高能球磨过程中金属粉末的粘附特性

研究了Al、Cu和W三种金属粉末及其混合粉末在高能球磨过程中粘附球磨体的特性。试验结果表明：Al具有强烈粘附效应，Cu和W粉末几乎不发生粘附现象。在循环水冷却下，控制剂加入量、球磨时间和球磨转速的改变，会对金属粉末中Fe的污染量产生很大影响。     

机械球磨对TiC/W复合材料组织性能的影响

采用机械高能球磨法制备出TiC/W纳米晶复合粉体,复合粉体经压制并在1823K烧结制备得到TiC/W复合材料.研究了机械球磨对TiC/W复合材料组织结构和力学性能的影响.结果表明,球磨后的烧结组织均匀致密,没有缝隙和空洞出现.机械球磨能够降低烧结温度,提高块体致密度和室温抗弯强度;抗弯断口形貌在球磨后逐渐变平整,断裂形貌由沿晶断裂转变为穿晶断裂.     

高能球磨中纳米亚稳相的合成

高能球磨是合成纳米亚稳相的一种重要方法。利用高能球磨可以合成纳米晶、金属间化合物、非晶相及过饱和固溶相等多种纳米亚稳相。在球磨过程中,被研磨物质晶粒尺寸逐步细化,并产生大量的界面、位错等结构缺陷。这磐结构缺陷在动力学上为原子的集聚和扩散的一条低能通道,为新相的形核提供了基础。     

高能球磨对3%C-Cu粉末压制特性的影响

针对石墨／铜基复合材料存在烧结膨胀的特点，提出用粉末压制、真空热压烧结和热挤压相结合的致密化工艺。为给后续的烧结提供相对密度较高、质量好的冷压坯，采用刚性模常温单向压制方法研究高能球磨3％C—Cu（质量分数）粉末的压制压力与相对密度的关系，用黄培云压制理论考察球磨粉末的压制特性。用扫描电镜和场发射扫描电镜分别研究高能球磨粉末的微观组织和微区成分。结果表明，压制压力相同时，粉末压坯相对密度随高能球磨时间的延长而逐渐减小。高能球磨时间相同时，粉末压坯相对密度随压制压力的增加而增大。随着高能球磨时间的延长，粉末体越来越难压制。压制压力和保压时间分别为700MPa和30s时，所得粉末压坯的质量较好。     

Al、Cu和W粘附GCr15球磨体特性分析

在研究Al、Cu和W三种金属粉末在高能球磨过程中粘附球磨体的特性基础上,对粘附现象进行了热力学和动力学分析.结果表明,Al和Cu满足粘附热力学条件,而W则相反;球磨动力学条件,包括弹性模量、弹性回复力和应力松弛时间,是决定Al粉和Cu粉能否与球磨体发生粘附效应的关键因素.     

Al、Cu和W粘附GCr15球磨体特性分析

研究Al、Cu和W三种金属粉末在高能球磨过程中粘附球磨体的特性,对粘附现象进行了热力学和动力学分析.结果表明,Al和Cu满足粘附热力学条件,而W则相反;球磨动力学条件,如弹性模量、弹性回复力和应力松弛时间,是决定Al粉和Cu粉能否与球磨体发生粘附效应的关键因素.     

球磨时间对Mg/HA复合材料组织与力学性能的影响

采用干磨方式对70％Mg+ 30％HA配比的复合材料进行高能球磨,随后在300 MPa下冷压成φ15 mm×4mm片状试样,用于显微组织观察与力学性能测试.然后在500℃下常压烧结1h.实验测定了复合材料烧结体的抗压强度和硬度,通过扫描电镜和光学显微镜分别观察了压缩试样的断口形貌和烧结体的表面形貌.结果表明:随球磨时间的延长,粉末得到充分混合及细化,HA相均匀分布在Mg基体中,烧结体的抗压强度和硬度均增大.     

球磨纳米TiO2的结构转变

采用X射线衍射研究锐钛矿型纳米TiO2在高能球磨过程中及球磨后的纳米TiO2在退火过程中的结构变化。结果表现在室温常压下高能球磨诱发锐钛矿相转变为金红石相和S相。随着退火温度升高，球磨纳米TiO2粉末的晶粒逐渐长大，锐钛矿相逐渐转变为金红石相，而S相并不直接转变为金红石相而是先转变为锐钛矿相，然后由锐钛矿相转变为金红石相。与未球磨的纳米TiO2相比，高能球磨导致的晶粒细化，显微畸变以及晶格缺陷密度的增加而引起的额外储能使球磨后纳米TiO2的锐钛矿相-金红石相转变温度明显降低。     

双步球磨法制备纳米晶结构TiAl基合金粉末的研究

以元素粉末为起始粉末,采用双步球磨法(球磨+热处理+球磨)制备TiAl基纳米晶多相结构粉末(粉末成分为Ti-47Al(at%)、Ti-45Al-2Cr-2Nb-1B-0.5Ta(at%)).采用xRD、SEM、EDs、DTA、粒度分布仪对两种粉末颗粒在球磨和热处理过程中的特性进行了表征和分析.结果表明,采用双步球磨法制备的多相结构纳米晶粉末杂质含量低,粒度分布均匀,合金元素弥散分布.一步球磨6 h获得Ti/Al均匀复合结构及实现Ti(Al)部分固溶;700℃,2 h热处理获得Ti3Al、Ti、Al3Ti、TiAl相,Al相已经消失;二步球磨实现晶粒尺寸、颗粒尺寸进一步细化.     

高能球磨法制备纳米晶Ni粉的研究

采用高能球磨法制备出了纳米晶镍粉,并利用X射线衍射仪（XRD）、扫描电镜（SEM）、透射电镜（TEM）等分析检测手段,研究了该纳米晶镍粉末的结构、形貌和相的变化。结果表明,镍粉末平均粒度和晶粒度随球磨时间增加不断减小,而应变随球磨时间增加不断增大;当高能球磨54h后,球磨产物为FCC结构的鳞片状多晶体,晶粒度为17nm左右,应变为0.48%,颗粒尺寸为150～200nm;球磨时间增加至98h,产物中出现非晶相,但仍以多晶为主,晶粒尺寸为7nm,应变为1.24%,粉末团聚严重。     

Influence of pretreatment conditions of Ti film on field emission properties of carbon nanotubes films

Carbon nanotubes (CNTs) films have been synthesized from methane and hydrogen gas mixture by microwave plasma chemical vapor deposition (MPCVD) on Ti-coated Al₂O₃ substrates, which mechanically grinded by SiO₂ powder with Fe dopant. It is found that the grindness is a crucial effect to produce CNTs. By varying pretreatment conditions of the substrates such as no grinding, grinding and grinded acidly washing, the grinding and acidly washing can lower the turn-on field and improve the emission current density and emission light dots. The current density of the un-pretreated sample attains 0.015 mA/cm², but the grinding sample and grinded acidly washing sample attain 12.6 and 3.8 mA/cm², at the electric field of 3.7v/μm, respectively. The grinding sample shows the excellent field emission properties.     

Cathodoluminescence from organic bilayer induced by field electron emission of carbon nanotubes

We report the observation and studies of cathodoluminescence (CL) of organic bilayer structures, such as tris-(8-hydroxyquinoline) aluminium (Alq3) and 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole (PBD) deposited on ITO-coated glass, with and without hole transport layer, N,N′-diphenyl-N,N′-bis(1-naphthyl)-(1,1′-phenyl)-4,4′-diamine (α-NPD). To excite the CL of such bilayer organic heterostructure, low energy electrons field emitted by single walled carbon nanotube cathodes were utilized. The dependence of CL spectrum and intensity on voltage (V), current (I), type of transport layer and the cathode–anode geometry has been studied. We propose carbon nanotubes as efficient cathodes for stable CL emission from organic multilayer heterostructures. The role of both electron and hole transport layers on stability and spectrum of CL is also discussed.     

Effect of multi-walled carbon nanotubes on tribological properties of lubricant

After purified by mixture of sulfuric acid and nitric acid, the multi-walled carbon nanotubes(MWNTs) were modified with stearic acid(SA). The modified carbon nanotubes as lubricant additive were utilized to prepare lubricant, and the effects of carbon nanotubes on the tribological properties were investigated by using a pin-on-plate wear tester. The surface structure of MWNTs was examined by transmission electron microscopy, Raman spectroscopy and infrared spectroscopy. The results show that the surfaces of MWNTs are coated with a modified layer of SA. Furthermore, the modified MWNTs as lubricant additive can effectively improve the friction-reduction and antiwear ability of lubricant. The friction coefficient of base lubricant decreases by about 10% and the wear loss of base lubricant decreases by 30%-40% when the concentration of modified MWNTs in lubricant is 0.45 %. In addition,the mass ratio of SA to MWNTs influences the friction-reduction and anti-wear ability of the modified MWNTs as lubricant additive. The optimum mass ratio of MWNTs to stearic acid is about 3 : 8 - 1 : 2.     

Enhancement of electron field emission of vertically aligned carbon nanotubes by nitrogen plasma treatment

The electron field emission (EFE) characteristics from vertically aligned carbon nanotubes (VACNTs) without and with treatment by the nitrogen plasma are investigated. The VACNTs with the plasma treatment showed a significant improvement in the EFE property compared to the untreated VACNTs. The morphological, structural, and compositional properties of the VACNTs are extensively examined by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and energy dispersive X-ray spectroscopy. It is shown that the significant EFE improvement of the VACNTs after the nitrogen plasma treatment is closely related to the variation of the morphological and structural properties of the VACNTs. The high current density (299.6 μA/cm²) achieved at a low applied field (3.50 V/μm) suggests that the VACNTs after nitrogen plasma treatment can serve as effective electron field emission sources for numerous applications.     

The oxidation kinetics of multi-walled carbon nanotubes

The kinetics of isothermal oxidation of multi-walled carbon nanotubes (MWNTs) in air has been investigated in the experimental range of 573-823 K using thermogravimetry. The results show that the oxidation of MWNTs is both chemically controlled and diffusion controlled depending on the temperature range. Chou’s model has been applied to treat the oxidation behavior of MWNTs and the comparison of the experimental data with the theoretical ones validates the applicability of the model. This model offers a quantitative expression for the weight loss as a function of time at constant temperature conditions. The possible mechanism for oxidation has also been discussed briefly.     

渐变掺氮碳纳米管场的发射性能

以二甲苯/吡啶为碳/氮源,二茂铁为催化剂,在800 ℃下,由化学气相沉积法(CVD)制得了直径为10～30 nm的掺氮碳纳米管(CNT)阵列.用扫描电镜、透射电镜和拉曼光谱对其形貌和结构进行了表征.发现该碳管阵列具有竹节状结构,其中的氮含量沿碳管管径方向呈渐变趋势.随着碳管中氮含量的增加,竹节长度减小.研究了阵列的场发射性能,结果表明该碳管阵列是一种优秀的场发射材料:开启场强为0.37 V/μm,阈值场强为0.9 V/μm,场增强因子为37700.     

Production of carbon nanotubes by single-pulse discharge in air

The production of carbon nanotubes (CNTs) has various methods, such as arc discharge, laser ablation, chemical vapor deposition (CVD), template-directed synthesis. These methods generally require, besides catalyst particles, vacuum environment and special ambient gas to prevent carbon from high temperature oxidation. However in this paper, CNTs were successfully produced on selected locations under atmospheric environment and room temperature by micro electrodischarge method. The micro electrodischarge system was composed with transistor circuit to offer discharging time of microseconds and peak current of several ampere. The effect of peak current and discharging time on the production of CNTs was addressed. Experimental results show that the structure and quantity of CNTs is different with different processing parameters. Multi-wall CNTs with the outer diameter of 17 nm and inner diameter of 5 nm were produced using peak current of 2.5 A and discharging time of 1000 μs.     

球磨石墨对银基复合材料组织和性能的影响

对原始粗片状石墨进行了球磨实验和相应的粒度分析以及粉末形貌观察,研究了球磨石墨取代原始石墨加入银基复合材料中对材料的烧结膨胀率、密度和硬度的影响.结果表明:球磨石墨初期,细化效果显著,当石墨粒度降到一定值时球磨细化很难继续进行,这是由石墨的晶体结构决定的;用球磨后的细石墨代替原始石墨,降低了材料的烧结膨胀率,提高了银基复合材料的密度和硬度.石墨含量对材料性能的影响分析表明,随着石墨含量的提高,烧结膨胀率增加,密度和硬度明显降低.     

高温空气氧化对高硅铝合金材料组织及物理性能的影响

采用高温空气氧化对Al-12Si与Al-30Si合金粉末进行预处理,结合包套热挤压,制备出Al2O3与SiO2增强的弥散强化型铝硅复合材料,通过金相及热物性测试,对材料显微组织、密度、气密性、热膨胀系数、导热系数进行了分析.结果表明合金粉末经高温空气氧化预处理后,Al-12Si晶粒长大不明显,而Al-30Si晶粒发生了明显长大;材料致密度随氧化时间延长略有下降,但均在97%以上,材料气密性均在1×10-9 Pa·m3/s左右;在相同工艺条件下,Al-30Si材料热膨胀系数明显低于Al-12Si材料,氧化时间对材料热膨胀系数影响不明显;导热系数随材料中硅含量增加而下降,随粉末氧化时间延长而增加,氧化24 h后,材料导热系数超过120 W/(m·K).     

Influence of graphite on concentration of carbon vacancies in ball-milled TiCx

In this work,the influence of graphite on the ball-milled TiCx was studied.The results show that the lattice parameter of TiCx is increased when TiCx particles are ball-milled with graphite,which indicates a decrease in the concentration of carbon vacancies in the TiCx.It is considered that this decrease in the concentration of carbon vacancies results from the diffusion of carbon atoms from graphite into the TiCx.When the TiCx is ball-milled with more graphite,the effectiveness of the ball-milling is better,and the diffusion process of carbon becomes much easier.Furthermore,besides diffusion into the TiCx,some graphite has transformed into amorphous carbon after the ball-milling.