氏   名
つぉん ぺいほん
CONG Peihong
本籍(国籍)
中国
学位の種類
博士(工学)
学位記番号
工博 第 59 号
学位授与年月日
平成 14年 3月 23日
学位授与の要件
学位規則第4条第1項該当 課程博士
研究科及び専攻
工学研究科 物質工学専攻
学位論文題目
Relationship between Tribochemical Reactions and Tribological Characteristics of Ceramics under Fluorine-containing Gases
(含フッ素化合物雰囲気におけるセラミックスのトライボ化学反応とトライボロジー特性に関する研究)
論文の内容の要旨

 Advanced engineering ceramics have good prospects for tribological applications because they possess high thermal stability, chemical inertness and very good wear resistance. In order to use the excellent properties of ceramic materials fully, it demands to understand the quantitative relationship between the surface chemical characteristics and the tribological characteristics. In this thesis, a tribometry connected with a surface spectroscopy (X-ray Photoelectron Spectroscopy, XPS) is used. The apparatus permits friction tests to be carried out in a well-controlled atmosphere and the surfaces to be analyzed after testing without exposure to air. The lubricating effects of hydrofluorocarbon gases, and the role of the tribochemical products on the tribological properties of ceramics have been investigated. The following main conclusions have been obtained.

  1.  When Al2O3 ceramic slides under HFC-134a (CF3CH2F) environment at different gas pressures and sliding speeds, AlF3 and AlOxFy, which have lubricity, are formed on the friction surfaces. When the quantity of the fluorides is above a certain value, the wear mode of Al2O3 ceramic changes from high mechanically dominated wear to lower tribochemically dominated wear.

  2.  Chemical bonding and ceramic combination significantly influence both the tribological properties and the tribochemical products when ceramics rub in HFC-134a gas. The friction and wear of ionic ceramics are lower than that of covalent ceramics, which result from the higher covering concentration of tribochemical products on the ionic ceramics. It is suggested that active Lewis acid sites and radical sites are produced on the friction surface of ionic and covalent ceramics, respectively. HFC-134a is liable to decompose at the Lewis acid sites, and the olefin formed polymerizes easily at the radical sites.

  3.  The tribochemical reactions on the frictional surface of ceramics in fluorocarbon gases are controlled by the presence of hydrogen atom in the surrounding molecules. The ceramics show the highest friction and wear in CF4, which is lest reactive compared with other hydrofluorocarbon gases. Hydrofluorocarbon molecules with higher reactivity correlate to higher friction and wear, which can be due to the severe corrosive wear of the ceramics under high reactive environments.

  4.  A study on the chemical wear map of ZrO2 ceramic in HFC-134a gas indicates that the products of tribochemical reactions and the friction-wear properties are strongly dependent on the operating conditions. Transitions to high wear are controlled by load and sliding velocity. ZrO2 ceramic exhibits high chemical wear under high loads and low velocities. ZrOxFy compounds that are the intermediates of fluorination reaction of ZrO2 correlate to the lowest friction and wear. ZrO2 ceramic is suitable to be used at moderate load (1.3〜2.5 N) and moderate velocity (> 0.15 m/s) under reactive environment.

 As above, this study has fundamentally investigated the relationship between the tribochemical products and the tribological characteristics under fluorine-containing gases, and has established the chemical wear map of ceramic under reactive environment. This research is important and necessary for understanding the tribochemistry of ceramic materials, and will save much time and effort that now goes into trial-and-error testing.