Mar 2013, Volume 7 Issue 1

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    Wei YAN, Wei WANG, Yi-Yin SHAN, Ke YANG

    The microstructural evolutions of advanced 9--12%Cr ferrite/martensite heat-resistant steels used for power generation plants are reviewed in this article. Despite of the small differences in chemical compositions, the steels share the same microstructure of the as-tempered martensite. It is the thermal stability of the initial microstructure that matters the creep behavior of these heat-resistant steels. The microstructural evolutions involved? in? 9--12%Cr ?ferrite ?heat-resistant ?steels ?are ?elabo- rated, including (1) martensitic lath widening, (2) disappearance of prior austenite grain boundary, (3) emergence of subgrains, (4) coarsening of precipitates, and (5) formation of new precipitates, such as Laves-phase and Z-phase. The former three microstructural evolutions could be retarded by properly disposing the latter two. Namely improving the stability of precipitates and optimizing their size distribution can effectively exert the beneficial influence of precipitates on microstructures. In this sense, the microstructural stability of the tempered martensite is in fact the stability of precipitates during the creep. Many attempts have been carried out to improve the microstructural stability of 9--12%Cr steels and several promising heat-resistant steels have been developed.

    Jun-Feng YANG, Yan JIANG, Jens HARDELL, Braham PRAKASH, Qian-Feng FANG

    Self-lubricating coatings have been widely used to reduce friction in moving machine assemblies. However, the tribological performance of these coatings is strongly dependent on the service temperature. In this paper, an extensive review pertaining to the influence of operating service temperature on tribological performance of self-lubricating coatings has been carried out. Based on the effective lubricating temperature range, the self-lubricating coatings developed in the past have been divided into three groups: low temperature lubricant coating (from--200°C to room temperature), moderate temperature lubricant coating (from room temperature to 500°C) and high temperature lubricant coating (>500°C). Ideas concerning possible ways to extend the operating temperature range of self-lubricating coatings have been presented as follows: hybridized tribological coating, adaptive tribological coatings, and diffusion rate limited solid lubricant coating. In addition, a new self-lubricating coating formulation for potential application at a wide operating temperature range has been proposed.

    Zhi-Ye QIU, In-Sup NOH, Sheng-Min ZHANG

    Bone defect is one of the most common diseases in clinic. Existing therapeutic approaches have encountered many problems, such as lack of autogenous allogeneic bone and immunological rejection to allogeneic implant. Synthetic hydroxyapatite (HA) provided solutions for bone repair, since the HA is the main inorganic component of animals’ bone. However, HA has good biocompatibility, but does not possess osteogenic capability, which is of significance for modern bone repair materials. Si is an essential trace element in bone tissue, and it has been demonstrated to be able to promote bone formation. Therefore, silicate-doped hydroxyapatite (Si--HA) may serve as a promising material for bone repair, and promote bone regeneration in the repair. The current review discusses development of Si--HA, focusing on its preparation and characterization, in vitro and in vivo evaluations of the material, positive effect of Si--HA on promoting bone formation in clinical applications, and molecular mechanism investigation of such promotive effect.

    Qing-Yuan MENG, Toshihiro AKAIKE

    Induced embryonic stem (ES) cells are expected to be promising cell resources for the observation of the cell behaviors in developmental biology as well as the implantation in cell treatments in human diseases. A recombinant E-cadherin substratum was developed as a cell recognizable substratum to maintain the ES cells’ self-renewal and pluripotency at single cell level. Furthermore, the generation of various cell lineages in different germ layers, including hepatic or neural cells, was achieved on the chimeric protein layer precisely and effectively. The induction and isolation of specific cell population was carried out with the enhancing effect of other artificial extracellular matrices (ECMs) in enzyme-free process. The murine ES cell-derived cells showed highly morphological similarities and functional expressions to matured hepatocytes or neural progenitor cells.

    Hua DENG, Xing-Can SHEN, Xiu-Mei WANG, Chang DU

    Various functional groups have been suggested to play essential roles on biomineralization of calcium carbonate (CaCO3) in natural system. 2D and 3D models of regularly arranged functional groups have been established to investigate their effect on CaCO3 crystallization. This mini-review summarizes the recent progress and the future development is prospected.

    Su-Ju XU, Fu-Zhai CUI, Xiao-Long YU, Xiang-Dong KONG

    Glioma cell line C6 cultured on silicon surfaces modified by different chemical functional groups, including mercapto (--SH), carboxyl (--COOH), amino (--NH2), hydroxyl (--OH) and methyl (--CH3) groups, was studied here to investigate the influence of surface chemistry on the cell proliferation, adhesion and apoptosis. AFM confirmed the similar characteristic of different functional groups occupation. The adhering C6 exhibited morphological changes in response to different chemical functional groups. The C6 adhered to--COOH, --NH2, --OH and--CH3 surfaces and flattened morphology, while those on--SH surface exhibited the smallest contact area with mostly rounded morphology, which led to the death of cancer cells. The results of MTT assay showed that the--COOH and--NH2 groups promoted cell proliferation, while the--SH significantly inhibited the proliferation. Compared with other chemical functional groups, the--SH group exhibited its unique effect on the fate of cancer cells, which might provide means for the design of biomaterials to prevent and treat glioma.

    Ning ZHU, David COOPER, Xiong-Biao CHEN, Catherine Hui NIU

    Recent research shows that the addition of chitosan microspheres (CMs) to poly(L-lactide) (PLLA) can result in a composite scaffold material with improved biocompatibility and mechanical properties for tissue engineering applications. However, research regarding the influence of CMs on scaffold degradation is absent in the literature. This paper presents a study on the in vitro degradation of scaffolds made from PLLA with CMs. In this study, the PLLA/CMs scaffolds with a 25% ratio of CMs to PLLA were immersed in phosphate-buffered saline (PBS) solution at 37°C for 8 weeks. The in vitro degradation of the scaffolds was investigated using micro-computed tomography (μCT), weight loss analysis, Raman spectroscopy, and differential scanning calorimetry (DSC). Microstructure changes during degradation were monitored using μCT. The μCT results were consistent with the results obtained from Raman spectra and DSC analysis, which reflected that adding CMs into PLLA can decrease the degradation rate compared with pure PLLA scaffolds. The results suggest that PLLA/CMs scaffold degradation can be regulated and controlled to meet requirements imposed a given tissue engineering application.

    Jing CAO, Hua-Jie YIN, Rui SONG

    We have observed the circular dichroism signal of dilute graphene oxide (GO), then systematically investigated the chirality of GO and established a probable chiral unit model. This study may open up a new field for understanding the structure of GO and lay the foundation for fabrication of GO-based materials.

    Jing HU, Xian-Ping WANG, Qian-Feng FANG, Zi-Qiang ZHAO, Yan-Wen ZHANG, Chang-Song LIU

    The aging behaviors of irradiated tungsten by high energy Si3+ and H+ ions are mainly investigated using internal friction (IF) method combined with SEM technology. The SEM analysis indicates that more severe irradiation damage appears in the surface of simultaneous dual Si3+ + H+ irradiated specimen than that in the sequential dual Si3+ + H+ irradiated specimen or the single Si3+ irradiated specimens because of the synergistic effect of Si and H irradiation. The IF background of the irradiated sample is about one order of magnitude higher than that of the unirradiated sample owing to the existence of high density fresh dislocations induced by Si/H irradiation. In the sequential dual Si3+ and H+ irradiated specimen, the hydrogen Snoek-Kê-K?ster (SKK) peak associated with the movement of dislocations dragging hydrogen atoms is observed and its height decreases with aging time at room temperature. As for the simultaneous dual Si3+ + H+ irradiated specimen, however, there is no such hydrogen SKK peak. The reason can be explained as hydrogen diffusion and pinning effect of dislocations.

    Xiao-Qiang FAN, Yong JIANG, Chang-Yong ZHAN, Yu ZOU, Jian-Chun WU, Ning-Kang HUANG

    Neutron detector based on perforated silicon structures backfilled with neutron converting materials could be operated at a low voltage and improves the detection efficiency of thermal neutron. It is found that the intrinsic detection efficiency of thermal neutron is affected by a lot of factors such as the geometry, size, and depth of the perforation and so on. In this study, the perforated silicon was prepared by electrochemical etching. Effect of etching current on geometry, size, and depth of the perforated silicon structures for neutron detectors was also reported.