Inhibitors pickling

Most pickling inhibitors function by forming an adsorbed layer on the metal surface, probably no more than a monolayer in thickness, which essentially blocks discharge of H+ and dissolution of metal ions. For example, both iodide and quinoline are reported to inhibit corrosion of iron in hydrochloric acid by this mechanism [19]. Some inhibitors block the cathodic reaction (raise hydrogen overpotential) more than the anodic reaction, or vice versa but adsorption appears to be general over all the surface rather than at specific anodic or cathodic sites, and both reactions tend to be retarded. Hence, on addition of an inhibitor to an acid, the corrosion potential of steel is not greatly altered ( 0.1 V), although the corrosion rate may be appreciably reduced (Fig. 17.3). 

Very effective inhibition of corrosion of iron is also provided by a small amount of iodide in dilute H2SO4 [25], Both CO and iodide chemisorb on the metal surface, interfering mostly with the anodic reaction [26]. Kaesche [27] showed that 10 M KI is a much more effective inhibitor for iron in 0.5M Na2S04 solution at pH 1 (89% efficient) compared to pH 2.5 (17% efficient), indicating that adsorption of iodide, particularly in this pH range, is pH-dependent. 

The interaction of factors just mentioned, plus perhaps others, enter into accounting for the fact that some compounds (e.g., o-tolylthiourea [28] in 5% 

H2SO4) are better inhibitors at elevated temperatures than at room temperature, presumably because adsorption increases or the film structure becomes more favorable at higher temperatures. Others (e.g., quinoline derivatives) are more efficient in the lower-temperature range [28], 

Typical effective organic pickling inhibitors for steel are quinolinethiodide, o- and p-tolylthiourea, propyl sulfide, diamyl amine, formaldehyde, and p-thiocresol. 

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Use Intermediate for polyesters, plasticizers, and plastics, nickel brightener in electroplating, corrosive inhibitor, pickling inhibitor prior to copper plating. 

Use Nickel brightener in electroplating, copper pickling inhibitor, corrosion inhibitor in aerosol cans. 

Use Synthesis of pharmaceuticals, dyestuffs, rubber chemicals, flotation agents, insecticides, fungicides, plasticizers, textile assistants, herbicides, oil additives, rust preventives, and pickling inhibitors. 

Duclean [Du Pont], TM for acids containing pickling inhibitors. 

Butoxyne. [ISP] Butynediol hydroxy-ethyl ethers corrosion inhibitor, pickling inhibitor, nickel brightener ftM electroplating applies. 

Acetaldehyde ammonia AI3-52423 Aldamine EINECS 200-868-2 Ethanol, 1-amino- Hexahydro-2,4,5-trimethyl-s-tria2ine trihydrate UN1841 Velsan. Exists as a trimer which is used in the manufacture of plastics and as a pickling inhibitor for steel, and is a rubber vulcanizing accelerator. A proprietary rubber vulcanizabon accelerator. Crystals mp = 97° bp= 110° soluble in H2O, less soluble in EtzO. 

Uses IWg. of benzyl compds., perfumes, pharmaceuticals, dyes, syn. tannins, artificial resins, bactericides, fungicides, flavors, insecticides, lubricants, plastics, plasticizers, quat. ammonium compds. photography gasoline gum inhibitors penicillin precursors chem. intermediate for n-butyl benzyl phthalate, other benzyl phthalates mbber accelerators pickling inhibitors blocking agent to prepare monoalkylated piperazine formerly as irritant gas in chemical warfare Regubtisy SARA 313 reportable... 

Hudson, R.M., and G.J. Warning. 1966. Effectiveness of organic compounds as pickling inhibitors in hydrochloric and sulfuric acid. Metal Finishing 64 (10) 58. 

An inhibitor is a chemical substance that, when added in small concentration to an environment, effectively decreases the corrosion rate. There are several classes of inhibitors, conveniently designated as follows (1) passivators, (2) organic inhibitors, including slushing compounds and pickling inhibitors, and (3) vapor-phase inhibitors. 

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