Isothermal Annealing Research Articles

Thermal Gradient Infrared Spectroscopy for Diffusion in Polymers.

Time-resolved Fourier transform infrared-attenuated total reflectance spectroscopy (FTIR-ATR) was used to measure diffusion in opaque and translucent samples. FTIR-ATR was used to measure the change in the absorbance near the heated ATR crystal surface. The infrared absorbance was then related to the concentration through the Beer-Lambert law. The sample used is a polymer electrolyte composed of lithium bis-trifluoromethanesulfonylimide (LiTFSI) salt in a block copolymer polystyrene-poly(ethylene oxide) (SEO). A new approach to introduce concentration gradients is presented using a temperature gradient that creates a small salt concentration gradient due to thermally driven mass diffusion (the Soret effect). This first method was compared to a second method that we reported using two laminated polymer electrolyte films of different salt concentrations. The thermal gradient study (method 1) covered three temperature differences of 10, 15, and 20 °C, while the second study (method 2) used three average molar ratios across isothermal temperatures ranging from 80 to 120 °C. The benefits and limitations of the new approach are reported, as is the activation energy for salt diffusion in this and similar SEO electrolytes. Developing new techniques to measure diffusion coefficients effectively will aid in the development of a variety of devices, including solid-state batteries and thermogalvanic cells, that are able to convert waste heat into electricity and improve the efficiency of power-generating systems. FTIR-ATR overcomes previous limitations in experimental techniques measuring diffusion coefficients. The results prove that thermal gradient FTIR-ATR is an effective and repeatable approach for determining Fickian diffusion coefficients in viscoelastic solids.

Effect of high temperature annealing on the microstructure evolution and hardness behavior of the Inconel 625 superalloy additively manufactured by laser powder bed fusion

Additive manufacturing of Inconel 625 components attracts great interest due to its ability to produce parts with complex geometries that are needed for high-temperature applications in the aerospace, energy, automotive and chemical industries. To take full advantage of the potential of additive manufacturing, an in-depth understanding of the effects of prolonged high-temperature annealing on microstructure and hardness evolution is needed. Previous research in this field has mainly focused on a limited range of temperature and time. This study aims to determine the effect of prolonged high-temperature annealing on the evolution of intermetallic phases and carbides, as well as changes in the dislocation substructure of Inconel 625 superalloy additively manufactured by laser powder bed fusion subjected to stress relief annealing and subsequent isothermal annealing at a temperature up to 800 °C for 5–500 h. The microstructure development is correlated with hardness behaviour. It is determined that the microstructure evolution proceeds in four stages with temperature and time increase. In the initial stress-relieved condition, a cellular microstructure with nano-sized precipitates of the Laves phase and NbC carbides at the cell walls occurs, and hardness is equal to 300 HV10. In the 1st stage of the microstructure evolution, the γ'' phase particles precipitate on the cell walls, which results in hardening up to 383 HV10 in the specimen annealed at 700 °C for 5 h. The 2nd stage involves the precipitation of the γ'' phase both on the cell walls and inside the cells, as well as the formation of dislocation networks, which contribute to the softening effect and hardness drop to 319 HV10. In the 3rd stage, at temperature 700 and 800 °C, the δ phase, M23C6 carbides, and the Laves phase precipitate and grow, and the subgrain boundaries are formed. The hardness is in the range of 340–350 HV10 and is higher than in the 2nd stage. In the 4th stage, as the annealing time is increased at a temperature of 800 °C, the δ phase and M23C6 carbides coagulate, and the Laves phase particles spheroidize or partially dissolve. Very intense precipitation and growth of the hard δ phase particles provide an increase in hardness to 402 HV10. As a result of systematic studies, the various strengthening and softening mechanisms acting during high-temperature annealing are determined.Graphical abstract

Phase transformation kinetics in a coarse-grain Ti17 alloy determined by laser ultrasonics and dilatometry

Different methods are used to determine the phase transformation titanium alloys. While ex-situ methods require a large number of samples and accurate quantification of the phases, in-situ methods can provide the kinetics of transformation continuously and with less samples. However, the results are based on the changes of physical properties, and the interpretation of the results in terms of phase transformation are not direct. This study compares two in-situ methods to measure the kinetics of phase transformation for a Ti17 alloy, namely: laser ultrasonics for metallurgy (LUMet) and dilatometry. While LUMet is coupled to a Gleeble® 3500 thermo-mechanical simulator with ohmic resistance heating, the dilatometer device uses induction heating. We performed two types of experiments by heating the specimens above the β-transus temperature (∼ 865 °C) and 1) and then fast cooled below the β-transus temperature and held at different temperatures, or 2) continuously cooled at different rates. The β→α + β phase transformation is inferred by the evolution of the longitudinal wave speed with the LUMet method and by the change in the length of the specimen by dilatometry. We obtained the information about the isothermal phase transformation using the normalized changes in length for the dilatometric data and in longitudinal ultrasonic velocity. In the investigated isothermal temperature range (580 – 700 °C), the β →α + β transformation is completed within one hour of holding with the fastest transformation rates at 580 °C. For the continuous cooling treatments, the small change in length measured by dilatometry makes it impractical to use the lever rule to accurately determine the relative transformation fraction. However, we could successfully apply the lever rule to the LUMet data. Furthermore, the derivatives of the change in length and ultrasonic velocity are used to estimate the transformation temperatures as a function of the cooling rates. Further, the in-situ measurements are supplemented with ex-situ characterization of the microconstituents after heat treatments using scanning electron microscopy.

Effect of Centrifugal Force of Gas Film on the Load Capacity of Thrust Gas Bearing

Abstract A modified Reynolds equation including centrifugal force of gas film was derived, and it was used to study the effect of gas film centrifugal force and associated streamline on the load capacity of both rigid and foil thrust bearings operating in hydrodynamic and hybrid modes. The thrust bearings have six pads with an outer diameter of 82 mm and an inner diameter of 47 mm with typical aper-flat geometry. The setup for the simulations is a single-acting air thrust bearing operating at various ambient pressures and isothermal temperature. Air was chosen for the gas film for the investigations, but the modified Reynolds equation can handle any general gas films through nondimensional parameter governing the centrifugal force. The simulations were performed with varying ambient pressure from 1 to 9 bar. The simulation results at different ambient pressures and temperatures are presented in forms of pressure profiles, streamlines, and bearing's load capacity. The bearings' load capacity becomes worse when the centrifugal force is considered at very low temperature, and the reduction of the load capacity grows more noticeable with the increase of the ambient pressure and the decrease of the ambient temperature. However, at higher temperature where centrifugal force is not large enough to create large leakage, the centrifugal force helps to redistribute the streamline to favorable way to increase the load capacity.

Pyrolysis and Combustion Characteristics of Two Russian Facemasks: Kinetic Analysis, Gaseous Emissions, and Pyrolysis By-Products

Pyrolysis and combustion experiments were performed on two facemasks (hereafter named Tissue and Surgical) commonly used in the Russian Federation, first in a thermobalance and under four low-temperature ramps (5, 10, 15, and 20 °C/min). The pyrolysis mass rate curves present a unique devolatilization peak. The combustion mass rate curves present a unique devolatilization peak followed by a shoulder or a small further peak on its right-hand side. Both processes mainly occur between 200 and 500 °C. Simulations of these pyrolysis and combustion processes are performed with good agreement using the extended independent parallel reaction (EIPR) model. The gas chromatography technique was used to analyze the by-products of pyrolysis experiments performed under isothermal temperatures of 300, 400, and 500 °C. Combustion experiments were finally performed in a horizontal oven under a temperature ramp approximately equal to 5 °C/min to measure the main gaseous emissions: CO2 emissions are the main emissions of the Tissue mask, while total hydrocarbons are the main emissions of the Surgical mask. Significant differences are observed between the results obtained for the two masks because of the fibers they are built with (natural or synthetic).

CRISPR-Cas12a test strip (CRISPR/CAST) package: In-situ detection of Brucella from infected livestock

BackgroundBrucellosis is a common zoonotic disease caused by Brucella, which causes enormous economic losses and public burden to epidemic areas. Early and precise diagnosis and timely culling of infected animals are crucial to prevent the infection and spread of Brucella. In recent years, RNA-guided CRISPR/Cas12a(Clustered Regularly Interspaced Short Palindromic Repeats and its associated protein 12a) nucleases have shown great promise in nucleic acid detection. This research aims to develop a CRISPR/CAST (CRISPR/Cas12a Test strip) package that can rapidly detect Brucella nucleic acid during on-site screening, especially on remote family pastures. The CRISPR/Cas12a system combined with recombinase polymerase amplification (RPA), and lateral flow read-out.ResultsWe selected the conserved gene bp26, which commonly used in Brucella infection detection and compared on Genbank with other Brucella species. The genomes of Brucella abortus 2308, Brucella suis S2, Brucella melitansis 16 M, and Brucella suis 1330, et al. were aligned, and the sequences were found to be consistent. Therefore, the experiments were only performed on B. melitensis. With the CRISPR/CAST package, the assay of Brucella nucleic acid can be completed within 30 min under isothermal temperature conditions, with a sensitivity of 10 copies/μl. Additionally, no antigen cross-reaction was observed against Yersinia enterocolitica O:9, Escherichia coli O157, Salmonella enterica serovar Urbana O:30, and Francisella tularensis. The serum samples of 398 sheep and 100 cattle were tested by the CRISPR/CAST package, of which 31 sheep and 8 cattle were Brucella DNA positive. The detection rate was consistent with the qPCR results and higher than that of the Rose Bengal Test (RBT, 19 sheep and 5 cattle were serum positive).ConclusionsThe CRISPR/CAST package can accurately detect Brucella DNA in infected livestock within 30 min and exhibits several advantages, including simplicity, speed, high sensitivity, and strong specificity with no window period. In addition, no expensive equipment, standard laboratory, or professional operators are needed for the package. It is an effective tool for screening in the field and obtaining early, rapid diagnoses of Brucella infection. The package is an efficient tool for preventing and controlling epidemics.

MODIFIED STEFAN CONDITION IN STEFAN PROBLEM

The two-phase one-dimensional Stefan problem (SP) with the boundary between the phases moving with time is considered. The position of the boundary is determined by the modified Stefan condition (MSC), which is obtained from the original nonlinear diffusion equation by integrating over a thin transition layer, and by tending its thickness to zero. Upon receipt of the MSC, the diffusion coefficient is represented by the sum of the Heaviside step functions. It is shown that the MSC differs from the standard one in that in the latter, the derivatives of the concentrations with respect to the phase coordinates are interchanged. An expression for the displacement of the interphase boundary is obtained, which, as in the standard SP, is proportional to the square root of time. The results of using the MSC are confirmed by experimental data on the displacement of the Cu/Sn interface during diffusion bonding during isothermal annealing.

In-situ characterization method for the delta phase precipitation kinetics in the nickel-base alloy 718 using high-temperature X-ray diffraction (HT-XRD) techniques

An innovative characterization approach for determining the precipitation evolution of the delta phase in nickel-base alloy 718 during thermal processing has been developed, where the phase fraction of the evolving delta phase was determined in-situ by high-temperature X-ray diffraction technique (HT-XRD). This method is based on the evaluation of the peak shift corresponding to the matrix phase, which is independent from effects of texture and peak overlap. The evaluation can be performed without the need of complex Rietveld refinement procedures.Isothermal annealing experiments have been performed in the temperature range between 850 °C and 950 °C for annealing times up to 30 h. The delta phase fraction was evaluated indirectly by quantification of the shift of the diffraction angle of a distinct matrix phase peak (200) which exhibits a strong correlation with the evolving delta phase fraction during isothermal annealing. A nomogram could be constructed from the results which shows the relation between the delta phase fraction and the shift of the diffraction angle of distinct matrix phase peaks. Data deduced by conventional determination from the intensity of diffraction peaks of the delta phase were recorded for comparison. Thus, the application of the Rietveld method for textured materials is not necessary. Finally, experimental results obtained by metallography were used to validate the innovative indirect characterization approach.

Fast reactive interdiffusion between solid brass and liquid aluminium

The formation mechanisms of intermetallic layers and the development of the interface between solid brass and molten Al alloy were experimentally investigated using semi-infinite solid-liquid diffusion couples. Isothermal annealing of commercial CuZn37 – AA7075 diffusion couples was conducted for the selected temperatures of 650 °C, 660 °C, 680 °C and 700 °C, for three annealing times of 10 s, 20 s and 40 s, followed by quenching. Regardless of the temperature, the interface consisted of three intermetallic layers that are reaction products as defined in the Al–Cu–Zn phase diagram. In order to explain the growth behaviour and bring insights into the interface formation mechanisms, the thermodynamics of the Al–Cu–Zn was investigated by CALPHAD (calculation of phase diagrams). Based on these ex-situ results, three distinct phenomena were observed. First, intermetallic layers dissolve simultaneously into the molten Al alloy when the annealing time exceeds 40 s. Second, parts of the intermetallic layer that are in contact with the molten Al, detach from the interface region in the direction of molten Al alloy leading to a decrease in the layer thickness and deviation from planar-like geometry. Third, the formation of the three intermetallic layers is exclusively the result of solid-liquid interactions followed by quenching. Previous studies have shown a scattered interface character between solid brass and molten aluminium which results from interactions in the solid-solid state due to low cooling rates. As a result, the concept of primary intermetallic layers was introduced to describe the interface formation upon the contact of solid brass with molten aluminium alloy.

Natural convection of nanofluid flow in a porous medium in a right-angle trapezoidal enclosure: a Tiwari and Das’ nanofluid model

The study uses Tiwari and Das’ nanofluid model to present a study on free convective flows in a right-angled trapezoidal cavity that is saturated with a porous bed and filled with Cu-water nanofluid material. This investigation aims to enhance the characteristics of hybrid fuel cells and energy depository devices by analysing the cavity's heat expansion and fluid flow properties. In trapezoidal enclosures, the inclined and right wall portions are maintained at different isothermal temperatures at all times. Finite difference-based stream function-vorticity numerical simulations are employed to carry out this analysis. The outcomes have been presented for isotherms, streamlines, and Nusselt numbers concerning nanoparticle volume fraction, Darcy number, and various Rayleigh numbers. It is found that the inverse relationship between the thermal Rayleigh number and the nanofluid’s volume has a significant impact on the average Nusselt number.

Growth and stability of epitaxial zirconium diboride thin films on silicon (111) substrate

The epitaxial growth of boron rich hexagonal zirconium diborides (h-ZrB2+δ) thin films on Si(111) substrates using the magnetron co-sputtering technique with elemental zirconium and boron is reported. The effect of process temperature (700–900 °C) on the compositions and epitaxy quality was investigated. The chemical composition of the films was found to have a higher boron to zirconium ratio than the ideal stoichiometric AlB2-type ZrB2 and was observed to be sensitive to process temperature. Films deposited at 700 °C exhibited intense diffraction peaks along the growth direction corresponding to (000ℓ) of h-ZrB2 using both lab and synchrotron-based x-ray diffractograms. The thermal and compositional stability of the epitaxial h-ZrB2+δ film was further evaluated under a nitrogen-rich environment through isothermal annealing which showed a reduction in in-plane misorientation during thermal annealing. The relative stability of deviating compositions and the energetics of impurity incorporations were analyzed using density functional theory simulations, and the formation of native point defects or impurity incorporation in h-ZrB2 was found to be endothermic processes. Our experimental results showed that an epitaxial thin film of h-ZrB2+δ can be grown on Si(111) substrate using a magnetron co-sputtering technique at a relatively low processing temperature (700 °C) and has the potential to be used as a template for III-nitride growth on Si substrates.

Plasma Spraying of Silicide Coatings to Protect Zirconium Alloys from Oxidation

The work is devoted to an experimental study of the possibilities of applying a protective silicide coating on an alloy based on zirconium (E110) by atmospheric plasma spraying. Coatings based on the binary eutectic Mo5Si3 + MoSi2 were deposited on the surface of E110 alloy sheet. The features of the structure and phase composition of the coatings after deposition and their evolution as a result of isothermal annealing at a temperature of 1300°C are studied. Upon rapid cooling of silicide particles during coating, nonequilibrium phases are formed. As a result of annealing, the phase composition changes, which corresponds to the phase diagram. The kinetics of diffusion interaction between the coating and the base material has been studied. The possibility of successfully protecting a zirconium alloy from oxidation at 1100°C in air by complex deposition of a coating of molybdenum silicides has been shown for the first time. The minimum radius of curvature of the surface of the protected samples was about 1 mm.

FORMATION AND DECOMPOSITION OF ANOMALOUS SUPERSATURATED MOLYBDENUM SOLUTIONS IN COPPER-BASED CONDENSATES


 Cu-Mo condensates in the concentration range of the latter from 0.3 to 1.5 at.%, obtained by simultaneous evaporation in vacuum with subsequent condensation of the resulting vapor mixture on a non-orienting substrate (PVD method), were studied. The components of this system do not form chemical compounds under equilibrium conditions and are mutually insoluble in liquid and solid states. The structure of Cu-Mo condensates was studied by transmission electron microscopy and X-ray diffractometry both in the derivative state and after a series of isothermal anneals in the temperature range from 300 to 900°C. It was found that small concentrations of molybdenum lead to significant dispersion of the matrix metal. Molybdenum tends to form segregations at the boundaries of copper grains and form a strong coherent bond with the matrix metal, which persists even after isothermal annealing. The conditions for the formation of an anomalous supersaturated solid solution of molybdenum in the copper matrix, as well as the conditions for its decomposition, have been revealed. An assumption is made about the mechanism of formation of such a solution during condensation from the vapor phase, which consists in the kinetic capture of molybdenum atoms by the crystallization front during condensation from the vapor phase. It was found that the decomposition of the supersaturated solid solution begins when heated to 0.5 of the melting point of copper and is accompanied by a dispersion solidification process. During the experiment, it was first recorded that the dispersion solidification process can have a two-stage character. The first peak is observed in the region of 30 minutes of annealing, and the second peak is observed after about 2 hours of isothermal annealing. The height of the dispersion hardening peaks increases with increasing molybdenum concentration. It is suggested that the appearance of the second peak of dispersion hardening is associated with the peculiarities of the interaction between copper grains and molybdenum segregations at the grain boundaries. It is shown that the structure after solution decomposition is typically composite. The advantage of this material over conventional dispersively hardening alloys is the fact that in these pseudo-alloys there is no reverse solution of hardening particles at an increase in temperature.

Removal of lead ions from wastewater using raw and activated carbon of Pterocarpus santalinoides shell

Removing toxic metals from the environment is a primary concern for researchers because of their hazardous effects. In this study, raw and activated Pterocarpus santalinoides shell was utilized in removal of lead (Pb) metal from an aqueous solution. The prepared adsorbents were analysed by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and mineral composition to identify their structural composition and understand the adsorption mechanism. The influence of various adsorption variables such as dose of adsorbents, initial concentration of lead metal, contact time, solution temperature, and adsorption isotherms, kinetics, and thermodynamic parameters was studied. Adsorption efficiencies and capacities for the adsorbents were calculated. Based on the results generated, the two different adsorbents utilised showed a good alternative to commercial materials, with removal efficiencies greater than 80%. The Langmuir isotherm and pseudo-second-order model showed good fits to the experimental data. Moreover, the thermodynamic results revealed that the adsorption of Pb ions via the raw and activated carbon of Pterocarpus santalinoides shell was an endothermic and spontaneous process. According to this research, Pterocarpus santalinoides shell, being an agricultural waste, might be explored as an efficient adsorbent for extracting Pb ions from wastewater.

The effect of the austenitisation temperaturefor the two-stage heat treatment of high-manganesesteels on its wear resistance under abrasiveconditions

Fine-grained high-manganese X120Mn12 grade steel was subjected to a two-stage heat treatment consisting oflong-term isothermal annealing at 510C, which was followed by resaturation in order to reduce the negativeeffect of the brittle carbide carbides of manganese cementite (Fe,Mn)3C. The objective of the experimentwas to elucidate the effects of distinct stages of heat treatment on the properties of high manganese steelwith regard to its resistance to abrasive wear. Supersaturation was performed for eleven different variationsof temperature values ranging from 600C to 1100C to verify its effect on the resistance to abrasion wearunder abrasion conditions. An increase in the supersaturation temperature results in the gradual coagulationand disintegration of the colonies of pearlite and needle-like carbides (Fe,Mn)3C formed during isothermalannealing. At the same time, as a result of the PSN (particle stimulated nucleation) process, the microstructureof austenite undergoes partial refinement, which ultimately increases the resistance to abrasive wear. As aresult of the final microstructural changes resulted in an increase in the resistance to abrasion of approximately6% compared to the initial state.

The phase transformation behavior of Mn-Al rare-earth-free permanent magnets

Rare-earth-free permanent magnet materials based on Mn show great promise for applications in electric motors and devices. The metastable ferromagnetic τ phase of the Mn-Al system has magnetic properties between those of the high-performance Nd-Fe-B magnets and the lower-performance ferrite magnets. However, the hybrid displacive-diffusional pathway of τ formation, from the parent ε phase through the intermediary ε’ phase, is still not fully understood. This phase transformation progression was studied in-situ using diffractive, calorimetric, and magnetometric techniques to show that the progression from ε to τ in Mn54Al46 at <450 °C involves the ordering of ε into ε’. Density functional theory calculations were performed on each phase and confirmed the experimental observation that the ε to ε’ to τ pathway is energetically favorable. Isothermal annealing of quenched-in ε at 350 °C demonstrated that ε’ is ferromagnetic, also in agreement with theoretical results, with a moderate coercivity of at least 50 kA/m. The τ phase was observed to nucleate along the prior ε phase grain boundaries and grow into the ε’ phase regions. A boundary front of ε’ was observed between the τ and ε phases. Both Kissinger and Flynn-Wall-Ozawa methods were used to determine the activation energies for the ε’ and τ phase transformations with values of ∼140 kJ/mol obtained for both phases. Therefore, the ordering transformation to ε’ and the hybrid displacive-diffusional transformation to τ were shown to overcome the same magnitude energy barrier. Both activation energies were less than previous τ phase activation energies measured on Mn55Al45 in the absence of a significant ε’ ordering exotherm, providing a kinetic benefit to the ε to ε’ to τ pathway at 350 °C. The results of this study give insight into the phase transformation of L10 binary materials as well as materials that undergo a disorder–order transformation followed by displacive shear.

Influence of humidity on the decomposition process of double base rocket propellant

The decomposition mechanisms of the polymer cellulose nitrate (NC) which is used in double base (DB) rocket propellants, have been extensively studied, and the influence of storage temperature on the lifetime of these energetic formulations is well known. However, the impact of humidity and water on the polymer decomposition process is poorly understood. This paper studies the influence of humidity on the decomposition chemistry of NC and its impact on shelf life. Stabiliser consumption was first analysed by ageing the propellant in sealed vials at different humidity levels for 7 days at an isothermal temperature of 90 °C. Samples were also analysed using heat flow calorimetry (HFC) at isothermal temperatures of 80 °C, 90 °C, and 100 °C. The results indicates that stabiliser depletion increases with increasing water content. Life assessment calculations (AOP 48 ed2) show that increasing the absolute humidity from 6 to 22 g m-3 will decrease the propellant life from 11 to 6 years (25 °C equivalents). The HFC results follow the same trend as the stabiliser depletion where greater absolute humidity increases the heat flow by up to 400 %. Unlike the pass/fail criteria for stabiliser depletion, the HFC samples passed the 10-year (25 °C equivalent) life criteria (STANAG 4582). A multi-temperature (80, 90, 100 °C) kinetic analysis of the initial heat flow showed that the heat flow rate increased with increasing humidity, but the activation energy for all humidity levels remained at 131 (± 3) kJ mol−1.

Thermal stability of microstructure and corresponding hardness variations in two high-carbon nanostructured bainitic steels

The autotempering phenomenon and carbon partitioning from bainitic subunits during the bainite transformation suggest that the tempering behavior of the nanostructured bainite may be different compared to that of martensite. This article aims to investigate the thermal stability of the microstructure in two low alloy nanostructured bainitic steels containing 0.89 wt% carbon content. Nanostructured bainite was obtained after austempering at 250 °C for optimum heat treatment time. Nanostructured bainitic steels were tempered at the temperature range of 300–700 °C for 30 min. Additionally, the effect of prolonged austempering beyond the optimum heat treatment condition at austempering temperature was studied. Microstructural characteristics were evaluated using optical and field emission gun scanning electron microscopes and X-ray diffraction methods. Hardness variations during tempering of nanostructured bainite compared with that of martensite microstructure obtained in the same primary steels after austenitizing and quenching. Results indicated that microstructural characteristics of nanostructure bainite didn’t change significantly at heat treatment times longer than that needed for bainite transformation completion at isothermal bainite heat treatment temperature. Moreover, results approved the higher tempering resistance of nanostructured bainite compared to that of martensite in the same steel. It has been shown that tempering the nanostructured bainite up to 400 °C didn’t change the microstructure and hardness, while the changes were pronounced at higher tempering temperatures. It has been suggested that cementite precipitation was more significant when a higher number of dislocations were present in nanostructured bainite before starting the tempering process.

Thermal stability of levopimaric acid and its oxidation products

Biofuels are renewable alternatives to fossil fuels. Levopimaric acid‒base biofuels have attracted increasing attention. However, their stability remains a critical issue in practice. Thus, there is a strong impetus to evaluate the thermal stability of levopimaric acid. Through thermogravimetry (TG) and a custom-designed mini closed pressure vessel test (MCPVT) operating under isothermal and stepped temperature conditions, we investigated thermal oxidation characteristics of levopimaric acid under oxygen atmosphere. Thin-layer chromatography (TLC) and iodimetry were used to measure the hydrogen peroxides generated by levopimaric acid oxidation. A high pressure differential scanning calorimeter (HPDSC) was used to assess hydroperoxide thermal decomposition characteristics. Gas chromatography-mass spectrometry (GC-MS) was used to characterize the oxidation products. The thermal decomposition kinetics of levopimaric acid were thus elucidated, and a high peroxide value was detected in the levopimaric acid. The decomposition heat (QDSC) and exothermic onset temperature (Tonset) of hydroperoxides were 338.75 J g−1 and 375.37 K, respectively. Finally, levopimaric acid underwent a second-stage oxidation process at its melt point (423.15 K), resulting in complex oxidation products. Thermal oxidation of levopimaric acid could yield potential thermal hazards, indicating that antioxidants must be added during levopimaric acid application to protect against such hazardous effects.

Microstructure and mechanical properties of Zr46Cu46Al8 bulk metallic glass after annealing treatment

The crystallization and mechanical behavior of Zr46Cu46Al8 MG is investigated. The small-angle neutron scattering (SANS) and extended X-ray absorption fine structure spectra (EXAFS) is used to reveal the microstructure of Zr46Cu46Al8 bulk metallic glasses (BMG) after isothermal annealing. The incubation period of Zr46Cu46Al8 BMGs was less than 10 min under a variable heating rate. Moreover, a stable crystallization point was determined with nanocrystalline particles sized at 32 Å at the equilibrium using SANS. The Zr and Al atoms shifted outward during crystallization. Thus, the crystallization mechanisms of the Zr46Cu46Al8 BMGs are discussed based on the results of the SANS, X-ray diffraction, EXAFS, and differential scanning calorimetry analyses. The mechanical properties of the BMG and its composites were investigated using a nanoindentation test.