1. “Axinte Uricariul” School, 707425 Scânteia, jud. Iaşi, RO.
2. Faculty of Materials Science and Engineering, “Gheorghe Asachi” Technical Univ. of Iaşi, Blvd. D. Mangeron 61A, 700050 Iaşi, RO.
3. Faculty of Materials Science and Engineering, “Gheorghe Asachi” Technical Univ. of Iaşi, Blvd. D. Mangeron 61A, 700050 Iaşi, RO (Corresponding author), e-mail: lgbujor@tuiasi.ro