Oxidation Protective Ability Research Articles

The potency of hydrophobic modification of alginate for a self-assembly matrix in fish oil encapsulation

To act as an emulsifier and a matrix for fish oil encapsulation, alginate is required to be modified due to its hydrophilicity. The purpose of this study was to modify alginate using dodecenyl succinic anhydride (DSA) under pH-controlled conditions and to apply it for stabilizing emulsion and encapsulating fish oil. The modification that followed the first-order reaction improved the hydrophobic properties of alginate as shown by the reduction of surface tension but improving the water contact angle, with CMC of 0.18 mg/l. A higher concentration of modified alginate was better in stabilizing fish-oil emulsion than the native one, as supported by the results of zeta potential, viscosity, and droplet size of the emulsion. Freeze-dried particle of this modified alginate emulsion showed better encapsulation efficiency and oxidation protection ability. Thermal properties of alginate were changed after hydrophobic modification and oil encapsulation. The freeze-dried particles of this modified alginate emulsion showed better encapsulation efficiency and protection ability. This study confirmed the protective ability of the modified alginate using DSA as an oil-based active ingredient encapsulant.

Long-term oxidation of MoSi2-modified HfB2–SiC–Si/SiC–Si coating at 1700°C

ABSTRACT Slurry impregnation and gaseous Si infiltration were effectively used to produce compact MoSi2-doped Si–HfB2–SiC/Si–SiC (HMSS/SS) coatings with a thickness of 250 μm to protect carbon fibre reinforced carbon (Cf/C) composites from oxygen corrosion at 1700°C. The HMSS/SS coating obtained with a mosaic structure makes it possible to protect Cf/C composites at 1700°C for 276 h and the mass reduction is only 0.99%. The pinning effect of the embedded hafnia, the generated MoB together with the Hf, Mo co-doped Si-based glass layer, which successfully prevented the migration of oxygen, was attributed to the superior oxidation protection ability of the HMSS/SS coatings. This work provides a practical method for successfully extending the service life of Cf/C composites in the aerospace industry.

Improved oxidation protective ability of SHS powder-synthesized ZrB2-MoSi2-SiC-Si coating on carbon/carbon composites

ZrB2-MoSi2-SiC-Si coatings were prepared by gaseous silicon infiltration on the carbon/carbon composites, and the powders synthesized by the self-propagating high-temperature synthesis method (SHS) were used as the raw materials to benefit the oxidation protective ability of the coatings. The ZrB2-MoSi2-SiC-Si coatings prepared from commercial powders (CP coated samples) were used as a comparison. After sintering, the structure of the coating prepared with SHS powders is denser than the CP coated sample with a density of 3.5 g/cm3. After 62 h of oxidation tests at 1500 °C, the mass loss of the SHS coated sample was only 0.28 %, which was 32 % lower than that of the CP coated sample. The ability of SHS coatings to exhibit better oxidation protection is attributed to the higher oxidation stability and sintering activity of the SHS powders than that of commercial ones.

Long-term oxidation behaviors of Si-Cr-W multiphase coating on SiC coated C/C composites at 1773 K and 1973 K

To obtain long-term oxidation protection for C/C composites at high temperatures, a dense Si-Cr-W multiphase ceramic coating was prepared on the surface of SiC coated C/C composites by a combined method of slurry brushing, heat treatment and liquid silicon infiltration, which drastically enhanced the oxidation resistance of SiC coated C/C composites at 1773 K and 1973 K in air. The microstructure evolution, phase composition and oxidation behavior of the multiphase coating were analyzed before and after oxidation. Results display that the Si-Cr-W coating with a thickness of ~ 115 µm possessed a dense and uniform multiphase mosaic structure (WSi2, CrSi2, Cr5Si3, SiC and Si). The mass loss of the coated sample was only 1.08 mg/cm2 after oxidation for 325 h at 1773 K in air owing to the formation of the compact compound glass layer (SiO2, Cr2O3 and WO3) acted as an oxygen diffusion barrier. The coating can effectively protect C/C substrate from oxidation for 76 h at 1973 K in air, demonstrating its outstanding high-temperature oxidation protective ability.

Effect of silicon/graphite ratio and temperature on oxidation protective properties of SiC/ZrB2–SiC coatings prepared by pack cementation

To investigate the silicon/graphite ratio and temperature on preparation and properties of ZrB2–SiC coatings, ZrB2, silicon, and graphite powders were used as pack powders to prepare ZrB2–SiC coatings on SiC coated graphite samples at different temperatures by pack cementation method. The composition, microstructure, thermal shock, and oxidation resistance of these coatings were characterized and assessed. High silicon/graphite ratio (in this case, 2) did not guarantee higher coating density, instead could be harmful to coating formation and led to the lump of pack powders, especially at temperatures of 2100 and 2200 °C. But residual silicon in the coating is beneficial for high density and oxidation protection ability. The SiC/ZrB2–SiC (ZS50-2) coating prepared at 2000 °C showed excellent oxidation protective ability, owing to the residual silicon in the coating and dense coating structure. The weight loss of ZS50-2 after 15 thermal shocks between 1500 °C and room temperature, and oxidation for 19 h at 1500 °C are 6.5% and 2.9%, respectively.

Oxidation protection of B4C modified HfB2-SiC coating for C/C composites at 1073–1473 K

B4C modified HfB2-SiC coating for C/C substrate was designed to expand the application of HfB2-SiC based coating in low-medium temperature environment. The oxidation protection behavior of HfB2-SiC based ceramic coatings with and without B4C at 1073, 1273 and 1473 K was tested and analyzed. The experimental results reveal that the oxidative damage of HfB2-SiC coated C/C reduces by over 20% after introducing B4C, which may be due to the protection of borosilicate glass with more suitable viscosity during oxidation. Meanwhile, B4C can improve the oxidation protection ability of HfB2-SiC coating best at 1473 K. And the introduction of B4C can reduce the mass loss of HfB2-SiC coated C/C sample by 77.6% after oxidation for 58 h at 1473 K. The fluidity of glass film becoming better with temperature-rising, and the fluid borosilicate glass layer makes the coated samples have the best anti-oxidation properties at 1473 K among these three temperatures.

Multicomponent (Hf0.25Zr0.25Ti0.25Cr0.25)B2 ceramic modified SiC–Si composite coatings: In-situ synthesis and high-temperature oxidation behavior

High-entropy ceramics, a novel type of multicomponent materials with broad application prospects, have stirred up world-wide interests for over a decade. In the current work, in-situ high-entropy (Hf0.25Zr0.25Ti0.25Cr0.25)B2 ceramic modified SiC–Si (HETMB2-SiC-Si) coating was deposited on carbon/carbon (C/C) composites via gaseous reactive infiltration of Si assisted slurry painting (GRSI-SP) method, to improve the oxidation protective ability of C/C composites at 1973 K. The formation and oxidation mechanisms of the coating was explored by first-principles simulation, experiment and thermodynamic analyses. The coating prepared at 2373 K shows dense mosaic structure filled with HETMB2-rich Si-based multiphase. This coating adheres well with the C/C substrate, which is ascribed to the formed zigzagged SiC–Si transition layer. This coating protected C/Cs from oxidation for more than 205 h at 1973 K. The enhanced oxidation protective ability is mostly ascribed to the subsequently generated compact and stable Hf-Zr-Ti-Cr-Si-O composite oxidation scale. This research will start up novel research ares of developing high-entropy materials modified coatings with improved protective ability under extreme environments.

Fabrication of food-grade Pickering high internal phase emulsions (HIPEs) stabilized by a dihydromyricetin and lysozyme mixture

This study evaluated the feasibility of fabricating food-grade HIPEs using a dihydromyricetin and lysozyme mixture. The effects of the oil phase volume fraction (φ), composition (lysozyme:dihydromyricetin, k), and addition amount (w) of the mixture on the formation and properties of the HIPEs were analyzed. Then, the interactions of dihydromyricetin and lysozyme were investigated. The results indicated that when w was 0.4%, HIPEs with φ value of 90% could be obtained. Furthermore, the k also affected the microstructure, mechanical properties, oil oxidation, and lutein protection ability of the HIPEs. However, the presence of dihydromyricetin did not affect lysozyme activity. Both isothermal titration calorimetry and molecular simulations proved that they did not form a typical host–guest complex. But, dihydromyricetin could absorb on the lysozyme surface. Therefore, we speculated that lysozyme and dihydromyricetin particles could overlap and form a 3D network structure to stabilize the HIPEs, which was consistent with the microstructure observations.

Oxidation inhibition behaviors of HfB2‐MoSi2‐SiC oxygen blocking coating prepared by spark plasma sintering

AbstractThe HfB2‐MoSi2‐SiC oxygen blocking coatings were prepared by the spark plasma sintering (SPS) technique, whose oxidation inhibition ability was further strengthened by the pre‐oxidation treatment. The effect of MoSi2 content and pre‐oxidation treatment process on the oxygen blocking ability of the HfB2‐MoSi2‐SiC coating at 1973 K were conducted. After SPS, for the HfB2‐MoSi2‐SiC coatings with 20 wt%, 40 wt%, and 60 wt% MoSi2, the relative density of the coatings are 92.6%, 93.9%, and 85.6%, respectively. Owing to the enhanced compactness of the coatings, increasing MoSi2 content can significantly improve the protection efficiency of the coatings during the activation oxidation stage. However, due to the increased formation of gaseous by‐products during the inerting oxidation stage, excessive MoSi2 weaken the oxidation inhibition ability of the coatings. The sufficient dispersion of Hf‐oxides nanocrystals in the glass layer conduces to enhance the oxygen blocking ability of the glass layer, making the 40HfB2‐40MoSi2‐20SiC coating present the best oxidation protective ability. The pre‐oxidation treatment at 1773 K conduces to form the steady glass layer with fewer defects at the cost of a lower oxidation consumption of the coating, which enhanced the protection efficiency of the coating from 96.9% to 99.8% and reduced the oxygen permeability from 0.13% to 0.028%.

Influence of MoSi2 on oxidation protective ability of TaB2-SiC coating in oxygen-containing environments within a broad temperature range

TaB2-SiC coating modified by different content of MoSi2 was fabricated on graphite substrate with SiC inner coating by liquid phase sintering to elevate the anti-oxidation capability of the TaB2-SiC coatings. As compared to the sample with the TaB2—40wt%SiC coating, the coating sample modified with MoSi2 exhibited a weight gain trend at lower temperatures, the fastest weight loss rate went down by 76%, and the relative oxygen permeability value reduced from about 1% to near 0. More importantly, the large amount of SiO2 glass phase produced over the coating during oxidation was in contact with the modification of MoSi2, which was proved to be beneficial to the dispersion of Ta-oxides. A concomitantly formed continuous Ta-Si-O-B compound glass layer showed excellent capacity to prevent oxygen penetration. However, when the TaB2 content was sacrificed to increase the MoSi2 content, the relative oxygen permeability of the coating increased instead of decreased. Thus, on the basis of ample TaB2 content, increasing the MoSi2 content of the coating is conducive to reducing the relative oxygen permeability of the coatings in a broad temperature region.

Constructing self-supplying Al2O3-Y2O3 coating for the γ-TiAl alloy with enhanced oxidation protective ability

The failure of the ceramic coating usually occurs at high temperatures due to the appearance of the cracks, which are caused by the accumulation of thermal stress. Here a self-supplying Al2O3-Y2O3/Al-Y coating was prepared by magnetron sputtering on the γ-TiAl alloy. After oxidation, the coating cross-section showed that three layers were formed, and the main phases consisted of Al2O3, Y2O3, and Y3Al5O12 (YAG). The isothermal oxidation test revealed that the coating efficiently prevented γ-TiAl alloy from degeneration for 100 h with a mass gain of 0.34% compared to the uncoated sample with a mass loss of 1.51% for 60 h at 950 °C. The study focused on the microstructure evolution of the coating during the oxidation process. We found that the improvement of oxidation resistance primarily could be attributed to three reasons: 1) the Y2O3 phase was more stable than Al2O3 and TiO2 at elevated temperature. 2) Al-Y layer, as the intermediate layer, can compensate for the element consumption of the ceramic layer caused by oxidation. 3) the Al3Ti layer efficiently suppressed the outward diffusion of Ti.

Oxidation behavior of SiC-HfB2-Si coating on C/C composites prepared by slurry dipping combined with gaseous Si infiltration

An effective monolayer SiC-HfB2-Si coating for long-time oxidation protection of C/C composites was designed and prepared by a combined technique of slurry dipping and gaseous Si infiltration (SD + GSI). This coating is dense and adheres well with the C/C substrate, which is ascribed to the formed zigzagged SiC transition layer. After oxidation at 1773 K in static air for >538 h, the mass loss of SiC-HfB2-Si coated samples is only 0.69%. By thermodynamic calculation, the oxidation process of SiC-HfB2-Si coated samples is mainly controlled by oxygen diffusion, and the stable oxidation products are HfO2 + B2O3 + SiO2 + CO. The excellent oxidation protective ability is mostly attributed to the formation of a composite Hf-Si-O glass layer on the coating surface to heal cracks and pores.

Oxidation protection of aluminum metaphosphate coating prepared by cathodic electrochemical treatment for graphite

Abstract In order to provide a short-term oxidation protection system for graphite at high temperature, an aluminum metaphosphate coating was prepared on the surface of graphite by cathodic electrochemical treatment, and its oxidation protective ability was investigated using an isothermal oxidation test. The microstructure, chemical composition, and phase components of the aluminum metaphosphate coating were respectively analyzed through scanning electron microscope, dispersive X-ray analysis, and X-ray diffraction. The results showed that aluminum metaphosphate coating with a thickness of about 24 μm provides good oxidation resistance for graphite at 1250 °C, and it reduces the oxidation rate of graphite in a 5-h period by a factor of two. The good oxidation protective ability of the as-prepared coating at 1250 °C is related to the formation of a layer consisting of aluminum metaphosphate and aluminum orthophosphate phases.

High temperature anti‐oxidation behavior of in situ and ex situ nanostructured C/SiC/ZrB2‐SiC gradient coatings: Thermodynamical evolution, microstructural characterization, and residual stress analysis

AbstractNanostructured C/SiC/ZrB2–SiC oxidation protective gradient coating was prepared by a two‐step reactive melt infiltration method. In order to reduce production cost, ZrB2 phase was synthesized by the in situ reactive that included low‐cost ZrO2 and B2O3 powders as raw materials. High‐temperature oxidation behavior of coatings was evaluated by isothermal oxidation test at 1773 K in air for 10 hours. Thermodynamical behavior of the coatings at various temperatures during oxidation test and coating process was predicted by HSC Chemistry 6.0 software. Compressive residual stresses of 36.9 MPa and 41 MPa were calculated for in situ and ex situ coatings by Williamson‐Hall method. After 10 hours of isothermal oxidation at 1773K, in situ and ex situ coatings showed 12.84% and 15.69% of weight losses with oxidation rates of 1.87 × 10−2 g cm−3 h−1 and 0.91 × 10−2 g cm−3 h−1, respectively. These results indicated that the oxidation protection ability of the coating produced by the in situ method was very close to ex situ coating.

A novel oxidation protective SiC-ZrB2-ZrSi2 coating with mosaic structure for carbon/carbon composites

An oxidation protective SiC-ZrB2-ZrSi2 coating with mosaic structure was designed to improve the oxidation resistance of carbon/carbon composites by a combined method of hydrothermal electrophoretic deposition and pack cementation. The phase composition, microstructure, thermal shock resistance and oxidation protective ability of the coating were investigated. Results show that the as-prepared SiC-ZrB2-ZrSi2 coating was dense and crack-free. After 50 thermal cycles between 1773 K and room temperature, the weight gain of the coated samples was 15.2 g m−2. The weight loss of the coated samples was only 15.6 g m−2 after oxidation in air at 1773 K for 580 h. The good thermal shock resistance and oxidation protective ability of the coated samples were attributed to the synergetic effect of the glass layer protection, compressive stress restraint and pinning role of ZrSiO4 inlaid phase.

Constructing self-healing ZrSi2-MoSi2 coating for C/C composites with enhanced oxidation protective ability

Cracks are fatal defects of ceramic coatings for carbon/carbon (C/C) composites, through which oxygen will severely destroy the substrate at ultra-high temperature environments. Therefore, the coating materials with rapid self-repairing ability should greatly improve their service stability. Here ZrSi2-MoSi2 coating was designed and fabricated by supersonic plasma spray on SiC coated C/C composites. Results show that it has narrower surface cracks and better self-healing ability at 1450 °C than pure MoSi2 coating. Moreover, it efficiently protects C/C composites from oxidation for 42 h with a mass gain of 1.89% compared to MoSi2 coating with a mass loss of 4.6% for 38 h at 1450 °C. The improvement of the self-healing ability and oxidation protective performance primarily owes to three reasons: 1) the preferential oxidation of ZrSi2 to rapidly form ZrO2/ZrSiO4 particles to reduce the formation of cracks. 2) Low viscosity SiO2 phase to completely heal the cracks. 3) Protective SiO2 layer pinned by ZrO2/ZrSiO4 particles to restrain re-cracking during cooling.

SiC nanowire-induced fabrication of fine-grained and highly-density SiC coating by pressure-less reactive sintering

Fine-grained and high-density SiC coating was fabricated on carbon materials by incorporating SiC nanowires during the pressure-less reactive sintering for the first time. The grain size, relative density, and fracture toughness of the as-fabricated coating are 1.5 ± 0.6 μm, 95%, and 5.03 ± 0.73 MPa m1/2, respectively, resulting in a good oxidation protective ability, which can efficiently protect carbon materials from oxidation at 900 °C for more than 70 h or at 1500 °C for more than 90 h. The formation of such microstructure may be associated to the increasing nucleation rate resulting from the microstructure evolution and phase transformation of SiC nanowires during the sintering process.

Preparation of TaB2-SiC oxidation protective coating for carbon materials by liquid phase sintering

To control the microstructure and amounts of TaB2 phase in the TaB2-SiC coating, a novel liquid phase sintering method was developed on the basis of in-situ reaction method to prepare the TaB2-SiC coating, which includes synthesis of TaB2 powders and further preparation of TaB2-SiC coating. With Ta2O5, B2O3 and C employed as raw materials, hexagonal TaB2 powders were prepared by carbothermal reduction method at 1500 °C, whose mean particle size is 491 nm. The TaB2, SiC, C powders, and the low melting point phases Si and silica sol were used to prepare the TaB2-SiC coating by liquid phase sintering at 2373 K. The thickness of the coating is about 350 µm. Compared with the SiC coating, the weight loss of the samples modified by TaB2 decreased from 17.7% to 11.8%, and the average weight loss rate of the fastest weightloss zone reduced from −6 × 10−3 mg cm−2 s−1 to −5 × 10−3 mg cm−2 s−1. During oxidation, the Ta-oxides would gradually dissolve in the silicate glass to form Ta-Si-O glass ceramics with dendritic structure, which significantly improved the toughness and stability of the glass layer. The Ta-Si-O glass ceramics possesses the ability of sealing and arresting the microcracks, which can enhance the oxidation protective ability of the coating.

Oxidation protective ZrB2-MoSi2-SiC-Si coating for graphite materials prepared by slurry dipping and vapor silicon infiltration

In order to protect graphite materials from oxidation, a dense single layer ZrB2-MoSi2-SiC-Si coating was for the first time prepared on the surface of graphite substrate by slurry dipping and vapor silicon infiltration process. The phase compositions and microstructure of the prepared coating were analyzed by XRD and SEM. The isothermal thermal cycle oxidation tests were conducted at 1600 °C in air. The results showed that the prepared coating exhibited excellent oxidation protection ability, after oxidation for 150 h, the weight loss was only 0.21%, which was considered to be the depletion of the outer coating and the appearance of defects in the coating. The excellent protection ability was attributed to the dense structure of the coating and the formation of thick oxide layer with immiscible ZrO2 on the outer surface of coating. Two layers could be observed in the coating after oxidation, namely, glassy oxide layer and ZrB2-MoSi2-SiC-Si layer. After thermal shock between 1200 °C and room temperature for 100 cycles, the weight gain was 0.11%. The good thermal shock resistance could be ascribed to the gradient thermal expansion coefficients of different components in the coating and the C/SiC interface layer between the substrate and coating.

Oxidation protective MoSi2-SiC-Si coating for graphite materials prepared by slurry dipping and vapor silicon infiltration

A novel kind of dense MoSi2-SiC-Si coating was prepared on the surface of graphite substrate by slurry dipping and vapor silicon infiltration process. Mo-SiC-C precoating was fabricated via slurry dipping method, and then MoSi2-SiC-Si coating with dense structure consisting of Si, MoSi2 and SiC was obtained by vapor silicon infiltration process. The isothermal oxidation tests at temperatures from 800 to 1600°C and TGA test from room temperature to 1500°C were used to evaluate the oxidation resistance ability of the MoSi2-SiC-Si coating. The experimental results indicate that the prepared coating has good oxidation protection ability at a wide temperature range from room temperature to 1600°C. Meanwhile, the oxidation of the coated samples is a weight gain process at temperatures from 800 to 1500°C due to the formed SiO2 layer on the surface of coating. After oxidation for 220h at 1600°C, the weight loss of the coated sample was only 0.96%, which is considered to be the excessive consumption of the outer coating and the appearance of defects in the coating. Two layers can be observed in the coating after oxidation, namely, SiO2 layer and MoSi2-SiC-Si layer.