The Production Of Strontium Hexaferrit (sro.6fe2o3) Magnets And Be Developed Their Magnetic Properties With Domestic Raw Material

Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2014Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2014Manyetik alan üreten malzemeler olan sürekli mıknatıslar, Fe, Ni, Co gibi elementlerin alaşımlarından oluşmakta olup yüksek artık mıknatıslanmaya, yüksek manyetik enerjiye ve histerisiz eğrilerine sahiptir. Bu alanda yapılan çalışmalarla mıknatıslarda çeşitliliğe gidilerek farklı özelliklerde ve alaşımlarda mıknatıslar sentezlenmiştir. Doğal mıknatıs olan manyetitin bulunmasından sonra mıknatıslarda önemli gelişmeler 20. yüzyılda olduğu görülmektedir. Sırasıyla AlNiCo, Sr-Ba hekzaferrit, SmCo ve NdFeB mıknatısları ihtiyaçlara paralel olarak sentezlenmiştir. Bu mıknatısları birbirinden ayıran manyetik özelliklerinin yanında hammaddelerin bulunabilirliğinin kolaylığı ve üretim maliyetlerinin farklılığıdır. Sr-Ba hekzaferritlerin manyetik enerjileri diğer mıknatıslara göre daha düşük olmasına karşın hammaddelerinin kolay bulunmasından dolayı maliyeti uygun, manyetik özellikleri optimum seviyede, yüksek kimyasal stabilitiye sahiptir. Sr-Ba ferritlerin en çok kullanıldığı alanlardan biri NdFeB ile birlikte motorlardır. Ayrıca; yüksek frekans cihazları, manyetik kayıt uygulamaları, otomotiv sanayi, bilgisayar ve elektronik alanlarda günlük hayatta bu mıknatıslar görülmektedir. Bu tez kapsamında, doğal atık maddelerden stronsiyum hekzaferrit sentezi tasarlanmıştır. Sentez sırasında demir çelik tesisinde haddehane atığı olan tufal kullanılmıştır. Tufal farklı demir oksitleri yapısında bulundurur ve atık sınıfında yer alır. Hematit, manyetit ve wüstit oksit yapıları ve bazı empüriteler tufali oluşturur. Temin edilen tufal yapısı 800ºC’de 2 saat süreyle tutularak farklı demir oksit yapısının hematite dönüşmesi istenmiştir. Kalsinasyon aşamasını saf SrCO3 ile doğrudan hematit (Fe2O3) yerine haddehane atığı olan ve farklı bileşimlerde demiroksit içeren tufalin hematite bir pirometalurjik yolla dönüşümü sağlanarak üç farklı stokiyometrik oranlarda SrFe12O19 sentezi gerçekleştirilmiştir. Kalsinasyon işleminden sonra attritör ile tozların şekillendirilmesine uygun öğütme işlemi gerçekleştirilmiştir. Daha sonrasında isotropik yapıda yüksek basma yoğunluğu elde edilecek şekilde presleme işlemi gerçekleştirilmiştir. Preslemeden çıkan numuneler yüksek sıcaklık fırınında sinterlenmesinin ardından Arçelik A.Ş. ARGE laboratuarlarındaki permagraf cihazı ile mıknatısların manyetik karakterizasyonu yapılmıştır. Atık sınıfında yer alan tufal hammaddesi kullanılarak ferrit esaslı mıknatıs sentezlenmesi v sinterlenmesi gerçekleştirilmiştir. Bilindiği kadarı ile ülkemizde sadece kompaktlama işlemi gerçekleştirilmektedir. İ k numunelerde paralellik sağlanamadığından manyetik ölçümlerde negatif yönde sapmalar gerçekleşmiştir. Yeni dizayn edilen kalıp ile presleme sırasında uygulanan yük ile manyetik özelliklerin değişimi incelenmiş, artan yük ile yoğunluk değerlerinin arttırıldığı, bunun d manyetik özelliklere pozitif yansıdığı görülmüştür. Fakat uygulanan yük aşırı yükselirse, beklendiği gibi, laminasyona sebep olmaktadır. B kontrollü kalıp ile paralel yüzeylere sahip tabletler preslenmiş v ardından sinterlenmiştir. B numunelerde elde edilen B değeri 231 m ve BHmaks değeri ise 8,2 kJ/m2 olarak tespit edilmiştir. Manyetik özelliklerin geliştirilmesi konusunda anizotropik yapıda mıknatıs üretimi için manyetik alanda presleme konusunun ö plana çıktığı görülmüş, b şekilde çalışabilecek kalıp tasarımının yapılması durumunda elde edilen manyetik özelliklerin 2-3 katına çıkılacağı tahmin edilmektedir.The magnetic properties of a material depend whether it has permanent dipole moment how these dipoles are oriented with respect to each other. Different materials respond to applied magnetic fields in different ways. On the basis of orientation, the magnetic materials are classified into five categories which are diamagnetic, paramagnetic, ferromagnetic, anti–ferromagnetic and ferrimagnetic. Magnetic phase of a material depends on temperature, pressure and the applied magnetic field. A permanent magnet is magnetized and creates its own magnetic field. Permanent magnets which are producing a magnetic field, is composed of alloys of elements such as Fe,Ni,Co. They have a high remanence, high magnetic energy and hysteresis curves. When an external magnetic field is applied to a ferromagnet, the atomic dipoles align themselves with it. Even when the field is removed, part of the allignment will be retained and the material has become magnetized. Its magnetizaston will trace out a loop called a hysteresis loop. To increase the variety of magnets, magnets are synthesized with different properties. Important developments in magnets are seen after the discovery of magnetite which is a natural magnet. Respectively AlNiCo, Sr-Ba hexaferrite, SmCo ve NdFeB were synthesized through needs. The differences between these magnets are magnetic properties, availability of raw materials and distinct production costs. Although the low magnetic energy properties of Sr-Ba hexaferrite, the cost is convenient because of the availability. Also these magnets have high chemical stability and optimum magnetic properties. One of the commonly used areas is motors with NdFeB. Furthermore these magnets are seen in daily life for example in high frequency devices, in magnetic recording applications,in automotive industry, in computers and electronic areas. Magnetic ceramics classified, as ferrites are iron oxide compounds that contain an additional metallic ion. Ferrites are commonly divided into two groups such as soft and hard ferrites. Soft ferrites are going to lose their magnetic properties slowly after removing them from magnetic field. Soft ferrites are the obvious choice for applications requiring ac power and high frequency operation since they must be magnetised and demagnetised many times per second. Hard ferrites show permanent magnetic behaviour. They are used in electrical motors, generators, relays and motors. Strontium hexaferrite is permanent magnet and its formula is SrFe12O19. Its crystal structure is hexagonal and has higher saturation magnetization, coercivity and the Curie temperature. Furthermore, it shows excellent chemical stability and corrosion resistance. The ferrite magnets are mainly low cost magnets since they are made from cheap raw materials which are iron oxide and Ba/Sr-carbonate. There has been an increasing degree of interest in the hexagonal ferrites, also know as hexaferrites since their discovery in the 1950s. The hexagonal ferrites are ferrimagnetic materials. In recent years, studies on magnets are especially focused on rare earth free magnets and on parameters that affect the magnetic properties. It is necessary to know the correlation between manufacturing parameters and the magnetic properties. These parameters are; • Temperature and time of calcination • Temperature and time of sintering • Grain size • Mole fraction of SrO3 / Fe2O3 • Effect of dopant metals. Also, Philip A. Cochardt (US), TDK Corporation (JP), BASF (DE) and Hitachi Metals LTD (JP) get a lot of patents on rare earth free magnets. Strontium hexaferrite powders have been a subject of continuous interest and intensive study for several decades. The conventional way to synthesis ferrites using solid-state reaction by mixing of oxide/carbonate and then calcined at high temperatures ( > 1200 °C). The ceramic product then usually has to be milled and powered to produce a finer material, and then sintered to increase density. There are many other methods to prepare hexaferrites. The most important factor for the production of strontium hexaferrite is the cost and availability of the raw materials. In this study, strontium carbonate (Aldrich Chemicals, % 98 SrCO3), waste oxide layer is provided from Eregli Iron and Steel Plant that is used as raw material. The aim of this thesis is synthesis of strontium hexaferrite from natural waste. It is seen that oxide scale can be used as source of iron oxide to produce strontium hexaferrite. Fe2O3 in the range of % 98,7–99,4 comprising in production of unalloyed low carbon steel meet the necessary amount of iron oxide. Oxide layer includes different compositions of iron oxide which are hematite, magnetite, wustite and some impurities. • The phases available in mill scale as follows. • Hematite (Fe2O3) layer are generally available exterior. This phase also have rich oxygen content. • Magnetite (Fe3O4) have lower oxygen content than hematites. • Wustite (FeO) have lowest oxygen content in the deepest layer. Different iron oxides are turned to hematite when oxide layer is heated for two hours at 800 ºC. In the calcination step instead of using Fe2O3, oxide layer is used with SrCO3 and different iron oxides are provided to turn to hematite, then hematite powders are mixed with strontium carbonate powders. Three different stoichiometric rates of SrFe12O19 is synthesised when these powders are heated for six hours at 1200 ºC. These stoichiometric rates are 1:6, 1:5,5 and 1:5 in order to minimize rate of nonmagnetic phase. After the calcination step, SrFe12O19 powders is milled by attritor to shape properly before sintering these powders. The other step is pressing in isotropic structure. When the dry powders press in the mould, they get enough green density. Thereafter the samples are sintered for four hours at 1200 ºC and surface preparation for smoothness, then in Arcelik Inc R&D laboratories magnetic characterizations of magnets are done. Tranformation of strontium hexaferrit is observed according to the choosen parameters by XRD analysis. Density measurements of samples are done by pycnometer. Density of strontium hexaferrite is nearly 4,9 gr/cm3 on MMPA standart No. 0100-00. As conclusion of this study, approximately 4,8 gr/cm3 density has been reached. Magnetic properties of magnets increase if grain size of powders are average 1 µm after milling step. Obtained grain size of powders are nearly 1-3 µm after experimantal studies. Grain size of calcined powders are analysed by sieve analysis and optical microscope. In chemical wet analysis of mill scale that provided from Eregli Iron and Steel Plant, ratio of iron oxide is % 98,33 and also there are % 0,21 SiO2, % 0,58 MnO, % 0,24 Cu2O, 0,29 % Cr2O3 and % 0,15 other oxides. In XRD analyses of calcination products that obtained from mill scale, the largest percentage of phases are SrO.5Fe2O3. The all phases of the scale which consist of low impurity and calcination products that producted at three different stoichiometric rates are SrO.6Fe2O3, SrO.5,5Fe2O3 and SrO.5Fe2O3. Magnetic properties of SrO.5Fe2O3 synthesised samples are that Br is 231 mT and BHmaks 8,2 kj/m3.. Also, magnetic properties of SrO.5,5Fe2O3 are 206 mT and 7,2 kJ/m2 and magnetic properties of SrO.6Fe2O3 are 179 mT and 5,6 kj/m3. Anisotropic pressing is important in order to develop magnetic properties of ferrite magnets. If design of mould is made for anisotropic pressing, magnetic properties will be increased to two-three times. Magnetic performance can be increased by applying magnetic field in a prefferd direction during the molding process. Oxide layer which is waste at rolling of iron and steel plant, is used and synthesised and sintered ferrite magnet. Magnet firms provide ferrite powders from abroad and only shape them in Turkey. The most important features of this work are showed that the starting waste iron oxides will make the process more economical to produce strontium hexaferrite magnets. The values of magnetic properties obtained in present work are within the range of MMPA standards.Yüksek LisansM.Sc