Characteristics of thermal insulation materials
Thermal insulation materials shall have a number of properties allowing them to perform their direct function, – protect the house from heat loss.
The most important characteristic of thermal insulation material is its coefficient of thermal conductivity. This magnitude shows how much heat the material is able to miss in a unit of time. The lower this coefficient, the better the material retains heat. For example, a 10-centimeter layer of mineral wool retains heat better than a 2-meter layer of silicate bricks, since its thermal conductivity coefficient is 20 times lower.
Thermal conductivity increases dramatically when the material is humidified, so low water absorption is important for thermal insulation. In some thermal insulation materials are introduced special fillers that prevent the accumulation of moisture. Also, the accumulation of moisture in the material is affected by its vapour permeability: the lower it, the better.
In many cases, it is important that the thermal insulation has a small weight, so the density of the material plays a great value. It is common to prefer thermal insulation, which has not only a small thickness, but also a minimum weight.
Characteristics such as fire resistance, chemical resistance, bio-resistance of the material do not directly affect its heat conservation functions, but make the material more durable and safer when used.
Very important characteristic of the material – porosity. It depends on it the thermal conductivity, density, moisture resistance of the material. In some materials, the number of pores is 98%. The nature of porosity may be different – small and large pores, closure and open; the selection of material by porosity depends on the conditions in which it will be exploited, but it is very important that the pores be are distributed evenly across the material.
Classification of thermal insulation materials
There are two main features by which thermal insulation materials are classified – the type used in manufacture of raw materials and the method of heat transfer.
According to the first classification, all thermal insulation materials are divided into organic, inorganic and mixed. Organic includes materials made of polymers that have good operational quality and low price. In addition, organic materials from wood and agricultural waste are included, such materials are rarely used in construction because they have low bio resistance, $ quickly spoil.
The most famous non-restrictive thermal insulation material is mineral wool. They also use glass fiber, foam glass, porous concrete.
Mixed thermal insulation materials most often consist of mineral fibers and asbestos.
According to the method of heat transfer, thermal insulation is divided into reflective, which does not leave the heat due to what reflects infrared radiation, and non-reflective, which has very low thermal conductivity.
Thermal insulation materials give reflective properties, foiling them.
Thermal insulation is also classified according to mechanical properties:
– block thermal insulation – blocks of foam materials such as glass or concrete, their used usually for insulation
of walls – cotton wool – is mats made of fibers sometimes quilted or sewn on a base
– plate insulation – wool reinforced with organic matter and formed into slabs;
– bulk thermal insulation – space is simply filled with individual pellets.
The most common insulation is mineral wool. It can be made of various minerals, its main feature is very high porosity – about 95%. Mineral wool has low thermal conductivity, low price, low weight, excellent bio-resistance, fire resistance, frost resistance, durability. Its main problem is the sharp loss of properties when wet. Modern mineral wool is impregnated with special substances that increase moisture resistance.
An interesting variant of material based on mineral wool is rocklight, it is hydrophobized plates of rock basalt. The main producers of mineral wool in Russia are companies such as “rockwool” and “TechnoNicol”
Mineral wool is not subject to shrinkage, therefore not requires renewal throughout the life of the building.
Styrofoam, foam and other polymer materials are
the cheapest insulation materials. They have many micropores, 80% consist of air, very light, do not absorb moisture, well protect not only from cold, but also from noise. Disadvantages include fragility and low fire resistance. However, the class of these materials is wide, and some are non-combustible.