A NOVEL PRECURSOR FOR SYNTHESIS OF ZIRCONIUM TUNGSTATE AND PRELIMINARY STUDIES FOR NANOFIBER PRODUCTION A THESIS SUBMITTED TO THE GRADUATE SCHOOL OF NATURAL AND APPLIED SCIENCES OF MIDDLE EAST TECHNICAL UNIVERSITY BY BERKER ÖZERCİYES IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN CHEMICAL ENGINEERING JANUARY 2009 Approval of the thesis: A NOVEL PRECURSOR FOR SYNTHESIS OF ZIRCONIUM TUNGSTATE AND PRELIMINARY STUDIES FOR NANOFIBER PRODUCTION submitted by BERKER ÖZERCİYES in partial fulfillment of the requirements for the degree of Master of Science in Chemical Engineering Department, Middle East Technical University by, Prof. Dr. Canan Özgen _________ Dean, Graduate School of Natural and Applied Sciences Prof. Dr. Gürkan KARAKAŞ _________ Head of Department, Chemical Engineering Prof. Dr. Güngör GÜNDÜZ _________ Supervisor, Chemical Eng. Dept., METU Assist. Prof. Dr. Bora MAVİŞ _________ Co-supervisor, Mechanical Eng. Dept., Hacettepe Univ. Examining Committee Members: Prof. Dr. Hayrettin YÜCEL _________ Chemical Engineering Department, METU Prof. Dr. Güngör GÜNDÜZ _________ Chemical Engineering Department, METU Prof. Dr. Işık ÖNAL _________ Chemical Engineering Department, METU Prof. Dr. Macit ÖZENBAŞ _________ Metallurgical and Materials Engineering Department, METU Assist. Prof. Dr. Ayşen YILMAZ _________ Chemistry Department, METU Date _________ SM 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 : BERKER ÖZERCİYES Signature : ABSTRACT A NOVEL PRECURSOR FOR SYNTHESIS OF ZIRCONIUM TUNGSTATE AND PRELIMINARY STUDIES FOR NANOFIBER PRODUCTION Özerciyes, Berker M.S., Department of Chemical Engineering Supervisor: Güngör Gündüz, Prof. Dr. Co-Supervisor: Bora Maviş, Assist. Prof. Dr. January 2009, 97 pages Zirconium tungstate (ZrW2O8) is a ceramic that shows large isotropic negative thermal expansion over a wide range of temperature. This unique property makes it an interesting candidate for applications where thermal expansion mismatch between components constitutes a problem. ZrW2O8 is typically produced by solid-state reaction between zirconium oxide and o tungsten oxide at 1200 C. In some studies, ZrW2O8 precursors have been produced from relatively expensive zirconium and tungsten sources. While the origin of negative thermal expansion has been the main focus in the majority of publications, production of particles with controlled size, distribution and morphology has not been studied extensively. iv Electrospinning is a simple technique for producing micron/nano sized fibers from polymer solutions. The method can also be used for producing ceramic or polymer/ceramic composite fibers by electrospinning of a mixture of ceramic precursors or ceramic nanoparticles with suitable polymers. Ceramic precursors could be synthesized either by sol-gel or chemical precipitation routes before mixing them with polymer solutions and a final burnout step would be needed, in case the fiber is desired to be composed of the ceramic phase. Electrospinning technique has not been employed to the production of ZrW2O8 ceramic fibers. In this study a novel precursor for ZrW2O8 from relatively cheaper and abundant starting chemicals, namely zirconium acetate and tungstic acid were used. Experimental details of development of the precursor are presented with a discussion on the effects of solution parameters on the phase purity of the fired product. Besides the solution parameters investigated (i.e. solubility of tungstic acid, adjustment of the stoichiometry, final pH of the solution, ageing time), evolution of the heat treatment protocol was used in the production of phase pure ZrW2O8. Second, the suitability of the developed precursor for producing ZrW2O8 in fiber form was investigated. Preliminary studies involved the adjustment of the viscosity of precursor solution for electrospinning with poly (vinyl alcohol) (PVA). Optimum PVA concentration leading to bead-free nanofiber mats and a method to increase the fiber production rate were reported. The characterization of the products was achieved by SEM and XRD. Keywords: zirconium tungstate, negative thermal expansion, sol-gel, ceramic fiber, electrospinning. v ÖZ YENİ BİR ÖNCÜLLE ZİRKONYUM TUNGSTAT SENTEZİ VE NANOLİF ÜRETİMİ İÇİN ÖN ÇALIŞMALAR Özerciyes, Berker Yüksek Lisans, Kimya Mühendisliği Bölümü Tez Danışmanı: Güngör Gündüz, Prof. Dr. Yardımcı Danışman: Bora Maviş, Yardımcı. Doç. Dr. Ocak 2009, 97 sayfa Zirkonyum tungstat (ZrW2O8), geniş bir sıcaklık aralığında yüksek eş yönlü (izotropik) negatif ısıl genleşme özelliği gösteren bir seramiktir. Sahip olduğu bu üstün özellik, ZrW2O8’i ısıl genleşmenin sorun yarattığı birçok kompozit malzemede kullanabilecek önemli bir aday yapmaktadır. ZrW2O8 genel olarak zirkonyum oksit ve tungsten oksidin 1200°C’de katı hal tepkimeleri sonucu üretilmektedir. Çözelti kimyası yardımıyla, görece pahalı zirkonyum ve tungsten kaynaklarıyla, ZrW2O8’in üretimine yönelik yapılan çalışmalar yapılmış ancak yayınlanan çalışmalarda, çoğunlukla negatif ısıl genleşme özelliğinin nedeni üzerine odaklanılmıştır. Buna karşılık denetlenebilir parçacık boyutu, dağılımı ve morfolojisi üzerine yaygın bir çalışma bulunmamaktadır. Elektro eğirme, polimer çözeltilerinden mikro/nano boyutta lif üretimi için kullanılan görece basit bir yöntemdir. Seramik veya polimer/seramik vi kompozit lifler, seramik öncüllerden veya uygun polimer eklenmesiyle viskozitesi ayarlanmış seramik nano parçacık içeren çözeltilerden, elektro eğirme işlemi sonucu elde edilebilmektedir. Eğirme işleminde kullanılacak seramik öncüller, çöz-pel veya ortak çökeltme teknikleriyle hazırlanabilir. Eğirme sonrası uygulanacak yakma işlemiyle de istenilen seramik lifler elde edilebilmektedir. ZrW2O8 seramik liflerinin üretimine dair, henüz yapılmış bir çalışma bulunmamaktadır. Bu çalışmada, ZrW2O8 öncüllerinin görece daha ucuz ve kolay elde edilebilen başlangıç kimyasallarından (zirkonyum asetat ve tungstik asit) üretimi sağlanmıştır. Deneysel gelişim ve yakılan ürünün saflığına etki eden deneysel değişkenler ayrıntılarıyla incelenmiştir. Çözelti değişkenlerinin (tungstik asidin çözünürlüğü, kimyasal oran ayarlaması, pH ve yaşlandırma etkileri gibi) incelemelerin yanı sıra, saf ZrW2O8 üretimine olanak veren önemli ısıl işlem basamakları gerekçelendirilmiştir. Çalışmada ikincil olarak, geliştirilen yeni öncülün elektro eğirme işleminde kullanıma uygun olup olmadığı incelenmiştir. Poli (vinil alkol) (PVA) yardımıyla viskozite ayarı yapılan öncüllerden, elektro eğirme yöntemiyle polimer/seramik nanolif üretimine yönelik ön çalışmalar gerçekleştirilmiştir. Boncuksuz nano lif hasırların oluşumuna olanak veren uygun PVA derişimi belirlenmiş ve lif üretim hızının arttırılmasına yönelik deneysel düzenek iyileştirmeleri ortaya konmuştur. Elde edilen ürünlerin tanımlanmasında SEM ve XRD yöntemleri kullanılmıştır. Anahtar Sözcükler: zirkonyum tungstat, negatif ısıl genleşme, çöz-pel, çökeltme, seramik lif, elektro eğirme. vii To My Exceptional Family viii ACKNOWLEDGEMENTS I would like to express my sincere gratitude to Prof. Dr. Güngör Gündüz for his expertise, understanding, and patience especially for accepting me as my supervisor and his insightful motivating speech during my thesis research period. I would like to thank my co-supervisor Assist. Prof. Dr. Bora Maviş for his endless helps on many occasions, his great ideas, and numerous helpful discussions. Additionally I would also like to acknowledge Prof. Dr. Üner Çolak for his valuable advice and support. I am very thankful to Korhan Sezgiker and Nasser Khazeni for their great supports in the final experiments and their collaborative manner. I would also like to thank to my laboratory friends Nihan Karakoç, Erkan Biber, Ahmet Göktaş, Burcu Berna Topuz, Gülden Eroğlu, Simge Çınar and Nagihan Keskin for their collaborative, motivating and friendly manner. I would also thank to Seçkin Öztürk and Sedat Canlı from Central Laboratory of METU and Evren Çubukçu and Orkun Ersoy from the Geological Engineering Department of HU, for helping me on SEM analysis and Necmi Avcı from Metallurgical and Materials Engineering Department of METU for helping me on XRD analysis. I also wish thank to Çiğdem Pulatsü for her help supplying the chemicals and equipments on time and Nur Merve Kazaroğlu from Chemical Engineering Department of Hacettepe University for her help in increasing the product efficiency in electrospinning. I would like to thank all of my friends for all their emotional support and motivation during this difficult accomplishment. ix Last but not least, I express my sincere thanks to my family for the support they provided me through my entire life. This work was supported by TÜBİTAK (The Science and Technical Research Council of Turkey) (Project Number: 107M006) and METU (BAP- 2008-03-04-01 – Scientific Research Project). x TABLE OF CONTENTS ABSTRACT……………………………………………………………………………………….iv ÖZ………………………………………………………………………………………………….vi DEDICATION………………………………………………………………………………….viii ACKNOWLEDGEMENTS…………………………………………………………………….ix TABLE OF CONTENTS………………………………………………………………………xi LIST OF TABLES……………………………………………………………………………..xiv LIST OF FIGURES…………………………………………………………………………...xv NOMENCLATURE……………………………………………………………………….….xviii CHAPTER 1. INTRODUCTION……………………………..……………………………………………1 2. LITERATURE