不同送粉速度对TC4钛合金表面激光熔覆的影响

采用光纤激光对TC4钛合金表面进行熔覆改性,研究送粉速度对熔覆工艺过程和熔覆层性能的影响。采用高速摄像机拍摄了加热粉末在空间的分布形貌,采用光学显微镜观察了熔覆层横截面形貌,采用EDS分析了熔覆层的氮含量分布,并测量了熔覆层横截面的显微硬度。实验表明,送粉速度较小时,粉末吸收少量激光能量,熔池较大,熔覆层宽而浅;送粉速度较大时,粉末吸收大量激光能量,熔池较小,熔覆层窄而深。当送粉速度较大时,熔覆层的氮元素含量和显微硬度均分布基本均匀,无明显梯度;随送粉速度增加,熔覆层显微硬度会增加,并稳定在约9.3 GPa。     

Ti(C,N)含量和烧结温度对梯度硬质合金脱β层厚度的影响

以Ti(C,N)为N源,在脱氮气氛下烧结制备WC-TiC-Ti(C,N)-TaC-NbC-Co硬质合金,研究Ti(C,N)含量和烧结温度对脱β层厚度及合金微观组织与性能的影响。结果表明:随Ti(C,N)的质量分数从0.5%增加到1.5%,脱β层厚度持续增大。随烧结温度升高,脱β层厚度增大,增大的幅度随Ti(C,N)含量增加而增大。合金的密度、硬度和矫顽磁力不受Ti(C,N)含量的影响,但随烧结温度升高,合金的硬度降低、矫顽磁力变小、WC平均晶粒尺寸增大且直边化。脱β层中无明显的WC晶粒异常长大现象,脱β层厚度由Ti的扩散和N含量决定。     

Numerical Simulations of Lubricating Grease Flow in a Rectangular Channel with and without Restrictions

This article presents numerical simulations of the laminar flow of lubricating greases in a channel with rectangular cross section. Three greases with different consistencies (NLGI grades 00, 1, and 2) have been considered in three different configurations composed of a rectangular channel without restrictions, one rectangular step restriction, and one double-lip restriction. The driving pressure drop over the channel spans from 30 to 250 kPa. The grease rheology is described by the Herschel-Bulkley rheology model, and both the numerical code and rheology model have been validated with analytical solutions and flow measurements using micro-particle image velocimetry.     

Cleaning capacity of octenidine as root canal irrigant: A scanning electron microscopy study

The aim of this study was to assess the cleaning capacity of the octenidine hydrochloride (OCT) used as root canal irrigant by scanning electron microscopy (SEM) analysis. Sixty human unirradicular extracted teeth were randomly distributed in 6 groups (n = 10) according to irrigant solutions which were used during root canal preparation: G1, 0.1% OCT; G2, 2% chlorhexidine (CHX); G3, 2.5% sodium hypochlorite (NaOCl); G4, OCT + 17% ethylenediaminetetraacetic acid (EDTA); G5, 2.5% NaOCl + 17% EDTA and G6, distilled water. All specimens were instrumented with ProTaper system up to F4. Teeth were sectioned and prepared for SEM. The smear layer was evaluated using a 5‐score system and the data were analyzed by Kruskal–Wallis and Dunn (α = 0.05). In all root canal thirds there was no significant difference between OCT, CHX, NaOCl, and water groups (p > .05), and these groups showed higher smear layer values than NaOCl + EDTA and OCT + EDTA groups (p < .05). There was no significant difference between NaOCl + EDTA and OCT + EDTA groups (p > .05). It was concluded that OCT used as a single root canal irrigant presented poor cleaning capacity and could be used in association with a final irrigation with EDTA to obtain smear layer removal.     

Co‐optimization of SnS absorber and Zn(O,S) buffer materials for improved solar cells

Thin‐film solar cells consisting of earth‐abundant and non‐toxic materials were made from pulsed chemical vapor deposition (pulsed‐CVD) of SnS as the p‐type absorber layer and atomic layer deposition (ALD) of Zn(O,S) as the n‐type buffer layer. The effects of deposition temperature and annealing conditions of the SnS absorber layer were studied for solar cells with a structure of Mo/SnS/Zn(O,S)/ZnO/ITO. Solar cells were further optimized by varying the stoichiometry of Zn(O,S) and the annealing conditions of SnS. Post‐deposition annealing in pure hydrogen sulfide improved crystallinity and increased the carrier mobility by one order of magnitude, and a power conversion efficiency up to 2.9% was achieved. Copyright © 2014 John Wiley & Sons, Ltd.     

无水试剂的制备及参与植物油转酯化效果的快速评估

本文旨在提供实验室内快速制备无水试剂的方法。方法:先在实验室内用钠法制备无水试剂(石油醚、四氢呋喃和甲醇钠),然后以植物油为反应底物,检验了所制备的无水试剂的转酯化效率,并用薄层层析技术和气相色谱技术对转酯化效率进行验证。结果表明,本次制备的无水试剂可稳定、高效、快速的对植物油脂进行转酯化反应,且运用薄层层析技术能快速评估转酯化效率。     

逐层组装多层膜对苝的固相萃取性能研究

利用聚电解质逐层自组装技术在氨基硅胶表面构筑聚(乙烯-alt-马来酸)的苯乙胺衍生物(PEMAPEA)/聚烯丙基胺盐酸盐(PAH)多层膜,制备性能稳定的新型固相萃取吸附材料。利用HPLC-UV/Vis检测,研究其对水体中苝的萃取性能,考察柱填料量、样品量、上样流速、洗脱溶剂等对多层膜萃取性能的影响。结果表明:含150 mg固相萃取填料的3 mL萃取小柱,以10 mL·min-1的流速萃取200 mL苝的水溶液,用丙酮作洗脱剂,萃取回收率达到90%以上。     

薄板弯曲时树脂基碳纤维智能层的力阻响应

将智能层附于足够大的矩形薄板表面,通过不同的弯曲试验构造出多种表面应变状态,基于三种工况下的试验结果,建立智能层电阻变化与平面二维应变状态之间的映射关系,该关系表明纵向应变对智能层的电阻变化的影响占主导地位。在此基础上对其它工况下智能层的电阻变化率进行了预测,其结果与实验结果具有较好的一致性。     

竹增强环氧乙烯基树脂的制备及性能研究

和传统的钢护拦相比较,竹片增强复合材料护拦具有重量轻、成本低、耐腐蚀、环境友善和可再生性等优点。但是竹纤维表面的复杂成分,影响了复合材料的界面性能。本文利用竹片作为增强材料,采用真空辅助成型方法制备了竹片增强环氧乙烯基树脂复合材料,研究了表面改性和铺层数对竹复合材料弯曲强度和冲击韧性的影响,并对单向复合材料的冲击断面破坏方式进行了分析。结果表明,在不同铺层结构条件下,用经过碱与硅烷偶联剂改性处理过的竹条制备的复合材料的弯曲强度分别提高了31.95%、46.72%、29.58%,冲击韧性分别提高了25.62%、29.74%、28.61%,而且单向复合材料的弯曲和冲击性能最佳。当单向复合材料中的竹片铺层为15层时,其冲击吸收功为13.55J,拉伸强度为270MPa,弯曲强度为340MPa,在主要性能上能满足公路防撞护栏对其原料Q-235B钢的要求;通过扫描电镜分析发现,竹片增强复合材料防撞护栏材料的防撞机理表现为竹纤维抽拔断裂、基体断裂、纤维/基体界面脱黏以及剪切分层。本文的结果对复合材料公路防撞护栏的制备有一定的指导作用。