HZSM5分子筛膜复合二氧化锡对甲烷的气敏性能研究

采用液相氧化法制备二氧化锡纳米颗粒,并利用浸渍法制备Pd负载二氧化锡纳米材料,通过丝网印刷得到气敏传感膜并在其表面印刷分子筛层。基于动态气敏测试系统探究传感器对甲烷气体的灵敏度及其在CO和乙醇干扰气体下的选择性。研究结果表明,在Pd-SnO₂敏感层表面印刷Pd-HZSM5层后,传感器对甲烷的响应能力显著提高,并且在体积分数为5×10^-4的CO存在时,对甲烷的选择性也得到明显的提升。同样,在质量分数为2×10^-5乙醇的存在下,传感器对甲烷的响应也没有受到干扰。通过对分子筛进行表征和催化分析,发现Pd-HZSM5对CO的催化效率可达100%,使得CO在扩散过程中被催化氧化,这可能是印刷Pd-HZSM5分子筛膜从而提高传感器选择性的主要原因。同时研究还表明,在敏感层表面印刷分子筛层并不会影响传感器的响应和恢复速率。     

Refinement mechanism of in-situ Al4C3 particles on AZ91 magnesium alloys

The effects of SrCO3 on the microstructure of AZ91 magnesium alloy were investigated by OM, SEM, EDS, XRD and DTA analyses. The results show that AZ91 magnesium alloy with 1.0% SrCO3 addition has the best refining effect at 730 ℃ for 20 min, the average size of the α-Mg grain in AZ91 matrix alloy is reduced from about 91 μm to 58 μm, with reduction of about 36%. Based on the analysis results of EDS, binding energy, and Gibbs free energy, it is evident that the grain is refined because of the generation of A14 C3 particles which can be used as the crystal nucleus of the magnesium alloy when SrCO 3 is added. Owing to the generation of A14C3 in AZ91 magnesium alloy, the grain boundary is pined and the grain growth is inhibited. In the accession to the Al4C3, small subcooling temperature difference leads to the formation of fine grain microstructure in alloy melt. Fine grain microstructure in AZ91 alloy melt with the addition of SrCO3 can be obtained on the condition of lower undercooling temperature according to the DTA analysis results.     

龙开口水电站定子组装施工工艺

对龙开口水电站发电机定子组装施工过程中的机座组装焊接、定位筋安装以及铁心叠片进行了详细介绍,其中在定位筋安装时采用的“片—筋—片安装法”先由预叠片定位、调整,安装焊接后再叠装铁心冲片,与传统工艺相比,具有定位筋分度、弦长与垂直度易于控制的优点,由于先焊接后叠片,也不存在施工干扰.工艺简单、技术先进,值得在同类型的定子组装过程中进行推广.     

MESHING THEORY AND DESIGN METHOD OF NEW SILENT CHAIN AND SPROCKET

Based on the study of the meshing theory of a new silent chain and sprockets, and the rolling cutting theory of sprocket and hob, the harmonious relations of dominating dimensions among the new silent chain, sprocket and hob is build, the meshing conditions are expatiated, and the resolved expression, which can instruct design and calculation, is educed. The tests show that the meshing design method is feasible.     

排土机俯仰液压系统的改进及仿真优化

排土机俯仰机构由机械系统和液压系统组成。排土机排料臂上下动作时,其升降速度也发生改变,这对排土机俯仰部分的稳定性极为不利。故对俯仰机构液压系统进行改进以保证其稳定性,并用AMESim软件进行仿真研究,对于代替液压系统试验十分必要。     

Cactus Stem Inspired Cone‐Arrayed Surfaces for Efficient Fog Collection

With the increasing world population and the rapid development of the global industry, clean water is becoming scarcer and scarcer. Means of translating latent water in fog to dominant available water, i.e., fog collection, therefore becomes highly desirable. Previously, it was demonstrated that the cactus O. Microdasys has an integrated fog collection system arising from the evenly distributed clusters of spines and trichomes on the cactus stem. Here, it is reported that the intersite of the clusters on the cactus stem is densely covered with cones, which are also capable of collecting water from fog efficiently. Inspired by these cones, using a simple method combining mechanical perforating and template replica technology, polydimethylsiloxane (PDMS) cone arrays are fabricated with different arrangements and the one in hexagonal arrangement proves to be more efficient due to the more turbulent flow filed around the staggered cones and the rapid directional movement of water drops along each cone. This investigation opens up new avenue to collect water efficiently and may also provide clues to research about dust filtering and smog removal, which is attracting increasing attention worldwide.     

微波烧结工艺对钨基合金挤压棒坯显微组织及力学性能的影响

研究了微波烧结温度和时间对钨基合金挤压棒坯显微组织及力学性能的影响。采用高倍SEM和光学金相显微镜分别对合金断口和显微组织进行了形貌观察;对合金相对密度、抗拉强度、延伸率和硬度进行了测定和分析。结果表明:当微波烧结时间为30min时,随着烧结温度的升高,合金性能呈峰值变化,烧结温度为1550℃时,合金的力学性能达到极大值,相对密度、抗拉强度、延伸率和HRC硬度分别为98.3%、920MPa、9.7%和30.5;当微波烧结温度为1550℃时,随着烧结时间的延长,合金的力学性能先上升后下降;随着微波烧结温度的升高及微波烧结时间的延长,钨晶粒的尺寸逐渐增大。     

钨基合金系挤压喂料粘度与流变特性研究

为了获得有利于成形的粘结剂优化配方,对相同粉末装载量的4种粘结剂体系的93W-Ni-Fe 粉末増塑挤压成形喂料粘度和流变行为进行了研究。采用英国AR2000EX旋转流变仪对钨基合金系挤压料在不同温度、不同剪切速率下的粘度进行测算。结果表明：对于不同粘结剂组成的喂料A、B、C和D中,A的粘度较低,流动性能较好,喂料D流变性能最不稳定;根据剪切速率与粘度的关系曲线可测算出130 ℃时喂料A、B、C的剪切稀化指数分别为0.048,–0.869和–1.717;由温度与粘度的关系曲线可测算出剪切速率为11.07 s-1时,喂料A、B、C的粘流活化能分别为8.524、8.107和31.310 kJ·mol-1;经模拟计算可得在130 ℃和11.07 s-1速率下A、B、C 3种喂料的流动性指数分别为7.2×10-6,4.8×10-6, 1.1×10-6,A喂料的综合流变学性能最好。     

存在错边时焊缝余高的测量

对接接头存在错边时,用现行方法测量会得到两个值,究竟那一个是真实余高值,大家莫衷一是。本文从石油、化工工业用焊制压力容器和钢管的生产实际出发,分析了余高定义的本质,指出了对接接头存在错边时究竟哪一部分金属是焊缝的余高,并通过理论分析提出了一种较为合理的测量方法。