Effect of Dilution and Porosity on Self-Propagating High-Temperature Synthesis of Silicon Nitride

Self-propagating high-temperature synthesis is a very easy and low-cost method to synthesize Si₃N₄. The nitriding of silicon powder takes place in a self-sustained regime under high pressures of nitrogen with dilution of silicon by Si₃N₄. In this work effects of dilution and green-mixture porosity on combustion velocity and phase content of reaction products are studied. Results are compared with previous work of other authors and different behaviors are found. An explanation of these behaviors is given.     

添加石英对莫来石－刚玉制品结构的影响

探讨了引入石英颗粒的莫来石－刚玉制品中大气孔的成因。认为与液相的生成及其在毛细管力作用下的转移有关；与莫来石生成膨胀效应对颗粒拉紧的阻碍有关；与石英相交所引起的体积膨胀有关。     

Evaluation of pore structure and its influence on permeability and moisture damage in asphalt concrete

This study evaluates the pore structure of asphalt concrete (AC) samples by measuring the different components of pore space and their contributions to permeability and moisture damage. Three components of the total pore space namely permeable, dead-end and isolated pores are quantified using tracer test, which is a combination of permeameter and salt concentration measuring meter. Permeable pores become impermeable if an AC sample is compacted below 5% air voids. Permeable pores increase with an increase in sample radius. It is observed from this study that the permeable pore has a good correlation with permeability, whereas total pore shows a poor correlation with permeability. The effects of permeable and dead-end pores on moisture damage of asphalt concrete are evaluated using a moisture induced sensitivity testing device and the AASHTO T 283 method. It is observed that permeable and dead-end pores do not contribute to moisture damage of AC samples.     

热处理制度对玻璃金属封接行为的影响

本文借助光学显微镜观测手段,通过分析玻璃金属封接过程中平均孔径和孔隙率随封接温度和保温时间的变化,详细研究了热处理制度包括封接温度和保温时间对玻璃金属封接行为的影响。随着封接温度的升高,平均孔径先增大后减小,然而孔隙率先出现增加趋势,当封接温度高于980℃时基本则保持不变。随着封接时间的延长,平均孔径先逐渐增加后迅速降低,孔隙率则显著增加然后缓慢增加,接着迅速降低。另外,封接温度的提高和保温时间的延长都将导致无气泡带的变宽。本文根据封接热处理制度的变化,提出了一种空间气泡演变结构模型。     

浅谈硫酸盐热化学还原作用与碳酸盐岩储层发育

在碳酸盐岩层系热化学硫酸盐还原反应（Thermochemical Sulfate Reduction,TSR）是普遍发生的地质现象,通过对现有资料的研究（主要以川东北地区飞仙关组为例）,发现TSR反应是形成高含H2S气藏的重要原因。本文总结了现有研究水平下TSR的反应原理以及参与反应的各个组分,以及TSR对储层,尤其是深部储层的作用（主要以川东北地区飞仙关组为例）。同时,本文提出关于TSR作用仍旧有很多没有解决的问题。如TSR反应体系中固体的硬石膏能否参与反应、TSR反应的阶段性、TSR作用与白云化作用之间是否存在关系,以及TSR反应产物与储层溶蚀机制等。     

Improving pore morphology of PM 316L stainless steels by prealloyed powder prepassivation in 20% nitric acid

Abstract

The effect of prepassivation of prealloyed powder of 316L stainless steels on pore morphology and powder particle shape was investigated. Image analysis technique was used to study the effect of prepassivation, compaction and sintering temperature on the pore morphology of powder metallurgy 316L stainless steels. Porosity, dimension and morphology of the pores were characterised by means of four basic parameters: fraction of surface porosity, equivalent circle diameter, shape factor and elongation factor. In addition, SEM macrographs of powder particles were also investigated by applying the image analysis technique. The Feret’s average diameter and elongation factor were employed to describe the size and roundness of powder particles respectively. Annealing treatment reduced the equivalent circle diameter of pores and simultaneously improved f_shape and f_elong towards higher values. It was proposed that the prepassivation treatment reduced irregularity of powder particles through elimination of sharp corners of powder particles by exposure to acid environment.     

Morphology of nanoholes formed in silicon by wet etching in solutions containing HF and H2O2 at different concentrations using silver nanoparticles as catalysts

Holes with diameters of tens of nanometers were bored in Si(1 0 0) in aqueous solutions containing hydrofluoric acid and hydrogen peroxide utilizing silver nanoparticles as catalysts. The holes grew deeply in the [1 0 0] direction when the concentration of hydrogen peroxide was about 0.18 M. In addition to these vertical holes, holes were generated horizontal to the surface in the 〈1 0 0〉 directions near the surface of the sample. We found that the silver particles making the deep holes in the [1 0 0] direction were more spherical than those making the horizontal holes near the surface. These results indicate that the shape of the silver particles is an important factor controlling the direction of the holes. When the hydrogen peroxide concentration was increased to 1.8 M, as well as the vertical and horizontal holes, a microporous layer was formed on the top surface region. On the other hand, when the hydrogen peroxide concentration was lowered to 0.0018 M, holes did not show any preference for growing direction and were crooked. Even in HF solutions that did not contain hydrogen peroxide, holes were generated at a very slow rate in random directions if the solutions contained oxygen.     

Dielectric breakdown behavior of ferroelectric ceramics: The role of pores

Dielectric breakdown is a fundamental issue for ferroelectric ceramics. In this work, a phase-field method is introduced to study the breakdown behavior of ferroelectric ceramics with pores randomly distributed. Effects of the position and the size of pores on the breakdown behavior are analyzed. Results indicate that the position of pores, for example in grains or at grain boundaries, has a significant influence on the breakdown strength of ferroelectric ceramics. The nominal breakdown strength of ferroelectric ceramics with 2 % pores at grain boundaries is almost 50 % higher than 2 % pores in grains. Further, for ferroelectric ceramics with a certain porosity, the smaller the pore size, the higher the breakdown strength. As the nominal pore size decreases from 2.5 to 1, the nominal breakdown strength is enhanced from 0.73 to 1.16. Such results agree well with the widely accepted Gerson-Marshall model and previously published experimental observations.     

鄂尔多斯盆地三叠系延长组富有机质页岩孔隙特征及发育机制

页岩储层孔隙发育特征是页岩储层评价的重要内容,也是开展页岩油气赋存机理研究的基础。提出了通过“基质类型—孔隙产状—孔隙成因”划分孔隙类型的方案。利用氩离子抛光和场发射扫描电镜技术观察孔隙发育情况,根据基质类型和孔隙产状,识别了4类孔隙：粒间孔、粒内孔、有机质孔和微裂缝,并根据孔隙成因将粒间孔分为碎屑颗粒间原生孔、黏土矿物片体间孔和颗粒间溶蚀孔,将粒内孔分为长石颗粒内溶蚀孔、黏土矿物片体内孔和黄铁矿晶体间孔。有机质孔主要为有机质颗粒内的微裂缝和有机质内孤立分布的孔径较小的孔隙。微裂缝主要表现为纹层缝或页理缝。综合孔隙图像分析、低温液氮吸附实验结果、孔隙结构参数与矿物组成、有机碳含量和有机质成熟度等参数相关性分析,认为沉积条件、成岩作用和有机质热演化控制了孔隙的形成和保存。半深湖—深湖沉积环境下,富有机质页岩中发育重力流成因的薄层砂质纹层,纹层段碎屑颗粒含量高,有利于形成碎屑颗粒粒间孔、碎屑颗粒粒内孔和顺层微裂缝。早期成岩作用阶段形成黄铁矿,有利于形成黄铁矿晶间孔,但黄铁矿也是压实作用的主要参与者;压实作用造成粒间孔和粒内孔的孔径变小和孔体积降低,碎屑颗粒和黄铁矿与有机质颗粒间呈凹凸接触,有机质孔在压实作用下闭合导致有机质孔不发育;溶蚀作用促进长石粒间溶孔和长石粒内溶孔的形成,一定程度改善储层质量。在成熟度达到一定阶段(R_O≈0.75%)后,开始出现有机质孔。有机质孔发育程度差,一方面受成熟度的影响,另一方面可能是压实作用造成的。此外,富有机质泥页岩渗透性较差,烃类被吸附在有机质表面或溶于干酪根内部,造成干酪根体积膨胀也可能是有机质孔不发育的一种原因。