Effect of relative density on cyclic oxidation resistance properties of MoSi2

MoSi2 powders were fabricated respectively by mechanical alloying technique and sintering at different temperatures to prepare materials with different relative densities. The relative oxidation behavior of all MoSi2 materials at 1 473 K was investigated by TGA,SEM and XRD. The results show that the ＂pesting＂ is not found in all materials after being oxidized for 480 h. The density has no essential relation to the ＂pesting＂. The oxidation curve of specimens with lower density shows two-step oxidation kinetics. Both the first stage （0-1 h） and the second stage （1-480 h） nearly obey linear kinetics,but the oxidation rates are obviously different. The oxidation kinetics of MoSi2 with higher relative density nearly follows parabolic law. The mass gains of MoSi2 with the lowest relative density （78.6%） and the highest relative density （94.8%） are increased by 10.390 and 0.135 mg/cm^2,respectively. The oxide scale of materials with lower densities is non-protective and makes the oxygen diffusion easy. A dense scale in the material with higher density is formed,which acts as a diffusion barrier to the oxygen atoms to penetrate into the matrix,showing much better high temperature oxidation resistance. The phases distribution of oxidation scale from the outside to the inside is SiO2→Mo5Si3→MoSi2.     

Cyclic oxidation behaviors of MoSi<Subscript>2</Subscript> with different relative density

The influence of different relative density on the cyclic oxidation behaviors of MoSi2 at 1 273 K were studied. ＂Pesting＂ was not found in all MoSi2 materials after being oxidized for 480 h. All samples exhibited continuous mass gain during the oxidation process. The mass gains of MoSi2 with the lowest relative density （78.6%） and the highest relative density （94.8%） are increased by 8.15 mg·cm^-2 and 3.48 mg·cm^-2, respectively. The surface of the material with lower relative density formed a loose, porous and discontinuous oxidation scale, which accelerated oxygen diffusion and aggravated the oxidation process. However, a dense scale in the material with higher relative density is formed, which acts a diffusion barrier to the oxygen atoms penetrating into the matrix. The high temperature oxidation resistance of MoSi2 can be improved by increasing its relative density.     

包渗法制备硅化物涂层的结构形貌及形成机理

采用包渗法在C-103铌合金基体上制备MoSi2涂层,通过X射线衍射、扫描电镜和能谱分析等手段研究涂层表面、截面形貌以及氧化后涂层结构变化,并分析硅化过程中涂层的形成机理。研究结果表明：包渗法制备硅化物涂层是通过反应扩散形成的,硅化过程服从抛物线规律;该涂层为复合结构：MoSi2相为主体层;以NbSi2相为主、并含少量Nb5Si3相的两相为过渡区;Nb5Si3相为扩散层。在高温氧化环境下,涂层表面生成致密的非晶氧化层,有效地阻止了氧向涂层内扩散。     

Low-temperature oxidation behavior of MoSi_2 powders

The oxidation behavior of molybdenum disilicide (MoSi2) powders at 400, 500, and 600oC for 12 h in air were investi- gated by using X-ray diffraction (XRD) and transmission electron microscopic (TEM) techniques. Significant changes were observed in volume, mass, and color. Especially at 500oC, the volume expansion was found to be as high as 7-8 times, the color changed from black to yellow-white, and the mass gain was about 169.34% after 8 h, with SiO2 and MoO3 as main reaction products. The gains in volume and mass were less at 400 and 600oC compared with those at 500oC, probably due to the less reaction rate at 400oC and the formation of silica glass scale at 600oC, which would protect the matrix and restrain the diffusion of oxygen and molybdenum. Thus, the accelerated oxidation behavior of MoSi2 powder appeared at 500oC and the volume expansion was the sign of accelerated oxida- tion.     

Study on the isothermal oxidation behavior in air of Ti_3AlC_2 sintered by hot pressing

The isothermal oxidation behavior at 900―1300℃ for 20 h in air of bulk Ti3AlC2 with 2.8 wt% TiC sintered by means of hot pressing was investigated in the work. The isothermal oxidation behavior generally followed a parabolic rate law. The parabolic rate constants increased from 1.39×10-10 kg2·m-4·s-1 at 900℃ to 5.56×10-9 kg2·m-4·s-1 at 1300℃. The calculated activation energy was 136.45 kJ/mol. It was demonstrated that Ti3AlC2 had excellent oxidation resistance due to the continuous, dense and adhesive protect scales consisted of a mass of α-Al2O3 and a little of TiO2 and/or Al2TiO5. In principle, the oxide scale was grown by the inward diffusion of O2- and the outward diffusion of Ti4 and Al3 . The rapid outward diffusion of cations usually resulted in the formation of cracks, gaps, and holes.     

微波辐射Fenton氧化处理络合铜废水研究

以络合铜生产废水为研究对象,考察了H2O2投加量、FeSO4投加量、pH值、微波辐射时间、微波辐射功率等因素对微波辐射Fenton氧化法去除污染物效果的影响.分析了最优条件下单独微波、单独Fenton以及两者联用对CODCr和Cu2+的去除作用,初步探索了各影响因子的作用效果和综合反应机理.结果表明,通过单因素实验优化微波辐射Fenton氧化处理络合铜生产废水的最佳工艺条件为:30%H2O2用量为130 mL/L、FeSO4.7H2O用量为5 g/L、pH值为3.5、微波功率680 W、微波辐射时间10 min.在此条件下,微波结合Fenton氧化使CODCr和Cu2+分别由14 750 mg/L、968 mg/L下降到1 327 mg/L、55 mg/L,单独微波下降到11 563 mg/L、681 mg/L,单独Fenton氧化下降到2 537 mg/L、99 mg/L.     

电流密度对电化学阻垢性能的影响

为研究电流密度对电化学阻垢性能的影响,设计了电化学阻垢实验装置,研究了不同电流密度（100~400?A·m-2）处理条件下,溶液的溶解性总固体（TDS）和电导率（EC）的变化规律。结果表明:增加电流密度可以提高电化学阻垢性能,在电流密度为200?A·m-2的条件下,阻垢率约为不通电条件下的6~8倍。在电化学水处理过程中,溶液TDS和EC随电流密度的增加而线性减小,其中电场增强、极板积垢和pH降低是TDS减小的主要原因,Ca2+浓度降低以及电极钝化是EC减小的主要原因。在电流密度为400?A·m-2的条件下,TDS和EC极小值分别为804?mg/L和1 482?μs·cm-1,TDS和EC降低率分别为47.0%和48.0%。     

氧化钌/聚苯胺复合材料的制备与电化学性能研究

以RuCl3.nH2O为原料通过溶胶-水热法制得纳米RuO2粒子,然后在RuO2溶胶体系中通过常规的化学氧化法由苯胺氧化聚合制备纳米RuO2/聚苯胺复合材料,采用扫描电镜（SEM）和X-射线衍射（XRD）对其形貌和微观结构进行表征,并用循环伏安法研究了不同RuO2质量分数的复合材料电极的电化学性能。结果表明,RuO2质量分数为5%时,RuO2/聚苯胺复合材料形成致密的表面包覆型结构,聚苯胺电化学电容消失,复合材料电极电容很小。RuO2质量分数大于或小于5%时,RuO2粒子呈弥散状分布在聚苯胺中;RuO2质量分数为3%时,复合材料比电容达到极值374.6 F/g,这种复合材料具有很好的电化学特性,适于用作超级电容器电极。     

加热温度对铸态Ti1100氧化及表面形貌的影响

研究了铸态Ti1100在不同温度下保温5小时的氧化增重和表面形貌.结果表明,随着加热温度的升高,铸造Ti1100氧化加重.300℃基本不氧化;500℃-700℃,Ti1100试样增重0.28-0.62%;1100℃氧化增重严重,达到12.73%;钛的氧化增重为吸氧.用JSM-6360LV型扫描电子显微镜观察试样表面形貌,300-600℃氧化膜极薄且致密;700℃试样表面有少量的氧化腐蚀坑,表面较致密;900℃试样表面有较多的突起氧化层,表面不致密;1100℃氧化层为板片状TiO2.氧化过程为高温时,氧化膜晶粒粗大变得疏松,氧通过氧化膜扩散进基体.     

包覆法制备Gp/SiC复合材料的显微结构和性能

以不同粒径的石墨颗粒和SiC粉体为原料,采用SiC粉体包覆石墨颗粒的方法,于2000℃热压制备了石墨/碳化硅（Gp/SiC）复合材料.利用扫描电子显微镜（SEM,EDS）分析了材料的金相和断口显微结构.研究表明,石墨粒径较小且质量分数较少的复合材料比石墨粒径较大且质量分数较多的复合材料在热压工艺中更致密.石墨颗粒呈岛状紧密地镶嵌在SiC基体中,石墨与SiC界面处C和Si的扩散不明显.复合材料的相对密度、抗折强度,断裂韧性和硬度随石墨粒径和质量分数的减少而增加.断口形貌表明SiC陶瓷基体为脆性,石墨为韧性断裂.当石墨粒径为125μm、SiC与石墨的质量比为3.5时,复合材料的综合性能最佳,开口气孔率为0.3%,相对密度为97.9%,抗折强度为75±15 MPa,断裂韧性为5.4±0.5 MPa.m1/2,硬度为26.8±3GPa.     

采用高通量测序分析全程自养脱氮（CANON）系统不同脱氮效能下的微生物群落结构

从微生物优势菌群构成角度揭示一体式全程自养脱氮反应器(completely autotrophic nitrogen removal over nitrite,CANON)启动、稳态运行及崩溃的微观机理,有助于优化调控微生物种群、增强CANON的脱氮效能.试验采用序批式反应器(sequencing batch reactor,SBR),以间歇曝气方式启动CANON系统(35℃±1℃),考察了CANON系统从启动、稳定到恶化过程的氮素转化率和微生物活性;同时对污泥样品采用16S rDNA宏基因组高通量测序技术,考察种泥和不同脱氮效能时期的微生物种群结构.试验结果表明:本CANON系统的厌氧氨氧化菌(anaerobic ammonium oxidation bacteria,AnAOB)为Candidatus Kuenenia,氨氧化菌(ammonium oxidation bacteria,AOB)和硝化菌(nitrite oxidation bacteria,NOB)分别为亚硝化单胞菌属(Nitrosomonas)和Uncultured Nitrospinaceae;系统启动时,AnAOB丰度达到0.44%,AOB和NOB分别占总菌的27.61%和1.33%,脱氮效果最佳时的总氮容积去除率达到218.0 mg/(L·d);由于系统溶解氧质量浓度较低(0.15~0.25 mg/L),好氧段发生厌氧氨氧化反应,好氧段结束时亚硝氮积累量持续下降,导致缺氧段亚硝酸盐基质不足,AnAOB受到抑制;长期运行条件下,反应器内生物多样性及AnAOB丰度均有所下降.反应末期,Nitrosomonas占总菌群数量的62%,成为优势菌种,而AnAOB仅占0.13%,与此时较低的总氮容积去除率(19.3 mg/(L·d))相吻合.     

絮凝-氧化-超滤相结合法处理造纸黑液的研究

研究采用复合絮凝技术—化学氧化—超滤技术相结合的方法处理造纸黑液.先经复合絮凝确定最佳工艺条件：PAC-PFS-CPAM=5∶2∶2（体积比）,pH=6.8,测其上清液,使废水的COD由102 984mg·L-1降至982mg·L-1;再经10%的过硫酸铵氧化,COD又降至203mg·L-1;最后采用自制的超滤膜离心处理,使废水的COD降至86mg·L-1.     

Physical and chemical performances of high Al steels

1INTRODUCTION Aluminumisnotonlyakindofnonferrous metalbutalsoaveryimportantelementfordeoxi dationandalloyinginsteelmakingprocess.Forsteelscontainingaluminumthefinecrystalparticle canmakesteelobtainlotsofadvantagesformachi ningperformance[1,2].Butatpresent,duetothelimitationofAl contentduringthecontinuouscastingofmolten steel,theapplicationsofAlinsteelarefocusedon twoaspects.Ontheonehand,Alisaddedintooilpipesteels,boltsteels,chainssteelsandhigh bridgesteelstoimprovetheirimpactionperform a…     

High temperature cyclic oxidation behavior of Y2O3-ZrO2 thermal barrier coatings irradiated by high-intensity pulsed ion beam

The high-temperature oxidation resistance behavior of 7% (mass fraction) Y₂O₃-ZrO₂ thermal barrier coatings (TBCs) irradiated by high-intensity pulsed ion beam (HIPIB) was investigated under the cyclic oxidation condition of 1 050 °C and 1 h. The columnar grains in the TBCs disappear after the HIPIB irradiation at ion current densities of 100–200 A/cm² and the irradiated surface becomes smooth and densified after remelting and ablation due to the HIPIB irradiation. The thermally grown oxide (TGO) layer thickness of the irradiated TBCs is smaller than that of the original TBCs. After 15 cycles, the mass gains of the original TBCs and those irradiated by ion current densities of 100 and 200 A/cm² due to the oxidation are found to be 0.8–0.9, 0.6–0.7, and 0.3–0.4 mg/cm², respectively. The inward diffusion of oxygen through the irradiated TBCs is significantly impeded by the densified top layer formed due to irradiation, which is the main reason for the improved overall oxidation resistance of the irradiated TBCs. Foundation item: Projects supported by The 2nd Stage of Brain Korea and Korea Research Foundation     

Low-temperature oxidation behavior of MoSi2 powders

The oxidation behavior of molybdenum disilicide (MoSi2) powders at 400, 500, and 600℃ for 12 h in air were investigated by using X-ray diffraction (XRD) and transmission electron microscopic (TEM) techniques. Significant changes were observed in volume, mass, and color. Especially at 500℃, the volume expansion was found to be as high as 7-8 times, the color changed from black to yellow-white, and the mass gain was about 169.34% after 8 h, with SiO2 and MoO3 as main reaction products. The gains in volume and mass were less at 400 and 600℃ compared with those at 500℃, probably due to the less reaction rate at 400℃ and the formation of silica glass scale at 600℃, which would protect the matrix and restrain the diffusion of oxygen and molybdenum. Thus,the accelerated oxidation behavior of MoSi2 powder appeared at 500℃ and the volume expansion was the sign of accelerated oxidation.     

Tribological Properties of MoSi2 Against AISI10045 Steel Under Sliding Friction

MoSi2 samples were prepared by a self-propagating high-temperature synthesis （SHS） and a hot-press technique. The sliding friction and wear properties of intermetallic MoSi2 against AISI10045 steel under dry friction and oil lubrication conditions were investigated with a MRH-5A type ring-on-block friction and wear tester. The elemental composition, microstructure and worn surface morphology of the MoSi2 material were observed and analyzed by means of scanning electron microscopy （SEM） and X-ray diffraction （XRD）. The synthetic parameter pv value reflecting friction work, was used to discuss the tribological properties of MoSi2 material. The results show that 1） oil lubrication can obviously improve the tribological properties of MoSi2, 2） the bigger the pv value, the greater the antifriction and the abrasive resistance of MoSi2 under oil lubrication, 3） with an increase in the pv value, the wear mechanism of MoSi2 material under dry sliding friction is the fatigue fracture and adhesive wear and 4） under oil lubrication the wear mechanism is mainly fatigue pitting.     

First-principle investigation on electronic structures and elastic properties of Al-doped MoSi_2

The electronic structures and elastic properties of Al-doped MoSi2 were calculated using the plane wave pseudo-potential method based on the density functional theory,in which the generalized-gradient approximation(GGA) was used to describe the exchange-correlation potential.Starting from the elastic constants,bulk modulus,shear modulus,elastic modulus and Poisson ratio of Al-doped MoSi2 were obtained by using the Hill method.The results indicate that conductivity of Al-doped MoSi2 is improved to some extent in comparison with that of pure MoSi2 due to the orbit hybridization of Mo 4d,Al 3p and Si 3p electrons.In addition,calculations show that the elastic modulus and the brittleness of Al-doped MoSi2 are smaller than those of pure MoSi2,which implies that it is feasible to toughen MoSi2 by doping Al.The agreement of the conclusion with experiment shows that the present theory is reasonable.     

Characterization of phosphorus removal bacteria in （AO）^2 SBR system by using different electron acceptors

The enhanced biological phosphorus removal (EB-PR) process is an economical and environmentallyfriendly technology for removing phosphorus fromwastewater, where the phosphorus removal bacteria isthe key functional organism[1]. According to the origi-nal c…     

Fenton氧化法处理双唑杂环废水

以含双唑杂环类化合物的模拟废水为对象,采用Fenton氧化和高效液相色谱法研究了pH、反应时间和Fenton试剂用量等影响因子对双吡唑模拟废水处理效果的影响,通过高效液相色谱测试探究了Fenton处理双唑杂环类结构的降解机理。结果表明,最佳处理条件为:初始pH=3、反应时间为30 min、 m（Fe²⁺）∶V（H₂O₂）=1∶20、FeSO₄·7H₂O投加量2.5 g/L、H₂O₂投加量50 mL/L,双吡唑去除率可达97.5%,COD去除率可达82.1%。Fenton氧化过程中依次产生更为亲水的中间物质,亲水性越强的物质更难被破坏。     

聚氨酯固定高效优势耐冷菌处理低温生活污水

为确保寒冷地区污水生物处理系统的运行效能,以生活污水为研究对象,以聚氨酯泡沫为载体固定高活性耐冷菌,通过实验室小试,考察活性污泥法与生物接触氧化法联用的内循环复合生物反应器处理低温污水的效果及主要影响因素.结果表明,该工艺解决了由于冬季水温低出水难以达标排放的问题.系统对COD、BOD5和总磷的平均去除率分别为86.66%、90%和89.67%;系统HRT为10 h,活性污泥法处理单元与生物接触氧化法处理单元的DO分别保持在2.0～4.0 mg/L和4.0～8.0 mg/L,污泥负荷为0.25～0.30 kgCOD/(kgMLSS.d),可以使系统出水在冬季达到一级B排放标准.