关键词： Tungsten   Thermal conductivity   Microstructure   Thermal stability   Spark plasma sintering   Plasma facing material  

摘要： In this study, we investigated thermal and microstructural properties of pure and dispersion strengthened tungsten fabricated by Spark Plasma Sintering (SPS) method in comparison to the tungsten materials produced by different commercial suppliers. We measured the thermal conductivity of the examined materials and compared them with chemical composition, density and microstructure of the samples. Thermal conductivity up to 900 degrees C was derived from thermal diffusivity and specific heat measurement and chemical composition was analyzed through glow discharge mass spectroscopy. Thermal conductivity values show a close correlation with content of compositional element. On the other hand, Vickers hardness shows correlation with the average grain size of the samples. The sample produced by different fabrication process shows different density and thermal conductivity. While TiC and Y2O3 added tungsten fabricated by SPS method shows improved stability in microstructure against recrystallization after exposure to high heat flux, the reduction of thermal conductivity is analyzed in comparison to the amount of contained additive elements.

关键词： 3D printing   mechanical properties   microstructure   pore size   durability  

摘要： Three-dimensional concrete printing (3DCP) has progressed rapidly in recent years. With the aim to realize both buildings and civil works without using any molding, not only has the need for reliable mechanical properties of printed concrete grown, but also the need for more durable and environmentally friendly materials. As a consequence of super positioning cementitious layers, voids are created which can negatively affect durability. This paper presents the results of an experimental study on the relationship between 3DCP process parameters and the formed microstructure. The effect of two different process parameters (printing speed and inter-layer time) on the microstructure was established for fresh and hardened states, and the results were correlated with mechanical performance. In the case of a higher printing speed, a lower surface roughness was created due to the higher kinetic energy of the sand particles and the higher force applied. Microstructural investigations revealed that the amount of unhydrated cement particles was higher in the case of a lower inter-layer interval (i.e., 10 min). This phenomenon could be related to the higher water demand of the printed layer in order to rebuild the early Calcium-Silicate-Hydrate (CSH) bridges and the lower amount of water available for further hydration. The number of pores and the pore distribution were also more pronounced in the case of lower time intervals. Increasing the inter-layer time interval or the printing speed both lowered the mechanical performance of the printed specimens. This study emphasizes that individual process parameters will affect not only the structural behavior of the material, but they will also affect the durability and consequently the resistance against aggressive chemical substances.

关键词： Calcium carbide residue   Calcium consumption   Electrical conductivity   Kaolinite   Microstructural change   Mix solution   Pozzolanic reaction   Rice husk ash  

摘要： Clay earthen materials can essentially be stabilized with calcium carbide residue (CCR) and rice husk ash (RHA) to produce compressed earth block (CEBs) with improved mechanical performances for application in building construction. Nevertheless, the curing process in mixtures of these materials needs to be monitored in order to assess the maturation of the reaction among these materials and their reactivity. This study investigated the curing process in mix solutions and microstructural changes in the cured mixtures made of kaolinite-rich earthen material, portlandite-rich CCR, and silica (amorphous)-rich RHA. Dry mixtures were prepared by adding 0-25% CCR and 10-25% CCR:RHA (various ratios) to the earthen material (5 g). The mix solutions were prepared by addition of 100 mL of deionized water to the dry mixtures. Stabilized CEBs were also produced by manually compressing moisturized mixtures in 295 x 140 x 95 mm(3) mold. The curing process was undertaken between 1 and 90 days at 40 +/- 2 degrees C. Throughout the curing, the chemical changes in mix solutions were monitored by measuring the pH, electrical conductivity (EC) and concentration of unconsumed calcium ions [Ca2+]. The microstructural changes in cured mixtures were characterized using X-Ray diffraction (XRD), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The EC and [Ca2+] decreased over the curing time mainly due to the consumption of calcium ions through pozzolanic reaction involving the earthen material with CCR and CCR with RHA. The minimum values of EC and [Ca2+] were reached after 45 days of curing in the mix solutions containing the earthen material and CCR alone and 28 days in those containing the earthen material and CCR:RHA. This was related to the end of the reaction and occurrence of optimum maturity in the respective mixtures. The XRD analyses revealed the consumption of kaolinite and portlandite from the raw materials and formation of calcium silicate hydrates (CSH)

关键词： 金刚石   硅空位色心   氧化   光致发光  

摘要： 制备了单个颗粒(domain)组成的纳米金刚石薄膜,薄膜中单个颗粒由尺寸超过 100 nm 的金刚石晶粒与非晶碳复合而成.对薄膜进行氧化处理后,其硅空位色心的光致发光强度增强了 22.7 倍.扫描电镜及拉曼光谱测试结果表明,不同时间氧化后的样品中存在由尺寸超过 100 nm 的晶粒组成的花瓣状金刚石聚集体,这些金刚石在较长氧化时间下仍能保持稳定.氧化后的薄膜内非晶碳大大减少,金刚石含量增大,纳米金刚石晶粒充分暴露引起了薄膜发光强度大幅增强,其发光半峰宽为 5.6 6.0 nm.继续增加氧化时间,薄膜的光致发光会因为部分细小纳米金刚石晶粒的损失而略微降低,但是稳定的大尺寸金刚石晶粒的存在使得薄膜的发光强度依然维持在氧化前的 8.3 倍以上.

关键词： 纳米银   纳米氧化锌   双眉虫   细胞毒性   超微结构  

摘要： 本文利用光学显微镜、电子显微镜技术研究了30 nm粒径圆球形纳米银颗粒及30 nm粒径圆球形纳米氧化锌颗粒对双眉虫(Diophrys sp.)细胞超微结构的影响.结果显示,这两种纳米材料均对细胞结构造成了一些相似的影响,主要表现在:(1)细胞内形成大量空泡;(2)线粒体出现肿胀、内部嵴断裂以及局部结构模糊和变空的现象;(3)细胞内出现大量自噬体,以及自噬后形成的髓鞘样小体.此外,纳米银颗粒处理组还出现细胞核核仁消失,核膜界限模糊的现象;纳米氧化锌处理组还发生了纤毛杆处质膜融合,细胞中产生大量溶酶体的现象.初步推测,纳米银颗粒主要通过影响细胞核功能,进而造成其他生命活动紊乱,而纳米氧化锌颗粒则会诱导细胞凋亡和破坏纤毛器结构从而限制细胞运动.

关键词： 材料表面微结构   循环肿瘤细胞   粘附和增殖   捕获率  

摘要： 目的探讨不同材料界面微观结构对循环肿瘤细胞(CTC)粘附、增殖及捕获率的影响。方法采用真空辅助软压印、水热法制备微米结构、纳米结构、微纳结构TiO2基底,连同氟掺杂氧化锡(FTO)玻璃共4种基底,修饰上皮细胞黏附分子抗体(anti-EpCAM)后进行人乳腺癌细胞系MCF-7和人宫颈癌细胞Hela的捕获实验,扫描电镜观察捕获细胞的形貌特征,荧光显微镜分析细胞增殖情况及捕获率。结果在微纳结构中,微米柱与纳米线在促进细胞粘附和铺展上具有协同作用,当微米柱间距合适时,细胞呈扁平状完全摊开。在捕获细胞孵育24 h后,微纳结构表面的细胞呈现明显增殖,细胞密度最大,单位面积细胞数为170个,明显多于其他3种结构界面(P<0.01)。随着孵育时间(30~60min)的延长,4种结构表面的捕获细胞逐渐增多(P<0.01),60 min后细胞捕获率基本不再增加;孵育60 min时,微纳结构的细胞捕获率最高,光滑表面则最低(P<0.01),且4种结构对Hela的捕获率均显著低于MCF-7(P<0.01)。结论相对于光滑表面、微米和纳米结构表面,仿荷叶微纳结构表面最有利于CTC粘附、铺展和增殖,具有最高的细胞捕获率。

关键词： 磺化碳纳米粉   二硫化钨   载流磨损率   抗磨性  

摘要： 为探究磺化碳纳米粉(SCN)和二硫化钨(WS2) 2种添加剂对树脂基炭刷材料抗磨性能的影响,以鳞片石墨粉为导电填料,环氧树脂为黏结剂,采用树脂分散添加剂,经混捏、破碎、冷压成型、固化等工艺制得树脂基炭刷材料,并对其进行性能测试。研究表明,在相同的载流磨损测试条件下,磺化碳纳米粉改性的炭刷材料平均载流磨损率为2.5 mg/h,相较于未加入添加剂的炭刷,其抗磨性能提升了67.7%;WS2改性的炭刷平均载流磨损率为3.35 mg/h,相较于未加入添加剂的炭刷,其抗磨性能提升了56.8%。经碳纳米粉和WS2改性的环氧树脂基炭刷材料其微观结构和抗磨性能均得到了显著改善,具体作用机制可推测是磺化碳纳米粉为力学增强型抗磨作用机制,WS2为减摩润滑型抗磨作用机制。

关键词： coexisting nanophases   lead-free piezoelectrics   phase boundary engineering   polarization rotation  

摘要： Piezoelectric materials interconvert between electrical energy and mechanical strain and are widely used for electronic and electromechanical devices. Owing to growing environmental concerns, development of lead-free piezoelectric materials with enhanced properties becomes of great interest. Key to the academic problem is a lack of fundamental understanding on the actual mechanisms involved at the microscopic (unit cell) level. While it is well known that giant responses occur near structural phase boundaries, and it has long been proposed that polarization rotation and nanodomains are major determinants, so far, atomistic understanding of the origin of the response has come mostly from theoretical simulations. Recently, notable breakthroughs have been achieved in improving the properties of piezoceramics and thin films. Precise mapping of atomic displacements by atomically resolved Z-contrast imaging has demonstrated that gradual polarization rotation bridges the coexisting nanophases. These structural features, which take place on a length scale of just a few nanometers, now visible through aberration-corrected microscopy, provide a new pivotal understanding on the outstanding piezoelectric behavior that has been obtained in all systems. They also provide key guiding principles for the development of lead-free piezoelectrics, especially in the form of thin films, which remain far behind bulk ceramics at the time being. Coexistence of nanophases with flexible interconversion, introduced via phase boundary engineering, holds much promise for achieving high performance in other material systems with phase transitions.

关键词： 共晶炸药   微结构设计   制备方法  

摘要： 共晶炸药具有较好的爆热、更高的氧平衡、更低的感度以及更高的安全性。共晶技术可有效改善单质炸药的不足之处,扩大其应用范围。综述了共晶炸药的微结构设计、模拟及制备方法,进一步评价了不同制备方法的特点,总结了共晶炸药发展现状,并对未来共晶炸药的研究方向进行了展望。