What gases can be passed through a customized rotary tube furnace with multiple temperature zones?

Customized rotary tube furnaces with multiple temperature zones can be filled with various gases according to process requirements, mainly divided into four categories: inert protective gases, reducing gases, reactive gases, and composite gases. The selection of different gases requires comprehensive consideration of material characteristics, process objectives, and equipment safety. The following are specific classifications and application instructions:

1. Inert protective gas: prevents material oxidation
Argon gas (Ar)
Characteristics: chemically stable, non reactive with most materials, density close to air, easy to form a uniform protective layer.
Application:
High temperature sintering of metal powders (such as titanium alloys and stainless steel) to prevent oxidation and the formation of oxide impurities.
Sintering of ceramic materials such as silicon carbide and aluminum nitride to avoid loss of carbon or nitrogen elements.
Heat treatment of semiconductor materials (such as silicon wafers) to protect the surface from contamination.
Nitrogen (N ₂)
Characteristics: Low cost, but may react with certain metals (such as titanium and zirconium) to form nitrides at high temperatures.
Application:
Sintering of iron-based and copper based powder metallurgy parts creates a protective atmosphere while reducing the risk of oxidation.
Heat treatment of carbon materials (such as graphite and carbon fiber) to prevent carbon oxidation loss.
Annealing non-metallic materials (such as glass and ceramics) to reduce surface defects.
Helium (He)
Characteristics: Good thermal conductivity, suitable for rapid temperature rise and fall processes, but high cost.
Application:
High thermal conductivity materials such as diamond and copper require a uniform temperature field for heat treatment.
Processing nuclear materials (such as uranium and plutonium) by utilizing their chemical inertness to ensure safety.

2. Reductive gas: removes impurities or promotes reduction reactions
Hydrogen (H ₂)
Characteristics: Strong reducibility, but flammable and explosive, requiring strict oxygen control (volume fraction ≤ 4%).
Application:
Deoxygenation of metal powder: such as reducing oxide impurities in iron powder to improve purity.
Carbide synthesis: such as tungsten carbide (WC) preparation, which reacts with carbon through H ₂ reduction of WO3.
Annealing of semiconductor materials: repairing lattice defects and improving electrical performance.
Carbon monoxide (CO)
Characteristics: Strong reducibility, but toxic, requiring exhaust gas treatment equipment.
Application:
Metal oxide reduction: such as reducing Fe ₂ O ∝ to iron powder for the preparation of magnetic materials.
Carbon thermal reduction reaction: such as the synthesis of titanium carbide (TiC), through the reaction of CO with TiO ₂ and carbon.
Methane (CH ₄)
Characteristics: Decomposition produces H ₂ and carbon, and the decomposition temperature needs to be controlled (usually ≥ 800 ℃).
Application:
Carburizing treatment: infiltrating carbon atoms into the metal surface to enhance hardness and wear resistance.
Carbon nanotube synthesis: Carbon nanotubes are grown on a substrate by catalytic decomposition of CH ₄.

3.Reactive gases: involved in material synthesis or modification
Ammonia gas (NH3)
Characteristics: Decompose to produce N ₂ and H ₂, while providing a nitrogen source.
Application:
Nitriding treatment: such as nitriding the surface of titanium alloy to TiN to improve corrosion resistance.
Synthesis of Aluminum Nitride (AlN): High thermal conductivity AlN ceramics are generated through the reaction of Al ₂ O ∝ and NH ∝.
Hydrogen chloride (HCl)
Characteristics: Strong corrosiveness, requiring the use of corrosion-resistant furnace tubes (such as quartz or PFA lining).
Application:
Preparation of metal chlorides: such as oxidizing metals to chlorides, used for catalysts or electronic materials.
Surface etching: Remove the oxide layer on the metal surface to enhance the adhesion of subsequent processes.
Carbon dioxide (CO ₂)
Characteristic: Oxidative gas, needs to be mixed with other gases for use.
Application:
Silicon carbide oxidation: Oxidation of SiC surface in CO ₂ atmosphere to form a protective SiO ₂ layer.
Metal oxidation: such as controlling the oxidation rate to prepare specific oxide thin films.

4. Composite gas: achieving multifunctional processes
Ar-H ₂ mixture
Proportion: Typically 95% Ar+5% H ₂ (volume fraction).
Application:
Metal powder sintering: Ar provides protection, H ₂ reduces surface oxides, and increases the density of the sintered body.
Semiconductor annealing: repairing lattice defects while preventing oxidation.
N ₂ – CH ₄ mixture gas
Proportion: Adjust according to carburizing requirements, such as 80% N ₂+20% CH ₄.
Application:
Metal carburizing treatment: Dilute CH ₄ with N ₂, control the carbon diffusion rate, and form a uniform carbon layer.
Nitriding of carbon materials: By the combined action of N ₂ and CH ₄, a nitrogen doped layer is formed on the surface of carbon.
Ar NH ∝ mixed gas
Proportion: such as 90% Ar+10% NH3.
Application:
Aluminum nitride synthesis: Ar protection, NH3 providing nitrogen source, reducing synthesis temperature.
Metal surface nitridation: Selective nitridation is achieved by introducing NH3 in an Ar atmosphere.

5. Gas selection principle
Material compatibility: Avoid reactions between gases and materials or furnace tubes (such as the formation of TiH ₂ between H ₂ and Ti at high temperatures).
Process objective: Select gas types and ratios based on sintering, reduction, carburizing, and other requirements.
Safety: Flammable and explosive gases (such as H ₂, CH ₄) require explosion-proof devices and oxygen content monitoring devices.
Cost effectiveness: Prioritize low-cost gases (such as N ₂ instead of Ar) while meeting process requirements.