Resistance of supersulfated cement to strong sulfate solutions

One of the principal uses of supersulfated cement has been for structures exposed to sea water and sulfate bearing ground waters. The resistance to such environments has been related to the absence of calcium hydroxide and the combination of much of the free alumina into ettringite during hydration. This paper reports the resistance of SSC to sulfate solutions in which ettringite has been decomposed. Prism samples were subjected to initial water storage at 25°C for both 28 days and 6 months. Samples were also cured for 6 months at 95°C and at both 11% and 100% R.H. The control samples of 28 days were compared with the 6 months samples of a more mature undecomposed SSC paste. After curing the prisms were measured and all the samples were immersed in three sulfate solutions (0.7M Na₂SO₄ , 0.7M MgSO₄ and saturated CaSO₄), and water at the same time. Measurements of linear expansion over 6 months were carried out. Core and surface material following immersion was examined by DTG and XRD. The study indicated that SSC is resistant to sodium and calcium sulfate solutions. Strong magnesium sulfate solutions decomposed the samples under all conditions. A possible mechanism for this attack is suggested. This revised version was published online in July 2006 with corrections to the Cover Date.     

植入用Co—Cr—Mo合金与Ti—6Al—4V合金的电偶腐蚀研究

组件式设计常被用地人工髋关节，钴络钼合金（Ｃｏ－Ｃｒ－Ｍｏ）与钛合金（Ｔｉ－６Ａｌ－４Ｖ）的压配最常用，本文应用电化学方法研究了静态条件下两种合金的电偶腐蚀行为，浸泡实验表明，钴络钼合金为阳极，但电偶电流与其维钝电流相近，并无明显加速度腐蚀效应，钛合金为阴极，受到保护，失重及金相观察结果显示，在４５天的浸泡实验周期内，未发现腐蚀痕迹，混合电位理论和电位处于两种合金的钝化电位区，电偶电流为合金的维钝     

Comparative EIS study of a paste electrode containing zinc powder in neutral and near neutral solutions

The corrosion and passivation of Zn powder particles dispersed in a paste electrode immersed in 0.5 M Na₂SO₄ and 5×10^–3 M Na₂HPO₄ solutions were studied mainly by electrochemical impedance spectroscopy. The role played by diffusion in the mechanism of anodic oxidation of zinc powder particles has been shown. It was demonstrated that the anodic reactionof Zn powder in neutral or near neutral media involves at least two adsorbed intermediates. By simulating the porous structure of the electrode, some information about porous nature of zinc electrode could be extracted. Electronic Publication     

Influence of Some Aggressive Media on Corrosion Resistance of Mortars With Spent Cracking Catalyst

The influence of spent catalyst from catalytic cracking in fluidized bed on the hydration process of cement and the properties of cement mortars were studied. The spent catalyst was used as an additive to cement in the mortars (10 and 20% of cement). The samples of mortars kept in water for28 days, then they were placed in sulfate and chloride media for 2 months (the control samples were kept in water for 3 months). After this time they were subjected to bending strength and compressive strength determinations. Thermogravimetric and infrared absorption studies were performed and capillary elevation, capability of binding heavy metals, and changes in mass and apparent density were determined too. The studies disclosed the pozzolana nature of spent catalyst and its influence on cement mortars being in contact with corrosive media. This revised version was published online in August 2006 with corrections to the Cover Date.     

主动冷却点阵夹层防热结构温度响应计算模型北大核心CSCD

针对点阵夹层结构主动热防护问题,建立了夹层结构面板和芯体导热与冷却剂对流耦合的非稳态传热理论模型,利用有限体积法离散控制方程并在MATLAB中进行了迭代求解.模型首次考虑了面板与夹芯杆之间的收缩热阻,并利用分离变量法得到了收缩热阻的近似解析解.基于单胞模型和周期性边界条件,模拟得到了模型所需的表面对流传热系数h_(b)和h_(fin).最后,选取多单胞计算工况进行数值模拟和理论模型对比,并讨论了收缩热阻对模型预测精度的影响.结果表明:理论模型能够准确预测夹层结构及内部流体的温度变化,理论与仿真之间的最大误差不超过1%;随着外加热流密度不断增大,忽略收缩热阻使得计算结果造成的误差不断增大;与数值模拟相比,理论模型可显著地减少计算时间并节省计算资源,尤其适用于非均匀、非稳态复杂热载荷下点阵夹层结构的温度响应计算.     

Normalized Dynamic Characterization and Application of Multiple Heat Storage Materials Based on Standard Thermal Resistance北大核心CSCD

基于标准热阻和能量流法,推导出储热材料与换热流体的瞬态换热热阻,通过类比电路分析法,获得了储热-换热过程的瞬态热量流模型及动态响应时间常数。进一步引入节点温度,重新定义换热热阻,获得了储热与换热过程耦合的三阶电路瞬态热量流模型,求解得到了加热、储热和释热三类时间常数,可用于协同表征储热材料中储热与释热的快慢程度,从而实现了多类储热材料的归一化动态表征。通过数值模拟验证与应用对比分析,发现基于多时间常数的归一化动态模型用于表征储热材料的动态特性是可行的,可直接对不同换热、储热材料进行对比分析。案例分析发现与固体储热材料换热时,液态金属的动态换热能力优于熔融盐,而相比于水蒸气和CO₂,空气与陶瓷材料换热能更快达到稳态。     

A new inorganic-organic polymer for the passivation of thin film capacitors

Inorganic-organic polymers with barrier properties against water vapor, excellent electrical data (3, 2, R _D>10¹⁶ cm, E _D up to 400 V/µm) and good adhesion to various substrate materials have been developed. Tailored modifications of these materials provide an excellent protective coating for thin film capacitors. Several mm thick, expensive, encapsulations could be replaced by thin coatings (up to 10 µm). The polymer coating allows the use of thin film chip capacitors in surface-mount technology. As a measure for the efficiency of the coating, the capacitance decrease under controlled humidity has been used. The influence of the material composition, the type of catalyst during sol-gel processing and the curing conditions have been studied. Adhesion and water vapor permeation properties of the polymers and rheological properties of the coating solutions have been investigated. A protective coating is developed, which increases the withstandness of capacitors against humid conditions (90°C, 100% rel. humidity) by a factor of about 30 (compared to uncoated capacitors) and shows no crack formation during thermal cycling.     

钇提高YT14硬质合金耐磨性的机制

研究了不同Ｙ添加量对ＹＴ１４硬质合金显微组织、结构和耐磨性的影响。结果表明，在ＹＴ１４硬质合金中添加微量Ｙ，可显著提高合金的耐磨性。Ｙ的主要作用是均匀细化碳化物相和Ｃｏ相；提高Ｃｏ粘结相中Ｗ、Ｔｉ元素的固溶量及αＣｏ相所占的体积分数，从而提高Ｃｏ粘结相的强韧性；Ｙ在合金中形成Ｙ２ＷＯ６，表明Ｙ还可还原和清除碳化钨表面氧化膜，增强Ｃｏ粘结相与硬质相之间的结合强度     

非晶态镍磷—镍钨磷双层组合镀层的耐蚀性能研究

本文对比研究了镍磷镀层、镍钨磷镀层及非晶态镍磷和镍钨磷双层组合镀层的耐蚀性能，分别进行了各种镀层的浸渍腐蚀实验，镀层的Ｘ射线衍射图象、镀层的扫描电镜图象、以及在工厂实际的腐蚀环境里进行的腐蚀实验。实验结果表明镍磷及镍钨磷双层组合镀层的耐 性优于镍磷镀层、镍钨磷镀层的耐蚀性。     

Amino acid overproduction by analog resistant mutants of the nitrogen fixing cyanobacteriumAnabaena sp 287

Two amino acid analog resistant mutants of the cyanobacteriumAnabaena sp 287 were isolated after MNNG mutagenesis.Anabaena ST 16, a mutant resistant to the alanine analog D-α-aminobutyric acid andAnabaena ST 25, another mutant resistant to the histidine analog l,2,4-triazole-3-alanine, released alanine and histidine, respectively, into the medium upon immobilization in alginic acid during diazotrophic growth in fluidized bed reactors. The rates of amino acid production by the mutants were 4.3 μmol mg chl^-1 h^-1 of D-alanine byAnabaena ST 16 and 16.6 μnol mg chl^-1 h^-1 of L-histidine byAnabaena ST 25. Nitrogen fixation by the mutants was not affected by the extracellular amino acid concentration. While the radioactive carbon flow was followed, the parent strain retained 93% of fixed¹⁴C and released only 7% into the medium. On the other hand,Anabaena ST 16 released 13% andAnabaena ST 25 released 29% into the medium. These mutants are beneficial in the production of radioactive amino acids using diazotrophic photobiotechnology.