CeO2催化强化高炉喷吹煤粉燃烧机制

为了研究稀土氧化物CeO2对高炉喷吹煤粉的助燃机制,以某炼铁厂高炉喷吹煤粉为原料,利用煤粉燃烧炉进行煤粉燃烧试验并收集未燃煤粉,通过热重-差热法分析CeO2对喷吹煤粉的助燃机制,结合XRD和SEM检测分析未燃煤粉.结果表明:助燃剂CeO2对喷吹煤粉的助燃效果显著,其添加比例控制在1.5％(质量分数)左右比较适宜;CeO2在煤粉固定碳表面上形成络合盐Ce4+(CO-)4,减弱了两相反应物间的势能垒,促使挥发分的开始燃烧放热温度降低,固定碳燃烧温度区间变窄;随着CeO2的加入,Ce4+ (CO)4成倍增长,在XRD图谱中表现为未燃煤粉的微晶尺寸逐渐增大;在CeO2的作用下未燃煤粉颗粒的平均粒径与原煤未燃煤粉颗粒的平均粒径相比减小了3.48 μm,表面出现大量孔洞结构.     

Effect of Process Parameters on the Characteristics of Nanocrystalline Alumina Particles Synthesized by Solution Combustion Process

Nanocrystalline ceramic oxide particles with high purity can be synthesized efficiently by the solution combustion synthesis route, which is based on redox reactions between metal salts and reducing agents such as urea and glycine. In the present study, nanocrystalline alumina powders were synthesized using aluminium nitrate nonahydrate as the metal salt and urea as the fuel. The powders were characterized primarily for the phases present and crystallite size (from X-ray diffractometry) and morphology (by scanning electron microscopy). When stoichiometric amounts of the starting chemicals were taken, X-ray diffraction (XRD) analysis of the synthesized powder revealed it to be phase-pure α-Al₂O₃, with a crystallite size of 42 nm. Electron microscopy of the synthesized powder revealed a flaky morphology. Further, the pH value of the solution containing the stoichiometric amounts of the aluminium salt and the fuel was systematically varied by dissolving in liquid ammonia. It was observed (from XRD analysis) that an increase in the pH progressively stabilized the metastable γ-Al₂O₃ phase. An increase in the fuel (urea) content had no effect on the phase stability, but decreased the crystallite size of α-Al₂O₃. A crystallite size of 29 nm could be achieved with an excess fuel ratio of 1.5 over the stoichiometric value.     

Influence of copper content on structural features and performance of pre-reduced LaMn_(1-x)Cu_xO_3 (0≤x<1) catalysts for methanol synthesis from CO_2/H_2

A series of pre-reduced LaMn1-xCuxO3 (0≤x<1) catalysts for methanol synthesis from CO2 hydrogenation were prepared by a sol-gel method. The catalytic performances were strongly dependent on the copper content. XRD investigation revealed that the single perovskite structure could be preserved after being reduced, when the substitution for Mn by Cu was less than 50%. The Cu-doped (x=0.5) LaMnO3 was much more active than the other catalysts for reaction, showing CO2 conversion up to 11.33% and methanol selecti...     

Green mediated synthesis of lanthanum doped zinc oxide: Study of its structural,optical and latent fingerprint application

The present paper summarises the synthesis of La³⁺ doped zinc oxide nanoparticles using Aloe vera gel by solution combustion method and the characterization using a powder X-ray diffractometer (PXRD), a transmission electron microscope (TEM), an X-ray photometric spectrometer (XPS), a Raman spectrometer and their applications in optical devices and latent fingerprinting. PXRD pattern confirms the crystallite size of La³⁺ doped ZnO varies from 13 to 20 nm. Crystallite size varies inversely with doping concentration. Photoluminescence properties are found to be the maximum for 2 mol% doping concentration. PL spectra extends the use of ZnO:La³⁺ nanoparticles in blue green LED. These nanoparticles also have superior property as a fluorescent labels in fingerprints.     

Gel-Combustion Synthesis of Nanocrystalline Cerium Oxide and Its Powder Characteristics

Nanocrystalline ceria powders were prepared by using citrate gel combustion. The influence of the composition of the combustion mixture on the characteristics of the final product was investigated. Ceria powders obtained by calcining the combustion residue in air at 1073 K were characterized for their specific surface area (SSA), X-ray crystallite size (XCS), bulk density (BD), particle size distribution (PSD) and residual carbon. The dependence of these properties on the fuel to oxidant ratio (R) of the initial mixture was investigated. The microstructure of the calcined ceria powders prepared from a mixture with R = 0.25 was investigated by using high resolution transmission electron microscopy. All the calcined powders were pelletised and sintered at 1473, 1673 and 1873 K, and their sinterability was compared by measuring the density of the sintered pellets. A maximum sintered density of 98 % theoretical density could be achieved at a temperature as low as 1473 K for the first time for the powder prepared from a mixture with R = 0.75. The systematic dependence of the properties of these powders on the composition of the initial mixture is being reported for the first time. Powders obtained from a mixture with an R value 0.25 showed a linear increase in sintered densities with the sintering temperature. Other powders exhibited anomalous decrease in the sintered density at high temperature, probably due to irregular grain growth coarsening.     

Combustion synthesis and stability of nanocrystalline La2O3 via ethanolamine-nitrate process

Pure nanocrystalline La2O3 powders were successfully prepared by the combustion method.The effect of ethanolamine-to-nitrate ratio on phase composition and crystallite size of the combustion products was systematically investigated.Pure hexagonal La2O3 powders were almost formed in stoichiometric reaction(ψ=1.15),while metallic La phase was obtained in fuel-rich conditions(ψ≥3.0).The as-synthesized hexagonal La2O3 was found to be chemically unstable in ambient air since a complete transformation to hexagonal La(OH)3 was detected after 24 h exposure to air.The resulting hexagonal La(OH)3 showed an excellent ability to remove water pollutant and could nearly remove 100% of the Congo red at room temperature with a removal capacity of 143.5 mg Congo red/g.The phosphate adsorption data on hexagonal La(OH)3 agreed well with the Langmuir model with the estimated maximum adsorption capacity of 57.8 mg/g.     

Ti-W-C体系燃烧合成产物颗粒形貌分析

研究了Ti-W-C体系燃烧合成产物相组成及颗粒及颗粒形貌特征。结果表明：W含量较低时，燃烧高温使燃烧前沿Ti粉熔化，能合成单相（Ti,W)C,且产物聚合颗粒致密，其组成晶粒生长完整，球磨后粉末粉度较粗，W含量增加，W与C反应不完全，TiC-WC固溶不充分，产物多晶聚合体颗粒疏松，球磨后粉末粒度较细。     

Synthesis of Nanoscale Nd-Doped Ceria Via Urea-Formaldehyde Combustion Method

Nanocrystalline neodymium-doped ceria solid solutions with Nd³⁺ concentrations varying from 4 to 20 mol pct have been synthesized by gel combustion method, using urea-formaldehyde as fuel for Nd doping. The combustion reaction is explained through differential scanning calorimetry (DSC)-differential thermogravimetric analysis (TGA), whereas the synthesized materials are characterized through X-ray diffractometry (XRD), field-emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). The phase obtained from the exothermic reaction contains Nd-substituted CeO₂. The deviation of the lattice parameter from Vegard’s law and the decrease in crystallite size with dopant concentration has been explained. The as-synthesized particles are largely nanoporous single crystallites, existing in loosely held spherical-shaped agglomerates. The size of the agglomerates increases with increasing dopant content. High-resolution TEM (HRTEM) reveals the fact that the unit cells are strained.     

Densification of Al 5083 Mechanically Alloyed Powder by Equal Channel Angular Pressing

Equal channel angular pressing (ECAP), one of the most important methods in SPD, is used for the consolidation of mechanically alloyed Al 5083 powder. This paper mainly focuses on the densification of Al 5083 mechanically alloyed powder by ECAP with and without application of back pressure up to three passes with four different routes at room temperature. Aluminum can is used to encapsulate the powder. The particle size, crystallite size, microstructure and density were evaluated by scanning electron microscope and X-ray diffraction peak profile analysis. The crystallite size was measured by Williamson Hall analysis. Density and hardness were increased with increasing number of passes and upon sintering after ECAP. Good densification as well as good powder bonding was observed after three passes of ECAP.     

Modeling the reaction synthesis of shock-densified titanium-silicon powder mixture compacts

The reaction behavior of shock-consolidated Ti-Si powder mixture compacts, densified at 5 to 7 GPa pressure, was investigated to determine conditions required for solid-state reaction synthesis leading to the formation of dense Ti₅Si₃ intermetallic compounds with fine-grained microstructure. It was observed that at temperatures greater than 1000 °C, the heat released following reaction initiation in the solid state exceeds the rate of heat dissipation causing a self-propagating combustion-type reaction to take over the synthesis process forming highly porous reaction products. A reaction synthesis model was developed to allow the prediction of optimum conditions necessary to ensure that the bulk of the reaction in dynamically densified Ti-Si powder compacts occurs by rapid solid-state diffusion and without being taken over by the combustion process. The model incorporates mass and heat balance with the kinetics evaluated using experimentally determined apparent activation energies for solid-state and combustion reactions. Considering the decrease in activation energy (as measure of degree of shock activation), average particle size, and compact porosity as the main variables, the model plots the fraction reacted as a function of time for various postshock reaction-synthesis temperatures, illustrating the dominant reaction mechanism and kinetics. The results show that although changes in average particle size and compact porosity influence the synthesis temperature above which the reaction may be taken over by the combustion-type process, lowering of the activation energy via shock-compression influences the time for reaction completion in the solid state.     

Study on reaction mechanism of low temperature preparation of nanocrystalline LaCoO3-λ

Perovskite-type oxide nanocrystalline LaCoO3-λ was prepared using the citrate method. The structure and morphology of the sampies were characterized by powder X-ray diffraction （XRD） and transmission electron microscopy （TEM）. The intermediate products were analyzed by thermal gravimetric and differential thermal analysis （TG-DTA） technology. The results showed that nanocrystalline LaCoO3-λ with a granula of 30-50 nm had a cubic perovskite structure. The reaction mechanism of low temperature preparation was suggested as follows： the metal complex was first formed by the combination of metal ion and citric acid; and then it decomposed into an aconitic acid complex, followed by an oxycarbonate, and finally a perovskite-type oxide.     

焦粉与兰炭对高炉混煤燃烧特性的影响

 为了探究焦粉、兰炭替代无烟煤进行喷吹对混煤燃烧的影响,使用新型高炉喷煤燃烧模拟试验装置与热重分析设备,研究了焦粉、兰炭以及混煤粒度对混煤燃烧的影响。利用扫描电镜(SEM)与能谱仪(EDS)观察了未燃煤粉的外观形貌。研究结果表明,粒度降低对燃烧有促进作用,焦粉用于喷吹的粒度应低于0.074 mm;兰炭替代无烟煤没有明显影响,而焦粉作用明显;当焦粉添加量超过15%时,混煤燃烧性能急剧下降。兰炭与焦粉对混煤燃烧性的影响不同,主要原因是兰炭与焦粉具有不同的化学性能与结构。从混煤燃烧性能的角度考虑,少量焦粉替代无烟煤用于高炉喷吹是可以被接受的。     

Preparation of La0.9RE0.1MnO3 Ultra-fine Particles Used for CH4 Oxidation

Ｐｅｒｏｖｓｋｉｔｅ ｔｙｐｅｏｘｉｄｅｓ (ｇｅｎｅｒａｌｆｏｒｍｕｌａＡＢＯ3 )ｈａｖｅｂｅｅｎａｔｔｒａｃｔｉｎｇｍｕｃｈａｔｔｅｎｔｉｏｎｆｏｒｍｏｒｅｔｈａｎｔｗｏｄｅｃａｄｅｓｄｕｅｔｏｔｈｅｉｒｐｏｔｅｎｔｉａｌｃｏｍｍｅｒｃｉａｌａｐｐｌｉｃａｔｉｏｎｓａｓｃａｔａｌｙｓｔｓｆｏｒｖａｒｉｏｕｓｒｅａｃｔｉｏｎｓ :ｏｘｉｄａｔｉｏｎｏｆＣＯ[1～ 3 ] ａｎｄｌｉｇｈｔｈｙ ｄｒｏｃａｒｂｏｎｓ[4～ 7] ,ｃｏｍｂｕｓｔｉｏｎｏｆｎａｔｕｒａｌｇａｓｏｒＣＨ4 [8～ 1 1 ] (ｔｏｃｏｎｔｒｏｌＮ…     

钙钛矿型稀土复合氧化物整体式催化剂的研究进展

概述了钙钛矿型稀土复合氧化物用于燃烧催化剂的发展动态 ,综述了钙钛矿型稀土复合氧化物整体式催化剂的研究进展 ,并分析和归纳了相关的影响因素及其中钙钛矿型稀土复合氧化物粉体的制备技术     

On the kinetics of mechanical alloying

The kinetics of solid-state displacement reactions during mechanical alloying have been investigated. The effects of charge ratio and ball size on the progress of the reaction between CuO and Fe have been evaluated from measurements of ignition temperature, combustion time, and crystallite size. The reaction kinetics are shown to increase with charge ratio. This is rationalized in terms of the effect of charge ratio on the number of ball/particle collisions. Ball size influences reaction kinetics through both the particle collision frequency and collision energy.     

Preparation of Freestanding Zn Nanocrystallites by Combined Milling at Cryogenic and Room Temperatures

The present investigation reports the preparation of freestanding nanocrystalline Zn by combined mechanical milling at cryogenic and room temperatures. The cryomilling is used as an effective means of rapid fracturing. The detailed scanning electron microscopy and transmission electron microscopy observations indicate that the minimum crystallite size is 6 ± 2 nm after 3 hours of cryomilling. The crystallite size increases to 30 ± 2 nm after 3 hours of room temperature milling of the cryomilled powder due to deformation-induced sintering. Detailed theoretical analysis allows us to obtain a diagram of size of the nanoparticles formed vs temperature to explain the experimental findings.     

低温燃烧法制备Ce_(0.8)Sm_(0.2)O_(1.9)电解质固溶体及其烧结性能的研究

采用柠檬酸–硝酸盐低温燃烧合成法,以Ce(NO_3)_3·6H_2O为氧化剂,柠檬酸为还原剂,制备Sm_2O_3掺杂的Ce_(0.8)Sm_(0.2)O_(1.9)(SDC)超细粉体,利用XRD、TG-DSC、FT-IR、SEM及FESEM等手段对制备样品的晶相结构、热分解过程、微观形貌以及团聚情况进行研究.结果表明:柠檬酸与硝酸盐组成的干凝胶自蔓延燃烧点火温度为270.0℃;粉体经600℃焙烧2 h后,形成了单一立方萤石型结构的固溶体,平均晶粒度为18.80 nm.粉体的结晶性能完善,分散性能良好,粒子间仅有微弱的软团聚.将素坯在1 250℃烧结2 h,即可得到相对密度为95.5%的陶瓷烧结体.     

Microalloying in sintered steels by mechanical alloying: evolution of nanostructure during attrition and thermal stability

Abstract

Microalloying as a technique to improve the mechanical properties has been used for decades in bulk steels. In order to transfer some of the benefits of microalloying to sintered steels, microalloying elements (Nb in this case) are introduced in the iron powder by mechanical alloying. Since mechanical alloying is a solid state alloying technique, the microalloying elements can be added not only in elemental form (Nb) but also in the form of carbides (NbC). Moreover, the use or not of wax as a process control agent during milling is considered. This work studies the evolution of the powder characteristics and nanostructure during milling and the thermal stability of the resultant powder (since for further consolidation the powder will be exposed to temperature). The evolution of the powder characteristics as a function of milling time is monitored by apparent and tap densities, SEM, particle size distribution, DRX, crystallite size and internal strain. The thermal stability of the resultant nanostructured powder is analysed by means of DRX (crystallite size and internal strain) after annealing the milled powder at different temperatures. The purpose of this study is to investigate the temperature influence on crystallite features and the release of stored deformation energy.     

Coal char reactivity and structural evolution during combustion—Factors influencing blast furnace pulverized coal injection operation

A fresh char was prepared and reacted with oxygen under conditions similar to those prevailing in the raceway region of the blast furnace (BF) during pulverized coal injection (PCI), using a well-characterized drop-tube furnace (DTF). Char combustion under the present conditions was found to be controlled by the combination of pore diffusion and chemical reaction. Both the char density and size gradually decrease with burnoff, while the char surface area increases up to a burnoff of 40 to 50 pct due to the formation of a large amount of meso- and micropores, which were observed by high-resolution field-emission scanning electron microscopy (FESEM) and gas adsorption measurements. Despite the obvious increase in surface area, the char combustion reactivity decreases with burnoff. This is due to the loss of the intrinsic reactivity of char during combustion, as confirmed by fixed-bed (FB) measurements of fresh char and chars partly burnt in a DTF. The structural characterization by quantitative X-ray diffraction analysis (QXRDA) shows that the amorphous concentration (f _am ) of the char decreases during combustion, while the aromaticity (f _ar ) and the average crystallite size (L ₀₀₂) of the char increase. The char becomes more ordered during combustion, which is in accordance with the observations made using high-resolution transmission electron microscopy (HRTEM). The char structural ordering observed was found to be responsible for the loss of char intrinsic reactivity during combustion. Based on the QXRDA, a char structure model has also been suggested to explain the char structural evolution observed during combustion. The implications of char structural evolution for char combustion during a PCI operation are also discussed.     

Synthesis of zirconium diboride-alumina composite by the self-propagating,high-temperature synthesis process

Synthesis of a ZrB₂-Al₂O₃ in-situ composite powder by the self-propagating, high-temperature synthesis (SHS) process using oxides as raw materials has been investigated. The combustion velocity was found to be about 5 mm/s. The combustion temperature varied in the range of 2173 to 2223 K, respectively. The SHS reaction was found to be mediated through melting of aluminum and, thereby, the SHS reaction. The ignition temperature is estimated to be about 1503 K by thermal analysis. Dendrite structures were also observed during SHS processing of the composite.