Differential Thermal Analysis Experiments Research Articles

Investigation of Host-Guest Inclusion Complex of Mephenesin with α-Cyclodextrin for Innovative Application in Biological System.

The goal of this study was to use coevaporation to look into how polyether compounds like mephenesin (MEP) can be encapsulated into the host molecule α-cyclodextrin's nanohydrophobic cage. Fourier transform infrared spectroscopy (FT-IR) investigations, powder X-ray diffraction (PXRD), and 1H NMR were among the spectroscopic techniques used to describe the inclusion complex. Additionally, Job's plot has been utilized to illustrate how MEP is encapsulated with α-cyclodextrin (α-CD) at a 1:1 molar ratio. The thermal stability of MEP increased after encapsulation according to thermogravimetric analysis (TGA) and differential thermal analysis (DTA) experiments. Mephenesin fits into the cavity of α-cyclodextrin in a 1:1 ratio, as observed by molecular docking for the inclusion complex to find the most appropriate orientation. This observation is further supported by the Job plot. Furthermore, a comparison was carried out based on a cell viability study between the medication and its inclusion complex.

Spectroscopic properties, Judd Ofelt analysis of U and Eu activated Li2O-ZnO-SrO-B2O3-P2O5 borophosphate glasses for solid-state lighting applications

Uranium and europium doped borophosphate glasses with the base composition of (Li2O)(ZnO)0.5(SrO)0.4(B2O3)2.55(P2O5)0.5 were synthesized by melt -quenching. The X-ray diffraction profile affirmed that all the synthesized samples were devoid of crystallinity and amorphous in structure. The absence of precipitations/grains in the scanning electron micrographs further validated the amorphous character and compositional homogeneity of the prepared glass. The FTIR spectra revealed several prominent vibrational bands in 713–1568 cm−1 range and were assigned to the corresponding B-O-B and P-O-P and B-O-P bonding. The thermal characteristics of the synthesised glass samples were investigated using differential thermal analysis experiments. The broad photoluminescence (PL) spectra observed for the uranium doped glass with emission maxima at 523 nm resembles the hexavalent U(VI) emission in a disordered amorphous environment. The emission profile of the Eu doped glass displayed several characteristics peaks due to 5D0 → 7FJ transitions. The phonon energy of the base glass was found to be 1005 cm−1. The Judd-Ofelt analysis showed that for all the doped glass, the JO intensity parameter Ω4 was always greater than Ω2 indicating that Eu3+ ions are primarily arranged in a centrosymmetric environment in the studied host. Radiative properties of 5D0 → 7FJ=1-4 transitions of the Eu3+ such as branching ratios, emission cross-section, and transition probabilities were computed. Energy transfer pathways of UO22+ → Eu3+ in the codoped borophosphate glass were described. The CIE chromaticity and PL results suggest that the intense red emission of Eu doped glasses could be useful for phosphor applications.

Thermodynamic assessment of hardmetals with alternative binders and experimental validation

Hardmetals are very well established due to their remarkable mechanical properties and wide range of applications. Cobalt is the favourite binder in WC-based cemented carbides, thus most sintering studies have been dedicated to the WC-Co system. However, the demand for carbide components with improved wear and corrosion resistance, is a reality in today's market. Sintering of hardmetals with alternative binders has revealed differentiated paths to reach the final microstructures but, in general, both a thermodynamic assessment and experimental studies to tailor and optimize the microstructural design are still missing.Alternative binders, constituted by Co and Ni alloys, and other alloying elements such as Cr and Mo, were used. This work aims to investigate the microstructural design of the new composites, using thermodynamic calculations based on CALPHAD methodology and Differential Thermal Analysis experiments. Wetting experiments were also conducted to measure the contact angle between the molten binder and the ceramic phase to further validate this approach. The microstructures of metal-ceramic interfaces and related composites were analysed by optical and scanning electron microscopy and the results were correlated with the reaction paths and overall hardmetal compositions.

Variation of the mass susceptibility of sandstone after high-temperature heating

Burnt rocks usually exhibit magnetic enhancement, which can be used to detect the spontaneous combustion zone of a coal fire or locate the resources in burnt rocks. To elucidate the mechanisms underlying magnetic enhancement, sandstone is heated to high temperatures between 100 and 1200°C. The mass susceptibility of the sandstone is measured after cooling, and the magnetic characteristics are explained based on the changes in colour and porosity, thermogravimetric and differential thermal analysis experiments and the observation of thin sections of rocks and scanning electron microscopy images. The findings are as follows: (1) the magnetic susceptibility of sandstone increases rapidly by two orders of magnitude as the temperature rises above 800°C. (2) The oxidation of iron ions and the formation of magnetite enhance the magnetic susceptibility of sandstone. The formation of magnetite at 800°C significantly enhances the magnetic susceptibility. (3) The highest temperature experienced by a burnt rock can be evaluated by analysing the different responses of the susceptibility of sandstone to temperature. Furthermore, it is possible to use the magnetic anomaly of the burnt rock to locate it and develop and utilise the beneficial resources in the burnt rock.

Phase diagram study and thermodynamic modeling of the MgO-Y2O3-MgF2-YF3 system

The phase diagram of the MgO-Y2O3-MgF2-YF3 system (Mg,Y//O,F reciprocal system) at 1273–1773 K was investigated for the very first time using a classical equilibrium/quenching and differential thermal analysis (DTA) experiments followed by electron probe microanalysis (EPMA) and X-ray diffraction (XRD) phase analyses. No ternary or quaternary crystalline phase was found, and the eutectic reactions in the reciprocal system were identified. The overall phase diagram of the reciprocal system was also calculated based on the thermodynamic modeling using the CALculation of PHAse Diagram (CALPHAD) method.

Effect of Coal Dust Content on the Low-temperature Oxidation of Silo Coal.

Coal’s low-temperature oxidation (LTO) poses a significant threat to the safety of storing coal in silos. This study investigates the impact of coal dust content on the LTO characteristics of silo coal samples. The results indicate that the larger the coal dust content the higher the oxygen (O2) consumption rate and carbon monoxide (CO) generation rate and the stronger the LTO capacity. To clear the mechanism of the impact, the thermal physical characteristics were studied and thermogravimetric and differential thermal analysis (TG-DTA) experiments were performed on various coal samples. The results show that, first, with the increase of coal dust content, the thermal conductivity of the silo coal samples initially increased and then decreased, whereas the thermal diffusion and heat capacity decreased and increased linearly, respectively. This indicates that the heat storage capacity of the silo coal sample is enhanced with the increase of the coal dust content. Second, the maximum oxygen absorption rate and differential thermal reduction value of the coal samples increased linearly with the decrease in their particle size; this result verifies that decreasing the particle size of silo coal can advance its LTO process. The study findings indicate that the risk of LTO and spontaneous combustion of silo coal can be effectively reduced by controlling the coal dust content (fine coal particles).

Investigations on the thermal response of a solid rocket motor with complex charge structure using CL-20/GAP propellant

The thermal safety of a solid rocket motor with a complex charge structure using CL-20 (Hexanitrohexaazaisowurtzitane)/GAP (Glycidyl Azide Polymer) propellant was evaluated. The morphology and thermal decomposition properties of the propellant were first studied by differential thermal analysis, thermogravimetric analysis and scanning electron microscopy experiments. A numerical model of cook-off for a solid rocket motor using GAP/CL-20 propellant was developed. This model takes into account the entire process of cooking off, i.e., the thermal decomposition before ignition and the combustion reaction after ignition. The model is verified, and the kinetic parameters are determined by bomb cook-off experiments. Comparisons between experiments and simulations show that the developed model can accurately predict the thermal response of the propellant. The cook-off processes of a 3D-solid rocket motor with complex charge structures are then simulated with different heating rates. It shows that the charge structure and the annular area of the motor casing play an import role in the ignition location of the propellant. Meanwhile, the heating rate has a dramatic effect on the ignition time. The reaction intensity after the ignition of the solid rocket motor using the GAP/CL-20 propellant is more intense than those using HTPE (hydroxyl-terminated polyether)/HTPB (Hydroxyl-terminated polybutadiene) propellant.

Study of Nanocrystallization Kinetics in Fe 73.5 Cu 1 Nb 3 Si 13.5 B 9 Finemet Type Alloy by Differential Thermal Analysis and Using Different Models

The study of the crystallization processes in the FINEMET type nanocrystalline amorphous alloy is interesting not only from the fundamental aspect of establishing reaction mechanism of crystal nucleation and growth, but also from a technological point of view. The process and nature of crystallization phase constitution of nanocrystalline amorphous alloy of composition Fe 73.5 Cu 1 Nb 3 Si 13.5 B 9 prepared by rapid quenching method is investigated in the present study. The amorphous nature of the alloy has been verified by x-ray diffraction (XRD). The differential thermal analysis (DTA) experiments were performed at different continuous heating rates of 10, 20, 30, 40 and 50 0 C/min. Two different crystalline phases are observed. The crystallization temperatures, the volume fraction of crystallizations and enthalpies of two different crystalline phases of the alloy have been determined from DTA traces. The dependence of on-set crystallization temperature (T x ) on the heating rate of different phases have been used for the determination of different crystallization parameters such as, the activation energy of crystallization, the order parameter or Avrami exponent (n). The results of crystallization were discussed on the basis of different models such as Kissinger’s approach and modification for non-isothermal crystallization of Matusita in addition to Kolmogorov, Johnson, Mehl, Avrami and Ozawa.

Architecture of a dinuclear Co(II) complex based on 3-amino-1,2,4-triazole-5-carboxylic acid: molecular structure, thermal behavior, optical properties, and DFT calculations

The dinuclear compound [Co2(Hatzc)2(H2O)6](NO3)2·4H2O containing the polytopic ligand Hatzc‒ = 3-amino-4H-1,2,4-triazole-5-carboxylate was synthesized and characterized. Single-crystal X-ray diffraction showed that two monoanionic N,O-chelating Hatzc‒ ligands bridge two Co(II) ions in a µ-N1,N2 fashion. Both Co(II) centers are further coordinated by three H2O ligands making up an octahedral coordination. A complex network of intra- and intermolecular O‒H···O and N‒H···O hydrogen bonding interactions characterize the structure. Hirshfeld surface analysis, ATR–FTIR, and FT-Raman spectroscopy in combination with density functional theory (DFT) calculation of vibrational modes confirm this multitude of H bonds. Thermogravimetric and differential thermal analysis experiments under an argon atmosphere in the temperature range of 25–900 °C showed thermal stability till about 100 °C and multi-step decomposition yielding Co2O3 at about 280 °C. The octahedral environment of Co(II) was confirmed by UV–vis absorption spectroscopy, which shows weak absorption bands at around 520 nm assignable to electronic d‒d transitions alongside with π‒π* transitions dominating the 250–350 nm range. Time-dependent DFT calculated excited states agree very well in terms of energy match with the observed transitions. The direct and indirect optical band gap values were determined using the Tauc plot method to 3.33 eV and 2.75 eV, respectively, indicating semiconducting properties.

Solidification curves for commercial Mg alloys obtained from heat-transfer modeled DTA experiments

AbstractAn improved method is presented for determination of solidification curves, i. e., solid fraction versus temperature, for commercial Mg alloys using heat-transfer modeled differential thermal analysis (DTA) curves. A better simulation of the measured DTA signal is attained through an independent measurement of the time constant as function of temperature for the applied equipment. This enables a better desmearing of the DTA signal. Challenging Mg alloys could be appropriately handled by redesigning the tantalum encapsulation. Due to high oxygen affinity and vapor pressure of the investigated magnesium alloys, this special adaptation of the DTA setup using sealed Ta capsules was indispensable for generation of reproducible and reliable data.

Production and characterization of non-leaching antimicrobial and hydrophilic polycaprolactone based nanofiber mats

Novel antimicrobial and hydrophilic nanofiber biomaterial was fabricated with a combination of surface modification and nanotechnology, in this study. For this purpose, firstly poly(lactic acid) (PLA) bearing quaternary ammonium salt as an antimicrobial agent on its backbone in the rates of 5% by mole were successfully fabricated with a combination of ring-opening copolymerization and copper(I)-catalysed azide-–alkyne cycloaddition click reaction in a two-step reaction procedure. Then, this synthesized polymer was blended into polycaprolactone (PCL) matrix in three different proportions via electrospining technique. The prepared nanofiber mats were then characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and contact angle analysis. In addition, thermal properties of mats were examined through differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) experiments. Its importance as an antimicrobial biomaterial was analyzed using Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) which were types of Gram-positive and Gram-negative bacteria, respectively. As a result, it was observed that as the rate of antimicrobial polymer in the nanofiber material increased, its antimicrobial activity against both bacteria also increased. As a result of the highest blending ratio of antimicrobial PLA copolymer, the bacterial population amount decreased by 99.5% and 92% for S. aureus and E. coli, respectively, as compared to neat PCL nanofiber mat. Besides, thermal properties of PCL nanofiber mats did not changed negatively after the blending process, even char yield increased slightly with increasing rate of antimicrobial PLA content. Also, the results showed that the blending of PCL nanofiber mat with antimicrobial PLA having quaternary ammonium salts on its backbone maked it highly hydrophilic.

Effect of Pouring and Mold Temperatures on Hot Tearing Susceptibility of WE43 Magnesium Alloy

The effects of different pouring temperature and mold temperature on the hot tearing susceptibility of WE43 magnesium alloy were studied using computer numerical simulation, hot tearing test and differential thermal analysis experiment. The microstructure of the hot tearing zone of the casting was observed using SEM, and the phase composition was analyzed using EDS. Numerical simulation results show that the change in pouring temperature and mold temperature could affect the hot tearing susceptibility (HTS) of WE43 alloy, and the influence of mold temperature was more significant with the conditions of pouring temperature (Tp) of 710–730 °C and mold temperature (Tm) of 240–320 °C. The experimental results are in good agreement with the simulation results. At the lower pouring temperature, the dendrite coherency began at a higher solids fraction, which could enhance the resistance to hot tearing at the end of solidification and reduce HTS of WE43 alloy. At the same pouring temperature, with the increase in the mold temperature, the number of dispersed eutectic phases in the alloy increased obviously, so that hot tearing could be well filled with the eutectic phase to reduce the HTS of WE43 alloy. In experimental conditions, the WE43 magnesium alloy had the lowest HTS at a pouring temperature of 710 °C and a mold temperature of 320 °C.

Hydrogen bonds induced polymorphism of pyrazoline derivative: Crystal structures, thermal and optical-physical properties

In this study, 1-acetyl-3-(3-hydroxyphenyl)-5-(9-anthracenyl)-2-pyrazoline (AHAP) was synthesized and afforded two types of polymorphs. Single crystal X-ray analyses revealed that AHAP molecules connect with each other in a head-to-tail fashion through O-H⋯O hydrogen bonds between the carbonyl and hydroxyl groups. However, through the above intermolecular interactions and stacking mode, the one-dimensional chain motifs are formed in the α polymorph and cyclic tetramers are formed in the β polymorph, which constitute their crystal structures as units. Compared with solvent-free α polymorph, the unit cell of the β polymorph includes a small region of disordered solvent molecules. CrystalExplorer program, Differential scanning calorimetry (DSC) and thermogravimetric thermal analysis (TGA) experiments revealed that the voids should be inside the tetramers and each void contains one disordered solvent molecule. 1H NMR spectra conformed the type of the disordered solvent molecule is consistent with the crystalline liquid phase. The optical-physical properties of the two polymorphs were also investigated. They emit similar fluorescence, which is assigned to monomer emission of anthracene, due to the monomer arrangement of anthracene fluorophores in the two polymorphs.

Effect of oxygen addition on the formation of isothermal ω phase in Ti-Fe alloys

The effect of the addition of oxygen on the formation of microstructure cooled from the β phase of Ti-Fe alloy was examined. The alloy ingots of Ti-(4, 5, 6, 7, 8, 9 and 10) at.% Fe and Ti-8 at.% Fe-(1 and 3) at.% O were arc-melted. They were homogenized at 1200 °C for 3.6 ks and then hot-rolled at 850 °C into 1.5-mm thick sheets. The disk specimen was fabricated and then put in the differential thermal analysis (DTA) apparatus. The disk in the DTA was heated at 1000 °C for 0.6 ks in the β phase and then cooled to room temperature at a rate of 50 °C/min. The microstructure was examined by an optical microscope after the DTA experiment. In the Ti-(7 and 8) Fe alloys the ω phase formed during cooling. The addition of oxygen in the Ti-8Fe alloy promoted the β→α transformation. Furthermore, the addition of one at.% oxygen in the Ti-8Fe alloy promoted β→ωi transformation, while the addition of three at.% oxygen suppressed the β→ωi transformation during cooling.

Synthesis, thermal, structural and electrical properties of vanadium-doped lithium-manganese-borate glass and nanocomposites

A glassy sample with a nominal formula LiMn1 − 3x/2VxBO3 (where x = 0.05) was synthesised using the melt-quenching method. Material was characterised by differential thermal analysis (DTA), X-ray diffactometry (XRD) at room temperature and as a function of temperature (HT-XRD), X-ray photoelectron spectroscopy (XPS), impedance spectroscopy (IS) and scanning electron microscopy (SEM). Dependences of glass transition and crystallisation temperatures on the heating rate in DTA experiments were determined. The initial value of electrical conductivity of the glass was 1.4 × 10− 15 Scm− 1. It was significantly increased by a proper thermal nanocrystallisation. The maximum value was higher by 6 orders of magnitude and reached 2.6 × 10− 9 Scm− 1 at room temperature. Expected crystalline phases (i.e. monoclinic and hexagonal LiMnBO3) upon heating were identified and assigned to thermal events observed with DTA. Microstructure of nanocrystalline samples observed by SEM revealed nanocrystalline grains noticeably smaller than 100 nm. Results explaining nanocrystallisation process are coherent.

Influence of the Base Element on the Thermal Properties of Non- Ferrous Chromium-Rich TaC-Containing Alloys Elaborated by Conventional Casting: Part 1: Thermodynamic Approach, Melting Ranges, as-Cast Microstructures and Thermal Expansion

After preliminary thermodynamic calculations for verifying their refractoriness, six (Ni,Co)-based alloys were synthesized by casting. They contain chromium, carbon and tantalum to achieve interesting chemical and mechanical high temperature properties. Their microstructures in the as-cast state were observed by electron microscopy (SEM) to discover the carbides characteristics. Differential thermal analysis (DTA) was carried out for all of them to assess their melting points notably, for having better knowledge about the level of high temperature at which they can be used potentially. Thereafter thermomechanical analyses (TMA) were run to explore their behaviour in thermal expansion. As shown by the thermodynamic calculations all the alloys are theoretically possible to be shaped by conventional foundry due to liquidus temperatures all below 1400°C. According to these same results, the solidus temperatures of all alloys would stay over 1250°C, this suggesting that all alloys would be able to be used under moderate mechanical stresses at temperatures as high as 1200°C. As suggested by calculations, the as-cast microstructures are all dendritic and the interdendritic spaces are occupied by carbides. According to calculations again, the Ni-richest alloys contain chromium carbides, but tantalum carbides are also present, a presence which was not expected. In contrast the Co-richest versions contain only TaC carbides. The DTA experiments show that the solidus and liquidus temperatures both increase by going from the Ni-richest alloys to the Co-richest ones. The TMA experiments demonstrate that the thermal expansions and thermal contractions are rather continuous, without any irregularities, and the average thermal expansion coefficients, all close to 20 × 10-6K-1, do not systematically depend on the respective proportions of nickel and cobalt. This first part of the whole work will be followed by two other parts dealing with the effect of these Ni and Co proportions on the high temperature oxidation phenomena, for temperature variations and for isothermal conditions respectively.

Syntheses and nanocrystallization of NaF–M2O3–P2O5 NASICON‐like phosphate glasses (M = V, Ti, Fe)

AbstractSix NASICON‐type phosphate glasses with a wide variety of compositions (Na3M2(PO4)2F3, where M2 = V2, Ti2, Fe2, TiV, FeV, and FeTi) were synthesized using melt‐quenching and double‐crucible techniques. Their glass transition and crystallization temperatures were determined from differential thermal analysis experiments. The electrical properties were studied with impedance spectroscopy. We found that depending on temperature and composition the studied materials exhibit predominant electronic, ionic, or mixed conduction. This observation is interesting from both fundamental and application point of view (eg, in all‐solid‐state batteries). In general, the conductivity of glasses ranged from 3·10−13 to 10−10 S/cm at room temperature, with activation energies varying from 0.65 to 0.73 eV. After crystallization at 600°C, the values of conductivity noticeably increased. For nanocrystalline materials, they were between 10−11 and 10−7 S/cm (at room temperature). The values of the activation energy spread from 0.53 to 0.70 eV. Most of the glasses exhibited predominant electronic conductivity. After nanocrystallization, the ionic transference number considerably increased in almost all samples. This study proves that thermal nanocrystallization can be used to synthesize nanocrystalline NASICON‐like cathode materials for Na‐ion batteries from their glassy analogs. We believe that this method can be adopted also to other interesting sodium compounds in the future.

TGA, DSC and DFT Studies of TKX‐50, ABTOX and Their Key Precursors

AbstractTKX‐50 (Dihydroxylammonium 5,5’‐bistetrazolate‐1,1’‐dioxide) and ABTOX (Diammonium salt of 5,5’‐bistetrazole‐1,1′‐diolate) being simple and cheap to prepare from commonly available chemicals, are emerging as promising energetic materials along with the advantages like required thermal insensitivity, low toxicity and safe handling. In order to synthesize such powerful materials with utmost care, it is essential to know about the precursors and reaction intermediates involved. Therefore, the detailed thermal analyses of various precursors such as glyoxime (I), dichloroglyoxime (II), diazidoglyoxime (III) and bistetrazoledihydroxide (IV) and final products viz., TKX‐50 (V) and ABTOX (VI) were carried out using differential scanning calorimetric and thermal gravimetric analysis experiments. The relative trend of band gap values calculated from the difference of HOMO and LUMO is well correlated with the decomposition temperatures (Tmax) values at a heating rate of 10 °C min−1 indicating the relative thermal stability of I–VI. The impact and friction sensitivity of ABTOX and TKX‐50 indicated that these compounds are safer than the currently known powerful explosives such as CL‐20. The calculated density impulse of TKX‐50 in rocket propellant formulations was found to be 499 g m−2 s−1 which is similar as that of HMX (494 g m−2 s−1). The theoretical performance prediction of TKX‐50 as the potential ingredient in gun propellant formulations indicated that the TKX‐50 could yield higher force constant (1471 J K−1) in comparison to currently known explosive such as RDX (1412 J K−1).

Some paradoxical observations about spheroidal graphite degeneracy

Differential thermal analysis experiments have been performed on samples machined from Y2-blocks cast with different high-silicon spheroidal graphite irons. Depending on magnesium, silicon, cerium and antimony content, the as-cast microstructure showed various levels of chunky graphite in the central part of the blocks. In contrast, the microstructure of the materials after remelting and resolidification during differential thermal analysis consisted of lamellar or compacted graphite. The formation of chunky graphite in the as-cast microstructure is rationalized using an index or silicon equivalent that has been recently suggested. The differences in the microstructures after differential thermal analysis are discussed in terms of available free magnesium. Emphasis is finally put on the striking differences in characteristic size of the microstructures made of compacted graphite as compared to lamellar graphite and chunky graphite. This leads to tentative conclusions about growth of compacted and chunky graphite which would be worthy of further experimental investigations.

Determination of liquidus temperatures in high-alloyed Fe–C–Mn–Si–Al steels using differential thermal analysis

The liquidus temperature of the Fe–C–Mn–Si–Al alloy was investigated by using an improved differential thermal analysis method, which effectively tackles down the manganese evaporation in the course of differential thermal analysis experiments for high-manganese twinning-induced plasticity (TWIP) steels at high temperature. It was found that the liquidus temperature is more strongly dependent on the silicon content than expected. By considering the high manganese content in the Fe–C–Mn–Si–Al TWIP steels, the effect of carbon content on the depression coefficient of manganese should not be ignored, which has considerable impact on the liquidus temperature. An equation was summarized to effectively predict the liquidus temperature for a wide range of high-manganese steels. Meanwhile, the prediction results of the equation are consistent with the experimental results, as well as those results acquired from ThermoCalc.