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학습트랜스크립트
00:04Hello students, we are moving on to Bube Diak, Marcel Bube. He is a Belgium guy,
00:19electrochemist and corrosion scientist. They might be the same thing. And a pianist.
00:29What's he doing? He's playing the piano and doing some corrosion scientist.
00:45I think he had been very rich. He had a piano and also electrochemical devices,
00:56which might be quite expensive at that time.
01:02See, he lived for at least like 90 years. He was born in 1906,
01:13and then he died in 1996 or something around. So he lived for 90 years.
01:34So scientists are very stressful these days. I don't know. Those scientists are pretty old,
01:44agey. They were also stressed. They were very rich. They are spending money with this experiment,
01:52so I don't think they were that much stressful. But anyway,
01:58we will see what this Pube diagram is representing. Here, the highlighted one, potential and pH diagram.
02:11We have learned about acid and base. Acid base gives some pH information.
02:20pH is obviously minus log H plus, correct? So this. These diagrams represent the stability of metal
02:35as a function of potential and pH. So we mentioned that this Pube diagram represents potential versus pH.
02:45pH. And then we can also get some information about a metal, which is not a function of this Pube
02:55diagram at the beginning.
02:56But we will see how it works. At a particular combination of pH and potential, therefore,
03:05stable phase can be determined. This is the main thing we will figure out from this Pube diagram.
03:14So I hope you remember that like a potassium, kuka, na, ma, r, r, m, e, d, hydrogen, kappa, silver,
03:28gold, and pt.
03:31We already know like this hydrogen exists as a reference. And then the all those metals in front of this
03:39hydrogen,
03:40they are unstable in an acid solution but that's just a rough idea what if we
03:49have a very low concentration of the proton if that pH is quite high enough
03:54then what's happening and also what's happening if we have like the alkaline
04:02solution or in other words like a high pH hydroxide anion exists in the solution
04:11a lot can you guess so that might be the main thing we we can figure out from this
04:20pool bed diagram let's move on in such diagrams the redox potential of the
04:28crowding system is plotted on a vertical axis and the pH horizontal axis we
04:34will see that pool bed diagram right away so just to keep this in mind these
04:40diagrams are constructed from calculations based on Nerensti equation so that's the
04:48one we would like to go for so we already know about it so Nerensti equation we will
04:56see that right away and solubility data for metal and its species such as this
05:03material let's let's move to the pool bed I am directly so this is the pool bed
05:09diagram so here the information is a pH on the x-axis and y-axis we see the
05:20voltage so if you are interested in that electrochemistry then you may already know
05:30about the potential for oxygen the oxygen reaction or the hydrogen reaction hydrogen
05:39reduces this way and that potential is zero we already know like that's zero so if
05:48that potential is less than zero this reaction may occur that's what we could
05:54see then also here oxygen the the this way but the but the other way the water can
06:10be dissolved into oxygen and acidic solution this way that's gonna happen so let's
06:23take a look at this equation first that's this one and water electrolysis occurs at
06:30one point two two three volt and then this is the E zero minus and zero point zero the nine
06:46something oh I'm sorry so this is zero I'm sorry zero five nine two and a log something but
06:56here oxygen gas is this activity is one remember that if that's not aqueous form we put that
07:06those value as a the partial pressure or if we set up the part as a one ATM that
07:16activity is just one so we we can remove that part so if we see this part that's
07:25p8 right you including this one so and then this one negative and negative negative so this one
07:37becomes p8 and then we still have this negative value the in front so that became like this and
07:45and this one is a four pH right so the four four can cancel out this way and negative log
07:56something becomes a pH so here and then for the for the hydrogen we we have this one zero potential
08:13minus zero point zero five nine two pH so when we have the regular molarity one one more and one
08:27ATM
08:28everything this is the potential we may expect for hydrogen evolution and oxygen evolution but when we
08:38change the pH that potential can be changed to this one that's what we observed during the from this
08:45equation right so if we plot this one according to the pH so see we we have a variable for
08:53pH so
08:54at here pH zero so we can put zero here then that becomes 1.23 and this is a zero
09:02but if we put seven
09:05then we multiply this number and then subtract that one so that will go down a little bit this way
09:15that's this so it started from 1.23 according to that net density equation that potential goes down to 0
09:28.4
09:28at this low potential may be that reaction may occur the hydrogen oxygen evolution and this one the hydrogen
09:40evolution needs this potential so we just saw like if we go over this potential then oxygen evolution may
09:54occur right so if we go over this potential then hydrogen evolution may occur right so so this area is
10:23stable area
10:27but actually the theoretically 1.23 is starting the voltage but when we have a different kind of metal as
10:38an electrode
10:39sometimes it needs some the over potential which requires the electron flows through the electrode
10:49that if we consider that if we consider that part this can be going up a little bit and then
10:56this one go down we need a higher potential for this one and this one that's the next one see
11:05we need some over potential
11:16so we know this is the the unstable thermodynamically unstable but due to that over potential required to make that
11:28reaction happen that's kinetically stable it means it takes a long time to
11:37let the equation occur so we believe this reaction will occur at this point but it takes some time like
11:45a more than we expect
11:55okay i hope you understood this pulver diagram a little bit for water so this is the thermodynamically stable area
12:05and these are kinetically stable area so it may take some time to uh that corrosion may occur in this
12:18area so if we need some the some metal or material can stay in that kind of a solution uh
12:29it can stay for a while but not forever okay that's what that kinetically stable area
12:35means okay this is for water normally the water is used for solvent a lot so that's why we are
12:49focusing on this water as a base the material then let's move on to the next material and let's take
12:57a look at this europeum 3 plus and europeum 2 plus so europe if europeum 3 plus
13:05accepts accepts one electron that becomes 2 plus that's the that reaction occurs at this potential
13:15but see um according to the equation we do not see any proton related to this reaction we don't see
13:26any H plus in this reaction so and uh we don't care much about
13:34thing until ph is 7 here we this is the H plus dominating area right so we don't see any
13:46H plus in this equation it's okay so that the reaction is the same up to this 7 but once
13:55that the pH is changing down to OH negative area the equation is changing to this way
14:04when we have hydroxide anion in the solvent europeum 3 plus does not exist as a europeum any longer 3
14:14plus it reacts with hydroxide ion ion and then that becomes european hydroxide 3 solid form it precipitates
14:26a very small amount of 2x and then very small amount of a H plus you know when we go
14:31over this 7 we still see the proton concentration inside right so europeum and the three H plus and accept
14:43the electron and then that goes europeum 2 plus so this reaction and this reaction both of the reaction goes
14:53for european
14:542 plus from europium 3 plus but the the reactants are quite different for each
15:03the pH area so on the right side it's it depends on the H plus the concentration
15:14so the reaction is this way and then we see pH over here the final equation is
15:25this way then this is the final one and then if we put 14 here that's 2.3
15:37something 8 something let's go for it so that one that europium something occurs
15:48that potential change it does not occur up to 7 and then after this 7 europium
15:57hydroxide is the main compound and it goes down to this way
16:07right so now we know like a thermodynamically stable for water and then
16:18also if we go around the 0.35 then europium 3 plus does not exist as itself it's
16:30changing to this one and then also if we go over pH 3 this becomes a europium
16:36hydroxide see and the so for europium 3 plus then it should go above this negative 0.35
16:49to exist as a europium 3 plus so this area is safe for europium 3 plus and this area
17:02is not safe for europium 3 plus but that's safe for europium hydroxide but once it goes down to this
17:13area we believe this may go to europium 2 plus but also the water reacts to the potential so we
17:28expect only europium 3 plus may
17:31convert to europium 2 plus but that doesn't happen but that doesn't happen the water goes to that reaction water
17:41is also working in that reaction but you know like electrodes are making a contact with water a lot because
17:49that's solvent so that solvent reaction may occur before this the species reaction may occur so
17:59so all these other areas are unstable so all these other areas are unstable only this area is for the
18:07stable for europium 3 plus right so the pulvet diagram gave us the information about which species is stable or
18:21not in some area that's what we can get from this the pulvet diagram
18:28so if we change the pulvet diagram so if we change the solvent this pulvet diagram also need to be
18:35changed but in most cases water is very abundant and also the outside the water rain that's the only solvent
18:46we can face in the nature
18:49so water so water so water purve diagram is the most of the the common one but if you'd like
18:56to have some other things you can make your own
19:03okay that's the the pulvet diagram he discovered and then also we can figure out any metal but in this
19:13case we saw some iron but that could be like the
19:18some metal pieces we can go through okay thank you for your attention I will come back with some other
19:32way
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