Technical Data Sheet & RFQ-Ready Product Page

High-Purity Alumina Thermocouple Protection Tubes (Al2O3)
Engineered for industrial thermal processing up to 1800°C. Designed to shield precious and base metal sensors from corrosive atmospheres, slag, and metal vapors, eliminating calibration drift and unexpected sensor failure.

Material Selection & Technical Parameters

Purity dictates performance. Trace impurities such as silica (SiO2) and alkali oxides form low-melting eutectic phases at elevated temperatures, drastically reducing mechanical strength and vacuum integrity.

Material Grade	Al2O3 Purity	Max. Service Temp.	Apparent Porosity	Primary Industrial Application
Alumina 95%	>= 95.0%	1400°C	< 0.1%	Standard heat-treating furnaces, annealing lines, and low-corrosion atmosphere kilns.
Alumina 99%	>= 99.0%	1600°C	0% (Gas-tight)	Metallurgy, non-ferrous metal melting, and structural ceramic firing.
Alumina 99.8%	>= 99.8%	1800°C	0% (Gas-tight)	High-vacuum furnaces, crystal growth reactors, and platinum-rhodium (Type S/R/B) sensor assemblies.

Dimensional Range: Outer Diameters (OD) from 3 mm to 62 mm; Lengths up to 2000 mm (multi-segment jointed tubes available for extended reach).
Dimensional Tolerances: OD/ID tolerances within plus or minus 0.1 mm to plus or minus 0.5 mm depending on diameter; straightness Total Indicator Reading (TIR) < 1.0 mm per 500 mm span.

Engineering & Application Guidelines

Vacuum & Reducing Atmospheres (> 1400°C): Specify Alumina 99.8% (SiO2 < 100 ppm). Lower purity tubes release volatile silica species under high vacuum, which chemically reduces platinum thermocouple wires and causes permanent calibration shift.
Thermal Shock Management: Alumina possesses high thermal expansion and low thermal conductivity compared to metallic sheaths. Maintain heating and cooling rates <= 150°C/hour. Pre-heat protection tubes by positioning them in the furnace throat (300°C to 400°C) for 15 minutes before hot-zone insertion.
Immersion Depth Calculation: Ensure an insertion depth of at least 10 times the tube outer diameter plus the sensor junction length to mitigate stem conduction errors.

Manufacturing Processes & Quality Control

Forming Methods:

Cold Isostatic Pressing (CIP): Utilized for large-diameter, thick-walled tubes to ensure uniform green density and eliminate internal micro-voids.
Extrusion / Slip Casting: Applied to small-bore, long-length thin-walled configurations.
Sintering: Densified in high-temperature electric tunnel kilns between 1650°C and 1820°C to promote full crystal grain growth and eliminate open porosity.

Inspection Protocols:

Helium Mass Spectrometer Leak Testing: Conducted on 99% and 99.8% grades to verify zero gas permeability for high-vacuum furnaces.
Chemical Trace Analysis: ICP-OES testing performed on every raw material lot to verify purity thresholds.
Dimensional Inspection: Laser micrometer and optical comparator checks for concentricity, wall thickness uniformity, and straightness runout.

Frequently Asked Questions

Q: What causes premature thermal shock cracking during furnace commissioning?

A: Rapid temperature gradients across the ceramic cross-section generate localized tensile stresses. Adhering to a strict thermal ramp rate (<= 150°C/hr) and pre-heating the protection tube near the entry port prevents catastrophic fracturing.

Q: Can you provide custom mounting flanges or hardware assemblies?

A: Yes. We supply closed-end alumina tubes permanently integrated with stainless steel (SUS304/SUS316L) or heat-resistant alloy flanges, compression fittings, or connection heads using high-temperature ceramic cement or mechanical gas-tight seals per customer drawings.

Q: What are the standard production lead times?

A: Standard catalog items in 99% and 99.8% purities ship within 2 to 3 weeks. Custom isostatic-pressed components requiring dedicated tooling or specialized grinding tolerances typically require 4 to 6 weeks.

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