Colloidal Processing for Advanced Alumina Ceramics (先進アルミナセラミックスのためのコロイダルプロセシング)

氏名 Shuwen Jiang(姜 淑文)
学位の種類 博士(工学)
学位記番号 博甲第401号
学位授与の日付 平成19年3月26日
学位論文題目 Colloidal Processing for Advanced Alumina Ceramics (先進アルミナセラミックスのためのコロイダルプロセシング)
 主査 教授 植松 敬三
 副査 教授 高田 雅介
 副査 教授 小松 高行
 副査 教授 齋藤 秀俊
 副査 助教授 内田 希

平成18(2006)年度博士論文題名一覧] [博士論文題名一覧]に戻る.


CHAPTER 1:Overview of the Thesis
 1.1 Motivation of the Work p.1
 1.2 Objectives and Contents p.2

CHAPTER 2:Literature Review
 2.1 Ceramic Manufacture and Colloidal Processing p.4
 2.1.1 The Need of Modern Ceramic Technology -Advanced Ceramics p.4
 2.1.2 Why Colloidal Processing and A Brief Introduction p.5
 2.2 Ceramic Structure Control by Colloidal Approach p.5
 2.2.1 Accesses and Key Points p.5
 2.2.2 Monitoring of Colloidal Stability p.6
 2.2.3 Forming of Colloids p.12
 2.2.4 Research Development and Problems p.13
 References p.14

CHAPTER 3:Characterization of Alumina Powders
 3.1 Introduction p.21
 3.2 Experimental Methods p.22
 3.2.1 Powder General Information p.22
 3.2.2 Characterization Methods p.22
 3.3 Results and Discussion p.23
 3.3.1 Particle Size Distributions and Particle Morphology p.23
 3.3.2 Powder Surface Chemistry p.27
 3.4 Summary of Chapter3 p.33
 References p.33

CHAPTER4:Evaluation of Rheology and Dispersibility of Alumina Colloids
 4.1 Introduction p.36
 4.2 Experimental Procedure p.37
 4.2.1 Raw Materials p.37
 4.2.2 Colloid Preparation p.38
 4.2.3 Colloid Evaluation p.38
 4.3 Results and Discussion p.39
 4.3.1 Rheological Behaviors of the Colloids p.39
 4.3.2 Sedimentation Behaviors of the Colloids p.47
 4.3.3 Zeta potential & pH p.49
 4.3.4 Adsporption isotherms of Ploymers on Alumina Particles p.53
 4.4 Summary of Chapter4 p.56
 References p.58

CHAPTER 5:De-airing of Alumina Colloids
 5.1 Introduction p.60
 5.2 Air Bubble Formation p.61
 5.2.1 Experimental Methods p.61
 5.2.2 Results and Discussion p.62
 5.2.3 Conclusion p.69
 5.3 De-airing in Vacuum p.70
 5.3.1 Experimental Methods p.70
 5.3.2 Results p.71
 5.3.3 Discussion p.82
 5.3.4 Conclusion p.92
 5.4 De-airing with 1-Octanol p.93
 5.5 Summary of Chapter5 p.95
 References p.96

CHAPTER 6:Drying-induced Forming (DIF) Based on Highly Concentrated Alumina Colloids
 6.1 Abstract p.98
 6.2 Introduction p.98
 6.3 Experiments p.100
 6.3.1 Procedure of DIF p.100
 6.3.2 Evaluations p.103
 6.4 Results and Discussion p.104
 6.4.1 Compositional Stability of the Colloid during DIF p.104
 6.4.2 Drying Rate of the Colloid during DIF p.106
 6.4.3 Viscosities of the colloids with glycerol addition p.106
 6.4.4 Green sample by DIF p.111
 6.4.5 Sintering shrinkage of DIF formed Green sample p.114
 6.4.6 Sintered Density, Strength and Defect p.114
 6.5 Conclusion p.118
 References p.118

CHAPTER 7:Summary of the Thesis p.120

List of Publication p.122

Acknowledgements p.124

Appendices p.125

 Colloidal processing has been studied extensively in recent years as a promising way to produce advanced ceramic with excellent properties and near net-shape.
 It is believed that homogeneous structure and high performance of ceramics can be produced reliably through proper control of initial colloidal "structure" and its evolution during forming. There still needs a better understanding of these two critical steps for improving ceramic quality and the reliability in engineering applications.
 This work aims to get a better understanding and more efficient control of colloidal homogeneity and the colloidal "structure" transfer during forming, in order to achieve defect-free microstructures and excellent properties of ceramics. The widely used aqueous alumina colloids were taken as an example, and ammonium poly-(acrylic acid) was used as dispersant to disperse the ceramic particles.
 Firstly, various types of commercial alumina powders were carefully characterized through SEM, XRD,XPS,ICP and FT-IR, etc. since powder characteristics (e.g., size, shape and surface chemistry) are one important part of colloidal systems and affect colloidal properties. Secondly, colloidal dispersibility and stability as well as the rheological properties were examined and evaluated by taking into account the effect of basic parameters of colloidal preparation, i,e., powder characteristics, solid content and dispersant concentration. Different alumina powder systems and various evaluation techniques (e.g., zeta potential measurement, viscosity measurement, sedimentation test, measurement of polymer adsorption isotherms) were applied to verify the findings and clarify the problems. The results indicate that not only the properties and dosage of dispersant, but also the characteristics of solid particles play an important role in determining colloidal properties such as flowability, diapersibility and maximum solid content. Thirdly, an important but yet ambiguous topic in colloidal processing-air buddle problem were studied systematically concerning with bubble formation and de-airing for enhancing colloidal homogeneity and reducing defects in compacts. It was found that powder characteristics and solid loading affected bubble stability greatly and thus determined bubble content in the suspensions The bubble content was obviously increased with increasing solid loading, as well as using powders of high specific surface area in both as-prepared and de-aired suspensions.
 No noticeable change in bubble content was resulted from varying the dispersant concentration. The stabilization mechanism of air bubbles in the suspensions is arrangement in suspension bulk, and the increased strength of bubble films at the suspension surface. A new parameter, Solid Surface Area per Unit Volume Suspension, has been introduced to interpret these effects of powders on bubble stability. Finally, A new drying-induced forming (DIF) of ceramics has been developed using high solid-loaded alumina colloids with addition of glycerol, in which the suspension was simply dried in an open mold at the ambient condition. The DIF approach is facilitated by the high stability of concentrated slurries during drying where glycerol was added to maximize the critical solid loading and play simultaneously as a drying control agent. The drying and rheological behaviors of suspensions were examined with respect to the glycerol addition. A slurry of 60 vol.% solid loading with 20 wt.% glycerol addition was chosen for the DIF test. The green samples exhibited no bending or cracks, and a small degree of shrinkage anisotropy during sintering. The sintered samples showed a high relative density of 99.2% and an average strength of 420 MPa. We demonstrated here a possibility of producing near-net shaped and bulk ceramic components in a simple scheme by using the DIF approach.
 This study reveals the great significance of colloid and forming control in improving ceramic performance. The possible influential factors that could affect the ceramic particle packing density and homogeneity were evaluated and discussed systematically which provide necessary and better understanding of colloidal processing for improving the final product quality.

 本論文は、「Colloidal Processing for Advanced Alumina Ceramics (先進アルミナセラミックスのためのコロイダルプロセシング)と題し、7章より構成されている。
第1章「Overview of the Thesis」では、セラミックスにおけるコロイダルプロセシングの概要とセラミックス製造における意義を示し、本研究の目的と範囲を述べている。
 第2章「Literature Review」では、従来の研究についての広範囲な調査を行い、セラミックスの工学分野に占める位置付け、コロイダルプロセッシングに関する従来の多岐にわたる研究成果をまとめている。
 第3章「Characterization of Alumina Powder」では、研究に使用する3種類のアルミナ粉体について、それらの種々の粉体特質を調べ、粉体の表面基やゼータ電位等の表面化学的特質、バルクの化学的特質である不純物、ならびに表面積、粒径とその分布等の物理的特質が、その粉体の製造法により著しく異なることを明らかにしている。
 第4章「Evaluation of Rheology and Dispersibility of Alumina Colloids」では、粉体に分散剤を添加してスラリーを調製し、その分散性とレオロジーを調べ、粉体特質との関連を明らかにしている。
 第5章「De-airing of alumina Colloids」では、スラリー中の気泡について、その安定性を表面科学的に論じるとともに、脱気処理によるその除去を調べている。スラリー中の気泡の一部は極めて安定であり、大気中では、長時間後にもその量は殆ど変化しないこと、また脱気処理を行った場合でも全量の半分程度はスラリー中に残留するを明らかにしている。
 第6章「Drying-induced Forming(DIF)Based on Highly Concentrated Alumina Colloids」では、グリセリンの添加が粉体の分散性を著しく向上させることを見出し、この現象を新しい成形法と新規セラミックス製造法の開発に利用している。すなわち、本法では粉体を高濃度に含むスラリーを調製し、これを所望の形状の鋳型に流し込み、乾燥させることにより成形体を得ている。さらに、この成形体を焼成して、高密度・高強度のセラミックスの調製に成功し、本コロイダルプロセシングが高性能セラミックスの製造に極めて有用であることを示している。
 第7章「Summary of the Thesis」では各章の成果をまとめ、論文を総括している。