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Formation of Zirconium Diboride and Other Metal Borides by Volume Combustion Synthesis and Mechanochemical Process

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FORMATION OF ZIRCONIUM DIBORIDE AND OTHER METAL BORIDES BY VOLUME COMBUSTION SYNTHESIS AND MECHANOCHEMICAL PROCESS A THESIS SUBMITTED TO THE GRADUATE SCHOOL OF NATURAL AND APPLIED SCIENCES OF MIDDLE EAST TECHNICAL UNIVERSITY BY BARIŞ AKGÜN IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN METALLURGICAL AND MATERIALS ENGINEERING FEBRUARY 2008 Approval of the thesis: FORMATION OF ZIRCONIUM DIBORIDE AND OTHER METAL BORIDES BY VOLUME COMBUSTION SYNTHESIS AND MECHANOCHEMICAL PROCESS submitted by BARIŞ AKGÜN in partial fulfillment of the requirements for the degree of Master of Science in Metallurgical and Materials Engineering Department, Middle East Technical University by, Prof. Dr. Canan Özgen ____________ Dean, Graduate School of Natural and Applied Sciences Prof. Dr. Tayfur Öztürk ____________ Head of Department, Metallurgical and Materials Engineering Prof. Dr. Naci Sevinç ____________ Supervisor, Metallurgical and Materials Engineering Dept., METU Examining Committee Members: Prof. Dr. Ahmet Geveci __________________ Metallurgical and Materials Engineering Dept., METU Prof. Dr. Naci Sevinç __________________ Metallurgical and Materials Engineering Dept., METU Prof. Dr. Yavuz A. Topkaya __________________ Metallurgical and Materials Engineering Dept., METU Prof. Dr. İshak Karakaya __________________ Metallurgical and Materials Engineering Dept., METU Prof. Dr. Gülhan Özbayoğlu __________________ Mining Engineering Dept., METU Date: 01.02.2008 I hereby declare that all information in this document has been obtained and presented in accordance with academic rules and ethical conduct. I also declare that, as required by these rules and conduct, I have fully cited and referenced all material and results that are not original to this work. Name, Last name : Barış Akgün Signature : iii ABSTRACT FORMATION OF ZIRCONIUM DIBORIDE AND OTHER METAL BORIDES BY VOLUME COMBUSTION SYNTHESIS AND MECHANOCHEMICAL PROCESS Akgün, Barış M.Sc., Department of Metallurgical and Materials Engineering Supervisor: Prof. Dr. Naci Sevinç February 2008, 109 pages The aim of this study was to produce zirconium diboride (ZrB2) and other metal borides such as lanthanum hexaboride (LaB6) and cerium hexaboride (CeB6) by magnesiothermic reduction (reaction of metal oxide, boron oxide and magnesium) using volume combustion synthesis (VCS) and mechanochemical process (MCP). Production of ZrB2 by VCS in air occurred with the formation of side products, Zr2ON2 and Mg3B2O6 in addition to MgO. Formation of Zr2ON2 was prevented by conducting VCS experiments under argon atmosphere. Wet ball milling was applied before leaching for easier removal of Mg3B2O6. Leaching in 5 M HCl for 2.5 hours was found to be sufficient for removal of MgO and Mg3B2O6. By MCP, 30 hours of ball milling was enough to produce ZrB2 where 10% of excess Mg and B2O3 were used. MgO was easily removed when MCP products were leached in 1 M HCl for 30 minutes. Complete reduction of ZrO2 could not be achieved in either production iv method because of the stability of ZrO2. Hence, after leaching VCS or MCP products, final product was composed of ZrB2 and ZrO2. Formation of LaB6 and CeB6 were very similar to each other via both methods. Mg3B2O6 appeared as a side product in the formation of both borides by VCS. After wet ball milling, products were leached in 1 M HCl for 15 hours and pure LaB6 or CeB6 was obtained. As in ZrB2 production, 30 hours of ball milling was sufficient to form these hexaborides by MCP. MgO was removed after leaching in 1 M HCl for 30 minutes and the desired hexaboride was obtained in pure form. Keywords: Zirconium Diboride, Lanthanum Hexaboride, Cerium Hexaboride, Volume Combustion Synthesis, Mechanochemical Process, Acid Leaching. v ÖZ HACİMSEL TUTUŞMA SENTEZLEMESİ VE MEKANOKİMYASAL YÖNTEM İLE ZİRKONYUM DİBORÜR VE DİĞER METAL BORÜRLERİN OLUŞUMU Akgün, Barış Y. Lisans, Metalurji ve Malzeme Mühendisliği Bölümü Tez Yöneticisi: Prof. Dr. Naci Sevinç Şubat 2008, 109 sayfa Bu çalışmanın amacı magnezyotermik indirgeme (metal oksit, bor oksit ve magnezyum’un reaksiyonu) ile hacimsel tutuşma sentezi (HTS) ve mekanokimyasal yöntem (MKY) kullanılarak zirkonyum diborür (ZrB2) ile lantan hekzaborür (LaB6) ve seryum hekzaborür (CeB6) gibi diğer metal borürleri üretmektir. Hava ortamında HTS ile ZrB2 üretimi, MgO’e ek olarak yan ürünlerin, Zr2ON2 ve Mg3B2O6, oluşumu ile birlikte görülmüştür. Zr2ON2’ün oluşumu HTS deneylerinin argon atmosferinde yapılmasıyla engellenmiştir. Mg3B2O6’ın kolay giderilmesi için liç öncesinde ıslak öğütme uygulanmıştır. 5 M HCl içinde 2,5 saat yapılan liç MgO ve Mg3B2O6’ın giderilebilmesi için yeterli bulunmuştur. MKY ile 30 saatlik öğütme %10 fazla Mg ve B2O3 kullanıldığında ZrB2 üretmek için yeterlidir. MKY ürünleri 1 M HCl içinde 30 dakika liç edildiğinde, MgO kolayca giderilmiştir. ZrO2’in kararlılığından dolayı, her iki yöntemle de ZrO2’in tam indirgenmesi sağlanamamıştır. Bu vi yüzden, HTS veya MKY ürünlerinin liçinden sonra, son ürün ZrB2 ve ZrO2’ten oluşmaktadır. Her iki yöntemle de LaB6 ve CeB6 oluşumu birbirlerine çok benzemektedir. Mg3B2O6 her iki borürün HTS ile oluşumunda yan ürün olarak görülmüştür. Islak öğütmeden sonra, ürünler 1 M HCl içinde 15 saat liçe tabi tutulmuştur ve saf LaB6 veya CeB6 elde edilmiştir. ZrB2 üretiminde olduğu gibi, 30 saatlik öğütme bu börürlerin MKY ile oluşması için yeterlidir. 1 M HCl içinde 30 dakika liçden sonra, MgO giderilmiş ve istenen hekzaborür saf halde elde edilebilmiştir. Anahtar Kelimeler: Zirkonyum Diborür, Lantan Hekzaborür, Seryum Hekzaborür, Hacimsel Tutuşma Sentezi, Mekanokimyasal Yöntem, Asit Liçi. vii To my family & in memory of my maternal uncle Ergun Erenkuş viii ACKNOWLEDGEMENTS I would like to express my sincere gratitude to my supervisor Prof. Dr. Naci Sevinç for his guidance, supervision, support, patience and encouragement throughout this study. I would also like to thank to Prof. Dr. Yavuz Topkaya for his valuable advices and guidance. I am very grateful to Dr. H. Erdem Çamurlu for his helps and support during this work. I should thank to Necmi Avcı for XRD analysis and Cengiz Tan for SEM analysis. I must thank to Çağla Özgit for her endless patience, motivation and support. I am also thankful to my best friends; Fatih Güngör, Alp Kol, Özgür Gülse, Serkan Yalçınkaya, Hakan Cenkçiler, H. Volkan Yaycı, Emre Erdem, Ali Mutlu, Ender Erdem for sharing my hard and bad times with me. I must also express my special thanks to Ergin Büyükakıncı, Volkan Kayasü, Arda Çetin, Deniz Keçik, Metehan Erdoğan and Evren Tan for their help and support. Finally, I would like to express my deepest gratitude to my family Kemal, Berrin, Başak, Nimet Akgün and Gönül Erenkuş for their endless love and support during my life. ix This study was supported by National Boron Research Institute (BOREN) Project No: BOREN-2006-Ç-04. x TABLE OF CONTENTS ABSTRACT..............................................................................................................iv ÖZ.............................................................................................................................vi DEDICATION...................................................................................................... viii ACKNOWLEDGEMENTS....................................................................................ix TABLE OF CONTENTS ........................................................................................xi LIST OF TABLES ..................................................................................................xiv LIST OF FIGURES .................................................................................................xv CHAPTER 1 INTRODUCTION................................................................................................. 1 2 LITERATURE SURVEY....................................................................................... 4 2.1 Binary Metal Borides .................................................................................... 4 2.1.1 Classification of Metal Borides............................................................. 6 2.1.2 Boride Structures.................................................................................... 7 2.1.3 Production Methods .............................................................................. 8 2.2 Zirconium Diboride ...................................................................................... 9 2.2.1 Crystal Structure of Zirconium Diboride.......................................... 10 2.2.2 Properties of Zirconium Diboride...................................................... 11 2.2.3 Applications of Zirconium Diboride ................................................. 14 2.3 Lanthanum Hexaboride and Cerium Hexaboride ................................. 15 2.3.1 Crystal Structure of Lanthanum Hexaboride and Cerium Hexaboride..................................................................................................... 15 2.3.2 Properties of Lanthanum Hexaboride and Cerium Hexaboride... 16 xi 2.3.3 Applications of Lanthanum Hexaboride and Cerium Hexaboride .......................................................................................................................... 18 2.4 Production Methods ................................................................................... 19 2.4.1 Volume Combustion Synthesis .......................................................... 20 2.4.2 Mechanochemical Process................................................................... 21
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  • Assessment of the State of the Art of Ultra High Temperature Ceramics

    Assessment of the State of the Art of Ultra High Temperature Ceramics

    Assessment of the State of the Art of Ultra High Temperature Ceramics Sylvia Johnson, Matt Gasch, NASA Ames Research Center, Moffett Field CA 94035 Mairead Stackpoole, ELORET Corp, Moffett Field CA 94035 1.0 Introduction Ultra High Temperature Ceramics (UHTCs) are a family of materials that includes the borides, carbides and nitrides of hafnium-, zirconium- and titanium-based systems. UHTCs are famous for possessing some of the highest melting points of known materials. In addition, they are very hard, have good wear resistance, mechanical strength, and relatively high thermal conductivities (compared to other ceramic materials). Because of these attributes, UHTCs are ideal for thermal protection systems, especially those that require chemical and structural stability at extremely high operating temperatures. UHTCs have the potential to revolutionize the aerospace industry by enabling the development of sharp hypersonic vehicles or atmospheric entry probes capable of the most extreme entry conditions. 2.0 Background UHTCs originated in the early 1960s. Some of the earliest and most thorough work to date was performed then by the company ManLabs, under a research program funded by the Air Force Materials Laboratory (AFML) 1-2. Work on UHTCs was initiated to meet the need for high temperature materials that would allow the development of maneuverable hypersonic flight vehicles. Since then, intermittent research has made some progress, but several significant challenges remain in the use of UHTCs, and these materials have yet to be widely implemented. Strong covalent bonding is responsible for the high melting points, moduli, and hardness of the UHTC family of materials3-4. High negative free energies of formation also give UHTCs excellent chemical and thermal stability under many conditions.