🔍 Key Concepts

• slagging and how slag forms/coats refractory surfaces in boilers • thermal expansion behavior of firebrick vs. slag coating under heating and cooling • mechanical vs. chemical causes of spalling/peeling in refractories

💭 Think About

• Think about what happens when two different materials that are bonded together are heated and cooled at different rates or to different temperatures. • Consider whether slag usually attacks the brick chemically first, or whether physical stresses are more commonly responsible for peeling off a surface layer. • Ask yourself which option best explains a thin layer of refractory lifting or flaking away from the backing brickwork right where slag has formed.

✅ Before You Answer

• Identify which choices describe a mechanical/thermal stress effect and which describe a chemical effect. • Consider which option directly involves both slag and refractory/firebrick changing size differently as temperature changes. • Eliminate any choice that does not clearly connect the peeling with the presence of a slag coating on the refractory surface.