Ni
Küçük Resim Yok
Tarih
2012
Yazarlar
Dergi Başlığı
Dergi ISSN
Cilt Başlığı
Yayıncı
Trakya Üniversitesi
Erişim Hakkı
info:eu-repo/semantics/openAccess
Özet
Bu tezde, kor/kabuk yapısında nano büyüklükteki Ni/Pd metalik atomik kümelerin (NK)/nanoparçacıkların (NP) yüzey erimesi; erime sürecindeki kararlılıkları ve bazı fiziksel özelliklerinin ebada ve geometrilerine bağlılığı teorik modeller kullanılarak incelenmiştir.Bu amaçla Ikozahedral (ICO) ve kübo-oktahedral (CO) geometrik yapılarına sahip 0.2-22 nm yarıçaplı NiPd nanokümeleri/nanoparçacıkları ile çalışılmıştır. Kor/kabuk yapısındaki Ni/Pd nanoparçacıkların ebada bağlı erimeleri; yüzey ve hacim içerisindeki atomik bağ uzunlukları; ICO ve CO geometrik yapılarının kor/kabuk koordinasyon sayıları kullanılarak modellenmiştir. Tezde ilk kez Ni(kor)/Pd(kabuk) ile Ni(kor)/ Pd_2 Ni (kor-kabuk-kor)/Pd(kabuk) olarak iki farklı kor/kabuk modeli öne sürülmüştür. Modellenen Ni/Pd kor/kabuk nanoparçacıklarının ebada bağlı erime sıcaklıkları ve bağlanma enerjileri hesaplanarak kararlı yapıları tayin edilmiş; kor/kabuk arasındaki ara difüzyon katsayıları hesaplanmıştır. Ayrıca karşılaştırma yapmak üzere tek bileşenli Ni, Pd nanokümeleri ve iki bileşenli Ni-Pd alaşım nanaoparçacıklarındaki yüzey erimesi de çalışılmıştır.Hesaplanan erime sıcaklıklarının kor/kabuk nanokümelerin ebadına, geometrik şekline bağlı olarak değiştiği gözlenmiştir. Nanokümelerin ebadı artıkça erime sıcaklığı da artmaktadır. ICO şekilli kor/kabuk nanoparçacıkların erime sıcaklığı her iki model içinde, CO şekilli nanoparçacıklara göre yüksektir. Çalışılan kor/kabuk modellerindeki Ni ve Pd nanokümelerinin farklı kararlılık trendi gösterdiği ancak hesaplanan fiziksel özelliklerinin, literatürdeki moleküler dinamik, teorik model ve deney sonuçları ile uyum içerisinde olduğu saptanmıştır.
In this thesis, the surface melting; the size dependent stability and the size and shape dependence of some physical properties during the melting process of nano-size metallic atomic clusters/nanoparticles of Ni/Pd with core/shell structure were investigated by using theoretical models. For this purpose, nanoclusters/nanoparticles of NiPd with diameters of 0,2-22 nm for Icosahedral (ICO) and Cubo-octahedral (CO) geometric structures were studied. The size depending melting of Ni/Pd core/shell nanoparticles is modeled by considering the atomic bond lengths in the surface and volume; using the calculated core- shell coordination numbers of ICO and CO geometric structures. The two different core/shell models such as Ni (core)/Pd_2 Ni (core-shell-core)/Pd (shell) have been proposed first in this thesis. The stable structures of modeled Ni /Pd core-shell nanoparticles have been determined by calculating the size dependent melting temperatures and cohesive energies; the interdiffusion coefficients of core/shell structures were also calculated. In addition to this, the surface melting of Ni, Pd nanoclusters and two-component Ni-Pd alloy nanaoparticles have also studied. We observe that the calculated melting temperatures of core/shell nanoclusters varied depending on their size and geometric shape; the melting temperature of nanoparticles increases with increasing the size of nanoclusters; the obtained melting temperatures of ICO nanoparticles for each model are higher than that of the CO nanoparticles. It has been shown the stability trends for Ni and Pd nanoclusters in the studied core/shell models are different; however the calculated physical parameters for nanoclusters, depending on the size and geometric structure of nanoparticles are in a good agreement with MD, theoretical model and experimental results.
In this thesis, the surface melting; the size dependent stability and the size and shape dependence of some physical properties during the melting process of nano-size metallic atomic clusters/nanoparticles of Ni/Pd with core/shell structure were investigated by using theoretical models. For this purpose, nanoclusters/nanoparticles of NiPd with diameters of 0,2-22 nm for Icosahedral (ICO) and Cubo-octahedral (CO) geometric structures were studied. The size depending melting of Ni/Pd core/shell nanoparticles is modeled by considering the atomic bond lengths in the surface and volume; using the calculated core- shell coordination numbers of ICO and CO geometric structures. The two different core/shell models such as Ni (core)/Pd_2 Ni (core-shell-core)/Pd (shell) have been proposed first in this thesis. The stable structures of modeled Ni /Pd core-shell nanoparticles have been determined by calculating the size dependent melting temperatures and cohesive energies; the interdiffusion coefficients of core/shell structures were also calculated. In addition to this, the surface melting of Ni, Pd nanoclusters and two-component Ni-Pd alloy nanaoparticles have also studied. We observe that the calculated melting temperatures of core/shell nanoclusters varied depending on their size and geometric shape; the melting temperature of nanoparticles increases with increasing the size of nanoclusters; the obtained melting temperatures of ICO nanoparticles for each model are higher than that of the CO nanoparticles. It has been shown the stability trends for Ni and Pd nanoclusters in the studied core/shell models are different; however the calculated physical parameters for nanoclusters, depending on the size and geometric structure of nanoparticles are in a good agreement with MD, theoretical model and experimental results.
Açıklama
Yüksek Lisans
Anahtar Kelimeler
Fizik ve Fizik Mühendisliği, Physics and Physics Engineering
