热带雨林环境中涂镀层表面的真菌群落研究

目的 研究热带雨林大气环境中5种常用涂(镀)层钢板表面的菌群分布及其变化规律,并深入讨论真菌对涂镀层材料的破坏作用.方法 对聚酯涂层、氟碳涂层、含铬耐指纹涂层、无铬耐指纹涂层和热镀锌板在内的5种材料,在西双版纳大气试验站进行2年的大气暴晒实验,干季和雨季共进行4次菌种采集.结合传统的培养法和现代分子生物学的方法,鉴定涂镀层材料表面生长的真菌,并对优势菌进行统计学分析.通过扫描电子显微镜(SEM)和能谱(EDS)研究霉菌对涂镀层材料的腐蚀行为.结果 从投试材料表面共分离纯化了真菌154株.根据ITS rDNA系统发育分析,鉴定为子囊菌门(Ascomycota)的3纲10目37属和担子菌门(Basidiomycota)的3纲6目12属.用统计学法得出,轮层炭菌属(Daldinia)、炭角菌属(Xylaria)、曲霉属(Aspergillus)、篮状菌属(Talaromyces)、弯孢属(Curvularia)、鬼伞属(Coprinellus)、链格孢属(Alternaria)、黑团孢属(Periconia)、拟鬼伞属(Coprinopsis)和皮司霉属(Pithomyces)等在数量、分布和季节上均为优势菌属.结论 以炭角菌属、弯孢属和曲霉属等为代表的真菌生命活动可能与涂层的劣化过程具有较强的相关性,可考虑作为相关材料霉菌实验的添加菌种.     

N–N interaction and nitrogen activity in the iron base austenite

The Monte Carlo computer simulation of the f.c.c. Fe–N alloy is performed using the data of abundances of different iron sites in the austenite lattice as obtained by means of Mössbauer spectroscopy. The validity of the interpretations of available Mössbauer spectra was tested based on the data of calculation of N–N interaction energies in the two first coordination spheres on the interstitial sublattice, which could satisfy the experimental data of nitrogen distribution in austenite derived from Mössbauer spectra. It is shown that no values of N–N interaction energies exist that could be consistent with the data of conversion electron Mössbauer spectroscopy (CEMS), where a thin surface layer only contributes to the Mössbauer spectra. A strong N–N repulsion (>0.14 eV) in the first coordination sphere and a soft N–N repulsion (<0.07 eV) in the second one was found to be consistent with the studies performed by means of transmission Mössbauer spectroscopy (TMS), according to which single nitrogen atoms and 180° N–N pairs exist in the nitrogen austenite. A possibility of the long-range order-like Fe₄N is shown at the energy values determined for two coordination spheres, provided a small N–N repulsion in the third coordination sphere occurs. It is also observed that the available data of nitrogen activity in Fe–N austenite are not consistent with the values of N–N interaction energies determined from the analysis of Mössbauer spectra, i.e. the available activity data do not correspond to the nitrogen distribution in the iron austenite as it follows from Mössbauer data. The concentration dependence of nitrogen activity and an effect of the N₂ gas pressure on the nitrogen solubility in Fe–N austenite are calculated using the values of N–N interaction energies in two coordination spheres.     

The morphology and crystallography of lath martensite in Fe-C alloys

The morphology and crystallography of lath martensite in Fe-C alloys containing various carbon contents from 0.0026 to 0.61% were studied by analyzing electron back scattered diffraction patterns in scanning electron microscopy and Kikuchi diffraction patterns in transmission electron microscopy. As carbon content increases, the sizes of both packet and block decrease. In low carbon steels (0.0026–0.38%C), a block which is observed as having different contrasts under optical microscopy contains two groups (sub-blocks) of laths which are of two K-S variants with a misorientation of about 10 degrees. On the other hand, in the high carbon alloy (0.61%C), a block consists of laths of a single K-S variant.