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학습트랜스크립트
00:00Hello students. We are almost at the end of the semester.
00:09Today we are going to talk about some corrosion.
00:14It also covers some degradation of material, but corrosion is the main thing.
00:20So I chose corrosion as a topic for today.
00:25We are going to learn about how to occur in the corrosion way,
00:35and which metals are most likely to corrode.
00:39We already know about this.
00:42Maybe you have a chance to learn about some ionization tendency in metals.
00:51That's the start of this corrosion part.
00:54What environmental parameters affect corrosion rate?
00:58This one is also clear for us.
01:01For example, we know the acid rain, right?
01:06Acid rain accelerates the corrosion rate because it has a proton inside.
01:18H+.
01:19That's acidic, right?
01:21So mainly that acidity changes because that changes the concentration of the proton.
01:30Then how do we prevent the control of corrosion?
01:35This is the most important part of this chapter because we learn about corrosion,
01:40and the mechanism, and the environmental condition, a lot of things.
01:46Why?
01:47Because we want to stop that corrosion for any material of service or intention.
01:54So that's the purpose of this chapter.
01:59Let's take a look at things here.
02:02The cost of corrosion.
02:04We can simply guess.
02:06So what do you throw away at home due to the corrosion?
02:16What's happening in your home in terms of this corrosion?
02:21In my case, I recently threw away one umbrella.
02:27The inside, the metallic part, it showed some corrosion.
02:33And then it showed like a very red color.
02:40And also it's not working properly clearly.
02:43And what else?
02:44I also worried about some corrosion for the air conditioner, the air blower outside.
02:56That is also in the harsh condition outside.
03:00It's raining outside.
03:01The sunshine all the way.
03:04And the weather is cold or hot all the time.
03:08That changes.
03:09But so far, it looks okay.
03:15We purchased that air conditioner almost like 10 years ago.
03:20But still, that looks okay.
03:27Somehow.
03:28Maybe in old times, I don't think that can survive for that long period.
03:35So we have like high technologies to prevent this kind of corrosion.
03:40My car is like, how long?
03:46I purchased it in 2022.
03:50So it's long.
03:54It has been long years to keep it.
04:00But I don't see any corrosion yet.
04:04But maybe sometime later.
04:07You know, if you see an old car running around the street, around on the street,
04:15some car is quite old brand one.
04:21But they look very clean somehow if the owner treated very carefully for preventing the corrosion.
04:31But sometimes the new car, but it has some corrosion on some parts.
04:40Maybe due to the some wrong manufacturing way or the owner is driving the harsh conditions such as around the seashore or something.
04:59So here, this picture, it looks quite nice, isn't it?
05:04So in the United States, some people are living outside the city.
05:11And then they have quite large area to stay.
05:16So they can keep some car when they do not use it as some kind of a symbol for their house.
05:25And the mainly this metallic compound.
05:30We learned about some polymer, but also this textbook mainly discussable with some metal compound or composite.
05:38So corrosion, the destructive, destructive electrochemical attack.
05:44That's quite important.
05:45That's why we have to learn about electrochemistry to understand this.
05:50The metal compound corrosion or some organic compound too.
05:56So the electrochemical attack over material.
06:01Example, rusting of all automobile and other equipment.
06:06Rusting.
06:08Here it's rusting gets red, right?
06:11Cost.
06:12Look at this.
06:13Four to five percent of GMP is corresponding to the corrosion.
06:22What do you think about this?
06:28Do we have to protect this corrosion or do we have to keep this way?
06:34Because, you know, like five percent of GMP is quite a large amount.
06:39Then if we develop this corrosion problem.
06:47So somehow, let's say we figure out we can totally prevent the corrosion for any metallic compound.
06:58So we don't have to replace or we have to do something to reinforce that metal, the product.
07:08Then five, four to five percent of GMP is disappearing.
07:12It's going to go away.
07:15That's economy part.
07:17So maybe, I don't know, but we are using more than metallic compound.
07:27And also, the tendency is always to improve the quality of the material, right?
07:36So in that way, we have to make some better way to control this corrosion too.
07:46In the United States, this amounts to just over 400 billion per year.
07:53So that amount of money will be gone if we make the better corrosion-preventing way.
08:06So let's see electrochemical corrosion.
08:10So I mentioned before, we have to learn about some electrochemical chemistry to understand the corrosion part.
08:17So mainly metal is the oxidizing for the corrosion phenomena.
08:24Take a look at here.
08:26Like two reactions are necessary.
08:29It says necessary.
08:31That means this is really happening in our corrosion chemistry.
08:38Oxidation occurs and reduction occurs.
08:41I believe you know about the basic terms of oxidation or reduction.
08:47In the case of oxidation, the oxidation number is increasing and then releasing electrons.
08:54In the case of reduction, the electron will be accepted or consumed to generate something like the hydrogen gas.
09:08So it was cation before and then accepted electron becomes, it could be, if it becomes over reduced, then it could be negative way too.
09:23So if something accepts the electron, that's always considered as a reduction.
09:29So let's take a look at here, this picture.
09:33Left side is a zinc metal.
09:36Actually, frankly speaking, I don't even know where this zinc can be used for ship or automobile.
09:47I know like they are using iron, but I don't know where they use zinc.
09:54Maybe some composite, but main zinc part, I have no idea.
10:01See, zinc is contacting this acid water.
10:08So right side is kind of a water condition.
10:13When?
10:14Maybe rain comes or just the dew is generated in the morning, early morning, something like that.
10:27Right?
10:28Or just the humid condition.
10:33So let's say I have zinc and then water droplet comes up like this.
10:40So this, this condition inside here, that might be this one.
10:45Okay, here the flow of electron.
10:48I mentioned that electron should the occupy in that electro, the corrosion part.
10:55So flow of electron in the metal.
10:58So here it's zinc first.
11:01And then that release the electron.
11:05And then that becomes the zinc ion.
11:08Zinc ion can be dissolved in water, right?
11:14So ion can easily, not all the ions, but zinc ion can easily be dissolved in the water.
11:24So zinc ion moves to the water.
11:29And then that electron moves to the proton.
11:34This is not a hydrogen yet.
11:36So proton accepts electron.
11:39And then that becomes hydrogen.
11:42So this is the hydrogen ion or proton.
11:46That's correct words, but that's not hydrogen yet.
11:49Okay?
11:50So this is hydrogen.
11:52This is hydrogen atom.
11:54And this is the hydrogen molecule.
11:57And this is not.
11:59Okay?
12:00That's a proton.
12:01Or hydrogen carion.
12:03That's the actual real name for understanding this corrosion electrochemistry.
12:10And other reduction reaction also shows this way.
12:17Oxygen.
12:18We are looking at the proton or oxygen.
12:23Because that's the environment.
12:25Our environment.
12:26If we have some metal or any material that is always contacting this oxygen.
12:33Or the proton through the water or some humid condition.
12:43So in this case, oxygen and the proton is involved here too.
12:49And then four electrons is accepted.
12:52And that generates the water too.
12:55So that's the reduction part.
12:58And neutral or basic solution indicates that if it's not an acidic solution.
13:04Then that generates like a hydroxide ion.
13:08That's quite toxic too.
13:11So these kind of reactions are involved in corrosion reaction.
13:23I also want you to know about the standard hydrogen electrode.
13:28Do you remember that the tendency of the metal compound for ionization?
13:38That's KK, Na, Ma, Al, A, Fe, Mi, and hydrogen.
13:47And some Kappa or silver and gold, PT or something like that.
13:58So this is the reference.
14:04That's the standard hydrogen electrode.
14:08So actually that's quite complicated.
14:11But they draw quite simply for the reference electrode system.
14:21So actually the contact is not this way.
14:25But they just simply drew like this.
14:30But anyway, most of the metal is located onto the left side of this proton hydrogen.
14:39So when we make the contact with the proton condition and the proton solution with metal.
14:47And then metal normally dissolves into the solvent.
14:54And then that electron moves through this way.
14:59And then that generates hydrogen.
15:04Okay.
15:05Because metal wants to ionize.
15:08That's the tendency here.
15:10So if we have like this proton.
15:15And what we have like zinc here.
15:17So if we compare those two elements.
15:20Then zinc wants to oxidize first.
15:23What if we compare this hydrogen and Kappa.
15:30So in that case the hydrogen wants to oxidize rather than Kappa.
15:36So normally that proton or acid rain may dissolve all this metal compound in front of this hydrogen.
15:52But this proton or acid rain cannot dissolve or corrode behind this metal.
16:01That's Kappa, silver, gold, and platinum.
16:06They are like quite expensive.
16:09Soft metal.
16:11The Kappa is also considered as that way.
16:15That's why we are using Kappa for some electrical conductor.
16:22It has many other kinds of properties.
16:26Such as it's a little bit flexible rather than the stiffness.
16:32Because the ion is quite stiff.
16:35So it's very difficult to use as the electrical conductor.
16:41And also we need a lot of this ion for other purposes.
16:46So we can use this Kappa for the electrical conductor in most cases.
16:56And also you know like a statue.
17:00The statue normally stands outside.
17:05And they are exposed to the protonated water.
17:10Regular water and or the acidic rain.
17:15Whatever.
17:16In that condition.
17:17If we make them using other metal.
17:22Then they might be the oxidized or ionized.
17:27Due to that proton in the water.
17:30But if we have like Kappa compound.
17:33Then they might be protecting the corrosion.
17:37But because they are very close to each other.
17:40The concentration also affecting the corrosion of this.
17:43The chemistry.
17:45And small amount of Kappa is also the oxidized.
17:50Not by proton.
17:51But also like some the oxygen.
17:54Or oxygen induced in some condition.
18:00So that.
18:03So this is the reference.
18:05So that is considered as a zero.
18:09And then.
18:12The other things are.
18:14Compared.
18:15That way.
18:16We will see that.
18:17In the.
18:18Next slide.
18:20So.
18:21If we have.
18:24Some.
18:25The.
18:26The.
18:27The.
18:28The.
18:29Voltometer here.
18:30Then if electron flows this way.
18:32Then.
18:33This.
18:34This could be oxidized.
18:36And then release the electron moving to the other side.
18:38Or.
18:40That's corrosion.
18:41That's what we normally see in this chapter.
18:44But the other way.
18:45Electrode deposition.
18:47If we.
18:48Apply.
18:49The negative potential to.
18:51This.
18:52The metal.
18:53The electrode.
18:54Then.
18:55The metal.
18:56Will.
18:57Sorry.
18:58This was not a zinc.
18:59This is just.
19:00Metal.
19:01I'm sorry.
19:02So most of the metal.
19:04And then.
19:05Metal.
19:06Is.
19:07Reduced.
19:08Then.
19:09They.
19:10Will.
19:11Make.
19:12Some.
19:13Deposit.
19:14So.
19:15Actually.
19:16This one.
19:17Looks.
19:18Thinner.
19:19Than.
19:20This one.
19:21Because.
19:22It has.
19:23Deposited.
19:24Metal.
19:25On.
19:26The surface.
19:27It's getting.
19:28Thicker.
19:29So.
19:30The metal.
19:31Is.
19:32The cathode.
19:33So.
19:34It.
19:35The.
19:36If you.
19:37Want.
19:38To learn.
19:39More.
19:40About.
19:41This.
19:42This.
19:43Might.
19:44Be helpful.
19:45The corrosion.
19:46I'm sorry.
19:47Like.
19:48Anode.
19:49Oxidation.
19:50And.
19:51Cathode.
19:52Reduction.
19:53Okay.
19:54Then.
19:55Let's.
19:56Take a look.
19:57At.
19:58The.
19:59Next.
20:00Slide.
20:01Here.
20:02Standard.
20:03The.
20:04Electromotive.
20:05And.
20:06Then.
20:07The.
20:08See.
20:09Like.
20:10Where.
20:11Is.
20:12The.
20:13Hydrogen.
20:14Part.
20:15The.
20:16Kuka.
20:17Nama.
20:18Arafeni.
20:19And.
20:20Kappa.
20:21Maybe.
20:22Around.
20:23Here.
20:24Oh.
20:25Yeah.
20:26That's.
20:27Positive.
20:28And.
20:29Though.
20:30They.
20:31Are.
20:32Negative.
20:33So.
20:34Here.
20:35Kuka.
20:36Nama.
20:37Arafeni.
20:38Tin.
20:39Or.
20:40Something.
20:41That's.
20:42The.
20:43Tendency.
20:44We.
20:45Already.
20:46Learned.
20:47In.
20:48Maybe.
20:49Middle.
20:50School.
20:51So.
20:52That's.
20:53Tendency.
20:54And.
20:55See.
20:56The.
20:57Potassium.
20:58Is.
20:59Quite.
21:00The.
21:01Strong.
21:02Tendency.
21:03Compared.
21:04To.
21:05The.
21:06Ionized.
21:07Compared.
21:08To.
21:09This.
21:10The.
21:11Hydrogen.
21:12Or.
21:13Proton.
21:14Whatever.
21:15And.
21:16Then.
21:17Even.
21:18Further.
21:19If.
21:20We.
21:21Go.
21:22Even.
21:23Further.
21:24This.
21:25Then.
21:26Lithium.
21:27Is.
21:28Located.
21:29For.
21:30The.
21:31The.
21:32Battery.
21:33It.
21:34Has.
21:35A.
21:36High.
21:37Tendency.
21:38To.
21:39Be.
21:40Oxidized.
21:41And.
21:42Also.
21:43If.
21:44We.
21:45Can.
21:46Keep.
21:47That.
21:48Lithium.
21:49As.
21:50A.
21:51Lithium.
21:52As.
21:53A.
21:54Battery.
21:55Something.
21:56Is.
21:57Quite.
21:58High.
21:59Value.
22:00Right.
22:01That's.
22:02The.
22:03Potential.
22:04We.
22:05Can.
22:06Utilize.
22:07What.
22:08Can.
22:09Use.
22:10Here.
22:11So.
22:12If.
22:13Lithium.
22:14Is.
22:15Working.
22:16That way.
22:17Then.
22:18This.
22:19Potassium.
22:20Or.
22:21Sodium.
22:22May.
22:23Work.
22:24The.
22:25Three.
22:26Volt.
22:27Is.
22:28Quite.
22:29High.
22:30Enough.
22:31I.
22:32Guess.
22:33But.
22:34If.
22:35We.
22:36Come.
22:37Down.
22:38To.
22:39Like.
22:40A.
22:41A.
22:42A.
22:43That's.
22:44Only.
22:451.5.
22:46Volt.
22:47Right.
22:48If.
22:49That.
22:50Works.
22:51For.
22:52Many.
22:53Of.
22:54That.
22:55Compound.
22:56Is.
22:57A.
22:58Combination.
22:59Of.
23:00Zinc.
23:01With.
23:02Or.
23:03Coppa.
23:04Or.
23:05Some.
23:06Other.
23:07Thing.
23:08Because.
23:09That.
23:10Generates.
23:11One.
23:12Volt.
23:13Maybe.
23:14Not.
23:15Copper.
23:16They.
23:17Even.
23:18Higher.
23:19Than.
23:20One.
23:21And.
23:22The corrosion.
23:23Occurs.
23:24And.
23:25If.
23:26We.
23:27Have.
23:28Like.
23:29A.
23:30Cadmium.
23:31Is.
23:32Located.
23:33Here.
23:34And.
23:35Then.
23:36Nickel.
23:37Is.
23:38The.
23:39Which.
23:40One.
23:41That.
23:42Is.
23:43The.
23:44Higher.
23:45Value.
23:46For.
23:47Negative.
23:48So.
23:49The.
23:50Cadmium.
23:51Will.
23:52Be.
23:53Oxidized.
23:54And.
23:55Then.
23:56Nickel.
23:57Will.
23:58Be.
23:59Deposited.
24:00Okay.
24:01So.
24:02If.
24:03Cadmium.
24:04Is.
24:05Oxidized.
24:06It.
24:07Becomes.
24:08Cadmium.
24:09Two.
24:10Plus.
24:11In.
24:12The solution.
24:13Then.
24:14Two.
24:15Electron.
24:16Will.
24:17Stay.
24:18Here.
24:19And.
24:20That.
24:21Will.
24:22Accept.
24:23Those.
24:24Electron.
24:25To.
24:26To.
24:27To.
24:28Be.
24:29Deposited.
24:30No.
24:31Grapefruit.
24:32What's.
24:33Grapefruit.
24:34Um.
24:35Grapefruit.
24:36That.
24:37The.
24:38Fruit.
24:39Name.
24:40And.
24:41Then.
24:42If.
24:43We.
24:44Have.
24:45Copper.
24:46Or.
24:47Zinc.
24:48We.
24:49Just.
24:50Saw.
24:51That.
24:52I.
24:53Emphasize.
24:54That.
24:55Something.
24:56Like.
24:57Copper.
24:58Do.
24:59Not.
25:00It.
25:01Will.
25:02Be.
25:03Oxides.
25:04But.
25:05Copper.
25:06Doesn't.
25:07But.
25:08In.
25:09This.
25:10Case.
25:11In.
25:12This.
25:13System.
25:14We.
25:15Do.
25:16Not.
25:17Have.
25:18Any.
25:19Copper.
25:20Iron.
25:21If.
25:22We.
25:23Have.
25:24We.
25:25Have.
25:26That.
25:27Proton.
25:28Will.
25:29Be.
25:30Reduced.
25:31On.
25:32The.
25:33Surface.
25:34Of.
25:35This.
25:36Kappa.
25:37So.
25:38If.
25:39We.
25:40Connect.
25:41Any.
25:42Light.
25:43Bulb.
25:44That.
25:45Will.
25:46Show.
25:47Some.
25:48Light.
25:49So.
25:50Here.
25:51They.
25:52Say.
25:53The.
25:54Proton.
25:55Will.
25:56Be.
25:57Reduced.
25:58Or.
25:59The.
26:00Oxygen.
26:01The.
26:02Grape.
26:03I.
26:04Don't.
26:05Think.
26:06They.
26:07Have.
26:08The.
26:09High.
26:10Concentration.
26:11Of.
26:12This.
26:13Oxygen.
26:14Because.
26:15It has.
26:16Cover.
26:17Right.
26:18A.
26:19Small.
26:20Amount.
26:21Oxygen.
26:22Will.
26:23Exist.
26:24There.
26:25But.
26:26That.
26:27Potential.
26:28Is.
26:29Related.
26:30To.
26:31Some.
26:32The.
26:33Concentration.
26:34Part.
26:35Here.
26:36Too.
26:37So.
26:38If.
26:39We.
26:40Combine.
26:41Some.
26:42The.
26:43Set.
26:44Cadmium.
26:45Nickel.
26:46Then.
26:47That.
26:48Generates.
26:49The.
26:50Basic.
26:51Potential.
26:52But.
26:53That.
26:54Potential.
26:55And.
26:56Then.
26:57That.
26:58Is.
26:59Also.
27:00The.
27:01Connected.
27:02To.
27:03The.
27:04Temperature.
27:05And.
27:06Then.
27:07This.
27:08Is.
27:09The.
27:10Faraday.
27:11Constant.
27:1296500.
27:13Coulomb.
27:14Per.
27:15And.
27:16Then.
27:17How.
27:18Many.
27:19Electrons.
27:20Are.
27:21Passing.
27:22On.
27:23That.
27:24In.
27:25This.
27:26Is.
27:27The.
27:28The.
27:29Occupying.
27:30In.
27:31This.
27:32Reaction.
27:33That.
27:34So.
27:35In.
27:36That.
27:37Is.
27:38That.
27:39This.
27:40One.
27:41Is.
27:42Around.
27:430.09.
27:44Something.
27:45So.
27:46We.
27:47Don't.
27:48Have.
27:49To.
27:50Memorize.
27:51This.
27:52One.
27:53Is.
27:540.5.
27:55Something.
27:56I.
27:57Yeah.
27:58That's.
27:59The.
28:00The.
28:01Galvanic.
28:02Series.
28:03The.
28:04Galvanic.
28:05Is.
28:06The.
28:07A lot.
28:08Of.
28:09History.
28:10For.
28:11This.
28:12Is.
28:13An.
28:14Actual.
28:15The.
28:16Electrochemistry.
28:17Scientist.
28:18He.
28:19Is.
28:20Kind.
28:21Of.
28:22Some.
28:23Bio.
28:24Bio.
28:25Energy.
28:26Researcher.
28:27And.
28:28And.
28:29Then.
28:30Somehow.
28:31The.
28:32He.
28:33Figured.
28:34Out.
28:35That.
28:36Potential.
28:37Difference.
28:38Between.
28:39The.
28:40The.
28:41The.
28:42Italian.
28:43Physics.
28:44Guy.
28:45That.
28:46Volta.
28:47Figured.
28:48Out.
28:49Everything.
28:50But.
28:51This.
28:52Galvanic.
28:53Guy.
28:54Galvanic.
28:55Gave.
28:56A.
28:57Hint.
28:58And.
28:59Some.
29:00Experimental.
29:01Data.
29:02In.
29:03The.
29:04Conference.
29:05Then.
29:06That.
29:07Volta.
29:08Didn't.
29:09Believe.
29:10Galvanic.
29:11Suggestion.
29:12Is.
29:13Correct.
29:14So.
29:15Volta.
29:16Actually.
29:17Ran.
29:18The.
29:19Same.
29:20Experiment.
29:21To.
29:22Figure.
29:23Out.
29:24What's.
29:25Happening.
29:26Inside.
29:27And.
29:28Then.
29:29See.
29:30Like.
29:31We.
29:32Already.
29:33Saw.
29:34This.
29:35Kind.
29:36Of.
29:37Thing.
29:38To.
29:40Kind.
29:41To.
29:42Some.
29:43To.
29:44To.
29:45This.
29:46Is.
29:47Alloy.
29:48아랍, 페, 니, 페, 니, 카파, 오, nickel is behind this.
30:00I don't think that's the one.
30:02But it says like some passive one.
30:04Passive means there is some treatment on the surface or something.
30:10The real nickel, kakarnama arathenine, so here, I'm sorry, this is active one and passive one.
30:20So nickel should be located behind, before the kapha.
30:25And silver, titanium, and graphite gold, platinum.
30:32So based on this one, platinum is the best stable metal, but somehow gold is more expensive
30:43than, platinum is also very expensive, but we don't purchase any platinum-based accessories.
30:56The gold is very shiny and yellow one, it looks like somehow, you know, we are brainwashed
31:03by just yellow, some the treasure and gold from our young age.
31:15So white, silver is not that expensive one because, you know, like iron or other metal
31:22compounds are all that gray and shiny one.
31:27So like a gold is quite the, I'm sorry, what, what, what, what am I was talking about?
31:34What am I talking about?
31:35Sorry.
31:36That's the way.
31:38And then the corrosion rate, and suddenly it came to some corrosion rate.
31:44So let me, let me explain one thing more in this like carbonic series.
31:51So this chapter is treating corrosion, not the oxidation in terms of electrochemistry.
32:01So that these metal becomes the cation, any metal cation, that's corrosion.
32:13So if this metal shows the electrochemical reaction, that's the corrosion part.
32:21So electrochemistry normally related to some reaction rate or reaction components, a lot
32:30of things, right?
32:31So here they are talking about the corrosion rate.
32:37We just saw that those metals can be easily oxidized, that's corrosion, and then that corrosion
32:45rate or the rate of material removal as a consequence of the chemical reaction is an important corrosion
32:54parameter.
32:55So that's what we observed in the previous slides, and then that corrosion, the penetration
33:02rate.
33:03If we have metal, then corrosion will occur from the surface and then move into the inside,
33:10right?
33:11That's like a penetration rate or the thickness loss of material per unit of time.
33:18And here that W is the weight loss.
33:25And this is constant.
33:27And then obviously the rate is directly related to this weight loss.
33:34If we lose the high mass of that metal, that means like a corrosion penetration rate is high.
33:43And also the density and the area or time should be divided by this value to make some rate.
33:57But that's the regular way.
34:00So if the KV is given, high KV means it's easily oxidizing.
34:08And the trend is also given in the previous slide, like Kukanama-Arafeni something.
34:14So basically we see this is the more active for the oxidation and more passive to the oxidation
34:25too.
34:26So that says like here, inert, but it's not inert, it's active.
34:34So corrosion penetration rate example here, millimeter per year, and KV could be either
34:42some values, then the unit should be this way.
34:48And we don't care much about the actual value here.
34:54Then the corrosion rate is also given as the current value.
35:02If we observe a high current value, that means the more reaction is involved inside that reaction.
35:11So high current means high rate, that's obvious, right?
35:17And then the electron, number of electron of that reaction is also the, we have to consider
35:28that because let's say in the case of aluminum, aluminum generates three electrons to become
35:35one aluminum, but in the case of the potassium generates only one electron to become the potential.
35:46So in the case of aluminum, let's say we have a six electron, and then potassium also has
35:54a six electron, then that current will be expressed as a six electron here for both systems.
36:04But in the case of aluminum, only two aluminum atom is involved in that reaction.
36:12But in here, six potassium is involved in that reaction.
36:19So we have to consider this, the n value to see which one has the higher the corrosion case.
36:29So although we observed the same amount of electron, this aluminum is
36:34much the lower for the rate, okay, right?
36:42And this value is also given as a here, that's constant.
36:51And prediction of corrosion rate.
36:54So we should be able to see where, when the, how much corrosion may occur.
37:01So that, that's activation polarization.
37:04So this is the system we observed in the previous slide, the same way.
37:08And then see like zinc can be oxidized, just one example.
37:13And then electron is moving the other way, and that generates a proton.
37:19So if we observe the higher amount of proton, that means the higher amount of oxidation might
37:27occur in that system, right?
37:30And then let's take a look at here.
37:32So proton accepts the electron, and then that becomes the hydrogen atom.
37:39And then two hydrogen atom will combine to generate hydrogen, the gas.
37:45Sometimes this gas may stay on the surface to, uh, before releasing onto the air that may
37:57like a closed surface area, right?
38:01So let's take a look at the mechanism, absorption of a proton ion, uh, from the, the solution
38:08onto the zinc surface, and then accepts the, to become a hydrogen atom.
38:14And then two hydrogen atom combines to make the hydrogen gas.
38:19And then this, the coalescence of many hydrogen, the molecule to form a bubble.
38:25And, uh, that, uh, that prevents next the proton, the, the electron, the electron, the electron.
38:35Let's say we have a surface, then the proton, the, make the hydrogen gas on the surface here.
38:42Uh, next time the surface has been blocked by this air, the, the bubble.
38:48So, uh, in the previous case, this amount of the surface was of the active and
38:55available for the next reaction.
38:57But after the hydrogen bubble, only this amount of the, the surface can be still exposed.
39:04So, uh, we may need some over potential to, uh, collect more the proton onto this small area.
39:15Because it needs a higher, uh, the distance to reach that limited area.
39:22So, uh, that over potential is given as, like, some eta.
39:28And then the, the, the current is i.
39:33And, uh, i0 could be just regular and like a term that exchange current density.
39:40Then we will see that one in the, the, uh, next slide.
39:45And beta is kind of some, um, what is that, a slope.
39:53So here, from now on, you have to pay very much attention to the, the graph.
40:02I will go through it here.
40:04And then, so let's say this is a zero potential.
40:07That's the reference we observed in, uh, for the, the standard hydrogen electrode.
40:13Then this is positive value.
40:15And this is negative value.
40:17That means the, this is the oxidation part.
40:21And this is the reduction part.
40:23If we give negative potential, that, that potential, that electron will jump to the proton.
40:30And then that'll make the hydrogen gas.
40:34The other way, if we go the positive potential, then the hydrogen will be,
40:41the hydrogen is already dissolved in that, uh, solution.
40:45Because that's the standard hydrogen electrode.
40:49That's the, uh, they are bubbling the hydrogen inside to keep the, the, the constant concentration
40:56inside the solution.
40:58So that'll make some, the oxidation reaction.
41:04And then the, um, that's the, at zero potential, if we move a little bit left,
41:10or the, the negative potential or positive potential, that's I zero.
41:16And then, uh, that'll split into the, the way.
41:21So that's the, some, the basic current value.
41:27Now, um, now, now, now we have to see what's happening once that the, the reduction reaction occurs.
41:39At the very beginning, we have a lot of proton around the electrode.
41:44But once that the proton arrives at the surface, they make some hydrogen gas.
41:52And then hydrogen gas, hydrogen gas, hydrogen gas, something.
41:56Then the, the outside, the proton needs to move onto the surface to make another reaction.
42:06But that's not, like, a very fast, the, very fast, the moving.
42:17So, um, maybe that may be, that might be some, causing some limited, the current value.
42:25Because the next proton ion is not still the arriving at the surface.
42:30So then they cannot make any reaction.
42:33Only this one can make a reaction.
42:35So, depending on the, the number of concentration or the number of the, the proton available at the surface.
42:42That, uh, that may, uh, like, control, that may be controlling the limitation of the, the current due to that, that the concentration, um, the grading.
43:05I'm sorry, I'm not quite English.
43:07I'm sorry, I cannot explain this one in detail.
43:12So here, in the, in the ideal condition, or somehow, due to that limiting the, the concentration, um, the moving,
43:29there might be still, uh, the limiting current value, if we go some negative way.
43:35Maybe the other way goes this way too.
43:39But that's the ideal case.
43:41Somehow, due to some bubbling or whatever the case,
43:47that limiting current cannot, uh,
43:51the,
43:53reach it directly after applying small amount of potential.
43:59So actually here, in this case, we observed very small amount of negative potential.
44:04But that brings us to directly to this high value of the current, right?
44:09But in this case, we went down the same potential negative potential.
44:13It gives only this small amount of the current value.
44:17But that's like activation polarization.
44:24I mentioned that like, uh, due to some bubble on the surface, or due to some activation energy for the,
44:32some, the system,
44:34some, many things inside, the detailed one will be, uh, teach, uh, will be taught in some, the high,
44:44the advanced course for the electrochemistry.
44:47So we are not going to go that, that far, but due to a lot of activation, uh, way,
44:54for example, the electron should jump from the metal, metal electrode to the proton.
45:00And also there might be some interaction between them.
45:04If they don't like each other or they do not make, um, the pre bonds between,
45:11to make some real reaction.
45:14So they need like a very high potential to reach,
45:17like this amount of over potential is required to reach that limiting current.
45:26That's some activation polarization.
45:29So, uh, how much potential we need further to, uh, to reach that actual, the current limit value.
45:42That's our potential.
45:44And also activation polarization.
45:48Phenomenal area.
45:50Okay.
45:50Now more complicated the graph.
45:53So you should pay very much attention to, uh, the previous
45:58graph and this one also too.
46:02It's not that difficult.
46:04So we just observed like a zero potential here.
46:07And then the oxidation or the reduction potential for the proton.
46:14So we just observed this one, this one.
46:17That's what I explained.
46:20But now that's for the hydrogen, uh, part or the proton part or whatever.
46:28Now we have one more thing metal, right?
46:31In the other, uh, the electrode we have here, for example, like we have zinc.
46:36Zinc, uh, zinc, uh, zinc, it's like a negative, uh, zero point, zero point seven something.
46:45So that's like, uh, the center of the reaction potential.
46:51And, uh, the same way,
46:54if we go, uh, like, uh, the positive part of this zinc part, that oxidation will occur.
47:02Or the other way, reduction may occur, right?
47:07Since we are looking at only this window area, window part.
47:12So, uh, the zinc will be oxidized.
47:16And then the hydrogen, the potent, the proton will be reduced.
47:23With some, the, if we increase the potential,
47:26then the more current will show up, up to some, the value.
47:33And then the zinc will be oxidized, some other value too.
47:39When they have the same current value, they will, uh, meet each other.
47:48Remember that we have one electrode and the other electrode here.
47:54And, uh, this is zinc electrode.
47:56This might be platinum and then the proton will, it will be reduced in this part.
48:03So, if zinc is oxidized, the same amount of electron must be consumed by the other electrode.
48:14Correct?
48:14This is a circuit.
48:19Now, if we, uh, if the left electrode generates only three electron,
48:25and then right electron consumes only two electron, this is not a circuit, right?
48:31In the circuit, the same amount of electron must be flowed through all this circuit.
48:37That's the circuit, right?
48:40So, only when they have the same amount of the current density for the reaction,
48:47that's where the, the corrosion may occur.
48:51That's corrosion potential.
48:54And this is corrosion current.
48:56I'm sorry, I'm not good at, like, uh, lining.
49:01I'm not good at drawing.
49:02I'm not good at English.
49:05So, sorry for that.
49:09Um, but actually, sometimes, uh, I draw, like, this one is a straight line,
49:15but we observe that actual graph is not a straight one.
49:20And then also, it shows some activation potential, uh, I'm sorry, polarization.
49:25If we consider that part, that's this way.
49:31That's, uh, the, the actual graph will, uh, appear.
49:39Okay, let's, then that's almost it for the electrochemistry
49:44explanation.
49:45And, uh, the, how the corrosion may occur.
49:48There are, like, many different kinds of things.
49:53I don't think you have to remember all those words.
49:56Like, stress corrosion and crack tips.
50:00We have a crack and tips.
50:03They have corrosion there too.
50:05Erosion corrosion.
50:06What's erosion corrosion?
50:09Chemical attack is erosion.
50:11And then make, uh, that's also corrosion occurs.
50:15And pitting, uh, like some, some small, like a pit.
50:23And crevice.
50:24You know, crevice is, uh, uh, in, in, in Korean words, like tin.
50:30And galvanic, that's what we observed in.
50:34And the intergranular, they are going through this granular part.
50:38And selective leaching, leaching, you know, leaching, bleaching.
50:44And, uh, uniform attack.
50:46But that's, like, a different kind of corrosion.
50:49Each one has a slightly different terms.
50:51But they are actually the same way.
50:56Then, uh, this is the final part, right?
50:58I, I, I emphasize that we are learning about this, the electrochemistry, something
51:05to learn about the, this one, like a prevention.
51:10How do we protect that?
51:12So we just observed like a,
51:14KK, K, K, N, A, M, A, R, A, P, N, something.
51:16Let's say we have to use it like a potassium or calcium for our,
51:21uh, uh, the, the material for the service or the purpose of interest.
51:32If that is export to the air or water, we just learned that they are very reactive to water
51:39and then proton things.
51:41In that case, we can simply passive the surface by applying some other material
51:48or metal oxide.
51:50In the case of metal oxide, aluminum oxide, that's already oxidized, right?
51:56And then, the main, one more thing.
51:59Aluminum oxide is almost the, the transparent a little bit.
52:04or, uh, the same color of this metal compound too.
52:10So it doesn't change the,
52:15the, the, the main, the design of this, the material itself.
52:21For example, if we have a, let's say we have an aluminum oil or aluminum.
52:26So if you measure the, the electrical conductivity for aluminum,
52:31you can see the, the high conductivity of this metal oil or something.
52:38But if we, the, if you have a regular, uh, the atomic scale aluminum on silicon wafer or something,
52:49and then just a few layers, if they are highly oxidized,
52:52if you, uh, put some, that four probe on the,
52:58the aluminum part of the silicon after the reaction,
53:02they, they are highly oxidized.
53:04So you don't see the high conductivity
53:09on that aluminum after the, the, the heat treatment.
53:13And also the lower the temperature, reduce the rate.
53:21So, uh, I, I don't know.
53:23You remember that in, in the high school, the chemistry part,
53:28if we increase the 10 degree up, that reaction normally goes like two times faster.
53:36And then apply physical barriers, films and coatings like the, you know,
53:44the car has many painting outside.
53:48And then add inhibitor.
53:51Some, we observed that like oxygen is also attending the, the reaction part.
53:56So we can remove the oxygen and proton can be protected by some other basic material.
54:04And also, zinc is also quite good way.
54:08You know, zinc can be easily oxidized.
54:11And then, uh, once it's oxidized, that, um, that's like kind of sacrificial layer.
54:19Zinc can be oxidized.
54:21And then when the water dries out and zinc oxide will stay there,
54:26zinc oxide has the same color to zinc or steel.
54:29So that might be, uh, protecting inside the steel part.
54:35You know, like if steel is exposed to the air, we saw that that's rust.
54:41It becomes very red, right?
54:43And also we can put some magnesium, uh, metal compound to connect that, the metal pipe.
54:53Normally the, I don't, in the long time ago, like that gas station, the gasoline was, uh,
55:04they stored in big tank in the basement and, uh, and under the, the, the ground.
55:10And, uh, that normally had some metal, the container inside.
55:16So they have some, the magnesium connection to prevent the, the corrosion.
55:22Okay, we, we just, uh, we learned about some metallic corrosion and then some mechanism.
55:32And then like how we can prevent the, the corrosion this way.
55:39So thank you for listening and then, um, think about what you learned in the, in this chapter.
55:54What's the main topic for this?
55:58Okay.
55:58Um, thank you for, uh, taking this, uh, the chapter again.
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