High Temperature Oxidation Process Research Articles

Temperature dependence mechanism of high-temperature oxidation of transition metal silicide MoSi2

Transition metal silicides represented by MoSi2 have excellent oxidation resistance and are widely used as high-temperature anti-oxidation coatings in hot end components of power equipment. However, the mechanism of temperature-dependent growth of MoSi2 oxidation products has not been revealed. Therefore, this study investigated the formation characteristics of oxide film and silicide-poor compound on MoSi2 at temperatures of 1000 °C–1550 °C through high-temperature oxidation experiments, combined with microscopic Raman spectroscopy, scanning electron microscope, and x-ray diffraction (XRD) characterizations. The result showed that MoSi2 underwent high-temperature selective oxidation reactions at 1000 °C–1200 °C, forming MoO2 and SiO2 oxide film on the substrate. As the oxidation temperature increased to 1550 °C, after 100 h of oxidation, along with the disappearance of MoO2 and the phase transformation of SiO2, a continuous Mo5Si3 layer with a thickness of approximately 47 μm was formed at the SiO2–MoSi2 interface. Thermodynamics and kinetic calculations further revealed the mechanism of temperature-dependent growth of oxidation products (MoO2 and Mo5Si3) during high-temperature oxidation process of MoSi2. As the temperature increased, the diffusion flux ratio of O and Si decreased, leading to a decrease in oxygen concentration at the interface and promoting the growth of the Mo5Si3 layer. Its thickness is an important indicator for evaluating the oxidation resistance of MoSi2 coatings during service. This study provides experimental and mechanistic insights into the temperature-dependent growth behavior of Mo5Si3 during the high-temperature oxidation of MoSi2 coating, and provides guidance for predicting the service life and improving the oxidation resistance of silicide coatings.

Extreme environmental micro-plasma electrolyte oxidation induced defect-rich Au nanoparticles catalyst improving the nitrophenol hydrogenation reaction

The defect-rich Au nanoparticles (NPs) catalyst on Mg surface was prepared by the micro-plasma electrolyte oxidation (MPEO) utilizing liquid nitrogen as the cooling medium. MPEO is a high-temperature plasma oxidation process that decomposes the [AuCl4]-precursor salt to form metastable state Au NPs. The rapid quenching effect of liquid nitrogen occurs during this non-equilibrium process and generates numerous defects on the Au NPs, thereby altering their electronic state. Consequently, the catalytic performance of this Au/MgO catalyst was outstanding, exceeding that of the sample prepared without using liquid nitrogen. This finding indicates that the harsh environment plays a crucial role in producing defect-rich Au NPs and improving the catalytic efficiency.

High-temperature oxidation behavior of AlCoCrFeNi2.1 eutectic high-entropy alloy: Microstructure evolution and microhardness

In this work, the high-temperature oxidation behavior at 820 °C of an AlCoCrFeNi2.1 eutectic high-entropy alloy (EHEA) prepared by vacuum induction melting was studied, while the evolution of microstructure and microhardness at different oxidation times (1 h, 3 h, 5 h, 10 h, 20 h, 30 h, and 50 h) were also investigated. The prepared AlCoCrFeNi2.1 EHEA shows a typical FCC/BCC bi-phase microstructure with Cr-rich precipitation phase. Compared to 304 stainless steels, the AlCrCoFeNi2.1 EHEA exhibits a better oxidation resistance, which is due to the continuous and dense Al2O3 generated during high-temperature oxidation process. The AlCoCrFeNi2.1 EHEA also has an excellent high-temperature structure stability, proved by that the phase composition and elemental composition of each phase remain almost unchanged with the increase in oxidation time. After high-temperature oxidation, the microhardness of AlCoCrFeNi2.1 EHEA decreases as expected, however, with the increase in oxidation time, the microhardness shows a noticeable increasing trend due to the solid solution strengthening of the σ phase and formation of the α-Cr phase.

Microstructure and high-temperature oxidation behavior of Al2O3/Cr composite coating on Inconel 718 alloy

In this paper, Al2O3/Cr composite coatings were prepared on the surface of Inconel 718 alloy by cathodic liquid plasma electrolytic deposition (CLPED) and double-glow plasma surface alloying (DGPSA) processes. The microstructure and high-temperature oxidation behavior of Al2O3/Cr composite coating were investigated. The results showed that the Al2O3 interlayer surface was fully covered with Cr coating. The interface between the Al2O3 layer and the Cr metal layer presents a mechanical interlock effect, which can absorb the deformation caused by thermal expansion, thereby reducing the adverse effects of thermal stress. The surface roughness of the Al2O3 coatings decreased after depositing Cr coating. The oxidation weight gain of the Al2O3/Cr composite coatings were significantly lower than that of the substrate, indicating that the Al2O3/Cr composite coatings improved the high-temperature oxidation resistance of Inconel 718 alloy. The oxidation weight gain of the Al2O3/Cr composite coatings at different frequencies were similar, while the Al2O3/Cr composite coating at 400 Hz was lowest. During the high-temperature oxidation process, the Al2O3 interlayer can effectively inhibit the external diffusion of Ni, Fe and other elements in the matrix, which helps to prevent the cracking of the outer oxide film, thereby reducing the oxidation rate.

(Invited) Design of Surface Oxidation and Nitridation Reactions on 4H-SiC for the Advanced SiC Gate Stack Formation Processes

Silicon carbide (SiC) MOSFETs are expected to replace Si bipolar transistors partially in applications such as automotive, railroad, and other high-voltage applications. But the resistance of the MOS inversion layer channel limits the performance of MOSFETs. It has been clarified that the effective carrier density in the inversion channel is significantly reduced by the carrier trapping by the high density of defect states distributed nearby SiO2/SiC interface. In this study, our understanding of oxidation and nitridation reactions of SiC for designing the gate stack formation processes to improve the MOS interface characteristics is presented.Choosing SiO2 as a gate dielectric for SiC is favorable from various aspects including its ability to form a thermodynamically stable interface with SiC, which is free of reactions at the process temperature. However, from a microscopic point of view, Si-O bond alone cannot cover the whole surface of SiC and the excess C atoms on the surface causes the formation of defect states. One of the possible approaches has been employing an appropriate thermal oxidation condition to enhance the excess carbon elimination by forming CO. For example, we have experimentally demonstrated a significant reduction of Dit by employing high-temperature thermal oxidation with a rapid heating furnace [1]. However, such approach seems to bring a serious drawback such as defect formation in the surface region of SiC, experimentally detected by a lattice distortion in the beneath of SiO2 after high-temperature oxidation [2]. One of the possible reasons for such deterioration would be an invasion of activated oxygen atoms into the surface region of SiC [3]. A possible approach to avoid such drawback of high-temperature oxidation process would be utilizing H2O vapor for the formation of SiO2/SiC interface at relatively lower temperature while avoiding the damages on SiC surface [4], since H2O oxidation was found to be advantageous to remove CO more efficiently than O2 oxidation even at low temperature.On the other hand, another approach to passivate SiC surface is the surface nitridation technique, which is the most common way in industry to fabricate SiC MOS interface typically achieved by high-temperature annealing in NO gas [5]. Nitridation can replace the topmost C sites with N without inducing significant distortion in the SiC surface structure, to suppress the C-related defect formation at the interface. The advantage of this reaction is that it proceeds self-limited manner and N atoms are introduced only on the topmost surface of SiC. Note that NO gas triggers the surface nitridation by removing the surface C atoms in the form of CO by oxidation. Actually, a very similar reaction occurs even when SiC is annealed in N2 [6] ambient with a slight addition of O2. We experimentally found that the surface N density saturated with different values when we employed various N2+O2 atmosphere with different O2 concentration. Therefore we setup a simple model to describe the saturation behavior, which is determined by the balance between the rate of N uptake (N+) and the rate of N desorption (N‒) mainly due to the oxidation reaction [7]. This model was found to represent the time-dependent change of surface N density well, by assuming that N+ remained constant during the reaction and N‒ was proportional to both the reaction rate of interface oxidation and the surface N density [8]. Based on this simplified model, it is possible to design a process to tune the N density. By choosing appropriate temperature and oxygen partial pressure we can increase N density at the surface to minimize the interface trap density. Further improvement of surface N density would be achieved by further controlling of the blance between N uptake and N desorption reactions.As we have discussed so far, the role of materials science to clarify the interface phenomena is significantly important to achieve a further improved SiC MOS interface characteristics for the next generation SiC power MOSFET process technology. [1] R. Kikuchi and K. Kita, Appl. Phys. Lett. 105, 032106 (2014).[2] A. D. Hatmanto and K. Kita, Appl. Phys. Express 11, 011201 (2018).[3] A. D. Hatmanto and K. Kita, Jpn. J. Appl. Phys. 59, SMMA02 (2020).[4] H. Hirai and K. Kita, Appl. Phys. Lett. Appl. Phys. Lett. 113, 172103 (2018).[5] J. Rozen et al., J. Appl. Phys. 105, 124506 (2009).[6] A.Chanthaphan et al., AIP Adv. 5, 097134 (2015).[7] T. Yang and K. Kita, Jpn. J. Appl. Phys. 61, SC1077 (2022).[8] T. Yang and K. Kita, SSDM 2023, Chiba.

Establishing the nature of kinetic effects of the high-temperature oxidation (combustion) process of some liquid organic matters by acoustic radiation

In this article, the results of the study on the physicochemical characteristics of some liquid organic matters on the kinetics of their high-temperature oxidation (combustion) were presented for the first time. These results were obtained by the method of acoustic emission spectrum from heat source. The research results of the amplitude-time characteristics (until cessation of combustion completely) and the frequency response functions (in a given frequency range) of oxidation (combustion) process of liquid organic matters showed that there are following unambiguous dependences: 1) the dependences of the number of the amplitude maximum of the frequency and time spectrum in a given frequency range, as well as of the fractal dimension of the received acoustic signal on the number of carbon atoms in the carbon frame of organic matters and their molar mass; and 2) the dependences of the time of beginning of the combustion (ignition) of primary cloud of organic matters vapors and the final combustion time of the primary cloud of organic matters vapors on the number of carbon atoms in the carbon frame of the organic matters and their partial vapor pressures. The practical aspect of using the results obtained is dictated by the need to develop standard samples of amplitude-time and amplitude-frequency characteristics, depending on the physicochemical and combustible properties of the organic matters. This is necessary for the data bank of the acoustic emission monitoring system to establish a fire hazardous state and make anti-crisis decisions at critical infrastructure facilities.

The Preparation and Properties of Ni2Al3 Intermetallic Compound Coating

In this work, a Ni2Al3 intermetallic compound coating was prepared on 45 # steel by combining methods of low-pressure cold spray and heat treatment. Firstly, powders mixed with Ni powders, Al powders, and Al2O3 powders as a mass ratio of 20:6:4 were sprayed on surface of 45 # steel by low-pressure cold spraying technology to prepare a Ni-Al pre-coating. Subsequently, the pre-coating was annealed at 570 °C in an argon atmosphere for 12 h to obtain the Ni2Al3 intermetallic compound coating. The composite coating was characterized using TEM, SEM, and XRD. High temperature oxidation performance of the composite coating was analyzed by isothermal oxidation tests conducted at 600 °C in air atmosphere for 96 h. The results show that the composite coating is composed of Ni2Al3 phase. Under a high-temperature oxidation environment, a protective oxide film composed by Al2O3 and NiO was formed on the coating surface, which resulting in a superior high-temperature oxidation resistance compared to 15CrMo heat-resistant steel. The mechanism of the Ni2Al3 coating resistance to high-temperature oxidation is that an oxide film mainly composed of Al2O3 and NiO formed on the surface during the high-temperature oxidation process; this oxide film can effectively resist oxidation and protect the substrate material from oxidation at a high temperature of 600 °C.

MORPHOLOGY OF Ni-TiN/Si3N4 COMPOSITE COATINGS AT HIGH-TEMPERATURE OXIDATION

Electrodeposited nickel coating has excellent physical and mechanical properties, however it does not withstand to high temperature oxidation for long time. The addition of nitride phase within the nickel based coating improve the oxidation resistance through dense surface morphology improvement. A preliminary study was performed to investigate the high temperature oxidation behavior on the coating morphology after exposed at high temperature. The Ni-TiN/Si3N4 composite coatings deposited at electrodeposition temperature of 35 ℃, 40 ℃ and 50 ℃. The electrolyte consists of 0.17 M NiCl2.6H2O, 0.38 M Ni2SO4.6H2O, 6 g/L TiN, 0,6 g/L Si3N4, 40 g/L H3BO3, 0,6 g/L Sodium Dodecyl Sulfate (SDS). High temperature oxidation process on the samples was performed by heating at temperature of 700 ℃ for 2 hours within air conditions. The morphology and composition samples were characterized by using SEM/EDS. In general, the result showed that the morphology of Ni-TiN/Si3N4 composite coatings became rough due to the oxidation process. Elements coating such as Ni, Ti, Si and N were disappeared after the oxidation process due to the outward diffusion process.

Effect of oxidation on the combustion flame characteristics of Jatropha biodiesel

This study investigated the effect of oxidation on the pyrolysis and combustion flame performance of Jatropha biodiesel. To analyze the escape characteristics of multi-component gas products during the pyrolysis and high-temperature oxidation processes of fresh and oxidized Jatropha biodiesel, the TG-FTIR-MS combined system was employed. In addition, various analytical equipment such as an OH-PLIF system, a flue gas analyzer, a spectral analyzer, and a transmission electron microscope were employed to examine the laminar premixed combustion flame and pollutant emissions of Jatropha biodiesel before and after oxidation. The results demonstrate that oxidation exhibits a nonlinear effect on the thermal decomposition of Jatropha biodiesel. Notably, the reaction activation energy exhibits an initial increase and followed by a decrease. Moreover, an increased oxidation degree led to a reduction in the activation energy of the high-temperature oxidation reaction of Jatropha biodiesel, without considerably affecting the total weight loss temperature. Furthermore, the peak temperatures of DTG and DSC exhibited a minor decrease. The production of C2, CH, and OH free radicals in the combustion flame of oxidized Jatropha biodiesel increased, along with an elevation in the spectral intensity of carbon smoke. With an increase in the degree of oxidation, the CO emission concentration from the combustion of Jatropha biodiesel decreased gradually from 75 mg/m3 to 36 mg/m3 after 6 h of oxidation. Additionally, NOx emissions gradually increased from 131 mg/m3 to 186 mg/m3 after 6 h of oxidation, and the particle size of carbon smoke exhibited a reduction of 28%.

Effect of refractory element addition on high temperature oxidation process of complex concentrated alloy coatings

The sluggish diffusion effect of complex concentrated alloys (CCAs) affords them considerable application potential in the field of high temperatures. In this study, the role of refractory elements in the high temperature oxidation process of denary complex concentrated alloy coatings (CCACs, namely NiCoCrFeAl0.8Si0.1(MoNbTaW)x, where x is 0.025, 0.05, 0.1 and 0.15) prepared via laser cladding was investigated. Four groups of the CCACs with different refractory contents were subjected to 100 h of high-temperature oxidation experiments, and the oxidation products and microscopic characteristics of the samples were observed via XRD and SEM, respectively. Atomic-scale characterisation and analysis of the oxidised samples were performed using TEM and XPS technology to explore the diffusion behaviour of elements in the high-temperature process. Results indicate that the solid solution limit of the CCACs is obtained by regulating the topological instability of the lattice matrix via the addition of refractory elements. Consequently, when 0.1 > x > 0.025, the coating is a body-centred cubic (BCC) + face-centred cubic (FCC); when x = 0.1, the coating maintains a single-phase FCC structure; and when x > 0.1, the coating changes to an FCC + BCC duplex structure. The x0.1 group exhibits the smallest relative strain among all coatings, which is conducive to maintaining the structural stability of the face-centred cubic at high temperatures and delaying atomic migration within the lattice. Furthermore, the oxidation kinetics curve of the CCACs with a single- phase FCC exhibits low Kp values. In a single- FCC lattice, the atom diffusion rate through volume slows down and grain boundary diffusion decreases. Considering the Weibull modulus for the hardness statistical value after coating oxidation, the modulus of single-FCC phase CCACs is also higher than others. This study has the potential to contribute to the application of high-temperature thermal protection for CCACs.

Characterization of surface coarse-grained structure and improved corrosion resistance for Zr-4 alloy at high temperature

A surface coarse-grained structure (SCGS) layer is introduced in Zr-4 alloy after surface mechanical rolling treatment and then vacuum annealed at 800 ℃. The microstructures and textures of SCGS is characterized by Electron Backscattered Diffraction, and grains orientation are analyzed in detail by Inverse Pole Figure and Pole Figure. The corrosion tests of the Zr-4 alloy with SCGS layer and as-received were carried out at 360 ℃/18.7 MPa in water and in steam at 700–800 ℃, respectively. The coarse grain in SCGS layer is 10 times larger than that of as-received samples and has <101¯0> preferred orientation in cross section of cylindrical samples. The weight gain of the SCGS specimens is lower than that of the as-received specimens at high temperatures. As for corrosion in steam at 700 ℃ for 1 hour, the weight gain of SCGS sample is 40% less than that of the as-received sample. The high temperature oxidation process is dominated by the diffusion of O2− along the grain boundaries. The grain boundary density of the SCGS layer is six times less than that of the as-received specimens, which reduces the grain boundary diffusion channels for oxygen ion, and improves corrosion resistance of Zr-4 alloy at high temperature.

Copper and nickel-based oxides delicately tailored via galvanic reaction as electrocatalyst for solid-state direct urea fuel cell

The sluggish kinetics of urea oxidation reaction (UOR) critically restrict the prevalence of direct urea fuel cell (DUFC), utilizing electrolyte containing urea/urine. In this work, the copper and nickel-based composite oxides are prepared by meticulously controlling the galvanic reaction of copper ion to metallic nickel and the high-temperature oxidation process. Based on a systematic electrochemical characterization of the catalyst, the as-fabricated nano-architectures are optimized toward UOR performance, showing a low potential of 1.39 V vs. RHE to drive 100 mA cm−2 in alkaline solution. The button-like DUFCs configuration of as-developed catalysts exhibits a maximum power density of 1.19 mW cm−2. Furthermore, the DUFCs assembled with bio-urine, including men, dogs, cats, and rats as electrolytes without further purification, show a similar voltage. These findings open up a direction to convert bio-waste into treasure.

In situ determination of high-temperature oxidation evolution using micro-pillar array and scanning probe microscopy

Understanding the chemo-mechanics during oxidation is of great importance for designing novel countermeasures for materials protections. However, it is yet challenging to accurately measure the coupled mechanical stress/strain components at micro-/nanoscale. In this work, we propose a novel method to combine surface markers (SiO2 micro-pillars) and high temperature scanning probe microscopy (HTSPM) for quantifying the growing oxide thickness, while mapping the local displacement and strain fields at the surface of a nickel-based alloy during high temperature oxidation. The proposed method displays great potential in quantitatively mapping the non-uniform oxide distribution, providing a novel approach to investigate the high-temperature oxidation process.

Optimizing In Situ Combustion with Manganese (II) Oxide Nanoparticle-Catalyzed Heavy Oil Oxidation

The combustion front is a crucial parameter in determining the efficiency of in situ combustion techniques during enhanced oil recovery. Nowadays, catalytic systems are widely believed to be an efficient tool to stabilize the combustion front. This study aimed to investigate the synthesis and catalytic activity of manganese (II) oxide nanoparticles in the high-temperature oxidation of heavy oils. The synthesis and catalytic activity of manganese (II) oxide nanoparticles in the high and low-temperature oxidation regions of heavy oil were investigated in this study. The obtained nanoparticles were characterized and studied by using X-ray powder diffraction (XRPD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), thermogravimetric analysis (TG), nitrogen adsorption and desorption measurements, and differential scanning calorimetry (DSC) thermal analysis combined with the Kissinger isoconversional method. The obtained results showed that the synthesized nanoparticles had an average size of 17 ± 4 nm and a specific surface area of 38.2 ± 0.1 m2 g−1, with a pore size distribution of ~8 nm. The low and high-temperature oxidation processes’ activation energies were found to be 98.9 ± 0.7 kJ/mol and 151.9 ± 0.6 kJ/mol, respectively, in the presence of nanoparticles. However, these parameters were found to be equal to 110.1 ± 1.8 kJ/mol and 142.8 ± 8.3 kJ/mol, respectively, in the absence of nanoparticles. These data were processed further by calculating the corresponding reaction rates. The obtained results indicated that the rate of heavy oil oxidation was higher in the presence of the synthesized nanoparticles, which could play a critical role in stabilizing the combustion front in the in situ combustion process.

High temperature oxidation behavior of Fe–3.0%Si steel with non-equilibrium reaction

The phase formation-transition process and microstructure evolution of Fe–3%Si steel oxide layers were systematically studied during the high-temperature oxidation process with oxidizing atmosphere when annealed at 1000–1240 °C for 200 min. The micromorphology, oxidation mechanism and crystal structure stability were characterized and discussed combining with the XRD, FESEM and XPS technology. The oxidized scale shows more and more complex multiple layers structure including single layer, double layers and three layers with the increasing of annealing temperature, which attributes to the diffusion effect and oxidation reaction oxygen anions and metal cations. The formation of SiO2, FeO and Fe2SiO4 layer also could inhibit the oxidation reaction of matrix. The oxidized scale mainly shows a single layer structure of Fe2O3 when annealed at 1000–1080 °C, which is easy to peel off from matrix. It shows a double oxide layers structure when annealed at 1080–1120 °C, the loose outer layer contains Fe2O3, and the grid inner layer contain SiO2, FeO and Fe2SiO4 compounds. It shows an outermost, intermediate and inner three layers structure when annealed at 1160–1240 °C. The outermost layer is Fe2O3, the main phases of intermediate layer are FeO and Fe2SiO4 compounds as well as some SiO2 particles, and the inner layer (joint layer) is SiO2.

Effect of Ni and Fe elements on microstructure and high temperature oxidation behavior of laser cladding aluminum bronze coating

In this work, two kinds of aluminum-bronze coatings were successfully prepared on 316 stainless steel substrate by laser cladding technology. The changes of microstructure and high temperature oxidation behavior of pure aluminum bronze laser cladding layer before and after adding Ni and Fe elements were studied and compared. The results show that a certain amount of κ phase and Fe–Cr phase are constituted in the modified coating with the addition of Ni and Fe elements, which refines the structure and grains. The main components of the oxide layer of the two coatings are Al2O3. In the high temperature oxidation process, both two coatings experienced the formation, spallation, and recovery of an oxide film. The time to form a stable oxide film on the surface of the modified coating is significantly shorter than that of the original coating. As a result of the formation of fine and dense oxide particles on the modified coating's surface, the stability and internal stress resistance of the oxide film is superior. Under the condition of 1000 °C oxidation for 100 h, the oxidation film thickness and oxidation rate constant (kp) of the modified coating are about 0.88 and 0.79 times of that of the original coating. The addition of Ni and Fe can greatly enhance the laser cladding aluminum bronze coating's resistance to high-temperature oxidation.

High-temperature oxidation induced layering process for Si–C–B–N ceramic fibers with SiC nanograins

High-temperature oxidation resistance is important for Si–C–B–N ceramic fibers when reinforcing ceramic matrix composites with superior reliability and faulting tolerance. At present, few studies have investigated on the high-temperature oxidation behavior of Si–C–B–N fibers, limiting their further applications. In this work, we analyzed the high-temperature oxidation process of Si–C–B–N ceramic fibers with SiC nanograins (SiBCN-SiCn fibers) at 1000–1500 °C in air. SiBCN-SiCn fibers stated to be oxidized at 1000 °C, with the formation of thin oxide layer. After oxidizing at 1300 °C, obvious oxide layer that mainly consisted of amorphous SiO 2 could be detected. Further oxidizing at 1500 °C caused the thickness increment of oxide layer, which could inhibit the oxidation products (CO, N 2 ) to release away from the fibers. The remained CO and N 2 may react with SiC nanograins to form SiO 2 and graphite-like g-C 3 N 4 , causing the formation of additional transition layer. Our finding may support useful information for the applications of SiBCN-SiCn fibers under harsh environment.

Directional growth of quasi-2D Cu2O monocrystals on rGO membranes in aqueous environments.

The preparation technology of unconventional low-dimensional Cu2O monocrystals, which exhibit specific crystal planes and present significantly unique interfacial and physicochemical properties, is attracting increasing attention and interest. Herein, by integrating a high-temperature oxidation process under vacuum and a pure-water incubation process under ambient conditions, we propose the self-assembled growth and synthesis of quasi-two-dimensional Cu2O monocrystals on reduced graphene oxide (rGO) membranes. The prepared Cu2O crystals have a single (110) crystal plane, regular rectangular morphology, and potentially well conductivity. Experimental and theoretical results suggest that this assembly is attributed to the pre-nucleation clusters aggregation and directional attachment of Cu and O on the rGO membranes in aqueous environment and cation-π interactions between the (110) crystal plane of Cu2O and rGO surface. Our findings offer a potential avenue for the discovery and design of advanced low-dimensional single-crystal materials with specific interfacial properties in a pure aqueous environment.

Influences of Al concentration and Nb addition on oxidation behavior of Ti2AlC ceramics at high temperatures

ABSTRACT A titanium aluminum carbide, Ti2AlC, which is classified among MAX phase ceramics, was studied as a potential candidate for various mechanical components used in high-temperature applications. The impact of its chemical composition on its high-temperature oxidation process was determined. Ti2AlC powders with various Al contents and with or without Nb addition were synthesized via a conventional reaction technique followed by 16 h of annealing in vacuum at 1300°C. The synthesized Ti2AlC powders were consolidated by means of 15 min of pulsed electric current sintering at a die temperature of 1300°C in vacuum under a uniaxial pressure of 30 MPa. In the presence of an aluminum reservoir in the form of TiAl3, Ti2AlC has excellent resistance against high-temperature oxidation. The promising results concerning the addition of Nb to TiAl provided the rationale for a similar modification of Ti2AlC. The results of oxidation tests on Nb-doped Ti2AlC likewise showed excellent oxidation resistance. Alloying with Nb can improve the oxidation resistance of Ti2AlC with low Al content, allowing the formation of a protective Al2O3 scale and inhibiting the growth of TiO2.

The road to commercialisation of an unutilised Cyclopia species for herbal tea production – the case of Cyclopia pubescens

• C. pubescens was shown to be suitable for production of honeybush herbal tea. • Its sensory profile is similar to that of commercially-cultivated C. subternata . • Other quality parameters were similar to that of C. subternata and C. genistoides . • High-temperature oxidation reduces the xanthone content more than 70%. Cyclopia pubescens is an unutilised species that could potentially be used for production of honeybush tea, if general quality criteria for the herbal tea product could be met. This species is at risk of extinction in the wild, but if suitable for production of honeybush herbal tea, its cultivation could be stimulated. Cyclopia pubescens shoots were used to produce conventional (oxidised) honeybush tea and its quality parameters for the infusion were compared with those of the commercially-cultivated Cyclopia species, C. subternata and C. genistoides . Oxidised C. pubescens had a similar sensory profile to that of C. subternata, displaying ‘woody’, ‘fynbos-floral’ ‘fynbos-sweet’ and ‘sweet spice’ aromas and a slightly sweet taste. The soluble solids concentration, colour and turbidity of the infusions, prepared from the herbal teas of the three species, were similar. The high-temperature oxidation process, essential for the development of the sought-after sensory profile of honeybush tea, reduced the phenolic concentration of the C. pubescens infusions, in particular, the concentration of mangiferin and isomangiferin decreased > 70%. Despite this reduction, C. pubescens infusions would contribute ≥ 8 mg/L to the dietary intake of each of these xanthones. Cyclopia pubescens , thus, passed the first hurdle for commercial herbal tea production, but cultivation would be required as wild-harvesting of this species is not an option.