水和酸化物皮膜に覆われたアルミニウムのアノード酸化

IV. 高温水中で生成する水和酸化物皮膜の電場脱水

抄録

Hydroxide films were formed on aluminum specimens by immersing them in water at temperature (T_b) of 100-180°C, and the specimens were then anodized galvanostatically in a neutral borate solution to form composite oxide films. The formation behavior of the hydroxide and composite oxide films were followed by gravimetry, X-ray photoelectron spectroscopy, electron microscopy, and electric capacitance measurements.
It was found that the growth rate of the hydroxide films increased with increasing T_b, and that the hydroxide/metal interface roughened increasingly due to the non-uniform growth of the hydroxide. The water content of the hydroxide (value of X in Al₂O₃·XH₂O) decreased from 2.7 to 1.8 when T_b increased from 100 to 180°C.
The composite oxide films that formed after boiling at different values of T_bS were all composed of an outer crystalline oxide layer (thickness δ_o) and an inner amorphous oxide layer (thickness δ_i), and while δ_i did not depend on T_b, δ_o decreased with increasing T_b. The composite oxide films formed by anodizing to E_a=300V showed thickness/voltage ratios ((δ_o+δ_i)/E_a) of only 1.10 to 0.87nm/V, decreasing with increasing T_b. The capacitance and dielectric loss of the composite oxide films increased with T_b.
The effect of T_b on the formation behavior of composite oxide films is discussed by considering the volume changes caused by the field-assisted dehydration of hydroxide to form a barrier oxide layer.