High-Pressure Quartz Tube Sealing Solutions (Part 6 of 6)

When quartz tubes are required to operate in high-pressure environments of 10 MPa or above, end-sealing becomes a critical technical challenge. As quartz is a brittle material, traditional adhesive or rubber seals are prone to failure. Instead, metal-quartz composite sealing structures must be used. Below are five engineering solutions for high-pressure sealing.

Solution 1: Metal Flange + Conical Compression Seal

Structural Features:

Quartz tube ends are machined into a 20° conical surface.
Stainless steel flanges with matching internal cones.
Axial pressure applied using hydraulic pre-tightening bolts.

Key Parameters:

Sealing pressure: ≤30 MPa
Applicable temperature: −200 °C to 500 °C
Leak rate: <10⁻⁹ Pa·m³/s
Annealed quartz tubes required (to prevent stress-concentration cracking).

Zalety: Detachable; suitable for frequent opening and closing during experiments.
Disadvantages: Requires precision machining (cone angle tolerance ±0.5°).

Solution 2: High-Temperature Glass Welding

Process Highlights:

Fill the gap between quartz tube and metal flange with borosilicate glass powder.
Melted and welded in a nitrogen environment at 850 °C.
Slow cooling and annealing to eliminate stress.

Performance Indicators:

Pressure resistance: 15 MPa (static).
Temperature resistance: ≤450 °C (glass softens above this point).
Must use Kovar flanges to match thermal expansion coefficients.

Zastosowanie: Suitable for permanent sealing, such as in sensor packaging.

Solution 3: Hydraulic Cold Press Sealing

Innovative Process:

Use ultra-high-pressure molds (1–3 GPa) at room temperature.
Achieve plastic deformation interlocking between quartz and metal.
No intermediate solder or adhesives required.

Breakthrough Parameters:

Pressure resistance: up to 100 MPa (world record).
Temperature range: −273 °C to 1000 °C.
Limited to short tubes with wall thickness ≥5 mm.

Quartz Tube Flange Sealing System for CVD Furnaces

Solution 4: O-Ring Dynamic Sealing

Special Design:

FFKM (perfluoroelastomer) O-rings are used.
Dual-stage pressurization structure:
- Primary seal: 5 MPa hydraulic pre-tightening.
- Secondary seal: metal bellows compensation.

Application Scenarios:

Systems requiring frequent disassembly and reassembly.
Maximum pressure: 12 MPa (short-term peak of 15 MPa).

Note: High assembly cost and requires skilled technicians.

Solution 5: Integrated Metallized Sintering

Military-Grade Solution:

Vacuum sputter multi-layer Ti-Pt-Au coating on quartz tube ends.
High-temperature sintering to form a metalized transition layer.
Laser welding to stainless steel flanges.

Performance Limits:

Burst pressure: up to 50 MPa.
Thermal shock resistance: withstands 1000 °C → liquid nitrogen cycles without failure.
Only applicable to thick-walled tubes with ID <20 mm.

Solution Comparison Table

Solution	Pressure Resistance (MPa)	Temperature (°C)	Detachable	Applicable Tube Diameter	Cost
Metal Flange	30	500	✓	5–100 mm	Moderate
Glass Welding	15	450	✗	3–50 mm	Low
Cold Press	100	1000	✗	3–20 mm	Very High
O-Ring	12	300	✓	10–200 mm	High
Metallization	50	1000	✗	3–20 mm	Very High

Implementation Considerations

1. Stress Concentration Control

Flange contact surfaces must be machined with R0.3 mm rounded transitions.
Quartz tube ends must be flame-polished.
(Not applicable for thick-walled tubes; polishing may reduce pressure resistance.)

2. Leak Detection Standards

Helium mass spectrometry leak detection ≤1×10⁻⁸ mbar·L/s.
Pressure-holding test: maintain 15 MPa for 1 hour, pressure drop <1%.

3. Safety Precautions

Install explosion-proof shields (recommend 6 mm polycarbonate).
Real-time pressure sensors + automatic relief valves are required.

For custom engineering sealing solutions under specific experimental conditions, CAD drawings or detailed process specifications (temperature, internal/external pressure, test gases, etc.) are required for further discussion.