This document summarizes information about refractory-magnesia carbon bricks and their use in the steel industry. It discusses that magnesia-carbon bricks are a non-fired basic refractory material used as a lining in basic oxygen furnaces. The bricks contain magnesia for its refractory properties and graphite for its corrosion and thermal conductivity properties. The document outlines the preparation process for magnesia-carbon bricks and explains the mechanisms of how iron oxide in slag can react with and dissolve the carbon component over time, exposing the magnesia grains to further corrosion. It also discusses how varying the graphite content can affect the thermal properties and spalling resistance of the refractory lining.

1. REFRACTORY- MAGNESIA CARBON
Presented by: Ankita Bilung (919CR5007)
Exe. PhD (Ceramic Engg), NIT Rourkela
Seminar and Technical Writing
Course Instructor: Professor D.Sarkar

2. Refractory
“...non-metallic materials having those chemical and physical
properties that make them applicable for structures, or as
components of systems, that are exposed to environments
above 1,000 °F (811 K; 538 °C).” ~ASTM C71

3. In Simple terms: A refractory material or refractory is a material that is
resistant to decomposition by heat, pressure, or chemical attack, and retains
strength and form at high temperatures.

4. Basic Properties
• Able to withstand high temperatures
• High Thermal Shock resistance.
• Abrasion Resistant
• Low Thermal expansion
• Heat insulation
• Chemically inactive
• Impermeable to Gases and Liquids
• Low electrical conductivity (if used in Electric Furnaces)

6. Steel Industry & Refractories
About 70 % of all refractory products are used in the steel industry.
• The diversification of steel products and their purity requirements in recent years have
increased the demand for high quality refractory.
• Steelmaking requires high temperatures of the order of 1600 °C.
• It involves chemically reactive high temper phases like molten steel, slag and hot gases,
which necessitates the use of refractories.
• Since the cost of refractory adds into the cost of the product, high quality refractory at a
cheaper cost is the main requirement.
• Refractories have the potential to make or spoil. Every high temperature operation needs an
assurance system of energy saving.
The right quality, quantity and engineering of refractories can save energy and prevent loss of revenue.

7. Steel Industry & Refractories
Pitch bonded dolomite bricks and magnesia-carbon
bricks are the widely used refractories for this purpose.
• Pitch bonded dolomite bricks find applications
mainly in steel industries as lining material. This is
because of their unique characteristics such as
cheaper availability, thermodynamic stability, greater
resistance to slag attack etc., in contrast to other
basic refractories.
• These bricks were gradually phased out by replacing
with seawater magnesia-carbon brick as lining
materials in steel making units because of high
basicity of slags at high temperatures.

8. Magnesia-Carbon
• Magnesia-Carbon brick is non-fired basic refractory material.
It improves the corrosion resistance and slag resistance with its
added graphite.
• It is known that the magnesia has excellent refractoriness
but its:
- heat shock resistance is very poor.
- Highly corrosive
- Not strong against Silica (major constituent of Steel
slag)

9. However, graphite has the characteristics stated below:
• Resistance to corrosion and infiltration from furnace slag and steel fluid.
• Resistance to high-temperature attack. When in the reduction, it can resist
extremely high temperature.
• Proper high temperature strength can be retained.
• But it is a natural mineral, hence has lot of impurities esp Ash.
Ash + Silica  Reduces the Application Temp

10. Preparation of MgO-C bricks
• Pitch impregnated MgO
− Initially Pitch / Tar were used but now resin is
used instead.
− These require no firing and are only pressed,
hence is quite profitable.
− The pitch is kept in Liquid form under pressure.
As pitch contains volatile matters, which
evaporates under pressure, leaving a net Carbon
coating of about 2.5%.
− Although it is better than MgO bricks, its life does
not increase.
• Pitch bonded MgO
− In this type, pitch is pressed into MgO
bricks at very High temperature and
then cured to remove the volatile
material.
− It leaves a net Carbon coating of about
5%.
− This is used for economical purposes
especially in Ladle's of Basic Oxygen
Furnace (BOF), where wear is less.

11. MgO-C
(with Carbon in Graphite form)
Carbon in graphite form is used for its:
− Higher Oxidation resistance.
− Higher Thermal conductivity.
− Lower Thermal Expansion.

12. • The MgO–carbon bricks of varying carbon concentration are used as refractory lining
material in BOF. Laser profiling of the lining is done at regular intervals to keep track of
refractory wear in different parts of vessels.
• The main factors which affect the kinetics of dissolution of graphite flakes lying between
the MgO grains in the belly region are attack by CO2 in gas and FeO in slag, and
temperature.
• FeO can easily penetrate the MgO grains along grain boundaries and reach those places
where graphite flakes are present.
• Kinetic models of refractory wear are analyzed on the basis of data obtained from actual
laser profile measurements. The bricks salvaged from the top cone region at the end of
the campaign have been subjected to scanning electron microscope (SEM) and electron
probe micro analyzer (EPMA) investigations.
• The possible cause of wear in topcone region is also the oxidation of carbonin the brick
by CO2 gas and direct attack by FeO thrown from the jet impact region.

13. Mechanism of FeO Attack on the
Refractory Lining.
As soon as a slag containing FeO comes in contact
with the carbon in the lining, a bubble of CO–
CO2 gas is immediately formed due to the
following reactions:
FeO + C = Fe + CO -----------------(1)
FeO +CO =Fe + CO2----------------(2)
A direct contact between slag and refractory is
hindered due to formation of gas. The reaction at
the interface A (Fig. 1) of carbon and the gas is
CO2 + C= 2CO ----------------------(3)

14. • The reaction taking place at the gas–slag interface
B (Fig. 1) is same as the reaction (2)
FeO +CO =Fe + CO2
The CO2 generated at the gas–slag interface B is
transported to gas–carbon interface A (reaction 3)
CO2 + C= 2CO where it oxidizes carbon to CO.
The partial pressure of CO2 gas in equilibrium
with carbon at temperatures of steelmaking in
BOF varies from 5 to 25%.
The mass transport of CO2 gas can become rate
limiting at low concentrations of CO2, in addition
to the individual chemical reactions (2) and (3).
Carbon removal due to its oxidation by FeO and
CO2 is one of the main causes of chemical wear
of MgO–C refractory bricks.
Once the carbon is dissolved (or eaten up) by the
reactions (2) and (3), the MgO grains become
exposed and begin to dissolve due to action of
CaO, FeO and SiO2 present in the surrounding
slag, or even become loose and fall of into slag.

15. High-purity graphite is often used as a component of
MgO-C bricks for the converter lining areas where high
corrosion resistance is required.
Higher the content of graphite with high thermal conductivity, the
smaller the temperature gradient in the thickness direction of the
refractory lining becomes. That is, the thermal expansion difference in
the refractory lining decreases and the spalling resistance improves.
Converters are generally lined with MgO-C bricks with a graphite
content of 15 to 20 mass%. Mechanical spalling is caused by the thermal
stress produced when the refractory lining thermally expands under
restraint conditions.
Effect of C % in MgO

19. Characteristics of MgO-C Bricks and Their Application to Specific Converter Lining Areas

20.  Good high temperature resistance
property
 Strong slag erosion resistance of
magnesia
 Non-wetting nature
 Good thermal shock resistance
 Low high-temperature creep
 Good heat stability
 High thermal conductivity and low
expansibility of carbon efficiently
Magnesia Carbon Brick utilizes:
This makes up for the biggest disadvantage
of worse spalling resistance of magnesia and
thereby securing its place as an efficient
Refractory in the Steel- Industry.

21. Thank You