Material · Engineered

Refractory brick

The lining every furnace is built from — and it is chosen to match what will be melted against it, not for how hot it can get.

Refractory Construction material

A refractory brick lines the inside of a furnace, kiln, boiler or ladle, and holding a high temperature is the easiest of its requirements. It also has to resist thermal shock as the furnace cycles, abrasion from whatever moves against it, and chemical attack from the slag, metal or glass being processed.

That last one decides the choice. An acidic refractory such as silica is destroyed by basic slag, and a basic one such as magnesia is destroyed by acidic slag — so the lining is chosen to match what will be run against it, and putting the right brick in the wrong furnace is the commonest way a lining fails early.

There is also a straight trade between insulation and durability. A porous brick keeps heat in and cannot take wear; a dense one takes wear and conducts heat out. Most linings are both, in layers.

Processing

Pressed or cast from graded refractory grain with a bond, then fired — or, increasingly, installed as an unfired monolithic castable that is poured or gunned in place and cured by the furnace's own first heat.

Monolithics have taken a large share of the market because a shaped brick lining takes skilled bricklayers and time, and a furnace not running is a furnace not earning.

Uses

Blast furnaces, steel ladles and converters; cement and lime kilns; glass tanks; incinerators; boilers; and every pottery kiln. Also domestic: the firebrick in a stove or a bread oven is the same material at a smaller scale.

The steel industry is the largest consumer by a wide margin, and refractory consumption per tonne of steel is one of the numbers that plant operators watch closely.

History

As old as metallurgy in the sense that any furnace needs a lining, and an industry from the eighteenth century, when coke smelting and glassmaking created demand for something better than local clay.

Silica brick was what made the Siemens-Martin open hearth possible; basic brick, from magnesia and dolomite, is what made the basic Bessemer and later the basic oxygen process possible, because those depend on a basic slag that would eat a silica lining.

Environmental impact

Spent refractory is a substantial industrial waste stream and an increasingly recovered one — used brick is crushed and returned to new refractory or used as aggregate, and the economics improved once landfill became expensive.

Some older linings contain chromium compounds that become hexavalent chromium in service, which makes their disposal a controlled matter rather than a routine one.

Medium confidence Weak evidence

How we know: checked recently · only one source, so there is nothing to cross-check it against · stated directly by the source.

How this connects

Where a connection has been confirmed by an outside reference, that reference is named beside it.

is sourced from

Clay — material · as fireclay for the general-purpose grades; the basic linings are magnesia and dolomite instead

is composed of

Aluminium oxide — compound · the general-purpose workhorse — raising alumina content above fireclay's raises the service temperature and the price together
Quartz — mineral · as silica brick, which is what made the Siemens-Martin open hearth possible and is destroyed by a basic slag
Chromite — mineral · in chrome-magnesite linings, and the reason spent refractory disposal is a controlled matter: chromium compounds oxidise in service to the hexavalent form
Graphite — mineral · in magnesia-carbon brick for steel ladles, where the carbon stops the slag wetting the grain and is why the lining survives the pour
Silicon carbide — compound · where abrasion and thermal shock both matter — blast furnace bosh, incinerators and kiln furniture
Forsterite — mineral · the magnesium end of olivine, used as a basic refractory where magnesite is not to hand
Bauxite — rock · calcined, as the alumina source for the high-alumina grades

is an input to

Firing — process · or installed unfired as a monolithic castable and cured by the furnace's own first heat

is used as

Refractory lining — application · chosen to match the slag it will meet rather than for how hot it can get

is used in

Chemical manufacture — industry · and the steel industry is the larger consumer, where refractory used per tonne of steel is a number operators watch

is an alternative to

Technical ceramic — material · brick is shaped, cheap and installed by the thousand; a technical ceramic is a component, and the two meet only at the small end of the furnace

is produced by

Firing — process · and the point of the firing is that the brick has already been to a higher temperature than the furnace it will line

Sources

Material World
Our own writing

Questions this page answers

Where it comes from, and what it becomes

Follow Refractory brick back to what it starts as, and forward into what it becomes. Each step is a documented one — a real route material takes, not a chain of inference.

Upstream — what it comes from

Refractory brick → is composed of (the general-purpose workhorse — raising alumina content above fireclay's raises the service temperature and the price together) → Aluminium oxide → is sourced from (dissolved out with hot caustic soda in the Bayer process) → Bauxite → is sourced from (the residue of prolonged tropical weathering, which strips the silica and alkalis out of an aluminosilicate rock and leaves the aluminium behind — basalt is one common parent among several) → Basalt → is sourced from (partial melting of mantle peridotite is what basalt magma is — the residue left behind stays peridotite, depleted of what went into the melt) → Peridotite → is composed of (the mineral that defines the rock and gives it its name — a peridotite is olivine-dominant by definition) → Olivine
Refractory brick → is composed of (where abrasion and thermal shock both matter — blast furnace bosh, incinerators and kiln furniture) → Silicon carbide → is produced by (the product the process was built for, crystallised out of sand and coke at around 2,500 °C) → Acheson process → takes as input (sand and coke, heated to 2,500 °C, which is how silicon carbide has been made since 1893) → Sand → is sourced from (the ultimate source of most of it — granite weathers, the feldspar becomes clay and washes out, and the quartz survives as grains) → Granite → is composed of (by volume, alongside feldspar and lesser mica) → Quartz
Refractory brick → is composed of (calcined, as the alumina source for the high-alumina grades) → Bauxite → is sourced from (the residue of prolonged tropical weathering, which strips the silica and alkalis out of an aluminosilicate rock and leaves the aluminium behind — basalt is one common parent among several) → Basalt → is sourced from (partial melting of mantle peridotite is what basalt magma is — the residue left behind stays peridotite, depleted of what went into the melt) → Peridotite → is composed of (the mineral that defines the rock and gives it its name — a peridotite is olivine-dominant by definition) → Olivine
Refractory brick → is produced by (and the point of the firing is that the brick has already been to a higher temperature than the furnace it will line) → Firing → takes as input (to 1200–1300 °C, which is the vitrification that separates it from earthenware — and it is a temperature rather than a recipe) → Stoneware → is sourced from (a clay that survives 1200 °C and above, which an earthenware clay does not) → Clay → is sourced from (clay is chiefly what feldspar becomes when it weathers) → Orthoclase
Refractory brick → is sourced from (as fireclay for the general-purpose grades; the basic linings are magnesia and dolomite instead) → Clay → is sourced from (clay is chiefly what feldspar becomes when it weathers) → Orthoclase
Refractory brick → is composed of (as silica brick, which is what made the Siemens-Martin open hearth possible and is destroyed by a basic slag) → Quartz

These are the most distinct paths back. Refractory brick can be traced through others besides.

Downstream — what it becomes

Refractory brick → is an input to (or installed unfired as a monolithic castable and cured by the furnace's own first heat) → Firing → produces (as sintering, from refined powders rather than clay) → Technical ceramic → is used in (the honeycomb monolith the metals are dispersed across, which supplies the surface area and survives the thermal cycling) → Catalytic converter → is used as (the largest catalytic application by metal value there is) → Catalysis
Refractory brick → is used as (chosen to match the slag it will meet rather than for how hot it can get) → Refractory lining
Refractory brick → is used in (and the steel industry is the larger consumer, where refractory used per tonne of steel is a number operators watch) → Chemical manufacture
Refractory brick → is an input to (or installed unfired as a monolithic castable and cured by the furnace's own first heat) → Firing → produces (fired in a continuous tunnel kiln, the atmosphere governing colour as much as the temperature) → Brick → is used in (load-bearing walls and cladding) → Construction
Refractory brick → is an input to (or installed unfired as a monolithic castable and cured by the furnace's own first heat) → Firing → produces (fired in a continuous tunnel kiln, the atmosphere governing colour as much as the temperature) → Brick → is used as (the same principle at a smaller and far cheaper unit size, which is why it outlasted stone for ordinary building) → Structural engineering
Refractory brick → is an input to (or installed unfired as a monolithic castable and cured by the furnace's own first heat) → Firing → produces (as sintering, from refined powders rather than clay) → Technical ceramic → is used as (alumina and silicon carbide are the dominant manufactured abrasives) → Abrasive

These are the most distinct paths onward. Refractory brick ends up in others besides.