Inhibitors vapor-phase

Whether an oil or a wax is chosen as the vehicle depends on (1) the relative length of time protection is desired, the wax usually providing longer life and (2) the ease of removal before the protected machine part is put into service, with an oil being easier to wipe off or dissolve in solvents. The thickness of an applied coat varies from 0.1 mm to more than 2.5 mm (5 to more than 100 mils). 

The mechanism of inhibition has not been studied in detail, but it appears to be one of adsorbed film formation on the metal surface that provides protection against water or oxygen, or both. In the case of volatile nitrites, the inhibitor may also supply a certain amount of NO2 that passivates the surface. 

Detailed data have been presented for dicyclohexylammonium nitrite [31], which is one of the most effective of the vapor-phase inhibitors. This substance is white, crystalline, almost odorless, and relatively nontoxic. It has a vapor pressure of 0.0001 mmHg at 21°C (70°F), which is about one-tenth the vapor pressure of mercury itself. One gram saturates about 550m (20,000ft ) of air, rendering the air relatively noncorrosive to steel. The compound decomposes slowly nevertheless, in properly packaged paper containers at room temperature, it effectively inhibits corrosion of steel over a period of years. However, it should be used with caution in contact with nonferrous metals. In particular, corrosion of zinc, magnesium, and cadmium is accelerated. 

Ethanolamine carbonate and various other compounds have also been described as vapor-phase inhibitors [23,32]. A combination of urea and sodium nitrite has found practical application, including use in impregnated paper. The mixture probably reacts in the presence of moisture to form ammonium nitrite, which is volatile, although unstable, and conveys inhibiting nitrite ions to the metal surface. 

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Inhibitors act and are classified in a variety of ways (1,3,37,38). The classifications used herein closely foUow the discussion in Reference 37. Types of inhibitors include (/) anodic, (2) cathodic, (3) organic, (4) precipitation, and (5) vapor-phase inhibitors. 

Precipitation and Vapor-Phase Inhibitors. Precipitation inhibitors are film-forming compounds that produce barrier films over the entire surface. Phosphates and siUcates, which are the most common, do not provide the degree of protection afforded by chromate inhibitors, but are useful in situations where nontoxic additives are required. Two main drawbacks to the use of phosphates and siUcates are the dependence on the water composition and the control required to achieve maximum inhibition (37,38). 

Vapor-phase inhibitors are volatile compounds that adsorb onto metal surfaces, and retard or prevent corrosion by a variety of mechanisms (37). Inhibitors such as dicyclohexamine nitrate [3882-06-02] can protect a variety of metals such as steel, aluminum, and tinplate. A number of vapor-phase inhibitors are commercially available as powders or tablets. However, vapor-phase inhibitors attack nonferrous metals to varying degrees, thus the manufacturers recommendations should be checked before appHcation. The system to be protected must be closed to maintain the volatile compound, but objects as large as the interior of an ocean-going tanker have been treated by this technique. 

In order to assure control of the reaction, the vapor-phase inhibitor concentration must be closely controlled in the ppm range. Although several compounds have been claimed to be useful, it is likely that commercial processes use only ethylene dichloride or some of the simpler chlorinated aromatics (102). In general, the choice between inhibitors is not based on their differences in performance, but rather on the designers preference for dealing with the type of control problems each inhibitor system imposes (102). 

Vapor phase inhibitors These are used for the temporary protection of new plant in transit or prior to commissioning. Volatile corrosion inhibitors such as cyclohexylamine derivatives are used. The plant must be sealed or contained to prevent rapid loss of the inhibitor. Sachets of these materials are placed in packing cases. Papers impregnated with them are available for wrapping steel items. These inhibitors are used primarily to protect steel. 

Chapter 11 completes the discussion on internal treatment programs with information on program primary support chemicals, including oxygen scavengers and condensate treatments (vapor phase inhibitors) and adjuncts. 

All-volatile programs (AVPs) These programs are employed in higher pressure boilers (generally power boilers) and utilize only volatile chemicals, such as ammonia, amines (such as diethylhy-droxylamine or DEHA), and other vapor phase inhibitors (VPIs). 

Figure 1.63 Mechanism of protection by vapor phase inhibitors...

Beilstein Handbrjok Reference) AI3-28026 BRN 1731349 CCRIS 964 Diethylhydroxyl-amine N,N-Diethylhydroxyamine EINECS 223-055-4 Ethanamine, N-ethyl-N-hydroxy- Hydroxylamine, N,N-diethyl- N-Hydroxydiethylamine Pennstop 1866. Free radical scavenger used by the rubber industry as an emulsion polymerization inhibitor vapor phase inhibitor for olefin or styrene monomer recovery systems in-process inhibitor for production of styrene, divinyl benzene, butadiene and isoprene. Liquid mp = 10° bp = 133° d = 0.8669. ElfAtochem N. Am. 

VAPOR PHASE INHIBITORS - A system using an organic nitrite compound, a powder which vaporizes slowly to protect ferrous metal from contact with oxygen. 

VCE vinyl chloride-ethylene VPI vapor phase inhibitor... 

Vapor phase inhibitors/volatile corrosion inhibitors (VCI)... 

J.M. Bastidas, E.M. Mora, S. FeHu, The protective action of two vapor-phase inhibitors on the corrosion of mild steel, Werkst. Korros. 41 (1990) 343—347. 

Vapor phase inhibitors (VPIs), also called volatile corrosion inhibitors (VCIs), are compounds that are transported in a closed system to the site of corrosion by volatilization from a source. In boilers, volatile basic compounds such as morpholine or octadecylamine are transported with steam to prevent corrosion in condenser tubes by neutralizing acidic carbon dioxide (Boles et al. 2009). Compounds of this type inhibit corrosion by making the environment alkaline. In closed vapor spaces, such as shipping containers, volatile solids such as the nitrite, carbonate, and benzoate salts of dicyclohexylamine, cyclohexylamine, and hexamethyleneimine are used. 

Industrial application of inhibitors involves acidic, neutral, and alkaline solutions as well as the gas phase. Physical and electrochemical inhibitors can be used for acids, whereas all three types are employed in neutral and alkaline solutions. Gas and vapor phase inhibitors (i.e., substances with high pressure) have gained importance, especially in atmospheric corrosion protection in storage and transportation. 

Protection of solid metal and even of metal powder, especially of iron, can be obtained by certain nitrites of organic bases classed as vapor phase inhibitors (VPI), such as dicyclohexylammoniuin nitrite (Shell Oil Co,), which is effective in the form of coated paper (MIL-P-3420B) for wrapping of sensitive metal parts. 

Uses Corrosion inhibitor in water treatment, vapor phase inhibitor programs Manuf./Distrib. Aldrich http //www.sigma-aldrich.com, Climax Molybdenum http //www. climaxmolybdenum. com, FI u ka http //www.sigma-aldrich.com, Noah http //www.noahtech.com, Quaker City http //WWW. chemical, net Varsal Instruments http //www.varsal.com Trade Name Synonyms ADM [Climax Molybdenum... 

Use of Vapor-Phase Inhibitors and Slushing Compounds. These are discussed in Chapter 17. 

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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