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İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Metalurji ve Malzeme Mühendisliği Anabilim Dalı / Üretim Metalurjisi ve Teknolojileri Mühendisliği Bilim Dalı

Ultrasonik sprey piroliz (USP) yöntemi ile nano yapılı kurşun oksit üretimi ve karakterizasyonu

Production and characterization of nano structured lead oxide via ultrasonic spray pyrolysis (USP)

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Özet:

21. yüzyılın ikinci yarısında ortaya çıkan "Nanoteknoloji" kavramı, üretilen nano boyuttaki malzemelerin özelliklerinin geleneksel malzemelere oranla ne kadar değişebileceğinin fark edilmesi sonrası hızla yaygınlaşmaya başlamış, günümüzün gelecek vaad eden teknolojisi haline gelmiştir. Gelişen teknoloji sayesinde verimi ve güvenilirliği artan karakterizasyon ve üretim uygulamaları, keşfedilecek çalışma alanları ve yeni özellikleri ortaya çıkarılacak pek çok malzemeye ön ayak olmuştur. Boyutları 100 nm altına düşen partiküllerin göstermiş olduğu ilginç özellikler sanayide de pek çok alanda kullanılmaya başlanmış, elektrik-elektronik, boya, tekstil, otomotiv, kimya ve çevre gibi çeşitli disiplinlerde uygulama alanları bulmuştur.Partikül üretim yöntemleri iki temel yaklaşım çerçevesinde sınıflandırılır. Bunların birincisi yukarıdan aşağıya diğeri ise aşağıdan yukarı yaklaşımıdır. Bu iki yaklaşım altında listelenebilecek pek çok yöntem mevcuttur. Ultrasonik Sprey Piroliz (USP) tekniği bu yöntemler arasında çok yönlülüğü, ekonomik oluşu ve uygulama kolaylığı ile çalışmamıza konu olmuştur. USP tekniği sayesinde çok geniş bir aralıkta kimyasal bileşim, morfoloji ve boyuta sahip metalik, intermetalik ve seramik partikül üretimi mümkündür.Kurşun oksit sağlık ve çevre alanındaki olumsuz etkilerinden sıkça bahsedilmesine rağmen kullanıldığı alanlarda uzun ve bir güvenilir geçmişe sahip yegâne malzemeler arasındadır. Enerji depolama, gaz sensörü uygulamaları, cam üretimi, pigment endüstrisi ve boya sanayi en önemli uygulama alanları olan kurşun oksit asıl ve en önemli somut faydasını enerji depolama alanında göstermektedir. Özellikle kurşun asit batarya teknolojisinin ortaya çıkışını takiben artan kurşun oksit kullanımı, enerji depolama ünitesi olarak kurşun asit bataryaların kendilerini kanıtlamaları ile birlikte ivmeli bir şekilde artan gelişim göstermiştir. Son yüzyıla damgasını vuran yegâne enerji depolama uygulaması olan kurşun asit bataryalar, yüksek enerji yoğunlukları ile günümüzün en önemli teknolojik gelişmelerinden biri olan elektrikli otomobillerde de diğer enerji depolama uygulamalarına yardımcı ünite olarak düşünülmekte, nanoteknoloji vasıtası ile gelinen noktada da elde edilen gelişmeler kurşun asit bataryaların yeterli verimde çalışmasına olanak sağlamaktadır. Bu sayede gelecekte karşılaşılacak elektrikli otomobillerde de kurşun asit bataryaların kullanılması, bu amaca yönelikte bu alanda nanoteknolojinin de içinde bulunduğu pek çok araştırmanın yapılması muhtemeldir.Bu tez çalışmamızda Ultrasonik Sprey Piroliz (USP) yöntemi ile mikron altı boyutta kurşun oksit partikülleri üretimi için yüksek safiyette kurşun asetat tuzları kullanılmıştır. Üretim sırasında 0,4M, 0,6M, 0,8M arasında değişen başlangıç çözelti konsantrasyonu, 600 ºC, 700 ºC, 800 ºC arasında değişen sıcaklıklar, 1,3 MHz ultrasonik frekans ve 0,5 lt/dk sabit gaz (hava) akışı kullanılmıştır. Çalışmalar sonucu üretilen partiküllerin faz analizleri için X ışınları difraktometresi (XRD), boyut ve morfolojilerinin tespiti için taramalı elektron mikroskobu (SEM) , kütle oralarının tayini için enerji dağılım spektroskopisi (EDS) kullanılmıştır. Çalışmaların sonucu olarak nihai ürünlerin özelliklerinin, başlangıç çözelti konsantrasyon ve deney sıcaklığına bağlı değişimi incelenmiştir.

Summary:

The concept of Nanotechnology came up in the middle of 21th century, spreaded its importance rapidly and became the most promising technology nowadays after understanding how nanotechnology can change whole properties of materials produced via nanotechnological processes compared to traditional methods of production. From the most general perspective, nanotechnology can simply be described as an interdisciplinary science field that involves the characterization, fabrication and/ or manipulation of structures, devices or materials that have at least one dimension that is approximately 1 100 nm in length. In nanotechnology, main dimension is nanometer which represents one part in a billion of meter. When a little mosquito scales only a few milimeters, it is easier to understand how small scale nanometer is so. Gaining such kind of small dimensions makes materials extraordinary, therefore the term of ?nano? achieves a big interest and initiates numerous advancements. All advancements regarding nanotechnology now help people to make life more efficient and easier, so that nanotechnology present many products in application fields such as space/aircraft technology, energy, electrics/electronics, chemistry, material science, automotive, medicine, environmental, and military sectors. All these advances are result of discoveries in production and identification techniques. Fabrication and characterization applications which have extremely rising dependability and efficiency through developing technology initiated not only numerous mateials to be discovered and came up with new properties out of ordinary, but also field of studies to be explored. Through this rate of increase in investment and investigation, it is not hard to forecast that market of nanotechnology will reach up to trillions of dollars in the world within a few years.? Nano size powder, nanoparticle, nano crystalline and nano structure? words have been using extensively since the early of the 1990?s. So, the synthesis of nano-structured materials has attracted considerable attention in the past few years. Instead of classical physics theories are obeyed by traditional materials, nano structured materials obey quantum mechanics and quantum laws due to their dimentions and special morphologies. Therefore, they can achieve extra-ordinary, unique properties.Among nano structured materials, metal oxides find considerable place with wide variety of usage with their assorted properties which make them significant engineering materials. Metal oxide nanoparticles often exhibit very interesting electronic, magnetic, optical, and chemical properties. Their unique features mainly depend on their size, shape, surface composition, and surface atomic arrangement. In order to reach desired features, some special production techniques are being used since the nanoparticles proved their importance.Particle production methods can be classified basically within the scope of two approaches. One of them these two approaches is bottom up and the other one is top down. Bottom-up approach is based on depositing atoms or molecules as nano-sized structures, whereas ?top-down? approach is based on sizing materials down to the nano-sized structures starting from macro-sized, bulk raws. High energy ball milling, electrodeposition, lithography are important examples of top-down approach. On the other hand, sol-gel, chemical vapour condensation (CVC), inert gas condensation (IGC), and aerosol based methods such as flame spray pyrolysis (FSP) and spray pyrolysis (SP) are widely-used methods in bottom-up approach. However, there are plenty of methods can be indexed under these two approaches, Ultrasonic Spray Pyrolysis (USP) method is at one step forward due to its versatile, economic and easy to use nature.Ultrasonic Spray Pyrolysis (USP) is an all-round method which has been came up by CENG (Center for Nuclear Studies in Grenoble) in 1971 as pyrosol technique. USP involves four major steps: (1) generation of drops from a precursor solution, (2) drop size shrinkage due to evaporation, (3) reduction/thermal decomposition, and (4) solid particle formation. Among other steps, the key step is aerosol formation. Ultrasound waves are generated in piezoelectric transducer and transferred into the solution. The special design of ultrasonic atomizer focuses ultrasound generated into one point that is called geyser. The effect of ultrasound wave can let aerosol drop free in the carrier gas atmosphere. With the help of the carrier and/or reduction gases, aerosol drops will go through the furnace at desired temperature for the chemical reaction. It?s relatively easy method that doesn?t need detailed experimental setup preparations. Additionally, it allows producing different kinds of nanomaterials such as metallic, intermetallic, ceramic or composites in very wide variety of chemical composition, morphology and size. As an advantegous method, USP is a simple, inexpensive choice with the added advantage that it allows the deposition of large thick films and can be adapted for on-line manufacturing processes and it is also convenient for the preparation of a large number of simple or complex oxides with its versatile and easy-applicable properties. Among all oxides, lead oxide powders remain widely used because they are cheap and reliable materials for energy storage applications.Lead oxide compounds have been commercially available for about as long as lead has been refined and used. The earliest uses were for pigmentation and as additives to glass and ceramic glaze formulas. Demonstrated in 1860, Gaston Plante?s secondary lead acid cell involved the anodic formation of PbO on sheets of lead in a slow, tedious process where reversal of the electrical charge converted the lead to the electrochemical components. Subsequent developments by Faure and Tudor for pasting lead oxide compounds on plates and grids dramatically improved both the time required to form the active mass and, due to greater quantities of active material, the capacity of the secondary cell. These developments created a market in the emerging lead acid battery industry for large quantities of lead oxide. It was also the impetus for researchers to identify and understand the properties of these compounds, their effect in the lead acid battery system, and which characteristics optimized that system. Lead oxide has many crystalline forms, such as PbO, Pb2O3, Pb3O4, and PbO2. Between these crystalline forms, lead oxide and lead dioxide (PbO & PbO2), which are used as positive active material in lead acid battery, has been extensively studied. Although the negative effects of lead oxides on nature and health are frequently mentioned, they are the unique materials that have been used for a long time for all current applications dependably. The basic and most significant impact of lead oxides occurs on the energy storing applications however there are many other respectable application fields such as gas sensing, glass production, pigment and paint industry. Particularly the increasing usage of lead oxides later then the invention of lead acid battery technology, showed a cumulatively rising trend after lead acid batteries proved themselves as a trustable energy storage unit.Modern technology, nowadays, appears impossible without the use of different rechargeable batteries in various electronic devices. Nevertheless, none of the new developed battery types (e.g. Li-ion and Ni-MH batteries) has so far reached the commercial success of the lead-acid batteries. This is partly a result of the continuous development and evolution of the lead-acid battery technology, which has led to major improvements in performance. Relatively good specific power has caused widespread use of lead-acid batteries in starting, lighting and ignition of engine (SLI) purposes for vehicular (e.g., automotive, marine and aviation) applications. Beside, lead acid technology currently remains the most reliable, safe and affordable power source. Lead acid batteries, unique energy storing application that stamped its remarkable impact on last century, are also considered as the supportive unit for automotive batteries, one of the leading technological developments nowadays, and some other energy storage applications such as solar cells, hydrogen storage units etc. with their high energy density. The main requirements for lead acid batteries in such kind of applications are high power and discharge rates, a long life and, increasingly, a substantial weight reduction. By the way, the obtained evolvements at the point science reached with the help of nanotechnology allow lead acid batteries to present adequate efficiency. Therefore it is extremely expectative to see lead acid batteries in electric vehicles will be common in soon time and other units and to face most of studies, including nanotechnology, goal-oriented for developing lead acid battery technology.In this study, commercial grade high purity lead acetate trihydrate salt was used in order to produce submicron sized lead oxide particles via Ultrasonic Spray Pyrolysis (USP). During production, precursor solution with different concentrations varying from 0.4M - 0.6M - 0.8M temperatures varying from 600 C, 700 C and 800 C, constant ultrasonic frequency fixed up to 1.3 MHz and 0.5ml/min carrier gas (air) flow rate were determined as experimental variables. Yield particles were subjected to X-ray diffraction analyses (XRD) for phase analyses, crystalline size and crystal structure, Scanning Electron Microscopy (SEM) for particle size and morphology, Energy Dispersive Spectroscopy (EDS) for mass ratio determination. As consequence, yield particles? properties such as crystal and particle size, morphology were investigated according to temperature and precursor solution concentration change. Primary and secondary particles can be clearly revealed from SEM images. The morphology of the particles is almost spherical and lamellar at lower temperature, but it turned into spherical and porous structure by temperature increase. According to EDS results, there were no impurity trace which breaks stochiometric rates. Crystalline size is also calculated with the help of well-knwns Debye-Scherrer equation. Results showed that crystalline size of lead oxide particles show ascending trend by temperature rise whereas there were no big change by concentration increase.