[0:03]We have discussed many property, that is your general properties of pigment. What pigment? And what are the various properties of pigments? Because whenever we are using the pigments, so depending upon the property, sometime we select the end application of the pigment. Say for example, if you have to apply a coating on a car. If you want to do coating on a car body. So can we use all the pigments? No, we can't use it, then we see its properties, which pigment has good lightfastness, which pigment has good fineness, which pigment has good hardness. So what are the properties required for a car body? So accordingly, we select the pigment. Suppose a pigment is to be used in a plant where ammonia gas is emitted. Okay? So what is the nature of ammonia gas? It is alkaline. It will react with moisture and form NH4OH. It is alkaline. So we have to take pigments that are alkali fast. For example, if you have used yellow oxide of iron there, then that yellow oxide of iron is acidic in nature.
[1:17]That will react with ammonium hydroxide and change its color. So, we are discussing all these properties. So, in this, the seven properties that I told you, those seven properties have been discussed in the lab, which video has also been made, and I hope you all have seen it. So we call it General Properties of Pigments / Extenders. And here, when we are talking about the general properties of pigment, the pigment include organic as well as inorganic both. These properties will be found in both. Okay? So under this, we have already discussed about the texture, color, tinting strength,
[2:26]reducing power, bulking value.
[2:39]Here there are two things: bulking value, bulk density and bulking value. So bulking density, yesterday we had calculated it, it is mass by volume, superficial volume. And the opposite of that, that is bulking value.
[3:13]So sometime in the book you may find, because this is basically related with the volume of the pigment.
[3:29]If we keep the volume same here in both, then both our things will be equal. Only volume is such that it differs. Mass will be same in both of us, right? It is only volume. So because of that, the volume is sometime given in percent, and it is also called bulking value, or it is also called bulking volume. And bulking density is also called bulking density. These are the words which are used, don't get confused with the words. Overall, you have to understand the words and you have to know its basic paint technology. And then the last one, oil absorption. These thing to discuss in the laboratory now and did practical also. Okay? We have also done practical on this. Apart from this, there are many more properties which we will discuss. That will not yet finish in one or two lectures. There are many lectures in it. For example, flooding and floating, bleeding, chemical resistance, acid resistance, alkali resistance, solvent resistance. Okay? There are many properties like this. Today we are going to discuss about the particle shape. This property we will discuss. Particle shape. Pigments are basically, most of the pigments are crystalline in nature. Okay? Some pigments are amorphous, some are semicrystalline in nature. But most of the pigments are crystalline in nature. So you understand crystal? I will tell you again what crystal structure is. Okay? For example, in crystal structure, orthorhombic, tetragonal. Have you heard these names? Okay? Monoclinic. So, for example, we talked about lead chrome, so in lead chrome, pingo is orthorhombic. And pingo has lemon and middle, that is your tetragonal. And we will tell you, beta, when we teach you pigment, then there are many things. So now you can correlate this, because orthorhombic is having some structure, because of that it appears to be greenish yellow.
[5:46]And tetragonal is having another structure, which appears to be either lemon or middle form. Like that. So crystal structure is having very important. And how this crystal structure develop? For example, you see rock candy. How is rock candy made?
[6:14]One child who understands, please tell me, how do they do it? They don't take anything. They take the thread and insert it into the concentrated rock candy particles. Then they hang the thread in the concentrated saturated solution of rock candy. And then, as the temperature goes down,
[6:38]or when the water comes in a supersaturation state, then crystals start forming on it. So the crystals they are growing. With this, another crystal is attached, so it can be like this. Crystals can grow in many ways.
[7:07]That will depend upon the nature of that crystal, how it is growing. Sometime it happens that the crystal grows like this. So this will give you a plate-like structure. And the one that formed in a single line, like this is in a single line, this can give you a needle-like structure. Or this can also give you a thread-like, that is called acicular or thread-like. The same structure can have all-round development.
[7:54]It is not exactly spherical in pigment. When we are crushing or grinding the pigment, it can be nodular. So these are the five crystal shapes, five shape of pigment that you will find.
[8:33]Needle-like pigments can be there, acicular or thread-like, long thread-like. For example, asbestos. You know asbestos sheet. You know asbestos? Well, asbestos sheet is banned now, because it is a bit carcinogenic, its fibers are carcinogenic, so asbestos is banned.
[8:52]Earlier, imagine, the tin sheet that we used to have, tin used to get very hot when the fan used to run. So instead of that, asbestos sheet was used. But now asbestos is banned. So asbestos used to be very fiber-like. So that is your acicular or thread-like structure. Spherical, like yesterday I told you that when we heat red oxide at a very high temperature, so when it reaches 900-1000 degree Celsius, then the structure of red oxide becomes slightly nodular or spherical. Okay? Spherical. It will become almost spherical, and nodular, which is slightly like this. It is disfigured, but it will have a sphere-like character. But it is not exactly a sphere. Okay? It can be slightly oval. Okay? It can be in the form of a ring. It can be like lemon. These are the different forms. So cubical, plate-like/lamellar.
[10:19]Plate-like structure or lamellar structure or leaf-like structure, for example, you must have seen mica. Mica is in a plate-like structure. We will study all these structures. What is their role? And what part they are playing in the paint or coating industry or printing industry or textile industry. What is their role? Shape is also very important. For example, imagine that you are making a paint. In that paint, there is a plate-like pigment, whose structure is plate-like. What will happen in that? When that plate is in the paint, it will not settle down quickly. That plate will be in a floating state. For example, if you put a plate in any sea, in any water, it will not settle down so quickly.
[11:10]And if you put a round ball, of the same weight, of the same density, then it will go down quickly. So that is the role of the plate-like structure. Similarly, like acicular. You have pillars in your walls, or when you make a pillar, you put rebar in that pillar to give strength. So suppose, if there is an acicular or needle-like shaped pigment somewhere, then it will develop strength in the coating. Think in the same way, in which you are thinking of it as a building. Okay? So it will create strength in that. So for strength, we use acicular shape. Sometime it happens that we don't have an option. We have to use it. So we use it, but if there is any disadvantage associated with it, we also try to remove it. Okay? So we study about each shape and see how this shape plays its role in the paint. Okay, nodular shape, spherical or nodular shape. Okay, let me tell you one more thing. This pigment, your pigment's shape is like this. But whenever we grind the pigment, its edges are slightly damaged. So the shape changes slightly, but the overall character remains the same. For example, the character of mica, mica will be ground, its edges will break, but even its smallest particle will have the shape of a plate. Okay? Similarly, this sphere, this sphere will be damaged. Its edges will be damaged when we grind it. When we grind it, the grinding media, whether it is ceramic or steel, when it strikes its surface, it will be damaged. It can be slightly like this, it can be slightly damaged. But the overall structure will be like this.
[13:17]Okay? Now, what is the beauty of this structure? What is the beauty of this structure? The best thing about this structure, the pigments with nodular shape, for example, as I told you, red oxide of iron, which is very dark in color, and this particular structure is produced at around 900-1000 degree Celsius. Otherwise, red oxide is at 500-600 degree Celsius, and its structure is nodular shape, like this shape. This is yellow oxide of iron. When we heat it, the water in it is removed. When it is removed, this becomes like this. Then when we heat it more, then sintering starts on it. Its particles will sinter. Its other particle will join with it like this. Like this.
[14:20]Its shifting will start. And gradually, as it grows, this total particle will become a round shape, nodular shape. Are you getting my point? When you increase the temperature, what happens? When you increase the temperature, the particles stick together and their shape changes. So the color changes due to the shape. Okay? Otherwise, Fe2O3, Fe2O3 is your, at 200-250 degree Celsius, Fe2O3 has come out. Now it is Fe2O3, whether it is this, or that, or this. It's all Fe2O3, but why is the color changing? The color is changing because the shape is changing. Its crystal shape is changing, that's why the color is changing. So why does this happen? What is color? Why do you see any color? Color is because of the wavelength of light which is being reflected after striking on the object. The light that falls on any surface, after falling, the light that is reflected, what is that wavelength? That is the color.
[15:33]So here what happens is that when it strikes on this, and after striking, it reflects, then yellow light comes to us. When it strikes on this, then red light comes. So this is because of this shape, so how the shape is behaving differently. Okay? Dispersion, see, pigment is very good in many ways. This shape, one is that the packing of this pigment is very good. Because whenever from any surface, you apply paint on any surface, okay? In this paint, there is a spherical shape of pigment. So what will happen? This pigment, whenever it settles, it will settle like this.
[16:22]Okay? And if there is an acicular shape in it, how will it settle? It can settle like this, or it can settle like this, or it can settle like this, in different ways it will come. When it comes like this, in acicular shape, then its packing is not very good. Its packing is good. So this gives you good hardness, good grip. This is also one reason that we add red oxide in primer. The shape of red oxide is almost nodular, that's why we add it, so that its packing is good, it gets good hardness. It goes to the surface and sticks firmly to the surface.
[18:00]Is that clear? Any doubt to anyone? Anyone wants to ask something else? So these are the properties of the spherical shape of pigment. Sometime, we add pigment to get this property, because sometime the color is not very important. The property is important. For example, primer. In primer, color is not important, because primer is the first coat. We will apply another paint over it, so the color will be hidden. So in primer, its property is important for us. So for the property of that primer, what do we do? First, we take a pigment whose specific gravity is slightly higher. When it is higher, then the settling of this pigment will be good. When the settling is good, then it will adhere very tightly to the surface. It will settle down. That's why we take red oxide. The specific gravity of red oxide is around 5. So that will also settle down. Its shape is nodular. Due to its nodular shape, one more thing happens is that the resistance that you have, when it is hard settled, then the scratch resistance will be good in it. Okay? So all these properties you get.
[19:35]Next, the next shape we will take is acicular. Okay? So acicular shape is used for reinforcement in coating. Its dispersion is poor. It also gives poor gloss. Needle-like, good dispersion. So we apply cotton to it. It has a gloss-like character, but when you apply it, it will not prick you. It is not that strong, it is brittle, it will break. But we apply it. And then we apply another layer of polish. So what happens is that its strength becomes very good. Due to fiber velocity. Okay? So similarly, our meaning is that acicular shape, this improves the reinforcement in coating. It gives reinforcement.
[20:15]Its dispersion, however, is poor. So it also gives poor dispersion, poor gloss. Needle-like, good dispersion. Needle-like, it has good dispersion.
[23:50]Plate-like. Plate-like/lamellar/leafy. You can also call it leafy, like a leaf. You can also call it lamellar, it has the same purpose. And plate-like. Plate-like. This is also one of the common names. You get it in different books in different ways. See, what role does this play? In any coating, suppose we applied a coating on this surface. Okay? Paint was applied on it. And after applying paint, there is a plate-like structure in it. How will it settle? It will settle in this speed. This plate will settle like this.
[24:30]This plate will settle like this. This plate will settle like this. Okay? And it is sandwiched between paint. Now what will happen? Suppose we pour water from above. And this is not just one layer. As I told you in the nodular shape, there are many layers of pigment, many pigments. So similarly, one more layer of another plate-like structure is coming on top of this. Then a third one comes, like this, two or three layers are there. Now, if we pour water on it from above, what do you think? Will that water penetrate through it? No, it won't be able to. So it is having a very good water resistance property. That plate-like structure has a very good water resistance property in it. It improves the water resistance property of the coating. For example, like electric poles, yesterday I told you, we apply aluminum paint on electric poles. Aluminum paint is applied because the aluminum metal, its structure is leafy structure, like a leaf, like a plate. So water does not penetrate. Metal sheet, even the thinnest sheet of metal will not let water penetrate. And on top of that, it will give a plate-like shape. If it was nodular, then it is possible that water would have penetrated through the gaps and gone down.
[26:09]But if there is a shape like this, then it is almost impossible. Okay? Howrah Bridge. You remember? You remember its shape? It's in aluminum shape, right? It's a metallic shape, aluminum shape. So on top of it, aluminum paint is also applied. But since aluminum is a metal, and now aluminum is also becoming expensive and heavy, so now what do we do? Now a new technology has come, that is called micaceous iron oxide. Iron oxide, just now I told you two shapes of iron oxide: acicular and nodular. Here I am telling you a third one, mica-like shape. So we develop this. We develop it in iron oxide. So iron oxide has high specific gravity, very good settling, that's why we use it in primer. And on top of that, it gets a mica-like shape.
[27:07]So there will be further water resistance property. So now we use this pigment, according to the new technology, all these bridges, which are exposed to the environment for a long time, which are exposed to the rain, exposed to the UV radiation. Okay? In iron oxide, what is the other property? It has a very strong ability to absorb UV radiation.
[27:35]It is a very good UV resistance absorber. So the chances of the binder getting damaged, it also takes that inside itself and protects it from UV. It has this quality, red oxide has it. Okay? All these properties combined together give us this property, a plate-like structure gives us this property. And another thing is that its dispersion is also easy. Okay? But this plate-like structure takes some time to align. When you apply paint on the surface, the paint should not dry. Before it aligns with the surface, when it is first applied, it may be like this, or like this, in plate. It will gradually, gradually fall. No paper can stand like this. It will fall. So when it falls, it takes time to settle. A binder in paint, when paint comes like this, then the material below should remain wet. If the material below dries up, then it will remain like this. Paint should not dry. It should have sufficient fluidity so that the plate-like structure can align with the surface. The surface aligns with it. Okay? So that's why sometime if you have a better gloss, then we are required to reduce the rate of drying. We slow down the rate of drying a bit, so that the pigment or the particles in it, they align with the surface. Or the binder molecules, they align with the surface, so that you can have a better coating. Okay? So in this way, we saw that different pigment shapes have different properties. Happy watching.
