Summer!The sun, the heat in the air the smell of freshly cut grass.Grass out how far away, and the smell is felt.This is physics, this phenomenon is called diffusion.And it is defined as a particle penetration of substances in contact with each other.For example, as of now, the grass comes into contact with air, and the smell of cut grass spreads through the air far away from mowing.A similar process is generally characterized as large as the diffusion coefficient.
can say that everything that happens around us is largely due to the processes of interpenetration.Because of this phenomenon, we even live.What's so surprising?Penetration of oxygen or nutrients in the blood - and this is the real diffusion of one material enters another.Widespread diffusion in nature is much broader than we think.This phenomenon is not something exotic, but on the contrary, is widely represented in the world.Even the fact that the air exhaled by the person does not accumulate around and dissipated in space, also due to the diffusion.
is the interpenetration can be in many different bodies - liquid, gaseous, solid.Its cause is the chaotic motion of molecules of the substance.By the way, the phenomenon of diffusion is considered in the molecular-kinetic theory one of the factors supporting it.So, returning to the state of aggregation of the body: the rate of penetration of a substance depends on its state of aggregation and of such magnitude as the diffusion coefficient.
What is this mysterious concept?So-called quantitative characteristics of transport velocity of the molecules of the substance in any other.The diffusion coefficient, the formula of which is quite specific, allows an assessment of the amount of material passing through the unit area (square meter) per unit of time (second).
In practice, found that gases interpenetration occurs with the greatest speed, and rate of penetration of solids is minimized.On the diffusion coefficient is influenced by body temperature and the concentration of close mutual substances.As the temperature increases the rate of interpenetration increases with increasing concentration of the substance - the same.
Thus, the phenomenon is due to the interpenetration of the so-called concentration gradient or temperature gradient.By type of diffusion is divided into free and forced.Forced arises under the influence of external forces.Depending on the type of emergency is defined as a thermal diffusion, electricity, baro and upward.
Diffusion is widely used in the art.One of the most typical examples - diffusion welding.The essence of this technology is simple: connect the two different bodies (let it be two metals), and then expose them to pressure and temperature.Last in magnitude less than the melting point substances.
The result is a combination of two different materials.This technology is widely used in electric and electronic industries, the manufacture of large components of complex shape, and in the experimental small-scale production.Such welding can be carried out under different conditions, up to vacuum conditions, all determined by the specific requirements for the finished product.
Another, no less prevalent, using the phenomenon of diffusion is its use for the preparation of semiconductor structures.One of the technologies for creating p-n junctions based on the phenomenon of interpenetration.When exposed to high temperatures, approaching the melting temperature, a crystal structure is obtained in the field with the desired concentration of contaminants.
Consideration of the concept of "diffusion coefficient" will ensure an extremely widespread phenomenon of the interpenetration of substances in nature, as well as in a variety of variants of its use in the art.
