Modified Atmosphere & Vacuum Equipment

Modifying the atmosphere in a laboratory or industrial furnace requires altering the atmosphere’s composition within a sealed vessel. This is necessary to achieve optimum conditions for a specific process.

There are several types of modified atmospheres, each with properties that determine their suitability for different applications. These atmospheres typically fall into one of three categories: inert, reactive, or vacuum.

This document introduces these different types of modified atmospheres and how they can be created.

AIR COMPOSITION

While our products are frequently used in air, some can contain a modified atmosphere with the help of additional equipment. Since air contains oxygen, heating a sample in air may cause oxidation, which may not be desirable for certain applications.

BENEFITS OF USING MODIFIED ATMOSPHERES

Working with materials under a modified atmosphere provides a well-regulated environment, high repeatability, and more uniform results.

Modified atmospheres can be tailored to either safeguard samples from oxidation during heating or to actively encourage certain reactions, based on the type of material and the specific environment needed. Inert gases like argon (Ar) or nitrogen (N₂), and reducing gases like hydrogen (H₂), are employed to ward off oxidation. Conversely, oxidizing gases such as oxygen (O₂) or nitrous oxide (N₂O), are used to stimulate oxidation.

Selecting the appropriate atmosphere is entirely driven by the demands of the heat treatment process.

HEAT TREATMENT WITH INERT ATMOSPHERES

NITROGEN

Nitrogen is often considered inert for applications under 1800°C. As it displaces oxygen, it’s ideal for situations where oxidation is unwanted.

Although not a “noble” gas, nitrogen can react with oxygen under specific conditions to form gases such as nitric oxide (NO) and nitrogen dioxide (NO2). These gases are collectively known as NOx gases, with “x” indicating the number of oxygen atoms present in the compound.

When an inert atmosphere is necessary, nitrogen serves as a cost-effective alternative to argon, as long as the material being heat-treated (or any resulting by-products) doesn’t react with it.

ARGON

Argon is a completely inert “noble” gas and will not react with any material it comes into contact with. It displaces oxygen, so is ideal for use in applications where oxidation is undesirable.

While more expensive than nitrogen, argon has the benefit of being able to be used at temperatures above 1800°C without any risk of reaction.

HEAT TREATMENT WITH REACTIVE ATMOSPHERES

HYDROGEN

Hydrogen is highly reactive because it only has one electron. This property enables it to be used as a reducing gas to react with and break down other materials, such as removing oxides from metals.

Hydrogen has an autoignition temperature of around 500°C (932°F). Therefore, it’s important to take adequate safety precautions during use. Before introducing hydrogen into a vessel, the air must be removed, typically by purging with an inert gas. The vessel must then be heated above the autoignition temperature to ensure the controlled burning of hydrogen.

For processes requiring the properties of hydrogen at lower temperatures, a less reactive forming gas can be used. A typical forming gas is a mixture of nitrogen and hydrogen, containing a maximum of 5% hydrogen. At such low concentrations, hydrogen is not typically explosive.

When working with gases that contain more than 5% hydrogen, a gas safety system is needed to protect against explosions.

HEAT TREATMENT WITH VACUUM

In addition to using inert and reactive modified atmospheres, you can also heat treat samples under vacuum in a furnace without introducing any gas into the sealed vessel. Using a vacuum pump offers the added advantage of removing unwanted air and molecules from porous samples.

However, be aware that vessels should not be evacuated with a vacuum pump while they’re hot, unless they’re specifically designed for this purpose. The shift in atmospheric pressure combined with the decrease in material strength due to temperature changes can cause vessels, especially those with a rectangular design, to break.

The level of vacuum you can achieve varies based on the type of pump used:

	Pressure (mbar)	Type
Rough vacuum	1000 – 1	Rotary vane pump
Fine vacuum	1 – 10-3	Roots pump
High vacuum	10-3  – 10-7	Turbo molecular pump
Ultra high vacuum	< 10-7	Turbo molecular pump

MODIFIED ATMOSPHERE EQUIPMENT

Optional modified atmosphere equipment and accessories allow for greater operational flexibility, as products can be used for multiple applications involving different gases, vacuum, or no modified atmosphere.

MODIFIED ATMOSPHERE TUBE FURNACES

Volta Furnace offers a range of options to enable modified atmosphere in the standard tube furnace. These options included special work tube accessories, inert gas accessories, vacuum pump as well a hydrogen safety system.

MODIFIED ATMOSPHERE CHAMBER FURNACES 

VACUUM ATMOSPHERE FURNACES 

MODIFIED ATMOSPHERE – FAQ

WHAT IS A MODIFIED ATMOSPHERE IN LABORATORY AND INDUSTRIAL FURNACES?

A modified atmosphere involves altering the atmospheric composition within a sealed vessel to create ideal conditions for a specific process. Modified atmospheres can be broadly categorized into three types: inert, reactive, or vacuum. The properties of each determine their application suitability.

WHY WOULD I NEED AN INERT GAS ATMOSPHERE IN A LABORATORY OR INDUSTRIAL FURNACE?

Inert atmospheres are beneficial for processes involving samples that could be damaged by oxygen exposure. Typically, argon (Ar) or nitrogen (N2) — deemed inert below 1800°C — are used. These gases displace oxygen and do not react with sample materials, creating a protective atmosphere during heat treatment.

WHY WOULD I NEED A REACTIVE GAS ATMOSPHERE IN A LABORATORY OR INDUSTRIAL FURNACE?

Reactive atmospheres catalyze or support chemical reactions within a sample during processing. They are commonly used to either promote oxidation reactions, resulting in oxide compounds (like iron oxide, carbon dioxide), or reduction reactions, which remove oxide compounds from a sample. Examples include using oxidizing gas (O2 / N2O) and reducing gas (H2).

WHY WOULD I NEED A VACUUM ATMOSPHERE / VACUUM FURNACE?

A vacuum atmosphere is necessary when an absolute absence of oxygen or other elements is required within an environment. Different vacuum pressure levels can be achieved using various types of vacuum pumps, including rough, fine, high, and ultra-high. The required level depends on the application.

HOW DO I CREATE A MODIFIED ATMOSPHERE WITHIN A LABORATORY OR INDUSTRIAL FURNACE?

A modified atmosphere can be created within a sealed vessel through “purging” or “evacuation and backfilling.” Although both methods result in low oxygen levels, “evacuation and backfilling” typically produces a purer atmosphere. This process is known as “atmospheric exchange.”

WHAT IS “PURGING”?

“Purging” involves introducing an inert gas flow into a sealed vessel to displace and remove oxygen. Typically, a high initial flow rate reduces oxygen levels, followed by a lower rate during processing to maintain desired gas concentration levels and minimize gas consumption. Purging quickly creates a usable atmosphere due to the initial high gas flow.

WHAT IS “EVACUATION AND BACKFILLING”?

The “evacuation and backfilling” method consists of two stages. Initially, a vacuum pump extracts oxygen and unwanted particles from the vessel and any porous samples inside. This evacuation stage is followed by “backfilling,” where an inert gas flow displaces any residual particles. This process can be repeated as necessary.

WHAT ARE THE DIFFERENT TYPES OF PUMPS USED IN VACUUM FURNACES?

Commonly used vacuum pumps include rotary vane pumps, roots pumps, oil diffusion pumps, and turbomolecular pumps. Each pump achieves vacuum pressures within a specific range, with the choice dependent on the application process. We offer standard rotary vane and turbomolecular vacuum pump packages, which can achieve vacuum levels of 5×10-2 mbar, and 1×10-5 mbar respectively.

WHAT IS VACUUM?

A vacuum is defined as a reduced number of gas molecules and atoms within a sealed volume at a constant temperature, compared to ambient conditions. Applying a vacuum to a sealed vessel reduces the number of particles inside. However, a perfect vacuum is unattainable, as even under ultra-high vacuum conditions, billions of particles persist within one cm3.

WHAT IS PRESSURE?

Pressure (P) is defined as the force (F) acting perpendicularly on a surface divided by the area (A) of that surface, i.e., “P=F/A”. The standard unit of pressure is “pascal” (Pa), but pressure can also be expressed in other units such as bar, mbar, etc.

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