Corrosion behaviour of CoW 0·013 C 0·001 in aqueous acidic sulphate solutions containing sodium lauryl sulphate and sodium citrate

Abstract

The corrosion behaviour of the CoW_xC_y binder alloy has been shown to be the key factor in the chemical stability of hardmetals of the WC–Co type. The anodic oxidation of the CoW_0·013C_0·001 alloy was studied in 0·1M H₂SO₄ with and without additions of 20 mM sodium lauryl sulphate or 20 mM tri-sodium citrate which were intended to act as organic corrosion inhibitors. In this investigation, use was made of linear sweep voltammetry, chronoamperometry, and ac impedance measurements (which can convey additional information on anodic activation processes occurring during corrosion). The reaction product morphology and composition were studied by scanning electron microscopy and energy dispersive spectroscopy. The inhibiting effects of the organic additives on the pseudo-passivating mechanisms were described. The precipitation of layers of corrosion products with different protective effectiveness was assessed and correlated with the electrochemical kinetics and with the morphological and chemical characteristics brought about by the presence of the organics. Sodium citrate proved more effective than sodium lauryl sulphate in inhibiting corrosion in the test conditions used in the present study.