Refractories

©2009 Dr. B. C. Paul

Credit is given to “Industrial Minerals” (SME), Geology.com, Yuprocks.com, Geology.about.com, Glendale Community College, The Robitics Institute-

Carnegie Melon, Tasaclips.com, Webmineral.com, gc.maricopa.edu, rocks-rock.com, Cochise Community College, mii.org, USGS

What Are Refractories

• Linings put in equipment to withstand high temperatures– Many devices are made of metal– But the temperatures inside the vessels would melt

the metal– They must be lined with something that takes a lot of

heat without breaking up or melting

• Base brick ingredient in clay– Flint clays or Kaolin with fusion temp over 425C

• Low alkali content helps with temp resistance

Alumina Refractories

• Alumina refractories hold shape at higher pressure and take more heat.– Mix incorporates

• Bauxite• Kyanite• Sillimanite• Andalusite

– Raw materials are calcined at high temperature– Action forms mixtures of silica and mullite glass– Glass is ground and dry pressed into form of bricks

Bauxite

gibbsite, Al(OH)3 boehmite, AlO(OH) diaspore, AlO(OH)

Really a combination of oxides andHydroxides

S.G. 2-2.5Hardness 1-3

Kyanite

Al2SiO5

S.G. 3.61Hardness 4-7Streak - White

Sillimanite

Same composition-Different crystal form thanKyanite

Andalusite

Same composition asKyanite and SillimaniteDifferent crystal structure.

What Are Alumina Refractory Raw Materials Worth

Record is forKyanite

About $240/ton

Magnesia Refractories

• They are not easily eaten by molten slags• Raw materials

– Magnesite– Brucite– Dolomite– Olivine– Serpentine (with extra step)

• Calcine them to make MgO magnesia– Can be used as a chemical but– Fired to Perclase makes a very resistant refractory

Magnesite

MgCO3

S.G. 3-3.3Hardness 3.5-4

Brucite

Mg(OH)2

S.G. 2.39Hardness 2.5-3

Dolomite

CaMg(CO3)2

S.G. 2.84Hardness 3.5-4

Limestone with a partial replacement ofCalcium with magnesium.

Olivine

Peridot(gem qualityOlivine)

Forsterite = Mg2SiO4

Olivine (Chrysolite) = (Mg,Fe)2SiO4

Fayalite = Fe2SiO4

Olivine is a solid solution with variable amountsOf iron and magnesiumS.G. 3.2 – 4.2Hardness 6.5-7

Serpentine

((Mg, Fe) 3Si 2O 5(OH)4)Hydrous magnesium iron silicateOne mineral variation is AsbestosS.G. 2.59Hardness 2.5-3

Value of Magnesia (MgO)

Around$500/$600/ton

(this price doesRequireProcessing ofThe raw material)

Other Refractories

• Zircon based– Fine ground pressed into bricks often used in

borosilicate glass manufacture

• Zirconia– Ultra high melting point 2710 C

• Artificial minerals – Silicon Carbide (also an abrasive)– Made from coke (a carbon source) and sand (a silicon

source) with sawdust and salt– Cook the mix at about 2200 C– Refractory very good at resisting oxidation