Hydrothermally grown uniform TiO2 coatings on ZrO2 fibers and their infrared reflective and thermal conductive properties

Improving the infrared reflectivity of ZrO₂ polycrystalline fibers is of great benefit to its thermal applications. In the present research, we cast a highly uniform TiO₂ coating with a thickness ranging from dozens to hundreds of nanometers on ZrO₂ fibers by utilizing hydrothermal growth. The coating bonds tightly to the ZrO₂ fibers via Zr–O–Ti chemical linkages, and the thickness of the coating can be tailored by varying the hydrothermal growth time. The TiO₂ coating, acting as a sheath towards electromagnetic radiation, not only reflected light with wavelengths ranging from the visible region to the infrared region and up to 8 μm but also shielded the Raman signals of the ZrO₂ fibers. The present research provides an efficient way to cast controllable and uniform coatings on flexible fiber materials. The obtained ZrO₂ fibers coated with TiO₂ may have applications such as reinforcement for bulk ceramics, thermal barrier coatings, aerogels, etc., thus performing the dual functions of mechanical strengthening and thermal insulation.     

Thermo-physical and mechanical properties of Yb2O3 and Sc2O3 co-doped Gd2Zr2O7 ceramics

Ceramic materials for the thermal barrier coating (TBC) application of Gd₂Zr₂O₇ (GZO), (Gd_0.94Yb_0.06)₂Zr₂O₇ (GYb_0.06Z), (Gd_0.925Sc_0.075)₂Zr₂O₇ (GSc_0.075Z), (Gd_0.865Sc_0.075Yb_0.06)₂Zr₂O₇ (GSc_0.075Yb_0.06Z), and (Gd_0.8Sc_0.1Yb_0.1)₂Zr₂O₇ (GSc_0.1Yb_0.1Z) were successfully synthesized by chemical co-precipitation. The effects of the doping of Sc₂O₃ and Yb₂O₃ on the phases, thermo-physical and mechanical properties of the ceramics were investigated. The results show that both Yb₂O₃ and Sc₂O₃ doping promoted the phase transition of GZO from pyrochlore to fluorite. All the Sc₂O₃-doped samples exhibited enhanced fracture toughness, as compared to the undoped sample. Furthermore, the GSc_0.075Yb_0.06Z sample revealed a thermal conductivity of ~0.8 W/mK at 1200 °C, which was nearly 30% lower than that of the undoped sample. The associated mechanisms related to the effects of the doping on the thermophysical and mechanical properties are discussed.     

Enhanced ionic conductivity and thermal shock resistance of MgO stabilized ZrO2 doped with Y2O3

The present work focused on the effect of Y₂O₃ co-doping on the phase composition, microstructure, ionic conductivity and thermal shock resistance of 8 mol% MgO stabilized ZrO₂ (Mg-PSZ) electrolyte ceramics for high temperature applications. The addition of Y₂O₃ could promote the process of monoclinic-to-cubic/tetragonal phase transformation and became the metastable phase at room temperature. Meanwhile, the grain size of Mg-PSZ decreased. It was demonstrated that an appreciable increase in the ionic conductivity and compressive strength occurred on substituting MgO with Y₂O₃ in the Mg-PSZ electrolyte ceramics across the measured temperature range. Moreover, the Y₂O₃ addition could restrain the adverse effect of the cyclic thermal shock on the ionic conductivity and compressive strength of Mg-PSZ. The main reason was that the increase of the amount of monoclinic phase caused by cubic/tetragonal-to-monoclinic phase transformation by the cyclic thermal shock was restrained after the Y₂O₃ addition.     

Tribological and corrosion behaviors of fluorocarbon coating reinforced with sodium iron titanate platelets and whiskers

A series of sodium iron titanate (NFTO)–fluorocarbon composite coatings have been prepared with the liquid-phase blending method. The effects of two types of NFTO, NFTO platelets, and NFTO whiskers, on the tribological and corrosion behaviors of the composite coatings, are systematically studied. The results show that the addition of NFTO can significantly enhance the friction-reducing and wear resistance performances of the fluorocarbon coating. Under dry sliding, the minimum specific wear rate is 1.67 × 10⁻⁴ mm³/Nm for the platelet-filled composite coatings and 1.15 × 10⁻⁴ mm³/Nm for the whisker-filled composite coatings, respectively, showing a decrease of 83.5 and 88.6% than that of pure coating. Under a simulated seawater environment, the minimum specific wear rate is 5.44 × 10⁻⁵ mm³/Nm for the platelet-filled composite coatings and 0.84 × 10⁻⁵ mm³/Nm for the whisker-filled composite coatings, respectively, showing a decrease of 90.5 and 98.5% than that of pure coating. The morphologies of worn surfaces, wear debris, and transfer films are analyzed, and the corresponding wear resistance mechanisms are discussed. The electrochemical impedance spectroscopy certifies a remarkably improved corrosion resistance of the composite coatings which have been immersed in 3.5 wt % NaCl solution for 30 days. The composite coating reinforced with 7.5 wt % platelets shows the highest resistance of 256.3 × 10⁶ Ω·cm², approximately two orders of magnitude higher than that of pure coating. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48936.     

SiO2气凝胶隔热保温涂料研究及保温结构优化设计

石油化工行业是国家节能减排重点工程之一，如果相关设备设施保温不当，不仅会造成严重的热量散失，还会对油水分离和输送等产生影响。本文系统介绍了传统的以中空玻璃微珠或陶瓷微珠为主要隔热功能填料的隔热保温涂料的保温机理、性能及其存在的问题；以 SiO₂气凝胶为主要功能填料的新型隔热保温涂料研究现状及研究中的技术难点；针对不同应用环境，开发兼具防腐、防开裂、隔热保温功能的复合保温结构设计。本文为研制新型耐高温、高效水性无机隔热保温涂料的研究提供了参考方向，为隔热保温涂料在石油化工领域的工程应用提供分析。     

Microstructure and interface-adhesion of thermally sprayed continuous gradient elastic modulus FeCrAl-ceramic coatings

The bond strength between thermally sprayed metal bond-coats and ceramic top-coats is a key factor in determining their service life. However, most studies focus on interface modifications. In this research, based on FeCrAl bond-coats prepared by arc spraying, top-coats (Al₂O₃-40 wt% TiO₂) were prepared by plasma spraying, and heat treatment was carried out in a hypoxic atmosphere. Continuous gradient elastic modulus FeCrAl-ceramic coatings were successfully prepared, and the microstructural and mechanical properties from the substrate to the top-coats were systematically investigated. The Al₂O₃ content gradually decreased from the top-coats to the substrate, forming continuous gradient elastic modulus FeCrAl-ceramic coatings. The oxide formed during the heat treatment filled the defects in the bond-coats and greatly improved the mechanical properties of the coating. The bonding strength of the continuous gradient elastic modulus coating was 21.7% greater than that of the as-received coating.     

3D thermo-electro-chemo-mechanical coupled modeling of solid oxide fuel cell with double-sided cathodes

A solid oxide fuel cell based on double-sided cathodes is developed in our group, showing special properties and many advantages under some harsh conditions. To optimize the cell further, a thermo-electro-chemo-mechanical coupled 3D model is developed to simulate the distributions of temperature, current density, fuel gas and thermal stress under different voltages. The numerical results indicate that the temperature distribution, current, fuel gases and thermal stress is non-uniform in the cell at different voltages. The distribution of thermal stress in the electrolyte is also non-uniform because of the un-even electrochemical reaction and convective heat transfer. Furthermore, the result shows that about 47%~54% of maximum 1st principal stress in SOFC is caused by the mismatch of coefficients of thermal expansion (CTEs) among materials, while the other part of the maximum 1st principal stress is mainly caused by temperature gradient.     

Microstructure evolution and grain growth mechanisms of h-BN ceramics during hot-pressing

Pure h-BN ceramic specimens were prepared by hot-pressing under different sintering temperatures and pressures using ball milled h-BN powders composed of amorphous and nanocrystalline BN. Microstructures and thermal conductivities of these h-BN ceramic specimens were characterized and measured. Higher sintering pressure is more favorable to the preferred orientation growth of plate-like h-BN grains along the pressure direction, forming microstructures where the c-axes of h-BN grains are preferentially oriented perpendicular to the pressure direction. However, such microstructures can only be obtained at appropriate sintering temperature. Thermal conductivities of h-BN ceramic specimens are strongly related to their microstructures, especially the grain orientation. Growth mechanisms of h-BN grains were investigated. There is multi-area co-growth phenomenon around the grain boundaries composed of the basal planes of h-BN grains, which results in the formation of stacking faults in the as-grown h-BN grains.