Effects of cyclic tensile loading on the rupture behavior of orthogonal 3-D woven SiC fiber/SiC matrix composites at elevated temperatures in air

This study examined the rupture mechanisms of an orthogonal 3D woven SiC fiber/BN interface/SiC matrix composite under combination of constant and cyclic tensile loading at elevated temperature in air. Monotonic tensile testing, constant tensile load testing, and tension–tension fatigue testing were conducted at 1100 °C. A rectangular waveform was used for fatigue testing to assess effects of unloading on the damage and failure behavior. Microscopic observation and single-fiber push-out tests were conducted to reveal the rupture mechanisms. Results show that both oxidative matrix crack propagation attributable to oxidation of the fiber–matrix interface and the decrease in the interfacial shear stress (IFSS) at the fiber–matrix interface significantly affect the lifetime of the SiC/SiC composites. A rupture strength degradation model was proposed using the combination of the oxidative matrix crack growth model and the IFSS degradation model. The prediction roughly agreed with the experimentally obtained results.     

Interaction of titanium diboride/boron nitride evaporation boats with aluminium

Hexagonal boron nitride/titanium diboride composites are widely used as evaporation boats for aluminium deposition to produce functional and decorative layers on different target materials. The lifetime of such a material is limited mainly by the interaction of the metal with the ceramic substrate, but the corrosion mechanism has still not yet been thoroughly investigated and understood. In this article the corrosion mechanism for the evaporation boats used was investigated using thermodynamic calculations, FESEM, EDX and XRD phase analysis. The analysis showed that hexagonal boron nitride (hBN), which is thermodynamically less stable than TiB₂, is passivated during the application process through the formation of AlN surface layers, whereas the thermodynamically more stable TiB₂ phase dissolves and Ti-rich components precipitate in cooler regions of the evaporation boats.     

浅谈滤料重量对其使用效果的影响

尽管在通常的概念里会认为重量大的玻纤织物比重量轻的同种玻纤织物的强度更高,耐磨性更好,但美国戈尔公司在长期的应用实践中发现,在水泥窑尾的脉冲收尘器中,使用重的玻纤滤料更有可能会发生问题。从最初的16.8oz/yd~2和22oz/yd~2的玻纤织物到覆膜滤袋的开发,戈尔过滤技术现在已经发展到了新一代的复合材料——Superflex~(TM)织物(18.5oz/yd~2)。这种18.5oz/yd~2的织物不仅能消除22oz/yd~2重磅玻纤滤料所存在的问题,达到6年以上的使用寿命,还能保证风量和压降的稳定。     

Deterioration behavior analysis of dysprosium and thulium co-doped barium titanate ceramics for multilayer ceramic capacitors

An accelerated testing method for barium titanate (BaTiO₃) dielectrics was proposed to elucidate deterioration behavior of dielectric constant based on the life-temperature relation. The accelerated degradation test (ADT) which was designed using various temperature ranges below and above Curie temperature (T_c) was focused on the optimized composition of dysprosium (Dy) and thulium (Tm) co-doped BaTiO₃. The statistical analysis of the failure time data was performed to determine the optimum distribution as a goodness-of-fitness test. A scale parameter (η) and activation energy (E_α) were calculated in order to predict the life time of the co-doped BaTiO₃, and there was difference between the expected life times according to the acceleration temperature rating of the ADT. The difference of deterioration mechanism around T_c could be deduced from the change of lattice parameter and polarization behavior. The drastic decrease of tetragonality and ferroelectric property caused by the phase transition of the co-doped BaTiO₃ was verified in the temperature above T_c. Accordingly, the acceleration factor over T_c should be considered as reliability study of the BaTiO₃ dielectrics for multilayer ceramic capacitors (MLCCs).     

Europium and erbium co-doped yttria-stabilized zirconia as a potential dual-sensor for simultaneous oxygen partial pressure and temperature measurements

In this study, the phosphorescence properties of Eu³⁺ and Er³⁺ co-doped yttria stabilized zirconia (YSZ: Eu³⁺, Er³⁺) as a function of oxygen partial pressure and temperature are investigated to explore the possibility of using this phosphor for pressure and temperature measurements at elevated temperature (up to 600 °C). The YSZ: Eu³⁺, Er³⁺ phosphors have a fixed Eu³⁺ concentration (1 mol%) and a varied Er³⁺ concentration (0.5–5 mol%). The phosphorescence intensity and lifetime of Eu³⁺ bands are sensitive to both oxygen partial pressure and temperature when temperature exceeds 400 °C. This oxygen/pressure sensitivity is related to the oxygen vacancy-induced non-radiative decay through charge transfer state (CTS), and is inversely correlated with Er³⁺ concentration. In contrast, the phosphorescence intensity and lifetime of Er³⁺ bands are temperature-sensitive but oxygen-insensitive, which is related to the dominant oxygen-independent ⁴S_3/2 → ²H_11/2 transition. Accordingly, two measurement strategies are proposed including an intensity ratio method and a lifetime method. The intensity ratio of the oxygen-sensitive Eu³⁺ bands and the oxygen-insensitive Er³⁺ reference bands is capable of 2D pressure measurement using a dual-camera system. But temperature-induced errors exist due to the temperature-sensitivity of intensity ratio. Simultaneous pressure and temperature measurements (point by point) can be achieved utilizing two PMTs that record the lifetimes of Eu³⁺ and Er³⁺, respectively. This method can resolve the issue of temperature sensitivity of Eu³⁺ and accurately correct the temperature-induced errors. The YSZ: Eu, Er phosphors show great potential for applications in high-temperature environment where the existing organic PSPs and TSPs cannot survive.     

延长窑用耐火材料使用周期的措施

Φ5.8 m×97 m回转窑用耐火材料的使用周期太短,吨熟料碱性砖砖耗曾达3.0kg以上。从配置、施工、 使用维护和质量管理等方面采取措施后,2003年吨熟料碱性砖砖耗降到0.6kg左右。     

层析介质使用寿命缩小模型的建立和确认

在现代生物制药工艺路线中,层析是最常用的一种技术手段。层析技术所需要的层析介质是药品监管的重点项目之一,其中层析介质的使用寿命(使用次数)必须经研究确认,并经药品监管部门审核和批准。在缩小模型上进行前瞻性研究是被广泛接受的层析介质使用寿命的研究方法。本文就层析介质使用寿命缩小模型的建立和确认作一简要综述。     

Mechanical and Thermal Properties of Poly(Phthalazinone Ether Sulfone)/Poly(Ether Sulfone) Blends

The mechanical and thermal properties of poly(phthalazinone ether sulfone) (PPES)/poly(aryl ether sulfone) (PES) blends prepared by melt-mixing were investigated by dynamic mechanical thermal analysis (DMTA) and thermogravimetric analysis (TGA). The dynamic mechanical thermal analysis results show that the incorporated PES has a large influence on the heat stability of PPES. The DMTA results display that the blends with a single glass transition temperature, which increases with increasing PPES content, indicates that PPES and PES are completely miscible over the studied composition range. The thermodegradative behavior of PPES/PES blends was used to analyze their thermal stability. The Friedman technique was used to determine the kinetic parameters (i.e., the apparent activation energy and order of reaction of the degradation process). The results indicate that the presence of the PES component influences the thermal stability of the PPES. On the basis of the kinetic data derived from Friedman' approach, the lifetime estimates for pure PPES, pure PES, and the blends generated from the weight loss of 5% were constructed.     

Improvement of carrier diffusion length in silicon nanowire arrays using atomic layer deposition

To achieve a high-efficiency silicon nanowire (SiNW) solar cell, surface passivation technique is very important because a SiNW array has a large surface area. We successfully prepared by atomic layer deposition (ALD) high-quality aluminum oxide (Al₂O₃) film for passivation on the whole surface of the SiNW arrays. The minority carrier lifetime of the Al₂O₃-depositedSiNW arrays with bulk silicon substrate was improved to 27 μs at the optimum annealing condition. To remove the effect of bulk silicon, the effective diffusion length of minority carriers in the SiNW array was estimated by simple equations and a device simulator. As a result, it was revealed that the effective diffusion length in the SiNW arrays increased from 3.25 to 13.5 μm by depositing Al₂O₃ and post-annealing at 400°C. This improvement of the diffusion length is very important for application to solar cells, and Al₂O₃ deposited by ALD is a promising passivation material for a structure with high aspect ratio such as SiNW arrays.     

Strength degradation and failure limits of dense and porous ceramic membrane materials

Thin dense membrane layers, mechanically supported by porous substrates, are considered as the most efficient designs for oxygen supply units used in Oxy-fuel processes and membrane reactors. Based on the favorable permeation properties and chemical stability, several materials were suggested as promising membrane and substrate materials: Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3?δ, La_0.6?xSr_0.4Co_0.2Fe_0.8O_3?δ (x = 0, 0.02) and Ce_0.9Gd_0.1O_1.95?δ. Although membranes operate at elevated temperatures, the ends of tubes in certain three-end concepts remain almost at room temperature. The current work concentrates on the failure potential of these membrane parts, where in a complex device also the highest residual stresses should arise due to differences in thermal expansion. In particular, sensitivity of the materials to subcritical crack growth was assessed since the long-term reliability of the component does not only depend on its initial strength, but also on strength degradation effects. The results were subsequently used as a basis for a strength–probability–time lifetime prediction.