Effects of calcination temperature on phase and microstructure evolution of BaTi4O9 powders

Calcining of the mixture of BaCO₃ and TiO₂ with a ratio 1:4 at different temperatures was carried out to synthesize BaTi₄O₉ powders. Phase evolution of the samples was studied using the differential thermal analysis (DTA) and X-ray diffractometry (XRD). Both techniques confirmed that the formation of BaTi₄O₉ started around 1000 °C. The XRD peaks showed that BaTi₄O₉ was most pronounced at 1250 °C. X-ray line broadening methods were employed to study the variation of particle size and microstrain of the BaTi₄O₉ powders. The Voigt function in a single line and the pseudo-Voigt function in the variance methods were used in our case. We found that both functions resulted in the same trends, i.e., the particle size increased with the temperature with the biggest size of 180 and 160 nm, whilst the microstrain yielded the opposite trend with the lowest values of 6.2 × 10^–3 and 1.1 × 10^–3. The scanning electron microscopy (SEM) study revealed the size of the large particles formed, due to agglomeration, to be about 0.5–1.9 μm. Furthermore, it was shown that irregular shapes of BaTi₄O₉ powders necked to each other appeared at 1000 °C and grew into ellipse and rod shapes at 1250 °C. Electronic Publication     

无线局域网中基于RC4的加密算法的分析与改进

分析RC4加密算法自身的缺陷和无线局域网WEP协议对RC4的误用,介绍了TKIP协议在安全性方面的改进。     

Comparative hall measurements on wet- and dry-oxidized 4H-SiC MOSFETs

Hall measurements have been used to compare the properties of 4H-SiC inversion-mode MOSFETs with “wet” and “dry” gate oxides. While the field-effect mobilities were approximately 3–5 cm²/Vs, the Hall mobilities in 4H-SiC MOSFETs in the wet and dry oxide samples were approximately 70–80 cm²/Vs. The dry-oxidized metal oxide semiconductor field effect transistors (MOSFETs) had a higher transconductance, improved threshold voltage, improved subthreshold slope, and a higher inversion carrier concentration compared to the wet-oxidized MOSFETs. The difference in characteristics between the wet- and the dry-oxidized MOSFETs is attributed to the larger fixed oxide charge in the dry oxide sample and a higher interface trap density in the wet oxide sample.     

厌氧反应除硫酸盐的新工艺

对目前消除硫酸盐对厌氧反应影响的几种方法进行了归纳评价 ,并提出了硫酸盐还原 微电解除硫化物 厌氧反应的新思路 ,从理论上分析了这种新工艺的特点 ,同时提出了存在的问题及对策。     

利用闲置设备生产均三甲苯的探索

介绍了利用闲置设备工业化生产均三甲苯的方法,并从理论上研究了生产的可行性。探讨了提高均三甲苯产品纯度和收率的途径。     

新一代静止图像压缩标准JPEG2000

随着多媒体应用领域的扩展,传统的图像压缩技术已无法满足人们对多媒体图像的要求,各种图像压缩格式应运而生,如JPEG、MPEG-4VTC、PNG等。其中新一代ISO/ITU-T静止图像压缩标准JPEG2000成为热点。文章重点介绍JPEG2000图像编码系统的基本思想及其特性。     

由1,4-萘醌催化合成1,4-二烷氧基萘-2,3-二甲腈

研究了以 1 ,4-萘醌为原料 ,通过溴代、氰化和 O-烷基化三步合成 1 ,4-二烷氧基萘 -2 ,3 -二甲腈。在溴代反应中以溴化试剂代替液溴 ;在氰化和 O-烷基化反应中以溴化十二烷基三甲基铵 (DTMAB)和聚乙二醇(PEG)作为相转移催化剂 ,并采用正交设计法考察了相转移催化剂、固体碱、反应温度等因素对反应的影响 ,其中氰化产物收率达 88.7%。     

叶绿素衍生物─CPD_4在人血清中的激发和发射荧光谱

叶绿素衍生物４号（ＣＰＤ４）是一种新型中药光敏剂，本文研究了不同浓度的ＣＰＤ４分别在含１０％不同血型人血清的生理盐水中以及纯生理盐水中的激发和发射荧光光谱，并对结果进行了分析，结论对ＣＰＤ４在光动力诊断恶性肿瘤的临床应用具有一定的指导意义．     

ZrO_2（Y－TZP）－Si_3N_4复合材料中抑制ZrN生成研究

研究了气氛加压烧成ＺｒＯ２（Ｙ－ＴＺＰ）－Ｓｉ３Ｎ４复合材料中抑制ＺｒＮ生成工艺问题，相组成分析表明：无论添加２０ｗｔ％工业ＺｒＯ２或者Ｙ－ＴＺＰ（３ｍｏｌ％Ｙ。Ｏ。）的氯化硅复合材料，在低于１８５０℃，３ＭＰａｋ气压力下烧成，表面无ＺｒＮ生成．通过加入有效的烧结助剂（Ｙ。Ｏａ＋ＡＩ。Ｏｓ）、增加埋粉中ＳＩＯ分压以及增加保护气氛氮气压力，适当的烧成条件等工艺措施可有效地抑制ＺｒＮ的生成．实验还证实了ＺｒＮ很容易氧化，含有ＺｒＮ的ＺｒＯ。（Ｙ－ＴＺＰ）－ＳｉｓＮ。复合材料试样经９００℃，０．ｓｈ热处理已粉碎性裂开．