What Are the Types of Refractory Raw Materials Used in the Industry?

Refractory raw materials fall into six families: alumino-silicate (fireclay and bauxite), silica, basic (magnesia, magnesia-calcia, magnesia-chrome), alumina-rich and synthetic (corundum, mullite, spinel), carbon-bearing, and zirconia-bearing. The family is decided by the dominant oxide — Al₂O₃, SiO₂, MgO, C or ZrO₂. The grade inside that family is decided by a number, never by the name alone: 45–50% Al₂O₃ for a YNS-45 hard-clay clinker, at least 89.5% for GL-90 bauxite, at least 98.0% MgO for MS98A sintered magnesia.

That distinction is where most purchasing problems start. A quotation that answers with a family name has not answered the enquiry, because the same family spans a wide range of density, refractoriness and impurity limits, and the price difference between the top and bottom grade of one family is often larger than the difference between two neighbouring families.

This guide sets out the six families, the grade codes that actually appear on certificates, the standard each code is tied to, and the checks that confirm a delivered lot matches the code on the paper.

What Are the Six Refractory Raw Material Families?

Alumino-Silicate Raw Materials Carry Most of the Volume

Alumino-silicate raw materials are the backbone of the industry, and they are the ones most often bought by name only.

Calcined hard-clay clinker, also sold as flint clay clinker or chamotte, is graded under YB/T 5207. The top grade, YNS-45, carries 45–50% Al₂O₃ with Fe₂O₃ at or below 1.0%, a refractoriness of 1780 °C, a bulk density of at least 2.55 g/cm³ and water absorption of at most 2.5%. The bottom grade, YNS-36, drops to 36–42% Al₂O₃, 1680 °C and 2.30 g/cm³. Two grades of the same material, one family name, and a service ceiling that differs by a hundred degrees.

Calcined bauxite is graded under YB/T 5179 and separates more sharply. GL-90 requires at least 89.5% Al₂O₃ with bulk density at or above 3.35 g/cm³; GL-88A sits at 87.5% and 3.20; GL-80 above 80% and 2.90; GL-60 between 60% and 70% and 2.65. Iron oxide, titania and alkali limits tighten as the grade rises, and those impurities — not the alumina figure — are usually what limits service life in a reducing atmosphere.

The sillimanite group (kyanite, andalusite, sillimanite) sits at 55–60% Al₂O₃ and behaves differently from both: these minerals expand as they convert to mullite on firing, which is why they are added to offset the shrinkage of clay-bonded bodies and to improve creep resistance. Synthetic mullite is the purified version of the same idea, at 70–78% Al₂O₃ with the stoichiometric 3Al₂O₃·2SiO₂ composition at 71.8%.

Silica Raw Materials Are Narrower Than They Look

Silica raw material is quartzite with SiO₂ typically at 96–98% and iron oxide held below about 1%. It produces one product family with one very specific behaviour: silica brick, covered by GB/T 2608, requires SiO₂ of at least 94–95% and delivers a refractoriness-under-load above 1650 °C.

What buyers must plan for is the expansion. Silica goes through crystalline transformations on heating that produce 2–3% linear growth, so a silica lining has to be brought up to temperature on a controlled curve and cannot be cooled and reheated freely. In exchange it gives the highest load-bearing stability of any commercial brick at temperature, which is why coke oven batteries and hot-blast stove domes are still built from it.

Fused silica is a separate product with the opposite thermal profile — very low expansion and excellent thermal shock resistance — and it is specified where cycling, not load, is the governing condition.

Basic Raw Materials Begin with Magnesia

Sintered magnesia is graded under GB/T 2273. MS98A requires at least 98.0% MgO, silica at or below 0.3%, and a particle bulk density of at least 3.40 g/cm³. MS97A sits at 97.0% and 3.33; MS96 at 96.0% and 3.25; MS95 at 95.0% and 3.20; MS92 at 92.0% and 3.18. For the high grades the standard also controls the CaO/SiO₂ ratio at 2 or above, because that ratio decides whether the silicate phase forms a continuous film around the periclase grains or stays isolated at the triple points — in practice, whether the brick develops a direct bond.

Fused magnesia reaches 97–99% MgO with much larger crystals and is the input for magnesia-carbon bricks rather than for fired oxide grades.

Magnesia-calcia material comes from dolomite, and its composition is fixed by mineralogy rather than by choice: a commercial sintered doloma runs roughly 55–60% CaO and 35–40% MgO. It offers excellent cleanliness for steel — the free CaO absorbs inclusions — but it hydrates, so storage and lining practice have to treat it as a moisture-sensitive material.

Magnesia-chrome was for decades the standard for high-duty basic linings. Hexavalent chromium restrictions in several markets have pushed buyers toward magnesia-spinel and magnesia-hercynite alternatives, and any enquiry specifying chrome should state the Cr₂O₃ level and the disposal route expected.

Alumina-Rich and Synthetic Raw Materials Set the Upper Grade

Above the bauxite range, the raw materials are manufactured rather than mined.

Fused white corundum runs at 99% Al₂O₃ or higher, with total impurities held below 0.8%. Brown fused alumina is lower, typically 94–97%, because it is smelted from bauxite rather than from calcined alumina. Tabular alumina is at 99% and above, but its value is not the purity — it is the closed porosity and the large, well-developed corundum crystals, which give thermal shock resistance and creep resistance that a dense fused grain cannot match.

Magnesia-alumina spinel, at 71.8% Al₂O₃ and 28.2% MgO, is the standard answer where a basic lining must tolerate alumina-rich slag or where thermal cycling rules out straight magnesia.

Silicon carbide is graded at 90–98% SiC for refractory use, in black and green forms, and belongs to blast furnace trough linings, where abrasion and alkali attack dominate.

Carbon and Zirconia Answer Specific Duties

Carbon-bearing raw materials mean flake graphite at 94–99% carbon, combined with magnesia or alumina in resin-bonded bricks, with aluminium or silicon powder as antioxidants. Carbon gives thermal shock resistance and slag non-wetting that no oxide provides, and the trade-off is oxidation: a carbon-bonded brick needs a protected atmosphere or an antioxidant package, and its grade is defined by carbon content plus the antioxidant addition, not by carbon content alone.

Zirconia enters in two forms. Zircon sand carries 60–66% ZrO₂ and 32–34% SiO₂ and is used where resistance to slag penetration matters more than absolute refractoriness. Fused zirconia-alumina (AZS) blocks, at 32–41% ZrO₂, are the standard material for glass furnace sidewalls and superstructures.

How Do Raw Material Grades Become Product Grades?

Raw material grades do not translate directly into product grades, and this is the second common purchasing error.

Dense shaped alumino-silicate products are classified under GB/T 17105, which sorts them by alumina content into groups: HA98 at 98% and above, HA95 for 95–98%, HA85 for 85–95%, HA75 for 75–85%, HA65 for 65–75%, HA55 for 55–65% and HA45 for 45–55%. Clay-bonded products fall into FC40 at 40–45%, FC35 at 35–40% and FC30 at 30–35%; low-alumina and semi-silica products into LF10 at 10–30%; silica products into SS85 at 85–93% SiO₂.

A brick made from GL-88 clinker does not automatically test as HA85. Binder additions, firing losses and the silica carried in by the clay fraction all move the finished analysis, and the product standard is applied to the fired brick, not to the raw material certificate. Buyers comparing a raw material quote against a product specification should ask for the finished-product analysis and the classification the supplier is claiming, not the clinker grade alone.

Which Tests Prove a Raw Material Lot?

A raw material certificate is only useful if the numbers on it come from named methods.

Chemical analysis is method-specific: GB/T 6900 for alumino-silicate materials, GB/T 5069 for magnesia and magnesia-alumina materials, GB/T 16555 for carbon-bearing and silicon carbide materials. A certificate quoting Al₂O₃ without naming the method cannot be compared with a certificate that does.

Physical checks matter as much as chemistry for clinker and magnesia:

• Bulk density and apparent porosity — GB/T 2997-2015, which is modified from ISO 5017:2013. For clinker this is the single best indicator of sintering degree, because under-burnt material shows low density and high water absorption.
• Water absorption — specified directly in YB/T 5179 and YB/T 5207, and the fastest way to detect a clinker that was burned at the wrong temperature.
• Refractoriness — GB/T 3001, reported as a cone number or a temperature, and the first screen for a new source.
• Loss on ignition — a high figure points to unburnt carbonate or moisture, which shows up later as shrinkage in the lining.
• Particle size distribution — for aggregate, the split between 5–3 mm, 3–1 mm, 1–0 mm and fines below 0.088 mm decides packing density, and a shifted split changes the water demand of the finished mix.

For magnesia, add the CaO/SiO₂ ratio and the lime level, since both govern hydration resistance as well as bond structure.

What Should a Buyer Put in a Raw-Material Enquiry?

Six entries turn a raw material request into something a supplier can quote against, and each one removes a decision the supplier would otherwise make on the buyer's behalf:

• The furnace or process and the exact zone — working lining, safety lining, or a repair area.
• Service conditions: peak and average temperature, atmosphere, slag composition and basicity, thermal cycling pattern, mechanical load and abrasion.
• The product form required — fired brick, precast shape, or an installed monolithic.
• The chemical window, with upper limits on the impurities that matter for that zone rather than a single alumina or magnesia figure.
• The physical targets — bulk density, apparent porosity, cold crushing strength — and the method for each.
• The acceptance basis: which tests, at what frequency, and how the lot is traced from raw material batch to dispatch.

Leaving any of these blank does not make the enquiry simpler; it moves the assumption to the supplier's side, where it is invisible until the lining fails.

How Does Jinheng Refractory(JHR) Support Raw Material Selection?

Jinheng Refractory(JHR) works from the raw material inward: the grade is chosen against the zone duty, and the finished product is released against the analysis of the fired brick rather than the clinker certificate.

The company operates from Bo'ai County, Jiaozuo City, Henan Province — a refractory production cluster with local bauxite resources, which shortens the supply chain for alumino-silicate grades. Quality control runs from incoming raw material through to finished-product dispatch, and the management system covers ISO 9001, ISO 14001 and OHSAS 18001. The company is listed on the National Equities Exchange and Quotations under NEEQ: 839391.

The technical scope covers material selection, lining design, and installation guidance, so a raw material enquiry and the lining it belongs to can be reviewed together rather than as two separate purchases.

FAQ

Q: What are the main types of refractory raw materials?

A: Six families: alumino-silicate (fireclay clinker, bauxite, sillimanite group, mullite), silica, basic (magnesia, magnesia-calcia, magnesia-chrome), alumina-rich and synthetic (white and brown corundum, tabular alumina, spinel), carbon-bearing (graphite with antioxidants), and zirconia-bearing (zircon sand, AZS). The dominant oxide defines the family; a numeric grade defines the product.

Q: What does the grade code on a bauxite certificate mean?

A: Under YB/T 5179, the number is the alumina content floor: GL-90 requires at least 89.5% Al₂O₃ and a bulk density of at least 3.35 g/cm³, GL-80 above 80% and 2.90 g/cm³, GL-60 between 60% and 70% and 2.65 g/cm³. Iron oxide, titania and alkali limits are specified alongside, and they often control service life more than the alumina figure.

Q: How is sintered magnesia graded?

A: Under GB/T 2273 by MgO content and bulk density. MS98A requires at least 98.0% MgO and 3.40 g/cm³, MS97A 97.0% and 3.33 g/cm³, MS96 96.0% and 3.25 g/cm³, MS95 95.0% and 3.20 g/cm³, MS92 92.0% and 3.18 g/cm³. High grades also control the CaO/SiO₂ ratio, which governs whether the brick develops a direct bond.

Q: Can a raw material grade be read straight off the finished brick grade?

A: No. Finished alumino-silicate products are classified under GB/T 17105 as HA98, HA95, HA85, HA75, HA65, HA55 or HA45 for high-alumina, FC40, FC35 or FC30 for clay-bonded, LF10 for low-alumina, and SS85 for silica. Binder additions and firing losses shift the analysis, so a brick made from GL-88 clinker does not necessarily test as HA85. Ask for the fired-product analysis.

Q: Which tests should accompany a raw material delivery?

A: Chemical analysis by GB/T 6900, GB/T 5069 or GB/T 16555 depending on the family; bulk density and apparent porosity by GB/T 2997-2015; refractoriness by GB/T 3001; water absorption and particle bulk density for clinker and magnesia; loss on ignition; and particle size distribution for aggregate. The acceptance list should be written into the purchase order rather than assumed.