Can high-temperature rotary furnace calcine powder with an atmosphere?

The high-temperature rotary furnace can provide an atmosphere during powder calcination, and this is one of its important functions, which can meet the process requirements of different materials, improve product quality and production efficiency. The following is a detailed analysis:

1. The necessity of creating a positive atmosphere
Prevent oxidation or reduction
Metal powders, such as titanium powder and nickel powder, are prone to react with oxygen at high temperatures to form oxides. Introducing inert gases (such as argon and nitrogen) can isolate oxygen and prevent oxidation.
Reduction reaction: When calcining iron ore or metal oxides, introducing reducing gases (such as hydrogen and carbon monoxide) can reduce metal ions to metallic elements, such as preparing reduced iron powder.
Control carbon content
Preparation of carbides: The synthesis of materials such as silicon carbide (SiC) and titanium carbide (TiC) requires calcination in a carbon atmosphere to ensure sufficient reaction between carbon and metal to form the target compound.
Decarbonization treatment: Some metal powders (such as stainless steel powder) need to control the carbon content and adjust material properties by introducing oxidizing gases (such as air).
Promote specific reactions
Nitriding reaction: When preparing ceramic materials such as silicon nitride (Si ∝ N ₄) and aluminum nitride (AlN), introducing nitrogen gas can accelerate the nitriding process and improve product purity.
Sulfurization reaction: When calcining sulfide ores, introducing hydrogen sulfide (H ₂ S) can promote the formation of sulfides or control the sulfur content.
Improve material properties
Crystal type control: The introduction of specific gases can affect the crystal transformation of materials, such as aluminum oxide (Al ₂ O3), which can be calcined in a hydrogen atmosphere to obtain highly active γ – Al ₂ O3.
Porosity adjustment: The pore structure of the material can be adjusted by introducing water vapor or carbon dioxide, which is suitable for catalyst carriers or filter materials.

2. Types of gases that can be introduced
noble gas
Nitrogen (N ₂): Low cost, commonly used to isolate oxygen and prevent oxidation.
Argon (Ar): It has stronger chemical inertness and is suitable for materials that are sensitive to oxidation at high temperatures, such as titanium and zirconium.
Helium (He): With high thermal conductivity, it can be used for rapid heating or cooling processes.
reducing gas
Hydrogen (H ₂): Strong reducibility, commonly used for metal oxide reduction or deoxidation treatment.
Carbon monoxide (CO): Strong reducibility, but toxicity should be noted, suitable for specific industrial scenarios.
Synthesis gas (H ₂+CO): Combining the advantages of hydrogen and carbon monoxide, used for complex reduction reactions.
oxidizing gas
Air (O ₂+N ₂): Used for processes that require oxidation, such as sludge incineration or metal surface oxidation treatment.
Pure oxygen (O ₂): increases the oxidation rate, but requires strict temperature control to prevent material sintering.
reactive gas
Nitrogen (N ₂): used for nitriding reactions.
Ammonia (NH3): decomposes to produce nitrogen and hydrogen, which can be used for nitriding or reduction reactions.
Hydrogen sulfide (H ₂ S): used for sulfide synthesis or sulfur content control.
Carbon dioxide (CO ₂): used for carbonization reactions or porosity adjustment.

3. Implementation method of atmosphere communication
Gas injection system
Multi point spraying: Gas nozzles are installed at the feed, middle, or discharge ends of the rotary furnace to achieve uniform gas distribution.
Flow control: Accurately adjust gas flow rate through mass flow meters to ensure process stability.
Pressure regulation: Maintain a slight positive pressure inside the furnace to prevent external air from infiltrating.
sealing design
Dynamic sealing: using graphite packing or labyrinth sealing to reduce gas leakage.
Static sealing: Use high-temperature resistant sealing rings at the connection of the furnace body to ensure airtightness.
Gas circulation and recovery
Circulating system: recycling inert or reactive gases to reduce production costs.
Exhaust gas treatment: Purification treatment of toxic or harmful gases (such as H ₂ S, CO) to meet emission standards.

4. Typical application cases
Preparation of positive electrode materials for lithium batteries
Process: When calcining nickel cobalt manganese hydroxide (NCM/NCA precursor), oxygen (O ₂) is introduced to promote oxidation reaction and improve the electrochemical performance of the material.
Effect: Accurate control of oxygen partial pressure, higher crystal conversion rate, and improved capacity retention rate.
Preparation of Titanium Alloy Powder
Process: Calcination of titanium hydride (TiH ₂) in a hydrogen (H ₂) atmosphere, followed by dehydrogenation to obtain high-purity titanium powder.
Effect: High hydrogen purity, complete dehydrogenation, low oxygen content in titanium powder.
Preparation of silicon nitride ceramics
Process: Calcination of silicon powder in a nitrogen (N ₂) atmosphere to generate silicon nitride (Si ∝ N ₄).
Effect: Stable nitrogen flow rate, high nitriding rate, and high bending strength of the product.
Harmless treatment of sludge
Process: Incinerate sludge by introducing air (O ₂).
Effect: The solidification rate of heavy metals is higher, and the ash residue can be used as roadbed material.