i surance as a part of corrosion today I am going to explain the very important topic which is very important from the examination point of view as well as from the knowledge point of view so that topic is theories of corrosion so basically we have two theories of corrosion the one else try our chemical corrosion and the second one is wet or electrochemical corrosion so before I explain the first theory which is the dry odd chemical corrosion I would like to what I would like to say that among the dry odd chemical corrosion I bet odd electrochemical corrosion threats or electrochemical corrosion is the major destroyer of the metal because it is the one which mainly destruct on the drawing with the major very complete two point now let us discuss about that the first two theory of origin which is dry are chemical corrosion the name itself suggests what exactly is this particular corrosion so there are two names associated with this particular corrosion the first is it is fought as the dry corrosion first of all we all discuss why it is fought as a dry corrosion because this particular corrosion occurs under dry conditions so that is the reason it is fought as the dry corrosion I now see why it is gone as chemical corrosion this particular corrosion is for as chemical corrosion because this particular corrosion is due to the direct attack of chemicals such as atmospheric gases like oxygen chlorine hydrogen sulfide onto the surface of the metal onto the surface of the vector so that is the reason this particular corrosion is for as chemical corrosion now by combining the bothers that is what is the dry corrosion what is the chemical corrosion which have defined at the beginning but combining or the decoration we can get the exact definition or precisely definition of tripod chemical pollution so dry or chemical corrosion is the corrosion which involves a direct attack of the chemicals such as atmospheric gases like oxygen chlorine hydrogen sulfide etc onto the surface of the metal under driving conditions so this is the precise definition of drive or chemical pollution nowadays drive this particular dry or chemical corrosion can be classified into three types the first one is of oxidation corrosion or corrosion by oxygen gas second one is of corrosion by other gases and third one is liquid metal corrosion so first time foremost we are going to discuss about the main corrosion of the dry audre chemical corrosion which is oxidation corrosion or corrosion pipe oxygen gas now the name itself suggests what exactly is the corrosion by the oxygen gas or oxidation corrosion this type of corrosion involves the attack or the direct attack of the oxygen gas onto the major surface under the dry conditions under the dry conditions and in both the temperatures the metal is attacked by the atmospheric loss our metals are attacked by the atmospheric gases that is at low temperatures this oxidation corrosion or corrosion by oxygen is responsible and high temperature also this oxidation corrosion or corrosion by oxygen gas as possible now let us see what are those metals which are attacked by the atmospheric oxygen I'm under more the oxidation corrosion at low temperatures and low temperatures al-khalili I'm alkaline estimators of the periodic table that is first a and second group elements of the periodic table or a backward by the oxygen gas at low temperature under bright condition I undergo the oxidation corrosion now let us see what are the metals which under both of oxidation corrosion or attack by the oxygen gas at high temperature and high temperature accept three measures of the periodic table which are the noble metals such as silver gold and platinum except these three metals all the other metals are attacked by the oxygen at high temperature and undergo the oxidation corrosion under - now the resistors the mechanism involved in this particular oxidation corrosion or corrosion by oxygen gas I do remember that this particular oxidation corrosion or corrosion by oxygen gas is very very important from the examination of you now let us say that this is one of the metal I this is the surface of the major I know this particular metal is in the environment where the oxygen concentration is more it's in the enviornment where the oxygen concentrations this is the loss now under the influence of that majority of season what happens initially is corrosion interface is Creator our corrosion interfaces are a generator interface in this perspective years that is the corrosion gates are open that is the gates are open for the corrosion once the gates are open to further corrosion then the major undergo the oxidation collision now as the metal is exposed directly to the oxygen I hear the concentration of the oxygen is high right under this condition already said that the corrosion interface is created on a generator this is how the corrosion interface is created or generator let us say that this is one interface and this is the second interface and what is the interface of corrosion students interface of corrosion means the gates are opened further corrosion to after right now when the gates are opened what happens is as this is the major metal let us say that it is the PI bond in metal since it is the PI valid metal it undergo oxidation oxidation is nothing but term already we know that loss of electrons let us say that it is the PI bond acquittal since it is the PI bond and beta definitely improve uses n plus 2 ions and losses the two right now what is happening when the corrosion interphase is created here we are discussing only about the two interfaces it doesn't mean that only to corrosion interfaces or voidable Creator number of interfaces are created based upon the concentration of the oxygen if the oxygen concentration is more maximum number of in corrosion interfaces already created if the concentration of the oxygen is less minimum number of corrosion interfaces are created in order to exemplify I have taken only two interfaces to English so now what is happening and the defense off for that mostly oxygen the major is undergoing the oxidation i from using the two electrons now whatever the two electrons which have been lost by the lost by the metal upon oxidation enters into the area where of Susan is we're optional is presenta no that particular oxygen-oxygen gave the two electrons which shall be entered into its vicinity vicinity Ida gets an accuser - OH - - let's reduce it - OH - - now here what is happening whenever the interface is created the major is undergoing oxidation and producing M plus 2 ions and whenever these two electrons which have been lost to by the metal upon oxidation are entering into the area where the oxygen is present now that oxygen is gaining those two Arab tones and getting reduced - OH - stone now M + 2 which are formed here diffuses from their side o - - which are formed here diffuses from their side now M plus 2 which have been diffused from each side reacts with o minus 2 which has been diffused from their side and converts to em - OH - which is nothing but her mo that is metal oxide is going to be metal oxide is going to be now this metal oxide is going to be now what is the metal oxide students the metal oxide here is the corrosive product the forest product is the metal oxide now further corrosion depends upon the nature of the metal oxide which has been formed on the surface of the major van when the metal is exposed to the oxygen and undergoing the oxidation corrosion or corrosion by the oxen yes now whatever the metal oxide before that one another interface is there the similar thing will happen here also you'll undergo oxidation and produces M plus 2 ions now whatever the M plus 2 ions I know the two electrons have been lost in a similar fashion same reaction now whatever the two electrons which have been released by the metal of Surveyor metal upon oxidation enters into the region where oxygen is present now the oxygen in the similar fashion under both the reduction and produces o minus 2 now M plus 2 oh minus 2 combines together resulting in the formation of metal oxide now whatever the metal oxide which is formed here can be classified into four knives and this is the metal oxide which it decides the further corrosion of the metal so there are four types of metal oxides that is basically whenever the metal is undergoing the oxidation corrosion or attacked by the oxygen gas under dry conditions four types of metal oxides are going to be formed the one is the stable metal oxide the second one is unstable metal oxide third one is volatile metal oxide I'm fourth one is porous metal oxide now let us discuss one by one first one is stable metal oxide stableman already the name itself suggests that it is the the stable one which is settling on the surface of the metal now let us see what are the examples of the metal on which this stable metal oxide is formed the metal oxide which are formed on the surface of lead aluminium copper chromium I'm ultra whatever the metal oxides which are formed on the surface of leader aluminum copper probiem I'm gold from of this particular type now second type of metal oxide which is going to be formed on the surface of the metal whenever the metal is attacked by the oxygen under dry conditions is unstable metals unstable metal oxide so unstable metal oxide means immediately after the formation of metal oxide it dissociate into ms2 I owe - - it won't be on the surface of the metal now whenever the metal oxide which has been formed is dissociating back to m+ - I know - - ion we can say that that particular metals though that particular mater's on which the metal oxide sensor it is dissociating into n plus - I know - - we can say that the we can say that those metals have not undergone the oxidation corrosion those majors have not been attacked by the oxygen gas under dry conditions and already have discussed that there are three metals there are three metals which do not undergo any sort of corrosion which are silver gold I'm platinum accordingly we can say dr. the Silver Gold and Platinum do not undergo any sort of now whatever the metal oxide which is going to be formed on the surface of the silver gold and the Platinum is of this now coming to the third category or third category of the metal oxide is a volatile Miller all that time well retirement evaporate to metal oxide evaporate too many locks it evaporates at once if the metal oxide which has been formed on the surface of the metal is evaporating at Verne's then we can say that it is the unstable metal offset since it is the unstable metal of sayyida we can say that the metal has not undergone the corrosion at all but it is volatile it is volatile either this volatile or evaporative metal oxide will not evaporate at once at once it will evaporate in fractions some part of the let us say that this is the metal let us say that this is the metal surface some point of the metal oxide is evaporated some part will be removed some part of the metal oxide is evaporated some part is really some part is evaporated some part is revealed now when some part of the metal oxide is evaporator and some part is the remainder what does it mean it is creating the heterogeneity on the surface of the metal it is creating the heterogeneity on the surface of the metal once the heterogeneity is created on the surface of the matrix the metal is more susceptible to undergo the vent or electrochemical corrosion which is the major destroyer of the metal because for undergoing the vent or electrochemical corrosion which is the major destroyer of the metal definitely heterogeneity is needed on the homogeneous surfaces wet or electrochemical corrosion is not but whenever it is volatile what is happening strength it is creating the heterogeneity once a hydrogenate is created then it under movement now whatever the metal oxide which is going to be formed on the surface of mortgage loan is of this moo3 of this type that distended volatile side Somali victim undergo vigorous corrosion and the last type of metal oxide which is going to be formed on the surface of the major whenever the metal is attacked by the oxygen under dry conditions and under hood absolute in corrosion is porous metals so porous metal oxide means what students porous which water whatever the metal oxide which is being formed down which is form a form that contains our comprises the force now by means of the pores or oxygen entry easy oxygen entry is easy oxidant reason under the hints of firm which substance the metal is undergoing oxidation strands the metal is undergoing oxidation in the presence of oxygen now whatever the metal oxide if it is porous in nature what will happen by means of those pores the oxygen will penetrate inside the metal thereby resulting in the formation of the heterogeneity once the heterogeneity is created the metal cannot be stopped from the bit or electrochemical corrosion so it is very dangerous metal oxide this is going to form on the surface oh I'll tell me I alkaline and the method I mean I'm of the length excavators so dear students remember that among the oxidation and reduction corrosion is oxidation corrosion is oxidation and for undergoing the dry or camel chemical corrosion homogeneity is sufficient but for undergoing the wet or help to the metal corrosion definitely heterogeneity is created and when the metal oxide which is going to form on the surface of the metal whenever the metal is directly attracted by the oxygen gas under dry conditions are undergoing the oxidation corrosion oxidation corrosion then heterogeneity sprayed at once the heterogeneity is theater definitely undergo the vectorial to the metal corrosion and already have said that the vet our electrochemical corrosion is the major destroyer of the vigil it is the one which mainly distracts our digital instrument so in this particular video I explained we about the oxidation corrosion or corrosion by the oxygen gas which is one subtopic of dry or chemical corrosion in the next video I will discuss about them the two other types of perversions which are part of one that's right for every the corrosion the worst first one is the that is I mean second with respect to this first is oxidation corrosion is corrosion by at the gases I hope you understood this concept this concept is very very important from the examination point of view as well as from the knowledge part of the students so thanks for watching if you really liked the video please do comment on the video and subscribe