Sr2+含量对红色荧光粉Ca0.85-xSrxMoO4:Eu3+0.075,Li+0.075发光性能的影响

采用溶胶-凝胶法制备了Ca0.85-xSrxMoO4:Eu3+0.075,Li+0.075(x=0,0.05,0.1,0.15,0.2,0.3,0.4)系列红色荧光粉.对样品前驱体的热重分析表明:温度升高到540℃后样品质量基本上保持稳定,不再发生失重现象;此外,还对样品的结构和发光性能进行表征,实验结果表明:适量Sr2+取代部分的Ca2+不但没有改变Ca0.85MoO4:Eu3+,Li+的物相结构,而且明显提高了荧光粉Ca0.85MoO4:Eu3+,Li+的相对发光强度,其主要是由于加入少量的Sr2+使晶体发生了畸变,从而导致发光强度的增加.实验结果表明,Sr2+的最佳掺杂量为15%(原子分数).     

放射性废物

随着原子能和平利用的发展,所产生的放射性废物也日益增多,这些放射性废物如果不很好地加以处理,会严重地损害居民的健康。放射性废物到底从那里来的呢?各种反应堆在运转中都不可避免地产生一批复杂的副产物,其中以在裂变过程中生成的为最多。因为铀-235在中子轰击下分裂,产生质量数大概从70到160的共约三十种以上元素的同位素。这些裂变产物都以不同的量生成,大部分是固体,有些是气体,并且大部分在形成时是具     

石墨烯/天然橡胶复合材料结构与性能研究

采用乳液共混、机械共混及两者并用制备了石墨烯(GNs)/天然橡胶(NR)复合材料,采用扫描电镜(SEM)、X-射线衍射(XRD)仪、高阻仪、动态热机械分析(DMA)仪、万能拉力试验机、热重分析(TG)仪对材料微观结构与宏观性能的相关性进行研究。研究表明:相比于机械共混,乳液共混有助于GNs的均匀分散和导电网络的形成,GNs/NR复合材料表现出较优的机械和导电性能,定伸应力和导电率分别是机械共混法的3倍和100倍;乳液共混后的机械共混则破坏了原有的导电网络,复合材料导电率下降;随后的机械共混打乱了原有的网络结构,并促使了GNs片层的卷曲化,降低了GNs与NR的接触面积,复合材料的综合性能下降。     

Design and characterization of a 3D encapsulation with silicon vias for radio frequency micro-electromechanical system resonator

In this paper, we present a three-dimensional(3D) vacuum packaging technique at a wafer level for a radio frequency micro-electromechanical system(RF MEMS) resonator, in which low-loss silicon vias is used to transmit RF signals.Au–Sn solder bonding is adopted to provide a vacuum encapsulation as well as electrical conductions. A RF model of the encapsulation cap is established to evaluate the parasitic effect of the packaging, which provides an effective design solution of 3D RF MEMS encapsulation. With the proposed packaging structure, the signal-to-background ratio(SBR) of 24 dB is achieved, as well as the quality factor(Q-factor) of the resonator increases from 8000 to 10400 after packaging.The packaged resonator has a linear frequency–temperature( f –T) characteristic in a temperature range between 0℃ and 100℃. And the package shows favorable long-term stability of the Q-factor over 200 days, which indicates that the package has excellent hermeticity. Furthermore, the average shear strength is measured to be 43.58 MPa among 10 samples.