MgO-based refractories

Question 1

What are MgO based refractories composed of?

Answer 1

> deposits of brucite (Mg(OH)2), magnesite (MgCO3), or hydromagnesite (MgCO3*xH2O)

Question 2

Where is high purity MgO obtained?

Answer 2

> seawater, mineral name for MgO is periclase

Question 3

Why and how is dolomite added to MgO refractories?

Answer 3

1. dolomite (Ca,Mg(CO3)) is HEAT TREATED at 1100C to form “BURNT DOLMA” (MgO + CaO)
2. Burnt dolma is mixed with water to form “SLAKED DOLMA” (Ca(OH)2 + Mg(OH)2)
3. Slaked dolma is agitated with seawater, magnesium ions in seawater precipitate onto Mg(OH)2 via SOLUBLE ION EXCHANGE with Ca(OH)2
4. precipitate is washed and filter pressed
5. CALCINED to MgO in rotary kiln at 750-900C to form ~1um particles
6. to avoid RE-HYDRATION from atmosphere, they are PELLETIZED and FIRED (“dead-burned”) at 1500-1800C to form an aggregate (3-4mm)
7. for highest quality, MgO particles are melted at 2852C

Question 4

What are MgO based refractories known as?

Answer 4

> “basic refractories”

Question 5

How do MgO refractories react with CaO slags?

Answer 5

> they do not form eutectic liquids with CaO rich slags used in iron/steel manufacture

Question 6

What are SiO2 based refractories known as?

Answer 6

> “acidic refractories”
hold up well against acidid (SiO2-rich) slags

Question 7

What happens with contact between acidic and basic slags?

Answer 7

> can lead to low temp eutectics