Can a tube muffle furnace be filled with gas?

The tubular muffle furnace can pass gas, and the ventilation function is one of its core advantages, which can meet the heat treatment needs of materials in specific atmospheric environments (such as oxidation, reduction, inert protection, carbonization, nitriding, etc.). The following is a detailed explanation of the ventilation function of the tubular muffle furnace:

1. The role of ventilation function
Protecting samples
Heating in inert gases such as nitrogen and argon can prevent sample oxidation or reaction with components in the air. For example, metal powder is prone to oxidation at high temperatures, and the introduction of argon gas can form a protective layer.
Heating in reducing gases such as hydrogen and carbon monoxide can achieve the reduction reaction of the sample. For example, reducing metal oxides to elemental metals.
Control reaction environment
Introducing specific gases can participate in chemical reactions, such as carbonization (introducing methane and propane), nitriding (introducing ammonia), and other processes.
In the CVD (Chemical Vapor Deposition) process, the introduction of gaseous precursors such as silane and methane can deposit thin films or nanomaterials on the surface of the sample.
Remove impurities
Introducing inert gas before heating can blow away impurities such as oxygen and moisture in the furnace, avoiding contamination of the sample. For example, in the preparation of semiconductor materials, it is necessary to strictly control the oxygen content inside the furnace.

2. Composition of ventilation system
Gas inlet and outlet
Entrance: usually located at one end of the furnace tube, connected to a gas source (gas cylinder or gas generator), and precisely controlled by a mass flow meter (MFC) for gas flow.
Export: located at the other end of the furnace tube, connected to exhaust gas treatment devices (such as gas washing cylinders, vacuum pumps) to prevent harmful gas leakage.
Types and selection of gases
Inert gases: nitrogen (N ₂), argon (Ar) – used to protect the sample from oxidation.
Reductive gases: hydrogen (H ₂), carbon monoxide (CO) – used for reduction reactions, but explosion-proof safety should be taken into account.
Reactive gases: methane (CH4), ammonia (NH3), oxygen (O ₂) – used in processes such as carbonization, nitriding, oxidation, etc.
Mixed gases, such as Ar+H ₂ (95%+5%) – used for specific reduction reactions, require precise proportioning through a gas mixer.
safety device
Explosion proof valve: Automatically releases pressure when the furnace pressure is too high to prevent explosion.
Gas leak alarm: detects the leakage of flammable gases such as hydrogen, triggers an audible and visual alarm, and cuts off the gas source.
Exhaust gas treatment device: If hydrogen needs to be treated through combustion or catalytic oxidation, it can avoid direct emissions and potential hazards.

3. Ventilation operation process
preparation
Check whether the gas source pressure is stable (usually 0.2~0.5 MPa), and ensure that the gas purity meets the requirements (such as high-purity argon gas ≥ 99.999%).
Connect the gas pipeline and check if there is any air leakage at the interface with soapy water.
Open the furnace door, place the sample, and then close the furnace door to ensure good sealing.
Ventilation steps
Blowing stage: First, introduce inert gas (such as N ₂) and blow the furnace at a flow rate of 50-100 mL/min for 10-30 minutes to remove air.
Heating stage: Introduce target gases (such as H ₂, CH ₄) according to process requirements, and adjust the flow rate to the set value (such as 10-50 mL/min).
Insulation stage: Maintain stable gas flow and monitor furnace pressure (usually slightly positive pressure to prevent air backflow).
Cooling stage: Stop introducing reaction gas and switch to inert gas to protect the sample until the temperature drops to room temperature.
Shutdown operation
Close the gas source valve and empty the residual gas in the pipeline.
Close the mass flow meter and exhaust treatment device.
Record experimental data and clean the furnace.

4. Ventilation precautions
Gas compatibility
Avoid introducing oxidizing gases (such as O ₂) and reducing gases (such as H ₂) into the furnace simultaneously to prevent explosions.
Silicon carbide furnace tubes are prone to react with hydrogen gas at high temperatures, and it is necessary to control the hydrogen concentration or choose corundum furnace tubes.
flow control
Excessive flow may lead to uneven temperature inside the furnace, while insufficient flow cannot effectively protect the sample or participate in the reaction.
Typical flow range: Inert gas 50-200 mL/min, reactive gas 10-100 mL/min (adjusted according to furnace volume and process).
safety protection
When handling flammable gases such as hydrogen, it is necessary to stay away from sources of ignition and equip with explosion-proof cabinets and ventilation systems.
Regularly inspect gas pipelines and valves, and replace aging components.

5. Application Cases
Heat treatment of metal materials
Annealing treatment of titanium alloy under argon protection to prevent oxidation and eliminate internal stress.
Ceramic material sintering
Sintering silicon nitride ceramics in nitrogen and promoting nitriding reaction by introducing ammonia gas.
Preparation of Semiconductor Materials
During the CVD process, silane (SiH ₄) and hydrogen gas are introduced to deposit polycrystalline silicon thin films on the surface of the silicon wafer.
Catalyst preparation
When loading metal particles on alumina support, hydrogen gas is introduced to reduce the metal precursor (such as nickel nitrate).