Controlling porosity and pore size distribution in green ceramics bodies via Freeze-casting method

Transcription

1 Controlling porosity and pore size distribution in green ceramics bodies via Freeze-casting method DISSERTATION zur Erlangung des akademischen Grades Doktor-Ingenieur (Dr.-Ing.) genehmigt durch die Mathematisch-Naturwissenschaftlich-Technische Fakultät (Ingenieurwissenschaftlicher Bereich) der Martin-Luther-Universität Halle-Wittenberg von Herrn Dipl.-Ing. Danail Donchev geb. am in Kazanlak / Bulgarien Dekan der Fakultät: Prof. Dr. habil. Altenbach Gutachter: 1. Prof. Dr. habil. Ulrich 2. Prof. Dr. König Halle (Saale) urn:nbn:de:gbv: [

2 Acknowledgments My grateful appreciation to my supervisor, Prof. Dr-Ing. habil. Joachim Ulrich for his help, guidance and a continued encouragement, which not only account for a major part of my knowledge but also strongly fuel my interest in direction crystallization and ceramic materials as this thesis shows. I would like to thank Prof. König for serving and helpful referring on my thesis. I would also like to thank Prof. Rogendorf for serving as the Chairman of the Ph.D. defense committee. I am grateful to Martin-Luther-University Halle-Wittenberg, especially Engineering Department, for admitting me as a graduate student in To me, M.L.U. is a very special place, and I thank all those who contribute to and are in stewardship of this unique and friendly environment. I acknowledge the DFG Fellowship for providing financial support during my Ph.D. study. I would like to thank Dr. L. Andresen, Dr. D. Koch and Prof. G. Grathwohl for their hospitality during my visits to the Bremen University, where I learned the techniques of Freeze-casting. I would like to thank Dr. Diter Möring for his support, fruitful discussions and camaraderie. I would like to thank Dr. Jung-Woo Kim, Dr. Tero Tahti and Dr. Jun-Jun Lu, you are all wonderful friends. I will always remember the many happy occasions and what I learned from you. I would like to thank all previous and present members of TVT group for their help during my studying. I must thank my dear wife Venelina who has supported me during the years. Special thank to my two kids Simona and Pavlin for their obedience during my study. I thank my mother, father, sister and grandmother for their fortitude and encouragements that helped build my character and stimulated my interest in science since childhood.

3 Table of contents 1 Introduction 1 2 Technical background and theory Nucleation Homogeneous Nucleation Heterogeneous Nucleation Active Site Nucleation Crystal growth Theory of crystal growth Crystal growth kinetics Porosity and pore size distribution Open, close, and total porosity Pores characteristics Methods and techniques for production of porous ceramics Methods for characterizing porous ceramic materials Freeze-casting. Bases and principles Colloidal systems. Introduction Freeze-casting Materials and Experimental Setup Materials Experimental procedure and setup 26 4 Instrumentation 29 5 Results Rheology Density Viscosity Nucleation and Crystal growth Nucleation Roughness of the cooling plates Contact angle Surface tension of suspensions Interfacial tension, suspensions-cooling plate 43 - i -

4 Nucleation kinetic Determination of freezing and melting 56 temperatures Cooling curves Melting points Crystal growth rate Influence on crystal growth rate in dependence of 61 the volume fraction of solids Influence on crystal growth rate in dependence 63 on cooling plate materials and properties Influence on crystal growth rate in dependence 64 of moulding form materials and properties 5.3 Porosity and pore size distribution Porosity Porosity dependence of solids load content Porosity dependence of freezing temperature Porosity in dependence of cooling plate materials Porosity in dependence of moulding form 71 materials Pore size distribution Pore size distribution in dependence of solid load 74 content Pore size distribution in dependence of freezing 76 temperature Pore size distribution in dependence of cooling 78 plate materials Pore size distribution in dependence of moulding 79 form materials 6. Discussions Discussions of rheological properties on the starting slurries and 81 the dependence on porosity as well as the pore size distribution 6.2 Discussions on contact angle, interfacial tension and nucleation 86 kinetics 6.3 Porosity and pore size distribution 95 - ii -

5 7. Conclusions Zusammenfassung List of Symbols Appendix References - iii -