基于声发射矩张量分析混凝土破坏的裂纹运动

从细观上看, 混凝土是一种由骨料、水泥浆基体、裂纹等组成的非均匀复合材料. 单轴准静态加载条件下, 应力应变曲线表现出明显的准脆性特征. 其变形破坏过程实质上是内部微裂纹产生、扩展和汇合的过程, 研究细观尺度的裂纹扩展演化将有助于深入了解混凝土的变形和破坏过程. 声发射作为一种物理检测方法可以获取材料内部细观损伤演化的物理信息. 本文基于声发射技术, 结合改进的时差定位算法和矩张量理论对声发射信号进行分析, 反演了混凝土巴西劈裂破坏中裂纹位置、裂纹类型以及裂纹面运动方向, 揭示了混凝土宏观拉伸破坏的细观裂纹扩展机制. 结果表明: 裂纹运动过程清晰地显示了混凝土内裂纹源首先在试件与载荷接触面附近产生, 之后聚集形成局部损伤区域, 并沿轴线向中心扩展(加载平面)以及裂纹从试件中间向表面扩展的动态过程(厚度方向); 裂纹运动体积可以作为裂纹形成、扩展过程中弹性能释放的度量, 初始裂纹成核时体积参数较小, 峰值载荷时, 裂纹运动体积最大达到$5.93\times10^{-4}$ mm$^{3}$; 混凝土宏观尺度的拉伸破坏在细观尺度上存在有拉伸裂纹、混合裂纹以及剪切裂纹; 拉伸裂纹最多, 占裂纹总数约为60%, 剪切裂纹最少, 约占裂纹总数的10%; 拉伸裂纹运动主导了试件的宏观劈裂破坏.      

On the Nature of Extra-Framework Aluminum Species and Improved Catalytic Properties in Steamed Zeolites

Steamed zeolites exhibit improved catalytic properties for hydrocarbon activation (alkane cracking and dehydrogenation). The nature of this practically important phenomenon has remained a mystery for the last six decades and was suggested to be related to the increased strength of zeolitic Bronsted acid sites after dealumination. We now utilize state-of-the-art infrared spectroscopy measurements and prove that during steaming, aluminum oxide clusters evolve (due to hydrolysis of Al out of framework positions with the following clustering) in the zeolitic micropores with properties very similar to (nano) facets of hydroxylated transition alumina surfaces. The Bronsted acidity of the zeolite does not increase and the total number of Bronsted acid sites decreases during steaming. O₅Al(VI)-OH surface sites of alumina clusters dehydroxylate at elevated temperatures to form penta-coordinate Al₁O₅ sites that are capable of initiating alkane cracking by breaking the first C-H bond very effectively with much lower barriers (at lower temperatures) than for protolytic C-H bond activation, with the following reaction steps catalyzed by nearby zeolitic Bronsted acid sites. This explains the underlying mechanism behind the improved alkane cracking and alkane dehydrogenation activity of steamed zeolites: heterolytic C-H bond breaking occurs on Al-O sites of aluminum oxide clusters confined in zeolitic pores. Our findings explain the origin of enhanced activity of steamed zeolites at the molecular level and provide the missing understanding of the nature of extra-framework Al species formed in steamed/dealuminated zeolites.     

催化裂化过程中含硫化合物转化规律的研究

选择丁硫醚、叔丁硫醚、四氢噻吩和乙基苯基硫醚作为模化合物,在模拟固定床催化裂化微反装置上考察含硫化合物转化和分布规律,在催化裂化过程中,烷基硫醚可以完全转化,转化产物为硫化氢,反应条件对转化程度没有明显影响;环状含硫化合物的转化程度与反应条件、溶剂性质有关,转化产物主要为硫化氢和汪量噻吩,生产的噻吩可进一步发生烷基化反应,反应温度升高,溶剂供氢能力增强,硫化氢的收率增加;乙基苯基硫醚也可以完全转化,转化产物主要为硫化氢和苯硫酚,生成的苯硫酚可进一步发生烷基化反应,反应温度升高,溶剂供氢能力增强,硫化氢的收率增加。     

有机硅橡胶裂解产物气相色谱-质谱联用分析

以室温硅橡胶和高温硅橡胶产品的边角废料及次品作为实验原料,进行到催化和碱催化裂解,将裂解产物进行气相色谱－质谱（ＧＣ－ＭＳ）联用分析,经过质谱数据检索,确定了两种酸催化产物的组成,高温橡胶的酸催化裂解产物主要是环状化物合;室温橡胶的酸催化一妥产物中有太和链状两类化合物,该实验为硅像胶废料利用提供了依据。碱催化产物太复杂,产物利用存在困难。     

Aging kinetics of porous media due to freezing-thawing cycles

The two-dimensional Ausloos et al. model of fluid invasion, freezing and thawing in a porous medium is elaborated upon and investigated in order to take into account the pore volume redistribution and conservation during freezing. The results are qualitatively different from previous work, since the damaged pore sizes are found to be much less than the possible maximum value and is reached after a large number of invasion-freezing-thawing cycles, e.g. the material is “slowly damaged”. The pore size distribution is thus found in better agreement with expected practical findings. The successive invasion percolation clusters are still found to be self-avoiding with aging. The cluster size decreases with a power law as a function of invasion-frost-thaw iterations. The aging kinetics is also discussed through the normalized totally invaded pore volume. Received 24 September 1999 and Received in final form 5 January 2000     

双相不锈钢在水溶液中之腐蚀疲劳与动态应变时效

本研究主要探讨 2 2 %Cr双相不锈钢在含氯离子水溶液中之腐蚀疲劳裂缝成长行为 ,以及在慢应变速率拉伸试验过程中所发生的动态应变时效现象 .同时以 31 6L沃斯田体系不锈钢及4 30肥粒体系不锈钢作为比较 ,藉以探讨不同晶体结构对腐蚀疲劳及动态应变时效行为的影响 .实验结果显示 ,在 80℃ ,3.5wt%NaCl水溶液中 ,3种不锈钢并未发生应力腐蚀破裂 ,但其中 31 6L沃斯田体系不锈钢及 2 2 %Cr双相不锈钢却发生动态应变时效 ,且动态应变时效的发生与温度 ,应变速率及沃斯田体相的组织有关 .在NaCl水溶液中 ,采用预裂试片量测疲劳裂缝生长速率 ,其结果表明 ,4 30肥粒体系不锈钢之疲劳裂缝生长速率最快 ,而氢脆是加快裂缝生长速率的主因 ,就双相不锈钢而言 ,腐蚀疲劳裂缝的生长主要与该不锈钢所含之肥粒体相的氢脆现象有关     

Decationization of BEA zeolite by conventional and microwave promoted ion exchange procedures

Summary A commercial NaBEA sample was exchanged, at different levels, with NH₄⁺cations through conventional and microwave promoted methods. The dependence of the acidic and catalytic properties of the HNaBEA samples with the exchange degree was analyzed. It was observed that the catalytic activity of the exchanged samples for methylcyclohexane cracking depends on the exchange method, whereas surface acidity, determined by pyridine adsorption followed by IR spectroscopy and temperature programmed desorption of NH₃, do not.     

Fatigue Crack Propagation in Copper Bicrystals Having the Grain Boundaries of Σ3 Vicinal Domain

The criterion for occurrence of intergranular fatigue cracking in copper has been investigated from the view point of both the grain boundary (GB) character and the cyclic deformation property of constituent grains. The copper bicrystals were prepared to have several orientation relationships close to 3(1 1 1) coherent twin (3 vicinal domain) so as to change the GB character rapidly with increasing deviation angles || from the 3 relation. These bicrystals were shaped to single-edge-notched specimens in which a GB plane was perpendicular to the tensile axis. The fatigue crack propagation tests were carried out in air at room temperature. The specimens having deviation angles || less than 3° involved no intergranular fatigue cracking. When the || values were ranged from 3° to 5°, the ratio of the intergranular cracking increased. In the specimens having the || values more than 9°, the intragranular cracking became predominate again. The increase in the intergranular cracking with increasing deviation angle at the || values less than 5° could be understood in terms of the increasing GB susceptibility to the GB damage due to air environment. On the other hand, the intragranular cracking at the || values more than 9° could be attributed to the formation of the persistent slip bands in the constituent grains and subsequent crack propagation preferentially along them.     

Effect of Hydrogen or Syngas Addition on Light Alkene Production by the Catalytic Oxidative Cracking of Hexane 氢气/合成气添加对正己烷催化氧化裂解制低碳烯烃反应的影响

 采用0.1%Pt/MgAl2O4催化剂研究了H2或合成气的添加对高碳烷烃模型化合物正己烷氧化裂解制低碳烯烃反应的影响. 添加H2实验中,随n(H2)/n(O2)从0增加到3,产物中COx的选择性迅速由22.4%降到4.3%,低碳烯烃的选择性则从61.5%增加到73.8%,正己烷的转化率从62.0%增加到72.8%. 添加合成气对低碳烯烃和CO选择性的影响与添加H2的影响相同,只是添加合成气时正己烷的转化率下降了6%左右. 添加合成气的正己烷氧化裂解过程可提供组成可调的产物(含有低碳烯烃、H2和CO),可不经分离直接用作加氢甲酰化生产低碳烯烃衍生物过程的原料.     

USY型分子筛与高岭土的水热热压固化及固化体性能研究

应用水热热压技术制备了各种USY型分子筛-高岭土的固化成型体,并对其进行物相分析、表面酸性以及对正十五烷裂解的催化性能测定。实验结果表明:USY型分子筛与高岭土的固化体具有较强的B酸中心,而几乎没有L酸中心。135℃下得到的固化体对n-十五烷的裂解活性及汽油转化率都高于未经处理的样品。水热热压固化温度是影响固化体性能的重要条件,可以利用固化体组分的改变及固化条件的控制来调节固化体表面酸性及其催化性能。