X-ray Photoelectron Spectroscopy studies have shown that acetone, when used as a cleaning agent for copper in the presence of ambient light and water vapor, slowly reacts to form acetic acid. This reaction does not occur in the absence of light. This suggests that copper acts as a photocatalyst for the reaction between acetone and water vapor. The use of acetone for degreasing copper and copper containing alloys as recommended by ASTM E1078-97 is questioned in this work.

Copper reacts photochemically with acetone and water vapor to form acetic acid. The acetic acid then reacts with copper to form copper acetate. Over a period of 18 hours the copper foil that was immersed in acetone and exposed to ambient light developed blue crystal deposits as shown in the optical photomicrograph in Fig. 1(left). The acetone in the beaker had evaporated leaving behind a strong odor of acetic acid. In contrast, there were no visible changes observed on the copper foil that was exposed to acetone in darkness as shown in Fig. 1(right). The acetone in the beaker in this case had evaporated, leaving behind no distinguishable odor of any byproduct. The decomposition of acetone appears to be completely inhibited in darkness. The following reaction sequence was proposed:

CH3COCH3 + H2O CH3COOH + CH4

2(CH3COOH) + Cu Cu(COOCH3)2 + H2

CH3COOH (aq.) + e- CH3COO- (aq.) + 1/2 H2

Cu(CH3COO)2 + Cu(0) 2 Cu(CH3COO)

Acetone should not be recommended for degreasing or cleaning of copper or copper bearing alloys containing discrete copper rich intermetallic particles. Though ASTM E1078-97 "Standard Guide for Specimen Preparation and Mounting in Surface Analysis" recommends that prior to surface analysis samples should be ultrasonically degreased in analytical grade acetone and isopropanol, based on this work acetone is not recommended to be used for degreasing copper or copper containing alloys. Also one of the other studies performed in this lab has shown that isopropanol has no such effects on copper, and hence we recommend the use of isopropanol alone for degreasing.