What is stable and metastable?
Stable VS. Metastable. The distinction between stable and metastable equilibrium is generally that the stable equilibrium state is “truly unchanging”, or unchanging given in- definite time, whereas the metastable state may be changing, but too slowly to be observed (see Quota- tions).
Is Fe3C metastable?
➢ Fe3C (iron carbide or cementite) This intermetallic compound is metastable, it remains as a compound indefinitely at room T, but decomposes (very slowly, within several years) into α-Fe and C (graphite) at 650 – 700 °C.
Why cementite is a metastable phase?
Cementite often is said to be metastable with respect to graphite. However, as shown in Figure 2, pure cementite when allowed to coexist only with graphite, is stable in the presence of graphite, pre- sumably because the iron does not dissolve in graph- ite.
What makes something metastable?
metastable state, in physics and chemistry, particular excited state of an atom, nucleus, or other system that has a longer lifetime than the ordinary excited states and that generally has a shorter lifetime than the lowest, often stable, energy state, called the ground state.
Why metastable is important?
In a three-level laser, the material is first excited to a short-lived high-energy state that spontaneously drops to a somewhat lower-energy state with an unusually long lifetime, called a metastable state. The metastable state is important because it traps and holds the excitation energy, building up a…
Why is a metastable state more stable?
A metastable state is then long-lived (locally stable with respect to configurations of ‘neighbouring’ energies) but not eternal (as the global minimum is). Being excited – of an energy above the ground state – it will eventually decay to a more stable state, releasing energy.
Why is the Fe-Fe3C phase diagram a metastable PD instead of a true equilibrium PD?
Why is the Fe-Fe3C phase diagram a metastable phase diagram instead of a true equilibrium phase diagram? The phase diagram is a metastable phase diagram rather than a true equilibrium phase diagram because the compound iron carbide ( ) formed, cementite, is not a true equilibrium phase.
What is Fe-C phase diagram?
The Fe – C diagram (also called the iron – carbon phase or equilibrium diagram) is a graphic representation of the respective microstructure states of the alloy iron – carbon (Fe-C) depending on temperature and carbon content. To explain this diagram, an introduction about metal structures and pure iron must be done.
What is C Fe?
Iron carbide (FeC) | CFe – PubChem.
What is metastable state in phase diagram?
What metastable means?
Metastable is a term used to refer to a close degree to normal stability ranges or values for any given measurable property of a material, varying slightly to a more unstable level due to the absence of certain chemical, physical or energy conditions. Metastability can be used to describe pitting corrosion.
What materials have metastable states?
Metastable materials, or materials that transform to another state over a long period of time, are ubiquitous in both nature and technology and often have superior properties. Chocolate, for example, is metastable, with a lower melting point and better texture than stable chocolate.
What phase mixtures are observed in Fe-C diagram?
Phase Mixtures Observed in Fe-C Diagram • 1. Pearlite The pearlite consists of alternate layers of ferrite and cementite. It has properties somewhere between ferrite and cementite.
Is there a metastable equilibrium between iron and iron carbide?
Therefore, the metastable equilibrium between iron and iron carbide should be considered, because it is relevant to the behavior of most steels in practice.
Is cementite metastable?
Cementite is metastable, and the true equilibrium should be between iron and graphite. Although graphite occurs extensively in cast irons (2-4 wt % C), it is usually difficult to obtain this equilibrium phase in steels (0.03-1.5 wt %C).
What are the important reactions in Fe–C system?
Important Reactions in Fe–C System Peritectic: 0.16% C, 14930 C δ (0.11% C) + L (0.51)%C ↔ γ (0.16%C) Eutectic: 4.30 wt% C, 1147 °C L (4.30% C) ↔ γ (2.14% C) + Fe3C Eutectoid: 0.76 wt%C, 727 °C γ (0.76% C) ↔ α (0.022% C) + Fe3C 14.