CHARACTERIZATION OF GAMMA-RADIATION CROSS-LINKED CRYSTALLINE POLYMERS BY CRYSTALLIZATION TEMPERATURE

The effect of gamma-radlatlon on plain crystalline polymers and crystalline polymers containing different amounts of difunctional monomer both in vacuum and in air at room temperature has been investigated with DSC. It was found that the crystallization temperature T_c of crosslinked sample measured on DSC at a constant cooling rate decreases with increasing radiation dose. The difference between T_c before and after crosslinking (T_(c_0)-T_(c_R)) is linearly related to the radiation dose for plain polymer....

组成和制备条件对Bi-Pb-Sr-Ca-Cu-O材料超导电性的影响

制备了一系列 Bi—Pb—Sr—Ca—Cu—O 超导材料。在一定范围内,不同组分的 Bi—Pb—Sr—Ca—Cu—O 样品都能得到接近单110K 相的材料,但样品性能差别极大.性能的好坏极大地依赖着组成条件。烧结温度过高或过低都不利于提高样品的临界电流密度,850℃的烧结温度是较合适的,长时间烧结有利于110K 相的形成。样品烧结完成后,应缓慢降温退火,以保证材料充分吸氧。

Bi-Sr-Ca-Cu-O体系中可能存在一个新的高T_c超导相

最近,Pb能加强BiSrCaCuO超导体中高T_c相(即2223相,其c(?)37,T_c(?)110K)的出现和掺入sb形成BiPbSbSrCaCuO的T_c可以达到132 K已见报道,我们希望通过其它元素的掺杂取代也出现类似的结果。我们做了大量掺Sb、Ba、In的实验,通过改变

LaMSb_2O_7:R~(3+)(M=Li,Na,K;R=Eu,Dy,Bi)的合成、组成、结构及发光性能

研究了激活离子Eu~(3+),Dy~(3+)和Bi~(3+)在具有相同结构的LaMSb_2O_7(M=Li,Na,K)中的发光特性,得到了发白光的磷光体LaNaSb_2O_7:Dy~(3+)。讨论了化学键的共价程度对Eu~(3+)和Dy~(3+)超灵敏跃迁强度比的影响。发现当用281nm激发试样时,Bi~(3+)对Eu~(3+)具有敏化作用并解释了其原因。

Bi-Ce二元氧化物催化剂上丙烯氧化脱氢二聚的动力学与反应机理

丙烯在氧化物催化剂上氧化脱氢二聚反应的研究,文献上主要是在Bi-Sn系催化剂上进行的,不同研究者根据各自的结果,对这一步反应提出了两种不同的机理:一种认为是催化剂表面上吸附丙烯间的二聚(Langmuir-Hinshelwood型机)理;另一种认为是气相丙烯与吸附丙烯间的二聚(Eley-Rideal型机理).我们发现Bi-Ce二元氧化物显示出与Bi-

Formation of nano-crystalline corrosion products on Zn-Al alloy coating exposed to seawater

Hot dip Zn-Al alloy coating performs better than hot dip galvanized coating and 55% Al-Zn-Si coating as well with regard to general seawater corrosion protection. A characterization of the corrosion products on Zn-Al alloy coating immersed in dynamic aerated seawater has been performed mainly based on transmission electron microscopy (TEM) for morphological analysis and X-ray diffraction (XRD) technique for crystalline phase identification. The XRD and TEM analyses showed that the corrosion products mainly were typical nanometer Zn4CO3(OH)(6).H2O, Zn-5(OH)(8)Cl-2 and Zn6Al2CO3(OH)(16). 4H(2)O microcrystals. This probably is connected to the co-precipitation of Zn2+ and Al3+ ions caused by adsorption. Zn-Al alloy coating being suffered seawater attacks, AI(OH)(3) gel was first produced on the coating surface. Zn and Al hydroxides would co-precipitate and form double-hydroxide when the concentration of adsorbed Zn2+ ions by the newly produced gel exceeded the critical degree of supersaturation of the interphase nucleation. However, because the growth of the crystals was too low to keep in step with the nucleation, a layer of nano-crystalline corrosion products were produced on the surface of the coating finally. (C) 2001 Elsevier Science Ltd. All rights reserved.

Perovskite-type B-site Bi-doped ceramic membranes for oxygen separation

Novel mixed conducting oxides, B-site Bi-doped perovskites were exploited and synthesized. Cubic perovskite structures were formed for BaBi0.2COyFe0.8-yO3-delta (y less than or equal to 0.4) and BaBixCo0.2Fe0.8-xP3-delta (x=0.1-0.5) The materials exhibited considerable high oxygen permeability at high temperature. The oxygen permeation flux of BaBi0.2Co0.35Fe0.45O3-delta membrane reached about 0.77 x 10(-6) mol/cm(2) s under an air/helium oxygen partial pressure gradient at 900 degrees C, which was much higher than that of other bismuth-contained mixed conducting membranes. The permeation fluxes of the materials increased with the increase of cobalt content, but no apparent simple relationship was found with the bismuth content. The materials also demonstrated excellent reversibility of oxygen adsorption and desorption. Stable time-related oxygen permeation fluxes were found for BaBi0.2CO0.35Fe0.45O3-delta and BaBi0.3Co0.2Fe0.5O3-delta a membranes at 875 degrees C.