Boron diffusion in bcc-Fe studied by first-principles calculations

The diffusion mechanism of boron in bcc-Fe has been studied by first-principles calculations. The diffusion coefficients of the interstitial mechanism, the B–monovacancy complex mechanism, and the B–divacancy complex mechanism have been calculated. The calculated diffusion coefficient of the interstitial mechanism is D_0= 1.05 ×10~(-7)exp(-0.75 e V/k T) m~2· s~(-1), while the diffusion coefficients of the B–monovacancy and the B–divacancy complex mechanisms are D_1= 1.22 × 10~(-6)f1exp(-2.27 e V/k T) m~2· s~(-1)and D_2≈ 8.36 × 10~(-6)exp(-4.81 e V/k T) m~2· s~(-1), respectively. The results indicate that the dominant diffusion mechanism in bcc-Fe is the interstitial mechanism through an octahedral interstitial site instead of the complex mechanism. The calculated diffusion coefficient is in accordance with the reported experiment results measured in Fe–3%Si–B alloy(bcc structure). Since the non-equilibrium segregation of boron is based on the diffusion of the complexes as suggested by the theory, our calculation reasonably explains why the non-equilibrium segregation of boron is not observed in bcc-Fe in experiments.     

Direct characterization of boron segregation at random and twin grain boundaries

Boron distribution at grain boundaries in hot-deformed nickel is directly characterized by the time-of-flight secondary ion mass spectrometry. The segregations of boron are observed at both the random and twin grain boundaries. Two types of segregations at random grain boundaries are observed. The first type of segregation has a high intensity and small width. Its formation is attributed to the incorporating of dislocations into the moving grain boundaries. The second type of segregation arises from the cooling induced segregation at the dislocations associated with the grain boundaries. The segregation at twin boundary is similar to the second type of segregation at random grain boundaries.     

5-甲基水杨醛缩对氨基水杨酸席夫碱的合成、表征及性质

用5-甲基水杨醛和对氨基水杨酸为原料,合成了一种新型席夫碱,用元素分析、IR、1 H NMR、MS验证其结构.采用荧光光谱法研究该化合物与牛血清白蛋白(BSA)的相互作用机制,采用位点结合模型公式、热力学公式求解出不同温度下的结合常数、结合位点数、热力学参数,得出其淬灭机制为静态淬灭,结合位点数为1,作用力类型为氢键和范德华力.