氏名　郭　露村
学位の種類　博士（工学）
学位記番号　博甲第170号
学位授与の日付　平成10年3月25日
学位論文の題目　Surface and Colloidal Chemistry for Processing of Advanced Alumina Ceramics　（ファインアルミナセラミックスのプロセシングにおける表面コロイド化学）
論文審査委員
　主査　教授　植松　敬三
　副査　教授　松下　和正
　副査　教授　小松　高行
　副査　助教授　内田　希
　副査　助教授　斎藤　秀俊

• 論文目次
• 論文要旨

［平成9（1997）年度博士論文題名一覧］［博士論文題名一覧］に戻る．

Content

1. Chapter I: High-tech Ceramics and Colloid Surface Chemisty －An Overview　p.9
　1.1. New Concept for High-tech Ceramics:－Shaping,a Key Step　p.9
　1.2. Colloid Processing,an Approach for Homogenization　p.9
　1.3. Basic Concepts of Surface Chemistry　p.10
　1.3.1. van der Waals attraction　p.10
　1.3.2. Electrical double layer and repulsion　p.11
　1.3.3. DLVO theory:　p.12
　1.3.4. Non-DLVO interaction and polymer effect　p.13
　1.4. Methods of Stabilizing Ceramics Particles　p.14
　1,5. Polymer Containing Ceramics Suspension System　p.14
　1.6. Aims and Approach of the Investigation　p.15
　1.6.1. Starting point:temperature effect　p.15
　1.6.2. An interesting but unknown phenomenon: saturated-adsorption-dependent-　stabilization　p.17
　1.6.3. Aims and approach　p.17
　1.7. References　p.19
2. Chapter II: Influence of Temperature on Stability of Aqueous Alumina Suspension with Polyelectrolyte　p.21
　2.1. Introduction　p.21
　2.2. Experiment　p.22
　2.3. Results　p.24
　2.4. Discussion　p.28
　2.4.1. Temperature effects on stability　p.28
　2.4.2. Effect of temperature on adsorption:　p.29
　2.4.3. Relation between "coverage" and stability:　p.30
　2.4.4. Mechanism of temperature effects on stability:　p.30
　2.5. Conclusions　p.31
　2.6. References　p.32
3. Chapter III: Adsorption Effects on the Rheological Properties of Aqueous Alumina Suspensions　p.34
　3.1. Introduction　p.34
　3.2. Experiment　p.36
　3.3. Results　p.38
　3.4. Discussion　p.47
　3.4.1. Optimum coverage: adsorbed polymer vs free polymer　p.47
　3.4.2. Impact of adsorption affinity: stabilization with unsaturated adsorption　p.48
　3.4.3. Relations between solids loading and coverage:　p.50
　3.5. Conclusion　p.54
　3.6. Reference　p.55
4. Chapter IV: Heterogeneity of Adsorption and Its Impact on the Stability of Suspension with Polyelectrolyte－Experimental Evidence　p.59
　4.1. Introduction　p.60
　4.2. Hypothesis and Model:　p.62
　4.3. Experiment　p.64
　4.4. Results　p.64
　4.5. Discussion　p.73
　4.5.1. Main factors affecting heterosorption:　p.73
　4.5.2. Impact on stability:　p.75
　4.5.3. Implication for colloidal study and processing:　p.77
　4.6. Conclusions　p.78
　4.7. References　p.80
5. Chapter V Mathematical Model for Estimation of Stability of Suspension with
　Heterogeneous Adsorption　p.82
　5.1. Introduction　p.82
　5.2. Theory and Model　p.84
　5.2.1. An approximate model: the cap model　p.86
　5.2.2. Uneven charge distribution: the UCD model　p.89
　5.3. Results and Discussion　p.90
　5.4. Conclusions　p.96
　5.5. Reference　p.97
6. Chapter VI A New Field: Homogeneity of Adsorption －General Summary　p.100

The ability of controlling the stability of ceramic suspension has been regarded as a key to improve the reliability and performance of ceramic products. For polymer containing system, it poses much more challenge because of the presence of the complicated interactions between polymer, ceramic particles and the media. The present study focuses on investigating these relations and their influence on the stability by the colloidal surface chemistry. Al2O3-H2O-PANH4 is chosen as a model system to study. The main findings of the paper are briefed as follows.
After an overview on the whole landscape of the ceramic processing and its relation with surface and colloidal chemistry in the Chapter I, the paper provides four major chapters describing the investigation in detail.
Chapter II focus on the effect of temperature on stability and adsorption. It shows that the adsorption of dispersant increases with an increase in temperature, and the adsorption saturation limit （plateau level） increases almost lineally with temperature. The increase of adsorption with temperature is responsible for the temperature-dependent stability of this system. At a relatively lower initial concentration in the suspension, the dispersant is insufficient to satisfy the increasing adsorption as temperature increases. Therefore unsaturation adsorption or "poor coverage" results and stability collapses. It is also found that t suspensions could be stabilized with an unsaturated adsorption, i.e., the saturation of adsorption is not necessarily a perquisite for stabilization at certain conditions.
In Chapter III, showing that as the adsorption affinity increased, the minimum coverage required to stabilize the suspension increased accordingly, the study indicated that the adsorption affinity is an important factor in determining the relationship between coverage and stabilization. It is explained that "additional attractive forces" may arise between partially covered particles due to the mutual attraction to satisfy adsorption. For high affinity adsorption, the additional forces are so strong that the saturation of the adsorption is actually required to achieve stabilization. On the other hand, in a suspension of non-high-affinity adsorption, the “additional forces” are too weak to influence the stability.
In order to improve conventional methods of the evaluation of stability, the relation between rheology properties and stability was well studied. It was found that the flow curves of the system follow the Casson model very well up to shear rate of 400 s-1 in observed coverage region.
Therefore, the Casson constants τc and ηc obtained by fitting can be used to evaluate the stability and characterize other rheological properties and behavior. The explored method of evaluation of stability involving rheological study by using the Casson model proves very effective.
Chapter III is the climax of the thesis, where a hypothesis concerning the adsorption state, called heterosorption or heterogeneous adsorption, and its relating concepts are proposed.
According to this concept, if the added polymer is not sufficient to provide saturated adsorption in a suspension, when the adsorption is of high-affinity, the distribution of adsorbed polymer on the particle surfaces can be heterogeneous. At a given coverage （Γ/Γlim<100%）, homogeneous adsorption can lead to good stabilization, while heterogeneous one will cause flocculation.
Adsorption affinity is a key factor in affecting the formation of heterosorption and determining its degree. For a high-affinity adsorption, the adsorption rate can be much greater than that of homogenization of particles with polymer, thus heterosorption is easy to happen.
Heterosorption can be avoided or largely reduced by controlling solution condition to lower adsorption affinity. By this approach better dispersion can be achieved with less dispersant at an unsaturated adsorption condition even if the final solution condition is unfavorable for stabilization.
Chapter V mainly provides theoretical analysis of the problems involved in heterosorption. Two mathematical models are established to describe the potential energy of interaction between particles with heterosorption. One is called the Cap Model （taking bare surface as "a cap" on a spherical particle and the other UCD Model （uneven distribution of charge）. The results of calculation with the two models shows that they can be used in estimation and prediction of the stability of heterosorption system.
Chapter VI gives a general summary highlighting the thesis.