#mechanial properties of hastelloyC22

[heanjiaalloys]

Hastelloy C 22 And Its Behavior In Aqueous Solutions

Hastelloy C22, an alloy containing nickel, chromium and molybdenum was noted for the formation of passive and resistive oxide layer. Moreover, the mobility of the ions and the donor density in the oxide layer is found to be a function of the electrical potential when the layers of alkaline water are present on the alloy to determine the inertness of the nickel alloy in corrosive environments. The metal alloys containing nickel are resistant to corrosion and serve the purpose of structural materials in environments that are extraordinary such heat exchangers with high temperature and in the aggressive chemical reactors. The stability is often due to the inertness of the oxides that tend to form on the alloys containing nickel. For instance, the behavior of Hastelloy C 22 in aqueous solutions makes it ideal to be used in the metal bipolar plates in the fuel cell stack.

Bipolar plate

This is one of the most expensive, voluminous, and the heaviest components in the fuel cell stack. Quite naturally, the materials to be used for the place must exhibit high thermal and electrical conductivity, and exceptional corrosion resistance.  Replacement of the machined, bulky, and brittle plates with thin and durable metal plates is desirable for mobile and portable applications and based on the corrosion screening test, the nickel alloy or Hastelloy C22 is considered as one of the most desirable materials to be used in the plates.

Environments and materials

Among the materials tested include Hastelloy C22 in aqueous solutions and the tests were primarily performed in alkaline, acidic, and deaerated brines containing a certain weight percent revealed the effectiveness of C22 in the alkaline salt solutions. For alloy C22, which does not reflect susceptibility of pitting corrosion, the important thing to note is its tendency to overlap the transpassive region. It is also recommended that when the potential of the passive anode is raised adequately, the drop in the double layer becomes high for the oxidation of the things present in the solution. According to the tests conducted, the following results have been achieved.

·         Alloy C22 is resistant to pitting corrosion under varied conditions to be used in specific environments.

·         By enhancing the concentration of sodium chloride from one to five percent weight resulted in a major shift of Ep to a higher active value in the acidic solutions. However, when the weight of sodium chloride solution was increased to 5-7 percent of weight, it appeared independent of chlorine concentration in the acidic solutions.

·         For alloy C22 that showed adequate noble critical potential for overlapping the transpassive region, the formation of oxides on the surface of the alloy fr4om oxygen evolution is due to the oxidation of the test solutions that can perhaps account for the absence of pitting.

Testing in acidic solutions

For determining the behavior of Hastelloy C22 in aqueous solutions on nitric, sulfuric, and hydrochloric acid has been investigated several times. Based on the electrochemical results, it shows that the corrosion resistance of the coatings in the solutions containing static acid os higher than the ones in cavitation. The results can be accounted to the aggressive ions in a solution containing HCL and the mechanical effect resulting from the cavitation bubble collapse.