Spin excitations in a K0.84Fe1.99Se2 superconductor as studied by Mssbauer spectroscopy

Mssbauer spectroscopy was used to probe the site-specific information of a K 0.84 Fe 1.99 Se 2 superconductor. A spin excitation gap,△ E ≈ 5.5 meV, is observed by analyzing the temperature dependence of the hyperfine magnetic field (HMF) at the iron site within the spin wave theory. Using the simple model suggested in the literature, the temperature dependence of the HMF is well reproduced, suggesting that, below room temperature, the alkali metal intercalated iron–selenide superconductors can be regarded as ferromagnetically coupled spin blocks that interact with each other antiferromagnetically to form the observed checkerboard-like magnetic structure.     

Microstructure and Corrosion Performance of Carbonitriding Layers on Cast Iron by Plasma Electrolytic Carbonitriding

The surface carbonitriding of cast iron is investigated in an aqueous solution of acetamide and glycerin. Microstructure, chemical and phase composition and corrosion performance of the carbonitriding layers are investigated by scanning electron microscopy, energy dispersive spectroscopy and x-ray diffraction, as well as potentiodynamic polarization testing. X-ray diffraction results show that the carbonitriding coatings are composed of martensite, anstenite（γ-Fe）, Fe2C, Fe3C, Fe5 C2, FeN and ε-Fe2-3N. After the plasma electrolytic carbonitriding treatment the corrosion resistance of cast iron is clearly improved compared to the substrate, and the coatings produced at 350 V for 30s give the best corrosion resistance.     

用瞬态形核理论研究钕对快凝Al-Fe-V-Si合金非晶形成倾向的影响

利用与时间有关的瞬态形核理论计算了不同Ｎｄ含量的Ａｅ－Ｖ－Ｓｉ－Ｎｄ合金中α－Ａｌ相的形核率、形核孕育期与过冷度的关系，并计算了α－Ａ１形成非晶的临界冷却速率。结果表明，随Ｎｄ含量增加，合金的液相线温度提高，α－Ａ１形核孕育期延长，形核过冷度增加，形核率降低临界冷却速率降低，从而增大其非晶的形成倾向。