What gases can be passed through a well crucible furnace?

Well type crucible furnaces can be filled with various gases according to process requirements to achieve purposes such as oxidation prevention, reduction, atmosphere control, or special reactions. The following is a detailed explanation of common gas types and their application scenarios:

1. Common gas types and functions
Inert gas: isolates oxygen to prevent material oxidation or combustion, sintering of metal powders (such as titanium alloys and aluminum based alloys), high-temperature ceramic sintering, and melting of active metals.
Reducing gases: reducing metal oxides, removing impurities or controlling material composition, metal purification (such as hydrogen reduction of copper oxide), carbide synthesis (such as methane cracking to produce silicon carbide).
Nitrogen: Inert protection, low cost, suitable for non active material processing, steel heat treatment, ordinary metal powder sintering, and atmosphere protection welding.
Argon gas: high-purity inert protection, suitable for high-temperature or active materials, high-temperature alloy melting (such as nickel based alloys), semiconductor material processing, and ultrafine powder sintering.
Hydrogen: Strong reducibility, suitable for metal purification or reduction of refractory metals such as tungsten and molybdenum in special chemical reactions, hydrogen atmosphere sintering (such as hard alloys), and preparation of fuel cell materials.
Mixed gas: Combining multiple gas functions, optimizing process parameters (such as Ar+H ₂, N ₂+CH ₄), special alloy sintering (such as Ar+5% H ₂ reducing atmosphere), and carbide coating preparation (such as N ₂+CH ₄ carburizing atmosphere).
Vacuum environment: No gas present, completely avoiding oxidation or reaction, suitable for high-purity material preparation, ultra-high purity metal melting, semiconductor single crystal growth, and nanomaterial preparation.

2. Key factors in gas selection
Material characteristics
Active metals (such as titanium and aluminum): require high-purity inert gas (such as argon) or vacuum environment to prevent oxidation.
Easy to oxidize ceramics (such as alumina): can be sintered in nitrogen or argon, but the oxygen partial pressure needs to be controlled.
Carbides/nitrides: require the introduction of carbon/nitrogen containing gases (such as methane, ammonia) for reaction synthesis.
technological requirements
Sintering temperature: At high temperatures (>1500 ℃), high-purity gas (such as argon) or vacuum is required to avoid gas decomposition or reaction.
Atmosphere purity: Semiconductor materials require ultra-high purity gas (such as 99.999% argon), while industrial grade gas can be used for ordinary metal processing.
Gas flow rate: Adjust according to the furnace volume (such as argon flow rate of 1-5 L/min) to ensure a uniform atmosphere.
Safety and Cost
Hydrogen: flammable and explosive, requiring explosion-proof devices, gas leak alarms, and automatic shut-off systems.
Cost comparison: Nitrogen<Argon<Hydrogen, additional vacuum pump equipment is required in a vacuum environment, resulting in higher costs. 3. Gas inlet method and equipment configuration Air intake system Quality flowmeter: precise control of gas flow rate (error ≤± 1%). Gas mixer: used for mixing gases (such as Ar+H ₂) to ensure stable proportions. Gas preheater: Avoid direct entry of cold gas into the high-temperature furnace, which may cause temperature fluctuations. exhaust system Exhaust pipe: high temperature resistant and corrosion-resistant (such as stainless steel or quartz material). Tail gas treatment: Hydrogen tail gas needs to be burned for treatment, and toxic gases (such as ammonia) need to be purified before being discharged. Sealing requirements The sealing ring of the furnace door needs to be checked regularly, and the air leakage rate should be ≤ 1 × 10 ⁻³ Pa · m ³/s. The vacuum furnace needs to be equipped with a mechanical pump and a molecular pump, with a maximum vacuum degree of ≤ 10 ⁻³ Pa. 4. Typical application cases Titanium alloy powder sintering Gas: High purity argon gas (99.999%). Process: Introduce argon gas to remove oxygen, heat up to 1300 ℃ for sintering, and prevent titanium oxidation. Hard alloy (WC Co) sintering Gas: A mixture of hydrogen (5%) and argon (95%). Process: Hydrogen reduction of tungsten oxide, argon protection to prevent cobalt oxidation, sintering temperature of 1450 ℃. Silicon nitride ceramic sintering Gas: High purity nitrogen (99.999%). Process: Introduce nitrogen gas, heat up to 1700 ℃ for reaction sintering, and generate Si ∝ N ₄. Steel heat treatment Gas: Nitrogen or decomposed ammonia (NH3 decomposes into N ₂+H ₂). Process: Nitrogen protected annealing, decomposition ammonia atmosphere nitriding treatment to improve surface hardness. 5. Safety precautions Hydrogen usage No open flames, equipped with hydrogen concentration alarm (threshold ≤ 4% volume fraction). The furnace needs to be grounded to prevent static electricity from causing explosions. toxic gas If ammonia, carbon monoxide, etc. are used, exhaust gas absorption devices (such as acid washing towers) need to be equipped. Operators are required to wear gas masks and protective clothing. pressure control The pressure inside the furnace needs to be slightly positive (5-10 Pa) to prevent the infiltration of external air. Install pressure sensors and safety valves to automatically release pressure in case of overpressure. 6. Summary and Suggestions Gas selection principle Preferred inert gases: such as nitrogen and argon, suitable for most metal and ceramic processing. Caution should be exercised with reactive gases: strict safety measures are required for hydrogen, carbon monoxide, and other gases. Vacuum environment: suitable for high-purity materials or ultra-high temperature processing. Equipment configuration suggestions High temperature furnaces (>1500 ℃) are recommended to be equipped with high-purity argon gas or vacuum systems.
Active metal treatment requires the use of gas purification devices such as deaerators and dehumidifiers.
Process optimization direction
Balance cost and performance by mixing gases such as Ar+H ₂.
Adopting a closed-loop atmosphere control system to monitor oxygen partial pressure and gas composition in real-time.

Direct conclusion:
Well type crucible furnaces can be filled with inert gases (nitrogen, argon), reducing gases (hydrogen), mixed gases, or vacuum environments. The specific selection needs to be evaluated comprehensively based on material characteristics, process requirements, and safety costs. High purity argon and nitrogen are the most commonly used protective gases, while hydrogen is suitable for special reduction processes but requires strict safety control.