Brick – Classification

Speaker's name Décembre 2007 4

Refractory brickdefinition :

Refractory products are ceramic materials which have a refractoriness above 1500°C.There are mainly composed of oxides (SiO2, Al2O3, CaO, MgO, Cr2O3 & ZrO2) and/or non-oxides (SiC …)

Raw material fineness A

Raw material fineness B

Raw material fineness C

Developed bonding

Bricks are a mixture of different particles / powders. Cohesion of the material is made by a sintered process.

Brick – Classification

Speaker's name Décembre 2007 5

Refractory brickSintered process :

The sintered process consists to heat up a powder without reaching the melting point. Under heat effect, the particles link together creating a ceramic bonding and give the cohesion to the brick.The sintered process is used to achieve the ceramic material densification :

•The process allows to control the material densification. As we start with a powder and the fact that the powder does not melt, we can control the particles size, the material density, depending on the initial pressure level applied to the material and/or doping products, binders addition.

•The process allows to obtain hard but fragile material with a controlled porosity.

•The process allows to master volumetric dimensions of the bricks. As there is no state changes, the volumetric dimension variations are minimum compare to a fused process (shrinkage phenomena).

Refractory workshop – Brick Selection

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What are the requirements?Heat resistance Must keep good insulation and protective

qualities over a wide range of temperature

Chemical corrosion resistance

Must resist reacting with the load and products of combustion

Cold mechanical strength Must withstand transport and installation

Hot mechanical strength Must have a good resistance to wear and load abrasion

Dimensional stability over awide range of temperature

Expansion or shrinkage can compromise lining structure

Very small thermal conductivity

Low installed cost

Must reduce wall heat losses, yet promote coating formation

Poor quality or poorly installed refractory is VERY expensive

Refractory workshop – Brick Selection

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Brick or castable? - Advantages• Brick

• Constant & homogeneous properties

• Low risk of defects in lining• Self-supporting lining• Quick heating up possible

• Castable• Very good product

properties• Quick & easy lining method• Reduction of

downtime/stoppage• Lower costs in case of

stoppage• Very versatile

• Can adapt to just about any shape or size

Refractory workshop – Brick Selection

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Intrinsic characteristics

• Thermal conductivity (W/m.K)

The coefficient of thermal conductivity is a measure of a material’s capacity to transfer heat.

The greater the coefficient of thermal conductivity, the greater the material’s capacity to transfer heat. The greater the coefficient of thermal conductivity, the hotter the walls, the greater the heat loss via the walls.Conversely, the lower the thermal conductivity the greater the material’s insulating capacities.

Thermal conductivity also has an affect on the material’s capacities to resist tothermal shock. When there is thermal shock, materials with high levels ofthermal conductivity offer less resistance to the transmission of heat throughoutthe body of the material. The greater the coefficient of thermal conductivity,the greater the resistance to thermal shock.

Refractory workshop – Brick Selection

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Brick size / format

• Standard

a = Cold faceb = Hot faceh = Height ou thicknessL = Length

E.g.: 320, 620

D

b

a

h L

Refractory workshop – Brick Selection

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Types of BricksInsulating

Alumina 40%- 50%

Alumina 60%- 75%

Alumina 75%- 85%

Dolomite

Magnesia - Chrome

Magnesia - Spinel

Magnesia hercynite - Spinel

Refractory workshop – Brick Selection

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Chemical Analysis

SiO2 65 - 69Al2O3 22 - 26Fe2O3 2.5

Not recommended by TCEA

Application Advantages LimitationsCalcining zone Excellent insulating

propertiesMust not be extended to

the safety zone (Too high T° for this brick)

Poor resistance to abrasion

Very poor alkali resistance

Lightweight Very poor resistance to mechanical stress

Insulating Physical Properties

Apparent porosity 25 – 35 %Cold crushing strength 20 N/mm2Refractoriness 1350°C (ta)Pyrometric cone 18Thermal shock 50Thermal conductivity 0,6 W/m – K (1000°C)

Refractory workshop – Brick Selection

Speaker's name October 2006 - 52

Chemical Analysis

SiO2 50 - 54Al2O3 39 - 43Fe2O3 1.5

Application Advantages LimitationsCalcining zone Very good insulating

propertiesT° < 1200 °C

Upper Safety Zone Quite good resistance to abrasion

Good alkali resistance Check raw material as alkali resistance is strongly impacted

Lightweight

Alumina 40-50% Physical Properties

Apparent porosity 14 – 16 %Cold crushing strength 50 N/mm2Refractoriness 1400°C (ta)Pyrometric cone 34Thermal shock >50Thermal conductivity 1,2 W/m – K (1000°C)

Refractory workshop – Brick Selection

Speaker's name October 2006 - 53

Chemical Analysis

SiO2 16 - 31Al2O3 59 - 74Fe2O3 1.5

Application Advantages LimitationsSafety Zone Good insulating

propertiesEutectic point @1200 °C with CaO => avoid contact with liquid phase

Good resistance to abrasion

Alkali resistanceLess resistant than 40 - 50%

(dependent on brick raw material)

Alumina 60-75% Physical Properties

Apparent porosity 18 – 20 %Cold crushing strength 70 N/mm2Refractoriness 1500°C (ta)Pyrometric cone 37Thermal shock 60Thermal conductivity 1,6 W/m – K (1000°C)

The higher the alumina content the worse resistance to Alkali

Refractory workshop – Brick Selection

Speaker's name October 2006 - 54

Chemical Analysis

SiO2 10 - 12Al2O3 80 - 85Fe2O3 1.5

Application Advantages LimitationsCooling

ZoneStill Good insulating

propertiesAvoid contact with liquid phase

(Do not go too far inside the kiln)

Very Good resistance to abrasion

Do prefer phosphate bonding

Higher operating temperatures than others

Alumina bricks

Alkali resistanceLess resistant than 60 - 75%

(dependent on brick raw material)

Alumina 75-85% Physical Properties

Apparent porosity 17 – 19 %Cold crushing strength 85 N/mm2Refractoriness 1600°C (ta)Pyrometric cone 40Thermal shock 80Thermal conductivity 2,1 W/m – K (1000°C)

The higher the alumina content the worse resistance to Alkali

Refractory workshop – Brick Selection

Speaker's name October 2006 - 55

Chemical Analysis

CaO 57.8MgO 40.0SiO2 0.8Al2O3 0.5Fe2O3 0.9

Application Advantages LimitationsBurning Zone Excellent coatability Prone to spalling

Areas of stable coating

Good insulating properties

Reacts with Alkali salts

Stable kiln operation

Economical Poor mechanical stress tolerance

Does not support thermal chocks

Sensitive to hydration (storage = sealed containers)

Dolomite Physical Properties

Apparent porosity xxxx %Cold crushing strength xx N/mm2Refractoriness xxxxx°C (ta)Pyrometric cone xxThermal shock xxThermal conductivity xx W/m – K (1000°C)

Refractory workshop – Brick Selection

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Chemical Analysis

MgO 80 – 84%Cr2O3 3 – 5 %Al2O3 2 – 4%Fe2O3 7 – 9%CaO 2.5 %SiO2 1.5%

Application Advantages LimitationsBurning Zone Good coatability

Lower transition Zone

Resistance to thermal shocks

Upper transition Zone

Good flexibility(especially under tire)

Good resistance to abrasion

Yellow color Mg-Cr = Chemical attacks

Cheapest Magnesia bricks

Mandatory bricks recycling with Raw meal

Magnesia - Chrome Physical Properties

Apparent porosity 17 - 19 %Cold crushing strength 50 N/mm2Refractoriness 1550°C (ta)Pyrometric cone 42Thermal shock 80Thermal conductivity 2.6 W/m – K (1000°C)

Refractory workshop – Brick Selection

Speaker's name October 2006 - 57

Chemical Analysis

MgO 84 – 89%Cr2O3 FreeAl2O3 9 – 12%Fe2O3 0.8%CaO 1.4 %SiO2 0.9%

Application Advantages LimitationsBurning Zone when

unstable coatingPoor coating ability

Lower transition Zone Excellent resistance to thermal shocks

Upper transition Zone Resistant to alkali salts

Cooling zone (but not for Satellite Cooler)

Good resistance to abrasion

Most expensive Magnesia bricks

Magnesia - Spinel Physical Properties

Apparent porosity 17 - 19 %Cold crushing strength 50 N/mm2Refractoriness 1700°C (ta)Pyrometric cone >42Thermal shock 100Thermal conductivity 2.7 W/m – K (1000°C)

Refractory workshop – Brick Selection

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Chemical Analysis

MgO 89 – 93%Cr2O3 FreeAl2O3 5 – 8%Fe2O3 3 - 5%CaO 1.5 %SiO2 0.5%

Application Advantages LimitationsBurning Zone Good coatability

Good resistance to thermal shocks

Reacts with Alkali salts

Good resistance to abrasion

More economical than Magnesia - Spinel

Magnesia Hercynite - Spinel

Physical Properties

Apparent porosity 17 - 19 %Cold crushing strength 50 N/mm2Refractoriness >1700°C (ta)Pyrometric cone >42Thermal shock >100Thermal conductivity 2.9 W/m – K (1000°C)