Fe2O3质量分数对粉煤灰颗粒电磁特性的影响

为研究Fe2O3质量分数对粉煤灰颗粒电磁特性的影响,采用高铁粉煤灰颗粒进行试验,通过不同工艺措施改变粉煤灰颗粒Fe2O3质量分数,测试了复合高铁粉煤灰水泥浆体的吸波性能.结果表明,高铁粉煤灰颗粒是电磁波有效损耗介质,是以介电损耗型为主的吸波剂;高铁粉煤灰颗粒介电损耗与磁性氧化铁的质量分数具有较明显的内在相关性;磨细磁选、分级技术可有效改善粉煤灰颗粒的吸波能力;高铁粉煤灰水泥基复合材料具有明显的吸波性能,在12.5～18GHz波段,反射率R<-5dB,最小反射率达-9.88dB,但复合材料的吸波性能与颗粒电磁特性规律有所不同.高铁粉煤灰在吸波建筑材料中具有应用前景.     

含铁氧体陶粒骨料电磁波损耗模型与性能研究

基于Mie理论建立了铁氧体负载于陶粒表面的包覆型骨料和铁氧体均匀分布于陶粒内部的混合型骨料的电磁波损耗模型,研究了吸波剂掺量、骨料粒径和入射波频率的变化对两种骨料电磁波损耗性能的影响.结果表明:(1)当吸波剂掺量为20％、粒半径为5～7.5 mm、入射波频段为8～18 GHz时,两种含铁氧体陶粒骨料的电磁损耗能力较好;(2)对比分析两种骨料在不同吸波剂掺量、粒径和入射波频率时的电磁损耗情况后可知,混合型骨料具有更好的电磁波损耗性能和更宽的高损耗频带.     

石墨烯-铁镍合金-聚乳酸复合材料的制备及其吸波性能

发展轻量化、宽频带的微波吸收材料来应对严重的电磁污染是一个巨大的挑战。本文通过熔融沉积成形(FDM)工艺制备出石墨烯(GR)-铁镍合金(FeNi50)-聚乳酸(PLA)复合材料,采用XRD、Raman、SEM和矢量网络分析仪(VNA)对复合材料的物相结构、微观形貌和电磁性能进行表征分析,并讨论了GR-FeNi50质量比对复合材料吸波性能的影响。结果表明,与未添加GR的复合材料相比,复合材料内部形成了触发极化损耗的异质界面,并产生了丰富的褶皱和孔隙,从而增强了微波的多次反射和散射;随着GR-FeNi50质量比的增加,吸波性能先增强、后减弱,当GR-FeNi50质量比为4∶20时,吸波性能最佳,最小反射损耗达到-40.5 dB,有效吸收带宽为4.7 GHz(13.28～18 GHz)。其优异的吸波性能归因于良好的阻抗匹配和界面极化损耗、偶极极化损耗、电导损耗、磁损耗之间的协同作用。此外,与湿化学法制备的吸波材料相比,GRFeNi50-PLA复合材料在环保、易加工和规模化生产方面具有优势。     

Fe-Co合金和中空碳纤维吸波材料的吸波特性研究

采用矢量网络分析仪测试了Fe-Co合金/石蜡和中空碳纤维/石蜡复合材料的微波电磁参数,并用电磁参数模拟计算了单层吸波材料的反射率.根据电磁波在损耗媒质中的传播规律,分析了2种吸波材料的吸收机理以及本征阻抗和衰减特性对吸波性能的影响.结果表明,Fe-Co合金吸波材料为吸收损耗型吸泼材料,阻抗越大、衰减越强,吸波性能越好;而中空碳纤维吸波材料则是干涉型吸波材料,需要适当大小的阻抗和衰减才能满足强吸收的条件,且吸收带宽相对较窄.     

羰基铁和FeSiAl共混制备宽频吸波材料

为提高材料在低频段(1～4GHz)下的吸波性能和拓宽吸波频带,选择羰基铁和FeSiAl颗粒作为吸收剂、石蜡作为粘结剂制作吸波材料,采用矢量网络分析仪测试材料的电磁参数,并在给定厚度(0.5和1mm)下分析吸波材料的吸波性能。随着质量添加比的增加,两类材料的介电常数和磁导率均升高,添加比相同下含FeSiAl颗粒吸波材料在1mm厚时具有优异的低频吸波性能(-8.6～-1.2dB),而高频段(14～18GHz)时不及羰基铁(-16.0～-10.1dB);两类颗粒共混后,通过改变FeSiAl颗粒的含量能获得具有良好低频吸收性能(-4.5～-1.1dB)和宽频带(<-4dB频带为3.8～18GHz)的吸波材料。该结果对于通过混合其它优良低频和高频吸波材料以获取宽频带的吸波材料具有指导意义。     

基于空心球壳结构的吸波平板的吸波性能研究

对炭黑包覆发泡聚苯乙烯（EPS）颗粒的吸波性能进行了研究。讨论其吸波机理表明,谐振损耗和散射损耗对这种空心球壳结构的吸波体具有重要的意义。调节导电层厚度和球体半径可以控制吸波体的吸收强度和谐振频率。将其应用于水泥基吸波平板中发现它可以显著提高复合材料的吸波性能,特别是低频段的吸波性能,而且降低了材料密度。因此,炭包EPS颗粒是一种轻质高效的吸波填料,具有广泛的发展前景。     

碳包覆铁/丙烯酸树脂水性纳米复合涂料的制备及电磁波吸收性能*

以"壳/核"型碳包覆铁(Fe(C))纳米颗粒为填料、水性丙烯酸树脂为基体,制备了纳米复合电磁波吸收涂料.采用不同含量的十二烷基苯磺酸钠(SDBS)对纳米颗粒改性,提高了纳米颗粒在基体中的分散性.选用吸收剂填充量为25%(质量分数)的涂料,测定了不同厚度涂层的电磁波吸波性能.涂层具有很好的吸波性能,当厚度为5mm时,反射损耗峰值为-17.2dB,吸收带宽为3.2GHz(7～10.2GHz).首次用实验结果证明了传输线理论对铁磁性纳米颗粒吸波性能的模拟结果.     

无定形炭/磁性粒子复合吸波材料的制备和电磁性能研究

以二甲基亚砜(DMSO)为溶剂进行溶液聚合制得聚丙烯腈(PAN)溶液,在此溶液中混入了微米级铁粉后将其压成薄膜,将烘干后的薄膜高温碳化处理制得一种碳基吸波材料。采用X射线衍射(XRD)、扫描电镜(SEM)等手段对材料的成分、形貌、结构进行了表征。采用矢量网络分析仪对该复合材料在2～18GHz频段内的电磁参数进行了测试,并作了微波反射率的数值模拟。研究了碳化温度对材料物相组成和电磁性能的影响以及碳化温度和涂层厚度对材料吸波性能的影响。此种吸波材料是无定形炭和铁的氧化物、铁的氮化物等磁性物质的复合材料,兼有电损耗和磁损耗,具有较好的吸波性能。     

羧基铁和FeSiAl共混制备宽频吸波材料

为提高材料在低频段(1～4GHz)下的吸波性能和拓宽吸波频带,选择羧基铁和FeSiAl颖粒作为吸收剂、石蜡作为粘结剂制作吸波材料,采用矢量网络分析仪测试材料的电磁参数,并在给定厚度(0.5和1mm)下分析吸波材料的吸波性能.随着质量添加比的增加,两类材料的介电常数和磁导率均升高,添加比相同下含FeSiAl颗粒吸波材料在...     

吸波剂含量和涂层厚度对微波吸收性能的影响

以具有强磁损耗特性的磁粉、电阻型和电介质型物质作为吸波剂,制备出了具有阻抗渐变结构的3层复合雷达吸波涂层,研究了吸波剂用量和涂层厚度对吸波性能的影响.结果表明,增加表层、中层或底层吸波剂含量及涂层厚度,均能使吸波性能曲线向低频端方向移动,反之,吸波性能曲线向高频端方向移动;选择适当的吸波剂含量或者一定厚度的涂层才能拓宽、加深吸波性能.制得的试样中反射损耗可达-35.74和-39.25dB,其频宽(＜-10dB)分别为3.52和2.84GHz.     

燃烧法所得含纳米氧化铁粉煤灰建筑吸波材料

为促进纳米材料的推广应用,研究了量大面广的燃煤工业副产物粉煤灰生产工艺对材料性质的影响,利用扫描电镜、能谱仪、X射线衍射仪等对高铁粉煤灰颗粒微观形貌与性质进行了分析.研究表明：在煤粉燃烧过程中,粘土、石英矿物形成硅酸盐玻璃微珠,矿物中的大部分铁元素在球形玻璃体颗粒表面析晶形成铁氧化物,以二价和三价氧化铁的形式存在,晶粒...     

Synthesis and characterization of nanocrystalline silver coating of fly ash cenosphere particles by electroless process

Electroless nanocrystalline Ag coating of fly ash cenosphere particles utilizing a Sn-Pd catalyst system is demonstrated in this article. The deposition of pure metallic nanocrystalline Ag on the fly ash cenosphere particle surface is confirmed by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) analysis. Under the described conditions of electroless coating, average nanocrystalline Ag-coating thickness is observed to be approximately 220 nm, using a focused ion beam technique, which is less than that observed by transmission electron microscopy (TEM) (260-360 nm). TEM observation further reveals that the Ag-coating is made up of 50 nm Ag nanocrystallites, which is comparable with the size of approximately 37 nm obtained from the XRD data. The mechanism of the electroless Ag-coating process is discussed. Ag-coated fly ash particles find applications in manufacturing conducting polymers for electromagnetic interference shielding applications.     

Microscopy and microanalysis of inorganic polymer cements. 1: remnant fly ash particles

Accurate and precise electron microscopic analysis of the remnant solid precursor (fly ash and blast furnace slag) particles embedded in an inorganic polymer cement (or “fly ash geopolymer”) provides critical information regarding the process of gel binder formation. Differential solubility of phases in the fly ash is seen to be important, with insoluble mullite crystals becoming exposed by the retreat of the surrounding glassy phases. High-iron particles appear to remain largely unreacted, and the use of sectioned and polished specimens provides a view of the inside of these particles, which can show a wide variety of phase separation morphologies and degrees of intermixing of high iron and other phases. Calcium appears to be active in the process of alkali activation of ash/slag blends, although the competitive and/or synergistic effects of ash and slag particles during the reaction process remain to be understood in detail.     

Fabrication and characterisation of Al–7Si–0.35Mg/fly ash metal matrix composites processed by different stir casting routes

In the present investigation, the effect of three different stir casting routes on the structure and properties of fine fly ash particles (13 μm average particle size) reinforced Al–7Si–0.35Mg alloy composite is evaluated. Among liquid metal stir casting, compocasting (semi solid processing), modified compocasting and modified compocasting followed by squeeze casting routes evaluated, the latter has resulted in a well-dispersed and relatively agglomerate and porosity free fly ash particle dispersed composites. Interfacial reactions between the fly ash particle and the matrix leading to the formation of MgAl₂O₄ spinel and iron intermetallics are more in liquid metal stir cast composites than in compocast composites.     

磁选粉煤灰砂浆的导电性研究

Fe3O4具有很强的磁性,利用简单的磁选工艺将普通粉煤灰中的铁氧化物(Fe1-δO)吸取出来,可得Fe3O4含量较高的磁选粉煤灰。Fe3O4在常温下的电导率为2.5×104Ω-1.m-1,和沥青基碳纤维的电导率为同一数量级。利用磁选粉煤灰作为导电材料可以制备出具有良好导电性能和力学性能且成本低廉的导电砂浆。随着磁选粉煤灰掺量的增加,粉煤灰颗粒互相接触并逐渐形成局部导电网络,使电子和空穴可通过隧道效应跃过水泥基体阻隔所形成的势垒进行传导;当磁选粉煤灰掺量超过"渗滤阈值"后,砂浆的导电性明显增强,与掺加细集料的碳纤维导电砂浆的导电性接近。     

A study of physico-chemical and mineralogical properties of Talcher coal fly ash for stowing in underground coal mines

This study examines the suitability of Talcher coal fly ash for stowing in the nearby underground coal mines based on their physico-chemical and mineralogical analysis. The physical properties such as bulk density, specific gravity, particle size distribution, porosity, permeability and water holding capacity etc. have been determined. From the chemical characterization it is found that the ash samples are enriched predominantly in silica (SiO₂), alumina (Al₂O₃) and iron oxides (Fe₂O₃), along with a little amount of CaO, and fall under the Class F fly ash category. In addition, the mineral phases identified in the ash samples are quartz, mullite, magnetite, and hematite. The particle morphological analysis revealed that the ash particles are almost spherical in shape and the bulk ash porous in nature. From the particle size and permeability point of view, pond ash may be considered a better stowing material than fly ash.     

Fly ash characterization and application in Al–based Mg alloys

Continuing study in metallurgical field calls for growing reinforcements of which fly ash plays an important role. In this study, Al alloys were reinforced with different solid fly ash particles. The X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray fluorescence (XRF) analyses were used to identify the fly ash particles, and they were also applied to the composite alloys. The X-ray diffraction (XRD) results indicated that the crystalline phase of the fly ash was an effective reinforced phase. Meanwhile, the SEM and optical micrographs of the composite samples indicated that fly ash could be reacted or settled in the matrix of the aluminium. The physical, tribological and microhardness analyses were also used to study the Al–fly ash composites. The best wear resistance corresponding to the lowest loss was obtained in the samples with as-received fly ash which were mostly in accordance with the results in the samples containing treated fly ash. Meanwhile, the proportion of the wear results to the hardness of the samples was observed. Finally, the light weight Al alloys was realized, and increasing the strength is a likeness.     

Size characterization of incinerator fly ash using sedimentation/steric field-flow fractionation

Fly ash particles emitted from municipal solid waste-incinerators are of environmental concern. This study aims to investigate the applicability of sedimentation/steric field-flow fractionation (Sd/StFFF) and to develop a Sd/StFFF method for the separation and size characterization of incinerator fly ash. This study focuses on the fly ash particles larger than approxiamtely 1 microm, which comprise more than 90% (w/w) of the fly ash. Fly ash is a complex mixture of particles having various chemical compositions, sizes, shapes, and densities. Prior to Sd/StFFF analysis, fly ash particles are prefractionated into six density classes using a modified centrifugal procedure. It was found that fly ash particles are most abundant in the density range between 2.4 and 2.8 g/cm3. Different density fractions seem to contain particles of different chemical compositions. The Sd/StFFF conditions for the size-characterization of fly ash are sample concentration, approximately 0.3% (w/v); dispersing medium, 50% ethanol in water; and carrier liquid, water with 1.0% FL-70 (ionic strength approximately 0.012 M). Sd/StFFF data show no significant differences in size distribution among different density fractions. Generally, the sizes obtained from Sd/StFFF are larger than those obtained from a Coulter Multisizer and microscopy, probably because of the irregular shapes of the fly ash particles.     

Modification of MSW fly ash by anionic chelating surfactant

This paper elucidates a study on the re-utilization and stabilization of municipal solid waste (MSW) fly ash in producing a high value-added product by the surface modification of anionic chelating surfactant on the particles. After modification, MSW fly ash can be expected using as a filler of ultra-high molecular weight polymers. The effects of anionic chelating surfactants (ACS) on surface modification of MSW fly ash and fixing capacity for heavy metals were explored. Meanwhile, the interaction mechanism between surfactants and MSW fly ash was suggested. The results showed that anionic chelating surfactants can be used to effectively modify MSW fly ash particles and achieve a high active ratio. At the same time, they also exhibited a strong fixing capacity for heavy metals. Of the two modified MSW fly ash, ED3A-modified MSW fly ash has a much higher active ratio than MAP-modified MSW fly ash at over 95%, although its fixing capacity for heavy metals was a shade lower than MAP-modified MSW fly ash.