Phosphorescence and Tarnish Resistance Properties of Copper with Strontium Aluminate Addition

The purpose of this research is to examine the effect of strontium aluminate (SrAl2O4) in copper samples on phosphorescence and tarnish resistance properties. The samples were fabricated by powder metallurgy using the compression moulding technique and then sintered in argon atmosphere. Phosphorescence, hardness, microstructure and tarnish resistance were studied. In the process of the compression moulding, the samples contain 100, 90, 80 and 70 percent of copper powder, by weight, with the addition of 0, 10, 20 and 30 percent of strontium aluminate, by weight, respectively. Polyvinyl alcohol (PVA) was used as a binder and mixed with copper and strontium aluminate powder to produce the green specimens using a hydraulic machine. Then, the green samples were sintered at 900 °C for one hour. After sintering, PVA was eliminated and the samples became denser. It was found that the hardness of the sample without strontium aluminate (30.5 HV) is higher than that of the sample with 10% of strontium aluminate addition (12.84 HV). Furthermore, copper samples containing strontium aluminate were fluorescent under ultraviolet at 517 nm. The sample with the largest amount of strontium aluminate (70Cu-30SrAl2O4) has higher phosphorescence than 90Cu-10SrAl2O4. In sulphur atmosphere, the tarnish resistance was found to be improved when strontium aluminate was added into copper. The colour difference (DE*) of 100Cu, which has no strontium aluminate, was 6.42 and higher than that of 90Cu-10SrAl2O4 (DE*= 3.5), 80Cu-20SrAl2O4 (DE*= 1.37), and 70Cu-30SrAl2O4 (DE*= 0.49), when testing in sulphur atmosphere for 30 min. 70Cu-30SrAl2O4, containing the highest amount of strontium aluminate, has the least colour changing on its surface resulting in the resistance in tarnishing.