High Temperature Ceramics: Limits, Shock and Selection
Updated: Aug 22
Written by: Gulzar Hussain & Reviewed by Mark Ma
Estimated Reading Time: 21 minutes
Ceramic Materials for High Temperature Applications
Maximum Service Temperature
Continuous service in air for standard grades. These are not melting points — and the difference is the subject of this page.
Material | Max continuous, air (°C) | Melting / decomposition (°C) | What sets the limit |
Alumina 99.5% (Al₂O₃) | 1,700 | 2,072 | Creep and grain-boundary glass softening |
Alumina 96% | 1,500 | 2,072 | Glassy phase content — more glass, lower limit |
Magnesia (MgO) | 1,700 | 2,852 | Creep; hydration on cooling |
Zirconia 3Y-TZP | 1,000 | 2,715 | Phase instability — not melting |
Zirconia, fully stabilised | 1,500–2,000 | 2,715 | Creep; loss of toughening |
Silicon carbide (SSiC) | 1,600 | 2,730 (subl.) | Passive oxidation; active oxidation in low pO₂ |
Silicon carbide (RBSiC) | 1,350 | — | Free silicon melts at 1,414 °C |
Silicon nitride (Si₃N₄) | 1,200 | 1,900 (decomp.) | Grain-boundary phase softening; oxidation |
Aluminium nitride (AlN) | 900 (air) / 1,800 (inert) | 2,200 (subl.) | Oxidation in air |
Boron carbide (B₄C) | 800 (air) / 2,000 (inert) | 2,450 | Oxidation in air |
Boron nitride, hexagonal | 900 (air) / 2,800 (inert) | 3,000 (subl.) | Oxidation in air |
Cordierite | 1,300 | 1,450 | Softening |
Fused silica | 1,100 | 1,713 | Devitrification |
Mullite | 1,700 | 1,840 | Creep |
Three things this table shows that a melting point never would:
Zirconia melts at 2,715 °C and is limited to 1,000 °C. The monoclinic-tetragonal transformation and the loss of transformation toughening happen far below melting. Specifying zirconia for a 1,400 °C furnace because of its melting point is a documented and expensive mistake.
The non-oxides have two limits. AlN, B₄C and BN work to 1,800–2,800 °C in inert or reducing atmosphere and 800–900 °C in air, because they oxidise. Always specify the atmosphere alongside the temperature.
Reaction-bonded SiC contains free silicon that melts at 1,414 °C, capping it at about 1,350 °C — roughly 250 °C below sintered SiC of the same nominal composition.
Why the Melting Point Is the Wrong Number
Five mechanisms end a ceramic's useful life well before it melts.
1. Creep. Above roughly half the absolute melting temperature, grain-boundary diffusion and sliding allow time-dependent deformation under sustained load. A part that is dimensionally correct on installation slowly deforms. Fine-grained ceramics creep more than coarse-grained ones, because there is more grain-boundary area — which is why refractories are deliberately coarse.
2. Grain-boundary glass softening. The sintering aids that made densification economical leave an amorphous film 0.5–2 nm thick at every grain boundary. That glass softens hundreds of degrees below the crystalline grains, and when it does, high-temperature strength and creep resistance fall together. This is the single biggest reason high-purity grades cost more and last longer in hot service.
3. Phase transformation. Zirconia is the clear case, but any polymorphic ceramic can transform in service, and transformations carry volume changes that crack parts.
4. Oxidation. Non-oxides burn. SiC and Si₃N₄ form a protective silica scale that slows further attack — passive oxidation, which is manageable. But in low oxygen partial pressure at high temperature, the reaction switches to active oxidation, producing gaseous SiO and consuming the material with no protective layer. Active oxidation is far more aggressive and catches people out in vacuum and reducing furnaces.
5. Chemical attack from the environment. Alkali vapours, molten salts, slags and water vapour all attack ceramics at temperature in ways they do not at room temperature. Water vapour is the underrated one: it accelerates silica scale volatilisation in SiC and Si₃N₄, which is a major concern in combustion environments.
Thermal Shock: A Different Property Entirely
This is the distinction that matters most, and the one most often missed. Maximum service temperature tells you whether a material survives being hot. Thermal shock resistance tells you whether it survives changing temperature. They are different properties, and a material can be excellent at one and poor at the other.
When a hot ceramic is cooled rapidly, the surface contracts while the interior is still hot and expanded. The surface goes into tension. Ceramics cannot relieve tension plastically, so it accumulates until the surface cracks.
The governing parameter:
R = σ(1 − ν) ÷ (E·α)where σ is strength, ν is Poisson's ratio, E elastic modulus and α thermal expansion coefficient. Thermal conductivity matters too — higher conductivity flattens the gradient.
So thermal shock resistance rewards high strength, low modulus, low thermal expansion, and high thermal conductivity — a combination that does not correlate with maximum service temperature at all.
Material | Thermal expansion (×10⁻⁶/K) | Thermal conductivity (W/m·K) | Thermal shock resistance |
Silicon nitride | 3.2 | 25–30 | Excellent |
Silicon carbide | 4.0 | 120–150 | Excellent |
Fused silica | 0.55 | 1.4 | Excellent (very low α) |
Cordierite | 1.5–2.5 | 3 | Excellent |
Aluminium nitride | 4.5 | 170–200 | Very good |
Boron carbide | 5.0 | 30–40 | Moderate |
Alumina 99.5% | 8.4 | 30 | Moderate |
Zirconia 3Y-TZP | 10.5 | 2–3 | Poor |
Zirconia illustrates the point exactly. It is a fine high-temperature material under steady conditions and a poor one under cycling — highest expansion in the table combined with the lowest conductivity.
Practical rule: if the duty cycle involves heating or cooling faster than about 10 °C per minute, select on thermal shock resistance first and maximum temperature second.
Choosing a High-Temperature Ceramic
Steady temperature, no significant cycling
Select on maximum service temperature, creep resistance and chemical compatibility.
To 1,200 °C: 96% alumina, cordierite, mullite
To 1,500 °C: 99.5% alumina, mullite, fully stabilised zirconia
To 1,700 °C: high-purity alumina, magnesia, mullite
Above 1,700 °C: stabilised zirconia, specialised refractories, graphite in inert atmosphere
Rapid cycling
Select on thermal shock resistance first.
Silicon nitride — the best all-round choice to 1,200 °C
Silicon carbide — where higher temperature and abrasion are also present
Cordierite — where cost matters more than strength; the reason it is in every catalytic converter
Fused silica — where expansion must be near zero and load is low
Non-oxidising atmosphere
Inert or reducing atmospheres unlock the non-oxides:
Boron nitride to 2,800 °C — machinable, lubricious, excellent dielectric
Boron carbide to 2,000 °C
Aluminium nitride to 1,800 °C
Graphite to very high temperatures where carbon contamination is acceptable
Watch for active oxidation of SiC and Si₃N₄ at low oxygen partial pressure — low oxygen is not the same as no oxygen, and the intermediate case is the dangerous one.
Molten metal contact
Silicon nitride — the standard for molten aluminium: not wetted, excellent thermal shock resistance
Boron nitride — for molten aluminium and evaporation applications
Alumina and magnesia — for steel and general melting, subject to slag chemistry
Zirconia — for specific melts where its chemistry suits
Always check the slag chemistry, not just the metal. Slag attack is usually the life-limiting factor.
Applications
Furnace and kiln hardware. Muffles, tubes, setters, saggars, kiln furniture, burner nozzles. SiC and cordierite for the cycled parts, alumina for the steady hot zone.
Crucibles and melting. Alumina and magnesia for general melting; silicon nitride and boron nitride for molten aluminium; zirconia for specialist melts.
Thermocouple protection. Alumina sheaths to 1,700 °C, SiC where abrasion or thermal shock accompany the heat.
Heat exchangers and recuperators. Silicon carbide, for the combination of thermal conductivity and corrosion resistance in flue gas.
Thermal barriers. Yttria-stabilised zirconia coatings on turbine blades — deliberately using zirconia's low thermal conductivity, the property that disqualifies it elsewhere.
Semiconductor process ware. Fused silica and SiC process tubes, boats and wafer carriers, at 1,000–1,200 °C under strict purity requirements.
Aerospace hot structures. Ceramic matrix composites in combustor liners and shrouds; ultra-high-temperature ceramics (HfC, ZrB₂) in hypersonic leading edges.
Insulation. Porous refractory brick, ceramic fibre blanket and board — here porosity is the point, and strength is secondary.
Design Rules for Hot Service
Specify the ramp rate, not just the temperature. A part rated for 1,600 °C will still crack if heated at 100 °C per minute. Ramp rate is a specification, and it belongs on the drawing.
Never constrain thermal expansion. A hot ceramic must be free to grow. Rigid mounting to a cooler or higher-expansion metal is the most common cause of failure in furnace hardware. Use slotted holes, sprung mounts, or compliant seats.
Allow for creep in load-bearing hot parts. Above half the absolute melting temperature, sustained load produces gradual deformation. Design in clearance, or reduce the stress.
Specify the atmosphere. For non-oxides, this is not optional — it changes the usable temperature by 900 °C or more.
Higher purity for hot service. Grain-boundary glass is what softens first. 99.5% alumina is not a marketing upgrade over 96% in hot service; it is a different material.
Design in compression. Hot ceramics creep in tension and hold up far better in compression.
Frequently Asked Questions
Which ceramic handles the highest temperature? In air, high-purity alumina, magnesia and mullite to about 1,700 °C, and sintered silicon carbide to 1,600 °C. In inert atmosphere, boron nitride reaches 2,800 °C, boron carbide 2,000 °C and aluminium nitride 1,800 °C.
Can ceramics withstand 1,000 °C? Comfortably. Alumina, silicon carbide, silicon nitride, mullite and cordierite all work well above 1,000 °C. Zirconia is at its practical limit there, and the non-oxides AlN and B₄C are already past theirs in air.
Why is zirconia limited to 1,000 °C when it melts at 2,715 °C? Because its useful properties depend on a metastable tetragonal phase. Above about 1,000 °C that phase becomes stable and stops transforming, so the toughening mechanism is lost, and phase changes on cycling introduce volume changes that crack the part.
What is thermal shock resistance? The ability to survive rapid temperature change without cracking. It depends on thermal expansion, thermal conductivity, strength and elastic modulus — not on maximum service temperature. Silicon nitride and silicon carbide are excellent; zirconia is poor.
Which ceramic is best for thermal shock? Silicon nitride for most applications to 1,200 °C, silicon carbide where higher temperature or abrasion is also present, and cordierite where cost dominates and loads are low.
Do ceramics expand when heated? Yes, at 3–11 ×10⁻⁶/K — less than metals at 10–24, but not zero. Never constrain a hot ceramic part rigidly; the resulting tension is a common failure cause.
Can silicon carbide be used above 1,600 °C? Sintered SiC can in inert atmosphere. In air it is limited by oxidation, and in low oxygen partial pressure it can enter active oxidation, which is far more aggressive than passive oxidation in normal air. Reaction-bonded SiC is capped at about 1,350 °C by its free silicon content.
Further Reading
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