Any of the materials has physical, mechanical, thermophysical, strength, chemical, hydrophysical and many other properties. But in this article we will specifically analyze the first - the physical properties of the material. Let's give a definition, list specifically what is hidden under them, and also describe in detail each of the properties.
Definition
Physical properties of a material - all properties that are inherent in substances without chemical action on them.
Any material remains unchanged (by itself) under one condition - as long as its composition is unchanged, as well as the structure of its molecules. If the substance is non-molecular, so far its composition and the bond between atoms remain the same. And already the differences in the physical properties and other characteristics of the material help to separate mixtures consisting of it.
It is also important to know that the physical properties of a material can be different for its various aggregate materials. Say thermal, electrical, mechanical, physical, optic althe properties of matter depend on the chosen direction in the crystal.
Filling the term
Physical properties of matter include:
- Viscosity.
- Melting point.
- Density.
- Boiling point.
- Thermal conductivity.
- Color.
- Consistency.
- Dielectric permeability.
- Absorption.
- Heat capacity.
- Issue.
- Radioactivity.
- Inductance.
- Curl.
- Electrical conductivity.
And the physical properties of the material are mainly represented by the following:
- Density.
- Emptiness.
- Porosity.
- Hygroscopicity.
- Water permeability.
- Moisture return.
- Water absorption.
- Air resistant.
- Frost resistance.
- Thermal resistance.
- Thermal conductivity.
- Fire retardant.
- Refractoriness.
- Radiation resistance.
- Chemical resistance.
- Durability.
The physical, chemical and technological properties of materials are equally important. But we will analyze the first category in more detail. Let's present the characteristics of the most important physical properties of structural materials.
Density
One of the most important properties in materials science. Density is divided into three categories:
- True. Mass per unit volumematerial that is considered absolutely dense.
- Average. This is already the mass of a unit volume in the natural state of the material (with pores and voids). Thus, the average density of products from the same material may be different - depending on the voidness and porosity.
- Bulk. It is used for loose materials - it is sand, crushed stone, cement. This is the ratio of the mass of powdered and granular materials to the entire volume they occupy (the space between the particles is also included in the calculations).
The density of the material affects its technological characteristics - strength, thermal conductivity. It will directly depend on porosity and humidity. With increasing humidity, respectively, the density will increase. This is also a characteristic indicator for determining the cost-effectiveness of the material.
Porosity
Among the physical, technological and mechanical properties of materials, porosity is not the last. This is the degree of filling the volume of the product with pores.
In this context, pores are the smallest cells filled with water or air. They can be large or small, open or closed. If small pores, for example, are filled with air, this increases the thermal insulation properties of the material. The value of porosity helps to judge other important characteristics - durability, strength, water absorption, density.
Open pores communicate both with the environment and with each other, can be artificially filled with waterwhen the material is immersed in a liquid. Usually alternate with closed ones. In sound-absorbing materials, for example, open porosity and perforation are artificially created - for more intense absorption of sound energy.
Closed pore distribution and size is characterized as follows:
- Integral curve of distribution of pore volume per unit volume along their radii.
- Differential pore volume distribution curve.
Emptiness
We continue to consider the physical properties of materials (density, frost resistance, and others). The next one is emptiness. This is the name of the number of voids that form between individual grains of loose, crumbly material. This is crushed stone, sand, etc.
Water permeability
Water permeability is the ability of a material to release liquid when it dries and absorb water when wet.
During the study of the physical properties of materials, you need to pay attention to the fact that saturation with water can take place in two ways: when exposed to a substance in a liquid state or when exposed to only its vapor.
From here come two other important properties - this is hygroscopicity and water absorption.
Hygroscopicity
How is this physical property of materials determined in materials science? Hygroscopicity - the ability to absorb water vapor and keep them insidedue to capillary condensation. It directly depends on the relative humidity and temperature of the air, the size, variety and number of pores of the substance, its nature.
If the material actively attracts water molecules with its surface, then it is called hydrophilic. If the material, on the contrary, repels them from itself, then it is called hydrophobic. In addition, some hydrophilic materials are highly soluble in water, while hydrophobic materials resist the effects of aqueous media.
Water absorption
If we talk briefly about the physical properties of building materials, then one cannot fail to mention water absorption - the ability to hold and absorb liquid. The property is characterized by the volume of water absorbed by a dry material when it is completely immersed in water. Expressed as a percentage of the mass (material).
Water absorption will be less than the true porosity of the product, since a certain number of pores in it remains closed. Therefore, it will vary from their number, volume, degree of openness. The nature of the material, its hydrophilicity will also affect the value.
As a result of saturation of the material with water, its other physical properties sometimes change significantly: thermal conductivity and density increase, volume increases (typical for clay, wood), strength decreases due to the breakdown of bonds between individual particles.
Moisture return
This is the ability of a material to release moisture into the environment. Being onair, raw materials and products retain their humidity only under certain conditions - at relative equilibrium air humidity. If the indicator is below this value, then the material begins to release moisture into the atmosphere, to dry out.
The speed of this process depends on several factors: on the difference between the humidity of the material itself and the humidity of the air (the greater it is, the more intense the drying), on the properties of the material itself - its porosity, nature, hydrophobicity. So, a raw material with large pores, hydrophobic will be easier to give liquid than a hydrophilic material, with small pores.
Air resistance
Air resistance is the ability of a material to withstand repeated systematic drying and moistening for a long time without loss of its mechanical density, as well as without significant deformation.
Some materials begin to swell when periodically moistened, some shrink, some warp too much. Wood, for example, is subjected to alternating deformations. Cement with frequent moisture-drying tends to break down, crumble.
Water permeability
This is a physical property - the ability of materials to pass liquid under pressure through them. It is characterized by the volume of water, which passes through 1 square meter in 1 hour. m of material under pressure of 1 MPa.
It is important to note that there are also completely waterproof materials. These are steel, bitumen, glass, the main types of plastics.
Frost resistance
An important physical property in Russian realities. This is the name of the ability of a material saturated with water to withstand repeated alternating freezing and thawing without a significant decrease in strength, the appearance of visible signs of destruction.
Destruction during this process is often due to the fact that when freezing, water increases in its volume by about 9%. At the same time, its greatest expansion upon transition to ice is observed at -4 °C. When filling the pores of the material with water, its expansion and freezing, the pore walls experience significant damage, which leads to the destruction of the material.
Accordingly, frost resistance will determine the degree of saturation of the pores with water, its density. It is dense materials that are considered frost-resistant. Of the porous, only those that are distinguished by a large presence of closed pores can be attributed to this category. Or whose pores are no more than 90% full of water.
Physical properties can represent important abilities of materials. Some of them we have already discussed in detail in the article. This is the ability to withstand cold, repeated filling with water and drying, retain, absorb, release liquid and other important characteristics.
