Refractory ceramic materials play an integral role in most (if not all) high-temperature processing industries. They demonstrate incredible thermal resistance and longevity. Many sectors now leverage their ability to withstand high temperatures without deforming or softening. Industries, hence, have a link between advanced processing techniques and new materials, which is crucial in creating scalable manufacturing solutions.
This article covers everything about these futuristic materials, including their fundamental role in different economic sectors.
Let’s start with the basics!
What is a Refractory Ceramic Material?
“Ceramic” is derived from an ancient Greek word “Keramos” which means burnt things. “Keramos” referred to items made from natural materials that had survived extreme temperatures. Broadly used now, ceramic describes inorganic, non-metallic materials used in or processed under high-temperature conditions.
At its core, a refractory material is a material that demonstrates high rigidity, resilience, and purity in extremely high-temperature conditions. It is used to either contain or transfer heat. It can also be used to shield against high-temperature chemical processes and reactions.
Refractory materials’ ability to remain chemically inert in such processes and mechanically stable is exploited in manufacturing liquid metals and alloys.
In glass processing, refractories contain heat and shield the glass product from chemical contamination. Cement manufacturing companies use them to protect their steelworks from heat and chemical reactions. Additionally, refractory products can be used to transfer heat in blast furnaces.
Refractory materials typically withstand highly gaseous, high-temperature environments to facilitate the manufacture of other products. They can be porous or non-porous. Depending on the level of crystallinity, refractory ceramics are classified as composite, amorphous, crystalline, or polycrystalline.
Chemists and physicists manipulate such elements as zirconium, silicon, magnesium, boron, and calcium to solve different industry needs. The elements are combined with carbides, oxides, or nitrides to form highly resistant, anti-corrosive, and thermal-resistant materials.
For instance, zirconium oxide (zirconia) and silicon carbide are two high-end refractory materials that remain rigid in extremely high temperatures. Binary compounds like boron nitride, tungsten carbide, and hafnium carbide are very refractory, with the latter’s melting point at 3,890°C.
Some of these compounds can withstand severe temperatures but may burn when exposed to oxygen atmospheres. Others like molybdenum disilicide are fit for use as heating elements while some are used as refractory lining materials.
The Manufacturing Process of Refractory Ceramics
Generally, a refractory material should withstand high temperatures not below 538°C (1,000°F). They should demonstrate high mechanical strength with high abrasion resistance. To survive extremely corrosive atmospheres, they should be resistant to chemical agents even in severe temperatures. This way, they’ll offer manufacturing equipment efficient protection and surface lining.
Such materials are manufactured under extreme conditions. Fireclay, which is formed by up to 87.5% of alumina and hydrous silicates of aluminum is used to form clay refractory materials. Due to varied industry needs, different clay minerals like ball clay, common clay, bentonite, and kaolin may be used.
Up to 87% of alumina, chromite, magnesite, silicon carbide, silica, and other nonclays including zircon are used to produce nonclay refractory materials.
Ceramic refractory products range from traditional high-fired refractory brick to bagged monolithic refractory, to advanced, complex, and modern finish fired products. Modern finish fired components include resistance rod furnaces, channel induction furnaces, coreless furnaces, reverberatory furnaces, impact shapes, etc.
The preformed components, called bricks and shapes, form excellent floor tiles, walls, and arches of different high-temperature equipment. Unformed components form internal, monolithic structures. They include refractory brick mortars, castables, plastics, gunning mixes, etc.
Refractory Manufacturing Processes
As we mentioned earlier, industrial ceramics are used in all high-temperature processes. For instance, a vehicle uses different types of materials like plastics, glass, and steel, all manufactured at severe temperatures. Steel is made from iron using particular processes, being melted in a crucible at temperatures above 2000°C.
The inner linings of the heating crucible are lined with ceramic materials to prevent it from melting or wearing out fast. Here’s how these wonderful products are manufactured:
1Raw Material Processing
This step involves preparing raw materials to ensure they are in the desired size, shape, and amount. Raw materials are crushed and ground before calcining and drying. Depending on customer preference, raw materials may be mixed dry with chemical compounds and minerals before packaging and shipping. This eases the subsequent steps.
2Forming
Sometimes raw materials come as separate products rather than pre-mixed. This is when the manufacturer mixes them, either dry or moist.
3Firing
The step involves subjecting the material to extreme temperatures in the tunnel kiln to form strong ceramic bonds that characterize refractory materials. The loose material is then transferred to a binder before shaping.
4Final Processing
The material will undergo thermal expansion, after which it will be milled, ground, and sandblasted for perfect size and shape. Depending on industry needs, the final product may be impregnated with tar and pitch before packaging.
Types of Refractory Materials
The most common types of ceramic refractory materials are monolithic, fireclay, high alumina, zirconia, chromite, magnesite, and silica. However, their categorization depends on their chemical composition, method of manufacture, and fusion temperature:
1Chemical Composition
Refractory ceramics under this category are either single or multi-component compounds with inorganic and non-metallic elements.
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Acid refractory materials: Used in slag and acidic atmospheres. Silica, zirconia, and alumina silica are the basic materials used. The main refractories include fireclay, quartz, and silica.
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Basic refractory materials: Used in basic, non-acidic conditions. MgO, CaO, chrome magnesite, and dolomite are the raw materials. Typical materials combine elements of dead burned magnesite, chrome ores, and dolomite.
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Neutral refractory materials: Used in non-basic, non-acidic conditions. Raw materials include oxides of aluminum and chromium (Al2O3 and Cr2O3).
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Zirconia refractory materials: Zirconium oxide (ZrO2) is the main raw material. It’s characterized by high-temperature endurance, high-volume stability, and high refractoriness.
2Method of Manufacture
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Fired refractories: These are industrial ceramics that use powdery or granular raw materials that are molded, kneaded, and dried. They are then fired at very high temperatures. Examples include high alumina, silica, and fireclay bricks.
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Non-fired refractories: Use granular and powdered refractory materials directly without firing.
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Functional refractories: These are ceramic materials that use powdered or granulated raw materials to meet specific shape and smelting requirements. They could be fired or non-fired.
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Monolithic refractories: The raw materials could be granular or powdery and are not fired at very high temperatures. Raw materials are also used right after mixing and grilling.
3Fusion Temperature
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Normal refractory materials: Fusion temperature ranges between 1580-1780°C. Eg: Fireclay
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High refractory materials: Fusion temperature ranges between 1780-2000°C. Eg: chromite
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Super refractory materials: Have fusion temperature above 2000°C. Eg: zirconia
Frequently Asked Questions About Ceramic Refractory Materials
1What are the most desired properties of a refractory material?
A refractory material should have high thermal resistance to endure severe temperatures, high oxidation resistance, and chemical attacks.
2Are refractory ceramic materials good electric conductors?
A typical refractory material resists or inhibits the flow of electric currents through them. Hence, they are used as good thermal and electric insulators. However, a few materials like silicon carbide, boron carbide, and titanium suboxide conduct electricity.
3Can clay deform at high firing temperatures?
Yes. Clay requires a not very high and not very low temperatures during kiln firing. Otherwise, it could deform or melt, causing glaze runoff. If fired at lower temperatures than required, the products may come out as dry and too soft to use.
4How long do refractory materials last in use?
This is subjective to the type of industry the material is used in. For instance, glass manufacturing industries can use a ceramic material for up to 10 years. Whereas, steel companies may need to replace their surface linings after every few weeks.
5What is the composition of heat-resistant clay?
The main raw materials of fireproof clay are alumina and silica. The compounds are mixed with additives and other ingredients that support the material’s refractoriness.
6Can refractory materials used in a crucible be recycled?
Yes. Refractory ceramic materials that have already been subjected to extreme heat can be reused for surface lining or other industrial needs.
7What are the industrial applications of ceramic materials?
Refractory ceramics are used in glass, plastic, and steel manufacturing industries, metallurgy, blast furnaces, and other high-temperature manufacturing companies.
8Where do I get a fireclay bag near me?
GGSCERAMIC.com is a leading ceramic company, running for almost two decades. With their state-of-the-art manufacturing processes, you’re assured of high-quality fireclay bags, castable refractory cement, and refractory concrete. GGSCERAMIC.com is an ideal starting point if you’re looking for a one-stop ceramic company that ships its products to wherever you are without costing a fortune.