Muffle Furnace
An electrically heated, insulated chamber that reaches several hundred to over 1000 °C. In QC it is used to ignite samples for sulphated ash (residue on ignition) and to bring crucibles to constant mass.
- Pharmaceutical
- Food
- Cement and ceramics
- Mining
- Environmental
What is Muffle furnace?
A muffle furnace is a box-shaped chamber lined with refractory insulation and heated by electric elements in the walls. The 'muffle' is the inner lining that separates the sample from the heating elements, so the sample is heated evenly by radiation and convection without direct contact.
A controller holds the chamber at a set temperature, such as 600 °C for sulphated ash. Samples are placed in porcelain, silica or platinum crucibles. After ignition, the crucibles are cooled in a desiccator and weighed.
In pharmaceutical QC, the main uses are sulphated ash / residue on ignition of APIs and excipients, ash of herbal materials and igniting crucibles to constant mass before a test.
Used for
- Sulphated ash / residue on ignition
- Total ash and acid-insoluble ash of herbal materials
- Igniting crucibles to constant mass
- Ashing samples before elemental analysis
- Loss on ignition of inorganic materials
How it works
- 01
Set point
Enter the required temperature, for example 600 °C.
- 02
Heat up
The elements heat the chamber; the controller watches the thermocouple.
- 03
Stabilise
Wait until the chamber is stable at the set point.
- 04
Ignite
Place crucibles in the centre of the chamber for the set time.
- 05
Cool & weigh
Cool crucibles in a desiccator and weigh them.
Advantages
- Reaches high temperatures (often up to 1100–1200 °C)
- Simple and robust
- Holds several crucibles at once
- Programmable ramps and holds on modern controllers
Limitations
- Slow to heat up and cool down
- Temperature is not perfectly uniform; corners and the door area run cooler
- Fumes from charring samples must be handled before ignition
- Only the controller probe is monitored; independent checks are needed for accuracy
1 calibration procedure
Methods that use Muffle furnace
Keep every Muffle furnace in control: usage logs, calibration and maintenance schedules, and automatic blocking of overdue instruments.