Description of an aerodynamic levitation apparatus with applications in Earth sciences

Abstract

Background: In aerodynamic levitation, solids and liquids are floated in a vertical gas stream. In combination with CO2 laser heating, containerless melting at high temperature of oxides and silicates is possible. We apply aerodynamic levitation to bulk rocks in preparation for microchemical analyses, and for evaporation and reduction experiments. Results: Liquid silicate droplets (similar to 2 mm) were maintained stable in levitation using a nozzle with a 0.8 mm bore and an opening angle of 60 degrees. The gas flow was similar to 250 ml min(-1). Rock powders were melted and homogenized for microchemcial analyses. Laser melting produced chemically homogeneous glass spheres. Only highly (e.g. H2O) and moderately volatile components (Na, K) were partially lost. The composition of evaporated materials was determined by directly combining levitation and inductively coupled plasma mass spectrometry. It is shown that the evaporated material is composed of Na > K >> Si. Levitation of metal oxide-rich material in a mixture of H-2 and Ar resulted in the exsolution of liquid metal. Conclusions: Levitation melting is a rapid technique or for the preparation of bulk rock powders for major, minor and trace element analysis. With exception of moderately volatile elements Na and K, bulk rock analyses can be performed with an uncertainty of +/- 5% relative. The technique has great potential for the quantitative determination of evaporated materials from silicate melts. Reduction of oxides to metal is a means for the extraction and analysis of siderophile elements from silicates and can be used to better understand the origin of chondritic metal.