Comparison of Different boiler tube materials and the corrosion resistance in burning of municipal waste

The aim of this paper is to investigate the corrosion risks in burning of pretreated municipal waste as additional fuel together with bark in a fluidized-bed boiler. It was deduced that the burning of bark alone did not cause corrosion in the materials tested. When the waste was burnt the corrosion of steels was insignificant when providing that the surface temperature of material was below 300°C. When the surface temperature was over this temperature, the burning of municipal waste caused corrosion in the conventional boiler steel. The stainless steels were not corroded even in these conditions. The impact of waste combustion on flue gas releases was also studied.     

Nanoparticles α-Al2O3 prepared by combustion synthesis method

Nanometer α-Al2O3 powders were synthesized by the method of low-temperature combustion synthesis (LCS) with aluminum nitrate nonahydrate and urea as raw materials. The prepared powders were studied by XRD,TG-DTA, FT-IR and TEM. It is found that the average size of particles is 60 -80 nm. The optimal synthetic conditions are obtained, i. e. , the suitable fuel is urea; the molar ratio of oxidizer to fuel is 1: 2 and the igniting temperature is 700 ℃. The results show that the size of particles is governed by synthesizing temperature, the fuel and the molar ratio of oxidizer to fuel. TEM image of the particles collected shows that the crystal habits of particles have a spheric structure and particles are polycrystal.     

The Effect of Fuel Types on Porous Alumina Produced via Soft Combustion Reaction for Implant Applications

This article describes the effects of fuel types on the porous structure of alumina produced using a soft combustion reaction. There are several combustion parameters that could affect the porous structure of the alumina produced such as fuel-to-oxidizer ratios, ignition temperature, and type of fuels. In this study, the effect of fuel types on alumina properties was studied. Citric acid, glycine, and urea were used as fuels along with aluminum nitrate as an oxidizer. The properties of porous alumina produced using three different fuels were compared to determine the optimum fuel that could produce the best properties for implant applications. X-ray diffraction analysis showed that single-phase alumina powder was obtained in all samples. Morphology observation using scanning electron microscope (SEM) on sintered bodies showed open pores which had potential to be used in implant applications. Porous alumina produced using glycine as fuel (AG) showed the best properties; high surface area of 8.7 m²/g, porosity of 70% and sintered density 1.37 g/cm³.     

过氧化甲乙酮安全使用

过氧化甲乙酮属强氧化剂,常应用于玻璃钢制品生产和工业防腐施工中做为不饱和聚酯树脂固化剂的有机强氧化剂。它对呼吸道有刺激作用,会灼伤皮肤和眼睛;对热敏感,可燃且助燃,遇火源、火花(电火花)、静电或接触还原剂会引起剧烈反应,产生燃烧或爆炸。为此必须对其进行正确使用和管理,做到安全使用。     

富氧燃烧条件下钢坯加热特性的数值模拟

以某轧钢厂步进式加热炉为研究对象,利用Fluent软件对炉内气相流动与燃烧和钢坯加热过程建立数学模型,并开发了用户自定义函数处理钢坯移动。炉膛内气体流动采用Realizable k-ε模型,燃烧过程采用非预混燃烧模型,辐射传热采用DO模型来计算。通过所建立的数学模型,模拟研究了氧气体积分数为21%～35%的助燃气体与燃料燃烧对钢坯加热特性的影响。结果表明,随着氧气浓度的增加,燃烧区的烟气温度逐渐升高,导致钢坯具有更快的升温速率;由于富氧燃烧在燃烧区产生了更均匀的温度场,因此在氧气浓度为35%时,钢坯的黑印温差仅为15 K,比空气工况下的黑印温差低了20 K;当助燃气体中氧气体积分数从21%增加至35%时,钢坯的辐射传热量也随之增加,加热炉热效率从41.1%提高至48.4%。     

Combustion-Supporting Effect of Common Carbonous Solid Waste on Anthracites

In order to study the combustion characteristics of anthracite with additives, the influence of common carbonous solid waste (CSW) on anthracite is studied by thermogravimetry. The results show that appropriate CSW additives mixed with pulverized coal (PC) at PZH Steel can promote the combustion of PC and increase the burning ratio of anthracite greatly. The greater the additive content, the higher the burning ratio at the same conditions. The dynamics models show that the particle size of CSW additives, oxygen concentration, and the diffusion coefficient of oxygen are all very influential for their combustion characteristics. The heat of CSW combustion is absorbed by coal powder, and it consists of part of the coal powder accumulated heat. Then, accumulated heat is higher than dissipation heat ahead of time, so CSW can support combustion of coal powder effectively.     

Burning products of TA15 titanium alloy by friction oxygen concentration method

The microstructural characteristics, elemental distribution law and microscopic formation mechanism of the burning products of TA15 titanium alloy were investigated by friction oxygen concentration method, associated with in situ observation, X-ray diffraction(XRD),scanning electron microscopy(SEM) and energy-dispersive spectroscopy(EDS) analyses, providing the thoughts to improve fireproof property. The results show that, when the friction contact pressure(p_(fric)) is 0.20 MPa and oxygen concentration of premixed air flow(c_0) is 60 vol%, TA15 titanium alloy produces violent sparks and presents dazzling white light during combustion. The generated products after burning are mainly TiO_2 and small amount of Al_2O_3 oxides. Four distinct zones form from the combustion surface to the alloy matrix, and they are in the sequence of combustion zone, fusion zone, heat-affected zone and transition zone. Further, combustion zone is composed of TiO_2 and A1203 compounds, containing obvious cracks. In the fusion zone, discontinuous oxygenrich Al-based solid solution forms, and the elemental distribution has strong volatility. In the heat-affected zone,there are abundant of Ti-based solid solution and small amount of Al-and Mo-based solid solution. Transition zone is made of lamellar structure. Two technical approaches are given to prevent oxygen diffusion inside the reaction zone and reaction-affected zone. On the one hand,the content of Al is designed as the upper limit of alloy composition; on the other hand, fireproof coatings are deposited on the surface of the alloy.     

Enhancing the Antibacterial Efficiency of ZnO Nanopowders Synthesized by Combustion Method Through Ag + Fe Co-doping

(Ag + Fe)-doped ZnO nanopowders have been synthesized using combustion method. Ag doping level was kept as 2 at.%, and Fe doping level was varied from 3 to 6 at.%, and the structural, optical, surface morphological, and antibacterial properties have been investigated. The structural studies show that ZnO/(Ag + Fe) nanopowders have hexagonal wurtzite structure with a preferential orientation along the (101) plane. The FE-SEM images indicate that there is a gradual decrease in the grain size with the increase in the doping level of Fe, and the TEM images are correlated well with FE-SEM images. The XPS profile clearly confirms the presence of expected elemental composition. Photoluminescence studies reveal the presence of extrinsic defects in the material. Antibacterial activity of Ag- and Fe-doped ZnO nanopowders against Vibrio parahaemolyticus, Vibrio Cholerae, and Staphylococcus aureus bacteria was also investigated.     

激光立体成形Ti-25V-15Cr合金的阻燃性能研究

本研究针对激光立体成形 Ti-25V-15Cr合金的阻燃性能展开,采用直流电弧激发燃烧法测试其阻燃性能并与锻造Ti40合金进行比较,在此基础上,基于二者原始组织分析、燃烧产物的观察与分析揭示其阻燃机理。结果表明,激光立体成形Ti-25V-15Cr合金的燃烧速率略低于锻造Ti40合金。燃烧后各区域组织分析结果表明,激光立体成形Ti-25V-15Cr和锻造Ti40合金燃烧产物区均由Ti的氧化物、V的氧化物以及基体组成,Ti-25V-15Cr燃烧产物区氧化物面积略小于锻造Ti40合金,同时燃烧热影响区的晶界和亚晶界处发现明显的V、Cr元素的偏聚。激光立体成形Ti-25V-15Cr合金中局部枝晶组织以及亚晶粒的形成增加了微观结构的缺陷,在受热条件下使得V、Cr元素的扩散能力增强,是其抗燃烧性能略优于锻造Ti40合金的原因。     

Special aspects of localized High-temperature corrosion

As in aqueous corrosion a localized corrosive attack can be important in high-temperature corrosion of metallic materials and become, unvoluntarily, a lifetime determining factor for combustion systems. Deposit-induced corrosion is the most important form of localized corrosion on alloy 800 and other materials in advanced coal combustion systems. Coal-ash deposits may cause a sulfidation/oxidation reaction which propagates preferentially along grain boundaries into the underlying metallic material. Preferred grain boundary corrosion may also occur in the walls of the fuel nozzle tubes of gas combustion systems. In this case, an oxidation reaction takes place. The lifetime of the tubes can be increased by use of a special alloy 601 H grade. Pitting may be observed in coal combustion systems. It has also been observed on alloy 601 after service in ceramic firing kilns where it is promoted by the presence of chlorine. Additionally, pitting occurs under carburizing conditions (metal dusting) as does cracking being similar in appearance to stress corrosion cracking in aqueous corrosion. Compared to deposit-induced and grain boundary corrosion, crevice corrosion is of minor importance in high-temperature corrosion. Only one example has been identified so far on alloy 600 but which may also be interpreted as a kind of deposit-induced corrosion.     

Synthesis and sintering of indium tin oxide nanoparticles by citrate-nitrate combustion method

Spherical indium tin oxide(ITO) nanoparticles were synthesized by combustion method using citric acid as fuel and nitrates as oxidizer.The obtained ITO nanoparticles were characterized by TG-DSC,FT-IR,XRD,BET,TEM,and SEM.The ITO nanoparticles grew steadily with the increase of heat treatment temperature,and the 700℃ calcined particles had a crystallite size of 25.3 nm and a specific surface area of 26.1 m2·g-1.The avoidance of chlorine ions in the synthesis process decreases particle agglomeration and promotes powder densification.The 900℃ sintered pellet had a density of 67.6% of theoretical density(TD) and increased steadily to 97.3% for the 1400℃ sintered ceramics,respectively.     

Role of the solid/liquid interface faceting in rapid penetration of a liquid phase along grain boundaries

A model is developed for describing rapid penetration of a liquid phase along a grain boundary. It is based on the assumption of a highly faceted solid/liquid interface. Experiments showing the faceting of the solid/liquid interface in grain boundary penetration experiments are presented. The basic hypothesis of the model are an undersaturated solid and a positive spreading coefficient of the liquid phase along the grain boundary. The model explains the apparent concave shape of the tip of the groove and the reason why penetration also occurs if the liquid phase is pre-saturated with the material of the solid. Moreover it predicts a power law with an exponent close to unity for the time dependence of the depth of penetration of the liquid layer along the grain boundary.     

Model analysis for combustion characteristics of RDF pellet

Fundamental studies of the combustion characteristics and the de-HCl behavior of a single refuse-derived fuel(RDF) pellet were carried out to explain the de-HCl phenomena of RDF during fluidized bed combustion and to provide data for the development of high efficiency power generation technology using RDF previously. For further interpreting the devolatilization and the char combustion processes of RDF quantitatively, an unsteady combustion model for single RDF pellet, involving reaction rates, heat transfer and oxygen diffusion in the RDF pellet, was developed. Comparisons of simulation results with experimental data for mass loss of the RDF samples made from municipal solid waste, wood chips and poly-propylene when they were heated at 10K/min or put into the furnace under 1073K show the verifiability of the model. Using this model, the distributions of the temperature and the reaction ratio along the radius of RDF pellet during the devolatilization process and the char combustion process were presented, and discussion about the inference of heating rate on the combustion characteristics were performed.     

搅拌摩擦焊中动态再结晶及硬度分布的数值模拟

使用率相关弹粘塑性本构模型模拟了搅拌摩擦焊接过程,并着重研究了过程参数对搅拌摩擦焊接动态再结晶过程以及搅拌区内材料硬度的影响．结果表明,在搅拌区内焊接构件上、下表面沿垂直于焊缝方向的硬度分布规律不同．焊接构件顶部材料的硬度分布符合实验得到的结果,即焊缝中心线附近材料硬度较低,热力影响区外材料硬度逐渐升高并最终达到母材的硬度;但是在焊接构件下表面并不显示这一硬度分布规律．搅拌区内材料的硬度与搅拌头转速无明显关系,但随焊速的增加而增加．焊接构件中部材料的晶粒尺寸大于焊接构件底部材料的晶粒尺寸,且搅拌区内晶粒尺寸随搅拌头转速的增加趋于均匀．     

等离子沉积直接成形传热传质与晶粒生长多尺度数值模拟

运用有限容积法(FVM)对等离子沉积直接成形(PDM)过程中的沉积层温度场、熔池液相流动场进行了数值模拟.采用水平集方法追踪液/气界面演变过程,采用焓孔隙率法处理固/液相变过程,并采用Monte Carlo(MC)方法模拟沉积温度载荷作用下成形件热影响区(HAZ)组织的晶粒长大过程.基于所提出的FVM-MC法耦合的宏/微观统一模型模拟了镍基高温合金K163薄壁零件PDM过程中沉积层HAZ晶粒的生长过程,预测了在重复热冲击作用下热影响区晶粒长大与转变过程.模拟结果表明,热冲击频率与温度幅值直接决定热成形件的组织形态;热扫描速度影响熔池液相流动与温度场分布,从而间接决定了成形件的最终晶粒尺寸与分布.随着热扫描速度的增加,成形件晶粒趋于细化.在保证粉末充分熔融条件下,提高热扫描速度可以细化HAZ的晶粒尺寸.     

On the development of grain growth resistant tantalum alloys

During exposure of pure Ta to temperatures up to 1800 °C pronounced grain growth combined with embrittlement becomes a major problem. Doping with elements which form nanometer to submicron sized oxide or silicide particles is an appropriate way to prevent, or at least to hamper, uncontrolled grain growth. In the present paper the effects of doping with varying combinations of Si and Y on microstructure and mechanical properties of cold-worked and annealed Ta have been investigated. For these purposes methods including small-angle neutron scattering and transmission electron microscopy as well as light-optical microscopy have been applied. Ta samples doped with Si show a higher hardness and strength than those doped with Y or made from pure Ta powder. However, the grain growth behaviour of all alloy variants is rather similar. The particle size distributions of doped Ta change significantly with varying annealing treatments as coarsening and dissolution of the prevailing particles (oxides and silicides) take place. Therefore, particles do not play a significant role in grain growth kinetics at temperatures as high as 1800 °C. However, this loss in retarding force is partially compensated for by an increased solution drag stemming from elements in solid solution.     

基于板温炉温串级调节的连退炉燃烧控制系统

介绍了一种基于板温、炉温串级调节的冷轧带钢连续退火炉燃烧控制系统,结合烧嘴管理、空燃比动态优化和双交叉限幅燃烧控制策略,该系统能够提供精确和高效的燃烧和带钢温度控制.     

稀土钨电极在电推进系统中的耐烧蚀性能研究

阴极作为电弧加热发动机的“心脏”,担负着加热工质气体产生推进力的作用,由于卫星服役周期长,点火次数频繁,对阴极材料的寿命及耐烧损性能提出了很高的要求。为寻求耐烧损性能优异的阴极材料,以W-La-Ce-Y与W-La-Y-Zr电极为基础,采用氢还原-中频烧结的方法制备W-La-Ce-Y-Re与W-La-Y-Zr-Re电极材料。模拟发动机实际工况在250A电流下进行燃弧试验,测量燃弧后电极的质量损失并对电极尖端的组织形貌进行观察表征。结果表明,加铼电极在燃弧2h后的烧损质量更少,尖端形貌变化程度更小,耐烧损性能更好。在扫描电镜下观察到铼的加入抑制了尖端表面枝晶的生长,弱化了钨基体晶粒的再结晶程度,并探讨了稀土氧化物的迁移途径;在金相显微镜下观察到加铼电极的再结晶晶粒更细小,铼起到了细化再结晶晶粒的作用。在不同工作电流下测得加铼电极的阴极压降更低,铼的加入提升了电极材料的电子发射性能。     

Low temperature processing of dense samarium-doped CeO2 ceramics: sintering and grain growth behaviors

Samarium-doped CeO₂ is a leading electrolyte for applications in solid oxide fuel cells (SOFCs), which requires a typical sintering temperature of 1400–1600 °C. By synthesizing reactive powders via carbonate precipitation, fully dense CeO₂ ceramics doped with 0–20 at.% of samarium have been fabricated in this work via pressureless sintering at a significantly lowered temperature of 1000 °C. The resultant ceramics show ultrafine grain sizes of ∼0.15–0.75 μm, depending upon the dopant concentration. Sintering studies indicated that samarium doping retards both densification and grain growth but increases the rate ratios of the two in the intermediate stage of sintering. Subsequent investigations on the grain growth in the fully densified ceramics also showed the suppressing effects of dopant, which tend to saturate at 10 at.% of samarium. The activation energy for grain growth increased from ∼186 to ∼254 kJ/mol by raising the samarium concentration from 5 to 20 at.%.