What are magnesia-chrome (mag-chrome) refractories primarily composed of?
A
Magnesia (MgO) and Chromite (FeCr2O4)
C
Silicon carbide and alumina
Analysis & Theory
Mag-chrome bricks are primarily made from magnesia and chromite to provide high-temperature stability and corrosion resistance.
Which property is enhanced by adding chromite to magnesia in mag-chrome bricks?
A
Electrical conductivity
C
Thermal shock resistance and slag resistance
Analysis & Theory
Chromite improves both slag resistance and thermal shock resistance in mag-chrome refractories.
Mag-chrome refractories are especially suited for:
A
Electric furnaces and non-ferrous smelting furnaces
B
Glass tank regenerators
Analysis & Theory
They are used in furnaces that handle both basic and acidic slags, such as non-ferrous metal and electric arc furnaces.
Which environmental hazard is associated with mag-chrome refractories?
A
Carbon monoxide emissions
C
Formation of hexavalent chromium (Cr VI)
Analysis & Theory
Cr(VI) is carcinogenic and can form under oxidizing conditions in mag-chrome refractories.
Mag-chrome bricks are generally not preferred in:
Analysis & Theory
Due to Cr(VI) risks, mag-chrome bricks are avoided in applications requiring clean and food-safe materials.
Which material is essential in carbon refractories?
Analysis & Theory
Carbon refractories are composed of carbon-rich materials like graphite, giving them resistance to chemical attack and high conductivity.
Carbon refractories exhibit excellent resistance to:
C
Chemical attack by fluorine and alkalis
Analysis & Theory
They have strong resistance to aggressive chemicals including alkalis, fluorides, and slags.
Carbon bricks are NOT suitable for:
C
Incinerators with oxidizing atmospheres
Analysis & Theory
Carbon reacts with oxygen at high temperatures, making it unsuitable for oxidizing environments like incinerators.
Which of the following is a disadvantage of carbon refractories?
C
Oxidation at high temperature
D
Low thermal conductivity
Analysis & Theory
Carbon oxidizes easily at elevated temperatures if not protected by a reducing atmosphere.
Carbon refractories are typically used in:
B
Steel ladles and blast furnace hearths
D
Ceramic tile manufacture
Analysis & Theory
They are ideal for areas exposed to aggressive slag and high thermal conductivity needs.
What is the primary mineral in chromite refractories?
Analysis & Theory
Chromite (FeCr₂O₄) is the main mineral used in chromite refractories for their stability and corrosion resistance.
Chromite refractories are classified as:
Analysis & Theory
Chromite refractories behave neutrally and can tolerate both acidic and basic environments to some extent.
In which application are chromite bricks commonly used?
B
Glass tank regenerators
Analysis & Theory
Due to their thermal shock resistance, chromite bricks are used in regenerator checkers of glass furnaces.
Which refractory has the highest electrical conductivity?
Analysis & Theory
Carbon refractories are highly conductive and are used in electrodes and hearth linings.
Which bonding method is commonly used in carbon bricks?
Analysis & Theory
Carbon bricks are often bonded using tar or pitch to improve cohesion and thermal resistance.
Which refractory type is best for thermal conductivity in electric arc furnaces?
Analysis & Theory
Carbon has high thermal conductivity and is widely used in EAF linings and electrodes.
Mag-chrome refractories are classified as:
Analysis & Theory
Magnesia imparts basic characteristics to mag-chrome refractories, making them suitable for basic slags.
Which refractories have dual resistance to both acidic and basic slags?
Analysis & Theory
Mag-chrome refractories offer good resistance to both types of slags due to their unique composition.
Which of the following refractories requires special storage to avoid oxidation?
Analysis & Theory
Carbon refractories must be protected from moisture and oxidation, especially during storage.
Refractoriness of carbon bricks is typically above:
Analysis & Theory
Carbon refractories can withstand temperatures above 2000°C in reducing environments.