Optimized Preparation of Elastically Soft,Highly Piezoelectric,Cellular Ferroelectrets from Nonvoided Poly(ethylene Terephthalate) Films

Electrically charged cellular polymer films can exhibit very high piezoelectric activity and are therefore more and more often employed in advanced electromechanical and electro‐acoustical transducers. In this paper, we report an optimized sequence of steps for preparing such ferroelectrets from commercial nonvoided poly(ethylene terephthalate) (PETP) films by means of foaming with CO₂, biaxial mechanical stretching, controlled void inflation, and bipolar electric charging. The nonvoided PETP films were foamed with supercritical CO₂ at a suitably high pressure and subsequently annealed for stabilization. The cellular foam structure was further optimized by means of well‐controlled biaxial stretching in a commercial stretcher and sometimes subsequent inflation in a pressure chamber. Bipolar electric charging of the internal voids was achieved through the application of high electric fields in an SF₆ atmosphere. The new optimized PETP ferroelectrets exhibit quite large piezoelectric coefficients up to almost 500 pC N^–1, for which unusually low elastic stiffnesses of only around 0.3 MPa are essential. The PETP‐foam ferroelectrets possess unclamped thickness‐extension resonance frequencies between approximately 120 and 250 kHz, and are thus highly suitable for several established as well as novel ultrasonic‐transducer applications.     

Effect of curing moisture on the indentation force deflection of flexible polyurethane foam

The moisture effect on the indentation force deflection (IFD) of flexible polyurethane foam was examined through the curing of the foam with different moisture contents. The employed foam was cured at 30, 40, 50, 60, 70, and 80% relative humidity, and the corresponding curing temperature was constant at 23°C. The experiments showed that the measured IFD and support factor of the flexible polyurethane foam decreased, and the hysteresis increased with the curing moisture. A statistical conversion formula was generated experimentally to correct the measured IFD of the flexible polyurethane foam to eliminate the deviation caused by the moisture effect. The measured IFD was inversely exponentially proportional to the curing moisture. The accuracy of the correction formula was verified by the conditioning of the foam again with different moisture contents. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1679–1682, 2007     

高速铁路无砟轨道挤塑板铺设技术研究

以某高速铁路无砟轨道挤塑板铺设为例,详细介绍了高强度挤塑板铺设要点及质量控制工艺,通过对挤塑板施工技术的研究,形成了满足高标准、高要求的成套技术,对提升无砟轨道施工质量具有重要意义。     

探究聚氨酯废弃软泡的资源化利用技术(上)

软质聚氨酯泡沫塑料废旧物的回收利用无疑对环境保护和资源利用是有利的,由于聚氨酯的用量较大,而近期原料价格居高不下,其废弃物回收资源化利用市场前景看好。针对废旧聚氨酯软泡塑料的循环利用形势所迫,分别论述了废旧聚氨酯软泡塑料的物理回收利用技术;废旧聚氨酯软泡塑料的化学回收利用技术;废旧聚氨酯软泡回收利用的粘结加压成型和挤出成型技术,以及废旧聚氨酯软泡回收利用热解法制作填料技术等的工艺特点、加工方法,同时指出其社会效益、经济效益和市场前景。     

中国与日本挤压工业铝材的消费结构

列举了2001年-2009年中国挤压铝材的产量,工业挤压铝材在挤压铝材总产量中的比例,此比例的平均值为31.64%;中国工业挤压铝材的表观消费结构。2002-2009年日本挤压铝材和工业挤压铝材产量及工业挤压铝材的消费结构,这8年日本工业挤压铝材占总(国内)发货量的37.35%,即建筑及结构挤压材消费量占总消费量的62.65%。     

烧结开孔金属泡沫壁的辐射和自然对流耦合换热试验研究

开展烧结开孔金属泡沫壁在大空间条件下的辐射和自然对流耦合换热试验研究,研究壁面倾角、瑞利数Ra*、泡沫厚度对换热性能的影响。试验所得竖直光铜板的结果与文献结果符合一致,验证了试验方案的有效性。试验结果表明:在一定的加热功率下,随着倾角的增加,纯自然对流努塞尔数和复合努塞尔数先增加后减小,在倾角为60o～80o达到极大值,且辐射换热量占总换热量的33%～44%;竖直放置时,烧结泡沫壁的辐射换热量占总换热量的比值小于光壁,且该值随泡沫厚度增加而增加。与光壁相比,烧结泡沫竖壁复合换热的平均努塞尔数和纯自然对流换热的平均努塞尔数分别提高了1.52～1.98倍和1.16～1.66倍。通过对红外相机拍摄的泡沫表面温度分布进行分析验证了基于泡沫表面平均温度的辐射换热量计算模型的有效性。     

以ZrH_2为发泡剂的泡沫铝制备和表征

使用氢化锆为发泡剂,通过熔体发泡法制备泡沫铝并研究其影响因素。制备工艺为：添加0.6%-1.4%的发泡剂,1.5%-3.0%Ca（质量分数）作为增粘剂,发泡温度933-1013K,搅拌时间为0.5-2.5min和保温时间为1.5-4.0min。利用XRD和SEM对泡沫铝样品进行表征,测试其力学性能。结果表明,在合适的工艺参数下能制备出孔径均匀的泡沫铝,采用氢化锆为发泡剂可以制备出平均孔径为1mm左右的泡沫铝。金属间化合物和Al2O3的存在影响熔体的粘度。泡沫铝的力学性能经历线弹性区、平台区和致密化区并表现出较高的能量吸收效率。     

Study on particle-stabilized Si3N4 ceramic foams

The stability of bubbles and the microstructures of sintered Si₃N₄ ceramic foams produced by direct foaming method were investigated. The bubbles produced by short-chain amphiphiles (propyl gallate) have higher stability as compared with that produced by long-chain surfactants (TritonX-114). Si₃N₄ ceramic foams using short-chain amphiphile are particle-stabilized one, the pore cells are spherical and closed, and cell surfaces are smooth and dense. The pore cells of sintered Si₃N₄ ceramic foams using TritonX-114 foaming are coarse and large, and pore cells are polyhedral. High gas-pressure sintering is conducive to the development of the whisker-like microstructures in Si₃N₄ ceramic foams. The sintered Si₃N₄ ceramic foams with the whisker-like microstructure are quite promising for improving the mechanical strength of the ceramics by a simple and safe way.     

Modeling failure modes of isotropic three-dimensional reticulated porous metal foams under several typical loads

Three dimensional reticulated porous metal foams are widely used engineering materials. A failure model with the simplified structure of these porous materials has been established, and the failure modes have been analyzed for the corresponding porous components under several typical loads, which include torsion, shearing and bending. The failure modes cover the tensile fracture, the shearing and the buckling of the strut, which may lead to the final destruction of the whole porous structure. The mathematical relationships, which characterize different failure modes, have been derived for the strut failure resulting from loading for these porous components under the above loading conditions. The results also show that the failure mode is related with the material species for these materials under the above loads. The tensile fracture of the strut will occur for the porous body with metallic materials in most cases, and the shearing fracture of the strut may occur for that in a relatively little cases. Moreover, the elastic buckling, the elastic–plastic buckling and the edge yielding may also occur on the strut of porous bodies when certain conditions are met.