โ Scribed by J.N. Gaur; G.M. Schmid
No coin nor oath required. For personal study only.
The effect of chloride ions on the passivity of iron commanded the attention of early electrochemists 1 and has since been investigated many times 2-4. It is generally assumed that, by a mechanism as yet unknown, chloride ions destroy the passive film either locally, as in pitting, or uniformly and thus lead to increased corrosion. Similar observations were made, e.9. on stainless steels 5-8, and on nickel 9. It has been known for many years, (cf Grahame et al. 1ยฐ) that chloride ions are strongly adsorbed on mercury, and it is generally assumed that they are adsorbed on other metals as well. Presumably the first step in the destruction of passivity is the adsorption of chloride in preference to the oxygenated species forming the passive film. Evidence for this is lacking but accumulation of radioactive bromide ions has been found in pits formed on iron 11.
The anodic dissolution of gold in chloride solutions occurs with formation of a soluble tetrachloro-gold complex at a standard potential of + 1.00 V x2. In acidic, chloride free solutions a potential of 1.0 V is frequently quoted for the start of the formation of an oxide and/or adsorbed "oxygen" film on gold electrodes 13'14. It seemed worthwhile to try to confirm and to complement the results of a previous study of the gold chloride solution system by Heumann and Panesar 15, to see if the gold dissolution reaction could be passivated by the formation of an oxide or "oxygen" film, and to determine the stability of this passivating film in the presence of chloride ions.
The test electrodes were gold beads, about 0.1 cm 2 in apparent area, made at the end of 0.5 mm wires (Engelhardt Industries, Fine Gold) by melting in a hydrogenair flame. The electrodes were sealed into a Teflon holder with Kel-F-200 wax so that only the bead was exposed to solution. The Teflon holder was mounted in an all Pyrex glass cell which also contained a platinum wire gauze polarizing electrode and, in a side compartment, a saturated calomel reference electrode.
Test solutions were 0.1 M in HCIO4 and 100, 50,10,8,6,4, or 2 x 10 -4 M in C1-. Some experiments were made in solutions containing Br-instead of C1-. All solns, were made up from Analyzed Reagent 70~ HC104, Analyzed Reagent KC1 or KBr, and triply distilled water prepared by distilling once from alkaline permanganate in Pyrex and twice from a quartz still. The solutions were deaerated and saturated with hydrogen gas taken from a Fisher-Serfass purifier. All gas ducts were made of Teflon
๐ SIMILAR VOLUMES
## Abstract The inhibitive action of the acid extracts of seeds' leaves and bark from the __Ficus virens__ plant towards hydrochloric and sulfuric acid corrosion of aluminium is tested using mass loss and thermometric techniques. It was found that the extract acts as a good corrosion inhibitor for