Influence of Particle Size on the Structure and Properties of 316L Hollow Fiber Membranes Sintered Under Argon Atmosphere

316L based stainless steel hollow fiber membranes (HFs) are used as an alternative for polymer and ceramic based membranes. Application areas of 316L hollow fiber membranes are applications such as support or particle filter of gas and liquid separations in chemical and waste treatment industries. Among various methods, dry-wet spinning technique was selected as the production method of hollow fiber membranes since it is the most popular one. The aim of the study is to produce hollow fiber membranes in different powder particle sizes (coarse, fine, and their mixture), and to examine their structure and also their properties such as chemical compositions, pore amount, average pore size, and pore distribution. 3-point bending tests were also used to determine their mechanical properties. HFs produced from fine particles show higher densification than coarse particle size samples. In terms of pore structure, mixed particle size yields lower porosity and pore size than the finest particle size. On the other hand, the finest particle size yields the highest bending strength and bending deflection

NiMH bataryalar için nadir toprak elementi içermeyen negatif elektrotların geliştirilmesi.

Ni/MH battery negative electrodes normally make use of rare earth AB5 compounds. Development of rare earth-free negative electrode materials for Ni/MH batteries is desirable so as to lower the cost, and widen the availability. Although there are a number of alternatives, of these AB2 alloys are particularly attractive, as they offer better capacities than AB5. A major problem in this group of alloys is that they are difficult to activate, i.e. they require a large number of cycles before they could reach their full capacity. The present work concentrates on a Laves phase C14 AB2 alloy, (TiZr)(VNiMnCrSn)2, and aims to develop methods for their rapid activation. The study examines the methods in two groups. In one, the methods aim to increase the surface area of the powders and in the other the methods aim for surface modifications. Pristine alloy had zero initial capacity, which has increased to and saturated at 220 mAh/g after 14 cycles. So as to examine the effect of surface area on activation two methods were used; sieving and ball milling. AB2 powder was sieved into different particle sizes, namely d(0.5)=37.3, 62.7 and 82.5 μm. It was found that with coarse particles, the activation was relatively fast reaching a capacity of 245 mAh/g after 7-8 cycles. The fast activation of coarse particles was attributed to the ease of particle fragmentation which led to the generation of new fresh surfaces. Electrodes with fine powders (e.g. d(0.5) = 37.3 μm) activates later with a lower saturation capacity. The low saturation capacity was attributed to ineffective utilization of the active powder, i.e. a fraction of powders not in contact with the electrode. Ball milling was more effective in improving the activation behaviour of the alloy. Milling of powders leads initially to a decrease in particle size. But with prolonged milling the particles do agglomerate yielding particle sizes similar to the initial one. A saturation capacity of 330 mAh/g was obtained after 5-6 cycles, which is slightly above the expected capacity of the powder based on the PCI curve measured with gas phase storage. The saturation capacity was less with prolonged milling. For surface modifications, the main method used involved hot alkaline treatment. This included treating the AB2 powder in boiling 6M KOH solution for various periods of time before the electrode was prepared. KOH treatment was effective in all cases, as the electrode was fully active after 1-2 cycles. SEM examination of treated alloy has shown that KOH treatment results in the leaching of powders leaving behind a nickel rich surface layer. The saturation capacity has steadily increased with increased duration of the treatment reaching a maximum value of 390 mAh/g after 80 minute-treatment. This capacity is very much higher than the gas phase storage capacity of the alloy expected at 1 atm hydrogen pressure, i.e. 1.2 wt. % H corresponding to 320 mAh/g. This was attributed to the formation of rough surfaces generated by the treatment, as such surfaces could stabilize hydrogen bubbles whereby allowing an increase in local hydrogen evolution pressure. Another method under investigation in the current study was NiO coating of AB2 powders. For this purpose, using sol-gel approach pristine particles were coated with NiO which upon charging in the electrode would be reduced to Ni, thus aiming for the formation of Ni rich surfaces as in KOH treatment. Two routes were employed; one with the use NiCl2, and the other with the use of NiNO3. Of these, with details used in the present work, only the second route gave a capacity, but overall activation performance in all samples were poor. M.S. - Master of Scienc

Influence of Particle Size on the Structure and Properties of 316L Hollow Fiber Membranes Sintered Under Argon Atmosphere

316L based stainless steel hollow fiber membranes (HFs) are used as an alternative for polymer and ceramic based membranes. Application areas of 316L hollow fiber membranes are applications such as support or particle filter of gas and liquid separations in chemical and waste treatment industries. Among various methods, dry-wet spinning technique was selected as the production method of hollow fiber membranes since it is the most popular one. The aim of the study is to produce hollow fiber membranes in different powder particle sizes (coarse, fine, and their mixture), and to examine their structure and also their properties such as chemical compositions, pore amount, average pore size, and pore distribution. 3-point bending tests were also used to determine their mechanical properties. HFs produced from fine particles show higher densification than coarse particle size samples. In terms of pore structure, mixed particle size yields lower porosity and pore size than the finest particle size. On the other hand, the finest particle size yields the highest bending strength and bending deflection

Surface Modified Metal Hydrides as Negative Electrodes in NiMH Batteries

Surface Modified Metal Hydrides as Negative Electrodes in NiMH BatteriesCavit Eyovge1,2, Ezgi Onur Sahin1,2 and Tayfur Ozturk1,21Center for Energy Materials and Storage Devices, Middle East Technical University, Ankara 2Dept. of Metallurgical and Materials Engineering, Middle East Technical University, Ankara There is a renewed interest in NiMH batteries with improved energy densities that could approach those of Li-ion batteries. Efforts to improve the energy density concentrates on alternative anode as well as cathode materials. For anode, AB2 and Mg based alloys are candidates with potentials that go beyond the capacity achieved with rare-earth based AB5 compounds. In a recent study [1] we have shown an AB2 alloy which is sluggish in its activation could readily be activated when it was surface modified with hot-alkaline treatment. The treatment resulting in fine porous surface rich in Ni not only activates the alloy but it also increases the discharge capacity by a significant amount. This was attributed to positive effect of porous surface where hydrogen evolution was made difficult by the associated stabilizing effect. For Mg based alloys, we have investigated A2B7 alloy where the amount of Mg is quite low and an amorphous Mg50Ni50 alloy. Here rather than modifying the powders, the electrode itself was modified by nafion coating. The electrodes were tested both in bare and coated form with a notable difference in discharge capacity. Nafion coating increased maximum attainable discharge capacity in both alloys up to 150%. Electrochemical impedance spectroscopy measurements showed that the charge transfer resistance increases with increased coating. The role of nafion coating in developing Mg based negative electrode materials is discussed. [1] Tan S., Shen Y., Sahin E. O., Noréus D., Ozturk T., "Activation behavior of an AB2 type metal hydride alloy for NiMH batteries" International Journal of Hydrogen Energy 41 (23), 9948-9953,201

Surface Modified Metal Hydrides as Negative Electrode s for NiMH Batteries

There is a renewed interest in NiMH batteries with improved energy densities that could approach those of Li-ion batteries. Efforts to improve the energy density concentrates on alternative anode as well as cathode materials. For anode, AB2 and Mg based alloys are candidates with potentials that go beyond the capacity achieved with rare-earth based AB5 compounds. In a recent study [1] we have shown an AB2 alloy which is sluggish in its activation could readily be activated when it was surface modified with hot-alkaline treatment. The treatment resulting in fine porous surface rich in Ni not only activates the alloy but it also increases the discharge capacity by a significant amount. This was attributed to positive effect of porous surface where hydrogen evolution was made difficult by the associated stabilizing effect. For Mg based alloys, we have investigated A2B7 alloy where the amount of Mg is quite low and an amorphous Mg50Ni50 alloy. Here rather than modifying the powders, the electrode itself was modified by nafion coating. The electrodes were tested both in bare and coated form with a notable difference in discharge capacity. Nafion coating increased maximum attainable discharge capacity in both alloys up to 150%. Electrochemical impedance spectroscopy measurements showed that the charge transfer resistance increases with coating. The role of nafion coating in developing Mg based negative electrode materials is discussed. [1] Tan S., Shen Y., Sahin E. O., Noréus D., Ozturk T., "Activation behavior of an AB2 type metal hydride alloy for NiMH batteries" International Journal of Hydrogen Energy 41 (23), 9948-9953,201

NiMH Bataryalar için Pozitif Elektrod Malzemesinin Geliştirilmesi

Bu projenin amacı NiMH bataryalara için üstün özellikli pozitif elektrod malzemesinin geliştirilmesidir. Bu amaçla klasik üretimden farklı olarak Ni(OH)2 termal plazmadan geçirlerek olabildiğince küçük parçaçıklı olarak üretilecektir. Çalışma parçaçık boyutuna ve elektrod mimarisine bağlı olarak bağlı Ni(OH)2 pozitif elektrod performansının belirlenmesini amaçlamaktadır

NiMH Pilleri İçin Enkapsüle Edilmiş Magnezyum Esaslı Malzemelerin Geliştirilmesi

Bu proje 2014 yılında TÜBITAK tarafından yürütülen lisans bitirme projeleri yarışmasında enerji alanında birincilik ve tüm alanlarda ikincilik ödülü alan projenin devamı niteliğindedir. Proje konusu olan NiMH pillerinde enerji depolama hidrojen aracılığı ile gerçekleşmektedir. NiMH pillerinde hidrojen genellikle nadir toprak elementleri içeren, AB5 tipi bileşiklerde depolanmaktadır. Mevcut NiMH pillerinde negatif elektrot olarak kullanılan AB5 tipi bileşiklerde depolanan hidrojen 380 mAh/g’lık bir kapasite sağlayabilmektedir. Önerilen bu projede negatif elektrot malzemesi olarak AB5 veya benzeri alaşım ve bileşikler yerine magnezyum esaslı alaşımların kullanımını konu alınmakta ve bu şekilde yeni nesil NiMH bataryaların geliştirilmesi hedeflenmektedir. Magnezyum esaslı alaşımların başarı ile adapte edilmesi durumunda depolanabilecek hidrojen miktarı negatif elektrotta kapasitede AB5’e kıyasla üç katlık bir artış ile 1000 mAh/g üstü değerlerin elde edilmesine olanak sağlayacaktır. Proje, magnezyum esaslı alaşımların pil uygulamalarında bir darboğaz niteliğinde olan korozyon sorununu termal plazma kullanarak parçacık yüzeyinde koruyucu tabaka oluşturma sureti ile aşamayı hedeflemektedir. Önerilen bu projenin amacı karbon bir kabuk ile enkapsüle edilmiş magnezyum yeni nesil negatif elektrot malzemeleri geliştirmek ve karakterize etmekti

Bitkisel kökenli atıklardan mikro-akışkan yöntemiyle nano boyutlarda reoloji düzenleyicilerinin üretilmesi: Emülsiyonlarda, kolloitlerde ve hamur ürünlerinde kullanılması

TÜBİTAK MAG01.06.2011Bu çalışmada sırasında mikroakışkan tekniği kullanılarak mikro ve nano lifler elde edilmiştir. Değişik bitkisel yan ürünler kullanılarak üretilen lifler model emülsiyon, koloit ve hamur ürünlerinde kullanılmışlardır. İlk aşamada düşük alkali tuz konsantrasyonlarında yapılan yumuşatma işleminde kullanılan alkali ajanlardan K2CO3’ın diğer ajanlara göre daha yüksek su tutma oranına ve viskoziteye sahip liflerin üretilmesine olanak sağladığı gösterilmiştir. Daha sonraki bölümde ise mikroakışkan işleme basıncı ve işleme sayıları denenmiştir. Mikroakışkan cihazında uygulanan basıncın üretilen liflerin fiziksel özelliklerine etkisi ortaya konmuştur. Artan basınç 1500 bara kadar viskozitede hızlı bir artışa sebep olmuş fakat daha yüksek basınçlarda bu artış yavaşlamıştır. Mikroakışkan cihazında tekrarlanan parçalama işlemi de liflerin su tutma kapasitesine ve viskozitesine direk etki etmiştir. Test edilen liflerden elma, portakal ve kayısı lifi domates, mısır koçanı ve yaprağına oranla daha yüksek su tutma oranına ve viskozite değerlerine sahip olduğu bulunmuştur. Daha sonra en uygun şartlarda üretilen lifler emülsiyon kararlılığına ve fiziksel özelliklerine etkisi bakımından araştırılmıştır. Üretilen nano liflerin emülsiyon hazırlama sırasında oluşan damlacıkların daha küçük olmasına neden olmuş ve karalılığın artmasını sağlamışlardır. Benzer çalışmalar bir emülsiyon olan mayonez tipi ürünlerde de tekrarlanmış, nano lifler kullanılarak daha az yağ içeren örneklerin hazırlanabileceği gösterilmiştir. Koloit tipi ürünlere örnek olarak seçilen ketçap ile ilgili yapılan çalışmalarda ise lif kaynağı olarak domates kabukları kullanılmıştır. Domates kabuğundan elde edilen liflerin ketçap viskozitesi ve kararlılığını arttırdığı tespit edilmiştir. Son aşamada ise elde edilen lifler kek ve bisküvi tipi ürünlerde kullanılmıştır. Değişik oranlarda yağ ve un oranları kullanılarak farklı içeriklerde liflerin etkileri incelenmiştir. Artan lif miktarı bisküvi tipi ürünlerde yayılma ve sertlik oranlarına 39 etki etmiştir. Keklerde ise sertlik lif miktarıyla artmış anca un ve yağ oranları düşürülünce kontrol ürüne benzer tekstürel özellikler elde edilmiştir.In this study microfluidization was used to produce micro and nano fibers. Various agricultural by-products were used to obtain fibers and these fibers were utilized in model emulsions, colloids, and bakery products. At the first stage, dilute alkali salts were tested in terms of their ability to soften fiber sources. K2CO3 was determined to be more effective in softening and producing fiber with higher water holding capacity and viscosity. In the next stage, effect microfluidization passes and pressure were evaluated. Increasing the pressure up to 1500 bar improved physical properties of the fibers but rate of improvement tampered as the pressure further increased. Number of passes in microfluidization also seemed to be effective in producing fibers with better physical properties. When the source of fibers were compared, apple, orange, and apricot pulps yield fibers with better physical properties than those obtained from corn stalk, tomato skin, and corn leaf. Fibers were also test in emulsions in terms of improving stability and viscosity. Addition of fibers into emulsions resulted in smaller dispersed droplets leading to improved stability. Incorporation of fibers in mayonnaise showed that oil content can be reduced in mayonnaise type products with fiber addition. In this study ketchup was also chosen as a model colloid food. Addition nano fibers obtained from tomato skin into ketchup significantly improved the physical properties. In final part cake and cookie type products were chosen as model bakery products and their properties were evaluated after fiber addition. In general, addition nano fibers increased hardness of the products. However, when the flour and fat content were reduced bakery products with acceptable quality parameters were obtained

Effect of HIP Process and Subsequent Heat Treatment on Microstructure and Mechanical Properties of Direct Metal Laser Sintered AlSi10Mg Alloy

Purpose – The purpose of this paper is to evaluate the effect of post process combinations, e.g. hot isostatic pressing (HIP) only, HIP 1 T6 heat treatments, and T6 only, with different aging time, on surface properties, microstructure and mechanical properties of stress-relieved AlSi10Mg parts produced by direct laser metal sintering. Design/methodology/approach – HIP process and HIP 1 T6 heat treatments were applied to as stress-relieved direct laser metal sintered (DMLS) AlSi10Mg parts. Aging times of 4 and 12 h are selected to examine the optimum duration. To analyze the advantages of HIP process, a T6 heat treatment with 4 h of aging was also applied. Densities, open porosities and roughness values of as stress-relieved, HIPed, HIP 1 T6, and T6-only samples were measured. The samples were characterized by OM and SEM together with EDX analysis. An image analysis study was made to evaluate the inner pore structure, thereby to understand the mechanical behavior. Findings – HIP process does not cause a significant change in surface porosity; yet it has a positive influence on inner porosity. HIP process results in a microstructure of the aluminum matrix surrounded by a network of micron and nano size Si particles. Additional heat treatment results in larger particles and precipitation. After HIPing, ductility increases but strength decreases. Samples aged 4 h present improved yield and tensile strength but decreased elongation, yet samples aged for 12 h reach a combination of optimum strength and ductility. The lower level of tensile strength and ductility in T6-only condition indicates that HIP process plays a crucial role in elimination of the porosity thus improves the effectiveness of subsequent heat treatment. Originality/value – The study investigates the effect of post-process conditions and optimizes the aging time of the T6 heat treatment after HIP process in order to obtain improved mechanical properties. The stress-relieved state was chosen as the reference to prevent distortion during HIPing or heat treatment