It is well known that artefact internal friction peaks appear when the atmosphere surrounding the tested specimen is not perfectly controlled o r i t s surface is not sufficiently cleaned. F o r example, humidity o r residual nitrogen /1, 2/ and also oil coating /3/ could induce such peaks.The purpose of this note is to give other examples of friction peaks due to a coating effect (which are sometimes erroneously attributed in the literature to a bulk effect).The specimen is a high purity, strongly cold worked iron wire. The internal friction of such a specimen is well known /4/ and composed of an cz peak (27 K) and a slowly increasing background from 30 to 300 K. The specimen coated by oil is an equiatomic Copt alloy in ordered state with a very low background of internal friction /5/. The torsion pendulum is an inverted one, oscillating a t 1 Hz and with an axial saturating magnetic field.Coating by oil oil (less than 0.1 ym) an asymmetric peak, with an associated modulus defect appears at a temperature Tm = 210 K (curve a, Fig. 1 ) and anneals out after heating at a temperature Td % 570 K. Tm and Td appear to be the melting temperature and the decomposition temperature, respectively, of the tested oil.Cleaning tests are made: after cleaning at room temperature, benzene, acetone, methanol, CHC13, and Rl3S 25 could not remove the peak. The peak is reduced by (C2H5)20, 20 min a t 300 K and suppressed when treated by ultrasounds. imen a mixture of helium and CH4 (curve a, b, Fig. 2) o r C7H16 (curve c, After covering the sample by a thin layer of vacuum paraffinCoating by solidified gas-The layer is obtained by cooling around the spec-1) ul. Majakowskiego 11/12, 80-952 Gdadsk, Poland.2) 85 X -3804l Grenoble C6dex, France.
