Definition Of Refractory
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What Are Refractories?

Refractories are heat-resistant materials that constitute the linings for high-temperature furnaces and reactors and other processing units. In addition to being resistant to thermal stress and other physical phenomena induced by heat, refractories must also withstand physical wear and corrosion by chemical agents. Refractories are more heat resistant than metals and are required for heating applications above 1000°F (538°C).

What Are Refractories Made Of?

Refractories are produced from natural and synthetic materials, usually nonmetallic, or combinations of compounds and minerals such as alumina, fireclays, bauxite, chromite, dolomite, magnesite, silicon carbide, zirconia, and others.

What Are Refractories Used For?

In general, refractories are used to build structures subjected to high temperatures, ranging from the simple to sophisticated, e.g. fireplace brick linings to reentry heat shields for the space shuttle. In industry, they are used to line boilers and furnaces of all types--reactors, ladles, stills, kilns--and so forth.

What Is The Property Of Refractories?

Different Refractory have different property, here simply introduce Some basic property of refractory for your reference:

Melting Point: The temperature at which the material changes state from solid to liquid at atmospheric pressure. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends on pressure and is usually specified at standard pressure. When considered as the temperature of the reverse change from liquid to solid, it is referred to as the freezing point or crystallization point. Below chart shows the melting point of some pure compounds used as Refractory.

Size And Shape: The size and shape of the Refractory is a part of the design feature. It is an important feature in design since it affects the stability of any structure. Accuracy of size is extremely important to enable proper fitting of the refractory shape which can minimize the thickness and joints in construction.

Bulk density: Bulk density is an indicator of Weight of a unit volume of a loose material (such as a powder or soil) to the same volume of water. Expressed in kilograms per cubic meter (kg/m3) or pounds per cubic foot (lb/ft3), it is a type of relative density and is used mainly in quality control, shipping, and soil analysis. Bulk density is a useful property of Refractory, which defines the material present in a given volume. An increase in bulk density of a given refractory increases its volume stability, its heat capacity, as well as resistance to slag penetration.

Porosity: Porosity is a term which is used to describe an important physical property of refractory. The porosity of refractory is determined by measuring the amount of void space inside, and determining what percentage of the total volume of the material is made up of void space. Porosity measurements can vary considerably, depending on the material, and high or low porosity will impact the way in which the material performs. This is an important property in cases where the refractory is in contact with molten charge and slags. A low apparent porosity is desirable since it would prevent easy penetration of the refractory size and continuity of pores will have important influences on refractory behaviour.

Cold Crushing Strength: The Cold Crushing Strength represents the ability of a product to resist failure under compressive load at room temperature. It has an indirect relevance to refractory performance, and is used as one of the indicators of abrasion resistance. The higher the Cold Crushing Strength of a material is the greater should be the resistance to abrasion. Refractory with high Cold Crushing Strength are also expected to have higher resistance to slag attack. The determination of cold crushing strength is also highly important in case of refractory insulating bricks where bricks have to be porous as well as strong.

Refractoriness Under Load: Refractoriness under load is a measure of the deformation behavior of refractory products subjected to a constant load and increasing temperature. The temperature range in which the softening of refractory products occurs is not identical with the melting range of the pure raw material; therefore it must be reliably determined.

Permanent Linear Change: Permanent Linear Change is a factor used to judge the suitability of Refractory in ranges of temperature limits. Refractory materials can undergo mineral formation, phase transformation or shrinkage when heated.

Thermal conductivity: Thermal conductivity is the intrinsic property of a material which relates its ability to conduct heat. Heat transfer by conduction involves transfer of energy within a material without any motion of the material as a whole. Conduction takes place when a temperature gradient exists in a solid medium. Conductive heat flow occurs in the direction of decreasing temperature because higher temperature equates to higher molecular energy or more molecular movement. Energy is transferred from the more energetic to the less energetic molecules when neighboring molecules collide.


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