Properties of RefractoriesThe properties of refractories are as follow. Chemical Properties
Usually refractories are divided into three categories acidic, basic and neutral. Although in many cases it is difficult to make sharp distinction. |
Silica is decided to be acidic and magnesia bricks are strongly basic. However, fire clay bricks are generally placed in the neutral group. Chemical reaction may take place when the refractory comes in contact with fuel ashes, slag, gases inside the furnace, and the products such as glass or steel.
PorosityIt is directly proportional to the resistance to chemical attack. The lower the porosity of the brick, the more difficult it is penetrated by molten fluxes and gases. Therefore, the bricks having the lowest porosity have greatest strength, thermal conductivity and heat capacity. Fusion PointFusion point is determined by the use of pyrometric cone with known softening point. Since the refractories are composed of both amorphous and crystalline material that is why they do not have sharp malting point and they get soften gradually. |
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Spailing
Any fracture or flaking off a refractory brick is called spailing. It is caused by uneven heat stresses or heat compression. It is the property of refractory to get expand on heating, the brick that undergo the greatest expansion are more susceptible to spailing when subjected to rapid heating or cooling.
Resistant to Temperature Change
Bricks that have the coarse texture and low thermal expansion are more resistant to rapid thermal change. Less strain is developed in these kinds of bricks. When the bricks are being used for long time, they can melt/corrode easily.
Thermal conductivity
The bricks that are densest and least porous possess highest thermal conductivity. Heat conductivity is desired in muffle furnace. Insulation is require in some special
Heat Capacity
The heat capacity of furnace depends upon thermal conductivity, heat capacity and specific heat of the refractory. When the low quantity of heat is absorbed by a weight brick, it gives advantage to the furnace working intermittently. Because in less time and consuming less fuel working temperature of furnace is achieve. The bricks made up of fire clay which are densest are best for regenerator checker work, as in stoves, blast furnace, coke and oven.
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