Farklı Destek Ve Katalizör Malzemeleri İle Tek Duvarlı Karbon Nanotüp Sentezi

Abstract

Nano boyut kavramının dile getirilmesi ve karakterizasyon cihazlarındaki üstün gelişmeler nanoteknoloji ve nanomalzeme alanına büyük ivme kazandırmıştır. 1991 yılından itibaren üstün özellikleri ile dikkatleri üzerine çekmeyi başaran karbon nanotüpler hakkında birçok çalışma yapılmıştır. Kimyasal buhar birikimi (KBB) yöntemi, KNT sentezinde özellikle seri üretim için yaygın olarak kullanılan bir yöntemdir. Karbon kaynağı, katalizör, destek malzeme (substrat), sentez sıcaklığı ve süresi, katalizör kalsinasyonu, karbon nanotüp yapısını-morfolojisini ve karbon verimliliğini etkileyen önemli parametrelerdir. Tez çalışması kapsamında, İstanbul Teknik Üniversitesi?Enerji Enstitüsü, Malzeme Üretim ve Hazırlama Laboratuvarı?nda kimyasal buhar birikimi yöntemi ile değişik destek malzemeleri ve katalizör kullanarak tek duvarlı karbon nanotüpler üretilmiş ve bu malzemelerin karbon nanotüp verimine etkileri incelenmiştir. Üretilen karbon nanotüplerin karakterizasyonu; termogravimetrik analiz (TGA), raman spektroskopisi ve XRD cihazları ile gerçekleştirilmiştir. Kimyasal buhar birikimi yöntemi ile akışkan yatak sisteminde; karbon kaynağı olarak asetilen gazı, katalizör olarak demir nitrat [Fe(NO3)3.9H2O], nikel nitrat [Ni(NO3)2.6H2O], kobalt nitrat [Co(NO3)2.6H2O] ve destek malzemeleri olarak magnezyum oksit (MgO), alümina (Al2O3), silika (SiO2) kullanılarak karbon nanotüp (KNT) üretimi gerçekleştirilmiştir. Katalizör ve destek malzeme miktarları, katalizör içerisinde hedeflenen metal ve destek malzeme kütlesel oranlarına bağlı olarak belirlenmiştir. Ayrıca, KNT üretimine metal katalizörlerin birlikte etkisini incelemek için demir ve kobalttan oluşan ikili katalizör sistemleri hazırlanmıştır. Tek duvarlı karbon nanotüp üretiminde, sentez süresi 30 dakika sıcaklık ise 800°C olarak seçilmiştir. Üretilen KNT?lerin karbon verimleri hesaplanarak farklı destek malzemesi ve katalizörlerin karbon verimine etkileri araştırılmıştır.

The use of the word ?nano? for the first time and following that the outstanding improvements of the characterization devices increased the importance of nanotechnology and nanomaterials. One of the most promising nanomaterials is carbon nanotubes. Since 1991, carbon nanotubes have been drawing too much attention by the researchers and engineers. A carbon nanotube can be described as a tubular structure made of carbon atoms. These kind of structures have diameter of nanometer order and length in micrometers. Carbon nanotubes have extraordinary properties such as being harder than diamond and stronger than steel. Their electrical conductivity is higher than copper and thermal conductivity is higher than diamond. Traditional methods of growing carbon nanotubes only produce a small amount per day. In order to solve this problem, the efforts have been made in the first decade of the invention and large scale synthesis of CNTs is now available for the commercial applications. Many methods have been developed for CNT synthesis such as arc discharge, laser vaporization and catalytic chemical vapor deposition. Among them, chemical vapor deposition is widely used because of its advantages. CCVD appears to be the most promising method because of its low-cost and high-yield production. CNT synthesis by CVD method involves hydrocarbon gas which passes through the tubular reactor in which a catalyst materials is present at high temperatures. At high temperature, hydrocarbon gas decomposes and CNTs grow on the catalyst in the reactor. In order to collect the CNTs, the system has to be cooled to room temperature. In this study, single-walled carbon nanotubes were synthesized by chemical vapor deposition method by using different support materials and catalysts at Material Production and Preparation Laboratory of Istanbul Technical University ? Energy Institute. The relation between support materials and catalysts were investigated and the carbon efficiencies are determined for each product. Termogravimetric Analysis, Raman Spectroscopy and XRD were used for the characterization of the synthesized carbon nanotubes. Carbon nanotube synthesis were performed by using acetylene as the carbon source, iron nitrade [Fe(NO3)3.9H2O], nickel nitrade [Ni(NO3)2.6H2O], cobalt nitrade [Co(NO3)2.6H2O] as the catalysts and magnesium oxide (MgO), alumina (Al2O3), silica (SiO2) as the support materials. The amounts of catalyst and suppert materials were determined in a mass proportion of the targeted metal to support materials. Beside, in order to investigate the relation between two different metal catalysts, iron and cobalt were mixed with appropriate ratio. In all the experiments, synthesis time and temperature were selected as 30 minutes and 800°C, respectively. Carbon efficiencies of the samples were calculated according to a formula and the effects of the different support materials and catalysts on carbon efficiency were investigated.