The Importance of Atmosphere in High Temp Furnaces
Numerous considerations must be considered when purchasing high temp furnaces, particularly for applications where the atmospheric composition of a hearth at process temperatures can affect the product yield. Select heat treatment processes are optimally carried out in vacuum conditions to reduce the risk of cross-reactivity and negate mechanical issues associated with gas permeation and adsorption. This is not an issue for alternative curing methods which can be routinely carried out in a regular air atmosphere.
This blog post will explore the importance of atmospheric composition in high temp furnaces in more detail:
Atmospheric Importance in Heat Treatment Procedures
Atmospheric controls are not often integral for high temp furnaces that are used to treat materials where the impact of process oxidation or gas integration is negligible, or where oxidation is the purpose of the process. Few special considerations need to be accounted for in these instances, as the materials can be processed at high temperatures in air with minimal risk of off-gassing and no requisite catalytic gases to encourage thermodynamic change.
Air atmospheres are usually comprised of up to 78% nitrogen (N2) and 21% oxygen (O2). While oxygen reacts with many chemical elements at varying temperatures, nitrogen is considered the chemically inert carrier gas of air. It has been shown to react with such high strength metals as molybdenum (Mo) and titanium (Ti) at elevated temperatures but is routinely used as a reducing gas to prevent material oxidation in high temp furnaces. This blanketing process is accomplished using gas inlets such as nitrogen flowmeters and an exhaust port to expel spent gas from the chamber via a fume hood or an external manifold piping. Electronic monitoring systems may be required to maintain distinct composition levels relative to the temperature values of the chamber. Nitrogen blanketing can be used to prevent the oxidation of ferrous metals and to decarburize the surface of steel products.
The reactivity of hydrogen with select metals at high temperatures can be problematic for heating elements manufactured from silicon carbide (SiC) and molybdenum discilicide (MoSi2). Nitrogen gas compounds can degrade the surface composition of carbon-rich materials, resulting in significant mechanical instability over time and increased maintenance requirements. Forming gases comprised of part hydrogen also require additional safety requirements as they may be explosive in nature. Argon gas is often preferable for maintaining inert atmospheres in such high temp furnace grades and is often used for atmospheric purging. Where hydrogen is critical for the process yield, high temp furnaces often use a retort to safely protect the furnace elements from chemical attack and to contain potentially hazardous compounds.
High Temp Furnaces from Thermcraft
Thermcraft is experienced in developing and manufacturing a range of high temp furnaces operating on multiple heat treatment principles. Our industrial and laboratory furnaces are equipped to perform curing, sintering, carburizing, and more, with distinct atmospheric solutions for processes with sensitive reaction kinetics.