Forsterite-type Mg2SiO4 was investigated systematically for thermal barrier coating (TBC) applications. Results showed that Mg2SiO4 synthesized by solid-state reaction possessed the good phase ...stability up to 1573 K. The thermal conductivity of Mg2SiO4 at 1273 K was lower ˜20% than that of yttria stabilized zirconia (8YSZ). Mg2SiO4 also presented moderate thermal expansion coefficients, which increased from 8.6 × 10−6 K−1 to 11.3 × 10−6 K−1 (473˜1623 K). Mechanical properties including hardness, fracture toughness, and Young’s modulus of Mg2SiO4 were comparable to those of 8YSZ. The sintering results indicated a promising low-sintering activity of Mg2SiO4. Mg2SiO4 samples were subjected to water quenching test at 1573 K and showed a superior thermal shock resistance compared to 8YSZ. Mg2SiO4 coating with stoichiometric composition was produced by atmospheric plasma spraying. The thermal cycling test result showed that Mg2SiO4 coating had a lifetime more than 830 cycles at 1273 K, which is desirable for TBC applications.
Considerable efforts are being invested to explore alternative ceramic materials to yttria stabilized zirconia (YSZ) for thermal barrier coating (TBC) applications. In this work, 18 mol% YO1.5 ...stabilized HfO2 (18YSH) is proposed as potential TBC material. Stoichiometric 18YSH was prepared by atmospheric plasma spraying. The 18YSH coating exhibits low thermal conductivity over the whole temperature range investigated and a minimum thermal conductivity of 0.832 W/m·K at 800 °C. Average hardness and Young's modulus values have been determined to be 7.01 ± 1.33 GPa and 111 ± 26.8 GPa respectively. These values are superior to those exhibited by YSZ coating. In addition, the sintering temperature of 18YSH coating is at least 100 °C higher than that of a 8 YSZ coating and thus 18YSH will be more resistant to sintering. Finally, 1) the coating reliability of 18YSH TBC has been studied by thermal cycling to 1100 °C and 2) calcium–magnesium–alumino-silicate-(CMAS)-induced degradation was investigated at 1250/1300 °C. The related failure mechanism was investigated and a model describing the CMAS degradation process is presented.
The mismatch of thermal expansion coefficient (CTE) between thermal barrier coatings (TBCs) and environmental barrier coatings (EBCs) is the key factor that affects the durability of T/EBCs in ...aero-engine environments. To alleviate the CTE mismatch, the novel TBC materials with relatively low CTE are needed. In this study, Lu4Hf3O12 with δ-phase rhombohedral structure was synthesized by solid-state reaction using Lu2O3 and HfO2 as the raw materials. Lu4Hf3O12 ceramics exhibited outstanding phase stability up to 1600 °C and comparable mechanical properties to 8 wt% Y2O3 stabilized ZrO2 (8YSZ) as well as great resistance against water-vapour/oxygen corrosion. Additionally, it possessed the thermal conductivity of 1.20 W/m·K at 1000 °C, about 43% lower compared to traditional 8YSZ material (2.1–2.22 W/m·K), and coefficient of thermal expansion (CTE) of 8.46 × 10−6 K−1 (10.38 × 10−6 K−1 for 8YSZ). These results preliminarily reveal that Lu4Hf3O12 could be considered as a potential material for thermal insulation top-coat in the field of T/EBCs.
Owing to excellent performance and dopability, spiro-OMeTAD remains an irreplaceable hole transporting material (HTM) in perovskite solar cells (PSCs). In order to further improve the performance of ...spiro-OMeTAD based PSCs, a Lewis base can be introduced into the structure of spiro-OMeTAD wisely, which can keep the advantages of spiro-OMeTAD while incorporating the functionality of a Lewis base in passivating the surface of the perovskite. Therefore, spiro-type HTMs (spiro-CN-OMeTAD with a dicyano group and spiro-PS-OMeTAD with a thiocarbonyl group) were synthesized and confirmed by density functional theory (DFT) calculations and X-ray single-crystallographic diffraction. Spiro-CN-OMeTAD as an HTM is certified to have a suitable interfacial band alignment with the perovskite, good film quality and effective defect passivation, which facilitate the resulting device to achieve an efficiency of 19.90% with a high open-circuit voltage, low hysteresis, and improved stability. This study provides an alternative strategy for the molecular design of better HTMs in high-performance PSCs.
Lewis base group containing spiro-type hole conductors (spiro-CN-OMeTAD and spiro-PS-OMeTAD) have been synthesized to be HTMs. This study provides an alternative strategy for the molecular design of better HTMs in high-performance Perovskite solar cells.
La2Ce2O7 (LC) is a new promising thermal barrier coating (TBC) material for high-temperature applications. However, the sudden decrease of thermal expansion coefficient (TEC) at ∼623 K limits its ...application. In this study, the plasma-sprayed La2Ce1.7Ta0.3O7.15 (LCT) coating was developed by partial substitution of Ce4+ in LC with Ta5+. LCT coating shows lower thermal conductivity between 298 K and 1273 K (0.54–0.71 W/(m·K)) than LC coating (0.65–0.85 W/(m·K)) and the traditional yttria partially stabilized zirconia (YSZ) coating (1.53–1.72 W/(m·K)). It also exhibits excellent thermal stability at least up to 1573 K for 1000 h. What is more, the sudden TEC drop is suppressed owing to the reduced oxygen vacancy concentration governed by Ta5+-substitution content. As a result, LCT TBC shows an improved thermal cycling lifetime in an air furnace as compared to LC TBC.
In this work, porous LaMgAl11O19 (LMA) thermal barrier coatings (TBCs) were deposited by atmospheric plasma spraying, using the powder mixtures LMA/graphite with different weight fractions. The ...effects of graphite contained in the powder mixtures on the amorphous phase content, microstructure and porosity of the coatings were investigated using X-ray diffraction and scanning electron microscopy. The mechanical properties, such as bonding strength, micro-hardness and fracture toughness, and the thermal cycling behavior of the coatings were investigated. Results indicated that the amorphous phase content and the porosity of the coatings increased with the increase of graphite content in the powder mixtures, whereas the bonding strength and the micro-hardness exhibited an opposite trend. Thermal cycling lifetimes of the coatings decreased with the increase of graphite content, owing to the increase of amorphous phase content and the decrease of the bonding strength. Failure of the coatings was mainly caused by the thermal expansion mismatch and growth of thermally grown oxides.
•Porous LMA coatings were obtained using the LMA/graphite powder mixtures.•Mechanical properties and thermal cycling behavior of the coatings were studied.•Graphite content in the feedstock affected the microstructure and phase composition.•Thermal cycling behavior of the coatings cannot be improved by porous structure.
Marine cold seeps are unique chemosynthetic habitats fuelled by deeply sourced hydrocarbon‐rich fluids discharged at the seafloor. Through oxidizing methane and other hydrocarbons, microorganisms ...inhabiting cold seeps supply subsurface‐derived energy to higher trophic levels, sustaining highly productive oases of life in the deep sea. Despite the central role of microbiota in mediating biogeochemical cycles, the factors that govern the assembly and network of prokaryotic communities in cold seeps remain poorly understood. Here we analysed the geochemical and microbiological profiles of 11 different sediment cores from two spatially distant cold seeps of the South China Sea. We show that prokaryotic communities belonging to the same methane‐supply regimes (high‐methane‐supply, low‐methane‐supply and non‐seep control sediments) had a highly similar community structure, regardless of geographical location, seep‐associated biota (mussel, clam, microbial mat) and sediment depth. Methane supply appeared to drive the niche partitioning of anaerobic methanotrophic archaea (ANME) at the regional scale, with ANME‐1 accounting for >60% sequence abundance of ANME in the high‐methane‐supply sediments, while ANME‐2 dominated (>90%) the low‐methane‐supply sediments. Increasing methane supply enhanced the contribution of environmental selection but lessened the contributions of dispersal limitation and drift to overall community assembly. High methane supply, moreover, promoted a more tightly connected, less stable prokaryotic network dominated by positive correlations. Together, these results provide a potentially new framework for understanding the niches and network interplay of prokaryotic communities across different methane seepage regimes in cold‐seep sediments.
In order to develop thermal-protection coatings, rare earth hafnates Sm2Hf2O7 (SHO) and Pr2Hf2O7 (PHO) coatings with pyrochlore structure were prepared on different substrates by atmospheric plasma ...spraying (APS). The infrared radiation, flame-ablation resistance, and thermal cycle performance were investigated in relationship with their morphologies, phase stabilities, thermophysical and mechanical properties. The results showed that both SHO and PHO coatings had compatible thermal-protection performance with lower thermal conductivity (0.711 and 0.779 W·m−1·K−1 at 1000 °C) and higher infrared emissivity (0.814 and 0.894 at 1000 °C) in the 3–5 μm band. Moreover, the supersonic flame ablation resistance of PHO coatings at high temperatures was greater than that of SHO coatings. Both SHO and PHO coatings have long thermal cycling life at low and medium temperatures and short thermal cycling life at high temperatures. The failure mechanisms of both type coatings were mainly associated with thermal expansion mismatch stress and fatigue stress generated during multiple thermal cycling.
•Sm2Hf2O7 (SHO) and Pr2Hf2O7 (PHO) coatings were found to have lower thermal conductivity than typical 8YSZ coating.•SHO and PHO coatings also have higher infrared emissivity (0.814 and 0.894) in 3–5 μm at 1000 °C.•Back temperature of Al substrate dropped by 269.8 °C and 328.5 °C after SHO and PHO coating protection in flame ablation.
A novel multi-layer HfO2-Si/YbSi1.5/Yb2SiO5/LaMgAl11O19 environmental barrier coatings (EBCs) was prepared using atmospheric plasma spraying method to restrain spallation failure and improve ...lifetimes of coating. The thermal cycling behaviors of SiCf/SiC completely covered with multi-layer EBCs were comparatively investigated at 1300 °C and 1350 °C in air. Meanwhile the water vapor corrosion behavior of coated sample was also investigated at 1300 °C for 100 h in 90% H2O-10% O2 steam. The coating at 1300 °C showed better thermal shock resistance than the coating at 1350 °C, due to the increase of tensile stresses at 1350 °C. The coating showed different forms of crack penetration due to the influence of thermal cycling temperature and water vapor. The formation of HfSiO4 phase thanks to solid-state reaction between HfO2 and SiO2 alleviate the β→α-cristobalite phase change and avoid the crack initiation. However, the thermal mismatch stress was contributed to the spallation of coating along the surface of the SiCf/SiC substrate.
•Multi-layer coatings consisting HfO2-Si bond coat are prepared on the surface of SiCf/SiC by atmospheric plasma spraying.•The HfSiO4 formation seems to suppress crack formation in the HfO2-Si bond coat.•The growth and penetration of cracks have different paths under different high-temperature test environment.
Amorphous phase is commonly found in plasma-sprayed LaMgAl11O19 coating. In this work, LaMgAl11O19 coatings were deposited by atmospheric plasma spraying with powders synthesized at the temperatures ...range from 1300 °C to 1600 °C. The melting degree of the feedstock was influenced by the amount of the second phase LaAlO3 and density of the powders, which was dependent on the synthesis temperature. Therefore, LaMgAl11O19 coatings with different amorphous phase contents and microstructures were produced. Results showed that the lower the amorphous contents, the lower the volume shrinkage of the coating during the recrystallization process and the longer the thermal cycling lifetime. However, when the amorphous contents were in the same level, the thermal cycling lifetime differences of these coatings seemed to be dependent on the grain size. LMA coating sprayed with powders synthesized at 1450 °C had relatively low amorphous content and moderate grain size, showing the longest thermal cycling lifetime.
