Temperature of tube muffle furnace

The key parameters of the tubular muffle furnace, such as temperature range, control accuracy, uniformity, and influencing factors, are the core indicators to meet different experimental and industrial needs. The following provides a detailed explanation from four aspects: temperature range, control characteristics, influencing factors, and optimization suggestions:

1. Temperature range: covering medium low temperature to ultra-high temperature requirements
The temperature range of a tubular muffle furnace varies significantly depending on the material of the furnace tube and the heating element. The common types are as follows:
Low temperature type (≤ 1000 ℃)
Applicable scenarios: material drying, pre-treatment for thermogravimetric analysis, low-temperature annealing (such as plastic and polymer materials).
Typical configuration: Quartz furnace tube (temperature resistance of 1200 ℃)+nickel chromium alloy heating wire, with a maximum temperature usually set at 1000 ℃ to extend the service life of the furnace tube.
Medium temperature type (1000 ℃~1400 ℃)
Applicable scenarios: ceramic sintering (such as Al ₂ O ∝, ZrO ₂), metal heat treatment (such as quenching and tempering of steel).
Typical configuration: corundum furnace tube (temperature resistance of 1600 ℃)+silicon carbon rod heating element, temperature uniformity can reach ± 5 ℃.
High temperature type (1400 ℃~1800 ℃)
Applicable scenarios: High temperature alloy melting, silicon carbide/silicon nitride ceramic sintering, crystal growth (such as sapphire, silicon carbide single crystal).
Typical configuration: High purity corundum or silicon carbide furnace tube (temperature resistance of 1800 ℃)+silicon molybdenum rod heating element, equipped with a water cooling system to prevent deformation of the furnace tube.

2. Temperature control characteristics: dual guarantee of precision and stability
control accuracy
PID control system: Real time adjustment of heating power through proportional integral derivative algorithm, achieving rapid temperature response and stable control.
Sensor type:
N-type thermocouple: suitable for medium and low temperatures (≤ 1200 ℃), low cost, fast response.
S-type/B-type thermocouple: suitable for high temperatures (>1200 ℃), high accuracy, and good stability.
Infrared thermometer: non-contact temperature measurement, suitable for ultra-high temperature or vacuum environments, but requires regular calibration.
temperature uniformity
Furnace design:
Single zone furnace: temperature uniformity of ± 5 ℃~± 10 ℃, suitable for simple processes.
Multi zone furnace (3 zones/5 zones): Each zone is independently controlled for temperature, forming a temperature gradient with uniformity of ± 2 ℃~± 3 ℃, meeting complex requirements such as CVD and crystal growth.
Hot air circulation: The built-in fan forces air flow, eliminating temperature blind spots and improving uniformity.
heating rate
Limiting factors: coefficient of thermal expansion of furnace tube material, power density of heating element, and specific heat capacity of sample.
Optimization suggestion: Rapid heating should be carried out in stages to avoid cracking of furnace tubes.

3. Key factors affecting temperature performance
Furnace tube material
Thermal expansion coefficient: Quartz (0.5 × 10 ⁻⁶/℃)Corundum (30W/(m · K))>Quartz (1.4W/(m · K)), poor thermal conductivity requires extended insulation time.
heating element
Nickel chromium alloy: temperature resistance ≤ 1000 ℃, low cost, suitable for low-temperature furnaces.
Silicon carbon rod: resistant to temperatures ranging from 1400 ℃ to 1600 ℃, with resistance increasing with temperature, requiring a transformer to regulate voltage.
Silicon molybdenum rod: resistant to temperatures of 1800 ℃, resistance decreases with increasing temperature, and needs to be used in series to balance power.
insulation layer
Material selection: ceramic fiber (temperature resistance 1260 ℃), aluminum silicate fiber (temperature resistance 1000 ℃), mullite fiber (temperature resistance 1600 ℃).
Thickness optimization: If the insulation layer is too thick, it will prolong the heating time, and if it is too thin, it will dissipate heat quickly. It needs to be designed according to the balance between power and furnace size.

4. Suggestions for optimizing temperature performance
periodic calibration
Calibrate the temperature control system with a standard thermometer (such as a platinum resistance thermometer) every 6 months to correct sensor drift errors.
Sample placement
The sample should be placed in the constant temperature zone of the furnace tube (usually one-third of the length in the middle of the furnace tube) to avoid temperature deviation caused by proximity to the furnace mouth or heating elements.
atmosphere control
Oxidative atmosphere (such as air) can accelerate the oxidation of heating elements and shorten their lifespan; A reducing atmosphere (such as H ₂) requires the use of heating elements that are resistant to hydrogen corrosion (such as molybdenum wire).
Cooling strategy
After high temperature, it is forbidden to directly open the furnace door or introduce cold air. The temperature should be slowly lowered according to the program (such as 5 ℃/min) to prevent the furnace tube from cracking due to thermal stress.