Heating In Air Research Articles

Changes of Structural Properties in Polycrystalline Y2O3 during Heating in Air and Vacuum

Changes of Structural Properties in Polycrystalline Y2O3 during Heating in Air and Vacuum

Oxidation regularities of the electroexplosive metal nanopowders during heating in air after microwave irradiation

Oxidation regularities of the electroexplosive metal nanopowders during heating in air after microwave irradiation

Sublimation rate of solid NaCl powders and evaporation rate of liquid NaCl upon heating in vacuum and air

The volatilization of sodium chloride (NaCl) is important for multiple applications, such as energy storage, manufacturing porous parts, and purification and recycling of composites. Until now, only limited information on this feature has been published. To expand the knowledge in this field, we investigated the sublimation and evaporation of two NaCl powders by thermal gravimetry in vacuum and air. The study has shown that the volatilization kinetics of powders with different shapes and sizes are identical. The volatilization of NaCl powders in vacuum occurs mainly by sublimation before melting. In contrast, the volatilization of NaCl in the air is preferentially caused by the evaporation of the melt. In a vacuum, the evaporation of NaCl powder after melting is significantly slower than the sublimation before melting, because of a drastic decrease in the volatilization area. The Hertz-Knudsen relation with an appropriate fitting coefficient satisfactorily describes the mass loss by volatilization in vacuum and air.

Structural and morphological features of magnetron nanofilms of TaN with different thicknesses

Purpose of research. Study of morphological and phase changes in the structure of tantalum nitride nanofilms formed by magnetron reactive sputtering on a silicon substrate.Methods. Magnetron sputtering on a silicon substrate was performed using the MVU TM-Magna T setup with the sputtering time parameter changing from 300 to 900 sec, and also with constant power parameters of 500 W and working gas pressure of Ar 0,5 Pa. The morphological and phase changes in the structure of tantalum nitride nanofilms were studied using atomic force microscopy and X-ray phase analysis. The fractal dimension was determined using the cube counting method. X-ray diffractometric analysis in the in situ measurement mode with discrete heating (in 100 °C increments) in air up to 1000 °C using the PAAR HTK-16 high-temperature attachment.Results. Using atomic force microscopy methods, it was found that the granulometric distribution of nanoclusters in the studied TaN nanofilms was Gaussian and an increase in the lateral size of particles was observed with an increase in the deposition time. The nanofilm with a deposition time of 300 s had minimal roughness. The statistical fractal dimension was calculated, the value of which corresponded to their three-dimensionality. According to the X-ray phase analysis data, the sizes of the coherence region, texturing, microdeformations and interplanar deformation distortions were determined, and a mixed Stranski-Krastanov mechanism of nanofilm formation was established.Conclusion. The surface roughness of nitride nanofilms formed at a constant power (500 W) depends significantly on the magnetron sputtering time and N2 concentration. In all studied nanofilm structures, the dominant growth mechanism was the mixed Stranski–Krastanov mechanism.

Robust and Density Tunable Kevlar/Hexagonal Boron Nitride Microribbon Aerogels with Excellent Thermal, Mechanical, and Oil-Absorption Properties.

With rapid advancements in aerospace and supersonic aircraft technology, there is a growing demand for multifunctional thermal protective materials. Aerogels, known for their low density and high porosity, have garnered significant attention in this regard. However, developing a lightweight multifunctional aerogel that combines exceptional thermal and mechanical properties through a straightforward and time-efficient method remains a significant challenge. Herein, a facile and universal approach is developed for the preparation of Kevlar/hexagonal boron nitride (h-BN) aerogels, in which a spin-assisted method is applied to create robust microribbons and further accelerate solvent displacement. The resulting microribbon scaffold, with its entangled nanofiber-nanosheet morphologies, exhibits sufficient strength to prevent volume shrinkage during drying, thereby allowing precise control over aerogel density. The porous hybrid aerogels, featuring controllable geometric characteristics and tailored densities ranging from 6.9 to 100 mg cm-3, can be successfully fabricated. These aerogels exhibit excellent thermal insulation properties, and the thermal conductivities of the as-prepared KBX aerogels have a wide distribution in the range of 0.0269-0.0450 W m-1 k-1. The thermal stability of the hybrid aerogels is enhanced to 566 °C. Moreover, the resulting hybrid aerogels exhibit an ultrahigh bearing ratio, supporting more than 2000 times their own weight while maintaining stable structural integrity. These aerogels also demonstrate high compressive strength, hydrophobicity, and excellent sorption performance for various oils and solvents. Additionally, the oil-saturated aerogels can be easily recovered through heat treatment or combustion in air. The features endow hybrid Kevlar/h-BN aerogels with significant potential for applications in thermal management, environmental protection, and neutron protection.

Dielectric anomalies and dc-resistivity degradation in PbNb2O6-based ceramics at high temperature

The lead metaniobate (PbNb2O6, PN) with high Curie temperature is widely used to fabricate transducer for high-temperature application up to 300 °C. However, evident dielectric anomalies and direct-current resistivity degradation were experimentally observed in PN-based ceramics at high temperature, which may significantly restrict the working temperature range for well logging application. When the sample was heat-treated at 260 °C for 3 h in silicon oil, the dc-resistivity of ceramics at 260 °C decreased from 3.8 × 108 to 1.0×107 Ω⋅cm, accompanied by 43 times increase in tanδ at 1 kHz. To investigate the cause of these phenomena, the in-situ piezoelectric, dielectric properties and dc-resistivity were systematically investigated in the samples subjected to heat-treatment at 260 °C in silicon oil. It is revealed that the porous structure of PN-based ceramics allows for the infiltration of silicon oil as a minor phase, and the accumulation of its decomposers within the pores would exert significant influence on the dielectric property and dc-resistivity of ceramics at elevated temperatures. However, the samples still demonstrate excellent thermal stability in piezoelectric property, with value of kt maintaining 0.39 at 260 °C in oil. In addition, the low Qm is not the intrinsic property of PN ceramics, but rather related to the phase transition of silicon oil within pores of ceramics, as indicated by the increase in Qm from 47 to 80 after heat-treatment in air.

Hydroflux Synthesis and Structural Phase Transition of Rare-Earth Borate Hydroxides Na2[RE(BO3)(OH)2] (RE = Y, Gd-Er).

Reacting RE2O3 and H3BO3 in an ultra-alkaline NaOH hydroflux at about 250 °C yielded pure, crystalline samples of Na2[RE(BO3)(OH)2] (RE = Y, Gd-Er). The compounds dehydrate to Na3RE(BO3)2 upon heating in air to about 500 °C. Na2[RE(BO3)(OH)2] (RE = Tb-Er) are photoluminescent under UV radiation. Their UV-Vis spectra show the typical absorptions associated with 4f-4f transitions and absorption edges in the UV (band gaps ≥ 5.7 eV). The RE3+ cation is coordinated by seven oxygen atoms, which define a distorted pentagonal bipyramid. The bipyramids share trans-edges of their base forming infinite chains. Triangular (BO3)3- groups connect the chains into layers. The crystal structure of Na2[Ho(BO3)(OH)2] was investigated at various temperatures in the range 100 K ≤ T ≤ 320 K. Above 310(2) K, the compound crystallizes in the orthorhombic space group Cmcm (β-phase), below, it undergoes a displacive phase transition of second order resulting in a monoclinic structure in space group C2/c (α-phase). The critical exponents derived from different structural parameters indicate a cooperative distortion of the borate layers, but a rather uncorrelated adaptation of the sodium cations to their local environment. The other compounds of the series also adopt the structure of the α-phase at 296 K.

Effects of heating media on microstructure and chemical composition of heat-treated Pometia pinnata

Changes of microstructure, crystallization, chemical composition, and equilibrium moisture content (EMC) of heat-treated wood (HTW) were investigated to explore the effects of heating media (saturated steam, superheated steam, air) and heat treatment (HT) temperature on HTWs. The results showed that the saturated steam induced more severe cell wall destruction than the other two media. Although the porosity slightly increased with the increasing HT temperature, superheated steam and air HT still decreased the porosity compared to that of control, whereas saturated steam HT increased the porosity. The HT increased both relative crystallinity and crystal size of HTWs. The increasing HT temperature slightly increased the relative crystallinity but decreased the crystal size. The highest crystallinity (55.0%) was observed after saturated steam HT. Leaching led to the increase of crystal size of HTW treated in saturated steam (about 0.15 nm), while those treated in unsaturated steam and air decreased. The increase in relative amount of lignin and cellulose due to the hemicellulose degradation were the main chemical changes of HTWs. Further lignin condensation reaction only occurred after saturated steam HT. Although saturated steam HT induced increased porosity, its lowest EMC (5.91%) indicated the decrease of hydroxyl groups.

Structural and morphological modification of the PEO coating on the Ti-25Ta-10Zr-15Nb alloy through heat treatment

This study aims to produce a Plasma Electrolytic Oxidation (PEO) layer on the Ti-25Ta-10Zr-15Nb alloy (TTZN) and analyze the influence of heat treatment at different temperatures without a controlled atmosphere to promote thermal oxidation, and in a vacuum (10−7 Torr), to prevent oxidation. The results showed that the PEO coating was initially amorphous, and heat treatments promoted the formation of crystalline compounds. Raising the heat treatment temperature led to higher surface roughness in all conditions. The heat treatment under vacuum reduced thickness (9 → 4 μm), while the heat treatment in air promoted a thickness increasing (10 → 174 μm) and decreased the wettability (82 → 25°) of the oxide layer. Due to oxygen diffusion, there was an increase in the hardness of the TTZN alloy at the oxide/metal interface after heat treatment in the air (268 → 504 HV, 268 → 845 HV, and 268 → 1011 HV, at 800, 1000, and 1200 °C).

Imaging Anisotropic Proton Intercalation in Photochromic MoO3.

Protonation represents a fundamental chemical process with promising applications in the fields of energy, environment, and memory devices. Probing the protonation mechanism, however, presents a formidable challenge owing to the elusiveness of intercalated protons. In this work, we utilize the atomic and electronic structure changes associated with protonation to directly image the proton intercalation pathways in α-MoO3 induced by UV illumination. We reveal the anisotropic intercalation behavior which is initiated by photocatalyzed water dissociation preferentially at the (001) edges and then propagates along the c axis, transforming α-MoO3 into HxMoO3 to realize photochromism. This photochromic process can be reversed via heating in air, leading to anisotropic proton deintercalation, also preferentially along the c axis. The observed anisotropic behavior can be attributed to the intrinsically low energy barriers for both proton migration along the c axis and water dissociation/formation at (001) edges.

Effect of air heat treatment on the color change and weight and density loss of six Korean oak woods

Effect of air heat treatment on the color change and weight and density loss of six Korean oak woods

Non-monotonic dependence of high-temperature stability of stone wool fibres on pre-oxidation time and temperature

Stone wool is a sustainable, fire-safe insulation material, and its fire-safety depends on its high-temperature stability (HTS). It is known that the HTS of stone wool fibres can be enhanced by pre-oxidation (i.e., heat treatment in air) at temperatures below or at its glass transition temperature (Tg). However, so far, a quantitative trend of HTS with varying pre-oxidation temperature (Tpre-ox) and time (tpre-ox) remains unknown. In this study, we quantified the change of HTS of stone wool fibres with a Tg of 677 °C as functions of both Tpre-ox and tpre-ox through a hot-stage microscope. The derived results revealed striking non-monotonic trends in the HTS of stone wool fibres. The HTS first increased with Tpre-ox from 500 to 630 °C for tpre-ox of 15 minutes, but declined beyond 630 °C. The HTS was significantly improved upon pre-oxidation for merely 2 minutes, at 677 °C, then dropped with extending tpre-ox to 16 hours, and finally increased again with tpre-ox up to 16 days. The origin of the non-monotonic trend was explored by characterizing the crystallization behaviour, thermal expansion, surface composition, and surface morphology in stone wool fibres after pre-oxidation.

Spectral-luminescence characteristics of solid solutions ZrO2-Eu2O3 crystals

Data on the structure of (100-x) mol.% ZrO2 - х mol.% Eu2O3 solid solution concentration series (x = 4, 6, 8, 10, 12, 15, 20, 27) have been presented. The crystals with x = 4 have a hexagonal structure, while those with x = 8 are a mixture of cubic and tetragonal phases. The crystals with x = 10, 12 and 15 have a cubic structure, and those with x = 27 are two-phase and contain cubic modification and pyrochlore phase.Luminescent spectra of the (100-x) mol.% ZrO2 - х mol.% Eu2O3 solid solutions have been taken in the as-grown and air-annealed states. The presence of Eu2+ ions was revealed in (100-x) mol.% ZrO2 - х mol.% Eu2O3 solid solution concentration series (x = 4, 6, 8, 10, 12, 15, 20, 27) after growth, the content of which decreases significantly after heat treatment in air. It has been shown that in (96-85) mol.% ZrO2 - (4–15) mol.% Eu2O3 crystals the relative proportion of optical centers of Eu3+ surrounded by oxygen seven-vertex is lower compared to crystals (96.7–85) mol.% ZrO2 - (3.6–15) mol.% Gd2O3 - 0.1 mol.% Eu2O3. The (73, 80) mol.% ZrO2 - (20, 27) mol.% Eu2O3 crystals contain optical centers of Eu3+ surrounded by oxygen six-vertex with two oxygen vacancies along the diagonal faces of the cubic crystal lattice. Their percentage being higher than in the (79.9, 76.9) mol.% ZrO2 - (20, 33) mol.% Gd2O3 - 0.1 mol.% Eu2O3 crystals.In crystals of (100-x) mol.% ZrO2 - х mol.% Eu2O3 solid solution concentration series (x = 4, 6, 8, 10, 12, 15, 20, 27), the presence of concentration quenching was revealed with increasing concentration of europium ions.

Functionally multilayered Yb‐silicate EBCs fabricated using slurry spraying‐reactive sintering technique

AbstractFunctionally multilayered environmental barrier coatings (EBCs) with the desired layer sequence of Yb2O3/Yb2SiO5/Yb2Si2O7/SiO2/Si were obtained using an unconventional yet simple technique of reactive sintering. Yb2O3 slurry was sprayed on polycrystalline silicon (used as a bond coat for SiCf/SiC composites) and reactive sintered to generate graded layers that provide a combination of mitigated thermal expansion mismatch as well as silica activity. The Yb2O3‐terpineol slurry produced a uniform deposit of the Yb2O3 topcoat. Reactive sintering of exploratory coatings (t ∼ 10–20 µm) was carried out in air by varying the temperature (1100–1400°C) and time (2–24 h). X‐ray diffraction and scanning electron microscopy‐energy‐dispersive spectroscopy technique confirmed the in situ formation of X2‐Yb2SiO5 and β‐Yb2Si2O7. Rietveld refinement was performed to know the volume fractions of the respective phases. The set of process parameters identified from the preliminary work was employed to fabricate EBCs with thickness ∼ 250 µm. The X2‐Yb2SiO5 and β‐Yb2Si2O7 phases formed next to the Si/SiO2 interface as two separate layers. Post‐sintering heat treatments in air at 1300, 1350, and 1400°C for 3–50 h elucidated the growth characteristics of the oxide layers to be a function of both temperature and time. The theoretical considerations of diffusional reactive phase formation of the EBC multilayer growth rates are discussed.

Thermal Stability of Chalcogenide Perovskites.

Chalcogenide perovskites (CPs) have recently attracted interest as a class of materials with practical potential in optoelectronics and have been suggested as a more thermally stable alternative to intensely studied halide perovskites (HPs). Here we report a comparative study of the thermal stability of representative HPs, MAPbI3 (MA = CH3NH3+, methylammonium) and CsPbI3, and a series of CPs with compositions BaZrS3, β-SrZrS3, BaHfS3, SrHfS3. Changes in the crystal structure, chemical composition, and optical properties upon heating in air up to 800 °C were studied using thermogravimetric analysis, temperature-dependent X-ray diffraction, energy-dispersive X-ray spectroscopy, and diffuse reflectance spectroscopy. While HPs undergo phase transitions and thermally decompose at temperatures below 300 °C, the CPs show no changes in crystal phase or composition when heated up to at least 450 °C. At 500 °C CPs oxidize on time scales of several hours, forming oxides and sulfates. The structural origins of the higher thermal and phase stability of the CPs are discussed.

An EPR study of point defects in zinc oxide thin films

We studied ZnO thin films deposited on glass slides by thermal evaporation in vacuum followed by heat treatment in open air or Ar flow. The samples were characterized using x-ray diffraction, Raman scattering, photoluminescence (PL), and electron paramagnetic resonance (EPR) spectroscopy. We observed a broad PL band in the visible region at spectral positions of 504 and 560 nm and a low-intensity band in the UV region at 390 nm. The EPR spectra display a clear first derivative structure at g=1.96 at temperatures below 200 K. The PL spectrum shows red-shifted valence to conduction band emission due to electron hole recombination through shallow surface states. We found an activation energy of E a = 4.2 meV using the Arrhenius plot and estimated concentrations of paramagnetic defects and spin–spin relaxation time constants of 1016 m−3 and 10–14 s, respectively.

Zirconium-modified organosiloxane resin for high-temperature-resistant coatings

Organosiloxane resins typically undergo significant thermal degradation, with notable mass loss between 400 °C and 800 °C, which limits its applications in wider fields. To address this problem, zirconium (Zr) was incorporated into the backbone of organosiloxane resins via the sol-gel process. The mass retention of the Zr-modified organosiloxane resins at 1000 °C increased with Zr content, reaching 95.47 wt% and 97.29 wt% in air and argon, respectively. The accretion of the mass retention can be attributed to the formation of crystalline zirconium oxide (ZrO2) structures within the resin matrix. The Zr-modified organosiloxane resins showed storage stability even after 3 months. Uniform, smooth and discernible defect free coatings with thickness of approximately 1 μm were obtained through spin-coating. Compared with the pure organosiloxane coating, the Zr-modified organosiloxane coating showed better thermal stability without significant cracks after heat treatment in air at 450 °C. The results suggest potential applications of this Zr-modified ploysiloxane in thermal barrier protection technologies.

Synthesis of graphene mesosponge using CaO nanoparticles formed from CaCO3

While graphene mesosponge (GMS) is a new type of mesoporous material with the potential for a variety of applications, its synthesis process requires costly templates such as Al2O3 and MgO nanoparticles. In this study, we present a new synthesis method for GMS, which achieves a high specific surface area of 1720 m2 g1 by employing calcium oxide (CaO) nanoparticles as templates. The CaO nanoparticles with an approximate diameter of 86 nm are formed through the thermal decomposition of calcium carbonate nanoparticles. However, the calcium carbonate nanoparticles contain a small amount of Mg (2 wt %), and the thermal decomposition process also yields impurities, including Mg. When the CaO nanoparticles, including the Mg-based impurities, are subjected to chemical vapor deposition, the CaO surface can be coated with a thin carbon layer, primarily consisting of single-layer graphene through the specific catalysis of the CaO surface in facilitating the CH4-to-C conversion reactions. However, at the same time, the presence of Mg-based impurities leads to the formation of low-crystalline carbons, which have a detrimental effect on the subsequent high-temperature annealing at 1800 °C, following the template removal process, resulting in an excessive number of edge sits in the GMS. We have found that the harmful low-crystalline carbons can be eliminated through heat treatment in air at 350 °C. By adopting such a removal process, high-quality GMS with a minimal number of edge sites can be produced.

Environmental response characteristics of epitaxial superconducting La0.8Sr0.2NiO2 thin films

Despite the discovery of superconducting properties in thin films with an infinite-layer structured nickelate has paved the way for exploring unconventional superconductivity, opening up new possibilities in this field. However, the challenges related to fabricating these samples have greatly restricted research in this area. In this study, we successfully fabricated superconducting thin films of La0.8Sr0.2NiO2 and investigated their tolerance to different environmental factors. To analyze the stability of the superconducting La0.8Sr0.2NiO2 thin films, we assessed their tolerance to temperature by examining the peak intensities in X-ray diffraction (XRD) and monitoring the changes in resistance curves at varying temperatures. In addition, we investigated the films’ sensitivity to acidity and alkalinity by immersing them in acidic and alkaline solutions for various durations. We also studied the stability of the thin films under various conditions, including heating in air, heating in a vacuum, exposure to acid and alkali, as well as exposure to the organic solvent acetone solution. Our findings highlight the successful preparation of superconducting La0.8Sr0.2NiO2 thin films and shed light on their stability in different environments. This research provides valuable insights for further exploration of their potential applications and laid the foundation for advancements in the field of unconventional superconductivity.

High Temperature Graphitization of Diamond during Heat Treatment in Air and in a Vacuum

High Temperature Graphitization of Diamond during Heat Treatment in Air and in a Vacuum