Since the oligomer state of the coupling agent plays an important role in the hydrophobicity of inorganic oxides, various factors affecting the time variation in the average polymerization degree, determined through GPC analysis of preliminary treatment solution and water content determined by the Carl-Fisher method, were studied for the VTES or VTMS-Alcohol-H2O system. The main findings obtained are as follows: (1) The existence of a close relationship between the decreasing rate of the coupling agent monomer and time variation of the height of GPC elution peaks for polymer was qualitatively detected. (2) Time variation of polymerization degree determined from water content of the preliminary treatment solution is intimately related to the progressive rate of oligomer formation reaction. (3) Decreasing rates of water concentration in the preliminary treatment solution were increased by the increase in the initial water concentration, decrease in the alcohol concentration as well as the pH value of the aqueous solution and the elevation of temperature and lowered by the sequence MeOH, EtOH and i-PrOH.
The crystal structure and chemical state of the surface of electrodeposited Zn-Fe-Cr coating were investigated by X-ray diffraction and XPS. The X-ray diffraction patterns of Zn-Fe-Cr deposits with different compositions indicated that the crystal structure of electrodeposited Zn-Fe-Cr coating was almost the same as that of electrodeposited Zn-Fe coating. The X-ray photoelectron spectra of the Zn-Fe-Cr deposit with 70.3 mass% Fe -6.5 mass% Cr obtained after Ar sputtering showed that the surface layer of the deposit consists of oxide or hydroxide, while the ratio of metallic elements gradually increased inside of the surface layer. This interesting structural feature of electrodeposited Zn-Fe-Cr coating can be explained by the deposition mechanism such as a hydroxide suppression mechanism and an induced co-deposition by iron-group metals proposed previously.
The behavior of anodic film growth on magnesium and magnesium alloys in sodium hydroxide solution was investigated with a focus on the effects of substrate composition, formation voltage, and aluminum addition. In the range of formation voltage between 2V and 110V, barrier films or semi-barrier films were formed except at around 5V and breakdown voltage. At the latter voltages, a porous type film was formed. The critical voltage of high current flow accompanied by breakdown was considerably dependent on substrate purity; namely, 60V for 99.6% Mg, 90V for AZ 31B, and 100V for AZ 91 D and 99.95% Mg. A peculiar phenomenon of high current density at around 5V may be caused by trans-passive state, similar to that associated with alkaline fluoride solution. The peak current at 5V decreased with increasing aluminum content of the substrates. These phenomena can be explained by the effects of aluminum incorporation into the film to prevent dissolution and to promote passivation of magnesium. When 1mol·dm-3 AlO2-ion was added in the electrolytes, the critical voltage of 99.95% Mg increased to 110V. The depth profiles of constituent elements showed that aluminum was distributed throughout the whole depth of the film. The atomic ratio of aluminum to magnesium increased with increasing voltage to attain an atomic ratio of approximately 2/3 at 100V and crystalline MgAl2O4 was found in the film.
Diamond surface reforming was performed using silane coupling reagents. Oxidation reaction with inorganic acid was utilized as the pretreatment of the diamond substrate. After the silane coupling reaction process, new peaks assigned to the silane coupling reagent appeared in the IR spectra. Moreover, the diamond surface property changed from hydrophilic to hydrophobic with the treatment of n-octyltrimethoxysilane. From the results of this study, it was confirmed that silane coupling reagents are effective for diamond surface reforming.