Durability of YSZ coated Ti2AlC in 1300°C high velocity burner rig tests

A thermal barrier coating (TBC) system survived 500 hours in aggressive, 1300°C burner rig testing. The yttria-stabilized zirconia (7YSZ) TBC was plasma sprayed on an oxidation-resistant Ti₂AlC-type MAX phase and tested in a jet fuel burner at 100 m/s, using 5 hours cycles. No coating spallation or surface recession was observed; Al₂O₃-scale growth produced a slight 2.4 mg/cm² mass gain. The coating surface exhibited craze-cracked colonies of [111]_flourite textured columns, with no visible moisture attack. The 20 μm alumina scale remained intact under the YSZ face, about twice that producing failure for TBC/superalloy systems. TiO₂ nodules, initially formed on the uncoated backside, were removed, and Al₂O₃ was etched through volatile hydroxides formed in water vapor (~10%). Overall, the test indicated exceptional stability of the YSZ/Al₂O₃/Ti₂AlC system under turbine conditions due in large part to close thermal expansion matching.     

相依样本下带有讨厌参数的经验似然比置信区域

本文将条件θ_0=EH(X,μ)推广到更一般的估计方程EH(X,θ_0,μ)=0,并且在样本为强平稳φ混合序列情形下讨论带有讨厌参数的经验似然比置信区域。     

电化学手性识别材料的研究与应用

手性是指物质分子互成镜像但无法重合的性质,手性对映体在生物体内因不同的手性识别而呈现截然不同的作用,所以手性识别在生命科学、医药、食品及材料等领域均具有十分重要的科学意义.手性电化学传感器由于具有制备简单、检测快速和响应灵敏等优点而引起广泛的关注.手性识别材料是构建手性电化学传感器的基础,因此有关手性识别材料的研究在手...     

Oxidation mechanisms in bulk Ti2AlC: Influence of the grain size

In this work, oxidation mechanisms were studied in fine-grained (FG) and coarse-grained (CG) Ti₂AlC bulk samples. Results showed that the oxidation kinetics are controlled by the grain size of Ti₂AlC. Bigger are the grains, faster is the oxidation. A dense and protective Al₂O₃ layer forms at the surface of FG-Ti₂AlC samples while for the CG-Ti₂AlC samples, a thick TiO₂ layer forms on top of a discontinuous Al₂O₃. CG-Ti₂AlC was observed to simultaneously transform into Ti₃AlC₂ and TiC instead of being directly transformed into TiC. This transformation result in the following crystallographically sandwich-like structure: (0001) Ti₂AlC // (0001) Ti₃AlC₂ // (111) TiC. The volume shrinkage associated to this transformation produces elongated holes that are partially filled by α-Al₂O₃. The stress caused by the volume shrinkage generates cracks at the surface, which makes the oxygen inwards diffusion easier and thus worsens the oxidation resistance the CG-Ti₂AlC bulk.     

Microstructure evolution and bonding strength of the Al2O3/Al2O3 interface brazed via Ni-Ti intermetallic phases

In this study, Al₂O₃ workpieces were vacuum brazed by using Ni-45Ti binary alloy. The interfacial microstructure evolution of the joints obtained at different brazing temperatures was investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The bonding strength of the joints was measured by shear testing. The results indicated that Ni₂Ti₄O and AlNi₂Ti were the main reaction products in the joint areas. Moreover, the Ti₂Ni intermetallic compound formed in the brazing seam. The typical layer structure of the brazed joints was Al₂O₃/AlNi₂Ti/Ni₂Ti₄O/Ti₂Ni + NiTi/Ni₂Ti₄O/AlNi₂Ti/Al₂O₃. With the brazing temperature increasing, the thickness of the Ni₂Ti₄O reaction layer adjacent to the Al₂O₃ substrate increased significantly, while the AlNi₂Ti phase had a tendency to dissolve with the brazing temperature increasing. The mechanism for the microstructure evolution was also discussed. The maximum shear strength of 125.63±4.87 MPa of the joints was obtained when brazed at 1350 °C for 30min. The fracture occurred hardly in the interface between Al₂O₃ and Ni-45Ti filler alloy.     

Models for circular data from time series spectra

Circular data are those for which the natural support is the unit circle and its toroidal extensions. Numerous constructions have been proposed which can be used to generate models for such data. We propose a new, very general, one based on the normalization of the spectra of complex-valued stationary processes. As illustrations of the new construction's application, we study models for univariate circular data obtained from the spectra of autoregressive moving average models and relate them to existing models in the literature. We also propose and investigate multivariate circular models obtained from the high-order spectra of stationary stochastic processes generated using linear filtering with an autoregressive moving average response function. A new family of distributions for a Markov process on the circle is also introduced. Results for asymptotically optimal inference for dependent observations on the circle are presented which provide a new paradigm for inference with circular models. The application of one of the new families of spectra-generated models is illustrated in an analysis of wind direction data.     

分离提取葡萄糖母液中异麦芽糖的色谱填料

应用硅胶的氨基键合改性方法,研究色谱分离提取葡萄糖母液中低聚糖组分中的同分异构体的工业色谱填料。经红外光谱、元素分析对最后的产物进行表征,考察了该键合相的pH值适用范围。用自合成填料自装色谱柱对该键合相进行了色谱评价。结果表明：改性后硅胶键合相具有较好的色谱性能,且在pH值为 2～11时稳定性能良好,可有效地用于低聚糖中的同分异构体的分析分离。     

手性分子识别中空纤维复合膜制备及其性能的研究

以聚砜(PSF)中空纤维超滤膜为基膜,采用表面热聚合方法制备了L-DBTA印迹中空纤维复合膜.由SEM分析表明经过表面聚合后的L-DBTA印迹中空纤维复合膜表面具有层叠交联状复合层,其厚度约3 μm.复合层表面与层内具有许多"空穴",其直径在200 nm以下.实验结果表明L-DBTA印迹中空纤维复合膜对模板分子L-DBTA具有很好的识别作用,对L,D-DBTA的分离因子α可达2.7,而非分子印迹复合膜对L-DBTA的识别选择性不明显.此外,当引发剂的浓度为4.0%,60℃表面热聚合48 h制得的L-DBTA印迹中空纤维复合膜对L-DBTA具有较好的识别性能,具有良好的应用前景.     

酶法合成阿托伐他汀侧链中间体（S）-4-氯-3-羟基丁酸乙酯的研究进展

第三代羟甲戊二酰辅酶A （HMG-CoA）还原酶抑制剂——阿托伐他汀是年销售额超过百亿的重磅降血脂药物,因其疗效显著而广受医生患者好评.阿托伐他汀主要通过疏水性母核及手性侧链进行合成,而手性侧链的制备是合成关键.目前,生物催化技术在手性药物合成中的应用备受关注,而阿托伐他汀手性侧链中间体（S）-4-氯-3-羟基丁酸乙酯的酶法合成也成为研究热点.本文主要介绍近年酶法合成在（S）-4-氯-3-羟基丁酸乙酯中的研究进展.     

扁桃酸的拆分和手性扁桃酸的合成研究进展

综述了扁桃酸拆分和手性扁桃酸合成的研究进展,对非对映体盐结晶法、萃取法、色谱法、电泳法、酶催化法拆分消旋扁桃酸的原理、工艺和特点进行了评述,并介绍了生物转化法、电化学法和直接化学法合成手性扁桃酸的研究状况。其中非对映体盐结晶法是目前工业生产手性扁桃酸的重要方法,而生物转化法合成手性扁桃酸具有良好的工业应用前景。