A state-of-the-art review on particulate wood polymer composites: Processing,properties and applications

In the present decade, the demands for recyclable, environmentally friendly and low-cost with good strength composites materials have been significantly increased. In this context, the particulate wood polymer composites have attracted the researchers owing to their eco-friendliness, low-cost as they are prepared using waste wood particles, and good mechanical and physical properties. These composites were prepared by filling the waste wood particles into the polymers using different fabrication methods such as extrusion, hand layup, compression moulding, injection moulding and additive manufacturing (3D printing). A good number of research works have been reported on the testing and characterization of wood composites for the various applications so far. This fact motivated to prepare a state-of-the-art review on the recent developments in processing, characterization, and applications of wood composites. This paper presents a discussion on the chemical structure and properties of different types of wood species. The mechanical, thermal and water absorption behaviour of thermosets, thermoplastics and biopolymers based wood composites have also been discussed. Further, characterization of the nano biocomposites prepared using nanocellulose/nanoparticles of wood are also presented. The outcomes of the present review provide a good understanding of wood composites that will encourage the researchers for further research works & developments of novel wood composites for the advanced applications.     

射流抛光材料去除机理及影响因素分析

 采用Fluent软件对射流抛光材料去除机理进行了流体动力学仿真研究,通过对射流流场压力、速度和工件表面剪切力的分析可知材料去除量应与表面剪切力的分布相对应,去除函数呈现W型;随后采用正交法对入射速度、工作距离和磨料浓度等工艺参数对抛光效果的影响进行了综合分析,结果表明：去除效率随入射速度和磨料浓度的增大而增大,随工作距离增大而减小,并且工作距离对去除率具有显著影响,为实验研究中工艺参数的选取提供了一定的指导意义。     

充气塑料柱腔的制备与保气半寿命

 研究了聚苯乙烯塑料柱腔的两种制备方法：采用聚苯乙烯溶液旋转涂层和熔体浸涂。聚苯乙烯熔融后浸涂制备的塑料柱腔存在一定的结晶取向和很多气泡,去掉铜芯轴后,塑料柱腔因缺陷太多几乎不能保气,成品率非常低,不到10％。利用聚苯乙烯溶液通过多次旋转涂层和烘干过程制备的塑料柱腔具有很低的表面粗糙度,柱腔厚度为10～30 m,表面粗糙度5～20 nm,采用0.3～0.4 μm聚酰亚胺膜封口保气,气体介质为氪气,通过X射线荧光谱仪测量柱腔保气半寿命约24 h。采用保气罐储存和运输无源塑料柱腔充气靶,打靶时腔内气体密度可保持在初始状态的92％左右。     

激光干涉光刻法制作100 nm掩模

 介绍了一种利用激光干涉光刻技术得到特征图形,并通过离子束刻蚀将图形转移到铬层上,从而获得掩模的方法。针对掩模透光率以及对干涉图形对比度可能产生影响的两个参数分别进行了数值仿真,从而证明此方法的可行性和参数的优化选择。自搭干涉光刻实验系统,用257 nm的激光光源实现光刻,得到特征尺寸为100 nm的图形,再经过离子束刻蚀,最终得到周期200 nm、线宽100 nm的掩模。     

Challenges and Solutions in Fabrication of Silica-Based Photonic Crystal Fibers: An Experimental Study

Abstract

The fabrication process of photonic crystal fibers based on a stack-and-draw method is presented in full detail in this article. In addition, improved techniques of photonic crystal fiber preform preparation and fabrication are highlighted. A new method of connecting a handle to a preform using only a fiber drawing tower is demonstrated, which eliminates the need for a high-temperature glass working lathe. Also, a new technique of modifying the photonic crystal fiber structural pattern by sealing air holes of the photonic crystal fiber cane is presented. Using the proposed methods, several types of photonic crystal fibers are fabricated, which suggests potential for rapid photonic crystal fibers fabrication in laboratories equipped with and limited to only a fiber drawing tower.     

Development of two-port surface acoustic wave resonator with Al/Au electrodes for gas sensing

Simple and efficient surface acoustic wave(SAW)two-port resonators with low insertion loss and high Q-values on ST-X quartz substrate using a corrosion-proof A1/Au-stripe electrode structure are developed for gas sensing.It was composed of two shorted grating reflectors and adjacent intedigital transducers(IDT),and an active metal film in the cavity between the IDTs for the sensitive film coating.The devices are expected to provide good protection towards metal electrode for gas sensors application in chemically reactive environments.Excellent device performance as low insertion loss,high Q factor and single-mode are achieved by carefully selecting the metallic electrode thickness,cavity length and acoustic aperture.Prior to fabrication,the coupling of modes(COM)model was performed for device simulation to determine the optimal design parameters.The fabricated single-mode SAW resonator at operation frequency of 300 MHz range exhibits matched insertion loss of~6.5 dB and loaded Q factor in the 3000 range.Using the fabricated resonator as the feedback element,a dualresonator-oscillator with excellent frequency stability(0.1 ppm)was developed and evaluated experimentally,and it is significant for performance improvement of SAW gas sensor.     

应用离子束修正大面形误差光学元件

为了获得超高精度面形的光学元件并验证离子束的修正能力,对应用离子束修正大面形误差光学元件的问题进行了实验研究。通过改变离子源光阑尺寸的方式获得了不同束径的离子束去除函数,并对一直径为101mm、初始面形峰谷(PV)值为417.554nm、均方根(RMS)值为104.743nm的熔石英平面镜进行了离子束修形实验。利用10、5、2mm光阑离子源的组合,进行了12次迭代修形,最终获得了PV值为10.843nm、RMS值为0.872nm的超高精度表面。实验结果表明,应用离子束可以对大面形误差光学元件进行修正,并且利用更大和更小束径离子束去除函数的组合进行优化,可以进一步提升加工效率和精度。     

I型全息凹面光栅制作误差对光谱像的影响分析

通过对I型全息凹面光栅制作参量误差对光谱像的影响进行数值计算发现|1)两记录臂长的相对误差而不是绝对误差决定光谱像的展宽程度,即使绝对误差较大,只要两记录臂长的误差值相同,像宽也没有明显改变|2)由于I型光栅的记录臂一般较长,记录角度误差对像宽的影响不大,但会影响光栅的刻线密度,导致光谱成像位置的偏移|3)曲率半径误差对像宽的影响较大.通过数值模拟明确了I型全息凹面光栅制作的误差容许范围,找到了对光谱像宽度影响较大的误差来源,从而为此类光栅的制作提供理论指导,有助于制作出高质量光栅,降低罗兰圆光谱仪的调节难度.     

Doping transition metal ions as a method for enhancement of ablation rate in femtosecond laser irradiation of silicate glass

We present a doping method to improve the femtosecond laser ablation rate and promote ablation selectivity. Doping transition metal ions, Co2＋ or Cu2＋, in silicate glass apparently change absorption spectroscopy and induce resonant absorption at wavelengths of 600 and 800 nm, respectively. Comparing with femtosecond laser processing of the same glass without doping, we find that the threshold fiuenee decreases and the ablation rate increases in resonant absorption in doped silicate glass. Resonant absorption effectively increases multiphoton ionization for seed-free electron generation, which in turn enhances avalanche ionization.     

In-situ tensile testing of nano-scale specimens in SEM and TEM

We present a new experimental method for the mechanical characterization of freestanding thin films with thickness on the order of nanometers to micrometers. The method allows, for the first time, in-situ SEM and TEM observation of materials response under uniaxial tension, with measurements of both stresses and strains under a wide variety of environmental conditions such as temperature and humidity. The materials that can be tested include metals, dielectrics, and multi-layer composites that can be deposited/grown on a silicon substrate. The method involves lithography and bulk micromachining techniques to pattern the specimen of desired geometry, release the specimen from the substrate, and co-fabricate a force sensor with the specimen. Co-fabrication provides perfect alignment and gripping. The tensile testing fits an existing TEM straining stage, and a SEM stage. We demonstrate the proposed methodology by fabricating a 200 nm thick, 23.5 μm wide, and 185 μm long freestanding sputter deposited aluminum specimen. The testing was done in-situ inside an environmental SEM chamber. The stress-strain diagram of the specimen shows a linear elastic regime up to the yield stress σ _y MPa, with an elastic modulusE=74.6 GPa.