Dinamik termokimyasal yöntem ile S3N4/SiC kompozit tozu üretimi ve özelliklerinin incelenmesi
Production of Si3N4/SiC composite powder by dynamic thermochemical method and investigation of its properties
Yazar: NAZLI ERKEN
Danışman: DOÇ. DR. NURAY CANİKOĞLU
Sakarya Üniversitesi / Fen Bilimleri Enstitüsü / Metalurji ve Malzeme Mühendisliği Ana Bilim Dalı
Derece: Yüksek Lisans, 2023
Konu: Metalurji Mühendisliği = Metallurgical Engineering

Özet:
Karbotermal indirgeme  yöntemi; nitrür esaslı ileri teknoloji seramiklerin üretilmesi için tercih edilen ve en etkili sonuca ulaşmamızda kolaylık sağlayan toz üretimi yöntemidir. Yapılan bu tez çalışmasında Karbotermal indirgeme ve nitrürleme yönteminin geliştirilmesi sonucu elde edilen dinamik termokimyasal yöntem kullanılarak, kompozit toz üretimi gerçekleştirilmiştir. Bu yöntemde kullanılacak olan hammaddelerin döner bir sistem içerisinde ve reaksiyon süresi boyunca haraket etmesi sağlanmaktadır. Geliştirilen bu sistem sayesinde nitrür ve karbür esaslı ileri tenolojik seramik tozlarının ekonomik ve kaliteli bir şekilde üretimini sağlamakla beraber üretim sıcaklığını ve üretim süresini azaltarak büyük avantaj sağlamaktadır.
Bu  çalışmada Dinamik Termokimyasal yöntemi ile silisyum nitrür/silisyum karbür (Si3N4/SiC) kompozit toz üretimi için gerekli olan üretim parametreleri belirlenerek, döner sistemin toz morfolojisi üzerindeki etkileri incelenmiştir. Başlangıç hammaddeleri olarak;  silisyum oksit (SiO2) Egesil Kimya A.Ş'den alınan UN2 POWDER saf hammadde ve karbon karası (C)  Körfez Petro Kimya'dan alınan yüksek safiyetteki ISAF N-220 kodlu ürün kullanılmıştır. Kullanılan hammaddeler farklı stokiometrik oranlar belirlenerek (C/SiO2=2.25 C/SiO2=3) karıştırılmış ve sonrasında granül haline getirilmiştir. Hazırlanan granüler; ölçüsü 1-3 mm olan eleklerden  geçirilmitir.  Elek altında kalan granüllere, grafit bir reaktör içerisinde azot (N2) gazı ve argon (Ar) gazı atmosferinde iki kademede gerçekleştrilen dinamik termokimyasal işlemi uygulanmıştır. Gerçekleştirilen  bu reaksiyon sonrasında silisyum nitrür/silisyum karbür (Si3N4/SiC) kompozit tozları elde edilmiştir. Bu tez çalışmasında geliştirilmiş bir sistem olan Dinamik Termokimyasal işlemle reaksiyonun ilk kademesi olan Si3N4 üretimi için reaksiyon sıcaklığı (1400°C-1450°C-1475°C-1500°C) ve reaksiyonun ikinci kademesi olan SiC üretimi  için reaksiyon  sıcaklığı (1450°C-1500°C), reaksiyon süresi (1-2 saat), 4dv/dk reaktör dönme hızı, 1lt/dk gaz akış debisi gibi, belirlenen test parametrelerinin etkileri araştırılmıştır. Reaksiyonun ardından elde edilen toz ürünlerin faz analizleri ve mikro yapıları XRD, SEM ve EDS analizleri kullanılarak karakterize edilmiş ve optimum şartlar belirlenmiştir. 
Yapılan analizler sonucunda 1450°C'de 2 saat süresince 1lt/dk N2 gaz akışı altında nitrürleme ve 1450°C'de 1saat süresince 1lt/dk Ar gaz akışı altında karbürleme işlemleriyle 4 dev/dk reaktör dönme hızında kompozit toz elde edilmiştir.

Abstract:
With the development of technology, it is insufficient to meet the increasing demands for the functions of natural materials used. For this reason, it is necessary to improve or change the properties of the materials used. This is where composite materials come into play.
Each material has its own characteristic feature. These characteristic features are combined in the structure of composite materials to provide superior properties. The purpose of producing composite powder is to improve some or all of the mechanical, chemical and physical properties of the obtained material. Contrary to popular belief, the history of composite materials, which are widely used in many fields today, does not date back to the Second World War or a few centuries back. Today, the composite industry is used in very wide areas (automotive, aviation, military). Among the reasons why high-tech ceramics are preferred in composite powder production is their high purity values, as well as the abundance of raw materials in nature. The easy availability of raw materials provides benefits in reducing the production cost. At the same time, the high purity value of the obtained products supports the production of quality products. In this study, it is aimed to produce composites of strategically important Si3N4 and SiC using raw materials that are easily found in nature and cheap.
Silicon nitride (Si3N4) and silicon carbide (SiC) are known as high-tech ceramics. Thanks to its many characteristic features, it has taken its place as the most preferred ceramic materials in the sector in recent years. Among the most important features of Si3N4; It has low density, oxidation resistance at high temperatures, and hardness and strength at high temperatures. Silicon nitride (Si3N4) is the most preferred ceramic material for high voltage, high temperature applications such as gas turbines, turbochargers and engine valves. Silicon carbide; abrasive is a material with exceptional hardness and high creep strength. It has very good resistance to chemical and erosional interactions in a reducing atmosphere. Being resistant to all alkalis and acids and having semiconductor properties has made it a promising compound. It is frequently preferred in metallurgy and refractory industry due to its high temperature resistance. Among the common features of Si3N4 and SiC; has good chemical stability and high temperature shock resistance. Its advanced technological ceramics, which attract attention, form a material group that performs better when compared to steels, which are widely used recently, when their oxidation and wear resistance, hardness, mechanical and thermo-mechanical properties at high temperatures are taken into account. These characteristic features of technological ceramics are engineering materials developed to show superior performance in high temperature applications.
Carbothermal reduction method; It is a powder production method that is preferred for the production of nitride-based advanced technology ceramics and provides convenience in achieving the most effective result. In this thesis study, composite powder production was carried out by using the dynamic thermochemical method obtained as a result of the development of the carbothermal reduction and nitriding method. 
The raw materials used in this method move in a rotating system during the reaction time. Thanks to this developed system, it provides economical and high quality production of nitride and carbide-based advanced ceramic powders, as well as providing a great advantage by reducing the production temperature and production time.
In this study, silicon nitride/silicon carbide (Si3N4/SiC) composite powder production parameters and the effects of rotary system on powder morphology were investigated by Dynamic Thermochemical method. As starting raw materials; silicon oxide (SiO2) UN2 POWDER pure raw material from Egesil Kimya A.Ş and high purity ISAF N-220 coded product from carbon black (C) Körfez Petro Kimya was used. First of all, different recipes were examined thermodynamically with the help of FactSage program. The mixtures were mixed in a dry environment at appropriate stoichiometric ratios (C/SiO2=2.25 C/SiO2=3) in a dry environment using zirconia balls in a polypropylene container with a ball/powder ratio of 5. The prepared mixture was granulated manually with a pure alcohol solution containing 5% glycerol. Granular; passed through sieves measuring 1-3 mm. The dynamic thermochemical process, which was carried out in two stages in a nitrogen (N2) gas and argon (Ar) gas atmosphere, was applied to the granules remaining under the sieve. After this reaction, silicon nitride/silicon carbide (Si3N4/SiC) composite powders were obtained. The reaction temperature (1400°C-1450°C-1475°C-1500°C) for the production of Si3N4, which is the first step of the Dynamic Thermochemical processes reaction, which is a system developed in this thesis, and the reaction temperature (1450°C-1500°C) for the production of SiC, the second step of the reaction, The effects of the determined test parameters such as reaction time (1-2 hours), reactor rotation speed of 4dv/min, gas flow rate of 1lt/min were investigated. Optimum conditions were determined by XRD analysis to define the phases formed, EDS to determine the elemental composition and SEM analysis to examine the powder size distribution for the powder products obtained after the reaction.
As a result of the analyzes made, nitriding under 1 lt/min N2 gas flow for 2 hours at 1450°C and composite powder was obtained at 4 rpm reactor rotation speed by carburizing processes under 1lt/min Ar gas flow for 1 hour at 1450°C.
The mobility of the system enabled the nitrogen gas given to the environment to be produced in a shorter time at lower temperatures by contacting the entire surface of the product. Again, with the effect of the rotating system, the gas in the environment is ensured to contact the entire surface of the product, which has a positive effect on the powder morphology and has ensured that the reaction is very efficient. A product with finer grain size was obtained.
 Compared with other production methods in the literature With the dynamic thermochemical method,it has been proven that inexpensive,high quality,finegrained, homogeneous composite powder can be produced at lower temperatures and in a shorttime.