5th-7th June, 2017: 3rd Mediterranean Conference on the Applications of the Mössbauer Effect, Jerusalem, Israel

[Z. Klencsar]

The 3rd Mediterranean Conference on the Applications of the Mössbauer Effect (MECAME 2017) was held during the days of June 05-07, 2017, in Jerusalem, Israel. On the conference Károly Lázár presented an invited lecture concerning the characterization of complex particle systems obtained via the electric explosion of steel wires in water.

The abstract book of the conference can be downloaded from https://mecame2017.irb.hr/content/download/10531/166192/file/MECAME2017-Book-of-Abstracts-v2.pdf

Vaporization of steel by electric wire explosion in water: phase transitions and oxidation

K. Lázár 1, L.K. Varga 2, V. Kovács Kis 3, L. Szabó 4, S. Stichleutner 1, Z. Klencsár 1

1 EKBI, Centre for Energy Research, Hung. Acad. Sci., 1525 Budapest, POB 49, Hungary
2 Wigner Research Center for Phyics, Institute for Solid State Physics and Optics, 1525 Budapest, POB 49, Hungary
3 MFA, Centre for Energy Research, Hung. Acad. Sci., 1525 Budapest, POB 49, Hungary
4 Research Centre for Natural Sciences, Hung. Acad. Sci., Magyar tudósok körútja 2, 1117 Budapest, Hungary

Electric wire explosion (EWE) is a known method for production of nanoparticles in various gases and liquids. In most of cases pure metals are vaporized, e.g. Al, Cu, Au, Fe, preferably in water. The process is rather complex, a series of steps results in the final product(s). A few reports have also been published on EWE of alloys. In the present communication comparison of products of vaporization of a low carbon and an austenitic steel (ASI 304; 18 % Cr, 10 % Ni, 68 % Fe) is presented. Steel wires with ca. 0.2 and 0.3 mm diameters were exposed to max. 7 kA impulses for ca. 6 microseconds in water. Core-shell structured, metal and metal oxide sol is formed, sedimentation takes place in several days afterwards. Different fractions were collected and analysed by Mössbauer spectroscopy, XRD, SEM (with EDX) and HRTEM (with electron diffraction).

Sizes of the formed metallic globuli cover a wide range (from nanometres to microns). Mössbauer spectrum of the fine fraction of the low carbon steel displays the expected shape, i.e. magnetic splitting of bcc phase is combined with some oxide. In contrast, four components can be identified in the fine fraction of products of the austenitic steel, namely singlet of the original fcc phase, an iron oxide (wüstite), sextet of an iron rich phase (~33 T) and a distribution of hyperfine fields (centered at ca. 30 T) originated from Fe,Cr,Ni alloy with local compositions.

The applied electric discharge results in melting and evaporation. A part of the excited metal vapour interacts with water immediately, water is decomposed, oxides are formed. The other, non-interacting part of the metal vapour is condensed, spheres of various sizes are formed, with compositions deviating from that of the original steel in an extent. Various stages of these processes are clearly manifested in XRD patterns (presence of different phases), in SEM (surface morphology and composition of oxides on metallic spheres) and in HRTEM images (high resolution images and electron diffractograms of oxides) as well. Thus, comparison of the products of the vaporization of two steel samples reveals that nanoparticles of pure metals can be prepared by EWE. In contrast, vaporization of alloy wires and condensation afterwards may result in significant compositional changes and structural phase transformations as well.

Acknowledgement
The study has been supported by the Hungarian National Research, Development and Innovation Office NKFIH (K115784).