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학습트랜스크립트
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00:19첫 번째 chapter, 우리가 그리스도를 알아듣는
00:27그리스도의 그리스도의
00:32심쿠빅, body-centred, face-centred
00:38그리스도의 그리스도의
00:41하나의 전체들이 분류가 완료되어 있습니다.
00:48기술은 보컬을 받을 때,
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00:56이 전체들이 분류가 완료되어 있습니다.
01:03그래도 우리가 어떤 진물리에 있는지 알 수 있습니다.
01:07we still believe that they do not make totally different structures from what we have learned but that imperfections some sort of defect that may be considered as a very important point or line in that solid
01:35in terms of the properties such as the ductility or hardness and the elongation depends the elongation depending structure changes
01:53so the real crystals are never perfectly ordered right and they contain defects at different lengths
02:05scales that strongly influence the properties that includes like mechanical electrical thermal and the chemical properties a compelling application is the automotive catalytic converter like all the pollutants will
02:29molecules are dissolved to like defect to reach the catalyst okay if we have like many defects then they make more
02:41their reactive sites so that will be very effective to change they convert the our reactants to the products
02:53the products
02:57the so it it it approaches to the catalyst and then make the reaction and leave as less harmful species
03:05right so we will connect how defects form and then how we classify them and how to quantify them and then why they
03:17they are that important by the end of this lecture we should be able to describe vacancy and self interstitial point defects
03:27which will be discussed in the the next slides very soon and we also be able to calculate the equilibrium number of vacancies
03:37at a specified temperature so that temperature can change the the the vacancies a little bit so it's a temperature depending the factor
03:51and also we should uh that be able to like define substitutional and interstitial those words like a substitutional and interstitial
04:01those are solid solutions solution we have new word like a solution and now also we can sketch them and convert between weight percent and atom percent for metal alloys but that's a quite easy part like a general chemistry so i i skipped that slide out of this the lecture slide
04:29the lecture slide and uh we also can see the difference between like h and screw and mixed dislocations
04:39you know dislocation do you know the words like dislocation
04:43um it i thought it's kind of like a tiger or something is like the coming off from the uh the original place it was supposed to be
04:55and um that's what we are going to learn and describe uh the atomic structure there are a grain boundary
05:07so the basically we will start from the defect and then that defect can make some boundary and uh and also
05:17so this boundary can uh have certain the the properties such as in terms of like a mechanical or chemical
05:28reaction properties so we will go that way okay so uh let's move on to the the first slide
05:37this slide this slide reviews how crystalline solids form form a liquid so here it's it's all liquid part
05:49and then you see very small like a nuclei form so here like a solidification has two steps the first one is
05:57in nuclei form and then then nuclei will nuclei nuclei grow to form crystals see it's growing
06:07point to like some some space occupying material and that
06:16as they expand crystals eventually impinge or meet on one another like producing a grain structure
06:28the the annotated figure shows nuclei in the in the melt and then growing crystals and the resulting
06:36polycrystalline grain the morphology once grows front front meet this process sees many of the defects
06:47and the interface we will study later so uh you know like when we grow the silicon wafer that the ingot is
06:57perfectly grown crystal it doesn't have this kind of grain boundaries but when we have this
07:04uh nuclei form and growing they have a lot of this grain at the end we will learn how to
07:12uh measure the size of this grain and also the what's the main inducing factor to make this kind of
07:24the boundaries yeah crystals grow until they meet each other that's what i explained a little bit
07:34and see polycrystalline materials so in the previous slide we just saw this a polycrystalline so each one
07:43is a crystalline the sizes are quite different from each other and then the so then it's not like a
07:56perfectly ordered crystal that's polycrystalline so we have many this this way crystalline and this way
08:06crystalline they have a different uh crystalline material right so most engineering metals are this way
08:16polycrystalline regions between crystals are grain boundaries here it's grain boundaries
08:24transitions from one lattice orientation to another right so the orientations are a little bit changing
08:32the boundaries are slightly disordered right like slightly disordered sometimes are like a
08:40a little bit bigger mismatch but normally like a slightly disordered and have a lower atomic packing
08:46density it's obvious right so we have an empty room so it's a lower atomic packing density than grain interiors
08:57as a result they exhibit uh high mobility for interfaces this the atoms can have a high mobility here
09:08and also high diffusivity i think those words are almost the same i guess and then also high chemical reactivity
09:16see all those uh the crevice or like empty space can be exposed to any uh chemical exposure so that could be liquid or gas
09:31so that can penetrate through this the gap otherwise this atom-atom interaction they are very close to each other so
09:41it's very difficult to penetrate through this one but it's this boundary region is much easier to uh go through
09:55so um the we can guess that like these three uh possible way right
10:03and then here uh all this the solid material that can be made by some casting like during casting
10:17temperature gradients and then and also under cooling control grain shape uh control the grain shape and size
10:26see we have like um what is it called like this could be some cup or any reaction vessel then full of liquid
10:38first and then we just let it cool down and um the inside maybe the temperature will
10:47it will slowly cool down but outside this temperature change is much bigger than inside it's it's obvious
10:57near a cold mold wall here it's cold mold more wall rapid cooling and the large under cooling big delta
11:07temperature change right so the delta t here delta t is greater on the the near the world but inside
11:17the delta t is much smaller
11:24so what's what's favorable and on each side inside and outside so lower on the the father from the wall
11:37father from the wall inside the lower under cooling favors the direction on the directional growth
11:44and leading to a columnar grain column the grain c or the columnar grain aligned with the heat flow
11:52heat is flowing all the way all the way direction grain refiners the interior like inoculants are often added
12:02to promote numerous nuclei and uniform fine equiaxed structures that improves like mechanical properties and
12:13reduces an isotropy but outside you see like the temperature change is much bigger and then they might have
12:25the higher number of nuclei sites so they can have many much like a higher number of grains and i'm sorry
12:36like crystals and then sometimes they have like equiaxed grains due to rapid cooling rather than columnar one
12:56there is no such things as a perfect crystal that's what we just saw from the
13:01the mold cooling or the previous slides they all showed like defects and what are these imperfections
13:11then what are why they are important how do we describe and quantify them and how do processing routes
13:22control their type density and distribution thereby they turn and like some tuning properties
13:35why do we have to study like imperfections
13:40so in the textbook like a catalytic converter
13:44can be shown as an example like defects profoundly influence behavior and then allowing introduces impurity
13:55atoms that distort the lattice and strengthen metals brass about 70 percent copper and 30 percent of zinc
14:05is much stronger than pure copper so when we add make it some imperfection in solid
14:14that will change their the its mechanical properties and also like some the catalytic effects
14:22and many things we will see and then we will understand the defects
14:30which let us like design microstructures for targeted performance
14:36here um we have some the uh classification so the here the textbook says like a point defect and line
14:51defect and area defects i don't think you don't you have difficulties understanding the word like a point
14:58and line and area point is like a zero dimension and line is one dimension and area is two dimension
15:06right so um the vacancy we will learn about this vacancy atoms in the next slides very quickly
15:14and interstitial atoms and interstitial atoms and substitutional atoms those two
15:20are like a mainly important to understand the the the solution the metal solution the properties
15:31and dislocations or grain boundary this is also very important to understand our like a solid system
15:40but this location this is the like a processing it's not a result
15:45so um you know if we understand those things we are always like focusing on the result right so
15:56uh i think the most important thing for our experimental process is like a grain boundaries
16:02and um this can be made by all this like point defects and line defects so these are like a consisting factors to make this area defects
16:18okay and then let's move on to this point defects that was described in the previous slide
16:26a vacancy is a missing atom missing him where did it go so that went to
16:33this self-interstitial here it went to this part vacancy vacancy you know the word like vacancy
16:42and self-interstitial so one is missing and that is added to um another like a structure
16:54in the ordered structure that makes us a little bit disorder in this area
17:00distortion of planes and also distortion of planes
17:07so uh we would like to know like how many vacancies are existing in in ordered metal
17:14or how many interstitial self-interstitial the same way whatever so that's that might be interesting part so here it's already given here we don't need to
17:29to go through to find out this equation so it's a kind of given let's see here equilibrium concentration varies with temperature so temperature is affecting
17:43the number of the defects that will be shown in the next slide and the number of potential defect sites is considered as n
17:53and then we are interested in number of defects here
17:56that's nv vacancy is related to some arrenews equation you know like arrenews is like a distribution is always some kind of activation energy divided by
18:08uh this uh the unit energy kt
18:14so this is the uh the always shown as a like arrenews equation
18:21and then the those are like uh the constant at a certain temperature or constant can be
18:30uh either this one or this one if we use like a consistent unit like a joule or electron volt
18:39so that's around like 0.9 electron volt or something
18:46so that's quite uh close to one electron volt which corresponds to
18:53um almost 11 000 kelvin a temperature degree celsius uh change and also that's around like a 10 20
19:0824 nanometer light one electron volt very close to that right so um
19:16um um let's measure the uh the activation energy then we can convert this equation into
19:27some log scale and do some mathematical way to figure out how we can do some graph so when we
19:35increase the temperature then this number is also increasing but this is a log scale so it's not that
19:42clear to figure it out but you know whenever we have this arrenews equation to figure out this uh the
19:49this the activation energy we always draw like a log scale the graph and then we figure out the slope
20:03and also uh let's check like some example problem calculate the equilibrium number of vacancies per
20:12cubic meter for kappa it's a cubic meter and one thousand degree celsius so density is given and uh atomic weight is given
20:25and and then the activation energy is given uh for a copper that's one electron volt sorry
20:34and uh the avocado number is here and uh do the math right it's it's given so we put those numbers and to calculate it
20:47and then uh this the how many coppers are existing in one cubic meter that's this number so we are supposed to see
20:58uh all these sites could be a possible vacancy site and then actually when we do the the math
21:08then that's this number so um here like that's almost 10 to the 29th and then this is 2.10 to the 25th
21:19so around like um uh 4 4 000 times so it means it means like every 4 000 copper has one vacancy spot
21:37do you think it's a large number or a small number um 4 000 coppers are existing as uh
21:45uh order the crystal position and then one of them is missing
21:544 000 so when we have like uh the all the chairs the 4 000 chairs and the one chair is missing inside
22:04uh i don't know that's a big number or not but uh that could affect very important characteristics in
22:11in the in in the the material in semiconductors and um or like uh insulator or something
22:24uh in in this textbook we do not go that far like uh the one the imperfection or one vacancy or
22:33the some concentration can change the the effect of the material we don't go that way that's totally
22:41different on the class so if you have a chance that you can take that kind of a class in the semiconducting
22:50class so uh what happens to that one missing copper so we have one thousand four thousand copper and then one
23:02one side is missing missing and then this goes to the top
23:07if we increase the temperature it'll move to go into this interstitial part and then finally we'll go up
23:18there so um the low energy electron microscope view of the one one zero surface of nickel aluminum and then
23:30they increase the temperature to to see what's happening uh based on what we have learned that
23:37when we increase the temperature that empty empty sides will increase then what's happening to them
23:46they will come up to the surface due to the temperature uh kinetic energy and then they will make
23:53some kind of this the terrace on on top of the the surface increasing the temperature normally causes like a surface island
24:07and uh also that here like the drawing empty side and then make another terrace on the on the surface
24:17right and that is also shown in the cooling temperature so all the terrace were going back to the uh the empty
24:28the the vacancy spots you see it's it's this side is lower or some other sides could be lower
24:36it's disappearing and it's changing depending on the temperature
24:41so that's 958 degrees to 740 degrees such as cooling down just in two minutes that's quite interesting
24:53isn't it
24:57we don't care much right
25:00uh okay here like a imperfection we we also mentioned that like um
25:07um here like solid solution sometimes uh substitutional here the copper and nickel uh copper nickel
25:19they are very important uh the elements they are all transition uh the metal and then the in
25:28periodic table their the location is uh close to each other
25:33so uh the sizes are very close so it's it's it's it's almost the same not exactly the same but almost the same
25:45so the here the size are almost the same way kapai is a little bit uh looks smaller but kapai is 29 so i guess it's um
25:57a little bit bigger i guess but but it doesn't matter so it's a position is all they very close to each other and then
26:11compared to this we will see like interstitial one to understand the substitutional ease in the easily
26:19see see like a carbon carbon carbon in iron you know like um the japanese knife or cutter or sword
26:34you know they are all made of like iron and long time ago and then the so japanese knife
26:43was very famous when i was very famous when i was very young and uh all the the
26:50housewives once wanted to have a knife from japan they added like a carbon in the iron to make it very
27:01stronger and uh the um very um like what is that like mechanical property is uh quite high so when you use it uh it doesn't
27:19it stays as a very sharp edge for a long time so that in that case the copper goes into this interstitial like
27:30in between them interstitial sites so when they have like a size changes science size difference is quite big
27:40then we see like interstitial solid solution otherwise we see this substitutional solid solution
27:49and uh solid solutions in uh the in a b in a plus particles of a new new phase
27:58sometimes like a second phase particles are existing in inside the the the the mixture different
28:07composition and different structures too
28:14then uh we just saw like a big difference between interstitial and also like substitutional
28:24then how can we guess which one occurs but it's a isn't it obvious to say like a which one comes
28:31substitutionally which one comes the interstitial solid solution so if their size change the size
28:38what the the difference is bigger than interstitial solid solution otherwise
28:48and substitutional solid solution so Hume Rotary made a rule to determine what kind of solid solution will occur when we have a mixture
29:02so if it follows this order then that'll go for a substitutional otherwise interstitial
29:12you know rule here uh remember that if you took some other classes uh from me then i mentioned this
29:22kind of things uh at the very beginning of the class all the time so when you have a hypothesis we have a
29:30hypothesis we should make some model to explain it and then we make some rule if it goes for every detail
29:41and uh it's very difficult to find the the the what is that exclusion then we call it a theory
29:51so a lot of things become theory vsp er model and then uh the that became like some kind of theory
30:01but here octet rule and uh Hume Rotary rule it's not a theory that means it's not like
30:10exactly um the matching to every cases and also it's empirical rule empirical rule you know what empirical
30:24means like experimental so um it's kind of some conject or uh guessing and then
30:35uh it's reasonable guessing so we just saw that way right like um atomic radius difference is less
30:44than 15 percent and proximity in periodic table so their sizes are but this is almost the same way but
30:53here in similar electronegativity and same crystal structure for pure metals like a simple cubic
31:03body centered cubic or the face centered cubic hexagonal close packing and valence is metals the oxidation
31:11number two plus or three plus or one plus so in this order so the number one is more important two is
31:22but if we have like um um three matching things then maybe that will go through this like substitutional
31:38otherwise interstitial okay
31:43so here's an example you will see this kind of exam example in your midterm exam i guess
31:49so um let's take a look here would you predict more aluminum or silver to dissolve in uh zinc
31:59here's zinc this is reference then we compare aluminum and silver here two thing then size is the number one
32:09thing uh their size are very close to each other although this one is more close to
32:18zinc but the difference is very small so it's very difficult to say uh this one is more favorable to
32:29zinc but let's take a look at the next one crystal structure
32:34um fcc fcc they are the same electronegativity 1.9 and 1.5 1.5 is more close to 1.6
32:44so here if this one is closer and this one is closer and one three that's two so
32:53the difference is one two both of them so based on this the atomic radius and electronegativity
33:02i will choose aluminum for um better um the substitutional the solid solution here dissolve in a zinc
33:18so why don't you uh start the slides and then figure out the answer for the the second case
33:27so uh and then let's take a look at the defects so um that's like a mixing solution and then
33:45sometimes it makes a line defect this locations are also like a defect and slip we will learn this
33:55slip way um hexagonal close packing the plane direction and uh also crystal direction um
34:05it doesn't explain that much thing but we can the we can say some some the atom interaction uh
34:18uh is much weaker than like a contactly matching so let's see like some some atoms are like making contact and some of the
34:35atoms does not make a contact and they have some gap and then if we uh like press down or elongate out of
34:45the its force then this might be the changing and making some gaps and uh along this one if we make uh make some
34:59then slide then that'll make this a slap slip steps
35:05so we will see that this normally happens for like a hexagonal close packing
35:11so that's that's normally happens for hexagonal close packing we will see that and then uh like a linear
35:19defects dislocations are one dimensional defects and edge dislocation and screw dislocation
35:27so uh we will see the image here like also we will learn like a burger specter here
35:33so uh burger specter is a kind of like a pressing direction why this this location occurs because
35:44some of the forces are like have the pushing the the crystal in a certain direction and then one of the
35:53the crystal's structure is not making order the way so it's like a perpendicular to each other
36:06so in that case like at this location
36:11line one and also the same way it's like the animation part but it doesn't work here
36:18uh when we press this way you know like um the this distance is getting smaller and then the half of
36:30them is still the same way so this location most requires a successive bumping of a half plane of the
36:38atoms half planes of atoms from left to the right here that's burger specter and then bonds across the
36:47slippery planes are broken here it's broken and then um they're remade in succession
36:59and uh screw dislocation is a push that this face has been pushed and uh uh it's moving direction is the
37:08the same way and then but actually when we take a look at the solids there in most cases
37:15uh they have like um some this screw and edge and uh mixed dislocation along this like in many spots
37:30that can be uh the viewed in the the virtual msc site the textbook sites but we couldn't see them
37:39but we can check some youtube to see this kind of this location if you are interested
37:51okay so these locations are visible in electron micro microbes like sem or tem whatever you prefer
38:01most likely sem and then this can be connected to uh some astm value um and see like um all the the dislocations are
38:17shown as line defects right
38:23okay all this uh the imperfection in solid part is uh quite important to
38:29um to make uh catalysts or some very smooth lines and everything so
38:36um the everyone who wants to work on this solid they are very sensitive to this kind of imperfection
38:47but in our cases we are like doing some uh solar cell or some energy materials we would like to
39:00make very flat without this kind of the imperfection part for our purpose but it's very difficult to
39:09to make that way so um uh let me stop here for the the the first part and then i will go through
39:21the next part like this location that's what i um showed you before like um this location especially
39:28for like a close packed one that uh close packed directions that's uh like a slip way so we will discuss
39:39over how they uh they show some kind of a slip way and then how when we do some tensile direction how
39:50what's happening onto this like a the cutting part and the other things are all the just the method
40:03how we can figure out all these kind of defects i will see you very soon thank you
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