Material Characteristics:
High-purity alumina micro-powder is used as the raw material, with purity ranging from 95% to 99.9%. Through batching, forming, and densification sintering in a high-temperature air atmosphere furnace, high-performance alumina ceramic materials can be obtained, featuring density of 95%–99.9% or higher, uniform microstructure, and no free impurity residues. The material exhibits high hardness, high wear resistance, good electrical insulation, excellent high-temperature strength, and thermal shock resistance.
Product Information:
Alumina ceramic thermocouple protection tubes are high-performance single-end closed tubular ceramic components made from high-purity alumina through isostatic pressing and high-temperature sintering. As the core protective component of high-temperature temperature sensors, their primary function is to enclose the thermocouple wires, completely isolating them from corrosive atmospheres, high-velocity gas flows, molten metals, and mechanical impacts within the furnace chamber, while efficiently conducting heat to ensure fast and accurate temperature measurement response. The protection tubes offer excellent high-temperature strength, thermal shock resistance, gas tightness, and electrical insulation properties. Under repeated rapid heating and cooling conditions, they do not crack, soften, or permeate, and no impurities volatilize during long-term use, reliably ensuring the stable operation and precise temperature measurement of thermocouples.
Performance Parameters：
| 95% (Al₂O₃≥95%) | 99% (Al₂O₃≥99%) | 99.5% | 99.9% |
Density (g/cm³)： | 3.70–3.75 | 3.85–3.90 | 3.90–3.93 | 3.95–3.98 |
Flexural Strength (MPa)： | 250–350 | 300–400 | 350–450 | 400–550 |
Compressive Strength (MPa)：
| 2000–3000 | 2500–3500 | 2800–3800 | 3000–4000 |
Fracture Toughness (MPa·m¹/²) | 3–4 | 3.5–4.5 | 4–4.5 | 4–5 |
Mohs Hardness： | 8.5–9 | 9
| 9 | 9 |
Elastic Modulus (GPa)： | 300–350 | 350–380 | 370–390 | 380–400 |
Volume Resistivity (Ω·cm) @25°C： | >10¹⁴ | >10¹⁴ | >10¹⁵ | >10¹⁶ |
Maximum Operating Temperature (°C) (long term)： | 1400–1500 | 1550–1650 | 1650–1700 | 1700–1750 |
Dielectric Strength (kV/mm)： | 12–16 | 15–20 | 18–22 | 20–25 |
Thermal Conductivity (W/(m·K)) @25°C： | 20–25 | 28–32 | 30–35 | 35–40 |
Product Dimensions:
Standard temperature sensor protection tubes have outer diameters ranging from 3 mm to 30 mm, inner diameters from 1.5 mm to 25 mm, and lengths from 100 mm to 1500 mm, with a maximum producible length of up to 2000 mm. Wall thickness can be flexibly designed according to insertion depth and response speed requirements, with a minimum thickness down to 0.8 mm. The products are supplied as standard with a single-end closed blind tube structure, and double-end open tubes can also be manufactured. Further processing techniques are available, including internal and external cylindrical precision grinding, closed-end ball or flat end machining, end chamfering, radial slotting, tail end expansion, and multi-step machining. Yuko Corporation can also customize non-standard outer diameters, non-standard lengths, variable-diameter blind tubes, flanged protection tubes, and multi-core combined protection tube assemblies based on customer drawings.
Product Applications:
Alumina ceramic temperature sensor protection tubes are widely used for temperature measurement in electronic ceramic sintering furnaces, magnetic material heat treatment furnaces, lithium battery cathode and anode material kilns, powder metallurgy sintering furnaces, glass melting furnaces, chemical reactors, and other high-temperature equipment. Specifically, they serve as temperature control thermocouple protection tubes in pusher kilns, bell-type kilns, and roller kilns, protecting precious metal thermocouples such as platinum-rhodium and base metal thermocouples such as nickel-chromium/nickel-silicon. In atmosphere furnaces and vacuum furnaces, they are used as temperature measurement blind tubes, isolating the thermocouple wires from corrosion by oxidizing or reducing atmospheres. They are also employed as corrosion-resistant temperature measurement sheaths in the melting of non-ferrous metals such as aluminum and copper, and can serve as tube furnace tubes for laboratory use and high-temperature insulation support tubes. They are key ceramic components for ensuring precise high-temperature measurement, process repeatability, and production safety.