基于第一性原理的α-Fe(001)/Mo2FeB2(001)界面性能的研究

采用第一性原理方法,研究了α-Fe(001)/Mo_2FeB_2(001)界面性能。建立了4种不同的原子堆垛方式界面模型,计算了其界面粘附功、界面结合能和断裂功。结果表明,以空心位置堆垛的Fe终端界面性能最稳定,而顶部位置的Fe+B终端界面性能最不稳定,两者的裂纹断裂均趋向于发生在基体相或硬质相内。在此基础上,进一步分析了空心位置Fe终端界面模型和顶部位置Fe+B终端界面模型的电子结构,电荷差分密度图显示在空心位置的Fe终端界面系统中,界面处Fe原子与Fe原子间形成金属键,界面处Fe原子与Mo原子间形成金属键。在顶部位置的Fe+B终端界面系统中,界面处的Fe原子与B原子间形成共价键,但界面强度比空心位置的Fe终端界面系统低。分态密度显示界面处原子间重新排列,发生杂化,形成共价键,揭示了界面成键特性。     

Mo2NiB2基金属陶瓷的研究进展

在金属陶瓷领域中,三元硼化物的研究已经取得了一系列的成果,但是对Mo_2NiB_2基金属陶瓷涂层的研究还比较少。主要论述了Mo_2NiB_2晶体结构、显微组织、Mo_2NiB_2基金属陶瓷的性能、Mo_2NiB_2基金属陶瓷的合金化、Mo_2NiB_2基金属陶瓷涂层研究进展,并且对Mo_2NiB_2基金属陶瓷的研究进行了展望。     

微波和真空烧结制备La2O3掺杂Al2O3透明陶瓷

通过共沉淀法制备La2O3掺杂Al_2O_3纳米粉,粉体经压制后分别采用微波和真空烧结制备Al_2O_3透明陶瓷。结果表明:Al_2O_3粉末颗粒大小均匀,近似球形,为40~60nm;两种烧结方式制备的试样XRD图中均为α-Al_2O_3,未检测到其它相。La2O3掺杂量为1%时,随烧结温度升高,两种烧结方法得到的Al_2O_3陶瓷的相对密度和抗弯强度均呈上升趋势,且微波烧结陶瓷的相对密度和抗弯强度明显高于真空烧结。1500℃烧结时,随La2O3掺杂量的增加,Al_2O_3陶瓷的相对密度均先增大后减小,当La2O3掺杂量为1%时,Al_2O_3陶瓷的相对密度和抗弯强度均最大。微波烧结陶瓷的透光率明显高于真空烧结,且其断口晶粒比真空烧结明显细少。     

反应烧结制备Li2Zn2Mo3O12微波介质陶瓷及其微波介电性能研究

采用反应烧结法制备了具有超低烧结温度的Li₂Zn₂Mo₃O₁₂微波介质陶瓷,研究了烧结温度对Li₂Zn₂Mo₃O₁₂陶瓷的烧结特性、物相组成、微观结构以及微波介电性能的影响。XRD表明：在550～650℃范围内,温度对陶瓷的物相组成影响不大;随着烧结温度的升高,Li₂Zn₂Mo₃O₁₂陶瓷的体积密度、相对密度、介电常数(ε_r)和品质因数(Q×f)均呈先增大后减小的趋势,谐振频率温度系数(τ_f)在-(70～90)×10^-6/℃波动。在625℃烧结2 h获得最大体积密度和相对密度：4.25 g/cm³和96.4%,以及优异的微波介电性能ε_r=10.9,Q×f=69 459 GHz,τ_f=-84×10<...     

煅烧气氛对Sol-gel制备MgAl2O4粉体烧结性能的影响

分别研究了空气气氛和氧气气氛下煅烧对溶胶凝胶制备MgAl₂O₄粉体性能的影响,并通过真空热压烧结成功制备出具有一定透光性的MgAl₂O₄透明陶瓷。用XRD、BET、SEM和TMA对粉体性能进行了分析。结果表明,煅烧气氛对粉体团聚状态和烧结活性有明显地影响;氧气气氛煅烧后粉体具有较小的粒径、较高的分散性和烧结活性;氧气气氛1 100℃煅烧后粉体经较低的1 500℃真空热压烧结后成功制备出具有一定透光性的MgAl₂O₄透明陶瓷(可见光波长范围透过率36%～47%)。     

MoS2/MoxN异质结构的制备及其电催化析氢性能研究

二硫化钼纳米片(MoS₂)是一种有望取代贵金属材料、非常有前景的电催化析氢材料。MoS₂不足在于导电性较差,析氢反应(HER)能垒较高。为了克服这一缺点,我们引入制备简单、导电性良好的Mo₂N作为基体。通过水热法,将MoS₂纳米片均匀生长在Mo₂N颗粒表面,一方面增加了材料导电性,另一方面MoS₂与Mo₂N形成MoS₂/Mo_xN异质结构有效增强水分子的解吸,从而提高HER性能。利用X射线衍射仪(XRD)、X射线光电子能谱仪(XPS)、扫描电子显微镜(SEM)、电化学工作站对MoS₂/Mo_xN进行结构、形貌以及性能的表征。实验结果表明,MoS₂纳米片均匀生长在Mo₂N颗粒表面,形成异质结构,水热12 h所得材料性能最佳。以MoS₂/Mo_xN作为工作电极,碳棒与Ag...     

MoS2/MoxN异质结构的制备及其电催化析氢性能研究

二硫化钼纳米片(MoS₂)是一种有望取代贵金属材料、非常有前景的电催化析氢材料。MoS₂不足在于导电性较差,析氢反应(HER)能垒较高。为了克服这一缺点,我们引入制备简单、导电性良好的Mo₂N作为基体。通过水热法,将MoS₂纳米片均匀生长在Mo₂N颗粒表面,一方面增加了材料导电性,另一方面MoS₂与Mo₂N形成MoS₂/Mo_xN异质结构有效增强水分子的解吸,从而提高HER性能。利用X射线衍射仪(XRD)、X射线光电子能谱仪(XPS)、扫描电子显微镜(SEM)、电化学工作站对MoS₂/Mo_xN进行结构、形貌以及性能的表征。实验结果表明,MoS₂纳米片均匀生长在Mo₂N颗粒表面,形成异质结构,水热12 h所得材料性能最佳。以MoS₂/Mo_xN作为工作电极,碳棒与Ag...     

MoS2/MoxN异质结构的制备及其电催化析氢性能研究

二硫化钼纳米片(MoS₂)是一种有望取代贵金属材料、非常有前景的电催化析氢材料。MoS₂不足在于导电性较差,析氢反应(HER)能垒较高。为了克服这一缺点,我们引入制备简单、导电性良好的Mo₂N作为基体。通过水热法,将MoS₂纳米片均匀生长在Mo₂N颗粒表面,一方面增加了材料导电性,另一方面MoS₂与Mo₂N形成MoS₂/Mo_xN异质结构有效增强水分子的解吸,从而提高HER性能。利用X射线衍射仪(XRD)、X射线光电子能谱仪(XPS)、扫描电子显微镜(SEM)、电化学工作站对MoS₂/Mo_xN进行结构、形貌以及性能的表征。实验结果表明,MoS₂纳米片均匀生长在Mo₂N颗粒表面,形成异质结构,水热12 h所得材料性能最佳。以MoS₂/Mo_xN作为工作电极,碳棒与Ag...     

SiO2对Al2O3凝胶纤维相变的影响

以尿素催化硅酸乙酯水解制得SiO2溶胶。采用29Si NMR、27 Al NMR、FT-IR、TEM、DTA、XRD和SEM等对SiO2溶胶、Al2O3凝胶纤维化学结构和微观结构研究结果表明,该SiO2溶胶稳定性好,含有大量的单硅酸Si(OH)4,能和Al2O3表面的Al—OH反应生成Al—O—Si键而有效地将其包裹,从而阻止了过渡态Al2O3微晶的相互接触,抑制了α-Al2O3的成核和生长。     

纳米SnO2/TiO2复合粉体制备及其红外特性研究

以溶胶-凝胶方法制备纳米SnO2/TiO2复合粉体,并用XRD、TEM等方法对其进行了表征,给出了相关的工艺参数.研究了纳米SnO2及SnO2/TiO2复合材料的红外吸收特性.结果表明,本文制备的纳米SnO2/TiO2复合材料在4000～1500cm-1和1000～400cm-1范围内有较好的红外吸收.     

Mo含量对牙科用Ti-Mo合金显微组织及性能的影响

采用LZ5型离心铸钛机制备了4种Ti-Mo（5％、10％、15％和20％（质量分数）Mo）合金，研究了其显微组织和力学性能，并对其在Hank’S溶液和0．9％NaCl溶液中的耐蚀性进行了研究。研究结果表明：Ti-5Mo合金由等轴的α相组成，Ti-10Mo合金由等轴的β相和针状的α相组成，Ti-15Mo和Ti-20Mo合金由单一的等轴β相组成。力学性能测试结果表明，随着Mo含量的增加，Ti-Mo合金的压缩强度降低，塑性增强。耐蚀性研究结果表明，Hank＇s溶液中Ti-10Mo合金的自腐蚀电位较高，且易钝化；0．9％NaCl溶液中，Ti-5Mo合金的自腐蚀电位较高。Ti-20Mo合金易钝化且钝化区间较宽，两种腐蚀介质中Ti-15Mo合金的钝化膜较稳定。     

成分配比对三元硼化物金属陶瓷Mo2FeB2性能的影响

三元硼化物金属陶瓷Mo2FeB2具有良好的硬度和耐磨性，且可通过原位液相反应生成。但不同的成分配比对生成三元硼化物Mo2FeB2性能的影响很大，本文通过实验，对不同Mo／B原子比的三元硼化物金属陶瓷Mo2FeB2的组织结构和硬度进行了对比研究，试验结果表明，当Mo／B原子比为1．1时，三元硼化物金属陶瓷Mo2FeB2具有较好的组织和性能。     

Cr含量对WC-Co硬质合金显微组织和力学性能的影响

采用低压烧结技术制备了不同Cr含量的WC-8Co硬质合金,通过XRD、SEM和力学性能测试等手段分析了Cr含量对硬质合金物相、显微结构和合金的力学性能的影响。结果表明,当Cr含量〈0.9%时,合金由WC＋γ-（WC）相组成,添加量增至0.9%及以上时,组织中出现缺碳相Co3W3C;随着Cr含量的增加,WC晶粒不断细化,当添加量为0.6%时,合金的综合力学性能最佳,其抗弯强度、维氏硬度及断裂韧性分别为3885MPa、1632.4HV30、9.82MPa.m1/2。     

TiO2纳米纤维微观结构的调控与制备

通过静电纺丝技术制备了具有一维纳米结构的SiO2/TiO2纳米复合纤维,基于热碱化学刻蚀技术对其微观形貌进行二次调制,制备出具有较高比表面积的多孔TiO2纳米纤维。TG表征表明550℃以上的焙烧温度才能完全烧掉纳米纤维前驱体中有机物组分,从而得到无机SiO2/TiO2纳米复合纤维。同时发现,SiO2掺杂可以有效抑制TiO2高温条件下从锐钛矿相向金红石相的转化,在700℃仍然可以得到结晶较好的纯相SiO2/TiO2锐钛矿。SEM表征表明NaOH热化学处理可以从复合纳米纤维SiO2/TiO2体相刻蚀掉大部分SiO2纳米晶粒,从而制备出多孔TiO2无机纳米纤维,相对未经处理的TiO2纳米纤维,该材料具有更高的比表面积和更加精细的微观结构。     

The effect of microstructure on thermal expansion coefficients in powder-processed Al2Mo3O12

Orthorhombic Al₂Mo₃O₁₂ was investigated as a model anisotropic phase to understand the influence of powder preparation routes and bulk microstructure (mean grain size) on the bulk coefficient of thermal expansion (CTE) and to compare it to the intrinsic CTE of powder samples. A co-precipitation route was used for the synthesis of pure single-phase nanopowders, while a polyvinyl alcohol-assisted sol–gel method was utilized for the synthesis of micron-sized powders. Sintered samples prepared from both powders exhibited different microstructures in terms of mean crystal sizes and porosity. Bulk samples obtained from nanopowders were highly porous and contained crystals of approximately 100-nm diameter, while the bulk pieces produced from the micron-sized powders were denser, contained crystals larger than 5 μm, and showed occasional intergranular and transgranular microcracks. Such different microstructures hugely impact the bulk CTE: the nanometric sample possesses a bulk CTE (0.9 × 10^?6 °C^?1, from 200 to 700 °C) closer to the instrinsic CTE (2.4 × 10^?6 °C^?1) than for the micrometric sample, which showed a negative CTE (?2.2 × 10^?6 °C^?1) from 200 to 620 °C, and an even more negative CTE above 620 °C (?35 × 10^?6 °C^?1). A finite element analysis showed that the local maximum thermal tensile stresses could be as high as 220 MPa when simulating a temperature drop of 700 °C as an example of thermal treatment following sintering. This tensile stress is expected to exceed the tensile strength of Al₂Mo₃O₁₂, explaining the origin of microcracks in bulk samples prepared from the micron-sized powders. The thermal behavior of the microcracks leads to differences between the intrinsic and bulk thermal expansion; we show experimentally that such differences can be reduced by nanostructuring.     

The influence of microstructure on the failure behaviour of PEEK

In this study, different molecular weight PEEK materials were used to determine the effect of spherulite size on fracture. Melt processing of the PEEK at different temperatures produced samples of different average spherulite size. A permanganic etching technique was used to reveal the spherulites. It was found that for low molecular weight 150P PEEK, the spherulite size increased with melt processing temperature; but, for the higher molecular weight 450G PEEK, the spherulite size remained approximately constant. Also, the average spherulite size was markedly lower for the material of higher molecular weight. The failure behaviour of these samples was studied using a compact tension test. It was found that the fracture toughness of PEEK varied with processing temperature. Also, the average spherulite size of a PEEK material had a profound influence on the fracture mechanism.     

The influence of microstructure on the failure behaviour of PEEK

In this study, different molecular weight PEEK materials were used to determine the effect of spherulite size on fracture. Melt processing of the PEEK at different temperatures produced samples of different average spherulite size. A permanganic etching technique was used to reveal the spherulites. It was found that for low molecular weight 150P PEEK, the spherulite size increased with melt processing temperature; but, for the higher molecular weight 450G PEEK, the spherulite size remained approximately constant. Also, the average spherulite size was markedly lower for the material of higher molecular weight. The failure behaviour of these samples was studied using a compact tension test. It was found that the fracture toughness of PEEK varied with processing temperature. Also, the average spherulite size of this material had a profound influence on the fracture mechanism.     

The influence of different preparation methods on the aggregation status of pyrogenic nanosilicas used in concrete

Investigation of the effects of nanosilica materials in cementitious mixtures has attracted considerable research attention due to the very high specific surfaces of these materials. However, high surface area leads to aggregation of these materials due to high surface attraction forces, which could seriously reduce their nano filler effect. In this research the dispersion of pyrogenic nanosilicas in water and parameters influencing it were investigated. The results show that serious aggregation of pyrogenic nanosilicas in water occurs. Increasing the amount of applied forces, particularly the use of ultrasonic waves, has considerable effect in breaking aggregates into smaller aggregates with maximum size up to 0.9 μm. Increasing the pH was found to be very effective in improving dispersion of nanosilicas and through combined use of high pH and applying high levels of energy such as ultrasonic method it is possible to break all the aggregates into primary aggregates with maximum size of about 0.06 μm.     

The influence of annealing twinning on microstructure evolution

This paper reports an experimental investigation on the effect of multiple twinning on the interface population in two low stacking-fault alloys. This is an important topic for grain boundary engineering because annealing twinning is the indirect cause of improved intergranular corrosion resistance in this class of materials. Proportions of Σ 3ⁿ (n = 1–5) boundaries were analysed in both a brass specimen and a superalloy specimen where the boundaries had been processed so as to be very mobile and less mobile respectively. When Σ 3 twin boundaries (as distinct from Σ 3 grain boundaries) are discounted, the Σ 3ⁿ distribution for both specimens had a peak at Σ 9, because Σ 3 + Σ 9 → Σ 3 occurs more frequently than Σ 3+Σ 9 → Σ 27. The distributions and reactions between various Σ 3ⁿ values are described and discussed in detail. A novel trace analysis procedure is used to extract information from Σ 3 boundaries to decide whether or not they are annealing twins, and so provide a convenient means to assess proportions of twin and non-twin Σ 3s. The data show unambiguously that a significant proportion of Σ 3s are not on 111, and these boundaries have on average higher angular deviations from the exact Σ 3 reference misorientation than do other Σ 3s. A population of Σ 3s which were vicinal to annealing twins were also recorded. These data support the contention that profuse annealing twinning produces concurrently many not-twin Σ 3s, which are pivotal in grain boundary engineering.     

The influence of processing on the microstructure of an aluminum-lithium alloy

The intrinsic microstructural features of a thermomechanically processed Al-Cu-Li-Mn-Cd alloy was characterized. The thermomechanically processed material had an unrecrystallized structure with large unrecrystallized grains. The subgrains within the large unrecrystallized grains were fairly uniform in size. Precipitation of fine particles during the thermomechanical treatment suppressed recrystallization from occurring. The major strengthening precipitates were identified by transmission electron microscopy. Precipitate free zones were found to be absent along the subgrain boundaries of the thermomechanically processed material.