1,720,996 research outputs found
Investigation of the effect of the surfactant on synthesis of alumi̇na
No full textAlümina sahip olduğu yüksek mekanik dayanımı ve erime sıcaklığı, elektrik-ısı direnci ve kimyasal dayanıklılık gibi özellikleri sayesinde birçok alanda uygulama imkânı bulmaktadır. İleri seramikler arasında en uygun maliyetli ve en çok kullanılan yapısal mühendislik malzemesidir. Bu uygulamaların en çok bilinenleri refrakter, aşındırıcı, aşınmaya dayanıklı seramik parça, kimyasal uygulamalar için ekipman ve yüksek voltaj izolatörü uygulamalarıdır. Entegre elektronik devre alt tabakalası, polimer takviyesi ve metal bazlı kompozit alanlarında da etkin olarak kullanılmaktadır. Morfoloji, saflık, kristal yapısı, hidrotermal stabilite, gözenek yapısı gibi özellikler alümina uygulamasını kısıtlamaktadır. Bu özelliklerin talebe göre iyileştirilmesi ve düşük maliyetli üretim sonucu katma değeri yüksek ürünler elde edilmektedir. Alüminanın kararlı tek fazı yüksek termal kararlılık, kimyasal direnç ve sertliğe sahip alfa formudur ve 1230°C üzerindeki kalsinasyon işlemleriyle elde edilir. α-Alümina sentezinde mekanik öğütme, buhar fazı reaksiyonu, çöktürme, sol-gel, hidrotermal sentez ve yakma metodu gibi çeşitli yöntemler bilinmektedir. Bu yöntemlerin hepsinde kendine has sınırlayıcı özellikler bulunmaktadır. Sol-jel yönteminde başlangıç malzemesi olarak kullanılan alkoksitlerin maliyeti yüksektir ve yöntem uzun jelleşme süreçlerine ihtiyaç duyar. Çöktürme yöntemi hem karmaşıktır hem de uzun yıkama ve olgunlaştırma süreçlerine ihtiyaç duyar. Hidrotermal yöntem ise çok miktarda yüksek kalitede kristaller elde edilebilmesi ve düşük maliyeti nedeniyle en çok tercih edilen yöntemdir. Kimyasal bir senteze sürfaktan ve yapı düzenleyici ajan ilavesinin üretilen parçacıkların yalnızca parçacık büyüklüğünü ve şeklini değil, aynı zamanda kümelenme derecesini de etkilemektedir. Bu çalışmada hidrotermal sentez yöntemi kullanılarak sürfaktan ve yapı düzenleyici ajan destekli α-alumina sentezi başarılı şekilde gerçekleştirildi. Sentez sonrası ham ürünler 3 ve 6 saatlik kalsinasyona tabi tutuldu. Çalışmada PEG-400, SDS ve CTAB katkılarıyla kalsinasyon süresinin parçacık boyutuna ve morfolojiye etkileri araştırıldı. Sentezlenen tozların yapısal karakterizasyonu XRD, Raman ve FTIR yöntemleri kullanılarak gerçekleştirildi. Termal özelliklerin araştırılmasında TGA yöntemi kullanıldı. Morfolojik özellikler ise SEM yöntemi kullanılarak araştırıldı. Çalışmanın sonuçları yapı düzenleyici ajan ve sürfaktan kullanılmadan gerçekleştirilen deneylerle karşılaştırıldığında daha küçük boyutlarda ve morfolojide saf α-Al2O3 elde edildiğini göstermektedir.Alumina has many applications in the field due to its high mechanical strength and melting temperature, electricity-heat resistance and chemical resistance. It is the most cost-effective and most widely used structural engineering material among advanced ceramics. The most known of these applications are the refractory, abrasive, abrasion resistant ceramic parts, the equipment for chemical applications and the high voltage insulators applications. Also, the integrated electronic circuit substrate, the polymer reinforcement and the metal-base composite areas are other effectively used applications. On the other hand, its properties such as morphology, purity, crystal structure, hydrothermal stability, pore structure restrain the application of alumina. Due to the improvements on demand in these products and the low cost production, high value added products are obtained. The stable single phase of alumina is the alpha form with high thermal stability, chemical resistance and hardness and this phase is obtained by calcination processes above 1230 °C. Various methods are known in α-alumina synthesis such as mechanical grinding, vapor phase reaction, precipitation, sol-gel, hydrothermal synthesis and combustion method. Each of these methods has inherent limitations. In the sol-gel process, using the alkoxides as starting materials is the expensive and it requires long gelation processes. The precipitation method is complex and it requires long washing and maturing processes. The hydrothermal method is the most preferred method because high quality crystals can be obtained in large quantities and in low cost. In a chemical synthesis, the addition of surfactant and structure regulating agent affects not only the size and shape of the particles produced, but also the degree of agglomerate. In this study, the α-alumina synthesis supported by surfactant and structure-regulating agent is carried out successfully. After the synthesis, the raw products are applied to the calcination for 3 and 6 hours. In this study, α-alumina structures successfully prepared via hydrothermal synthesis supporting with surfactant. The effect of the PEG-400, SDS, and CDAB as structure directing agent on the particle size and morphology are investigated. The structural characterization of the prepared powders is carried out using XRD, Raman and FTIR techniques. TGA analysis is used for the investigation of the thermal properties of the powders. Morphological properties are investigated using SEM technique. Experimental results show that comparing with the experiment without the use of the structure directing agent, pure α-Al2O3 was obtained in smaller size
Boehmit Production, Characterization and İnvestigation of its Effects on İndustrial Alumina Production
No full textYüksek Lisans TeziBoksit mineralinden başlanarak metalik alüminyuma kadar üretim yapan entegre tesislerden birisi olan Eti Alüminyum A.Ş Seydişehir işletmesi, cevherden başlayıp saf metal üretimi yapan Dünya'da ender tesislerdendir. Eti Alüminyum A.Ş aynı zamanda ülkemizdeki tek alüminyum hidroksit üreticisi konumundadır ve Türkiye'de çıkarılan böhmitik yapıdaki boksit madenine de sahiptir. Boksit mineralinden elde edilebilen alüminyum hidroksit (Al(OH)3), böhmit (AlOOH), bayerit, diaspor yapılarının kristal yapıları farklı olup üretimi ve kullanım alanları da farklılık göstermektedir. Dünyada önemi giderek artan ve kullanım alanı da oldukça fazla olan böhmitik alüminyum hidroksitin üretimi ülkemizde yapılmamaktadır. Alüminyum tuzlarından ve alüminyum hidroksit gibi kaynaklardan kristallendirme ve hidrotermal proses ile üretimi yapılabilen böhmit; katalizör, cam, absorban, kompozit dolgu maddesi gibi geniş bir uygulama alanına sahiptir. Bu çalışmada gibsitik alüminyum hidroksit kaynağından başlanarak hidrotermal proses ile böhmit sentezi yapılmıştır. Hidrotermal proseste çeşitli sıcaklık, reaksiyon süresi ve ortam pH'ının etkilerinin araştırılması amacıyla çeşitli deneyler gerçekleştirildikten sonra optimum şartlar 200°C, 60 dakika ve pH=7 olarak belirlenmiştir. Deneylerden elde edilen numunelerin safsızlık analizleri X-ışınları floresans (XRF) (Thermo Arl advant'x) spektroskopisi, kristal yapı analizi X-ışınları kırınımı (XRD) (Gnr Explorer) spektroskopisi kullanılarak gerçekleştirilmiştir. Ayrıca yapısal analizde FTIR (Nicolet iS5 ) ve Raman (Renishaw Invia Reflex Confocal) spektroskopilerinden faydalanılmıştır. Üretilen tozların parçacık boyut analizleri Malvern 2000S cihazıyla gerçekleştirilmiştir. Ayrıca morfolojik özelliklerin belirlenmesinde taramalı elektron mikroskobu (SEM) (Leo-Evo 40xVP) kullanılmıştır. Deneyler sonucunda elde edilen böhmit yapısında soda miktarının \%80 oranında azaltılarak saflığı yüksek böhmit elde edildiği belirlenmiştir. Sentezlenen böhmit kullanılarak \%99,9 saflıkta düşük sodalı ve yüksek alfa fazında kristallenmiş alümina elde edilmiştir. Böhmit kalsinasyonuyla hazırlanan bu ürün, firmanın hali hazırda ticari olarak ürün listesinde bulunan alfa-alumina ile karşılaştırılarak ürün kalitesindeki değişim araştırılmıştır. Elde edilen verilere göre böhmit üzerinden hazırlanan alümina \%80 daha az sodalı, \%99,9 saflıktadır. Ayrıca elde edilen ürünün nihai ürüne kadar geçireceği işlemlerin enerji hesaplamaları ve piyasa değeri dikkate alınarak yapılan değerlendirmelerde ürünün ticari değerinin de \%50 oranında arttığı belirlenmiştir.Eti Aluminum A.Ş Seydişehir facility, which is one of the integrated facilities producing from bauxite mineral to metallic aluminum, is one of the rare facilities in the world that starts from ore and produces pure metal. Eti Aluminum A.Ş is also the only aluminum hydroxide producer in our country and has a boehmitic bauxite mine extracted in Turkey. The crystal structures of aluminum hydroxide (Al(OH)3), boehmite (AlOOH), bayerite and diaspore, which can be obtained from bauxite, are different, and their production and usage areas also differ. The production of boehmitic aluminum hydroxide, which is increasingly important in the world and its usage area is quite high, is not made in our country. Bohmite, which can be produced by crystallization and hydrothermal process from aluminum salts and sources such as aluminum hydroxide; It has a wide range of applications such as catalyst, glass, absorbent, composite filler. In this study, boehmite was synthesized by hydrothermal process starting from gibbsitic aluminum hydroxide source. After various experiments were carried out to investigate the effects of various temperatures, reaction times and ambient pH in the hydrothermal process, the optimum conditions were determined as 200°C, 60 minutes and pH=7. The impurity analyzes of the samples obtained from the experiments were performed using X-ray fluorescence (XRF) (Thermo Arl advant'x) spectroscopy, crystal structure analysis using X-ray diffraction (XRD) (Gnr Explorer) spectroscopy. In addition, FTIR (Nicolet iS5) and Raman (Renishaw Invia Reflex Confocal) spectroscopies were used in structural analysis. Particle size analyzes of the produced powders were carried out with the Malvern 2000S device. In addition, scanning electron microscopy (SEM) (Leo-Evo 40xVP) was used to determine morphological features. As a result of the experiments, it was determined that the amount of soda in the bohmite structure obtained was reduced by 80\% and high purity bohmite was obtained. By using the synthesized boehmite, 99.9\% pure low-sodium and high alpha phase crystallized alumina was obtained. This product, which was prepared with Böhmit calcination, was compared with alpha-alumina, which is currently in the product list of the company, and the change in product quality was investigated. According to the data obtained, the alumina prepared from bohmite has 80\% less soda and 99.9\% purity. In addition, it has been determined that the commercial value of the product has increased by 50\% in the evaluations made by considering the energy calculations of the processes that the obtained product will go through until the final product and market value
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Full text linkWe 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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