In refractory engineering, highly porous bricks exhibit which combined behaviors in service? Select the most complete statement.

Introduction:
Refractory bricks with high porosity are widely used in furnaces, kilns, and reactors for insulation and lining. Understanding how porosity affects penetration by slags and gases, thermal conductivity, strength, and thermal-shock behavior is essential for selecting the right brick for each zone of a high-temperature unit.

Given Data / Assumptions:

• “High porosity” means a larger fraction of interconnected pores within the refractory body.
• Service involves contact with slags/metals/flue gases and cyclic heating.
• Choice requires comparing multiple properties simultaneously.

Concept / Approach:
Porosity influences transport, strength, and thermal response. More pores generally reduce thermal conductivity (good for insulation) but diminish bulk strength and allow easier penetration if pores are open and connected. However, pores also blunt thermal stresses, improving thermal-shock (spalling) resistance because the material accommodates expansion gradients.

Step-by-Step Solution:
Relate porosity to permeability: higher open porosity increases pathways for slag/metal/gas ingress → poorer penetration resistance.Relate porosity to thermal transport: more voids mean lower solid-to-solid contacts → lower heat conductivity.Relate porosity to strength: reduced load-bearing cross-section → lower cold crushing strength and modulus.Relate porosity to thermal shock: pores distribute and arrest thermal stress → better spalling resistance.Hence all listed effects occur together.

Verification / Alternative check:
Materials handbooks consistently show inverse relationships between porosity and both strength and thermal conductivity, alongside improved resistance to thermal spalling for lightweight or more porous refractories.

Why Other Options Are Wrong:

• Only any one benefit (like improved spalling) ignores the trade-offs in strength and permeability.
• Claiming insulation improves “with no other trade-offs” is incorrect; strength and penetration resistance decline.

Common Pitfalls:
Confusing closed porosity (beneficial for insulation) with open porosity (raises permeability). Also, assuming higher porosity always better—zone duty determines the acceptable porosity level.

Final Answer:
All of the above