What are the factors influencing diffusion? The benefits and disadvantages of the diffusion phenomen

Factors influencing diffusion: temperature, density of crystals, atomsCombine keysStrength and weakness, etc.

When the density of the parts inside the gas is not uniform, there is a thermal movement in the molecules.

In the process, the number of molecules that diffuse from a place with a high density to a place with a low density is greater than the number of molecules that diffuse from a place with a low density to a place with a high density.

The result of this exchange is the transport of the mass of the gas from a place with a high density to a place with a low density, i.e. the diffusion phenomenon is the process by which gas molecules transport mass during thermal movement at the microscopic level.

Physical Significance:

Two containers containing two different gases are connected, and after a period of time, the two gases are mixed evenly in these two containers, and the same gas with different densities is experimented, and diffusion will also occur, and the result is that the density of the gas in the whole container is the same everywhere, and diffusion will also occur between liquids and solids.

In the diffusion process, the gas molecules move from the denser region to the less dense region, and after a period of mixing, the density distribution tends to be uniform. In the process of diffusion, the number of molecules migrating from the dense region to the city with low density is more than the number of molecules migrating from the low-density region to the high-density region.

1.When the temperature increases, the probability of the diffuser atoms gaining energy to exceed the barrier increases, and the vacancy concentration increases, which is conducive to diffusion.

2.The weaker the atomically bound bond, the smaller the q and the larger the d.

3.In the interstitial solid solution, the diffusion activation energy is smaller, and the atomic diffusion is faster. Diffusion activates the energy specific gap in the displacement solution.

The diffusion is much larger.

4.The higher the density of the crystal, the narrower the path of the atoms during diffusion, the greater the lattice distortion and the greater the atomic binding energy.

The larger it is, the greater the diffusion activation energy and the lower the diffusion coefficient.

5.The smaller the grain size, the more grain boundary area the metal has, and the greater the contribution of grain boundary diffusion to the diffusion coefficient.

6.Dislocations in crystals also contribute to diffusion.

7.Effect of chemical composition: If the concentration increases the Q of the atom decreases, and D0 increases, D increases.

What kind of diffusion is it? Physics or Chemistry? Liquid or solid?

Diffusion is the phenomenon of the transfer of molecules of a substance from a region of high concentration to a region of low concentration until it is uniformly distributed, and the rate is proportional to the concentration gradient of the substance. Diffusion is a phenomenon of mass migration due to the thermal movement of molecules, mainly due to density differences. Molecular thermal motion is currently thought to be non-occurring below absolute zero.

A large number of facts, such as diffusion, show that the molecules of all substances are constantly moving in an irregular motion.

Benefits: Put a solid freshener in the room, and the whole room will smell like a fragrance.

Disadvantage: A large amount of gasoline diffuses into the air, which is easy to cause**. Wu Dan Shed.

The factors that affect diffusion are as follows:

1. The partial pressure difference of the gas is in the mixed gas, the pressure generated by the movement of each gas molecule is the partial pressure of each gas, which is not affected by the existence of other gases or their partial pressure, and when the temperature is constant, the partial pressure of each gas is only determined by its own concentration. The total pressure of the mixture is equal to the sum of the partial pressures of the gases.

2. The molecular weight and solubility of the gas are light, and the gas diffusion is faster. Under the same conditions, the diffusion rate of each gas and the square root of the molecular weight (MW) of each gas are inversely proportional.

3. The larger the diffusion area and the distance diffusion area, the larger the total number of molecules diffused, and the diffusion rate of the bridge is proportional to the diffusion area (a). The greater the distance over which the molecule spreads, the longer it takes for the diffusion to pass through the whole process, so the diffusion rate is inversely proportional to the diffusion distance (d).

4. The temperature diffusion rate is proportional to the temperature (t). In the human body, the body temperature is relatively constant, and the temperature factor is negligible.

Mass transfer and diffusion are two concepts related to the transport of matter, and their differences and connections are as follows:

Distinctions: Definitions are different: Mass transfer refers to the process by which a substance is transferred from one location or the same state to another or to a different state. Diffusion is a chaotic transport in a gas, liquid, or solid caused by the thermal movement of molecules.

Scope: Mass transfer is a broad concept that includes heat transfer, transport of matter, and transport of radiation, while diffusion refers to only one of the transport of matter.

The mechanism is different: mass transfer is the transport of substances by mass flow, which may be due to the presence of concentration, temperature, or pressure gradients, while diffusion is due to direct collisions between molecules.

Connection: Flow of matter: Both mass transfer and diffusion involve the flow of matter, mass transfer is a flow of mass, the transfer of substances from a high concentration area to a low concentration area, and diffusion is a thermal movement from a high concentration area to a low concentration area through the collision between the molecules of a substance.

Concentration gradient change: Whether it is mass transfer or diffusion, it is related to the concentration gradient, when the concentration gradient exists, the substance will naturally flow or diffuse from the high concentration to the low concentration.

It is of great significance to the natural world: mass transfer and diffusion are common phenomena in nature, and they have important application value in biochemical reactions, gas exchange, pollution control, etc.

The phenomenon that different substances enter each other when they come into contact with each other is called diffusion.

It shows that the molecules are moving in a random way that never stops.

The phenomenon of diffusion only shows that the molecules are in motion. 1.It does not explain the irregularity of the movement.

On the contrary, it allows us to see the consistency of their movement, that is, to enter into the other. Who can say how the irregularity is reflected? 2.

It doesn't mean that the movement never stops. Because we see through the diffusion of gas and liquid, the mixture of two different substances is complete, and we can no longer see even the occasional inhomogeneity of this homogeneous mixture. It is the diffusion motion that shows that the molecular motion has a beginning and an end.

Diffusion motion shows that the movement of molecules is closely related to heat.

What are the factors influencing diffusion?

1.Effect of temperature on diffusion.

The relationship between the diffusion coefficient d and the temperature t conforms to Arrhenius' formula: d d 0 e-q rt, so temperature is the most important factor affecting the diffusion coefficient. As the temperature increases, the diffusion coefficient increases dramatically.

Cause: As the temperature increases, atoms are more likely to jump over barriers through energy fluctuations. Furthermore. With the increase of temperature, the vacancy concentration increases sharply, which is conducive to the realization of atomic burial migration.

2.Bond energy and crystal structure on diffusion.

1) The greater the binding energy between atoms, the greater the diffusion activation energy. Metals with high melting points have a low diffusion coefficient.

2) In the crystal structure with high density, the atomic diffusion activation energy is higher and the diffusion coefficient is smaller. (The diffusion coefficient of carbon in austenite is less than that of ferrite, but carburizing is generally selected in the austenite zone because of the high temperature).

3.Effect of solid solution type on diffusion.

Different types of solid solutions have different diffusion activation energies of solute atoms. The activation energy of the interstitial atoms is smaller than that of the displacement atoms, so the diffusion velocity is also larger.

4.Effect of crystal defects on diffusion.

For a certain crystal structure, the surface diffusion is the fastest, followed by the grain boundary, the subgrain boundary is the second, and the intragranular diffusion is the slowest. In general, vacancies and dislocations accelerate the diffusion process in crystals. The dislocation density increases and the diffusion rate increases.

Reason: The crystal lattice undergoes deformed growth, the energy is high, and its diffusion activation energy is small.

5.Effect of chemical composition on diffusion.

1) When the addition of alloying elements affects the melting point of the alloy, the alloying element will increase the diffusion coefficient of the solute or solvent component: conversely, when the alloying element is added to increase the melting point of the alloy, the alloying element will reduce the diffusion coefficient of the solute or solvent component.

2) The influence of alloying elements on the diffusion coefficient of carbon in Y-Fe can be divided into the following three cases:

The elements that form carbides, such as W, Mo, Cr, etc., can strongly prevent the diffusion of carbon due to their greater affinity with carbon, thus reducing the diffusion coefficient of carbon.

Elements that cannot form carbides, but are soluble in carbides, such as MN, have little effect on the diffusion coefficient of carbon.

Elements that do not form carbides but are dissolved in solid solutions, such as c. , Ni, S1, etc., two of which increase the diffusion coefficient of carbon, while S1 decreases the diffusion coefficient of carbon.