RESUMEN
In this study, the prestressed coating reinforcement method was employed to create kyanite-coated zirconia toughened alumina (ZTA) prestressed ceramics. Due to the mismatch of the coefficient of thermal expansion (CTE) between the coating and substrate, compressive residual stress was introduced in the coating. The effects of compressive residual stress on the mechanical properties of ZTA have been demonstrated. Results show that the flexural strength of the kyanite-coated ZTA ceramics improved by 40% at room temperature compared to ZTA ceramics. In addition, the temperature dependence of mechanical properties has also been discussed. And the results show that the reinforcement gradually diminished with increasing temperature and eventually disappeared at 1000 °C. The modulus of elasticity of the material also exhibits a decreasing trend. Furthermore, the introduction of the prestressing coating enhanced the thermal shock resistance, but the strengthening effect diminished as the temperature increased and completely disappeared at 800 °C.
RESUMEN
It is predicted that the thickness of a coating has major effects on a substrate in terms of mechanical and thermal properties. In this study, an Al2O3-ZrO2-SiO2 slurry was prepared as a coating material, which formed an alumina-zirconia-mullite composite coating after sintering. The alumina-zirconia-mullite composite coating was coated on a zirconia substrate to generate compressive stress in the coating due to the mismatch of the coefficient of thermal expansion (CTE). A series of coated samples with different coating thicknesses from â¼10 µm to â¼200 µm were prepared to investigate the effects of coating thickness. The residual compressive stress, thermal conductivity, CTE, and Young's modulus of the coating material were determined by relative methods, and the flexural strength of the coated and uncoated samples was measured by 3-point bending. The strength of the coated samples was 1362.98 ± 30.29 MPa, which is a 54.07% enhancement compared to the uncoated samples. The thermal conductivity of the coated samples was also increased compared to that of the uncoated samples. For a given thickness of the substrate of 2 mm, there was an optimum thickness of the coating of 90 µm, which showed the greatest strength compared to the other samples. Coatings that were too thin or too thick did not show the best reinforcement. Moreover, the porosity of the coated samples was also determined and discussed in this study. Comparison samples without SiO2 were also manufactured, and their flexural strength and thermal conductivity were found to not be as good as the samples with SiO2.
RESUMEN
Chemical reorganization and interfacial engineering in hybrid nanomaterials are promising strategies for enhancing electrocatalytic performance. Herein, MoO3@zeolitic imidazolate framework-67 (ZIF-67) heterogeneous nanoribbons are designed through coordination assembly. By following heat treatment, a Mo/Mo2C@CoO@NC heterostructure with nitrogen-doped carbon-encapsulated CoO hexagons (CoO@NC) anchored on the Mo/Mo2C jag matrix was fabricated. Notably, through controllable experimental optimization, the as-prepared Mo/Mo2C@CoO@NC heterostructure exhibits numerous active centers (e.g. Mo, Mo2C, CoO, and NC), fully exposed active sites (numerous pores and jagged structures), and abundant heterointerfaces (Mo/Mo2C, Mo2C/CoO@NC, Mo2C/amorphous, and CoO@NC/amorphous), and exhibits good conductivity (localized single-crystal behavior, graphitized carbon). As a result, the as-developed Mo/Mo2C@CoO@NC heterostructures inherit impressive oxygen evolution reaction (OER) performance with an overpotential of only 215 mV at 10 mA cm-2. Furthermore, Mo/Mo2C@CoO@NC heterostructures exhibit excellent stability with a current density retention of 98.4% after 20 h chronoamperometry. This work provides deep insights into chemical reconstructions and tuning heterointerfaces to efficiently enhance the OER activity of heterostructure-based electrocatalysts.
RESUMEN
In this work, the rapid thermal shock behavior of Ti2AlC ceramics was studied using induction heating. The present evaluation method possesses the merits of very rapid heating within tens of seconds and fast quenching in water of less than 0.1 s, removing the shortcomings of traditional thermal shock. For comparison, the samples were also quenched in the air to investigate the thermal shock mechanisms. The results showed that the abnormal shock occurred in the samples when quenching in water, ascribed to the formed oxide layer on the surface of Ti2AlC ceramic inhibited the water penetration into the substrate. The quenched Ti2AlC samples still had a high residual flexural strength above 167 MPa up to 1150 °C, exhibiting promising applications in the high-temperature fields.
RESUMEN
In this work, waterborne epoxy resin and graphene/ZnO (Gr/ZnO) were employed as the matrix and nanofiller to construct composite coatings with enhanced anticorrosive performance. The corrosion protection properties of the coatings were significantly improved by the dispersed Gr sheets, as well as the parallelly assembled ZnO nanoparticles. The most remarkable improvement was achieved by adding 0.04 wt% of Gr and 0.4 wt% of ZnO in the Waterborne Epoxy (WEP) coatings, where the highest impedance was 200 530 Ω cm2 on Gr0.04-ZnO0.4, far more than pure epoxy with 6186 Ω cm2 after 7 days of immersion in electrolytes. Furthermore, the Gr0.04-ZnO0.4 coatings and corresponding corrosion products immersed in a 3.5% NaCl solution for 30 days were also characterized, which could further reveal anticorrosion mechanisms of the graphene modified WEP coatings and the passivated effect of ZnO. Through the mechanism analysis, we also found that ZnO could be employed as the barrier reinforcement to improve the dispersibility of graphene in WEP coatings, and the parallel assembly of graphene occurs spontaneously, leading to remarkable improvement of anticorrosion properties.
