Carbon deposition on stainless steel in oxidising environments

Abstract

The formation of low-density carbon deposits onto metallic heat transfer surfaces in industrial environments of high carbon activity can have a deleterious effect on thermal efficiency. Often this deposition occurs under reducing conditions and involves carbide (typically of iron) formation as part of the process. It is possible, however, for filamentous carbon deposits to form at much higher oxygen potentials where carbide formation is not favoured thermodynamically. This study considers one such situation by examining the behaviour of a 20Cr25Ni austenitic steel used as fuel cladding in Advanced Gas-cooled nuclear reactors (AGRs). Carbon deposition has been produced in laboratory by exposure at 550°C to CO₂ containing 1%CO and 1000 vppm C₂H₄; the dissociation of the latter additive generates carbon activities much greater than unity. The oxygen potential of this gas is sufficient to oxidise iron and chromium, of the major alloy constituents, but not nickel. The deposition takes place onto substrates that are prepared as electron microscope samples which are subsequently examined by SEM and HREM (high resolution electron microscopy) techniques. The deposits formed consist of solid carbon filaments, approximately 30 nm in diameter, with turbostratic atomic layering. Each filament contains a 10–20 nm metallic nickel particle near its tip. It is argued, and supported by HREM evidence, that such particles are produced as a direct result of the oxidation of the alloy and that prior oxidation is necessary to produce the observed carbon deposition. It is also shown that inhibition of carbon deposition occurs when the oxygen potential of the depositing gas is increased sufficiently to oxidise nickel.     

European patents for biotechnological inventions – past, present and future

It is now well accepted that although biotech inventions may relate to living materials it is possible to secure patent protection for all but a limited number in certain defined categories. The author traces the development of biotech patents from the early days, when decisions of the Courts and the EPO set the necessary precedents, to the adoption of the European Directive in July 1998. He then goes on to explain in more detail the key features of the Directive and refers to a number of precedent decisions which, in combination with the Directive, show how certain problem areas have been tackled. Although emphasis is placed on the key areas of plant and animal patents, the patenting of gene sequences and issues of morality the author stresses that the established principles of novelty, inventive step and industrial application are, more often than not, adequate to decide the patentability of the vast majority of biotech inventions.     

凡口铅锌矿深部开拓方案的确定

本文根据凡口铅锌矿深部矿体赋存特点和开采技术条件，对四种可能的开拓方案：主井延深、主斜坡道汽车运输、盲主井和胶带输送机斜井运输方案进行了分析、比较，确定了主井延深方案为最佳开拓方案。     

矿山补充地质资源综合利用的研究

河台金矿建矿14年来．累计开采矿石量近200万t，生产黄金10t多，已关闭2个中段。将要关闭3～4个中段。由于黄金地质资源消耗快，研究如何有效综合回收部分表外矿、残矿、残余存窿矿石等补充地质资源，具有十分重要的现实意义。     

74××164芯片在微电脑家电中的应用及仿真

移位寄存器74××164因具有串并数据转换功能而在微电脑家电中广泛使用,文章对74××164在电路中实现按键扫描及显示功能的应用进行分析,并利用Proteus软件加以仿真演示。     

A study on the importance of dependent radiative effects in determining the spectral and total emittance of particulate ash deposits in pulverised fuel fired furnaces

This paper presents the results of an experimental and theoretical investigation on the importance of dependent effects in determining the emittance of ash deposits. A model has been developed to predict the spectral emittance (directional, normal, hemispherical) of semi-transparent and opaque particulate deposits without considering dependent effects. Predictions from this model have been presented to illustrate the effects of particle size and composition. Hemispherical transmission and reflection measurements have been performed on semi-transparent and opaque particular deposits over a wavelength range typical of pf fired furnances and spectral emittance has been deduced therefrom. Well characterised slag particles, with composition and size similar to ash deposits formed in pf fired furnances, have been used in the measurements. For the opaque deposit, difference between the model predictions and measurements, in terms of emittance, have been found to be significant at wavelengths up to 7 μm. This difference is believed to be largely due to dependent effects. Such measurements and comparisons appear to be the first of its kind and more experiments are recommended to quantify the effects.     

肾组织内特殊有形结构形成的肾脏病的电镜诊断

本研究对我院电镜室收集的12,332例肾活检标本进行透射电镜观察,对超微结构表现特殊有形结构或形成特殊形态沉积的肾脏病进行超微病理特点分析,根据电镜在其病理诊断中的作用分为三类:分别为决定性诊断作用、重要诊断价值和辅助参考作用。结果显示,肾组织内特殊有形结构形成的肾脏病占肾活检病例的1.65%,其中,以淀粉样变为最常见,其次为冷球蛋白血症肾损害。电镜检查对于大多数超微结构表现特殊有形结构的肾脏病的诊断具有重要诊断价值;尤其是对于早期淀粉样变、纤维样和免疫触须样肾小球病、致密物沉积病和Fabry氏病的诊断具有决定性诊断作用。     

大红山铜铁矿区多层复杂矿体开采对象优化圈定研究

为了解决多层价值差异较大的矿体互层产出条件下开采对象合理选择圈定的问题,采用了三维数字化手段,通过建立矿床数学模型及价值模型,客观分析矿体价值及其分布规律,结合技术经济判据,合理优化、选择和圈定开采对象。本文的探索和实践,为类似矿床开采对象圈定和选择提供了有价值的思路和分析方法。     

甘肃省瓜州县截山庙铅锌矿点地质特征及找矿方向

截山庙位于瓜州县南部的敦煌地轴上,是敦煌古陆核的中心部位,由一套太古界-古元古界的深变质二云斜长片麻岩、透辉石岩、斜长角闪岩、变粒岩等组成,铅锌矿化体赋存于红柱石-片岩和透辉石化大理岩的接触带内。矿化体受北西南东向断裂构造控制。铅锌矿化点属于接触交代型。矿化同时受构造裂隙系统的控制。     

Mathematical modelling of two-phase flow in a vertical well considering paraffin deposits and external heat exchange

Processes, occurring during exploration of gas-oil wells in frozen rock are simulated. A system of differential equations, describing hydro and thermal dynamics of an ascending two-phase flow of a hydrocarbon system in a vertical channel taking into account phase transitions and structure of a flow is developed. Kinetics of paraffin deposits on internal walls of an elevating column of a well are considered. The effect of the heat exchange of a well within frozen rock is developed using differential equations that describe the evolution of the radius of thermal influence of the well and the radius of the melting zone. We conclude with numerical research of some preventive ways of dealing with paraffin deposits.