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 ones â the physical properties of the material. We 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 are all properties that are inherent in substances without chemical attack 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, its composition and bond between the atoms remain the same. And already differences in physical properties and other characteristics of the material help to separate the 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, the thermal, electrical, mechanical, physical, optical properties of a substance depend on the chosen direction in the crystal.
Term filling
Physical properties of a substance include such as:
- Viscosity.
- Melting temperature.
- Density.
- Boiling temperature.
- Thermal conductivity.
- Color.
- Consistency.
- The permeability is dielectric.
- Absorption.
- Heat capacity.
- Emission.
- Radioactivity.
- Inductance.
- Fluidity.
- Electrical conductivity.
And the physical properties of the material are mainly represented by the following:
- Density.
- Emptiness.
- Porosity.
- Hygroscopicity.
- Water permeability.
- Moisture recovery.
- Water absorption.
- Air resistance.
- Frost resistance.
- Thermal resistance.
- Thermal conductivity.
- Fire resistance.
- Fire resistance.
- 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 us present a characteristic 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 The mass of a unit volume of material recognized as absolutely dense.
- Medium. 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 can be different - depending on the voidness and porosity.
- Bulk. Used for bulk materials - this is sand, gravel, cement. This is the name of the ratio of the mass of powdery and granular materials to the entire volume occupied by them (included in the calculations and the space between particles).
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 a characteristic indicator for determining the profitability of the material.
Porosity
Among the physical, technological and mechanical properties of materials, porosity is not the least. This is the degree of filling the volume of the product with pores.
In this context, pores are tiny cells filled with water or air. They can be large and small, open and 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 water when 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 intensive absorption of sound energy.
Closed pores by distribution and size are characterized by the following:
- Integral curve of the distribution of pore volume per unit volume over their radii.
- Differential distribution curve over the radii of the pore volume.
Voidness
We continue to consider the physical properties of materials (density, frost resistance and others). The following is voidness. This is the number of voids that are formed between individual grains of loose, friable material. This is crushed stone, sand and so on.
Water permeability
Permeability refers to the ability of a material to give off liquid when it is dried and absorb water when wet.
During the study of the physical properties of materials, it is necessary 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 only to its vapor.
Two other important properties come from here - this is hygroscopicity and water absorption.
Hygroscopicity
How is this physical property of materials in materials science determined? Hygroscopicity - the ability to absorb water vapor and hold them inside itself as a result of capillary condensation. Directly depends on relative humidity and air temperature, size, variety and number of pores of a substance, its nature.
If a material actively attracts water molecules with its surface, then it is called hydrophilic. If the material, on the contrary, pushes them away from itself, then it bears the name of hydrophobic. In addition, individual hydrophilic materials are highly soluble in water, while hydrophobic materials are resistant to the effects of aqueous media.
Water absorption
If we talk briefly about the physical properties of building materials, then one can not help but mention water absorption - the ability to retain and absorb liquid. The property is characterized by the volume of water absorbed by the dry material when completely immersed in water. It is 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 quantity, volume, degree of openness. The value will be influenced by the nature of the material, its hydrophilicity.
As a result of saturation of a 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 breaking bonds between individual particles.
Moisture return
This is the ability of a material to release moisture to the environment. While in the air, raw materials and products retain their moisture content only under certain conditions - with relative equilibrium air humidity. If the indicator is lower than this value, then the material begins to give moisture to the atmosphere, to dry.
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 higher it is, the more intensive the drying), on the properties of the material itself - its porosity, nature, hydrophobicity. So, raw materials with large pores, hydrophobic, it will be easier to give a liquid than a hydrophilic material with small pores.
Air resistance
Air resistance is the ability of a material to withstand repeated systematic drying and moisture for a long time without losing its mechanical density, as well as without significant deformations.
Some materials during periodic wetting begin to swell, some - shrink, some - too warp. Wood, for example, undergoes alternating deformations. Cement with frequent wetting-drying tends to collapse, crumble.
Water permeability
This physical property is the ability of materials to pass fluid under pressure under themselves. It is characterized by the volume of water, which in 1 hour passes through 1 sq. Km. m of material under a pressure of 1 MPa.
It is important to note that there are also completely waterproof materials. These are steel, bitumen, glass, the main varieties of plastics.
Frost resistance
An important physical property in Russian realities. This is called the ability of a material saturated with water to withstand multiple alternate freezing and thawing without a significant decrease in strength, the appearance of visible signs of destruction.
Destruction in this process is often due to the fact that during freezing, water increases in volume by about 9%. Moreover, its greatest expansion upon transition to ice is observed at -4 ° . 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 pores with water, its density. Dense materials are considered frost resistant. From porous to this category can be attributed only those that are distinguished by a large presence of closed pores. Or whose pores water fills no more than 90%.
Physical properties are capable of representing the important capabilities of materials. We have already examined some of them in detail in the article. This is the ability to withstand cold, repeated filling with water and drying, hold, absorb, give away liquid and other important characteristics.