In this installment of Answers in the Atmosphere, David (Dave) Wolff, an independent expert focusing on industrial atmospheres for heat treat applications, examines the cost dynamics of hydrogen as a process gas and the blended atmospheres strategies thermal processors use to manage them. Drawing on insights from Stephen Feldbauer PhD of Abbott Furnace, Wolff walks through the key gas blend options available to operators and how operators select the most cost-effective mix for the job.
This informative piece was first released in Heat Treat Today’s May 2026 Sustainable Heat Treat Technologies print edition.
In last month’s column, we discussed hydrogen as a process gas and addressed key attributes. In that column and in the one that follows, Stephen Feldbauer PhD, director of Research & Development at Abbott Furnace, provided key insights.
A Question of Cost
Director of Research & Development
Abbott Furnace
Hydrogen gas is relatively expensive; in fact, case studies conducted by Abbott Furnace have demonstrated that atmosphere costs often constitute over two-thirds of the variable costs of thermal processing. Hence, cost savings in hydrogen-containing atmosphere supply are important.
As a result, thermal processors will preferentially employ gas blends, containing just the right amount of hydrogen to get the job done, diluted in a larger volume of inert or non-problematic diluent gas. Think of it like using a small amount of powerful dish soap diluted with a large volume of water to effectively clean a large amount of pots and pans. The primary advantage to using hydrogen-blended atmospheres is that they are much less expensive than using pure hydrogen.
Hydrogen-Nitrogen Blended
Pure hydrogen, delivered or generated on-site, may be blended with pure nitrogen to reduce atmosphere costs. While nitrogen can be delivered as a gas or liquid, it can also be separated from atmospheric air on-site at low cost to produce a hydrogen-nitrogen blended atmosphere. Hydrogen-nitrogen blended atmospheres typically range in hydrogen content from about 3% to 75% hydrogen, with the balance nitrogen. Nitrogen costs the thermal processor about 20% of the cost of hydrogen for a similar volume of gas, so blending hydrogen with nitrogen may be a useful approach to obtaining the benefits of a hydrogen-based atmosphere at substantially lower cost.
The actual blend of hydrogen and nitrogen used is primarily determined by the metal that is being thermally processed. As the oxide of one metal may be more stable and difficult to reduce than another, the amount of hydrogen is often increased to make the atmosphere more active. Some metals will be adversely affected by nitrogen at high temperatures. Thermal processors using a hydrogen-nitrogen atmosphere will use furnace atmosphere mixers to blend the leanest (lowest hydrogen) atmosphere that yields acceptable results in the finished metal parts.
A widely used generation approach to a hydrogen-nitrogen atmosphere is to use a thermal catalytic reactor (a “dissociator”) to crack metallurgical grade ammonia (NH₃) to a gas blend of nominal 75% hydrogen, 25% nitrogen (based on the ratio of nitrogen and hydrogen atoms in the ammonia starting gas). Because ammonia is a commonly used agricultural and industrial chemical, ammonia is widely available and cost-effective. Ammonia is delivered by truck in pressurized liquid form and stored in a tank for use.
The resulting atmosphere gas blend is generally called dissociated ammonia (DA). Significantly less expensive than using pure hydrogen, DA gas is a popular gas blend if a nitrogen-containing gas blend can be used. If decreased reducing potential is acceptable, generated DA gas can be further diluted with pure nitrogen to reduce costs even more.
Generation from Hydrocarbon
Another approach to cost-reducing hydrogen-containing atmospheres is to generate a hydrogen-containing atmosphere from a readily available hydrocarbon, such as natural gas, propane, or even methanol. This is possible because these hydrocarbons can be thermally cracked using a catalytic reactor to liberate free molecular hydrogen gas in a blend with other constituents. These reactors may use partial combustion in the case of Exothermic reactors to make Exo gas, or they may use pure thermal cracking, avoiding combustion, in which case the technique is called Endothermic gas generation, and the resulting gas is often called Endo gas.
Because Exo gas is a result of partial combustion with air, an Exo gas blend has approximately 10% hydrogen and considerable nitrogen in it, whereas Endo gas has approximately 40% hydrogen and very low levels of nitrogen. Because both Exo and Endo gases contain considerable carbon (originating from the fuel gas), their uses are limited to processes and materials where the carbon content does not create processing issues.
Argon-Hydrogen Blend
Many of the stainless steel grades cannot be thermally processed in nitrogen-containing atmospheres because the nitrogen gas will react with the chromium, damaging the alloy. In that case, an argon-hydrogen blend may be employed. Because argon is more expensive than hydrogen, the economics of an argon-hydrogen gas blend may result in much higher levels of hydrogen in the furnace atmosphere.
About The Author:
Industrial Gas Professional
Wolff Engineering
Dave Wolff has over 40 years of project engineering, industrial gas generation and application engineering, marketing, and sales experience. Dave holds a degree in engineering science from Dartmouth College. Currently, he consults in the areas of industrial gas and chemical new product development and commercial introduction, as well as market development and selling practices.
For more information: Contact Dave Wolff at Wolff-eng@icloud.com.
