氏名　白井　孝
学位の種類　博士（工学）
学位記番号　博甲第333号
学位授与の日付　平成17年3月25日
学位論文題目　Surface Hydroxides Layer of Commercial High Purity α-Al2O3 Powders Evaluated by Diffuse Reflectance Infrared Fourier Transform （DRIFT） Spectroscopy and Temperature Programmed Desorption Mass Spectrometry （TPDMS）　（昇温脱離質量分析（TPDMS）及び拡散反射フーリエ赤外分光（DRIFT）による市販高純度α-アルミナ粉末の表面水和物層の評価）
論文審査委員
　主査　教授　石崎　幸三
　副査　教授　松下　和正
　副査　教授　佐藤　一則
　副査　助教授　末松　久幸
　副査　助教授　南口　誠

• 論文目次
• 論文要旨

［平成16（2004）年度博士論文題名一覧］ ［博士論文題名一覧］に戻る．

INDEX

Chapter 1:INTRODUCTION　p.1

　1.1　Aluminum Oxide　p.1
　1.2　Production Methods of High Purity α-Al2O3 Powder　p.3
　1.2.1　Hydrolysis of Aluminum Alkoxides　p.3
　1.2.2　Chemical Vapor Deposition　p.4
　1.2.3　Thermal Decomposition of Ammonium Alum　p.4
　1.2.4　Thermal Decomposition of Inorganic Aluminum Salts　p.5
　1.3　Necessity of Grinding in Manufacturing Process for High Purity α-Al2O3 Powder　p.5
　1.4　Alumina Structure　p.6
　1.4.1　Structural Transformations　p.6
　1.4.2　Crystal Structure of α-Al2O3　p.7
　1.4.3　Structure of Transition Alumina　p.8
　1.4.4　Structure of Aluminum Hydroxides　p.10
　1.4.4.1　Gibbsite　p.10
　1.4.4.2　Bayerite　p.11
　1.4.4.3　Nordstrandite　p.12
　1.4.4.4　Boehmite 12
　1.5　Reported Alumina Surfaces　p.13
　1.6　Analysis Methods for Ceramics Surfaces　p.18
　1.7　Scope of Present Dissertation　p.21

Chapter 2:EXPERIMENTAL　p.23
　2.1　Materials　p.23
　2.1.1　As-receive α-Al2O3 Powders　p.23
　2.1.2　Surface Hydration α-Al2O3 Powders by Hydrothermal Treatment　p.25
　2.2　Surface Characterization Methods for this Study　p.26
　2.2.1　Diffuse Reflectance Infrared Fourier Transform （DRIFT） Spectroscopy　p.26
　2.2.1.1　DRIFT Measurement in Dry Air Atmosphere and Vacuum　p.26
　2.2.1.2　DRIFT Measurement at Elevated Temperatures in Vacuum　p.27
　2.2.2　Temperature Programmed Desorption Mass Spectrometry （TPDMS）　p.27
　2.2.2.1　TPDMS System　p.27
　2.2.2.2　Data Collection　p.29
　2.2.2.3　Identification and Quantification of Desorbed Species　p.29

Chapter 3:SURFACE HYDRATED LAYER ON α-Al2O3 POWDERS EVALUATED BY TPDMS AND DRIFT SPECTROSCOPY　p.30
　3.1　Introduction　p.30
　3.2　Results and Discussions　p.31
　3.3　Conclusions　p.40

Chapter 4.EFFECTS OF MANUFACTURING PROCESS ON HYDRATED ABILITY OF HIGH PURITY α-Al2O3 POWDERS　p.42
　4.1　Introduction　p.42
　4.2　Results and Discussions　p.44
　4.2.1　Grinding and Hydration Ability　p.44
　4.2.2　Coordinately Unsaturated Al Atoms　p.51
　4.2.3　Proportion of Coordinately Unsaturated AlV Atoms and Grinding　p.67
　4.3　Conclusions　p.71

Chapter 5:INTERACTION BETWEEN SURFACE HYDROXYL GROUPS AND ADSORBED MOLECULES ON α-Al2O3 POWDERS EVALUATED BY TPDMS　p.73
　5.1　Introduction　p.73
　5.2　Results and Discussions　p.74
　5.3　Conclusions　p.82

Chapter 6:SUMMARY AND CONCLUSIONS　p.84

Chapter 7:REFERENCES　p.87

Research Activities　p.97

Acknowledgments　p.100

In the case of high purity α-Al2O3 powder, the surface may contain an aluminum hydroxide phase, which can also generate surface condition differences in the α-Al2O3 powders. The aluminum hydroxide phase present on the surface sometimes causes some pores in sintered bodies. Therefore, the investigation for hydrati on ability of powder surfaces is very important for ceramic manufacture.
The main objective of the present work is to understand the effects of manufacturing process of commercial high purity α-Al2O3 powders on their surface characteristics.
Commercially available sub-micron high purity α-Al2O3 powders produced by three different processes; in-situ chemical vapor deposition; "A" powders （Sumitomo Chemical Co., Ltd. ）, hydrolysis of aluminum alkoxide; "B" powders （ditto）and thermal decomposition of ammonium alum; "C" powders （Showa Denko K. K. ） methods, are used for this study.
The surface hydration states of three different grades powders manufactured by the hydrolysis of aluminum alkoxide method, which differ each other in SSA, are evaluated by temperature programmed desorption mass spectrometry （TPDMS） and diffuse reflectance infrared Fourier transform （DRIFT） spectroscopy. The presence of hydrogen bonded water molecules, amorphous Al（OH）3 and AlOOH structures, as well as associated and isolated hydroxyl groups on the surface of all the α-Al2O3 powders investigated is demonstrated. On the surface of one of the powders the presence of crystalline Al（OH）3 structures, as evidenced by an additional sharp peak in the H2O TPDMS spectrum, is confirmed. The interaction between surface hydroxyl groups and adsorbed molecules are studied by combining TPDMS and DRIFT spectroscopy techniques revealing differences in the proportion of surface AlIV.
Commercial sub-micron high purity α-Al2O3 powders "A", "B" and "C", are thermally hydrated and the effects evaluated by DRIFT spectroscopy in dry air atmosphere.
From the results, after the hydrothermal process, all the powders ground in the manufacturing process show aluminum trihydroxide, Al（OH）3 peaks on the DRIFT spectra, meanwhile, the not ground powders do not. The surface of powders ground in the manufacturing process is easily hydrated by hydrothermal treatment. Moreover, the state of adsorbed molecular water on the surface of the as-received α-Al2O3 powders are evaluated by DRIFT spectroscopy in atmosphere at room temperature and after heating in situ under vacuum up to 250℃. In the difference spectra, bands centered around 1640, 1580, 1530, 1460 and 1380 cm-1 are interpreted to be related to water molecules, physically adsorbed and coordinated to unsaturated AlVI, AlV, AlIV-AlVI and/or AlVI-AlVI, and AlIV, respectively, that can be desorbed under vacuum up to 250℃. The difference spectra of powders "A" present mainly the band centered around 1640 cm-1, meanwhile powders "B" and "C" show mainly water coordinated bands. The surface proportion of coordinately unsaturated aluminum atoms present on the surface of the powders "B" and "C" is larger than for the powders "A". Furthermore, the surface proportion of uncoordinated Al atoms with coordination V is increased by grinding, besides, these powders show aluminum trihydroxide, Al（OH）3 peaks on the DRIFT spectra after hydrothermal treatment.
The results demonstrate that grinding in the manufacturing process affects the hydration ability of the high purity α-Al2O3 powder surfaces. From the results, the surface proportion of coordinately unsaturated aluminum ions such as AlIV and AlV might be affected by thermal activation and dehydration processes. Additionally, the grinding process specially affects increasing the proportion of coordinately unsaturated AlV. It is possible that the different hydration ability of the powders might be linked to differences in the surface proportion of coordinately unsaturated AlV atoms by different manufacturing processes.
The interaction between surface hydroxyl groups and CO2 adsorbed molecules on powders "A" and "B" were evaluated by TPDMS. The maximum of the CO2 desorption peak is in the range 230 - 270℃ for all powders. This peak is considered to evolve from adsorbed CO2 molecules forming hydrogen carbonyl groups by interaction with AlIV-OH groups on the α-Al2O3 surfaces. The amount of hydrogen carbonyl groups on the surface of the "B" powders is larger than for the "A" powders, indicating that on "B" powder surfaces the amount of AlIV-OH groups is larger.
The difference in coordination number of aluminum ion on high purity α-Al2O3 powders produced by different manufacturing processes evaluated by DRIFT spectroscopy, are in agreement with the these TPDMS results.
It is concluded that the different hydration ability might be linked to differences in the surface population of coordinately unsaturated AlV atoms, resulting from differences in the manufacturing process. The combination of TPDMS and in-situ heating DRIFT spectroscopy techniques used in the present study probed to be useful in the elucidation of the surface states of different α-Al2O3 powders and may be useful in the study of other powder surfaces.