纳米TiO_2增强NaNO_3-KNO_3-NaNO_2熔盐的中温储热特性

NaNO_3-KNO_3-NaNO_2(Hitec)熔盐作为一种理想的中高温传储热介质,未来有望在太阳能热利用等领域展开广泛应用。但其作为中温储热介质而言,其比热和导热性能相对较低,若能提高其比热和导热系数无疑将在太阳能热利用等实际应用中具有很重要的意义。采用水法技术制备了纳米TiO_2/Hitec熔盐复合储热介质,采用不同的表征技术研究了不同粒径、不同添加量纳米TiO_2颗粒对复合储热介质的比热、导热系数和热稳定性的影响。结果表明:与Hitec熔盐相比,纳米TiO_2颗粒明显提高了熔盐复合储热介质的储热特性。其中25 nm粒径,添加质量分数为0.062 5%纳米TiO_2对Hitec熔盐复合储热介质的比热(提高12%)和导热系数(增大15%)增强显著,同时热稳定性也得到改善。     

The effect of Nb additive on Te-induced stress corrosion cracking in Ni alloy: a first-principles calculation

Nb can improve the resistance of Ni-based Hastelloy N alloy to Te-induced intergranular embrittlement. First-principles calculations are performed to research this mechanism by simulating the Ni（111） surface and the ∑ 5（012） grain boundary. The calculated adsorption energy suggests that Te atoms prefer diffusing along the grain boundary to forming the surface-reaction layer with Nb on surface of the Ni alloy. First-principles ten- sile tests show that the Nb segregation can enhance the cohesion of grain boundary. The strong Nb-Ni bonding can prevent the Te migration into the inside of the alloy. According to the Rice-Wang model, the strengthen- ing/embrittling energies of Nb and Te are calculated, along with their mechanical and chemical components. The chemical bonds and electronic structures are analyzed to uncover the physical origin of the different effects of Te and Nb. Our work sheds lights on the effect of Nb additive on the Te-induced intergranular embrittlement in Hastelloy N alloy on the atomic and electronic level.