Refractories - Magnesia - Carbon Refractories, History, Development, Types and Applications

The evolution and use of magnesia refractories in combination with carbon started over forty years ago in the early 1950’s with pitch bonded dolomite refractories, developed primarily for the basic oxygen furnace. In these early days some of these linings in the basic oxygen furnace lasted only 100 heats, often not giving sufficient time to reline the second vessel in a two furnace shop.

The 1970’s

Very measurable improvement came when magnesia fines were used in conjunction with the dolomite coarse fractions bonded with pitch. Further improvements came with the all magnesia pitch bonded brick. In the 1970’s the burned and impregnated magnesia brick with finite pore size became the standard for the charge pad and other high wear areas, starting the beginning of the zoned lining for basic oxygen furnaces. About that time magnesia purity became a factor and a special low boron 96% magnesia grain having a lime to silica ratio of 2 to 3:1 was used extensively.

The 1980’s

The 1980’s saw the development of resin bonded magnesia-graphite, first with higher carbon content and then with the addition of antioxidants to preserve the carbon content.

More Recently

Recently fused magnesia grain, magnesia sinter with larger crystallite size, and very high purity magnesia sinter were introduced to further improve the corrosion resistance.

Other Types of Magnesia-Carbon Bricks

In addition to conventional pitch and resin bonded and burned and impregnated magnesia brick, the following three types of magnesia carbon brick are available on the market.

        The first series contains regular sintered magnesia (97% Mg0) with medium quality graphite (95% C)

        The second contains high purity sintered magnesia (99% Mg0) with high purity graphite (99% C)

        The third contains high purity sintered magnesia with high purity graphite plus antioxidants.

Properties of Magnesia-Carbon Refractories

Table 1 contains the physical properties of the conventional pitch and resin bonded brick and the burned and impregnated magnesia brick. Table 2, 3, and 4 contain a comparison of the three series containing 10%, 15%, and 20% graphite, the left column representing the previous product, labelled conventional, in each class.

Table 1. Physical properties of various types of magnesia refractory bricks.

Property

Pitch Bond

Resin Bond

Resin + Antioxidant

Burned + Impreg

Burned + Impreg

Bulk Density (pdf)

192

192

191

196

193

Mod. of Rup. (psi)

 

 

 

 

 

At 70°F

1100

3000

3000

3500

2500

At 950°F

500

--

--

--

--

At 2550°F

150

300

1500

--

--

At 2800°F

--

--

--

1250

1400

Porosity (%)

 

 

 

 

 

As received

4.5

4.5

4.5

 

 

Coked

9.0

9.0

9.0

 

 

Ignited

16.0

16.0

16.0

 

 

Residual Carbon (%)

5.0

5.0

5.0

 

 

Slag Resistance (%)

100

100

75

 

 

Pore size <4µm

25

20

60

 

 

 

Table 2. Physical properties of magnesia-carbon BOF bricks containing 10% graphite.

Property

Conventional

97 MgO + 95 Graphite

99 MgO + 99 Graphite

Bulk Density (pdf)

180

185.5

185.5

Porosity (%)

 

 

 

As received

3.5

3.0

3.0

Coked

9.2

8.5

8.5

Mod. of Rup. (psi)

 

 

 

At 70°F

1800

2500

2500

At 2550°F

1700

1700

1700

After Coking at 2550°F

1000

1200

1200

Chemical Analysis

 

 

 

Graphite

10

10

10

SiO2

0.9

0.6

0.2

CaO

1.98

1.98

0.6

B2O3

0.035

0.035

Trace

Table 3. Physical properties of magnesia-carbon BOF bricks containing 15% graphite.

Property

Conventional

97 MgO + 95 Graphite

99 MgO + 99 Graphite

97 MgO + 99 C + Antiox.

Bulk Density (pdf)

177

182

182

170

Porosity (%)

 

 

 

 

As received

5.75

4.35

4.30

4.25

Coked

10.75

9.35

9.00

3.40

Mod. of Rup. (psi)

 

 

 

 

At 70°F

1910

2220

2160

2210

At 2550°F

2160

2100

2160

2050

After Coking at 2550°F

870

970

1060

2180

Chemical Analysis

 

 

 

 

Graphite

15

15

15

15

SiO2

1.00

0.70

0.20

0.20

CaO

1.90

1.90

0.60

0.60

Fe2O3

0.20

0.10

0.10

0.10

B2O3

0.03

0.03

Trace

Trace

Table 4. Physical properties of magnesia-carbon BOF bricks containing 20% graphite.

Property

Conventional

97 MgO + 95 Graphite

99 MgO + 99 Graphite

Bulk Density (pdf)

173.2

176.0

176.0

Porosity (%)

 

 

 

As received

6.50

4.60

4.70

Coked

12.30

8.60

9.40

Mod. of Rup. (psi)

 

 

 

At 70°F

1545

1770

1750

At 2550°F

1520

1800

1760

After Coking at 2550°F

900

950

900

Chemical Analysis

 

 

 

Graphite

20

20

20

SiO2

1.10

0.80

0.30

CaO

1.75

1.75

0.70

Fe2O3

0.30

0.10

0.10

B2O3

0.02

0.02

Trace

Applications

Magnesia-carbon brick were originally designed for water cooled electric furnaces, have been used in the basic oxygen converter, in combined blowing vessels, and with the improvement through the years, their use has spread to many other applications such as ladle slag lines, degassers, etc.

Note – A complete list of references can be obtained by referring to the original text.

 

Primary author: Edwin Ruh

Source: Abstracted from International Ceramic Monographs, Vol. 1, no. 2, pp. 772-93, 1994.

 

 

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