Thermal Stability Parameters Research Articles

Four three-dimensional metal–organic frameworks assembled from 1H-tetrazole: Synthesis, crystal structures and thermal properties

Four tetrazole-based energetic metal–organic frameworks (EMOFs), {[Zn5(Tz)9](NO3)·6H2O}n (1) [Zn(Tz)2]n (2) {[Cd5(Tz)9](NO3)·6H2O}n (3) and {[Mn5(Tz)9](NO3)·6H2O}n (4) (Tz = tetrazole) have been prepared by hydro/solvo thermal conditions using 1H-tetrazole and corresponding metal salts. X-ray single crystal diffraction analyses indicated that EMOFs 1, 2, 3 and 4 possess 3D porous structure. The metal ions in 1, 3, and 4 form an acs topology net with the six nitrogen atoms from μ3-Tz and μ4-Tz ligands. The Zn2+ ions in 2 form a diamond-like structure with four μ2-Tz ligands which was reported previously. The thermal stabilities were investigated by differential scanning calorimeter (DSC) and thermogravimety (TG). The results showed that four EMOFs exhibit high thermal stability (decomposition temperature up to 324.1 °C (1), 351.4 °C (2), 279.41 °C (3) and 332.75 °C (4), respectively). The thermal stability parameters (Te.0, Tb) were calculated. In addition, the standard molar enthalpies of formation (ΔfHmΘ) were calculated on the basis of the constant-volume combustion heat (ΔU) measured by using oxygen-bomb calorimetry. Lastly, the detonation performance (D, P) and mechanical sensitivity (IS, FS) of the four EMOFs were investigated.

Model for the analysis of thermal conductivity of composite material of natural origin

Thermal properties of the wall structure elements made from gel and straw (?Ethno-eco-passive houses?) have been investigated. The gel was made from a mixture of clay, lime, and water. A 1-D mathematical model based on the continuum mechanics, for predicting the thermal conductivity, is proposed. The results obtained by applying the proposed mathematical model were compared with the measurement data of experimental tests, using the Isomet 2114 instrument. The program envisages the measurement of thermal conductivity of three specimens, 5-year-old, comprising three series within 365 days. In the theoretical analysis, the same parameters of thermal stability were treated as in the experiment. The average value of the material thermal conductivity is 0.0990 W/mK, so it can be concluded that, the composite material intended for the envelope of the proposed constructive system ?Ethno-eco-passive house? is verified as thermally suitable.

Thermal Stability and Kinetic of Decomposition of Mono- and Dicationic Imidazolium-Based Ionic Liquids

Phase transitions, thermal stability, thermokinetics and activation parameters of degradation reaction of the dicationic ionic liquids (ILs), 1,n-bis(3-methylimidazolium-1-yl)alkane ([BisAlk(MIM)2][2Br]) and monocationic ILs, 1-(3-methylimidazolium-1-yl)alkane ([Alk(MIM)][Br]), where Alk = Dec, DoDec, TetDec, (decane, dodecane, tetradecane) were evaluated. The influence of an additional cationic head and the alkyl chain length in thermal parameters were also evaluated. The dicationic ILs are more stable than monocationic and thermal degradation of ILs mono- and dicationic did not show linear dependence on the alkyl chain length. Thermokinetic parameters indicated degradation in multiple steps. The monocationic ILs showed a more persistent crystalline phase than dicationic IL, which became totally amorphous after heating. The estimate temperature decomposition, activation energy and thermal transitions enable the determination of which types of ILs are applicable for specific purposes, such as lubricants or solvents at high temperatures, while maintaining ILs physical and chemical properties.

Adsorption and structural study of the chelating resin, 1,8-(3,6-dithiaoctyl)-4-polyvinyl benzenesulphonate (dpvbs) performance towards aqueous Hg(II)

The characterized 1,8-(3,6-dithiaoctyl)-4-polyvinyl benzenesulphonate (dpvbs) resin was used as an effective sorbent for aqueous Hg removal. The adsorbed Hg on dpvbs at the optimum conditions and the synthesized Hg-dpvbs complex were characterized utilizing EDS, XPS, BET and FT-IR. The spectral data for both samples are identical showing that Hg(II) is bonded to dpvbs through sulfur and oxygen atoms. The XPS data indicated that Hg is adsorbed as Hg((NO)3)2.The surface morphology of dpvbs before and after sorption processes was studied utilizing SEM and AFM. The thermal stability and thermodynamic parameters were estimated showing an endothermic behavior with less order transition state. Batch adsorption tests were conducted to identify the optimum conditions at which dpvbs have the highest mercury capacity. The resin has the maximum capacity of 435.13 mg g−1 resin (98.95%) and distribution coefficient of 249.36. The adsorption kinetic data fitted best with the pseudo-second-order model. Upon studying the Langmuir, Freundlich, Temkin and Dubinin–Radushkevich isotherm models, the equilibrium data fitted well with Freundlich isotherm. Relying on the value of ED–R, the mechanism of adsorption process is proposed as physisorption. The modified resin was applied for the removal of metal ions from marine water, utilizing column system and showed high sorption capacity.

Crystallization kinetics of the Fe40Ni40P14B6 metallic glass in an extended range of heating rates

The effect of heating rate (in the range of 0.083–3.333 K s−1) on the parameters of thermal stability and crystallization kinetics of the Fe40Ni40P14B6 metallic glass has been investigated by differential scanning calorimetry and X-ray diffraction. An analytical model of glass crystallization describing the homogeneous nucleation rate, the velocity of interface-limited growth, the number of crystal volume density in crystallized samples as well as the crystallization kinetics at constant rate heating is presented. A modified procedure of estimation of thermodynamic and kinetic parameters governing the rate of crystal nucleation and growth based on the use of the measured heating rate-dependent variations of the volume fraction crystallized and the average grain size is proposed. The values of the effective diffusivity have been estimated by the Kissinger-like isoconversional method accounting the contribution of both the free energy difference and the specific interfacial nucleus-melt energy changes estimated from the structural data. It has been shown for the first time that the shapes of the non-isothermal experimental kinetic crystallization curves measured at the heating rates ≤ 1.333 K s−1 are well described by the approximate analytical equation and the values of the Avrami exponent lowering from 5.5 to 2.3 with the heating rates increasing have been estimated. The evaluated ranges of the nucleation rate (1.4 × 1016–2.5 × 1017 m−3 s−1) and growth velocity of crystals (2.05 × 10−9–3.0 × 10−7 m s−1) in Fe40Ni40P14B6 glass at temperatures from 653 to 714 K are in reasonable agreement with the experimental data. Possible variations of the established eutectic crystallization mechanism revealed by changes of the Avrami exponent with the heating rate increasing are discussed.

A new coordination compound based on 4-amino-3-(tetrazol-5-yl)-furazan (HAFT): preparation, crystal structure, and thermal properties

The green nitrogen-rich coordination compound Cd(SCZ)2(AFT)2 (1) (AFT =4-amino-3-(5-tetrazolate)-furazan and SCZ = semicarbazide) was first synthesized and characterized by EA and Fourier Transform Infrared (FT-IR). The single crystal was cultivated and determined with X-ray diffraction. It revealed that 1 crystallizes in the monoclinic space group P21/c. A Cd2+ ion is coordinated by four N atoms and two O atoms to form a distorted octahedral structure. Among them, two nitrogen atoms are from the two AFT ions and the other four atoms are from two SCZ molecules. The thermal decomposition behavior of 1 was studied with DSC and TG-DTG methods. The apparent activation energy (E), thermal stability, and safety parameters (TSADT, TTIT, and Tb) were calculated for 1. Moreover, entropy of activation (ΔS≠), enthalpy of activation (ΔH≠), free energy of activation (ΔG≠), specific heat capacity (Cp), and impact sensitivity were also discussed in detail.

Size effect of carbon black on the structure and mechanical properties of magnetorheological elastomers

Four types of carbon black (CBN330, CBN550, CBN660 and CBN990) with increased particle size were chosen as the reinforcing filler for magnetorheological elastomers (MREs) preparation. The size effect of CB on the structural and mechanical property of MREs was investigated experimentally. Fourier transform infrared spectroscopy was adopted to characterize the structure of CB and MREs. Mooney viscosity, vulcanization curve, thermogravimetric analysis and mechanical property test were conducted to obtain the processing and vulcanization characteristics, thermal stability and mechanical parameters of MREs. It showed that MRE-CBN660 possessed a relatively better overall performance. Furthermore, the mechanical model of MREs and adsorption property of CB on carbonyl iron were studied theoretically. The theoretical results were coincidence with the experimental results, which interpreted the size effect of CB essentially.

Relation between switching time distribution and damping constant in magnetic nanostructure

It is widely known that the switching time is determined by the thermal stability parameters and external perturbations such as magnetic field and/or spin polarized current in magnetic nano-structures. Since the thermal stability parameter and switching time are crucial values in the design of spin-transfer torque magnetic random access memory, the measurement of the switching time is important in the study of the switching behavior of ferromagnetic nano-structures. In this study, we focus on the distribution of the switching time. Within the limit of a large energy barrier, a simple analytical expression between damping constant and anisotropy field with switching time distribution is obtained and confirmed by numerically solving the Fokker-Planck equation. We show that the damping constant and anisotropy field can be extracted by measuring the full width half maximum of the switching time distribution in the magnetic nano-structure devices. Furthermore, the present method can be applied to not only single nano-structure, but also inhomogeneous nano-structure arrays.

Thermal hazard analysis and thermokinetic calculation of 1,3-dimethylimidazolium nitrate via TG and VSP2

In this study, the thermal stability and thermokinetic parameters of 1,3-dimethylimidazolium nitrate ([Mmim]NO3) were investigated by thermogravimetric analysis under non-isothermal conditions in a nitrogen atmosphere. The results showed that [Mmim]NO3 exhibited three decomposition stages from 93.3 to 350.0 °C, and the onset temperature of [Mmim]NO3 was obtained at approximately 161.0–182.0 °C under five heating rates. The apparent activation energy was 119.0–124.0 kJ mol−1, as calculated by different well-known equations, and the pre-exponential factor was 3.6 × 1012 min−1. The reaction mechanism of [Mmim]NO3 was carried out with the reaction order n = 1.0, and the decomposition mechanism function was further obtained. Moreover, vent sizing package 2 was employed to acquire the maximum self-heating rate (39,828.0 °C min−1) and pressure rise rate (73,331.0 psig min−1) for simulating cooling system failure in a practical process. The findings indicated that [Mmim]NO3 showed the possibility of a runaway reaction, leading to a potential thermal hazard. The approach of these results is vital for obtaining inherently safer process information for [Mmim]NO3 during production, storage, and transportation.

Structure property relationship in (TiZrNbCu)1−xNix metallic glasses

Abstract

Preparation and characterization of RDX/BAMO-THF energetic nanocomposites

ABSTRACTNovel 1,3,5-trinitro-1,3,5-triazine/3,3-bis (azidomethyl) oxetane-tetrahydrofuran copolymer (RDX/BAMO-THF) energetic nanocomposites were successfully prepared by a facile sol–gel freezing–drying method. The as-prepared RDX/BAMO-THF energetic nanocomposites were characterized by Raman and Fourier transform infrared spectroscopy, which revealed that RDX particles were incorporated into BAMO-THF gel matrix. Scanning electron microscopy was used to characterize the morphology and the particle size of the as-obtained samples. The results showed that RDX particles were trapped in the BAMO-THF gel matrix and the particle sizes were in nanoscale. Differential thermal analyzer (DTA) was performed to determine the thermal decomposition behaviors of BAMO-THF, raw RDX and RDX/BAMO-THF nanocomposites. The results indicated that the thermal decomposition process of RDX/BAMO-THF nanocomposites was enhanced compared with that of BAMO-THF and RDX. The kinetic, thermodynamic and thermal stability parameters were calculated according to DTA analysis. The calculated results revealed that RDX/BAMO-THF nanocomposites presented high thermal reactivity. The results of impact sensitivities for RDX/BAMO-THF nanocomposites indicated the sensitivity was effectively reduced compared to raw RDX.

Lactase (β-galactosidase) immobilization by complex formation: Impact of biopolymers on enzyme activity

In this study, a novel way to immobilize the enzyme β-galactosidase (Kluyveromyces lactis) through complexation with polysaccharides (sodium alginate (ALG) or Ɩ-carrageenan (CA)) was described. The kinetic parameters of the formation of the complexes and the immobilization efficiency of the enzyme as a function of pH and ratio of biopolymers were studied. The temperature profile, thermal stability, and kinetic parameters of the immobilized and free lactase were also analyzed. At pH 4.0, the results for the zeta potential associated with complex yield showed that the highest complex yield (97.14% ± 2.14) was reached for LAC/ALG at a 5:1 ratio, whereas the highest complex yield (95.26% ± 2.44) was reached an 8:1 ratio for LAC/CA. The process of complexation decreased the activity retained by the enzyme after dissociation. However, this decrease was less substantial for the LAC/ALG (83.2 ± 3.7%) complex than for LAC/CA (69.4 ± 7.6%) complex. The Michaelis–Menten constant (Km) increased from 2.91 mM (native enzyme) to 3.43 mM (LAC/ALG complex) and 4.15 (LAC/CA complex), while the apparent turnover number (Kcat) and the specificity constant (Kcat/Km) of both systems were not significantly different. The immobilization of the enzyme by complexation did not increase its thermal stability. However, the activity of the complexed lactase remained higher than that of native enzyme when exposed to low pH (pH 4.0) after 200 and 250 min for the LAC/ALG and LAC/CA complexes respectively. Our findings suggest that complexation can be a useful method for the immobilization of β-galactosidase.

Molecular dynamic simulation of melting copper-silicon nanoparticles

The research defines parameters of thermal stability of core-shell copper-silicon composite nanoparticles of different sizes and structures by means of molecular-dynamic calculations. The researchers found temperature points of the sudden change of the potential energy for the particles under study. Such changes are shown to be associated with the nanocomposite structure break. It was determined that the temperature rise initiates the copper atoms diffusion to the surface, which causes the reversing structure of the particle.

Biocatalytic action of proteases in ionic liquids: Improvements on their enzymatic activity, thermal stability and kinetic parameters

This study evaluated the effect of the addition of the following ionic liquids (IL): choline chloride (CC), tetramethylammonium bromide (TB) and 1‑ethyl‑3‑methylimidazolium bromide (EM), on some biochemical properties including enzymatic activity and different kinetic parameters of commercial proteases. The enzyme-IL combinations that showed the highest increases in enzyme activities were as follows: CC (0.5mM) and Neutrase® 0.8L; CC (5mM) and Flavourzyme® 500L; TB (2000mM) and Alcalase® 2.4L, with relative increases of 20, 15 and 150% in protease activities, respectively, compared to the control assays. The combination TB and Alcalase® 2.4L showed a reduction of 50% of the activation energy (Ea), an increase of the relation Vmax/Km of 35% and a 16-fold rise in the values of t1/2, and D. Neutrase® 0.8L combined with CC showed an increase of 20% in the relation Vmax/Km. The combination Flavourzyme® 500L and CC presented a 20% higher value of the relation Vmax/Km and a 2-fold increase in the values of t1/2 and D compared to the control assay. In summary, the most positive effects observed in this study included proteases with improved activity and stability properties and a greater affinity for the substrate.

Preparation, characterization and microwave absorption properties of porous nickel ferrite hollow nanospheres/helical carbon nanotubes/polypyrrole nanowires composites

Porous nickel ferrite hollow nanospheres/helical carbon nanotubes/polypyrrole nanowires (PNFHSs/HCNTs/PNWs) composites were successfully fabricated by in situ chemical oxidative polymerization method of PNWs with PNFHSs and HCNTs. The phase structure, chemical state, morphology, thermal stability and electromagnetic parameters of samples were analyzed and characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscope, transmission electron microscope, thermogravimetric analysis and vector network analyzer. The possible mechanism of microwave absorption of composites and the influence of the matching thickness on microwave attenuation is also discussed. The results indicate that at the thickness of 2.1 mm, PNFHSs/HCNTs/PNWs composites exhibit strong microwave absorption capacity (RL = − 33.94 dB at 11.39 GHz) and the effective absorption bandwidth is 3.22 GHz (9.18–12.4 GHz).

Secreted protein extract analyses present the plant pathogen Alternaria alternata as a suitable industrial enzyme toolbox

Lignocellulosic plant biomass is the most abundant carbon source in the planet, which makes it a potential substrate for biorefinery. It consists of polysaccharides and other molecules with applications in pharmaceutical, food and feed, cosmetics, paper and textile industries. The exploitation of these resources requires the hydrolysis of the plant cell wall, which is a complex process. Aiming to discover novel fungal natural isolates with lignocellulolytic capacities, a screening for feruloyl esterase activity was performed in samples taken from different metal surfaces. An extracellular enzyme extract from the most promising candidate, the natural isolate Alternaria alternata PDA1, was analyzed. The feruloyl esterase activity of the enzyme extract was characterized, determining the pH and temperature optima (pH 5.0 and 55–60 °C, respectively), thermal stability and kinetic parameters, among others. Proteomic analyses derived from two-dimensional gels allowed the identification and classification of 97 protein spots from the extracellular proteome. Most of the identified proteins belonged to the carbohydrates metabolism group, particularly plant cell wall degradation. Enzymatic activities of the identified proteins (β-glucosidase, cellobiohydrolase, endoglucanase, β-xylosidase and xylanase) of the extract were also measured. These findings confirm A. alternata PDA1 as a promising lignocellulolytic enzyme producer. SignificanceAlthough plant biomass is an abundant material that can be potentially utilized by several industries, the effective hydrolysis of the recalcitrant plant cell wall is not a straightforward process. As this hydrolysis occurs in nature relying almost solely on microbial enzymatic systems, it is reasonable to infer that further studies on lignocellulolytic enzymes will discover new sustainable industrial solutions. The results included in this paper provide a promising fungal candidate for biotechnological processes to obtain added value from plant byproducts and analogous substrates. Moreover, the proteomic analysis of the secretome of a natural isolate of Alternaria sp. grown in the presence of one of the most used vegetal substrates on the biofuels industry (sugar beet pulp) sheds light on the extracellular enzymatic machinery of this fungal plant pathogen, and can be potentially applied to developing new industrial enzymatic tools. This work is, to our knowledge, the first to analyze in depth the secreted enzyme extract of the plant pathogen Alternaria when grown on a lignocellulosic substrate, identifying its proteins by means of MALDI-TOF/TOF mass spectrometry and characterizing its feruloyl esterase, cellulase and xylanolytic activities.

Effect of replacement of selenium by indium on the thermal stability and crystallization kinetics of quaternary Se90−x–Zn5–Te5–Inx glassy alloys

This paper reports the effect of replacement of selenium by indium on the thermal stability and crystallization kinetics of Se90−x–Zn5–Te5–Inx (x = 0, 2, 4, 6, 8, 10) glassy alloys. Assessment of the thermal stability of these glassy alloys was achieved using various simple quantitative methods based on the characteristic temperatures of DSC curves. In this case, kgl may be more suitable for estimating the glass thermal stability in the above composition range. The kinetic parameter Kr (T) is added to the stability criteria. The results of all thermal stability parameters confirm that the thermal stability increases with increasing indium at expense of selenium in Se90−x–Zn5–Te5–Inx glassy alloys. These results have been discussed in terms of cohesive energy and average heat of atomization. Finally, according to the average values of Avrami indices, $$\left\langle n \right\rangle$$ = 2 for the crystallization peaks means volume nucleation and two-dimensional growth for all the compositions.

Computer Modeling of the Formation Process of Core-Shell Nanoparticles Cu@Si

The process of nanoparticle Cu@Si formation by the molecular dynamic method using MEAM-potentials was studied. Modeling the droplet behavior demonstrates that a core-shell structure with a copper core and a silicon shell can be formed if the drop is in the liquid state, until the material is finally redistributed. The parameters of thermal stability of Cu@Si composite nanoparticles of different sizes have been determined. It is concluded that as the temperature increases, the diffusion of copper atoms to the surface begins, which leads to a change in the structure and the formation of particles with a core of the Cu@Si type.

Studies on Se75Te25–xInx chalcogenide glasses; a material for phase change memory

This research paper describes the non-isothermal crystallization during phase transformation in Se75Te25–xInx glasses synthesized by melt quenching method. For crystallization studies in these glasses, non-isothermal differential scanning calorimetry (DSC) measurements was done at constant heating rates of 5, 10, 15, 20 and 25 K min−1 in air atmosphere. The glass transition temperature (Tg), on-set crystallization temperature (Tc), peak crystallization temperature (Tp) and melting temperatures (Tm) were derived by DSC thermograms. Using various thermal parameters the activation energy of glass transition and crystallization were determined by using Kissinger, Moynihan and Ozawa approaches and found to be in good agreement. The value of the activation energy of glass transition (ΔEt) was found to be minimum for Se75Te19In6 alloys confirming its maximum probability of transition in a metastable state. Thermal stability parameters of Se75Te25–xInx were determined and found to be increased with indium content. High resolution x-ray diffraction and field emission scanning electron microscopy studies were employed for the study of phase transformation in Se75Te25–xInx glasses. The outcome of these studies shows that the investigated materials may be suitable for phase change memory devices.

Synthesis, characterization, thermal properties and theoretical investigation on Bis(guanidinium) 4,4′- Azo-1H-1,2,4-triazol-5-one

Bis(guanidinium) 4,4′-Azo-1H-1,2,4-triazol-5-one [G2(ZTO)] was synthesized and characterized by X-ray single crystal diffraction, elemental analyzer and Fourier Transform Infrared (FT-IR) spectrometer. The result from X-ray single crystal diffraction indicates that G2(ZTO) crystallizes in the monoclinic space group P2(1)/c with parameters of a = 4.779(2) Å, b = 9.081(4) Å, c = 14.676(6) Å, α = 90.00°, β = 92.43(7)°, γ = 90.00°, V = 636.4(5) Å3, Z = 2, μ(Mo Kα) = 0.131, F(000) = 328, S = 1.071, Dc = 1.640 g·cm−3, R1 = 0.0510 and wR2 = 0.1389. Interestingly enough, its structure does not contain crystallization water, which is a unique characteristic in this material. Besides, the molecular geometry of the compound was optimized by using Density Functional Theory (DFT) method at B3LYP/6-31G (d, p) level in the ground state, revealing that the obtained geometric parameters are in accordance with the X-ray result of the structure. The experimental vibrational spectrum was compared with the calculated spectrum. Besides, molecular electrostatic potential (MEP) of G2(ZTO) was computed with the same method in gas phase, theoretically. The thermal properties of this compound were investigated by DSC, TG/DTG and micro-DSC methods. The results manifest that its thermal behavior can be divided into two main decomposition stages, the first intense decomposition peak temperature is 248.11 °C at the heating rate of 10 °C·min−1, which is higher than that of RDX (219 °C) but slightly lower than that of G(ZTO)·H2O (252.08 °C). The constant-volume combustion heat (ΔcU) of G2(ZTO), G(ZTO)·H2O and ZTO were determined and then the enthalpy of formation were calculated. The results show that G2(ZTO) possesses the highest standard molar enthalpy of formation, which may be explained by the fact that G2(ZTO) contains no water and possesses the highest nitrogen content in all guanidine salts. Moreover, the apparent activation energy (E), thermal stability and safety parameters (TSADT, TTIT, Tb) were also calculated. Besides, the calculated thermodynamic functions (ΔS≠, ΔH≠ and ΔG≠) for the main exothermic decomposition process of the title compound are 47.25 J·mol−1·K−1, 169.20 kJ·mol−1 and 144.24 kJ·mol−1, respectively.