Passive films maintenance

When the boiler is placed back online, certain types of anodic inhibitors (which are generally employed to act as polishing treatments in the maintenance program) also may prove beneficial in further strengthening the passive film. 

Titanium metal has a pronounced tendency for spontaneous passivation and this gives the metal a very good corrosion resistance. The passive film consists of TiOj with a thickness of 10-100 A. The film has a remarkable stabihty in chloridechemical plants commercially pure and palladium-containing titanium lead to an increased Hfetime, reduced maintenance and reduced iron contamination of products. This has made titanium a very important alternative material in equipment for the production of cellulose. 

It will be evident from the underlying thermodynamics and kinetics (Fig. 10.25) that successful anodic protection of a metal relies upon the maintenance of a stable passivating film. A simple example of galvanic anodic protection is the addition of alloying elements (0.1% Pd or 1% Cu) to stainless steel which form local cathodes (Fig. 10.34). 

The mechanism by which calcium nitrite prevents corrosion of reinforcing steel can be briefly described as follows the use of calcium nitrite results in the creation and maintenance of a stronger, flawless and stable passive film on steel embedded in concrete, even in the presence of chloride levels much higher than the critical chloride concentration for corrosion onset for conventional concrete (about 0.9 kg of chloride km/m ). 

Oxidising or non-oxidising inhibitors These are characterised by their ability to passivate the metal. In general, non-oxidising inhibitors require the presence of dissolved oxygen in the liquid phase for the maintenance of the passive oxide film, whereas dissolved oxygen is not necessary with oxidising inhibitors. 

Passivation under a wide range of operating conditions and in all boiler designs is a goal of all BW treatment programs. It is achieved through the formation of a stable, continuous, uniform, self-limited, and nonporous magnetite film. (This objective also applies to the maintenance of cuprous oxide, the copper equivalent of a film of passive iron.)... 

Online passivation involves elevating the corrosion inhibitor concentration as high as three times normal maintenance levels. At higher concentrations, the rate at which the protective film forms is accelerated. This, in turn, reduces the degree of initial corrosion on clean but unprotected metal surfaces. The rate at which corrosion protection takes place depends on the temperature, pH and inhibitor used. 

Lately, specific medical treatments that avail themselves of biological or synthetic materials have been applied to support and improve wound healing. These materials may act as passive, interactive, or bioactive dressings. Passive materials include gauzes, tulles, or other traditional products aimed at wound protection, maintenance of suitable moisture, and prevention of microbial infections (Livshits, 1988 Cornelius et al., 2007 Takeoka and Saitoh, 2012). Interactive dressings are mainly biostable polymeric films or foams that can improve gas exchange and permeability at the wound interface. Bioactive dressings have the ability to deliver active biomolecules to the lesion site (Paul and Sharma, 2004). 

The oxide film on the surface of the reduced catalyst generated in passivation process isolates the active a-Fe from the air, which is favorable for package, store, transportation and loading of the catalyst. Therefore, the passivation treatment also can be adopted to prevent the catalyst from spontaneous combustion during the break of production and maintenance of equipments. The loading of the prereduction catalyst should be carried out under the protection of pure nitrogen gas. 

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