Zirconia Fused Alumina (ZFA), also known as Zirconia-Alumina Composite or ZA, is a high-performance fused refractory material produced by co-fusing high-purity alumina (Al₂O₃) with zirconia (ZrO₂, typically 10–40 wt.%) in an electric arc furnace at temperatures exceeding 2,000°C. ZFA is prized in refractory applications for its exceptional thermal shock resistance, high-temperature strength retention, and resistance to corrosive slags and glass melts.
Zirconia Fused Alumina (ZFA), also known as Zirconia-Alumina Composite or ZA, is a high-performance fused refractory material produced by co-fusing high-purity alumina (Al₂O₃) with zirconia (ZrO₂, typically 10–40 wt.%) in an electric arc furnace at temperatures exceeding 2,000°C. The resulting microstructure features alpha-alumina crystals embedded in a zirconia matrix, or a eutectic structure, which imparts unique properties not found in standard fused aluminas. ZFA is prized in refractory applications for its exceptional thermal shock resistance, high-temperature strength retention, and resistance to corrosive slags and glass melts.
ZFA’s performance edge in harsh thermal environments is derived from the synergistic effect of alumina and zirconia:
• Phase Transformation Toughening: Zirconia undergoes a martensitic transformation (tetragonal to monoclinic) at around 1,100°C, accompanied by a 3–5% volume expansion. This expansion closes microcracks that form under thermal stress, significantly increasing fracture toughness and thermal shock resistance—far exceeding that of white (WFA) or brown (BFA) fused alumina.
• High Hot Modulus of Rupture (HMOR): Maintains high mechanical strength at temperatures up to 1,600°C, resisting creep and deformation under load in heavy-duty applications.
• Excellent Corrosion Resistance: The dense, zirconia-rich structure provides superior resistance to alkaline slags, molten glass, and non-ferrous metal melts (e.g., aluminum, copper). Zirconia is particularly resistant to attack by vanadium oxides and other corrosive fluxes.
• Low Thermal Conductivity: Compared to pure alumina, ZFA has lower thermal conductivity, offering better thermal insulation properties in refractory linings.
ZFA is a critical component in advanced monolithic refractories for the steel industry:
• Steel Ladle Working Linings: ZFA is used as an aggregate in alumina-magnesia castables and gunning mixes for ladle linings. Its thermal shock resistance prevents spalling during teeming and emptying cycles, while its corrosion resistance extends lining life in the presence of aggressive slags (especially those high in CaO, MgO, and FeO).
• Tundish Refractories: In continuous casting tundishes, ZFA-based castables and boards are used in the working layer and impact pads. They withstand the thermal shock of molten steel entry and resist erosion from high-velocity steel flow and slag attack.
• Slide Gate Plates & Nozzles: ZFA micro powder is used in the production of high-alumina slide gate plates and submerged entry nozzles (SENs), enhancing their thermal shock resistance and preventing clogging by inclusions.
ZFA is the material of choice for glass furnace components exposed to severe thermal and chemical stress:
• Glass Furnace Regenerators & Checker Bricks: ZFA-based checker bricks line the regenerator chambers of glass melting furnaces. They efficiently store and transfer heat while resisting corrosion from alkaline glass vapors (Na₂O, K₂O) and thermal shock from cyclic heating/cooling.
• Glass Contact Zones: For color TV glass, optical glass, and high-borosilicate glass production, ZFA refractories are used in feeder channels and forehearths. They minimize contamination of the glass melt and resist erosion by the highly corrosive glass.
• Glass Tempering Furnace Rollers: ZFA coatings on furnace rollers provide excellent resistance to thermal shock and abrasion, ensuring smooth handling of glass sheets during rapid heating and cooling.
ZFA’s resistance to molten non-ferrous metals makes it ideal for this sector:
• Aluminum Smelting & Casting: ZFA-based refractories line launders, crucibles, and holding furnaces for molten aluminum. They resist attack by molten aluminum and its alloys, as well as by fluoride fluxes (e.g., cryolite), preventing contamination of the metal.
• Copper Converter Linings: ZFA is used in refractories for copper smelting converters, where it withstands the high temperatures and corrosive acidic slags encountered during the conversion of copper matte to blister copper.
In cement production, ZFA addresses the most demanding zones prone to alkali attack and thermal shock:
• Cement Kiln Burners & Secondary Air Ducts: ZFA refractories line burner pipes and hot air ducts, resisting erosion from high-velocity clinker particles and thermal shock from flame impingement.
• Rotary Kiln Transition Zones: Blended with high-alumina castables, ZFA improves the resistance of refractories in the cement kiln’s transition zone to alkali-sulfate attack and thermal cycling, a major cause of refractory failure in this area.
ZFA’s combination of strength and toughness makes it suitable for high-temperature furnace components:
• Kiln Furniture: ZFA is used to produce setter plates, batts, and beams for firing advanced ceramics (e.g., zirconia toughened alumina, silicon nitride) and technical glass. It withstands temperatures up to 1,700°C without warping and resists thermal shock during rapid firing cycles.
• Heat Treatment Furnaces: ZFA-based refractories line furnaces used for the heat treatment of high-alloy steels and superalloys, where high-temperature strength and resistance to scale formation are essential.
ZFA is utilized in various physical forms to optimize refractory performance:
• Aggregate (1–50mm): Crushed, angular ZFA aggregate is the primary component in high-performance castables, gunning mixes, and bricks, providing structural strength and corrosion resistance.
• Fines & Micro Powder (<0.088mm): Used as a matrix material, sintering aid, or anti-spalling additive in monolithic refractories. The fine zirconia particles distribute throughout the matrix, providing uniform toughening.
• Grained Powders: Sized powders (e.g., 0–1mm, 1–3mm) are used in ramming masses and dry vibratable mixes for induction furnace linings and other applications requiring high density and thermal shock resistance.
Zirconia Fused Alumina (ZFA) is a premium refractory raw material that bridges the gap between pure alumina and zirconia refractories. Its unique microstructure, combining the hardness of alumina with the toughening effect of zirconia, delivers unmatched performance in environments characterized by extreme thermal shock, high-temperature corrosion, and heavy mechanical load. ZFA is indispensable in the most critical applications in steelmaking, glass manufacturing, non-ferrous metallurgy, and advanced ceramics processing, where it significantly extends refractory service life and reduces maintenance costs.
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