Grafen oksit lif eğirme cihazı tasarımı
Design of graphene oxide yarn spinning device
Yazar: İSMAİL KAYA
Danışman: YRD. DOÇ. DR. VEDAT TEMİZ ; YRD. DOÇ. DR. ELİF ÖZDEN YENİGÜN
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Makine Mühendisliği Ana Bilim Dalı / Konstrüksiyon Bilim Dalı
Derece: Yüksek Lisans, 2016
Konu: Makine Mühendisliği = Mechanical Engineering ; Tekstil ve Tekstil Mühendisliği = Textile and Textile Engineering

Özet:
Malzeme teknolojisinin gelişmesiyle birlikte farklı alanlarda yeni ve mekanik özellikleri daha kuvvetli malzemelerin kullanımı önem kazanmıştır. Bu malzemelerin başında karbonun iki boyutlu allotropu olan 'grafen' gelmektedir. 
Grafen alanında yapılan teorik çalışmalar 1940'lı yıllara dayanmaktadır. Ancak teknolojinin yetersizliği sebebiyle deneysel çalışmalara 2000'li yıllarda başlanabilmiştir. Manchester Üniversitesi'nden Geim ve Novoselov'un grafen alanındaki çalışmaları 2010 yılında Nobel Fizik Ödülü'ne layık görülmüştür. Bu ödül sonuncunda da grafen üzerine yapılan akademik ve endüstriyel çalışmalarda büyük bir ivmelenme meydana gelmiştir.
Grafen, üstün mekanik, termal ve elektriksel özellikleri sebebiyle transistör, sensör, esnek ekran, enerji depolama, dokunmatik ekran, elektrik iletim malzemesi gibi birçok alanda mevcut malzemelerden iyi olduğu düşünüldüğü için kullanılmak istenmektedir.
Grafenin kullanılabilir hale getirilebilmesi için, öncelikle grafenin nano ölçekten makro ölçeğe getirilmesi gerekmektedir. Ardından kullanım alanlarına göre film, lif, köpük ve benzeri formlarda üretimleri gerçekleştirilmelidir. Hem nano ölçekten makro ölçeğe geçiş, hem de istenilen forma getirilmesi grafen kullanımında halen önemli problemlerdir. 
Bu çalışmada grafen malzemesinin lif formuna getirilmesi amaçlanmıştır. Bu doğrultuda yapılan literatür araştırmalarında sıklıkla karşılaşılan ıslak çekim yöntemi ile grafen lif elde edilmesi üzerine yoğunlaşılmıştır. 
Islak çekim yönteminde, istenen özelliklere bağlı olarak farklı oranlarda hazırlanan grafen çözeltisi enjektör pompası vasıtasıyla belli bir kesitte katılaşma banyosuna aktarılmaktadır. Dış ortam ile temas etmeden katılaşma banyosuna aktarılan grafen çözeltisi banyo ortamında lif formunu almış olur. Daha sonra methanol banyosundan ve yıkama banyosundan geçirilen grafen lifler bir tambur vasıtasıyla toplanır. 
Bu projede ıslak çekim hattı sistemi enjektör pompası kullanılarak kurulmuştur ve bu sistemle grafen lif elde edilmiştir. Ancak elde edilen grafen liflerin çaptaki düzensizliği ve enjektör hacimlerinin sınırlı olması sebebiyle yeni bir cihaz tasarımına ihtiyaç duyulmuş ve bu ihtiyaca yönelik bir çalışma yapılmıştır.
Yapılan bu konstrüksiyonda, konstrüktif geliştirme süreci takip edilerek adım adım ilerlenmiştir. İlk olarak ödev tarif edilmiş ardından istekler listesi hazırlanmıştır. Giriş ve çıkış büyüklükleri belirlenerek temel fonksiyon oluşturulmuştur. Sırasıyla fonksiyon strüktürü oluşturulmuş ve alt fonksiyonlar belirlenmiştir. Bu işlemler sonrasında sistemde kullanılacak parçalar belirlenmiş ve boyutlar tespit edilmiştir. Gerekli malzemeler tedarik edilerek imalatlar gerçekleştirilmiş ve bir teknik yapıt ortaya konulmuştur.
İmal edilen sistem kullanılarak grafen lif üretimi gerçekleştirilmiş olup, enjektör pompalı ıslak çekim hattından üretilmiş grafen liflerle karşılaştırılmıştır. Yeni sistemden elde edilen grafen lif sonuçları çapta süreklilik ve mekanik özellikler bakımından tatmin edici bulunmuştur.

Abstract:
With the developments in material technology, the need for materials with new and stronger material properties raised over time. There has been various research and studies for enhancements of materials. A pioneer for these materials is graphene, which is one of the two dimensional allotrope of carbon. 
The theoretical studies promoting 'The Band Theory of Graphite' regarding graphene started in the mid 1940's by Philip Russell Wallace. Experimental studies started in 2000's because of technological shortcomings. Sir Andre K. Geim and Sir Konstantin S. Novoselov's studies regarding graphene technology won the Nobel Prize on Physics in 2010. This reward helped the recognition of the graphene technology and a resulted a rapid increase on academic and industrial studies in this area.
In latest studies graphene density is calculated as 0,77 mg⁄m^2 . When compared to steel (ultimate tensile strength of steel is between 250-1200  N⁄〖mm〗^2 . This value equals to  0,084-0,40  N⁄m when steel is treated as a 2 dimensional structure where in graphene this value is (42 N)⁄m), graphene shows a 100 times higher ultimate tensile strength on average. When compared to copper in terms of bulk conductivity, which represent electrical conductivity, graphene has a value of 0,96.〖10〗^7  Ω^(-1) 〖cm〗^(-1) while in copper this value is 0,60.〖10〗^7  Ω^(-1) 〖cm〗^(-1). In terms of thermal conductivity graphane has a value of  (50 W)⁄((cm.K) ) where as in copper it is (4 W)⁄((cm.K) ). Moreover, many studies are concentrated on other mechanical properties of graphene.
Graphene's higher mechanical, thermal and electrical properties results led to its use in areas such as transistors, sensors, flexible screens, energy storage materials, touch screens and electric conducting materials since it proved better results than the materials that are already in use. Moreover, it is estimated that in the near future, graphene will also be used in satellites and aircrafts as a component of composite materials.
In order to make use of graphene in desired areas it has to be in macro scale rather than the micro scale that it is already in. The production of the desired forms such as film, fiber, foam etc. is the following step. The transition from micro scale to macro scale and the production of the desired form are still major problems limiting graphene's use in desired areas. 
Fiber form of graphene is the desired structure in order to make use of its high electrical conductivity. As an example, a Boeing 737 contains 23 km's of cabling which may be expressed in tons. This is a serious weight considering the total weight of the airplane. In addition, sensors that detect forces acting on the plane and align course accordingly can be replaced with its graphene competitors. There is very effective replacement in graphene usage instead of other metal cables usages in airplanes.   
This study aims to produce graphene fibers via wet spinning process, which is the most common technique in this area in related literature. Producing graphene fibers and using as a cable will compensate requirements of lightness in airplanes, likewise producing graphene as a composite material and using as a sensor, will improve accuracy of sensor output signals.
In wet spinning process graphene dispersions are prepared beforehand in order attain the final desired properties of the product. This dispersion is injected to the coagulation bath via a syringe pump. The graphene dispersion that is transferred to the coagulation bath in a closed environment in order to obtain the fiber shape. The graphene fibers are collected by a drum collector after passing through a methanol bath and a washing bath respectively.
In order to produce fiber form of graphene, one of the most important equipment of the wet spinning line is the spinneret. Studies show that single or multiple holed spinnerets can be used for the production of graphene fibers. Additionally the length to diameter ratio of these holes is higher than certain values. Moreover thinner fibers can be obtained with the use of lower hole diameters. Although smaller diameter holes are preferred, due to limits of manufacturing such equipment, existing technologies are used. As a result, the search for a proper material led to the use of a syringe needle.
The wet spinning line in this project is constructed with the use of a syringe pump and graphene fibers are obtained. Due to the diameter of the graphene fiber being unstable throughout the length of the graphene fiber and the limited volume of the syringes required the development of a new device in order to attain the desired mechanical properties.
While investigating the production methods of graphene fibers, it can be seen that most of the production methods are kept hidden since most of the research regarding the subject is a relatively new work in progress. No other equipment than the syringe pump is observed in the commonly used wet spinning process.
The device is designed following the traditional systematical design steps. Firstly, the problem is carefully constructed and the needs regarding the project are identified. Input and output values are specified and basis function is formed. Function structure and sub-functions are formed, respectively. Following steps are the determination of the necessary equipment for the system and calculation of dimensions. Specified materials and equipment are obtained for the manufacturing of the technical structure.
In this device a DC motor, worm drive with a high transmission ratio, power screw, syringe barrel, piston seal and syringe needle are essentially used. Furthermore, in order to mate all these components, some supports and sheet metals are attached to the system.
In order to achieve the desired volumetric flow rate, both dimensions of the syringe barrel and linear velocity of the piston must be known. In order to calculate linear velocity of the piston, rotational speed of the power screw and pitch of the power screw must be chosen appropriately. After constructing the necessary equations and electing required parameters, the relationship between the flow rate and rotation speed of the DC motor is observed and calculated since the DC motor is driven by controlling the input voltage generated by the power supply. Afterward, the system is reduced to input voltage value in aim to achieve the desired volumetric flow rate. Since therefore, modulating the voltage value directly effects the volumetric flow rate value.
The system is designed with two layers in mind, which are made of steel sheets. Rectangular steel profiles are used for supports. DC motor and worm drive are mounted on the top layer where the syringe barrel sits at the bottom layer. Power screw is positioned between the layers and nut of the power screw is connected to the piston of syringe barrel. Coagulation bath is at the end of the setup and syringe needle is in contact with the bath. Thus, a vertical system is obtained in this arrangement. Additionally, graphene fibers are collected horizontally arranged collector drum.
With the use of the newly constructed structure, graphene fibers are produced without any difficulty. Compared to the previous wet spinning line specimens, which made use of the syringe pumps, the resulting materials of the new structure are identified and found satisfactory in both dimensional consistency and mechanical properties.