氏名　Tran Thi Thu Hien
学位の種類　博士（工学）
学位記番号　博甲第347号
学位授与の日付　平成17年08月31日
学位論文題目　Commercial Silicon Nitride Powder Surfaces Analyzed by Diffuse Reflectance Infrared Fourier Transform （DRIFT） Spectroscopy and X-ray Photoelectron Spectroscopy（XPS）　（市販窒化ケイ素粉末表面の拡散反射フーリエ変換赤外線分光（DRIFT）とX線光電子分光（XPS）による解析）
論文審査委員
　主査　教授　石崎　幸三
　副査　教授　新原　皓一
　副査　教授　佐藤　一則
　副査　教授　斎藤　秀俊
　副査　産業技術総合研究所　渡利　広司

• 論文目次
• 論文要旨

［平成17（2005）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　Silicon NItride（Si3N4）　p.1
　1-2　Nature of Silicon Nitride Powder Surfaces as Reported　p.3
　1-2-1 Surface Layer Thickness　p.3
　1-2-2 Surface Oxygen Content　p.4
　1-2-3 Surface Layer Composition　p.7
　1-2-4 Surface Groups　p.11
　1-3　Importance of Powder Surface Characteristics and Their Influences on the Mechanical Properties of Sintered Si3N4 Bodies　p.16
　1-4　Scope and Contents of the Present Dissertation　p.18

Chapter 2　EXPERIMENTAL　p.20
　2-1　Materials　p.20
　2-2　Diffused Reflectance Infrared Fourier Transform （DRIFT） Spectroscopy
　2-2-1 Principle　p.21
　2-2-2 Experimental System and Conditions　p.22
　2-3　X-ray Photo-election Spectroscopy（XPS）　p.23
　2-3-1 Theory　p.23
　2-3-2 XPS Instrument Operation　p.24
　2-3-3 Experimental Conditions　p.25

Chapter 3　SURFACE GROUPS ANALYZED BY DIFFUSE REFKECTANCE INFRARED FOURIER TRANSFORM（DRIFT） SPECTROSCOPY　p.27
　3-1　NHX/OH Stretching Absorbance Bands （4000-2500cm-1）　p.27
　3-1-1 Wave Numbers Range of NHX/OH Stretching Bands Reported for Different Silicon Compounds　p.27
　3-1-2 OH/NHX Groups　p.28
　3-1-2-1 NH and NHX groups　p.32
　3-1-2-2 OH groups　p.35
　3-2 SiHx Stretching Absorbance Bands （2300-2000cm-1）　p.37
　3-2-1 Wave Numbers Range of SiHx Stretching Bands Reported for Different Silicon Compounds　p.37
　3-2-2 SiHx groups　p.38
　3-3 Agreement Between Absorbance Intensitied of O and NH Related Bands in both Stretching Regions　p.48
　3-4 Effects of Manufacturing Process on the Proportion of Surface Groups for the Different Si3N4 powders Investigated　p.48
　3-5 Summary　p.49
　3-5-1 NHx/OH Groups　p.49
　3-5-2 SiHx Groups　p.50

Chapter 4　SURFACE STRUCTURE ANALYZED BY X-RAY PHOTOELECTRON SPECTROSCOPY（XPS）　p.52
　4-1 Reported Binding Energy for Different Silicon Compounds　p.52
　4-2 Binding Energy Calculation　p.53
　4-3 Most Outer Surface Layer Structure　p.54
　4-4 Surface Components After 5 Second Etching Period　p.62
　4-5 Surface Components After 10 Second Etching Period　p.68
　4-6 Agreement Between Independent Signals　p.74
　4-7 Fractions of NH2, OH and O Related Configurations　p.75
　4-8 Summary　p.83

Chapter 5　SUMMARY AND CONCLUSIONS　p.84

ACKNOWLEDGEMENTS　p.87

REFERENCES　p.88

RESEARCH ACTIVITIES　p.1

　Silicon nitride is one of the most promising ceramic materials for high temperature structural applications. A major technical issue in the processing of these ceramic materials is the sinter ability of the silicon nitride starting powders. Since the sinter ability depends on the surface features of the powder particles at the sintering temperature, it is therefore important to clarify the nature of Si3N4 powder surfaces.
　The objective of the present work is to investigate about the surface layer structure state of silicon nitride powders by combining two different analytical techniques; diffuse reflectance Fourier transform infrared spectroscopy （DRIFT） and X-ray photoelectron spectroscopy （XPS）. The reported results obtained by temperature programmed desorption mass spectroscopy （TPDMS） of the same powders are also used in the discussions. So far as the knowledge of the author, this thesis is the first extensive attempt to understand the silicon nitride powder surface layer structure. The surface structures of seven commercial Si3N4 powders produced by three different processes （diimide precipitation （A）, carbothermal reduction （B） and nitridation of silicon （C）） and four nitriding media （NH3 gas （A2, B2）, NH3 liquid （A1）, N2 gas （B1, C4） and mixture of N2 + H2 gas （C5, C6）） with different final treatments （C4, C6） were investigated. The effects of nitriding media and further acid treatment during the manufacturing process on the surface structure of the Si3N4 powders were discussed.
　Surface OH, NHx and SiHx groups were observed for all the seven commercial Si3N4 powders but in different proportions and tetrahedral configurations.
　There is good agreement between the FTIR results of this work with the kinds and amounts of desorbed molecules measured by TPDMS. For five of the powders （A, B and C4） the intensity of the NH groups is in good agreement with the amounts of N2 desorbed molecules above 1300℃. The powder produced by diimide process using NH3 gas as nitriding media （A2） shows the highest NH surface groups content and the one produced by carbothermal reduction using N2 （B1） the lowest.
For all of the Si3N4 powders the intensity of the NH2 bands identified and quantified by DRIFT （this work） correlates with the amounts of NH3 molecules desorbed below 1300℃measured by TPDMS. The powder produced by the carbothermal reduction and nitridation process using NH3 gas as nitriding media exhibits the largest amount of NH2 surface groups and desorbed NH3 molecules. For all the powders the fraction of infrared OH group absorbance intensity to the total OH+NHx absorbance intensity measured by DRIFT in this work has a linear correlation with the fraction of desorbed H2O to the total amount of desorbed molecules measured by TPDMS. It is shown that the powder produced by the carbothermal reduction process using N2 as nitriding media （B1） shows the highest OH absorbance intensity and desorbed H2O molecules fraction. The powder produced by direct nitridation of silicon using a mixture of N2 + H2 as nitriding media and acid washed as final treatment （C6） shows the least. All other powders fall in between.
　The wave numbers of the H-Si absorption bands obtained by deconvolution of the spectra show the presence of tetrahedral units with different atoms （O, N, Si, H） and groups （NH, NH2, OH） configurations, which bond to the same silicon atom.
　The combination of these different tetrahedral units in different proportions makes the surface layer composition of Si3N4 powders very complex and different for each powder. Six powders present the largest fraction of H-Si groups linked to Si rich tetrahedra. Only in the case of the powder produced by the carbothermal reduction process using N2 as nitriding media （B1） are linked to O rich tetrahedral units.
　Surface layer structures were also characterized by XPS measurement. All the Si3N4 powders present tetrahedral structures （Si-XYZW） with different atoms （Si; H; N; O） and groups （NH; NH2; OH） configurations that bond to the same silicon atom in agreement with the DRIFT results. For five out of the seven Si3N4 powders （A, B and C5） the two main tetrahedra present on the most outer surface layer are Si-SiSiN（OH） and tetrahedral containing O; Si-O（NNN; SiSiH; SiNN; NNO）. The two powders produced by nitridation of silicon with HF acid washing in the final treatment （C4 and C6） present Si-SiSiN（NH2） and tetrahedra containing OH; Si-SiN（Si; N）（OH）. The powder produced by carbothermal reduction process using NH3 （g） presents the highest fraction of O containing tetrahedra. After 5 second etching the composition of the powder produced by nitridation of silicon using a mixture of N2 + H2 as nitriding media with acid washing （C6） does not considerable change but for the other powders does. Instead of Si-SiSiN（OH） all powders present Si-SiSiN（NH2） tetrahedra and the proportion of tetrahedra with O increased for B1, decreased for B2 & C5 and almost did not change for the A1 and A2 powders. The composition of all powders changed after 10 second etching. Instead of NH2 groups configuration as at 5 second etching they show NH groups configurations Si-SiN（Si; N）（NH）. All powders show O containing tetrahedra, including C6. In the washed powders C4 and C6 the tetrahedra are different than in the other powders.

The fraction of OH groups containing configurations without etching for all powders correlates with the fraction of desorbed H2O molecules below 750℃ measured by TPDMS and the total fraction of OH groups containing configurations obtained from 0 to 10 sec etching time measured by XPS correlates with the fract ion of infrared OH groups absorbance intensity to the total OH+NHx absorbance in tensity measured by DRIFT. Also there is good agreement between the fraction of NH2 containing configurations ［NH2/（OH+NH2） obtained from 0 and 5 s etching time and the fraction of NH3 desorbed molecules ［NH3/（ H2O+NH3）］ from TPDMS measurements.
　It is concluded that the surface of Si3N4 powders for any production method can not be regarded as having a composition close to SiO2, Si2N2O or an intermediate between them as commonly accepted. The surface is composed of a mixture of Si-XYZW tetrahedral units with different atoms （Si; H; N; O） and groups （OH; NH; NH2） configurations that bond to the same silicon. The combination of those different tetrahedral units in different proportions makes the surface layer composition of the powders very complex and different in each powder.