钆、氟掺杂二氧化钒的晶体结构演变行为与相变机理

二氧化钒(VO_(2))是一种热致相变材料,其过高的相变温度制约了其潜在应用.元素掺杂能够使VO2的能带结构、态密度、键长和晶胞体积等晶格参数改变,引起其相变行为的变化.借助Materials Studio软件,基于第一性原理和分子轨道理论研究了钆、氟掺杂二氧化钒的晶体结构演变行为与相变机理.结果表明,无论F掺杂于VO_(2)(M型)中间O的位置还是两侧O位置,都会引起O-O键收缩,V-V键增长,β角增大,体系亥姆霍自由能增加,带隙相对减小,F侧位掺杂效果最好,随着V^(4+)-V^(4+)同极结合的减少,在1 at%F掺杂时相变温度达到最低;当Gd以0-1.8 at%掺杂于VO_(2)(M)中V位置时,O-O键和V—V键发生收缩,β角减小,亥姆霍自能增加,带隙减小,Gd 4f态与tⅡ轨道重合,使相变能垒变低,相变温度显著降低.钆、氟两种元素掺杂VO2相变机理更符合Peierls-Mott协同相变.

Effect of surfactants on hydrodynamics characteristics of bubble in shear thinning fluids at low Reynolds number

In this study,the effects of surfactants on the hydrodynamic characteristics of bubbles in shear-thinning fluids at low Reynolds number(Re<50)are investigated.The bubble terminal velocity and drag coefficient of bubble in clean and contaminated carboxymethylcellulose(CMC)solutions are obtained using a high-speed camera for examining differences.The results show that the existence of surfactant could reduce the terminal velocity of bubble at small volume(0.25wt%CMC:<100 mm3;0.50wt%CMC:<110 mm3),attributed to stiffening the bubble interface.However,this negative effect decreases and finally disappears with increasing bubble volume.The drag coefficient curves of the bubble in contaminated CMC solution exhibit behavior similar to that exhibited by a solid sphere at Re<10,indicating that internal circulation flow is absent at the bubble interface as compared to that in clean CMC solution.However,for 10<Re<40,a transition of drag curve from 24/Re to 16/Re in contaminated CMC solution is observed,which is easy at low SDS concentrations and high CMC concentrations.

表面活性剂对石蜡@SiO_(2)复合相变储热材料形貌和热性能的影响

通过原位聚合的方法,以石蜡(PA)为相变储热材料、正硅酸乙酯(TEOS)水解生成的SiO_(2)为壳层材料,成功制备出PA@SiO_(2)相变材料.通过傅里叶变换红外光谱仪(FT-IR)、场发射扫描电子显微镜(SEM)、差示扫描量热仪(DSC)、同步热分析仪(TG)等测试方法,探究了吐温-80、十六烷基三甲基溴化铵(CTAB)及其共同使用对储热微囊结构和热性能的影响.结果表明,添加不同表面活性剂制备的PA@SiO_(2)相变材料粒径大小有差异,但均表现出良好的相变性能和可靠的热稳定性,具有较高的包封率和储热能力.合成的PA@SiO_(2)相变材料在余热利用、太阳能热量储存与回收等领域具有潜在的应用前景.