Fabrication of a Novel Nanoporous Film via Chemical Dealloying of a Cu–Cr Alloy for Sensing Moisture in Oil

Based on our prior combinatorial analysis aimed at materials discovery, Cu
₈₂
Cr
₁₈
and Cu
₈₀
Cr
₂₀
were selected in chemical dealloying experiments as candidates for incorporation in sensors for the first time. The Cu
₈₂
Cr
₁₈
film was Cu-dealloyed, altering its composition to Cu
₂₅
Cr
₇₅
after 7 min of dealloying. The dealloyed Cu
₈₂
Cr
₁₈
film exhibited a Cr-based nanoporous structure with 20-40-nm-diameter pores, indicating that Cu was sufficiently dealloyed. In contrast, the Cu
₈₀
Cr
₂₀
film could not be sufficiently Cu-dealloyed, which was consistent with the results of the combinatorial analysis; the original composition was changed to Cu
₄₆
Cr
₅₄
after 7 min, and the pores were not visible. Sensors A and B were fabricated via chemical dealloying of Cu
₈₂
Cr
₁₈
and Cu
₈₀
Cr
₂₀
, respectively, and they were evaluated with respect to a reference sensor in both air and oil. The measured hysteresis in the air was 7.4% full scale (FS) for sensor A, which was below the acceptable limit of 10.0% FS, whereas that for sensor B was 13.3% FS. Moreover, the 90% response time in oil was 8 min for sensor A and 10 min for sensor B, as compared to 12 min for the reference sensor; thus, the response time of sensor A was below the acceptable limit of 10 min.