Study of tribological properties of polymer derived ZrB2-SiC ceramics

ZrB₂–SiC composite ceramics with different compositions (20 and 60?vol% ZrB₂–SiC, 20ZS and 60 ZS, respectively) were prepared. Wear tests were conducted on the obtained ceramics in multiple distances using ball-on-flat tribotester. Volume loss and cross-sectional profiles of samples were measured by three–dimensional (3D) profilometer to study the onset of track wear damages. Pressure–depth curves and hardness were measured by indentation to investigate defects produced in the tribo-film by the debris. The debris of 20ZS was found to be joined to the tribo-film and accumulated with distance, shifting from microcrack (＜10,000 cycles) to abrasive wear (50,000 cycles). Compared to 20ZS, lower debris accumulation of 60ZS resulted in better wear resistance, leading to thinner and more stable non-substrate regions for this sample. These differences between both samples basically resulted from different particle sizes. Fine grains were easily pulled out in the experiment, resulting in abrasive wear of the specimen. While transgranular fracture of grains and the pinning led to larger grains with less debris, the damage mode remained transgranular fracture.     

Moderate lameness leads to marked behavioral changes in dairy cows

Lameness is one of the most prevalent diseases affecting the welfare of cows in modern dairy production. Lameness leads to behavioral changes in severely lame cows, which have been investigated in much detail. For early detection of lameness, knowledge of the effects of moderate lameness on cow behavior is crucial. Therefore, the behavior of nonlame and moderately lame cows was compared on 17 Swiss dairy farms. On each farm, 5 to 11 nonlame (locomotion score 1 of 5) and 2 to 7 moderately lame (locomotion score 3 of 5) cows were selected for data collection in two 48-h periods (A, B) separated by an interval of 6 to 10 wk. Based on visual locomotion scoring, 142 nonlame and 66 moderately lame cows were examined in period A and 128 nonlame and 53 moderately lame cows in period B. Between these 2 periods, the cows underwent corrective hoof trimming. Lying behavior, locomotor activity, and neck activity were recorded by accelerometers (MSR145 data logger, MSR Electronics GmbH, Seuzach, Switzerland), and feeding and rumination behaviors by noseband sensors (RumiWatch halter, ITIN + HOCH GmbH, Liestal, Switzerland). Furthermore, visits to the brush and the concentrate feeder, and the milking order position were recorded. In comparison with nonlame cows, moderately lame cows had a longer lying duration, a longer average lying bout duration, and a greater lateral asymmetry in lying duration. Average locomotor activity, locomotor activity during 1 h after feed delivery or push-ups, and average neck activity were lower in moderately lame cows. Eating time and the number of eating chews (jaw movements) were reduced in moderately lame compared with nonlame cows, whereas no effect of moderate lameness was evident for ruminating time, number of ruminating chews and boluses, and average number of ruminating chews per bolus. Moderately lame cows visited the concentrate feeder and the brush less frequently, and they were further back in the milking order compared with nonlame cows. In conclusion, nonlame and moderately lame cows differed in a biologically relevant way in many of the behavioral variables investigated in this study. Therefore, the use of these behavioral changes seems to be promising to develop a tool for early lameness detection.     

New anti-ablation candidate for carbon/carbon composites: Preparation,composition and ablation behavior of Y2Hf2O7 coating under an oxyacetylene torch

Y₂Hf₂O₇ possesses low thermal conductivity and high melting point, which make it promising for a new anti-ablation material. For evaluating the thermal stability and the potential applications of Y₂Hf₂O₇ on anti-ablation protection of C/C composites, Y₂Hf₂O₇ ceramic powder was synthesized by solution combustion method and Y₂Hf₂O₇ coating was prepared on the surface of SiC coated C/C composites using SAPS. Results shown that the coating exhibits good ablation resistance under the heat flux of 2.4?MW/m² with the linear and mass ablation rates are 0.16?μm?s^?1 and ?0.028?mg?s^?1, respectively, after ablation for 40?s. With the prolonging of the ablation time, the increasing thermal stress causes the increase of cracks. Moreover, the chemical erosion from SiO₂ and the physical volatilization of low temperature molten products aggravate failure of the Y₂Hf₂O₇ coating.     

Effect of texture on oxidation resistance of Ti3AlC2

Oxidation resistance of textured Ti₃AlC₂ ceramics was measured in the temperature range 1273–1573?K. It was found that the oxidation was markedly anisotropic and the samples exhibited a better oxidation resistance when tested along a direction transverse to the c-axis. This behavior was attributed to the rapid diffusion of Al within its basal planes to form a passivating Al₂O₃ scale and it respected Ellingham diagrams. The scales formed had different compositions depending on the testing direction; this response was clearly resulting from the crystallographic orientation. Even at 1473?K after 20?h exposure, the samples tested in a direction transverse to the c-axis showed a reduced weight gain which was 45 times lower than one seen on a basal plane.     

Protective nature of nano-TiN coatings shaped by EPD on Ti substrates

The hardness and corrosion resistance of TiN coatings, processed by Electrophoretic Deposition (EPD) to cover polished and unpolished Ti substrates, have been evaluated. A deposition time of 5 min has been enough to obtain a cohesive layer of 7–8 μm in thickness. The coatings were thermally treated in vacuum atmosphere at 1200 °C for 1 h with heating and cooling rates of 5 °C min^?1. The surfaces have been covered homogeneously optimizing the properties of the Ti substrates. Uniform and dense TiN coatings have been obtained onto polished substrates, while on unpolished Ti the nitrogen diffuses toward the substrate, moderately dissolving TiN coating. The nanohardness values of the polished samples have been increased from 2.8–4.8 GPa up to 6.5–8.5 GPa. Besides, the corrosion current density has been reduced more than one order of magnitude obtaining a protective efficiency of 82%. These values have been compared with other works in literature where authors used complex and costly processing techniques, demonstrating the strong impact of the colloidal processing over the specific properties of the material.     

Influence of whisker-aspect-ratio on densification,microstructure and mechanical properties of Al2O3 whiskers-reinforced CeO2-stabilized ZrO2 composites

A novel composite of 12 mol% CeO₂-stablized tetragonal ZrO₂ reinforced with Al₂O₃ whiskers (designated as Ce-TZP/A_w) has been prepared and studied in this work. The objective of this investigation was to systematically study the influence of whisker-aspect-ratio on the densification behaviors, microstructure evolution, and mechanical properties of Ce-TZP/A_w composite. Results showed that the sintered density of composite increased and the grain growth tended to diminish with the decrease in whisker aspect radio. Both the fracture toughness and flexural strength reached maximum values of 475 ± 12 MPa and 11.4 ± 0.2 MPa m^1/2, respectively at a whisker aspect ratio of about 12. It was also observed that the fracture toughness, flexural strength and tetragonal to monoclinic ZrO₂ transformation of the dual-phase composite exhibited similar variation trend as a function of the whisker-aspect-ratio, which suggested that the stress-induced phase transformation should be the main toughening and strengthening mechanism in the Ce-TZP/A_w composite.     

黄芩苷对H2O2氧化损伤人黑素细胞的保护机制研究

目的:探讨黄芩苷对H2O2氧化损伤正常人黑素细胞的保护作用及其机制研究。方法:构建H2O2氧化损伤黑素细胞模型，通过观察不同浓度的黄芩苷处理H2O2氧化损伤正常人黑素细胞，采用倒置显微镜观察黄芩苷对黑素细胞形态的影响；cell counting kit-8（CCK-8）法检测黄芩苷对黑素细胞增殖活力作用；乳酸脱氢酶（lactate dehydrogenase,LDH）法检测黄芩苷对黑素细胞LDH表达的影响, 并通过流式细胞仪检测活性氧（ROS）水平，荧光实时定量RT-PCR检测过氧化氢酶（catalase,CAT）、谷胱甘肽过氧化物酶1（peroxidase 1,GPX1）mRNA表达情况，通过ELISA试剂盒检测黄芩苷和H2O2处理黑素细胞后分泌的热休克蛋白70（heat shock protein 70,HSP70）。结果:镜下观察黄芩苷给药后细胞较对照组形态明显改变，细胞数增多；黄芩苷作用黑素细胞后增殖率较对照组升高（P<0.05）；黄芩苷明显抑制黑素细胞中LDH表达，呈剂量-效应关系（P<0.05）。黄芩苷能显著促进CAT和GPX1 mRNA表达，且明显抑制HSP70分泌。结论:黄芩苷对H2O2氧化损伤的正常人黑素细胞具有明显保护作用，可为临床白癜风的治疗提供参考。     

西曲煤矿水文地质类型划分探讨

矿井水文地质类型划分,对煤矿的安全生产划分有着重要的意义。探讨西曲煤矿矿井水文地质类型的划分,对井田内水文地质条件及矿井充水因素进行分析,得出该矿开采受水害影响程度以及防治水工作开展的难易程度均为中等。具体为,2+3#煤层矿井水文地质类型为中等,4#煤层矿井水文地质类型为复杂,8#、9#煤层矿井水文地质类型为复杂。分析认为,该矿应加强对陷落柱的物探和钻探、本矿采空积水探放水、矿界防隔水煤柱的留设等工作,研究结果可为煤矿防治水工作提供依据,在一定程度上可确保矿井安全生产。     

Anionic Redox Chemistry as a Clue for Understanding the Structural Behavior in Layered Cathode Materials

The anionic redox chemistries of layered cathode materials have been in focus recently due to an intriguing phenomenon that cannot be described by the number of electrons of transition metal ions. However, even though several studies have investigated the anionic redox chemistry of layered materials in terms of the charge compensation, the relationship between the origin of the structural behavior and anionic redox chemistry in layered materials remains poorly understood. In addition, a simultaneous redox process of transition metal ions could occur through the d bands interaction. Here, it is demonstrated that the anionic redox chemistry is associated with the anisotropic structural behavior of the layered cathode materials albeit without providing additional capacities exceeding the theoretical values. These findings will provide a foundation of a new chapter in the understanding of the properties of materials.