Knowledge

Refractory Glossary

The vocabulary that appears on refractory datasheets and in technical correspondence, defined plainly. Search in your own language or by chemical name.

72 terms

Raw materials & compounds

Alumina Alumina (Al₂O₃): Aluminium oxide; the principal raw material of high-temperature refractories, melting near 2050 °C.
Corundum: The alpha phase of alumina (α-Al₂O₃); the most stable and most refractory crystalline form.
Mullite: An alumina-silicate compound (3Al₂O₃·2SiO₂) with high creep resistance and thermal stability.
Bauxite: The principal ore of aluminium; once calcined, the economical source of alumina for refractories.
Magnesia / Periclase: Magnesium oxide (MgO), the basis of basic refractories; its crystalline phase is called periclase.
Spinel: An alumina-magnesia compound (MgAl₂O₄) with excellent thermal-shock resistance and chemical stability.
Zircon Zircon (ZrSiO₄): Zirconium silicate; a glaze opacifier and a refractory material with low thermal expansion.
Silicon Carbide Silicon Carbide (SiC): A non-oxide refractory of very high hardness and thermal conductivity, with exceptional wear resistance.
Chamotte / Fireclay: Calcined fireclay; the economical alumina-silicate aggregate for bricks and refractory mixes.
Kaolin: A white clay of the kaolinite mineral; the basis of white ceramic bodies and an alumina source in glazes.

Refractory types & products

Shaped Refractory: Pre-formed products such as firebrick, supplied to defined dimensions and shapes.
Monolithic Refractory: Unshaped refractory placed by casting, ramming or gunning, forming a lining without joints.
Castable: Refractory concrete placed with added water, becoming a monolithic body after setting and firing.
Low-Cement Castable Low-Cement Castable (LCC): A castable below 2.5% CaO, giving better refractoriness and higher hot strength.
Calcium Aluminate Cement Refractory Cement (CAC): Calcium aluminate cement; the bonding phase of refractory mixes and castables.
Insulating Firebrick Insulating Firebrick (IFB): Lightweight porous firebrick used in the backup lining to cut heat loss.
Ramming Mass: Granular refractory rammed dry or semi-dry that sinters on first heat; the usual induction-furnace and tundish lining.
Gunning Mix: Refractory sprayed onto a surface with compressed air and water added at the nozzle; used for fast installation and local repair.
Ceramic Fibre Ceramic Fiber: Alumina-silicate refractory wool of very low conductivity and heat storage; a light furnace insulator, not a working lining in contact with melt.
Bio-soluble Wool (AES): Calcium-magnesium-silicate fibre that dissolves in body fluids; a safer alternative to RCF, at a lower service temperature.
Magnesia-Carbon Brick Magnesia-Carbon (MgO-C): Basic brick containing graphite, combining the chemical resistance of magnesia with the non-wetting and thermal-shock resistance of carbon.
Magnesia-Chrome Brick Magnesia-Chrome: Basic refractory containing chrome spinel; the dominant choice in copper smelting for its resistance to fayalitic slag and matte penetration.

Properties & tests

Refractoriness: The ability of a material to withstand high temperature without melting or appreciable softening.
Cold Crushing Strength Cold Crushing Strength (CCS): The maximum compressive load a specimen bears at room temperature before failure.
Apparent Porosity: Open pore volume as a percentage of total volume; the key indicator of permeability and corrosion resistance.
Bulk Density: Mass per unit volume including pores; a measure of compaction and body quality.
Thermal Shock Resistance: Resistance to cracking caused by sudden changes in temperature.
Creep at High Temperature: Gradual deformation under constant load at high temperature over time.
Thermal Expansion: Dimensional change with rising temperature; a low value helps dimensional stability.
Refractoriness Under Load Refractoriness Under Load (RUL): The temperature at which a specimen begins to deform under a specified load.
Hot Modulus of Rupture Hot Modulus of Rupture (HMOR): Flexural strength measured at high temperature; the realistic measure of load-bearing in service, unlike CCS which is measured cold.
Permanent Linear Change Permanent Linear Change (PLC): Permanent shrinkage or expansion after re-firing; an indicator of dimensional stability in service.
Loss on Ignition Loss on Ignition (LOI): Percentage weight loss on heating, from moisture, carbonates and volatiles leaving the material.
Non-wetting: A surface property that stops melt and slag spreading into the refractory; the main benefit of adding carbon.
Pyrometric Cone Equivalent Pyrometric Cone Equivalent (PCE): A relative refractoriness index determined by comparing the bending of a specimen with standard cones.

Process & industry terms

Calcination: Heating to drive off water and gases and form stable refractory phases.
Sintering: Densification of particles below the melting point to produce a dense, strong body.
Fusion (Fused): Complete melting in an electric arc furnace and recrystallisation, for higher density and purity.
Dead Burned: Calcined at very high temperature to remove chemical reactivity and raise stability.
Coating: A protective layer, typically clinker, that forms on the refractory of a cement kiln and extends its life.
Slag: The non-metallic molten phase in metallurgical processes; the principal cause of refractory corrosion.
Aggregate: The coarse granular fraction of a refractory mix, forming the skeleton of the body.
Matrix: The fine fraction that fills the space between aggregates and densifies the body.
Basicity: The ratio of basic to acidic oxides in slag (usually CaO/SiO₂); it governs desulphurisation power and how aggressively the slag attacks the lining.
Beneficiation: Separating valuable mineral from gangue — by gravity, magnetic or flotation methods — to bring the grade up to industrial use.
Concentrate: The upgraded product of a processing plant, fed to a furnace or a refractory production line.
Alkali Cycle: The evaporation-and-condensation loop of sodium and potassium compounds between a cement kiln and its preheater, multiplying their concentration and destroying refractory.
Dry-out: Controlled heating of a freshly installed lining to release water gradually; rushing it causes steam bursts and cracking.
Creep: Gradual deformation of a refractory under constant load at temperature; the measure of dimensional stability over a long campaign.
Structural Spalling: Layered loss of the hot face where slag penetration creates a densified zone that expands differently and detaches on thermal cycling.
Explosive Spalling: Sudden bursting of a castable during rapid heating, when trapped steam pressure finds no way out.
Antioxidant: A metallic addition (aluminium, silicon, magnesium) or SiC in carbon-bearing refractory that oxidises before the carbon does, protecting the graphite.
Anchoring: The metallic or ceramic system tying a monolithic lining to the furnace shell so it cannot fall away.
Hexavalent Chromium Hexavalent Chromium (Cr⁶⁺): The water-soluble, carcinogenic form of chromium that forms in chrome refractories at high temperature under oxidising, alkaline conditions; the reason spent chrome linings are classed as hazardous waste.
Spent Refractory: Lining removed at the end of its life; sorted and cleaned properly, it is a secondary raw-material source.
Specific Consumption: Kilograms of refractory consumed per tonne of product; the correct basis for comparing refractories economically, rather than price per tonne.
Fayalitic Slag: The iron-silicate slag (2FeO·SiO₂) of copper smelting; its low viscosity and high FeO make it strongly penetrating and aggressive.
Matte: The copper-iron sulphide phase from smelting concentrate; its wetting behaviour and fluidity let it penetrate refractory pores.
Tuyere: The port injecting air or oxygen into a furnace; the zone around it is usually the hottest and most heavily worn part of the lining.

Flow control & continuous casting

Slide Gate: Coaxial refractory plates that slide over one another to regulate the flow of steel from a ladle or tundish.
Ladle Shroud: The alumina-graphite tube between ladle and tundish that shields the stream from air and reoxidation.
Submerged Entry Nozzle Submerged Entry Nozzle (SEN): A nozzle whose tip sits below the mould metal level, setting the flow pattern and the surface quality of the slab.
Stopper Rod: A refractory rod that seats like a valve on the tundish nozzle, holding the mould level precisely.
Purging Plug: The porous element in the ladle bottom that admits argon to homogenise composition and temperature and float inclusions into the slag.
Well Block: The refractory block set into the ladle bottom, into which the nozzle and slide-gate assembly seat.
Clogging: Alumina deposition on the nozzle bore that narrows and eventually blocks the flow; controlled by argon and calcium treatment.
Free Opening: The filler sand running out freely when the ladle gate opens, with no oxygen lancing needed; a key steelmaking performance indicator.
Tundish: The intermediate vessel between ladle and mould that steadies the flow and allows several heats to be cast in sequence.
Reoxidation: Killed steel picking up oxygen from air along the casting route; the origin of alumina inclusions and nozzle clogging.
Impact Pad: The wear-resistant block beneath the incoming ladle stream in the tundish, absorbing the impact and cutting turbulence and floor erosion.
Weir & Dam: Flow-guiding walls inside the tundish that lengthen and lift the steel path, increasing residence time and inclusion flotation.
Working Lining: The thin consumable layer in direct contact with the melt, renewed each casting sequence so the permanent lining behind it is not damaged.