Microporous Carbon Brick for Blast Furnace Hearth & Bottom

Microporous carbon brick protects a blast furnace hearth by controlling something that total porosity figures do not capture: pore size. Molten iron cannot enter a pore below a critical throat diameter. Hold the pores small enough and iron penetration simply stops, regardless of how much total porosity the material contains.

Why Pore Size, Not Porosity Percentage

Two carbon blocks can both measure 18% apparent porosity and behave completely differently. If one has large, connected pore throats, molten iron wicks in; if the other has the same void volume distributed as sub-micron pores, iron cannot enter at all. This is why "low porosity carbon block" is an incomplete specification and "microporous carbon" is a meaningful one.

XZK microporous grades hold average pore diameter at or below 1 μm, with the majority of pore volume below that threshold. We supply pore size distribution data with the material, because it is the only way to verify the claim — total porosity alone proves nothing.

What Penetration Actually Costs You

When iron penetrates carbon, it forms a brittle, cracked layer with different thermal and mechanical properties from the parent material. That layer then drives further cracking and erosion — a self-reinforcing loop that is the usual mechanism behind hearth wall thinning and, in the worst case, breakout risk. Limiting penetration at the pore level is the cheapest place to break that loop.

Conductivity Is the Other Half

Pore control protects the material; conductivity keeps it cool enough to survive. At ≥12 W/(m·K), the hearth conducts heat into the cooling system and holds the 1150 °C isotherm — the temperature at which iron solidifies — inside the lining. That single fact governs hearth life more than any other: if the isotherm sits inside the refractory, liquid iron cannot reach the carbon’s interior.

Always Specified With a Ceramic Cup

The two materials do different jobs. The ceramic cup is a high-purity corundum barrier that protects the carbon during start-up and against early alkali and zinc attack; the carbon behind it provides the thermal pathway to the cooling system. Specifying either alone leaves one of those jobs undone, which is why modern hearth designs pair them.

Supply and Installation

Hearth packages are quoted as complete sets against the furnace drawing. Blocks are individually machined, numbered to the installation sequence, and dry trial-fitted before shipment, with controlled joint gaps. Lead time is typically 35–60 days. Send your furnace drawing, cooling configuration and campaign history for a complete zonal hearth proposal.

Where This Grade Sits in the Lining System

Silicon carbide and carbon grades are selected for what they do with heat rather than for what they resist. Thermal conductivity decides whether the cooling system ever sees the load, and the bonding system decides how long the material survives alkali attack and oxidation once it does.

XZK supplies microporous carbon brick as one zone of a zoned package rather than as a standalone item: the grades normally zoned alongside it — among them ceramic cup — are documented on the silicon carbide and carbon refractories page, and the vessel-level architecture — where each zone starts and ends, and which mechanism actually limits the campaign — is set out on the blast furnace page.

For a complete vessel programme built on this class of material, including the wear survey that set the zoning, see the MMK Magnitogorsk No.10 BF and 375 t ladle programme project reference.