Do You Know the Five Classification Methods for Refractory Raw Materials?

Refractory raw materials are essential in many industrial processes because they maintain stability at high temperatures. Here, we will detail the five classification methods to help you better understand these materials.

Refractory raw materials come in various types, and there are multiple ways to classify them. Overall, there are six classification methods.

PART 01: Classification by Chemical Composition

Refractory raw materials can be divided into oxide and non-oxide materials. With modern scientific and technological advancements, some organic compounds have become precursor materials or auxiliary raw materials for high-performance refractories.

PART 02: Classification by Chemical Properties

According to their chemical properties, refractory raw materials can be divided into:

1. Acidic Refractory Raw Materials: Examples include silica and zircon.
2. Neutral Refractory Raw Materials: Examples include corundum, bauxite (slightly acidic), mullite (slightly acidic), chromite (slightly alkaline), and graphite.
3. Basic Refractory Raw Materials: Examples include magnesia, dolomite, and magnesia-calcium sand.

PART 03: Classification by Production Process Role

Based on their role in the production process of refractories, raw materials can be classified as primary or auxiliary materials.

1. Primary Raw Materials: These form the main body of the refractory materials.

2. Auxiliary Raw Materials: These can be further divided into binders and additives.

   • Binders: Used to provide sufficient strength during production and use. Common binders include sulfite pulp waste liquid, pitch, phenolic resin, aluminate cement, water glass, phosphoric acid and phosphates, and sulfates. Some primary raw materials also act as binders, such as binding clay.
   • Additives: Used to improve production or construction processes or to enhance certain properties of refractory materials, such as stabilizers, water reducers, inhibitors, plasticizers, foaming agents, dispersants, expansion agents, and antioxidants.

PART 04: Classification by Acidity and Alkalinity

Refractory raw materials can be classified into five main categories based on their acidity and alkalinity.

1. Acidic Materials: Mainly silica-based materials, such as quartz, cristobalite, tridymite, chalcedony, flint, opal, quartzite, and diatomaceous earth. These materials contain at least 90% silicon dioxide (SiO2), with some pure materials having over 99% SiO2. They react chemically with metal oxides to form fusible silicates.

2. Semi-Acidic Materials: Primarily refractory clays, which have lower free silica content compared to purely silica-based materials. Refractory clays contain 30-45% alumina, often combined with silica to form kaolinite. At high temperatures, they decompose into free silica and alumina, which further react to form mullite. Therefore, clays have weaker acidic properties than pure silica.

3. Neutral Materials: These include chromite, graphite, and synthetic silicon carbide, which do not react with either acidic or basic slags at any temperature. Natural neutral materials include chromite and graphite.

4. Basic Materials: These include magnesite (magnesium carbonate), dolomite, lime, olivine, serpentine, and high alumina materials. These materials resist basic slags but react with acidic slags to form salts.

5. Special Refractory Materials: These include zirconia, titania, beryllia, ceria, thoria, and yttria. These materials have varying degrees of resistance to different slags but are limited in availability and used only in special applications.

PART 05: Classification by Raw Material Origin

Based on their origin, refractory raw materials can be classified into natural and synthetic categories.

1. Natural Refractory Raw Materials: These still form the bulk of refractory materials. Natural minerals are abundant, with the main elements being oxygen, silicon, and aluminum. Major natural refractory raw materials include silica, quartz, diatomaceous earth, clay, bauxite, kyanite, magnesite, dolomite, limestone, olivine, serpentine, talc, chlorite, zircon, and natural graphite. Most natural raw materials require purification, grading, or calcination to meet the production standards of refractory materials.

2. Synthetic Refractory Raw Materials: These are designed to meet specific requirements for high-quality and high-tech refractory materials. Synthetic materials can have predetermined chemical compositions and structures, providing stable quality and suitability for advanced refractory products. Major synthetic refractory raw materials include magnesia-alumina spinel, synthetic mullite, seawater magnesia, synthetic magnesium silicate, sintered alumina, aluminum titanate, and silicon carbide. These materials have seen significant development in the past two decades.