Refractory

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Refractory

A refractory material is one that retains its strength at high temperature

Temperature

In physics, temperature is a physical property of a Physical system that underlies the common notions of hot and cold; something that feels hotter generally has the greater temperature....
s. ASTM

ASTM International

ASTM International , originally known as the American Society for Testing and Materials, is an international standards organization that develops and publishes voluntary consensus technical standards for a wide range of materials, products, systems, and services....
C71 defines refractories as "non-metallic materials having those chemical and physical properties that made them applicable for structures, or as components of systems, that are exposed to environments above 1000 °F (800K, 500 °C)".

Refractory materials are used in linings for furnace

Furnace

File:Piec krepa.JPGA furnace is a device used for heating. The name derives from Latin fornax, oven. The earliest furnace was excavated at Balakot, a site of the Indus Valley Civilization, dating back to its mature phase ....
s, kiln

Kiln

Kilns are thermally insulated chambers, or ovens, in which controlled temperature regimes are produced. They are used to harden, burn or dry materials....
s, incinerators and reactor

Reactor

Reactor can mean:* Bioreactor#Bioreactor, any device or system that supports a biologically active environment.* Chemical reactor, a device for containing and controlling a chemical reaction...
s. They are also used to make crucible

Crucible

A crucible is a heat-resistant container in which materials can be heated to very high temperatures.The use of crucibles to manufacture Crucible steel, introduced in England in the eighteenth century, was an important part of the Industrial Revolution....
s.

actory materials must be chemically and physically stable at high temperatures.

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Encyclopedia

A refractory material is one that retains its strength at high temperature

Temperature

ASTM International

Furnace

Kiln

Kilns are thermally insulated chambers, or ovens, in which controlled temperature regimes are produced. They are used to harden, burn or dry materials....
s, incinerators and reactor

Reactor

Crucible

Refractory materials

Refractory materials must be chemically and physically stable at high temperatures. Depending on the operating environment, they need to be resistant to thermal shock

Thermal shock

Thermal shock is the name given to cracking as a result of rapid temperature change. Glass and ceramic objects are particularly vulnerable to this form of structural failure, due to their low toughness, low thermal conductivity, and high thermal expansion coefficients....
, be chemically inert

Inert

In English, to be inert is to be in a state of doing little or nothing....
, and/or have specific ranges of thermal conductivity

Thermal conductivity

In physics, thermal conductivity, , is the List of materials properties of a material that indicates its ability to conduct heat. It appears primarily in Heat conduction#Fourier's law for heat conduction....
and of the coefficient of thermal expansion

Thermal expansion

Thermal expansion is the tendency of matter to change in volume in response to a change in temperature. When a substance is heated, its constituent particles move around more vigorously and by doing so generally maintain a greater average separation....
.

The oxide

Oxide

An oxide is a chemical compound contaning at least one oxygen atom as well as at least one other element. Most of the Earth's crust consists of oxides....
s of aluminium

Aluminium

Aluminium or aluminum is a silvery white and ductile member of the boron group of chemical elements. It has the symbol Al; its atomic number is 13....
(alumina), silicon

Silicon

Silicon is the most common metalloid. It is a chemical element, which has the symbol Si and atomic number 14. The atomic mass is 28.0855....
(silica) and magnesium

Magnesium

Magnesium is a chemical element with the symbol Mg, atomic number 12, atomic weight 24.3050 and common oxidation number +2.Magnesium, an alkaline earth metal, is the ninth most abundance of the chemical elements in the universe by mass....
(magnesia

Magnesium oxide

Magnesium oxide, or magnesia, is a white solid mineral that occurs naturally as periclase and is a source of magnesium . It has an empirical formula of ....
) are the most important materials used in the manufacturing of refractories. Another oxide usually found in refractories is the oxide of calcium

Calcium

Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft grey alkaline earth metal, and is the fifth most abundant element by mass in the earth's Crust ....
(lime

Lime (mineral)

Lime is a general term for calcium-containing inorganic materials, in which carbonates, oxides and hydroxides predominate. Strictly speaking, lime is calcium oxide or calcium hydroxide....
). Fireclays

Fire clay

Fire clay is a specific kind of clay used in the manufacture of ceramics, especially fire brick. The fire attribution is given for its refractory characteristics....
are also widely used in the manufacture of refractories.

Refractories must be chosen according to the conditions they will face. Some applications require special refractory materials. Zirconia is used when the material must withstand extremely high temperatures. Silicon carbide

Silicon carbide

Silicon carbide is a Chemical compound of silicon and carbon bonded together to form ceramics, but it also occurs in nature as the extremely rare mineral moissanite....
and carbon

Carbon

Carbon is a chemical element with chemical symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalence?making four electrons available to form covalent bond chemical bonds....
are two other refractory materials used in some very severe temperature conditions, but they cannot be used in contact with oxygen

Oxygen

Oxygen no O2 produced; 2) O2 produced, but absorbed in oceans & seabed rock; 3) O2 starts to gas out of the oceans, but is absorbed by land surfaces and formation of ozone layer; 4-5) O2 sinks filled and the gas accumulates]]...
, as they will oxidize and burn.

Types of refractories

Acid

An acid is traditionally considered any chemical compound that, when dissolved in water, gives a solution with a hydrogen ion Activity greater than in pure water, i.e....
ic refractories cannot be used in a basic

Base (chemistry)

In chemistry, a base is most commonly thought of as an aqueous substance that can accept protons. A base is also often referred to as an alkali if OH- ions are involved....
environment and basic refractories cannot be used in an acidic environment because they will be corroded

Corrosion

Corrosion means the breaking down of essential properties in a material due to chemical reactions with its surroundings. In the most common use of the word, this means a loss of electrons of metals reacting with water and oxygen....
. Zircon, fireclay and silica are acidic, dolomite

Dolomite

Dolomite is the name of a sedimentary carbonate rock and a mineral, both composed of calcium magnesium carbonate calciummagnesium2 found in crystals....
and magnesite are basic and alumina, chromite

Chromite

Chromite is iron magnesium chromium oxide: Cr2O4. It is an oxide mineral belonging to the spinel group. Magnesium can substitute for iron in variable amounts; also, aluminium and ferric iron commonly substitute for chromium....
, silicon carbide, carbon and mullite

Mullite

Mullite, or porcelainite, is a rare clay mineral aluminosilicate. It can form two stoichiometric forms 3Al2O32SiO2 or 2Al2O3SiO2....
are neutral. Refractory metals

Refractory metals

Refractory metals are a class of metals that are extraordinarily resistant to heat and wear. Refractory metals are said to be poorly resistant to oxidation and corrosion....
are also frequently used.

Refractory materials are used extensively in the metal industries, along with glass melting and other heat treatment operations.

There are two common forms of refractories, bricks and monolithics. Bricks (also known as firebrick) are pre-sintered forms which can hold their shape. Monolithics are loose material which can be formed into complex shapes, or sprayed into place, and have to be sintered before use. Castable refractory cement

Cement

In the most general sense of the word, a cement is a binder, a substance which sets and hardens independently, and can bind other materials together....
is also commonly used.

Refractory anchorage

Anti-abrasion refractory attached to pipes, chambers, etc, will require anchorage systems such as wire formed anchors or hexmetal to support the refractory linings. The anchorage used for refractory on roofs and vertical walls are more critical as they are to support the weight of refractory even at the elevated temperatures and operating conditions. The commonly used anchorages have circular or rectangular cross-section. Circular cross-section are used for low thickness refractory and they support relatively less weight per unit area; whereas the rectangular cross-section is used for high thickness refractory and can support higher weight of refractory per unit area. The number of anchors to be used depend on the operating conditions and the refractory materials. The choice of anchors shape, numbers and size has significant impact on the useful life of the refractory.

Refractory heat-up

Usually, refractories require special heat-up techniques

Refractories heat-up

After building of a new refractory-lined industrial furnace or equipment, or refractory maintenance or relining of existing equipment, a necessary step is the start-up of the operation, which usually involves heating-up the unit in a controllable way, in order to prevent spalling or shortening of the materials' predicted lifetime....
to ensure that their performance will be attained as designed, and to avoid thermal shock and drying stresses until the operational status is achieved.

Refractory

Refractory materials

Types of refractories

Refractory anchorage

Refractory heat-up

See also

External links