电触头用TiB2颗粒增强/Cu基复合材料组织与性能分析北大核心

采用热压烧结方法制备电触头用TiB2颗粒增强/Cu基复合材料,通过XRD、OM、SEM等测试手段研究不同TiB2颗粒含量对其组织和性能的影响。研究结果表明:复合材料生成了强度很高的Cu衍射峰,Cu基体内已经形成由TiB2与TiB共同构成的混杂增强相。所有复合材料试样中的增强相都形成了均匀分布形态,TiB2颗粒含量6%的试样含有颗粒与晶须两种增强相。当TiB2颗粒含量的比例上升后,所有Cu基复合材料试样的硬度都发生了增大的现象,而密度发生了减小,导电率增加。TiB2(6%)/Cu复合材料试样在DSC升温过程中形成了4个特征峰。当温度到达800℃时形成了Cu3Ti金属间化合物;随着温度上升到1100℃后,试样基体内开始同时生成TiB2颗粒与Ti B晶须。     

电触头用TiB_2颗粒增强/Cu基复合材料组织与性能分析

采用热压烧结方法制备电触头用TiB_2颗粒增强/Cu基复合材料,通过XRD、OM、SEM等测试手段研究不同TiB_2颗粒含量对其组织和性能的影响。研究结果表明:复合材料生成了强度很高的Cu衍射峰,Cu基体内已经形成由TiB_2与TiB共同构成的混杂增强相。所有复合材料试样中的增强相都形成了均匀分布形态,TiB_2颗粒含量6%的试样含有颗粒与晶须两种增强相。当TiB_2颗粒含量的比例上升后,所有Cu基复合材料试样的硬度都发生了增大的现象,而密度发生了减小,导电率增加。TiB_2(6%)/Cu复合材料试样在DSC升温过程中形成了4个特征峰。当温度到达800℃时形成了Cu_3Ti金属间化合物;随着温度上升到1 100℃后,试样基体内开始同时生成TiB_2颗粒与Ti B晶须。     

镍铬?莫来石复合陶瓷涂层热障及抗热震性能的研究

使用球磨法混制了五组不同比例的镍铬?莫来石复合粉末,利用超音速等离子喷涂技术在45钢基材表面制备相应的镍铬?莫来石复合陶瓷涂层,测定涂层导的热系数和抗热震性能,采用扫描电子显微镜观察涂层表面、截面显微形貌,利用能谱仪分析涂层特征区的组织成分,通过X射线衍射分析涂层组织结构。结果表明,镍铬?莫来石复合涂层以镍铬固溶体为基体,其上均匀分布着莫来石颗粒,莫来石与基体之间形成了扩散相,提高了莫来石与基体之间的润湿性,使莫来石被基体牢固包覆;莫来石颗粒的加入强化了基体,在莫来石体积分数38%～75%范围内,随着莫来石含量的增加,涂层强韧性增加,抗热震性提高,热导率降低。     

微波烧结原位合成(Ti_5Si_3+TiC)/TC4复合材料组织性能研究

通过Ti-SiC反应体系,选择粒径为45μm的基体TC4,5μm的增强相SiC(质量分数为5%和10%),经过低能球磨混粉后,微波烧结原位合成颗粒增强钛基复合材料。采用X射线衍射仪(XRD)、扫描电镜(SEM)和能谱仪(EDS)对制备的钛基复合材料进行组织结构分析,并对钛基复合材料的致密度、显微硬度、压缩强度、抗拉强度、耐磨性和抗氧化性进行测试研究。结果表明,钛基复合材料主要由增强相TiC,Ti_5Si_3及基体Ti_3种物相组成。TiC呈颗粒状,有明显的棱角,而Ti_5Si_3呈熔融状颗粒,但是颗粒没有明显的棱角,增强相呈准连续网状分布,随着SiC含量的增加,网状结构不清晰,部分增强相团聚在一起。复合材料的相对密度、显微硬度和压缩强度随SiC含量的增加而增加,分别达到98.76%,HV729和2058MPa,但是复合材料的室温拉伸强度随SiC含量增加而降低。引入增强相后,复合材料的抗氧化性和耐磨性均高于基体,且耐磨性和抗氧化性随SiC含量增加而增加,其室温磨损机制主要为粘着磨损。     

β-SiAlON-cBN陶瓷复合材料的制备与性能

采用放电等离子烧结(SPS)在1 500℃下制备不同立方氮化硼(cubic Boron Nitride,即cBN)含量的β-SiAlON-cBN陶瓷复合材料,研究cBN含量对陶瓷复合材料的物相组成、显微组织和性能的影响.XRD分析表明:在添加复合烧结助剂的条件下合成的β-SiAlON-cBN陶瓷复合材料,β-SiAlON的量随着cBN含量的增加而增加.FESEM观察结果表明:cBN颗粒较均匀地分布在β-SiAlON基体中,一些cBN颗粒表面出现可剥离的层片状物质六方氮化硼(hBN).随着cBN含量的增加,β-SiAlON-cBN陶瓷复合材料的相对密度先下降后略有上升,硬度呈现降低趋势,断裂韧性则先升高后略有降低.β-SiAlON-10%cBN(质量分数)的相对密度和硬度分别为96.8%和13 GPa,β-SiAlON-30%cBN的断裂韧性可达到KIC=3.2 MPa·m1/2.     

钢渣基高碱度微晶玻璃的一步法制备及工艺参数研究

为了提高微晶玻璃原料中高钙冶金渣的掺量,需要制备出碱度更高的微晶玻璃.本文采用一步法,以钢渣为主要原料,制备碱度（CaO与SiO₂的质量比）为0.9的钢渣基高碱度微晶玻璃.通过X射线衍射分析、扫描电镜和性能测试等手段,研究热处理条件对微晶玻璃微观形貌及线收缩率、体积密度和抗折强度等性能的影响规律.研究表明,高碱度微晶玻璃适合采用一步法制备工艺,当在1100℃保温120 min时,微晶玻璃烧结过程基本完成,此时获得最大体积密度2.4 g·cm-3,最高抗折强度56.4 MPa.微晶玻璃的主晶相为钙铝黄长石,副晶相为辉石.基础玻璃颗粒在升温过程中完成了成核和析晶过程,而在保温过程中主要进行的是基础玻璃颗粒的烧结致密化和晶体的进一步发育.升温至1100℃保温30 min,微晶玻璃的抗折强度超过45 MPa,微晶玻璃内部晶体呈方柱状交织排列并构成晶体骨架分布在残余的玻璃基体中;随着保温时间的增加,微晶玻璃的线性烧结收缩率、体积密度和抗折强度均逐渐增大,而晶相的含量基本保持不变,晶体逐渐由球形颗粒状和短柱状发育为长柱状.晶体的形状以及与残余玻璃相构成的整体致密结构是导致高碱度微晶玻璃力学性能提高的主要因素.      

添加氮化硅对莫来石碳化硅材料性能的影响

以莫来石、红柱石为主要原料,加入不同含量的氮化硅、碳化硅细粉,探讨了添加氮化硅对莫来石碳化硅材料性能的影响。结果表明:在1 450℃下制备的材料的显气孔率基本维持在15%左右,体积密度在2.45 g/cm~3左右,烧后线变化率相差不大,高温抗折强度和荷重软化温度也分别能够达到29.8 MPa和1 560℃,都表现出了较高的水准,且基本不受氮化硅加入量的影响;添加氮化硅能够提高材料的抗热震性能,但材料的常温耐压强度随着氮化硅含量的增加呈降低趋势;材料在烧结过程中,氮化硅和碳化硅均发生了氧化并在材料表面形成一层黄褐色氧化产物,其主要为玻璃相;在材料的截面出现致密层,且致密层的厚度随着氮化硅含量的增加而减小。     

铬渣微晶玻璃析晶行为的研究

利用熔融法对以铬渣和硅石为原料制备微晶玻璃进行研究,通过DTA、XRD、SEM等分析方法,对铬渣微晶玻璃的晶相组成、晶体形貌特征等进行了分析,研究结果表明,随着铬渣含量的增加,微晶玻璃的主晶相为普通辉石,晶体的析出量增大,密度和显微硬度呈先增大后降低的趋势.     

Eu~(3+)/Tb~(3+)掺杂硼硅酸盐玻璃的发光性能

为了弥补目前白光LED显色指数的不足,用传统熔融法制备了Eu3+/Tb3+掺杂的硼硅酸盐玻璃,研究了Eu3+/Tb3+掺杂的硼硅酸盐玻璃在391 nm和462 nm激发下的下转换发光性能和能量传递特征。结果表明,用462 nm激发Eu3+掺杂的硼硅酸盐玻璃样品,发现随着Eu3+浓度的增加,Eu2O3含量为0.5%(摩尔分数)时达到发射强度最大值。对于Eu3+/Tb3+共掺的硼硅酸盐玻璃,在462 nm处呈现最强激发峰,其最强发射峰为612 nm的红光。而且随着Tb3+浓度的增加,Eu3+和Tb3+之间的能量传递加强,大大提高了612 nm红光的发射强度。     

原位合成莫来石柱状晶强化羟基磷灰石材料

以羟基磷灰石(HA)为基体,经硅溶胶表面包覆处理的Al2(SO4)3(AES)为第二相,采用原位反应合成法制备自生莫来石柱状晶增强羟基磷灰石材料。研究莫来石晶体的形成过程以及复合材料的相组成、微观形貌和力学性能。结果表明,添加AES可以提高HA的抗弯强度,经1 050℃烧结、含10%AES的复合材料抗弯强度可达71.21 MPa,比基体提高185%;硅溶胶在加热过程中结晶化转变的顺序是:800℃以下为非晶态,800~950℃晶化成方石英,950～1 100℃为方石英+磷石英;Al2(SO4)3与SiO2反应原位生成柱状莫来石,柱状莫来石可起到类纤维的增强作用使材料强度提高。     

微波消解-电感耦合等离子体质谱法测定粉煤灰中铀

粉煤灰是一种宝贵的铀资源,为了满足我国日益增长的核电对铀的需求,必须加大对粉煤灰中铀的综合回收利用,因此准确测定粉煤灰中铀含量意义重大。采用HNO₃-HF-HClO₄体系微波消解样品,选择¹⁸⁷Re为内标元素,²³⁸U为铀测定同位素,建立了微波消解-电感耦合等离子体质谱法(ICP-MS)准确快速测定粉煤灰中铀的分析方法。对溶样条件进行了优化,确定溶样酸用量为5.0mL HNO₃、3.0mL HF、0.50mL HClO₄,消解程序如下所示:消解功率为800W,15min从室温升到150℃,保温10min,15min从150℃升到200℃,保温30min。实验表明,当铀的质量浓度范围为0.5~20ng/mL时,铀的质量浓度与其对应的信号强度呈线性关系,线性相关系数为0.9999,方法检出限为0.05μg/g。将实验方法应用于粉煤灰实际样品分析,测定结果的相对标准偏差(RSD,n=6)为3.2%,加标回收率为95%~104%。选取来自不同地方燃煤电厂的粉煤灰,按照实验方法进行铀的测定,并与激光荧光法进行对比,两种方法测定结果基本一致。     

配煤对煤灰熔融过程的矿物演变的影响

对高钙烟煤和低钙无烟煤以及这两种煤组成的混合煤进行灰熔融特性研究。利用灰熔点测试仪测定煤灰的灰熔融特征温度,通过FactSage热力学软件的Equilib模块和Phase Diagram模块计算煤灰熔化过程的物相变化。结果表明,煤的灰熔点与煤灰的成分密切相关,酸性物质能使混煤灰的熔融特性温度升高,碱性物质使混煤灰的熔融特性温度降低;通过FactSage的Equilib模块得到的熔化过程可以看出,烟煤和无烟煤煤灰的熔融特性差异是温度高于1 000 ℃时莫来石和钙铝黄长石的含量变化导致的。对于混煤灰,随着低钙无烟煤比例的增加,在1 000 ℃的矿相成分中莫来石含量增加,钙铝黄长石含量减少,导致混煤灰熔点提高。     

活性粉煤灰代替白炭黑作橡胶填料的研究

对阜新发电厂粉煤灰的矿物组成进行了分析研究，该粉煤灰中晶体与非晶态矿物共存，具有密度低、表面活性高的特点。经对粉煤灰／化学改性药剂／橡胶三相界面分析及其相容性设计研究，选择了三种化学改性药剂，采用正交试验，取得了作橡胶粘合助剂的初步成果，可以实现等量替代白炭黑，且成本大幅度降低。     

低品位煤矸石制备莫来石的研究

以酸洗处理后的南方地区煤矸石及氧化铝为原料,研究了不同试验条件下合成莫来石物相的影响。结果表明:1 200℃开始有棒状莫来石晶体的生成,1 500℃以后莫来石大量生成,温度升高到1 600℃莫来石进一步生成;改变最高温度下的保温时间,莫来石化程度呈现先增后减的趋势;改变煤矸石的用量,随着煤矸石用量的增加,物相中刚玉峰增强,说明煤矸石用量的增加不利于莫来石的合成;改变配料中的铝硅比,由3∶2降低到1∶1过程中,莫来石化程度逐渐加强,在铝硅比1∶1时物相中刚玉峰消失,说明低品位煤矸石在较低的铝硅比下有利于莫来石的合成。     

Chemical reactions between aluminum and fly ash during synthesis and reheating of Al-fly ash composite

Thermodynamic analysis indicates that there is the possibility of chemical reactions between aluminum melt and cenosphere fly ash particles. These particles contain alumina, silica, and iron oxide, which, during solidification processing of aluminum-fly ash composites or during holding of such composites at temperatures above the melting temperature of aluminum, are likely to undergo chemical reduction. These chemical reactions between the fly ash and molten aluminum have been studied by metallographic examination, differential thermal analysis (DTA), scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDX) and X-ray analysis after holding the aluminum-fly ash composites for different periods above the liquidus temperature. The experiments indicate that there is progressive reduction of silica and mullite in the fly ash, and formation of alumina with holding time of composites at a temperature of 850 °C. The walls of the cenosphere fly ash particles progressively disintegrate into discrete particles as the reaction progresses. The rate of chemical reaction was high at the start of holding the composite at a temperature of 850 °C, and then the rate significantly decreased with time. The reaction was almost complete after 10 hours.     

Compaction and sintering behaviour of A356–fly ash composites: a preliminary investigation

Abstract

In the present study, A356–fly ash metal matrix composites were developed through powder metallurgy route. The composites were mixed by using the ball milling technique, shaped through uniaxial and cold isostatic compaction, and then sintered at 520°C. Scanning electron microscopy and X-ray diffraction were used for microstructure and phase characterisation. The density and microhardness of the composites were evaluated as a function of fly ash content, compaction pressure, sintering time and age hardening time. Uniaxial cold compaction of the composites increased their green density and cold isostatic compaction of the compacts led to a further increase in the density. At a constant compaction pressure, the density decreased with increasing fly ash content, resulting in light weight composites. The microhardness of the composites increased with the addition of 10 wt-% fly ash while it decreased with the addition of 20 and 30 wt-% fly ash. Sintering at 520°C increased the density of the composites and the grain size of the α-Al phase of the matrix. The matrix alloy and the composite containing 10 wt-% fly ash showed some response to age hardening at 160°C. However, no response to age hardening was observed at 200°C.     

光度法快速测定铌铁中铌

铌铁易溶于硝酸和氢氟酸的混合酸中，当用酸分解试样时，铌极易水解析出沉淀；但在氢氟酸存在下，又能成为可溶性络合物（H2NbF7），所以在分析方法中，常用此特性，使铌保持于溶液中而用光度法进行铌的测定，实现光度法高速分析铌铁中的铌。     

Effect of Y3＋, Gd 3＋and La3＋dopant ions on structural,optical and electrical properties of o-mullite nanoparticles

Dielectric ceramics of M(x) Al6(1–x) Si2 O13 doped mullite were synthesized via co-precipitation technique. The X-ray diffraction profiles revealed that these nanoparticles were crystallized well and the volume of mullite unit cell was increased as a function of the ionic radius of dopant ion. TEM images showed regular orthorhombic crystal morphology for the pure mullite sample. Meanwhile, the doped samples exhibited slightly distorted crystal morphology of larger particle sizes. DSC thermograms evinced that the exothermic peak temperature of mullite was shifted to the lower value with M3+ion insertion. The photoluminescence spectra were studied for mullite samples, and it was found that the intensity of the emission spectra was affected by the M3+ion type. It was found that, Y3+doped mullite achieved the minimum dielectric loss value of 0.01 in the radio wave frequency region(1 MHz). Meanwhile, Gd3+ doped mullite achieved the minimum dielectric loss value of 0.09 in the microwave frequency region(1 GHz).     

Rare earth elements of fly ash from Wyoming's Powder River Basin coal

The advancement and increasing interests in green energy production and environmental protection technologies have spurred the demand for rare earth elements.On the other hand,the U.S.has to rely 100% on import of these materials as the industry was crashed because of the environmental issues associated with mining and processing,and more importantly lack competitiveness.As rare earth elements have many applications in defense and national security sectors,some of the elements were listed as strategic materials or critical materials because of the uncertainties in supply and prices.Therefore,it has become imperative in searching for alternative resources for supplying rare earth elements including unconventional resources.With the strong incentive,coal fly ash is identified as one of the candidates among them.In this study,we present rare earth element data for the 42 ash samples(all derived from Powder River Basin coal) that we collected from seven states(UT,WY,10,WI,ND,CO,and MI) representing 158 million tons of fly ash.The results indicate scattered distributions of rare earth elements with concentration ranging from 156 to 590 ppm although all the ash samples originated from the same coal basin(Powder River Basin).The rare earth element resource in these ashes is estimated between 74000 and 106000 t.The ash samples were also characterized by elemental analysis,XRD,SEM-EDS and BET surface area.The characterizations of the ashes were discussed as they might have implications in the subsequent rare earth element extraction processes.In summary,fly ash may represent a potential resource for rare earth element production.     

粉煤灰改性高水材料力学性能试验研究及机理分析

为解决矿山高水充填材料成本较高、粉煤灰等工业废料大量剩余造成资源浪费、环境污染等问题,借助微机控制电子万能试验机(ETM)力学试验系统、扫描电镜扫描装置和X射线衍射分析仪,研究粉煤灰掺量对高水材料物理力学性能的影响规律,并通过物相和微观结构分析探讨其影响机理.结果表明:随着粉煤灰掺量的增加,高水材料的凝结时间逐渐延长,含水率逐渐降低,容重基本不变;掺杂粉煤灰前后高水材料均是一种弹塑性材料,其变形破坏过程可以分为孔隙压密阶段、弹性阶段、屈服阶段和破坏阶段;高水材料的峰值强度、弹性模量和变形模量均随粉煤灰掺量的增加略有降低,残余强度却有所提高;综合考虑高水材料的强度、模量和成本,粉煤灰掺量a为15%是最优掺量,此时峰值强度、弹性模量和变形模量仅分别降低了25%、8.6%和10%,残余强度却提高了50%.物相和微观形貌分析结果表明:粉煤灰的掺量影响了β-C₂S的水化进程,导致钙矾石生成量减少,其他水化产物生成量增多,进而破坏了钙矾石结构的整体性和均匀性,最终降低了高水材料的抗压强度.