further, physical properties such as elasto-mechanical, thermal and optoelectronic properties of ternary ScMC2 (M = Fe, Co, Ni, Cu) carbides have been calculated. Stiffness constants and elastic moduli are calculated and compared with previously reported results. Poisson's and Pugh's ratios suggest the ductile nature of ScMC2 (M = Fe, Co, Ni) carbides, while ScCuC2 carbide bears brittle behavior. The thermal shock resistance ranking is ScNiC2> ScCoC2> ScCuC2> ScFeC2. These carbides also show improved thermal properties, machinability, rigidity, melting point, resistance to bond elongation and torsional deformations. DOS (density of states) spectra indicate the metallic behavior of ScMC2 (M = Fe, Co, Ni, Cu) carbides with electronic states decreasing progressively at the Fermi level (EF) with different transition metals. Optical properties reveal anisotropy in ScMC2 carbides up to 30 eV and reflectance spectra suggest that ScCoC2 carbide is the most suitable candidate for shielding and solar heating mitigation among the studied compounds.

Sb induced effect on glass transition, crystallization kinetics and optical properties of Se96Sn4 alloy

Se96-xSn4Sbx (x = 0, 2, 4, 6, and 8) glassy alloys were prepared using the melt quench technique. Thermal measurements were carried out using differential scanning calorimetry (DSC) in non-isothermal mode. Kissinger and Moynihan methods are used for glass transition kinetics, while Kissinger, Takhor, and Augis-Bennet methods are used to study crystallization kinetics. The inclusion of Sb in the alloy increased the glass transition temperature (Tg), activation energy of the glass transition (Et), and activation energy of crystallisation (Ec). The chemical bond approach has been used to explain the results. The rising trend of Ec is explained by the production of SnSe4/2 structural units with energies greater than those of Se–Se and Se–Sb bonds, increasing the degree of cross-linking. The dimensionality of crystal growth changes from one to two with the addition of Sb to the Se-Sn alloy. The criterion for thermal stability was addressed by using the enthalpy emitted during the crystallization process. In addition, Kubelka-Munk transformation and Tauc plots were used to calculate the band gaps. The energy gap (Eg) decreases from 3.72 to 1.60 eV as the Sb concentration increases from 0 to 8 atm%.

Thermal characterization, polymorphism, and stability evaluation of Se-NSAID derivatives with potent anticancer activity

Stability, thermal characterization, and identification of possible polymorphism are relevant in the development of novel therapeutic drugs. In this context, thirty new nonsteroidal anti-inflammatory drug (NSAID) derivatives containing selenium (Se) as selenoesters or diacyl diselenides with demonstrated anticancer activity were thermally characterized in order to establish thermal stability criteria and detect possible polymorphic forms. Compounds were analyzed by a combination of thermogravimetry, differential scanning calorimetry, and X-ray diffraction techniques, and five different calorimetric behaviors were identified. Two compounds based on naproxen (I.3d and I.3e) and an indomethacin-containing derivative (II.2) presented two crystalline forms. The stability under acid, alkaline and oxidative conditions of selected polymorphs was also assessed using high-performance liquid chromatography. In addition, the cytotoxic activity of Se-NSAID crystalline polymorphs was studied in several cancer cell lines in vitro. Remarkably, no significant differences were found among the polymorphic forms tested, thus proving that these compounds are thermally qualified for further drug development.Graphical abstract

Thermal Analysis of a Reactive Variable Viscosity TiO2-PAO Nanolubricant in a Microchannel Poiseuille Flow.

This paper examines the flow structure and heat transfer characteristics of a reactive variable viscosity polyalphaolefin (PAO)-based nanolubricant containing titanium dioxide (TiO2) nanoparticles in a microchannel. The nonlinear model equations are obtained and numerically solved via the shooting method with Runge-Kutta-Fehlberg integration scheme. Pertinent results depicting the effects of emerging thermophysical parameters on the reactive lubricant velocity, temperature, skin friction, Nusselt number and thermal stability criteria are presented graphically and discussed. It is found that the Nusselt number and thermal stability of the flow process improve with exothermic chemical kinetics, Biot number, and nanoparticles volume fraction but lessen with a rise in viscous dissipation and activation energy.

HAMR switching dynamics and the magnetic recording quadrilemma

We investigate the dynamical switching process of Heat Assisted Magnetic Recording (HAMR) by numerical calculations of switching probability using an atomistic model. Calculations show that at the elevated write temperature of HAMR there is a loss of information arising from ’backswitching’: a thermodynamic phenomenon which comes into play when the ratio of the Zeeman energy to the thermal energy is insufficiently large to completely stabilise the switched direction. We consider the special case of Heated Dot Magnetic Recording, where a reduction of switching probability can be related to a bit error rate. We show that the backswitching becomes more pronounced at faster write times. Also, we show that in the case of current recording media, based on the binary alloy FePt, backswitching will be a more stringent limitation on recording density than the usually assumed thermal stability criterion.

Experimental study of thermal stability of HTS cable under DC overcurrent

High-temperature superconducting (HTS) direct current (DC) cables have advantages of large capacity, low transmission loss, and small size over conventional cables under normal operating conditions, which give a promising potential to upgrade the power grid. However, under fault current, which is 10–30 times larger than the rated current, the quench and the subsequent heat generation of HTS tapes pose a great challenge to the thermal stability of the HTS cable stability. Therefore, it is important to study the quench behaviors, recovery characteristics, and thermal stability criteria of HTS cables. In this paper, we studied the transient thermal stability of the superconducting cable through theoretical analysis and experimental verification. The influence of the thickness and the structure of the insulation layer, and parallel connected stabilizing layers are considered. The results show that the thickness and structure of the insulation layer affect the heat transfer efficiency between HTS tapes and liquid nitrogen thus affecting the thermal stability criteria, and the parallel connected stabilizing layer has a current shunt effect and contributes to the heat capacity so that stabilized the cable against thermal impulse.

Computational discovery of two-dimensional copper chalcogenidesCuX(X= S, Se, Te)

We investigate the energy landscape of 2D CuS, CuSe, and CuTe compounds using a global evolutionary algorithm in combination with density functional theory. Four low-lying energy ${\mathrm{Cu}}_{2}{X}_{2}$ (X=S, Se, Te) slabs with $P\overline{3}m1$, $P4/mmm$, $P4/nmm$, and $Pmmn$ symmetries have been identified on their respective potential energy surfaces. Three structures present tetrahedral ${\mathrm{Cu}X}_{4}$ motifs which pave the 2D slabs, while the latter is based on shared ${\mathrm{Cu}}_{4}{X}_{2}$ octahedra. The viability of each phase was examined by looking at dynamical, thermodynamic, and thermal stability criteria. We find that 2D copper monosulfide crystallizes in the $P\overline{3}m1$ phase, reminiscent of the covalent slab found in the $\mathrm{Ca}{\mathrm{Al}}_{2}{\mathrm{Si}}_{2}$ prototype. Two polymorphs of 2D copper selenide with symmetries $P\overline{3}m1$ and $P4/mmm$ are close in energy. The latter ${\mathrm{Cu}}_{2}{\mathrm{Se}}_{2}$ slab is made of fused ${\mathrm{Cu}}_{4}{\mathrm{Se}}_{2}$ square bipyramids with electronegative Se atoms in apical positions. Finally, the ground-state 2D CuTe has a $Pmmn$ space group containing distorted ${\mathrm{CuTe}}_{4}$ tetrahedra with some Te--Te bonding. The electronic and bond analyses show that all of these predicted 2D CuX phases are metallic with ionocovalent bonds.

Dying AdS Schwarzschild black hole

The criteria for thermal stability of a most general quantum black hole derived by us appeared in the form of a series of inequalities connecting second-order derivatives of black hole mass with respect to its parameters, which determine the mass of the black hole. These nullify the concept of positivity of specific heat as the sole criteria for thermal stability. Using this most general stability criterion, we prove here that AdS Schwarzschild black holes are no longer stable anywhere in their parameter space if cosmological constant is allowed to vary. We also calculate the fluctuations of both horizon area and cosmological constant of this black hole. We calculate specific heat of it and compare this with Hawking’s prediction.

Structure enhancement of energetic materials: A theoretical study of the arylamines to arylpentazoles transformation

A theoretical study of the effect of amines-to-pentazoles transformation on the detonation performance is reported in this paper. A quantitative description of the latter is performed for the general case according to our recently developed compositional criterion evaluation algorithm. It is shown that increments of crystal density and enthalpy of formation are both positive meaning a higher detonation performance of the resulting pentazoles. Since the known arylpentazoles are thermally unstable compounds, a simple descriptor of the thermal stability was revealed (R2 = 0.98), which allowed modeling of new pentazoles with expected thermal stability up to 77 °C. Five the most thermally stable structures were then analyzed using high-level first-principles calculations, which provided negative values of the detonation energy for all ionic compounds; this may allow proposing them as safe gas-forming agents. Meanwhile, the relative gain in detonation energy caused by the studied reaction is always positive and can reach 600%. Thus, we have shown that amines-to-pentazoles transformation is an effective tool for enhancing detonation properties when the resulting compound satisfies the thermal stability criterion. Also, we have demonstrated that aromatic/heterocyclic pentazoles may be considered as self-sufficient materials without further modifications by detachment of the aromatic ring.

Formulation Development and Improved Stability of a Combination Measles and Rubella Live-Viral Vaccine Dried for Use in the NanopatchTM Microneedle Delivery System

ABSTRACT Measles (Me) and rubella (Ru) viral diseases are targeted for elimination by ensuring a high level of vaccination coverage worldwide. Less costly, more convenient MeRu vaccine delivery systems should improve global vaccine coverage, especially in low – and middle – income countries (LMICs). In this work, we examine formulating a live, attenuated Me and Ru combination viral vaccine with Nanopatch™, a solid polymer micro-projection array for intradermal delivery. First, high throughput, qPCR-based viral infectivity and genome assays were established to enable formulation development to stabilize Me and Ru in a scaled-down, custom-built evaporative drying system to mimic the Nanopatch™ vaccine coating process. Second, excipient screening and optimization studies identified virus stabilizers for use during the drying process and upon storage in the dried state. Finally, a series of real-time and accelerated stability studies identified eight candidate formulations that met a target thermal stability criterion for live vaccines (<1 log10 loss after 1 week storage at 37°C). Compared to −80°C control samples, the top candidate formulations resulted in minimal viral infectivity titer losses after storage at 2–8°C for 6 months (i.e., <0.1 log10 for Me, and ~0.4 log10 for Ru). After storage at 25°C over 6 months, ~0.3–0.5 and ~1.0–1.4 log10 titer losses were observed for Me and Ru, respectively, enabling the rank-ordering of the stability of candidate formulations. These results are discussed in the context of future formulation challenges for developing microneedle-based dosage forms containing stabilized live, attenuated viral vaccines for use in LMICs.

Thermal characterization and stability evaluation of leishmanicidal selenocyanate and diselenide derivatives

In this study, the thermal behavior of a series of leishmanicidal selenocyanate and diselenide biological active compounds has been studied by means of differential scanning calorimetry, X-ray diffraction and thermogravimetry in order to establish thermal stability criteria and investigate their polymorphism. Moreover, stability under acid, alkaline and oxidative media was tested using high-performance liquid chromatography with fluorescence detection. The results of the experiments show that there are five types of polymorphic behaviors for the studied compounds. In addition, relationship is found among stability and a series of structural effects and stress conditions of compounds.

Thermodynamics of asymptotically flat Reissner–Nordstrom black hole

We established the criteria for thermal stability of a most general black hole in the form of a series of inequalities connecting second-order derivatives of the black hole mass with respect to its parameters. The mass of a black hole depends solely on these parameters, e.g. horizon area and electric charge are these parameters for non-rotating charged black hole. We also introduced the notion of “Quasi stability”. It is known how to calculate the fluctuations of these parameters for both stable and quasi stable black holes. In this paper, we consider the simplest black hole having nontrivial parameter, i.e. electrically charged non-rotating asymptotically flat Reissner–Nordstrom black hole (AFRNBH). We will show here that this black hole is not stable anywhere in its parameter space, but it is actually quasi stable, having positive specific heat in some region, violating Hawking’s prediction. In fact, this black hole will be shown to exhibit phase transition which is structurally quite different from that in case of Schwarzschild black hole, as predicted first by Hawking. This black hole will also be shown to try to resist its decay under Hawking radiation, but ultimately remains unsuccessful.

Grain boundary segregation and relaxation in nano-grained polycrystalline alloys

The present study carries out systematic thermodynamics analysis of Grain Boundary (GB) segregation and relaxation in Nano-Grained (NG) polycrystalline alloys. GB segregation and relaxation is an internal process towards thermodynamic equilibrium, which occurs naturally in NG alloys without any applied loads, causes deformation and generates internal stresses. The analysis comprehensively investigates the multiple coupling effects among chemical concentrations and mechanical stresses in GBs and grains. A hybrid approach of eigenstress and eigenstrain is developed herein to solve the multiple coupling problem. The analysis results indicate that the GB stress and grain stress induced by GB segregation and relaxation can be extremely high in NG alloys, reaching the GPa level, which play an important role in the thermal stability of NG alloys, especially via the coupling terms between stress and concentration. The present theoretic analysis proposes a novel criterion of thermal stability for NG alloys, which is determined by the difference in molar free energy between a NG alloy and its reference single crystal with the same nominal chemical composition. If the difference at a temperature is negative or zero, the NG alloy is thermal stable at that temperature, otherwise unstable.

Thermal Stress Reduction of Power MOSFET with Dynamic Gate Voltage Control and Circulation Current Injection in Electric Drive Application

While operating an electric drive under different load conditions, power switch devices experience thermal stress which provokes wear-out failures and compromises lifetime. In this paper, a model-based dynamic gate voltage control strategy is proposed to reduce the thermal stress by shaping the profile of conduction losses. Thermal stability criteria are investigated, which limit the gate voltage operating range; thus, current focalization and associated local heat up are avoided. After that, simulations and lifetime estimation are conducted for performance evaluation in two different operation scenarios, which show promising results at high speed operation conditions. Furthermore, a current injection method is applied for low-speed operating conditions to improve the compensation effort. This method is experimentally verified by using a custom proof-of-concept gate driver that supplies an adjustable three-level gate voltage. A three-phase electric drive is prototyped, on which power cycling tests are conducted. The junction temperature is measured and the results confirm the thermal control method.

Phase transition in decaying black holes

We had earlier derived the most general criteria for thermal stability of a quantum black hole, with arbitrary number of parameters, in any dimensional spacetime. These conditions appeared in form of a series of inequalities connecting second order derivatives of black hole mass with respect to its parameters. Some black holes like asymptotically flat rotating charged black holes do not satisfy all the stability criteria simultaneously, but do satisfy some of them in certain region of parameter space. They are known as “Quasi Stable” black holes. In this paper, we will show that quasi stable black holes although ultimately decay under Hawking radiation undergo phase transitions. These phase transitions are different from phase transition in ADS Schwarzschild black hole. These are marked by sign changes in certain physical quantities apart from specific heat of the black hole. We will also discuss the changes in the nature of fluctuations of the parameters of these quasi stable black holes with different phases.

Improved Electrical and Thermal Aging Properties of DBSA-Doped PANI Using MWCNT and GO

Electrical conductivity deterioration of polyaniline (PANI) at elevated temperatures has limited its applications for commercial usages. In this study we endeavored to improve the thermal aging resistance of PANI and its conductivity stability at elevated temperatures using a high molecular weight dopant, dodecylbenzenesulfonic acid (DBSA), along with the addition of carbon-based nanoparticles. DBSA-doped PANI (DBSA-PANI) and its nanocomposites with graphene oxide (PANI/GO) and multi-walled carbon nanotube (PANI/MWCNT) were prepared through in situ polymerization. The samples were aged at 90°C up to 1000 h and characterized by Fourier transform infrared spectroscopy (FTIR), x-ray diffraction (XRD), scanning electron microscopy (SEM), and electrical conductivity measurements. It was observed that electrical conductivity deteriorates more rapidly in DBSA-PANI than in GO and MWCNT nanocomposites. The FTIR results confirmed a strong retention of DBSA groups in the nanocomposites after aging, but not for DBSA-PANI. This showed more stability of DBSA dopant in PANI/GO and PANI/CNT. The characteristic time (τ), as a criterion for thermal stability, was found to be 91, 172, and 295 h for DBSA-PANI, PANI/MWCNT, and PANI/GO, respectively. It was suggested that the retardation of the de-doping process is the major reason for the higher τ value and more electrical conductivity stability of PANI/GO. The obtained thermal stability for the electrical conductivity of DBSA doped PANI/GO nanocomposites was nearly 30 times higher than that of HCl-doped PANI.

Thermosensitive Tm3+/Yb3+ co-doped oxyfluorotellurite glasses – spectroscopic and temperature sensor properties

Oxyfluorotellurite (65-x)TeO2–20ZnF2–12PbO–3Nb2O5–xTm2O3 (x = 0.5, 2 and 5) and (65-x-y)TeO2–20ZnF2–12PbO–3Nb2O5–xTm2O3–yYb2O3 (x = 0.5, y = 2 and x = 0.5, y = 5) glass systems were manufactured. Glass thermal stability was examined by means of differential thermal analysis (DTA) and some thermal stability criteria ΔT, H’ and S were determined. Absorption spectrum was utilized to prepare Judd-Ofelt (J-O) calculations and consequently oscillator strengths, intensity parameters Ω2,4,6, radiative transition probabilities, branching ratios and radiative lifetimes of luminescent levels were estimated. Emission spectra and luminescence decay curves were measured as a function of temperature in the 300–625 K range. Based on the upconversion luminescence of Tm3+ the optical temperature sensor qualities have been evaluated for Tm3+/Yb3+ co-doped sample. The fluorescence intensity ratio (FIR) between transitions 700 nm (Tm3+:3F2,3 → 3H6)/800 nm (Tm3+:3H4 → 3H6) for 975 nm excitation and 700 nm (Tm3+:3F2,3 → 3H6)/470 nm (Tm3+:1G4 → 3H6) for 803 nm excitation were determined and an adequate relative thermal sensitivity S was estimated. The significant value of relative thermal sensitivity 1.12 %K−1 was determined when NIR Yb3+ and Tm3+ emission bands were analyzed, however. Effective emission cross section was calculated for 3F4 → 3H6 potential laser transition of thulium around 1.9 μm in single-doped Tm3+ glass. Furthermore, effect of temperature on down-converted and up-converted thulium and ytterbium emission and on relaxation dynamic of involved excited states was studied in details.

Size-Dependent Switching Properties of Spin-Orbit Torque MRAM With Manufacturing-Friendly 8-Inch Wafer-Level Uniformity

We have developed a manufacturing-friendly spin-orbit torque magnetic random access memory (SOT-MRAM) technology in CMOS compatible 8-inch fab process. The proposed SOT-MRAM process technology resolves etching non-uniformity and reduction of high resistivity heavy-metal nanowire resistance issues. Besides, we present device size-dependent switching current threshold in the proposed SOT-MRAM cell structure. To realize the potential of our fabricated SOT-MRAM, wafer-level uniformity, cycling and temperature dependence SOT switching have been comprehensively investigated. Furthermore, the thermal stability factor (△) was calculated from temperature-dependence SOT switching to fulfill the thermal stability criteria, i.e., > 10 years of this emerging SOT-MRAM technology.

Thermal stability criterion of complex reactions for batch processes

Thermal stability of batch processes is a major factor for the safe and efficient production of polymers and pharmaceutical chemicals. The prediction of the thermal stability for such processes was shown in Kähm and Vassiliadis (2018d) to be unreliable with most stability criteria found in literature also presenting a novel criterion, K, which was shown to give reliable stability predictions for single reactions of higher order.This work provides a detailed derivation for the generalization of thermal stability criterion K applied to reaction networks of arbitrary complexity, consisting of parallel and competing reactions of both exothermic and endothermic nature. The generalized thermal stability criterion K is then applied to Model Predictive Control (MPC) frameworks to intensify batch processes in a safe manner, reducing the time required to reach the target conversion. Several illustrative computational case studies are presented, highlighting the proposed methodology and verifying its validity.

Inorganic Associates in a High-Temperature Vapor

Experimental data and results of quantum chemical calculations on the structure and thermodynamic properties of inorganic associates in a high-temperature vapor were systematized. A criterion for thermal stability was proposed, and the dependences of the atomization enthalpies of these compounds on the atomization enthalpies of the anion-forming fragment were revealed.