Formation of metal microspheres by ultrasonic cavitation
- PDF / 931,039 Bytes
- 4 Pages / 584.957 x 782.986 pts Page_size
- 26 Downloads / 209 Views
Ze’ev Porata) Department of Analytical Chemistry, Nuclear Research Center-Negev, Be’er-Sheva 84190, Israel; and Department of Biomedical Engineering, Ben-Gurion University of the Negev, Be’er sheva 84105, Israel
Itzhak Halevy Department of Physics, Nuclear Research Center-Negev, Be’er-Sheva 84190, Israel
Shimon Reichb) Department of Materials and Interfaces, Weizmann Institute of Science, Rehovot 76100, Israel (Received 17 September 2009; accepted 1 November 2009)
A new physical method is described for the preparation of metal microspheres by ultrasonic cavitation of low-melting point metals ( 900 C, and significantly lower vapor pressure than the oil at the dispersion temperature, T < 390 C, the cavitation process occurs in the oil and not in the molten metal. However, this experimental setup is not adequate for the emulsification of mercury. The boiling temperature of mercury is 356.5 C and internal cavitation, in the mercury metal, below this temperature is possible,13 thus precaution measures are required to contain the mercury vapor. We present the preparation of lead and Au–Si eutectic microspheres. The experimental setup is depicted in Fig. 1. A 99.999% pure lead granule, about 2 mm in diameter, was etched in 32% hydrochloric acid to remove the native oxide film, and then washed with deionized water. The etched lead was immersed in 3-mL silicone oil [AP 100 (Fluka), polyphenyl methoxysiloxane], in a 13-mm-diameter and 6-cm-long quartz test tube. The silicone oil was heated above the melting point of lead, Tm = 327 C, using a portable commercial burner. Substantial decomposition of the oil is observed above 410 C. The molten lead was then exposed to ultrasound energy at 20 KHz for 10 s using a power of 100 watts while still being heated. The dispersion of the molten lead in the oil occurs the moment the acoustic field is applied. The test tube is then kept at a temperature above Tm for another 10 s and then cooled to room temperature. All necessary safety precautions have been taken: gloves, goggles, and ear protectors were worn. The procedure was performed in a hood, free of inflammable items and chemicals, and the door was kept at the lowest possible position. A small volume of oil was used to control the flame in case the oil ignites. The sample is transferred to a centrifuge test tube with n-hexane, a good solvent for the oil, and spun down at 4000 rpm for 5 min. Decantation, and then addition of n-hexane to the original test tube for another spin down was applied. This procedure was repeated three times, and afterwards the lead microspheres were kept in n-hexane to prevent oxidation. The resulting lead spheres, shown in Fig. 2, are mostly 25–50 mm in diameter. 634
http://journals.cambridge.org
FIG. 1. Schematic description of the setup for preparation of metallic microspheres by ultrasonic cavitation (quartz test tube, 6 cm long and 13 mm in diameter, silicone oil Fluka AP 100).
The Au–Si deep eutectic is of interest in bonding of electronic microdevices.14 Gold diffuses into silicon to f
Data Loading...
