Silicon nitride (Si₃N₄) thermocouple sheath is a high-performance temperature measuring protection tube made mainly of silicon nitride ceramic via advanced forming and sintering processes.
Matched with thermocouples, this product provides reliable physical isolation and chemical protection for thermocouples in molten non-ferrous metals such as aluminum, zinc, copper and magnesium, as well as in high-temperature corrosive gas and liquid environments. It ensures long-term stability and accuracy of temperature measurement.
Silicon nitride is an advanced structural ceramic with extremely excellent comprehensive properties. Thanks to its outstanding strength, hardness, thermal resistance and chemical stability, it is known as "ceramic steel" and "all-round champion in the material world".
Thermocouple sheaths made of silicon nitride are high-end products that cannot be easily replaced by conventional protective tubes of corundum, high-alumina, graphite, oxide and silicon carbide materials currently available in the domestic market. For high-temperature applications above 1200℃, silicon nitride ceramic sheaths stand as the preferred solution.
| Test item | Unit | Index range |
| Bulk Density | g/cm³ | 3.2 |
| Porosity | % | ≤1.5 |
| Flexural Strength | MPa | ＞600 |
| Young's Modulus | GPa | 260~280 |
| Fracture Toughness | MPa·m¹/² | ≥6.5 |
| Thermal Conductivity | W/(m·K) | 16~22 |
| Coefficient of Thermal Expansion (20–1000°C) | ×10⁻⁶ K⁻¹ | 3.2~3.4 |
| Maximum Service Temperature (at Atmospheric Pressure) | ℃ | 1400 |
| Thermal Shock Resistance | 700~800℃ | |
| Vickers Hardness | HV | ＞1400 |
1. Superior thermal conductivity: With thin walls (only a few millimeters thick) and a high thermal conductivity coefficient, it responds extremely quickly to temperature changes and can accurately measure the temperature of molten metal within one minute.
2. Excellent thermal shock resistance: It has an extremely low coefficient of thermal expansion and can withstand drastic temperature changes; it will not crack even when rapidly heated or cooled at temperatures above 1000°C.
3. Exceptional High-Temperature Stability: No melting point at atmospheric pressure; decomposes only at 1900°C; does not oxidize below 1200°C; forms a protective oxide layer between 1200°C and 1600°C.
4. Superior Corrosion Resistance: Exhibits exceptional resistance to most acids, alkalis, and molten metals (except hydrofluoric acid); does not wet molten non-ferrous metals and is resistant to slag accumulation.
5. High mechanical strength: High flexural strength, wear resistance, and resistance to mechanical impact, enabling long-term stable operation under high-pressure, high-flow-rate conditions.
6. No contamination of molten metal: Does not react chemically with molten metal, does not produce contaminant leaching, and maintains the purity of the molten metal.
7. Excellent electrical insulation properties: The product itself is an electrical insulator, preventing interference with thermocouple signals.
8. Exceptionally long service life: Service life can exceed 12 months and may last for several years, offering excellent value for money.
1. Thanks to their excellent overall performance, silicon nitride thermocouple protection tubes are widely used in the following industries and applications:
2. Non-ferrous metal smelting: Temperature measurement and process monitoring of molten non-ferrous metals such as aluminum, copper, zinc, and magnesium;
3. Foundry Industry: Continuous temperature measurement in applications such as aluminum alloy wheel casting and molten aluminum holding furnaces;
4. Chemical Industry: Temperature measurement in high-temperature, highly corrosive acid and alkali media, suitable for equipment such as reactors;
5. Powder Metallurgy: Temperature monitoring during the sintering of magnetic materials and electronic ceramics;
6. Glass Industry: Temperature measurement and control within glass melting furnaces;
7. Ceramic Industry: Thermocouple protection in high-temperature kilns.
