材料科学与工程专业课程总结

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Inorganic materials are the general name of all the materials except polymers materials. In this course we have mainly learned two kinds of materials, they are pottery and cement.

1. Pottery is a kind of inorganic materials, it is fired of natural or synthetical powder materials under high temperature. It can be divided into common pottery like our cup, plate and bowl, and special pottery, they have a number of special functions, like wear resistance, heat resistance and corrosion resistance.

In our daily life, we can see a glaze whether in the surface of a bowl, or in the surface of a flower vase. This glaze can isolate gas and liquid, can make the surface easily wash and increase the sense of beauty. The body of pottery can't be without the glaze, but we must be careful, when we choose the materials of glaze. In theory the glaze is the most safe when the thermal expansion coefficient of body and glaze is equal (shows the change ability of volume and length when the materials is heated or cooled). Actually it is impossible. (because the component of body and glaze are different, then the thermal expansion coefficient are different). When the thermal expansion coefficient of glaze is bigger than body, in the cooling process after firing, the glaze shrink more and exist tensile stress, it reduces the strength of pottery and make the glaze breach. But when the thermal expansion coefficient of glaze is smaller than the body, in the cooling process after firing, the glaze shrink less and exist compressive stress, this even distributed compressive stress can increase the strength, but if the thermal expansion coefficient of glaze is too much smaller than the body, the glaze will peel off.

2.Cement is also a kind of common materials, it is used for roads, houses and so on. It is a powder materials, and have a strength and hardness after stiffen in the water or in the air, thus satisfy the requirements of people.

Here I want to mainly introduce the primary components of silicate cement, they are C3S, C2S, C3A, C4AF.

C3S is the maximal component of silicate cement. The content is the most and the

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strength is the highest, but the water resistance is not good. Its establishment is as follows:

the earlier strength of C2S is low, but it can continual increase later, and it has good water resistance. Its establishment is as follows

C3A can stiffen in a short time, its earlier strength is high but it will not increase later and it is easily corroded. Its establishment is as follows.

④the earlier strength of C4AF is high and it will increase later and is not easily corroded. Its establishment is as follows:

Other components: f-CaO, MgO, glass

This course is an experiment methods course and it is about of analysis of structures and components of materials. We have learned the analysis method by X-ray diffractometer and electron microscope.

1. Engineering materials are used mostly in polycrystal, so I will mainly introduce the analysis method of polycrystal, the most convenient and exact method is X-ray diffractometer.

The sample D is on the test beds H, it can move, S is the X-ray source. When a bunch of emanative X-ray shine on the sample, the reflected ray of crystal face, who meets the Bragg equation, will become a convergent light beam. There is a receive crack in F, C is a counter tube, it can also move, when it goes to a suitable place, it will receive a reflected ray, the position of counter tube can we read from the degree scale. When the sample and the counter tube continual move, the diffractometer will draw the change of diffracted intensity with the change of angle. Then by means of analysis of phase can we get the crystal lattice parameters of the phase.

Bragg equation: 2dsinθ=λ

d is the distance of crystal face, θ is the angle of incident ray and crystal face, λ is the wavelength of X-ray.

2. The qualitative analysis

①get the diffraction pattern from the X-ray diffractometer, the computer will output d

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and I of every diffraction maximum automatically.

②size the price of d down, choose the 3 biggest .

③find the corresponding d1 in the index book, then find the approximate lines according to d2, then according to d3. If d1,d2,d3 of a line are within in the error and the other price of d are also within in the error, then we can make sure this phase is the one we find, record the number of this phase.

④find the corresponding card of this number, on which there is the parameters of this phase.

3. The quantitative analysis

The diffraction intensity in the pattern increase with the content of the phase, if we want to know the content of one phase, we can use the K value method.

IA ,IS are the diffracted intensity of phase A and S, wA ,wS are the mass fraction of phase A and S.

Add the known content wS of phase S into the sample, get the pattern from the diffractometer, we can read the IA and IS from the pattern, then we can calculate wA . We can get the value of K by means of experiment: mix the same quantity of phase A and phase S, that is to say, mA=mS, here K =

Other method: internal standard method, external standard method

4. In the analysis method by electron microscope we have learned transmission electron microscope. Its core is imaging system in lens cone. It consists of objective lens, intermediate lens and projective lens. The diffraction pattern is firstly magnified by objective lens, if the magnification factor of intermediate lens is greater than 1, then the pattern will be magnified again, if the magnification factor of intermediate lens is less than 1, the pattern will be shrank. The function of projective lens is to magnify the pattern in the intermediate lens and cast its shadow on the negative picture.

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1.Silicate materials is mainly made up of pottery, cement and glass. In this course we have mainly learned glass. The production of glass is a conversion process of melts and vitreum. Melts and vitreum are the two state of aggregation of substance except solid, gas and liquid.

The conversion process of melts and vitreum is a gradual change, it finishes in a temperature range, so the glass have no fixed melting point. For example in this picture, the ordinate is the internal energy and the volume, the horizontal ordinate is the temperature, when the melts is cooled down, when it meets point f, this moment the temperature is Tg and have finished the transmission to the solid glass, the dynamic viscosity is 1012 pas, usually we defined the temperature as Tf when the dynamic viscosity is 108 pas, with the increase of temperature, the dynamic viscosity decrease, so the Tf is on the right. When the temperature is higher than Tf, all is melts, that is to say, when it meets point b, it begin to turn to the solid glass. The conversion process takes place in the temperature range between Tg and Tf, so the glass have no fixed melting point. (dynamic viscosity shows the obstruction when the fluid flows, the fluid is a substance that change its shape under a surface paralleled force).

2. Diffusion is a common phenomenon in our daily life, the diffusion of solids is the foundation of reactions between solids. For example there is a pile of coal in the corner, after long time, the corner will become black like the color of coal, that is the diffusion of solids, this process is very slow and the path of the particle have no rule, for example like this.

When we want to know how many particles take part in this diffusion, then we can use the first law of Fick, J is the quantity of atoms when they pass the cross section in unit time, D is a coefficient, ** is the change of concentration in unit length, the minus sign represent the particle spread along the direction of decrease of concentration.

For a solid, its concentration is not uniform, like this, on the left the concentration of a substance is higher than on the right, then this substance will spread from left to right, at last the concentration will be equal , for example in this chart, this is the original

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concentration of left and right, after the diffusion process, the last concentration is between C1 and C2.

In this course we have learned shaping method. There are many metal products in our daily life, like metal buckets, metal hammers, they are made of raw materials through a certain shaping method. Actually in the production, the most common method is liquid forming. That is to say, melt the metal from solid to liquid , then pour the liquid metal into a mould with a certain shape and size, after the cooling and solidification process we get the product we need. For example, we want to produce a batch of art works with a shape of gourds. Firstly just like I said, melt the metal from solid to liquid, then put the liquid metal into a mould, after cooling and solidification, open the mould and get the work with a shape and size we need.

This method is low cost, many obsoleting elements can be used again. On the other word we can get all kinds of shape and size of elements by this method. But the production maybe have a few holes on the surface or inside, it will affect the use and properties of the products, the technology is old and the efficiency is low.

2. We have learned another method, for example there is a metal rod, we want to turn it into a shape of cup or U-shape. We put the metal rod on the machine and open the switch, the roller on the machine will bring to bear on the metal rod, then the metal will be out of shape. When we control the height that the roller drop and choose a suitable radius of the roller, then we can get the product with a shape and size we need.

3. Actually in the daily life there are many elements, they must bear torsion, bending and changing current and voltage, for example the roller, its surface withstand greater force than the core, if there is a friction force, the surface will gradually wear away. It causes a great damage to the element and decrease the useful life. So we must have a series of treatments on the surface, make it has a higher hardness and strength, but the