path & process

It has been demonstrated that the condition of chemical equilibrium can often be perdicated by thermodynamic considerations and therfore thetendency of areaction to proceed can be measured.The thermodynamic approach dose not however, give any indication of the rate at which a reaction will proceed,and two examples of methallurigically phenomena show the importance of the study of the mechanism and rate of reaction.If aplain carbon steel in the austenitic stracture say at 850c is quenched in watera metastable martensitic structure is produced.this structure will tend to transform to a mixture of ferrite and cementite of lower free energy but the rate of transformation at room tempreature is so slow that the martensite remains apparently unchanged .Tempering at 650 allows the transformation to be completed within an hour.The reaction between carbon and oxygen in liguid steel to form carbon monoxide is accompanid by a substantial negative free energy change but the the carbon and oxygen contents can be raised well above the equilibrium values without any apperciable reaction. If an inrt gas such as argon is bubbled through the liguid steel ,introdusing suitable nuclei for reaction avigorous boil caused by carbon monoxide gas evaluation can be produced ,