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Effects of Solution pH on the Growth Characteristics of Phosphate/Permanganate Conversion Coatings on AZ31 Magnesium Alloys
No full text隨著鎂合金的應用日益廣泛，提升其抗蝕性成為相當重要的課題。長期以來，鎂合金之鈍化處理以鉻酸鹽處理為主，但由於鉻酸鹽對環境及人體具有毒性，已逐漸被世界各國所禁用。在許多取代鉻酸鹽的處理系統當中，本實驗針對極具潛力之磷酸鹽/錳酸鹽系統，以微結構分析技術與電化學量測方法，探討化成液pH値對化成皮膜性質影響之研究。 實驗結果發現，在pH值4.0的化成液中，皮膜呈現兩層結構，分別為與底材相接觸的多孔層，與批覆於多孔層上之柱狀層。當化成液pH値提升至5.7後，皮膜除了多孔層與柱狀層之外，還有結晶性的磷酸鹽析出物批覆其上。相較於pH值4.0下生成之皮膜，pH值5.7下所得的皮膜較薄且顏色較淺，同時具有良好的光澤度與附著性，且在極化曲線量測中表現出較低的腐蝕電流。 此外，本實驗利用厚度量測與SEM橫截面影像觀察，針對磷酸鹽/錳酸鹽化成皮膜進行動力學參數之討論。結果顯示，在pH4.0化成液中處理時，構成皮膜主體之柱狀層在完全潤濕的情形下對於底材之保護性相當有限，而抗蝕性主要來自於多孔層。提升pH值後，磷酸鹽結晶的析出可以抑制柱狀層的成長，進而降低裂紋的生成，並獲得較厚的多孔層，提升皮膜抗蝕性。Magnesium alloys have become a group of the most widely used materials for their outstanding mechanical properties. However, the poor corrosion resistance is a critical weakness of most magnesium alloys. Among the various surface modification treatments, chromate conversion coating has received most attention in the past decades; however, the use of hexavalent chromate is prohibited due to environmental concerns. The phosphate/permanganate system, which is more environmental friendly and has been shown to have comparable corrosion resistance as compared to the chromate counterpart, is now the developing system with most expectation. In former researches, the pH value has been mentioned to be the key factor of the phosphate/permanganate conversion coating. Nonetheless, the pH effects on both growth behavior and coating properties are less well studied. Therefore, this study, with the aids of microstructural analyses and electrochemical measurements, aims at detailing the pH effects on the phosphate/permanganate conversion coating on AZ31 magnesium alloys. The results show that the coating formed under pH 4.0 is composed of two layers: the inner porous layer contacting the substrate, and the outer cellular layer, which shows litter protection during the conversion coating treatment. On the contrary, the coating formed under pH 5.7 is covered by crystalline struvite (MgNH4PO4‧6H2O) precipitates, which seems to inhibit the formation of the cellular layer. Compared to the coating formed under pH 4.0, the thinner coating with lighter color formed under pH 5.7 shows enhanced adhesion property and better performance in corrosion test.摘要 ibstract ii目錄 iii目錄 v目錄 vii號表 viii1章 序論 12章 文獻探討 2.1 鎂合金的發展與應用 2.1.1 鎂的性質 2.1.2 常用的鎂合金種類 3.1.3 鎂的工程應用 3.2 鎂合金的腐蝕行為 6.2.1 均勻腐蝕(General Corrosion) 6.2.2 局部腐蝕(Localized Corrosion) 7.3 鎂合金的化成皮膜處理 10.3.1 鉻酸鹽化成處理 10.3.2 磷酸鹽/錳酸鹽化成處理 11.3.3 稀土金屬元素化成處理 12.3.4 錫酸鹽化成處理 133章 實驗方法 16.1 實驗流程 16.1.1 試片前處理 16.1.2 化成處理 18.2 化成皮膜性質觀察與量測 19.2.1 皮膜顏色觀察與厚度量測 19.2.2 皮膜附著性量測 19.2.3 開路電位量測 21.2.4 極化曲線量測 21.3 化成皮膜微結構與成分分析 22.3.1 掃描式電子顯微鏡 22.3.2 能量散佈光譜儀 22.3.3 低掠角X光繞射儀 234章 實驗結果 25.1 化成處理製程監測 25.1.1 開路電位監測 25.1.2 化成液成分監測 25.2 化成皮膜性質觀察與量測 28.2.1 化成皮膜顏色觀察 28.2.2 化成皮膜厚度量測 30.2.3 化成皮膜附著性量測 33.3 化成皮膜微結構分析 34.3.1 皮膜表面形貌觀察 34.3.2 皮膜微結構之橫截面影像觀察 41.3.3 低掠角X光繞射分析 50.3.4 能量散佈光譜儀分析 50.4 化成皮膜抗蝕性質量測 53.4.1 開路電位量測 53.4.2 極化曲線量測 555章 討論 57.1 化成液pH值於化成皮膜微結構之影響 57.2 化成液pH值於化成皮膜性質之影響 58.3 磷酸鹽/錳酸鹽化成皮膜之動力學參數討論 59.4 磷酸鹽/錳酸鹽化成處理製程參數之討論 676章 結論 697章 未來研究方向 708章 參考文獻 7
Citrate Conversion Coating on AZ31 Magnesium Alloys
No full text鎂合金具有良好的比強度、比剛性與生物相容性，然而當暴露於腐蝕環境時，鎂合金的腐蝕速率極高，大大限制了鎂合金的工程應用。本研究以檸檬酸鹽為主要反應物種，嘗試建立一可應用於鎂合金之無鉻環保鈍化系統，以調控鎂合金之腐蝕速率及腐蝕行為。實驗包含三個部分：第一部分包含在水溶液與甘油溶液系統中以輥塗製程進行檸檬酸鹽化成處理，藉此探討鎂合金上檸檬酸鹽化成皮膜之成長機制；第二部分藉由添加銅離子與硫酸根離子，探討不同添加物在水溶液與甘油溶液系統中對檸檬酸鹽化成皮膜之影響；第三部份則是透過一後處理製程，在檸檬酸鹽化成皮膜上披覆一以檸檬酸基聚醯胺醯亞胺為主結構之高分子，以嘗試更進一步提升其抗蝕能力。 實驗發現，不論是水溶液或甘油溶液，檸檬酸鹽化成處理可以在AZ31鎂合金表面形成一層具有獨特微結構特徵的化成皮膜，且此化成皮膜可以降低AZ31鎂合金於動電位極化曲線中的腐蝕電流，並提高電化學交流阻抗分析中的阻抗值。在添加物的方面，硫酸根有抑制檸檬酸鹽化成皮膜成膜的傾向；在甘油溶液系統中添加銅離子時，可以觀察到富含銅的顆粒在鎂合金表面析出，且動電位極化曲線中的腐蝕電位也會隨之提高，而在水溶液中添加銅離子時，則會析出銅氧化物顆粒，造成動電位極化曲線中的腐蝕電流大幅提升。在電化學交流阻抗測試評估中，檸檬酸鹽化成處理可將AZ31鎂合金之阻抗值自5,000 Ωcm2左右提升至約10,000 Ωcm2， 當再披覆檸檬酸基聚醯胺醯亞胺之高分子作為後處理時，更可進一步提升至約20,000 Ωcm2。Magnesium alloys are known for their high specific strength, high specific stiffness, and good biocompatibility. However, their engineering applications are still limited, due to their extremely high corrosion rate when exposed in corrosive environment. In order to develop an environmental friendly passivation process for magnesium alloys, a citrate conversion coating system has been developed in this study. To investigate the formation mechanism of the citrate conversion coating on AZ31 magnesium alloy, the conversion coating process is performed in both aqueous and glycerin solutions. As the result, citrate conversion coatings formed in aqueous and glycerin solutions are similar in both microstructure and corrosion properties, which includes the reduced corrosion current density in potentiodynamic polarization and the elevated total impedance in electrochemical impedance measurement. Despite the similarity of pure citrate conversion coating, the effect of cupric ion shows significant difference in aqueous and glycerine solutions. In glycerin solution, the copper-rich clusters are formed on the citrate conversion coating with cupric ion added, and an apparently higher corrosion potential in potentiodynamic polarization can be observed. On the other hand, oxide particles are formed with cupric added in aqueous solution, which leads to an intense increase in corrosion current density. A post treatment using a citrate-based polyamide-imide (PAI) is also proposed in this study. It was found that the impedance of the AZ31 in EIS increases from around 5,000 to 10,000 Ωcm2 after citrate-based conversion coating, and can be further elevated to near 20,000 Ωcm2 with the PAI post treatment
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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