When to Use furnace refractory？

Materials resistant to decomposition under high temperatures This article is about heat resistance. For other uses, see Refractory (disambiguation).

In materials science, a refractory (or refractory material) is a material that is resistant to decomposition by heat or chemical attack and that retains its strength and rigidity at high temperatures.[1] They are inorganic, non-metallic compounds that may be porous or non-porous, and their crystallinity varies widely: they may be crystalline, polycrystalline, amorphous, or composite. They are typically composed of oxides, carbides or nitrides of the following elements: silicon, aluminium, magnesium, calcium, boron, chromium and zirconium.[2] Many refractories are ceramics, but some such as graphite are not, and some ceramics such as clay pottery are not considered refractory. Refractories are distinguished from the refractory metals, which are elemental metals and their alloys that have high melting temperatures.

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Refractories are defined by ASTM C71 as "non-metallic materials having those chemical and physical properties that make them applicable for structures, or as components of systems, that are exposed to environments above 1,000 °F (811 K; 538 °C)".[3] Refractory materials are used in furnaces, kilns, incinerators, and reactors. Refractories are also used to make crucibles and molds for casting glass and metals. The iron and steel industry and metal casting sectors use approximately 70% of all refractories produced.[4]

Refractory materials

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Refractory materials must be chemically and physically stable at high temperatures. Depending on the operating environment, they must be resistant to thermal shock, be chemically inert, and/or have specific ranges of thermal conductivity and of the coefficient of thermal expansion.

The oxides of aluminium (alumina), silicon (silica) and magnesium (magnesia) are the most important materials used in the manufacturing of refractories. Another oxide usually found in refractories is the oxide of calcium (lime).[5] Fire clays are also widely used in the manufacture of refractories.

Refractories must be chosen according to the conditions they face. Some applications require special refractory materials.[6] Zirconia is used when the material must withstand extremely high temperatures.[7] Silicon carbide and carbon (graphite) are two other refractory materials used in some very severe temperature conditions, but they cannot be used in contact with oxygen, as they would oxidize and burn.

Binary compounds such as tungsten carbide or boron nitride can be very refractory. Hafnium carbide is the most refractory binary compound known, with a melting point of  °C.[8][9] The ternary compound tantalum hafnium carbide has one of the highest melting points of all known compounds ( °C).[10][11]

Molybdenum disilicide has a high melting point of °C and is often used as a heating element.

Uses

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Refractory materials are useful for the following functions:[12][2]

1. Serving as a thermal barrier between a hot medium and the wall of a containing vessel
2. Withstanding physical stresses and preventing erosion of vessel walls due to the hot medium
3. Protecting against corrosion
4. Providing thermal insulation

Refractories have multiple useful applications. In the metallurgy industry, refractories are used for lining furnaces, kilns, reactors, and other vessels which hold and transport hot media such as metal and slag. Refractories have other high temperature applications such as fired heaters, hydrogen reformers, ammonia primary and secondary reformers, cracking furnaces, utility boilers, catalytic cracking units, air heaters, and sulfur furnaces.[12] They are used for surfacing flame deflectors in rocket launch structures.[13]

Classification of refractory materials

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Refractories are classified in multiple ways, based on:

1. Chemical composition
2. Method of manufacture
3. Size and shape
4. Fusion temperature
5. Refractoriness
6. Thermal conductivity

Chemical composition

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Acidic refractories

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Acidic refractories are generally impervious to acidic materials but easily attacked by basic materials, and are thus used with acidic slag in acidic environments. They include substances such as silica, alumina, and fire clay brick refractories. Notable reagents that can attack both alumina and silica are hydrofluoric acid, phosphoric acid, and fluorinated gases (e.g. HF, F2).[14] At high temperatures, acidic refractories may also react with limes and basic oxides.

• Silica refractories are refractories containing more than 93% silicon oxide (SiO2). They are acidic, have high resistance to thermal shock, flux and slag resistance, and high spalling resistance. Silica bricks are often used in the iron and steel industry as furnace materials. An important property of silica brick is its ability to maintain hardness under high loads until its fusion point.[2] Silica refractories are usually cheaper hence easily disposable. New technologies that provide higher strength and more casting duration with less silicon oxide (90%) when mixed with organic resins have been developed.
• Zirconia refractories are refractories primarily composed of zirconium oxide (ZrO2). They are often used for glass furnaces because they have low thermal conductivity, are not easily wetted by molten glass and have low reactivity with molten glass. These refractories are also useful for applications in high temperature construction materials.
• Aluminosilicate refractories mainly consist of alumina (Al2O3) and silica (SiO2). Aluminosilicate refractories can be semiacidic, fireclay composite, or high alumina content composite.[clarification needed][15]

Basic refractories

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Basic refractories are used in areas where slags and atmosphere are basic. They are stable to alkaline materials but can react to acids, which is important e. g. when removing phosphorus from pig iron (see Gilchrist–Thomas process). The main raw materials belong to the RO group, of which magnesia (MgO) is a common example. Other examples include dolomite and chrome-magnesia. For the first half of the twentieth century, the steel making process used artificial periclase (roasted magnesite) as a furnace lining material.

• Magnesite refractories are composed of ≥ 85% magnesium oxide (MgO). They have high slag resistance to lime and iron-rich slags, strong abrasion and corrosion resistance, and high refractoriness under load, and are typically used in metallurgical furnaces.[16]
• Dolomite refractories mainly consist of calcium magnesium carbonate. Typically, dolomite refractories are used in converter and refining furnaces.[17]
• Magnesia-chrome refractories mainly consist of magnesium oxide (MgO) and chromium oxide (Cr2O3). These refractories have high refractoriness and have a high tolerance for corrosive environments.

Neutral refractories

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These are used in areas where slags and atmosphere are either acidic or basic and are chemically stable to both acids and bases. The main raw materials belong to, but are not confined to, the R2O3 group. Common examples of these materials are alumina (Al2O3), chromia (Cr2O3) and carbon.[2]

• Carbon graphite refractories mainly consist of carbon. These refractories are often used in highly reducing environments, and their properties of high refractoriness allow them excellent thermal stability and resistance to slags.
• Chromite refractories are composed of sintered magnesia and chromia. They have constant volume at high temperatures, high refractoriness, and high resistance to slags.[18]
• Alumina refractories are composed of ≥ 50% alumina (Al2O3).

Method of manufacture

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1. Dry press process
2. Fused cast
3. Hand molded
4. Formed (normal, fired or chemically bonded)
5. Un-formed (monolithic-plastic, ramming and gunning mass, castables, mortars, dry vibrating cements.)
6. Un-formed dry refractories.

Size and shape

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Refractory objects are manufactured in standard shapes and special shapes. Standard shapes have dimensions that conform to conventions used by refractory manufacturers and are generally applicable to kilns or furnaces of the same types. Standard shapes are usually bricks that have a standard dimension of 9 in × 4.5 in × 2.5 in (229 mm × 114 mm × 64 mm) and this dimension is called a "one brick equivalent". "Brick equivalents" are used in estimating how many refractory bricks it takes to make an installation into an industrial furnace. There are ranges of standard shapes of different sizes manufactured to produce walls, roofs, arches, tubes and circular apertures etc. Special shapes are specifically made for specific locations within furnaces and for particular kilns or furnaces. Special shapes are usually less dense and therefore less hard wearing than standard shapes.

Unshaped (monolithic)

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These are without prescribed form and are only given shape upon application. These types are known as monolithic refractories. Common examples include plastic masses, ramming masses, castables, gunning masses, fettling mix, and mortars.

Dry vibration linings often used in induction furnace linings are also monolithic, and sold and transported as a dry powder, usually with a magnesia/alumina composition with additions of other chemicals for altering specific properties. They are also finding more applications in blast furnace linings, although this use is still rare.

Fusion temperature

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Refractory materials are classified into three types based on fusion temperature (melting point).

• Normal refractories have a fusion temperature of – °C (e.g. fire clay)
• High refractories have a fusion temperature of – °C (e.g. chromite)
• Super refractories have a fusion temperature of >  °C (e.g. zirconia)

Refractoriness

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Refractoriness is the property of a refractory's multiphase to reach a specific softening degree at high temperature without load, and is measured with a pyrometric cone equivalent (PCE) test. Refractories are classified as:[2]

• Super duty: PCE value of 33–38
• High duty: PCE value of 30–33
• Intermediate duty: PCE value of 28–30
• Low duty: PCE value of 19–28

Thermal conductivity

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Refractories may be classified by thermal conductivity as either conducting, nonconducting, or insulating. Examples of conducting refractories are silicon carbide (SiC) and zirconium carbide (ZrC), whereas examples of nonconducting refractories are silica and alumina. Insulating refractories include calcium silicate materials, kaolin, and zirconia.

Insulating refractories are used to reduce the rate of heat loss through furnace walls. These refractories have low thermal conductivity due to a high degree of porosity, with a desired porous structure of small, uniform pores evenly distributed throughout the refractory brick in order to minimize thermal conductivity. Insulating refractories can be further classified into four types:[2]

1. Heat-resistant insulating materials with application temperatures ≤  °C
2. Refractory insulating materials with application temperatures ≤  °C
3. High refractory insulating materials with application temperatures ≤  °C
4. Ultra-high refractory insulating materials with application temperatures ≤  °C

See also

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• Fire brick
• Masonry oven

Refractory material is a heat-resistant material that can withstand extreme heat and is used to line furnaces, kilns, and reactors. These materials do not break down under extreme heat, chemical reaction and mechanical stress. They are critical for industries like metal processing, glass manufacturing, cement production, and energy generation. Without these systems, high-temperature operations would be effective and safe.

Refractory Materials Definition

Refractories are specific materials that oppose high heat without liquefying, cracking, or becoming weaker. They resist thermal shock, maintain structural integrity, prevent heat loss, and are thus irreplaceable in industrial applications. They can also be tailored to meet specific needs such as resistance to abrasion, mechanical impact and chemical corrosion.

Why Do You Need Refractory Materials for Furnace?

This is because the materials for manufacturing furnaces need to exist in higher temperature conditions. Use of refractory materials for furnace protection guarantees:

Furnace lifespan – Avoid premature wear and tear, prolonging equipment life

Energy efficiency – Minimize heat loss and maximize energy use

Thermal shock resistance – Resists rapid temperature changes without fracture

Thermal insulation – Withstands melted metals and gaseous corrosion

A more secure environment — Reduces the potential hazard of accidents leading to steady operations

Sustainability — Minimizes energy waste and optimizes furnace performance

Without these refractory bricks, the floors of the furnaces would deteriorate in no time, and frequent repairs would drive up costs and waste energy. This leads to more downtime and less efficiency.

Types of Refractories Products

Preformed refractories – Pre-designed bricks/blocks for certain structures, typically used as linings in furnaces

Unshaped refractories – Castables, coatings, and ramming mixes applied directly in place

Ceramic refractory materials – Offer superior resistance and stability at high temperatures

Furnace refractory cement – For repairs on lining and patching to hold strength through heat

Depending on the application within the industry, as well as the environment within a given furnace, each type has a unique intended use. Selection of types of refractory products depend upon their temperature requirements, conductivity of heat, quotes of petration of destructive materials.

Ceramic Refractory Materials

More recent research has focused on enhancing the thermal, mechanical, and chemical properties of ceramic refractory materials for various applications. Some areas where these materials are routinely encountered include the following:

Steel and metallurgy – The lining of blast furnaces, ladles and converters ensures longevity in processes such as steelmaking

Glass production – Are used in glass melting furnaces for resistance to high temperatures

Cement production – Necessary for kiln linings and precalciner zones in cement plants

Petrochemicals – Used in reactors and refining units where there are intense amounts of heat

We offer high-performance ceramic refractories that can withstand extreme conditions for longer periods of time and at higher and higher speeds.

Furnace Refractory Cement

Furnace refractory cement is a high-temperature bonding agent used to repair and line furnaces. It is designed to:

Resist intense heat – Endures high temperatures, impeding any impairment

Offers a strong, heat-resistant bond – Improves structural durability and lifespan

Protect against cracks and heat loss – Fills in crevices, minimizing energy leakage

Provide corrosion resistance — Resists chemical stability from molten metal – gas exposure

Ease of application – Can be applied in maintenance and repairs without long downtimes

This quick-set cement is used to repair or extend the life of furnace linings, permitting undisturbed operation in high-temperature services.

Common Refractory Materials Used for Furnaces

There are various types of refractory materials used for specific functions in furnaces. So, you might be wondering: what are the most common?

Fire Bricks

Using silica, alumina, or clay-based compounds

Great protection and resistance against heat and thermal shock

The company is the world’s best magnesia carbon bricks supplier. We are your one-stop shop for all needs. Our staff are highly-specialized and will help you find the product you need.

Used in furnaces, kilns and fireplaces for insulation and durability

This is the simplest and most effective example: durable inexpensive very used in the industry

Castables

Pourable or trowellable mixtures of refractory aggregates and cement

Make them suitable for repairs and linings.

Great for complex furnace structures and specific applications

Resistant to high temperatures and mechanical stress

Ceramic Fiber

Great for lins and seals in high- temp areas, preventing heat migration

Lightens its overall weight through the body, making it energy efficient

For industrial furnaces, kilns, and high-temperature piping

Insulating Bricks

Low thermal conductivity ensures low energy loss

Used as load bearing insulation behind furnaces to improve energy efficiency

Accompanies in lowering down whole power consumption and preserving warmth stability

Applies commonly in reheating furnaces, annealing ovens, and kilns

Refractory Cement

Furnace Linings Sealing & Patching: High-Temperature Bonding Agent

Guarantees enhanced durability and protection against thermal and chemical damage

Applied to fixed furnace refractory material for rapid repair and prolonging service life

Provides a high level of heat resistance and adhesive strength

Graphite Brick

Constructed of high-purity graphite for optimal thermal conductivity

Thermal shock and chemical corrosion resistant

Thermocouples — Used in high-temperature applications such as furnaces and reactors;

It lubricates perfectly and protects from wear.

Carbon Magnesia Brick

Made from magnesia and carbon, it’s far more fire resistant

Perfect for high mechanical and thermal stress applications

Used in steelmaking furnaces, converters, and ladles

Offers good slag resistance and durability

Refractory Material for Furnace: How It Works

Using refractories in furnace in the form of the heat-, chemical- and mechanical-stress-protective layer The key functions include:

Heat-Absorbing and Retaining – Efficiently retains high temperatures and minimize the heat escape

Damage protection for furnace walls –Avoids structural failure due to thermal and mechanical stress

Thermal shock prevention – Prevents cracking and material degradation from sudden temperature fluctuations

Resisting chemical attacks – Shields against molten metal, slag, and corrosive gases

Enhancing Operational Safety – Avoids unsafe condition from materials failure

A better refractory system leads to longer life span of furnace and lower maintenance costs and improves overall industrial efficiency.

Refractory Material Properties

High thermal resistance – Resistance to extreme temperature up to °C or more

Chemical Resistance – Resists corrosion from acids, alkalis, and molten metals

Mechanical strength — Resistant to pressure, wear, and heavy loads without degradation

Thermal shock resistance — Adjusts to sudden temperature changes without creating cracks

Porosity and permeability – Enables regulated gas flow in the desired region

Abrasion resistance — Resists physical damage due to molten materials and mechanical forces

Each of these properties is critical to maximizing furnace life and maintaining throughputs in high temperature applications.

Finding Refractory Materials Near Me

Say, you are in the quest for refractory materials near me, you can think about these:

Local industrial suppliers — Many manufacturers and dealers carry quality refractory goods

Marketplace: Online nearly all furnace refractory materials with delivery

Specialized high-temperature materials – Suppliers that specialize in high-temperature materials for very specific solutions

Factory direct – Some companies bypass distributors and sell factory direct for bulk with advantageous pricing

Final Thoughts

High-temperature industrial processes rely on the most important piece of equipment: bricks, or so-called refractory materials. No matter if your project involves furnace lining with refractory materials or furnace refractory cement for repairs and ceramic refractory materials for insulation, choosing the right product ensures efficiency and durability.

High-quality refractory bricks help improve energy efficiency, safety, and operational stability. Talk with the right supplier if you want to find refractory materials near me to have the best solution for your requirements. They also ensure a high level of heat resistance and material stability, which is essential for many industries that rely on high-temperature processes.