Monoclinic Zirconia Powder — Unstabilized ZrO₂ for Refractories, Foundry & Thermal Processing
SEMITECH Monoclinic Zirconia is an unstabilized (undoped) zirconium dioxide powder in the thermodynamically stable monoclinic crystal phase. With ZrO₂+HfO₂ ≥99.0%, melting point of 2715°C, and low thermal conductivity (2.0–2.5 W/m·K), monoclinic zirconia is the baseline zirconia material for refractory linings, investment casting shell systems, thermal barrier bond coats, ceramic pigment synthesis, and abrasive applications where the highest refractoriness is required without the cost of yttria stabilization.
SEMITECH supplies both fused (electric-arc melted and crushed) and chemically precipitated grades, with controlled particle-size distributions ranging from sub-micron precipitated powder (d50 ~1 μm) to coarse fused granules (d50 10–45 μm) for different processing and end-use requirements.
Technical Specifications — Fused Grade
| Parameter | Unit | Typical Value | Test Method |
|---|---|---|---|
| ZrO₂ + HfO₂ | wt% | ≥99.0 | XRF |
| HfO₂ | wt% | ≤2.0 | XRF |
| SiO₂ | wt% | ≤0.15 | ICP-OES |
| Fe₂O₃ | wt% | ≤0.05 | ICP-OES |
| TiO₂ | wt% | ≤0.10 | ICP-OES |
| Al₂O₃ | wt% | ≤0.10 | ICP-OES |
| Na₂O | wt% | ≤0.05 | ICP-OES |
| Crystal phase | — | Monoclinic ≥95% | XRD |
| Melting point | °C | 2715 | — |
| Density (theoretical) | g/cm³ | 5.68 | — |
| Particle size d50 | μm | 10–45 (adjustable) | Laser diffraction |
| Particle size d90 | μm | ≤100 | Laser diffraction |
| Color | — | White to off-white | Visual |
Technical Specifications — Precipitated Grade
| Parameter | Unit | Typical Value | Test Method |
|---|---|---|---|
| ZrO₂ + HfO₂ | wt% | ≥99.5 | XRF |
| HfO₂ | wt% | ≤2.0 | XRF |
| SiO₂ | wt% | ≤0.05 | ICP-OES |
| Fe₂O₃ | wt% | ≤0.02 | ICP-OES |
| Na₂O | wt% | ≤0.10 | ICP-OES |
| Cl⁻ | ppm | ≤500 | Ion chromatography |
| Loss on ignition (1000°C) | wt% | ≤1.5 | Gravimetric |
| BET surface area | m²/g | 5–25 | N₂ adsorption (ISO 9277) |
| Particle size d50 | μm | 0.5–5.0 (adjustable) | Laser diffraction |
| Crystal phase | — | Monoclinic ≥90% | XRD |
Application Suggestions
Refractory Linings and Furnace Furniture
Monoclinic zirconia is used in high-temperature refractory applications where alumina (mp 2072°C) and magnesia (mp 2852°C) cannot provide the required combination of chemical inertness and thermal stability. Zirconia crucibles, nozzles, and linings are standard in glass melting, steel continuous casting (submerged entry nozzles, SENs), and specialty metal processing. The fused grade (d50 10–45 μm) is blended with zirconia or alumina binders and cast or pressed into refractory shapes. SEMITECH fused monoclinic zirconia with SiO₂ ≤0.15 wt% meets the purity requirements for glass-contact refractories where silica pickup causes seed defects.
Investment Casting Shell Systems
Monoclinic zirconia flour and stucco are used as the face-coat material in investment casting shells for aerospace superalloy components (turbine blades, vanes). The face coat — typically 50–200 μm thick — must resist chemical reaction with molten nickel-based superalloys at 1500–1600°C. Zirconia's chemical inertness to reactive metals (Ti, Hf, Zr alloy additions in superalloys) makes it superior to alumina and silica face coats for directionally solidified and single-crystal castings. SEMITECH supplies precision-graded fused zirconia flour (d50 5–15 μm for slurry, 50–150 mesh for stucco) meeting AMS 2175 requirements.
Thermal Barrier Coating Bond Coats
In thermal barrier coating (TBC) systems for gas turbines, a zirconia-based bond coat layer between the metallic substrate (MCrAlY) and the 8Y-CSZ topcoat improves adhesion and provides additional oxidation resistance. Monoclinic zirconia powder (d50 15–45 μm, spheroidized by plasma processing) serves as feedstock for atmospheric plasma spray (APS) bond coat deposition. The monoclinic-to-tetragonal phase transformation during plasma melting and quenching produces a metastable tetragonal coating with high strain tolerance.
Ceramic Pigment Synthesis
Monoclinic zirconia is the host lattice for zirconium-based ceramic pigments, including zircon blue (ZrSiO₄:V), zircon coral (ZrSiO₄:Fe), and praseodymium yellow (ZrSiO₄:Pr). The zirconia reacts with SiO₂ and dopant oxides at 900–1200°C to form the zircon (ZrSiO₄) pigment structure. Precipitated monoclinic zirconia (d50 1–3 μm, BET 10–20 m²/g) provides the reactivity and intimate mixing required for complete pigment formation at economical firing temperatures.
Abrasive and Polishing Applications
Fused monoclinic zirconia (Mohs hardness 6.5) is used as an abrasive grain in coated abrasives and bonded grinding wheels for metalworking, and as a polishing compound for glass and gemstone finishing. The toughness of the monoclinic phase provides superior grain integrity under grinding loads compared to alumina, resulting in longer abrasive life and cooler cutting action — particularly beneficial for grinding heat-sensitive materials (tool steels, titanium alloys).
Technical Support & FAQ: Monoclinic Zirconia Powder
+Q1: What is the difference between fused and precipitated monoclinic zirconia?
Fused zirconia is produced by melting zircon sand (ZrSiO₄) or baddeleyite in an electric arc furnace at >2800°C, then crushing and classifying the solidified ingot. It produces dense, angular particles with low surface area and minimal chemical activity — ideal for refractories, abrasives, and thermal spray feedstock. Precipitated zirconia is produced by chemical precipitation from zirconium salt solutions (ZrOCl₂), yielding fine, high-surface-area powder with controlled purity — preferred for ceramic pigments, catalyst precursors, and applications requiring chemical reactivity.
+Q2: Why not use stabilized zirconia for refractories?
Yttria-stabilized zirconia costs 3–5× more than monoclinic zirconia and is unnecessary for most refractory applications. The monoclinic-to-tetragonal phase transformation at 1170°C does cause a 3–5% volume change, but in refractory service this is managed through controlled heating rates and composite formulation (ZrO₂ blended with Al₂O₃ or MgO). For thermal-cycling applications requiring dimensional stability (e.g., kiln furniture), partially stabilized zirconia (PSZ with MgO or CaO) is a cost-effective alternative to fully yttria-stabilized grades.
+Q3: What purity is needed for glass-contact refractories?
Glass-contact applications require SiO₂ ≤0.15 wt% and Fe₂O₃ ≤0.05 wt% to prevent seed defects and coloration in the molten glass. TiO₂ should be ≤0.10 wt% for optical glass applications. SEMITECH's fused grade meets these thresholds. For borosilicate and specialty glass melting, request the low-impurity variant (SiO₂ ≤0.05 wt%, Fe₂O₃ ≤0.02 wt%) at MOQ 500 kg.
+Q4: What are pricing, MOQ, and lead times?
Fused grade: MOQ 500 kg, stock lead time 7–14 business days, pricing competitive with Saint-Gobain ZirPro and Imerys. Precipitated grade: MOQ 25 kg, lead time 10–21 days. Custom particle-size classification: 2–3 weeks additional. Free 1 kg evaluation samples with COA. Contact info@semitechnm.com for quotation. Payment terms: T/T, L/C, D/P.
Packing & Storage Information
Fused Grade 25 kg woven PP bags with PE liner, or 1000 kg FIBC (jumbo bags) for bulk users. Palletized for container loading. 20' FCL capacity: approximately 24 MT.
Precipitated Grade 25 kg multi-wall kraft paper bags with PE inner liner, or 500 kg FIBC. Vacuum-sealed packaging available for high-surface-area grades (BET >15 m²/g) to prevent moisture uptake.
Storage Conditions Store in a dry warehouse. Fused zirconia is chemically inert with unlimited shelf life. Precipitated zirconia should be stored at <60% RH to prevent agglomeration — shelf life 18 months in sealed packaging.