A STRUCTURAL ANALYSIS OF THREE-DIMENSIONAL BRAIDS

This paper describes a study of three-dimensional braids produced by a four-step 1 × 1 method. An analytical approach is employed in conjunction with experimental investigations to establish the relationship between the braid structure and braiding parameters. Based on microscopic observations, we divide a three-dimensional braid structure into three representative regions, i.e., the interior, surface and corner, and treat the three regions, respectively. Three types of microstructural unit-cell models are then established. The surface characteristics and the relationship between the interior and surface unit-cells have been derived. Good agreement has been obtained between the calculated and measured values of fiber volume fraction of the braided composite samples.     

(Ba,Sr)TiO_3/Mg_xZn_(1-x)O核-壳复合陶瓷的制备及表征

纳米粒子由于具有大量的潜在应用,近年来已引起人们极大的关注.通过纳米复合技术(如制备核壳结构的纳米粒子)可以使其获得更多的特殊性质.以氢氧化钡、氢氧化锶、钛酸丁酯为主要原料,采用化学溶液法,在80℃左右的温度下制备了钛酸锶钡纳米晶.硝酸镁和硝酸锌的混合溶液同钛酸锶钡混合并超声搅拌,在室温下制备了具有核壳结构的(Ba,Sr)Ti O3/MgxZn1-xO(BST/MZO)纳米晶.x射线衍射(xRD)和场发射扫描电子显微镜(FESEM)确定所制备样品为纯钙钛矿结构,透射电镜(TEM)表明产品的形貌是核壳结构小球,电子衍射图案进一步证实核和壳均是由十几个到几十个纳米的(Ba,Sr)Ti O3/MgxZn1-xO纳米晶组成的聚集体.采用常规的陶瓷制备技术获得具有核壳结构复合陶瓷,其介电性能明显改善.研究结果表明具有核壳结构的(Ba,Sr)Ti O3/MgxZn1-xO适合作为微波介电材料.     

PLT/P（VDF-TrFE）纳米复合材料的热释电性能研究

采用溶胶－凝胶方法制备出ＰＬＴ纳米晶微粉，并用该微粉在超声分散下与Ｐ（ＶＤＦ－ＴｒＦＥ）进行均匀复合，成功地制备了ＰＬＴ／Ｐ（ＶＤＦ－ＴｒＦＥ）纳米复合材料。测定了不同体积分数下样品的介电湿谱；结合ＳＥＭ形貌观察，利用Ｂｒｕｇｇｅｍａｎ模型较好地解释了复合样品的介电特性；对不同极化电场下复合样品的热释电性能和优质因子进行了研究，结果显示，当极化电场为４５ｋＶ／ｍｍ，样品的优质因子可高达１．７３μＣ