Dynamic Fracture Responses of Alumina and Two Ceramic Composites

A hybrid experimental-numerical procedure was used to characterize the dynamic fracture response of alumina (Al₂O₃) and TiB₂-particulate/SiC-matrix and SiC-whisker/Al₂O₃-matrix composites. Unlike metals and polymers, dynamic arrest stress intensity factors (SIFs) did not exist in the monolithic ceramics and the two ceramic composites considered. Thus a running crack in these materials cannot be arrested by lowering the driving force, i.e., the dynamic SIF. Fractography study of the alumina specimens showed that the area of transgranular failure varied from about 3% to about 16% for rapid crack extensions in statically and impact loaded specimens, respectively. The influence of kinematic constraints which enforces transgranular flat crack extension, despite the higher fracture energy of transgranular fracture, is discussed.     

Fracture Energy of an Aligned Porous Silicon Nitride

The fracture energy of a porous silicon nitride with aligned fibrous grains was investigated, using a chevron-notched-beam technique. A crack was constrained to propagate normal to the grain alignment. The obtained fracture energy was ∼500 J/m², which was ∼7 times larger than that of a dense silicon nitride with randomly oriented fibrous grains. The large fracture energy was attributable primarily to the sliding resistance associated with interlocking grains.     

Effect of Light Exposure and Ultrasound on the Formation of Porous Silicon

We have investigated the effect of light exposure and ultrasonic (US) treatment on the formation of porous Si layers grown by electroless stain-etching technique. It was shown that; the He-Ne laser exposure resultedin a considerable increase in both the hydrogenation and the oxidation amounts in n-type Si, but a decrease in p-type wafers. The effect is attributable to effective change in the concentration of free hole carriers. The UV light exposure has led to the shift at the peak positions, indicating probably a change in bonding configuration, and increase in oxidation. Also, a correlation was established between the ultrasonic treatment and the microstructure. The US treated samples exhibit a decrease in hydrogenation and oxidation. UV exposure together with the US has led to a further decrease in both hydrogen and oxygen amounts, which was rather indicative of an excessive surface etching.     

唐山国丰高炉生产低硅生铁的分析

唐山国丰钢铁有限公司１号高炉，有效容积１７９ｍ＾３，自１９９６年１０月开炉以来，重视原燃料的质量，不断探索合理的炉料结构和装料制度，严格控制渣中ｗ（ＭｇＯ），加之其它技术的采用，生铁中的含硅量一直处于较２低水平，降低了焦比，提高阴产量，取得了良好的经济效益。     

Analysis of Publications on Porous Silicon: From Photoluminescence to Biology

The issue of porous silicon has attracted much research during last seven years due to perspectives of the formation of all-silicon optoelectronic devices (first of all—LEDs). The work presents a bibliographic analysis of publications made during the period from 1990 (when red-light photoluminescence from porous silicon was first reported by Dr. L. Canham) to the present time in order to reveal the existing tendencies of the researches (what particular field attracts the most research, who is the most fruitful in publishing articles related to porous silicon, etc.). The contributions of different research centres and countries are also evaluated. Personal contributions of leading researchers are disclosed and their citation ranking is given. It is concluded that emerging applications of porous silicon in micro-machining, chemical and biological monitoring will stimulate further activities in studying the mechanism of porous silicon growth and its physical and chemical properties.     

Novel Structures for Porous Silicon Light-Emitting Diodes

In this paper, two novel structures of porous silicon (PS) light-emitting diodes (LEDs) are proposed aiming at the reduction of series resistance, R_s. The basic idea of the novel structures is to suppress the excessive growth of nanoporous silicon (nano-PS) layer that is electroluminescence- (EL-) active but highly resistive. The initial wafer of the first structure consists of a lightly-doped layer stacked on a highly-doped substrate. As a consequence of anodization, nano-PS layer is formed only in the lightly-doped layer, while meso-PS layer with moderate resistivity is formed in the highly-doped substrate. The second structure consists of alternately stacked nano- and meso-PS layers, since it is expected that multiple thin nano-PS layers connected in series are less resistive than a single thick nano-PS layer. Preliminary experimental results proved the effectiveness of these novel structures on the reduction of R_s.     

Superlattices as Characterisation Tool for the Beginning of PS Formation

Initial stage of porous silicon (PS) formation has been studied in an original way. Multilayer structures constituting of very thin layers of low porosity and thick layers of high porosity have been fabricated and characterised by optical tools and electron microscopy. The non linear behaviour resulting in a change in the dissolution velocity has been quantified by using a stack layer structure. Finally using thermal oxidation it has been shown that, due to the selective oxidation as a function of the porosity, porous silicon can be used to produce a Si/SiO₂ like structure.     

Infrared Reflection Spectroscopy and Effective Medium Modeling of As-Anodized and Oxidized Porous Silicon Carbide

We present a study of the infrared reflectance of porous silicon carbide (PSC) formed by the electrochemical dissolution of silicon carbide substrates of both 6H and 4H polytypes. The reflectance from n-PSC, both as-anodized and passivated, is reported for the first time. The passivation of PSC has been accomplished using a short thermal oxidation. Fourier transform infrared (FTIR) reflectance spectroscopy is employed ex situ after different stages of the thermal oxidation process. The characteristics of the reststrahlen band normally observed in bulk SiC are altered by anodization; further changes in the reflectance spectra occur following oxidation for different periods of time. An effective medium theory model that includes air, SiC and SiO₂ as component materials is shown to characterize the observed changes in the reflectance spectra after different stages of PSC oxidation.     

新型高性能高速烧嘴护套的研制

本文介绍了新型高性能高速烧嘴护套所用的材料－Ｓｉ３Ｎ４结合ＳｉＣ的特性，根据实验确定了工艺路线。在简介氮化烧成机理的基础上，对试验结果及现场使用情况进行了分析。作为替代进口产品，具有良好的推广应用价值。     

聚丙烯装置制氢系统的改造

概述了武汉石油化工厂聚丙烯装置制氢系统存在的问题和改造措施。改造后制氢系统运行可靠，氢气质量有所提高，供应稳定，并降低了制氢系统的能耗和水耗，确保了聚丙烯装置长周期运行。