- 标题
- 摘要
- 关键词
- 实验方案
- 产品
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Chemical Vapor Infiltration of the Hexagonal Boron Nitride Interphase for SiC Fiber-Reinforced HP-Si<sub>3</sub>N<sub>4</sub> Matrix Composite
摘要： This work describes the processing of SiC fiber-reinforced Si3N4 matrix composites with boron nitride (BN) interphase. The BN interphase was processed by chemical vapor infiltration (CVI) with BF3/NH3 gaseous precursors. The BN interphase modification involved the continuous treatment of Hi-Nicalon SiC fibers. The relations between (i) the processing parameters, (ii) the mechanisms controlling the kinetics of the CVI of the BN, and (iii) the structure of the deposited BN are presented. A single- or multi-layer BN interphase can be produced depending on the CVI conditions imposed on the fibers during the continuous process. A surface reaction mechanism controlling the CVI promotes a smooth, isotropic BN coating. An anisotropic BN coating can be produced when the CVI kinetics are controlled by a mass transport mechanism. With a controlled temperature gradient, the BN interphase is then made by stacking successive isotropic and anisotropic layers.
关键词： SiC fibers (Hi-Nicalon),CVI,boron nitride interphase
更新于2025-09-23 15:22:29
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Choroidal imaging biomarkers
摘要： The choroid is the vascular coat of the eye,and its role has been studied in multiple chorioretinal disorders. The recent advancements in choroidal imaging techniques including enhanced depth imaging optical coherence tomography (EDI-OCT), swept source (SS-OCT), enface OCT and OCT angiography have facilitated an in-depth analysis of choroid. The gradual shift from manual to automated segmentation and binarization methods have led to precise and reproducible measurements of choroidal parameters. These qualitative and quantitative parameters, called choroidal imaging biomarkers, have evolved over the past decade from a simple linear subfoveal choroidal thickness to more complex 3 dimensional (3-D) choroidal reconstruction thus widening the spectrum encompassing multiple parameters. These biomarkers have provided a better understanding of the pathogenesis, are helpful in diagnostic dilemmas, and in future may also help to devise treatment options. The lack of normative data, absence of standardized parameters and limitations of the imaging techniques, however, have led to ambiguity and difficulty in the interpretation of these variables. We attempt to address these lacunae in the literature and provide a basic understanding of the choroid in both health and disease using these choroidal biomarkers.
关键词： Optical coherence tomography angiography (OCTA),En-face OCT,Swept source optical coherence tomography (SS-OCT),Choroidal thickness,Choroidal vascularity index (CVI),Choroidal imaging biomarkers,Choroidal volume
更新于2025-09-23 15:21:21
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Effects of initial density during laser machining assisted CVI process and its influence on strength of C/SiC composites
摘要： Novel laser-assisted chemical vapor infiltration (LA-CVI) technique has been used to improve the density and strength of carbon fiber reinforced SiC composites (C/SiC). Initial density of C/SiC before laser machining played an important role in determining the final density and strength of composites. Results show that final density and bending strength of lower initial density composites were better than that of higher initial density samples after LA-CVI process, while the porosity exhibited opposite behavior. Micro-CT and COMSEL simulation results verify that after LA-CVI process, dense band width of C/SiC with initial density of 1.5 g/cm3 was twice as that of C/SiC with initial density of 1.8 g/cm3. This led to crack propagation bypassing the micro-hole. In conclusion, low initial density when laser machining was carried out resulted in better properties of final composites.
关键词： Bending strength,LA-CVI,C/SiC composites,Micro-structure
更新于2025-09-19 17:13:59