What Types of Special Kiln Furniture are Used to Support Ceramic Blanks?
Sintering vessels are specialized kiln furniture used to support the fired ceramic blanks or to hold powders, such as cathode materials, magnetic powders, and high-purity ceramic materials, which are calcined and synthesized before undergoing heat treatment in roller kilns, pusher kilns, or tunnel kilns. Depending on the firing process of the user, this kiln furniture will be subjected to different heating conditions, and the material of these products depends on the type of sintered body and the heat treatment process.
Saggers/Crucibles
Saggers are used to hold powders (lithium-ion battery cathode materials, magnetic powders, high-purity ceramic powders) for heat treatment in roller kilns, pusher kilns, and tunnel kilns. They are generally formed using extrusion, machine pressing, casting, and isostatic pressing processes, with the appropriate forming process selected based on the composition and structure of the product. Widely used materials include cordierite-mullite, corundum-mullite, silicon carbide, and graphite. Their application is most prevalent in the synthesis of lithium-ion cathode materials.
Cordierite-mullite saggers are widely used in the field of lithium-ion battery cathode materials due to their excellent thermal shock resistance and economic efficiency.
Aluminum-silicon saggers generally have a short lifespan due to the strong alkalinity and low melting point of lithium carbonate/lithium hydroxide, which are highly corrosive to acidic refractory materials.
Corundum saggers are mainly used for calcining some high-purity powders in environments with less severe thermal shock conditions and high operating temperatures. For example, the calcination of high-purity alumina powder requires the sagger to be fired at 1800℃, using alumina active powder with an Al2O3 content of 99.9wt% and low-sodium white corundum. The binder uses low-ash content (Ash ≤ 0.01wt%), ensuring effective impurity control throughout the raw material process, and achieving a low coefficient of thermal expansion through sufficient high-temperature firing.
Graphite and silicon carbide saggers possess high thermal conductivity, high-temperature resistance, and excellent thermal shock resistance. While their oxidation resistance is poor, they exhibit excellent resistance to alkaline corrosion under reducing atmospheres. Graphite saggers are commonly used as containers for loading materials during high-temperature sintering in reducing atmospheres, applied in lithium iron phosphate sintering and electromagnetic material sintering. Traditional graphite saggers are produced through machining, which is inefficient and costly. Silicon carbide saggers are also widely used in pharmaceuticals, fine chemicals, engineering metallurgy, and pickling industries.
Firing Plates
Firing plates must withstand the thrust of movement and the friction of loading and unloading products during service, and must not crack under thermal cycling. While meeting the thermal shock resistance requirements, improving the bending and crack resistance of the firing plate is crucial. The firing plate material must have excellent chemical inertness and not react with the products it supports. Firing plate materials include alumina, zirconium oxide, and composite materials, mainly used in electronic ceramics and special ceramics.
Corundum firing plates refer to high-end kiln furniture with α-Al₂O₃ as the main crystalline phase. They possess excellent properties such as high strength, corrosion resistance, high temperature resistance, and wear resistance. They exhibit minimal deformation at high temperatures (>1650℃), but have high sintering temperatures and poor thermal shock stability. During the firing process of lead zirconate titanate piezoelectric ceramics, corundum firing plates face phenomena such as central warping, surface layered powdering, and peeling.
Zirconia is a corrosion-resistant, high-temperature refractory oxide. Zirconia sintering plates are frequently used as sintering pads in dielectric ceramics, powder metallurgy, chip capacitors, and ferrite magnetic materials to prevent parts from sticking together during sintering and to prevent the loss of electromagnetic properties of electronic components.
The firing temperature of conductive ceramics and device ceramics is generally between 1400 and 1650℃, and they are mostly corundum-mullite, corundum, or composite materials.
Barium titanate ceramics are a star product in the electronic ceramics industry. Sintering is a crucial step in its preparation process, determining the densification and microstructure of barium titanate; therefore, the quality of the sintering plate is particularly important. Because barium titanate has a low melting point (1625℃), high density, and is alkaline, traditional aluminosilicate kiln furniture easily reacts with it, leading to product contamination. Foreign kiln furniture manufacturers have applied plasma spraying technology to the sintering plate preparation process. The firing plate features a corundum-mullite interlayer and a zirconium oxide cladding coating, offering high thermal shock resistance and preventing reaction or adhesion with the fired chip-type multilayer ceramic capacitors.
With industrial development, the variety of products fired has increased, expanding the application areas of kiln furniture beyond ceramics to include fine chemicals and lithium-ion batteries. The performance requirements for kiln furniture materials, considering the characteristics of the fired products, are no longer limited to mechanical strength and thermal shock stability. Some applications also require excellent corrosion resistance and non-contamination of the fired products. Different corrosive media necessitate different requirements for kiln furniture materials. For example, in the production of lithium-ion battery cathode materials, kiln furniture materials must possess excellent thermal shock stability and resistance to alkaline lithium compounds. In the production of piezoelectric ceramics, kiln furniture materials must resist lead and its compounds.
With the rapid development of science and technology and the economy, magnetic materials, functional ceramics, and electronic ceramics have been widely used in information, electronics, machinery, and chemical industries. This has also driven the rapid growth in demand for high-performance corundum-mullite kiln furniture materials.
Kiln furniture is a special type of refractory material, primarily serving to support and protect fired products. Product forms mainly include pushers, firing supports, and saggers. During service, kiln furniture is subjected to high temperatures, compression, friction, and thermal cycling, and its damage often manifests as fracture or deformation. Therefore, the key performance requirements for kiln furniture materials lie primarily in their high-temperature mechanical properties, which determine their performance, such as high-temperature flexural strength, high-temperature creep resistance, and thermal shock resistance. Improving these performance characteristics involves the design of the material’s microstructure and its resistance to damage under complex stress conditions under high-temperature loads. This requires in-depth research and development in areas such as raw material selection, matrix material treatment, process control, and thermal stress distribution.
Through rational selection of raw materials, optimized microstructure design, scientific product firing process, and stress distribution calculation, high-performance corundum-mullite kiln furniture has been developed. It can be widely used in the sintering of structural ceramics, electronic ceramics, and powder metallurgy parts.
Technical Advantages of High-Performance Corundum-Mullite Kiln Furniture
Operating temperature up to 1750℃.
Strong creep resistance.
Meets the requirements of environments with strong thermal shock.
Applications of Corundum-Mullite Kiln Furniture
Corundum-mullite kiln furniture is an essential consumable refractory material in the ceramics industry, characterized by high demand and wide application. It is mainly used in the sintering of high-tech ceramics and powder metallurgy parts, such as electronic ceramics (MLCCs, varistors, magnetic materials, filters), Al2O3 structural ceramics (substrates, ceramic films, spark plugs, grinding media), ZrO2 structural ceramics (zirconia knives, mobile phone backplates, bearings, fiber optic ferrules), stainless steel, titanium alloys, etc.
High-performance corundum-mullite kiln furniture is used in pusher kilns to fire zirconia knives. High-performance corundum-mullite kiln furniture is used in pusher kilns to fire alumina ceramics.
