氏名　プルワディ　ラハルジョ
学位の種類　博士（工学）
学位記番号　博甲第206号
学位授与の日付　平成12年3月24日
学位論文の題目　Moist Labi1ity of Submicron High Purity α-Alumina Powders（サブミクロン高純度α一アルミナ粉末の湿潤不安定性）
論文審査委員
　主査　教授　石崎　幸三
　副査　教授　小松　高行
　副査　助教授　斎藤　秀俊
　副査　助教授　佐藤　一則
　副査　新潟大学　助教授　堀田　憲康

• 論文目次
• 論文要旨

［平成11（1999）年度博士論文題名一覧］ ［博士論文題名一覧］に戻る．

Acknowledgements
Abstract
List of Figures
List of Tables
1. Introduction　p.1
1.1 Production of Alumina　p.3
1.2 High Purity Alumina　p.3
1.3 Problems in Powder Quality Control　p.5
1.4 Purposes and Outline of This Study　p.6

2. Alumina Structures and Surfaces　p.9
2.1 Alumina Structures　p.9
2.1.1 Structural Transformations　p.9
2.1.2 Crystal Structure of Alpha Alumina　p.9
2.1.3 Structure of Transition Aluminas　p.11
2.1.4 Structure of Aluminum hydroxides　p.12
2.1.4.1 Gibbsite　p.12
2.1.4.2 Bayerite　p.13
2.1.4.3 Nordstrandite　p.13
2.1.4.4 Boehmite　p.14
2.2 Alumina Surfaces　p.14

3. Surface Evaluation by Using Cryogenic Specific Heat Measurements　p.21
3.1 Introduction　p.21
3.2 Experimental　p.22
3.3 Results and Discussion　p.23
3.4 Conclusions　p.28

4. Surface and Bulk Characterization of As-received α-Alumina Powders　p.31
4.1 Introduction
4.2 Bulk Analysis
4.2.1 Influence of Particle Shape on the FTIR Spectra in the One Phonon Region　p.32
4.2.1.1 Experimental　p.33
4.2.1.2 Results　p.34
4.2.1.2.1 FTIR Transmission Results　p.34
4.2.1.2.2 SEM Observation Results　p.34
4.2.1.3 Discussion　p.34
4.2.1.3.1 Comparison with Reported Spectra in the Literature　p.34
4.2.1.3.2 Theoretical Spectrum for Nearly Spherical Shape α-Al2O3 Particles　p.38
4.2.1.4 Summary　p.41
4.2.2 Bulk Analyses by FTIR and XRD　p.41
4.2.2.1 Experimental　p.42
4.2.2.2 Results and Discussion　p.42
4.2.2.3 Summary　p.46
4.3 Surface Analysis　p.46
4.3.1 Experimental　p.47
4.3.2 Results and Discussion　p.47
4.3.3 Conclusions　p.59

5. Hydration and Dehydration Process of the α-Alumina Powders　p.63
5.1 Introduction　p.63
5.2 Experimental　p.63
5.3 Results and Discussion　p.64
5.3.1 Dehydrated Powder Spectra　p.64
5.3.2 Rehydrated Powder Spectra　p.66
5.3.3 Hydrated Powder Spectra　p.67
5.3.4 Comparison of Hydration Ability in Commercial As-received Powders　p.69
5.4 Summary　p.72

6. Effects of Surface Hydration on Alumina Powders Characteristics　p.75
6.1 Introduction　p.75
6.2 Experimental　p.76
6.3 Results and Discussion　p.77
6.4 Conclusions　p.85
7. Summary and Conclusions　p.87

Research Activities

　As frequently found in industrial problem, the behavior differences in raw powder will lead to different quality in the ceramic products. Therefore, controlling quality of raw powder is indispensable in the future ceramic industries.
　Surface hydration of alumina powders is an important parameter, which may influence the physical behavior of the raw powders. For the first time, in this study the surface hydration of commercial high purity submicron α-alumina powders is observed with different behavior from the lot to lot of the powders even in the same codification powders. Hydration in the alumina surface of the high purity alumina powders is also revealed in the excess entropy of the powders measured by cryogenic specific heat measurements. Comparison of three types of commercial high purity alpha alumina powders produced by different processes: in-situ chemical vapor deposition （A powders）, hydrolysis of aluminum alkoxide （B powders）, and a pioneer chemical vapor deposition （no longer in the market） （C powder） methods evaluated by FTlR （Fourier transform infrared） transmission and Diffuse Reflectance Infrared Fourier Transform （DRIFT） spectroscopy suggest that the surface characteristics of as-received high purity alpha alumina powders are not the same for all high purity alpha alumina powders. In some of the B powders with small size, a mixture of aluminum trihydroxides （gibbsite, bayerite, and norsdtrandite） like bands is observed. A specific band at 3472 cm-1observed on the B and C powders does not belong to band spectra of the aluminum hydroxide references. Relating to the predicted band on infrared spectra of hydrated alpha alumina surface obtained from reported molecular dynamics calculation, this band is associated with hydrogen bonded hydroxyl groups of a fully hydroxylated alpha alumina surface.
　Powder characteristics after hydration and dehydration of high purity alpha alumina powder are evaluated from the results of BET specific surface area, particle size distribution, DRIFT, XRD, SEM analyses. Water steam hydration of high purity submicron α-alumina powder causes formation of large particle size powder （higher than 0.5μm） through a process of hard agglomeration of the powder particles. Consequently, the hydration process also influences the BET specific surface area to become smaller than non-hydrated powder. Hydration for 100h decreases the specific surface area from 9.4m2/g to a value of 8.9 m2/g （about 5%）. Particle size distribution of the powder changes after hydration or dehydration process. The amount of 0.2 μm particle size fraction in the as-received powder decreases, and the 0.6 μm fraction increases after a 40h hydration period and large fractions of 1-6 μm particle size are generated after dehydration of as-received powder.
　The general conclusion is that surface hydration of α-alumina powders is a time dependent dynamic process, with different behavior depending on the production condition. The surface hydration can significantly influence the powder characteristics. The author suggests that powder storage humidity conditions should be taken into consideration during handling of submicron α-alumina powders. The hydration method implemented in this study together with DRIFT powder surface characterization also could be useful for a quality control method to evaluate submicron high purity α-alumina powders.