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Important acid refractories are quartz, sand, dinasrock, Ganister.

Silica brick are made from hard dense fine grainedquartz, have following properties ;

Low porosity & free from air pockets,

Good thermal expansion & conductivity Excellent load bearing capacity mainly at high temp.

Not susceptible to thermal spalling at temp above400.

Silica bricks are extremely suitable for those parts offurnace which are subjected to uniform high temp.like fire bridge, roofs of acid & basic open 7 hearthfurnace, electric furnace, refining furnaces

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FIRE CLAY : Main constituent of fire clay iskaolinte,Al2O3.2SiO2.2 H2O. At high temp the

fire clays lose their water of hydration & mainlyconsists of alumina & silica.

Fire clay bricks have low coefficient of thermal

expansion, sufficient strength at high temp.Resist spalling.

Fire clay bricks are used as linings of blast

furnaces for the melting of Fe, Cu, lead ores.

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Basic Refractories : Consists mainly of basicoxides without free silica & resist the action of

bases.Most common basic refractories are

magnesite,dolomite,lime etc

Magnesite is made by dead burning the mineralmagnesite which is magnesium carbonate.

Magnesite starts losing strength at temp above

1500.Used for hearths of basic open hearth & copper

reverberatory furnaces. Electric & induction

furnace lining of L.D. crucible.

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Neutral refractories : are substances which donot combine either acidic or basic oxides & for

this reason constitute the most satisfactoryfurnace lining . Example chromite & carbon ingraphite form.