Engineering Chemistry S Datta

432 ENGINEERING CHEMISTRY
Properties
• Light yellow-reddish brown in colour
• Low porosity and lower refractoriness than silica bricks
• Fusion temperature 1350°C
• Crushing strength 200 kg/cm 2
• Better resistance to thermal spalling than silica bricks.
• Cheaper than silica bricks.
Uses
• In blast furnaces
• In kilns
• Charging doors etc.
3. High alumina bricks: Composition—50% or more alumina.
Properties
• Low coefficient of expansion
• High porosity
• Little tendency to spall
• Excellent wear resistance and stability.
Uses
• For linings for Portland cement rotary kilns
• Furnace hearths and walls
• In reverberatory furnaces
• In combustion zones of oil-fired furnaces.
4. Magnesite bricks: Magnesite is naturally occurring magnesium carbonate (MgCO 3
)
and is the raw material for the magnesite refractories. Calcined magnesite (at 1600°C) i.e.,
MgO is powdered to a proper size and then mixed with caustic magnesia or iron oxide as
binding material and then ground. The prepared powder is pressed into bricks in hydraulic
presses. The bricks are then slowly heated to 1500°C and kept for about eight hours at this
temperature and cooled then slowly.
Properties
• They are generally grey or brown in colour
• They can be used upto 1500°C under a load of 3.5 kg/cm 2
• They possess good crushing strength, good resistance to basic slags and very little
shrinkage
• Their resistance to abrasion is poor.
Uses
• For the lining of basic converters and open hearth furnaces in steel industry
• They are used in hot mixer linings, copper convertors
• In reverberatory furnaces for smelting lead, copper
• In refining furnaces for gold, silver and platinum etc.
5. Dolomite bricks: They are made by mixing calcined dolomite (i.e., mixture CaO
+ MgO) in equimolar proportion with silica as binding material. Other binding materials used