What is graphitic corrosion?
Graphitic corrosion is a form of de-alloying or selective leaching that occurs in cast iron material. This corrosion mechanism is unique to gray cast irons and is caused by the graphitic matrix present. The graphite is cathodic to the iron matrix.
What does Graphitization mean?
Graphitization is a form of material degradation occurring when the microstructure of some carbon and low alloy steels breaks down after long exposure to elevated temperatures (825 – 1300 F), causing the metal to weaken and be susceptible to cracking failures.
Is graphene corrosion resistant?
Besides several other unique properties, graphene possesses remarkable chemical inertness. Graphene coatings either a single or a few atomic layers thick on metals has been shown to improve their corrosion resistance by up to one-and-half orders of magnitude.
What is Graphitisation of cast iron?
Graphitization is the formation of graphite (free carbon) in iron or low-alloy steel, which occurs when their components are exposed to elevated temperatures over a long period. Graphite is a weak material with very low ductility and low resistance to thermal or mechanical fatigue or shock.
What causes graphitic corrosion?
Graphitic corrosion is usually a form of galvanic corrosion that takes place in wet or moist environments where water acts as an electrolyte and allows a weak electrical current created by dissimilarities in the iron and graphite to remove the iron from the more cathodic graphite.
What type of pipe material can be affected by graphitic corrosion?
cast iron pipes
Graphitic corrosion refers to the deterioration of grey cast iron pipes, in which the metallic constituents are leached or turned into corrosion products, leaving the graphite intact and exposed.
What is the difference between carbonization and graphitization?
The key difference between carbonization and graphitization is that carbonization involves the conversion of organic matter into carbon, whereas graphitization involves the conversion of carbon into graphite.
Is Graphitization a corrosion?
Graphitization refers to electrolytic corrosion most often seen in iron or low-alloy steel in which the metallic components are converted into corrosion products.
How does graphene prevent corrosion?
One common way of protecting metal surfaces is by coating them with anti-corrosive substances. Graphene is studied extensively as a candidate for anti-corrosive coating, as it serves as a barrier to gas molecules.
What corrodes cast iron?
A crucial problem occurs when ordinary cast irons are exposed to seawater, other salt solutions, and soil, causing the metal matrix to corrode preferentially, leaving a structure of hydrated iron oxide and graphite particles. This form of attack is called graphitization or graphitic corrosion.
Which is the best description of graphitic corrosion?
Graphitic corrosion is selective leaching of iron from gray cast iron, where iron particles are removed and graphite grains remain intact. Graphitic corrosion is also known as selective leaching, dealloying, demetalification, parting and selective corrosion.
What causes Graphitic corrosion in cast iron pipelines?
Moist soils, especially those containing sulfates, will frequently produce graphitic corrosion of unprotected gray and nodular cast iron. Stray currents have also been identified as causes of graphitic corrosion in subterranean pipelines.
Are there any cast irons that are free of graphite?
White cast iron, which is essentially free of graphite, is immune to graphitic corrosion. Corrosion-resistant cast irons containing chromium, nickel, and silicon are also immune to graphitic corrosion.
Why does selective leaching take place in graphite?
The potential difference between the alloying elements is the driving force for the preferential attack on the more active element in the alloy. Selective leaching takes place because graphite is cathodic to iron, and gray iron’s structure develops an excellent galvanic cell.