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Microstructural stability of 9--12%Cr ferrite/martensite heat-resistant steels
Wei YAN, Wei WANG, Yi-Yin SHAN, Ke YANG
Front Mater Sci. 2013, 7 (1): 1-27.
https://doi.org/10.1007/s11706-013-0189-5
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.
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Influence of service temperature on tribological characteristics of self-lubricant coatings: A review
Jun-Feng YANG, Yan JIANG, Jens HARDELL, Braham PRAKASH, Qian-Feng FANG
Front Mater Sci. 2013, 7 (1): 28-39.
https://doi.org/10.1007/s11706-013-0190-z
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.
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Silicate-doped hydroxyapatite and its promotive effect on bone mineralization
Zhi-Ye QIU, In-Sup NOH, Sheng-Min ZHANG
Front Mater Sci. 2013, 7 (1): 40-50.
https://doi.org/10.1007/s11706-013-0193-9
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.
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Glioma cell line proliferation controlled by different chemical functional groups in vitro
Su-Ju XU, Fu-Zhai CUI, Xiao-Long YU, Xiang-Dong KONG
Front Mater Sci. 2013, 7 (1): 69-75.
https://doi.org/10.1007/s11706-013-0195-7
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.
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A study on the in vitro degradation of poly(L-lactide)/chitosan microspheres scaffolds
Ning ZHU, David COOPER, Xiong-Biao CHEN, Catherine Hui NIU
Front Mater Sci. 2013, 7 (1): 76-82.
https://doi.org/10.1007/s11706-013-0188-6
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.
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Effect of electrochemical etching current on prepared perforated silicon structures for neutron detectors
Xiao-Qiang FAN, Yong JIANG, Chang-Yong ZHAN, Yu ZOU, Jian-Chun WU, Ning-Kang HUANG
Front Mater Sci. 2013, 7 (1): 96-101.
https://doi.org/10.1007/s11706-013-0197-5
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.
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