Laboratory annealing experiment using a small tube furnace

The laboratory small tube furnace has the advantages of high-precision temperature control, flexible atmosphere control, and independent temperature zone design in annealing experiments, and is suitable for annealing treatment of metal materials, semiconductor materials, and ceramic materials. The following provides a detailed explanation from five aspects: experimental principles, operating procedures, parameter control, safety precautions, and typical application cases:

1. Experimental principle
Annealing is a heat treatment process that improves the internal structure of materials, eliminates internal stresses, and enhances material properties through heating, insulation, and cooling operations. Small tube furnaces achieve the following effects by precisely controlling temperature, atmosphere, and cooling rate:
Stress relief annealing: eliminates internal stress generated during the processing of metal materials, preventing deformation and cracking.
Recrystallization annealing: Recrystallizes the metal after cold deformation and restores its plasticity.
Spheroidization annealing: reduces the hardness of high carbon steel and improves machinability.
Homogenization annealing: Eliminating component segregation in castings or welded parts and improving tissue uniformity.

2. Operation steps
Sample preparation
Metal samples: cut into appropriate sizes, with a clean and oil-free surface.
Semiconductor samples, such as silicon wafers, need to be cleaned and dried.
Ceramic samples: Ensure no cracks and a smooth surface.
Furnace tube and atmosphere preparation
Choose high-purity quartz tube or corundum tube, and seal both ends with stainless steel flanges.
Introduce inert gases (such as argon and nitrogen) to evacuate the air inside the furnace to prevent oxidation.
If a reducing atmosphere is required, hydrogen gas can be introduced (concentration must be strictly controlled to avoid detonation).
Parameter Settings
Heating rate: Set according to material characteristics (such as metal usually 5-10 ℃/min, semiconductor 2-5 ℃/min).
Insulation temperature: determined based on the phase transition point of the material (such as the recrystallization temperature of steel being 650-700 ℃).
Insulation time: Ensure sufficient organizational transformation (e.g. 30 minutes to several hours).
Cooling method: In furnace cooling (FC) or controlled cooling rate (such as rapid cooling required for quenching).
Experimental execution
Start the tube furnace and heat it up to the target temperature according to the program.
Maintain temperature stability during the insulation stage (temperature control accuracy ± 1 ℃).
During the cooling phase, cool down at the set rate to avoid cracking caused by thermal stress.
Sample extraction and testing
After cooling to room temperature, remove the sample.
Use metallographic microscope, X-ray diffraction (XRD) or hardness tester to detect changes in microstructure and properties.

3. Key points of parameter control
temperature control
Using PID intelligent temperature control system, supporting multi-stage program temperature control.
The length of the constant temperature zone should cover the sample to ensure temperature uniformity (within ± 5 ℃).
Avoid excessive temperature fluctuations (such as exceeding ± 10 ℃), otherwise it may lead to uneven tissue.
Atmosphere control
Inert atmosphere: Protect the sample from oxidation (such as nitrogen flow rate of 50-100sccm).
Reductive atmosphere: The hydrogen concentration should be strictly controlled within a safe range (usually ≤ 5%).
Vacuum environment: Some experiments need to be conducted under vacuum (with a vacuum degree of up to 10 ⁻ ² Torr).
Cooling rate control
In furnace cooling (FC): suitable for stress relief annealing, with a slower cooling rate (such as 5-10 ℃/min).
Controlled cooling: such as oil cooling or water cooling, suitable for quenching processes, requiring rapid passage through the phase transition point.

4. Safety precautions
Gas safety
Before using hydrogen, it is necessary to check the sealing of the gas path to avoid leakage.
The pressure inside the furnace tube should not exceed 0.02 MPa to prevent bursting.
The experimental site is equipped with hydrogen gas detectors and fire extinguishers.
high-temperature protection
Wear heat-resistant gloves and goggles during operation to avoid burns.
When the temperature of the furnace body is above 100 ℃, do not touch the surface of the furnace body.
Electrical safety
Ensure good grounding of the equipment to avoid electrical leakage.
After the experiment, turn off the heating power first, and then turn off the gas path and vacuum pump.
Sample processing
High temperature samples need to be removed with high-temperature resistant tools to avoid cracking caused by sudden cooling.
After the hydrogen containing atmosphere experiment, it is necessary to continuously introduce inert gas until the furnace temperature drops below 100 ℃ to prevent hydrogen embrittlement.

5. Typical application cases
Annealing of metal materials
Experimental objective: To eliminate work hardening of cold-rolled steel plates and restore plasticity.
Parameter settings: heating rate of 8 ℃/min, insulation temperature of 680 ℃, insulation time of 2 hours, and cooling with the furnace.
Result: Hardness decreased and elongation increased.
Semiconductor material annealing
Experimental objective: To repair ion implantation damage and activate dopants.
Parameter settings: nitrogen atmosphere, heating rate of 5 ℃/min, insulation temperature of 1000 ℃, insulation time of 30 minutes, rapid cooling.
Result: The carrier concentration increases and the resistivity decreases.
Ceramic material annealing
Experimental objective: To eliminate sintering stress and improve density of alumina ceramics.
Parameter settings: Vacuum environment, heating rate of 10 ℃/min, insulation temperature of 1500 ℃, insulation time of 4 hours, cooling with furnace.
Result: Increased density and improved flexural strength.