Laboratory furnaces are specially built instruments essential for research, development, and experimental applications. This apparatus uses heat to process materials, such as biohazard waste and other instruments. In metal fabrication, a special type of oven and furnace is utilized to attain the desired product output. This is called a controlled atmosphere lab furnace

A controlled atmosphere lab furnace brings about many benefits for different procedures. Continue reading to learn more about the capabilities and advantages of this type of furnace. 

What is a Controlled Atmosphere Furnace? 

A controlled atmosphere furnace creates a specialized or protective environment to encompass the specific projects during heating and cooling procedures. Controlling the laboratory temperature with precision and sealing the furnace tightly—without room for error—ensures a successful outcome for the end product. Tightly sealing the chamber maintains the insulated condition throughout the process. 

The atmosphere plays a critical role in achieving the desired result during the heating process. Generally, these conditions are used for two purposes: to preserve and safeguard the material from surface reactions, making it chemically inert or protective, and to enable the material’s surface to change during the process for it to be chemically active or reactive. 

Below is a shortlist of the common gases and vapors involved in furnace atmospheres. 

  • Air (NH3): This is a major component in many controlled atmospheres. The air’s composition is roughly 79% nitrogen and 21% oxygen, with trace amounts of carbon dioxide. 
  • Oxygen (O2): This element reacts with diverse types of metals to produce oxides and carbon dissolved in steel to reduce surface carbon content. 
  • Nitrogen (N2): In its passive state, this component can be manipulated in an atmosphere for annealing low carbon steels. It can also be used as a protective atmosphere in the heat treatment of high-carbon steels. 
  • Hydrogen (H2): Under controlled environments, hydrogen can decarburize steel and decrease iron oxide to iron. 
  • Carbon dioxide (CO2) and Carbon monoxide (CO): CO2 reacts with surface carbon to generate carbon monoxide. The reaction persists until the CO2 supply is consumed and the steel surface no longer has carbon. 
  • Water vapor: This property is reactive with steel substances at extremely low temperatures and pressures. 
  • Inert gases: Inert gases can be used as protective atmospheres in thermal treatments of metals and alloys. 

Researchers must understand how pertinent creating a specific atmosphere is for a successful material fabrication of the heat-treating process and why that certain environment is used. 

Common Types of Furnace Atmospheres

Various types of controlled atmospheres are used for different purposes. You’ll need to consider your goal of the heating process to determine which type is best for heating metal or steel materials. 

1. Exothermic Atmosphere

Exothermic reactions generate heat. The term “exothermic” refers to a chemical change that occurs with the liberation of heat, meaning without the heating of gas and air. This atmosphere helps prevent surface oxidation during metal heat treatment. There are two types of exothermic atmosphere for heating steel: 

  • Rich exothermic: The nominal composition for this is N2 = 71.5%; CO = 10.5%; CO2= 5%; H2 = 12.5%; methane (CH4) = 0.5%
  • Lean exothermic: The nominal composition for this is N2 = 86.8%; CO = 1.5%; CO2 = 10.5%; H2= 1.2%

Rich exothermic conditions are generally used for steel tempering, copper and silver brazing, annealing, and powdered metal sintering. Since the carbon potential of the gas mixture is lower than 0.10%, low carbon steels are heat-treated with this process. Otherwise, decarburization occurs, which can result in poor wear resistance. 

Meanwhile, lean exothermic atmospheres don’t find applications in heat treatment. Instead, these are utilized when deliberate surface oxidation is required. Its common applications include copper annealing and other low-temperature workloads. 

2. Endothermic Atmosphere 

It’s common to create endothermic gas conditions during the heating of steel. Endothermic gas is released when a meager air-to-gas ratio is present and initiated into an externally heated chamber containing an active substance (e.g., propane, methanol. etc.) to crack the mixture. When the gas exits the retort, it is quickly cooled before reaching the furnace. 

The usual composition for endothermic reactions is 40% H2, 20% CO or CO2, and 40% N2. 

To differentiate exothermic from endothermic, remember that the endothermic atmosphere needs heat to stimulate the reaction. This controlled atmosphere is common in bright hardening, sintering, annealing non-ferrous metals, brazing, and carbon restoration in metal parts. 

3. Prepared Nitrogen-Based Atmosphere

This specialized environment applies to heat treatments that do not need extremely reducing atmospheres. Due to the absence of any oxygen-bearing contaminants in the chamber operations and low dew point and carbon dioxide, this type of furnace atmosphere is neither oxidizing nor decarburizing. 

Prepared nitrogen-based atmospheres are often used in annealing. This condition uses methane or other hydrocarbons as carrier gases in annealing, carbon restoration, and gas carburizing. 

Lean, nitrogen-based atmospheres (N2 = 97.1%; CO = 1.7%; H2 = 1.2%) are utilized in massive, semi-continuous, and continuous annealing treatments. Meanwhile, rich nitrogen-based atmospheres (N2 = 75.3%; CO = 11%; H2 = 13.2%; CH4 = 0.5%) can be applied in iron powder sintering. 

4. Commercial Nitrogen-Based Atmosphere

This furnace atmosphere pertains to industrial nitrogen gas-based atmospheres, which use commercially pure N2. Commercial nitrogen-based conditions allow the variation of composition by blending at will when necessary and at certain times during a cycle. They also enable this at different zones in the chamber. There are three types of commercial nitrogen-based atmosphere based on function:

  • Protective atmospheres: This averts oxidation or decarburization during the heating process. Common applications of this type include batch and continuous annealing of ferrous metals. 
  • Reactive atmospheres: This type uses a great concentration of reactive gases to decrease metal oxides or transfer tiny levels of carbon to ferrous materials. 
  • Carbon-controlled atmospheres: For this type of environment, the purpose is to promote a reaction with steel, so the amount of carbon can be reduced from or added to the surface of the substance. 

The composition of gas atmospheres in this are as follows:

  • For hardening: N2 = 97%; H2 = 1%; CO = 1%; CH4 = 1%
  • For decarburizing:  N2 = 40%; H2 = 40%; CO = 20%
  • For carburizing: N2 = 90%; H2 = 10%

5. Dissociated Ammonia-Based Atmosphere

A dissociated ammonia-based generator is a medium-cost atmosphere that offers a pure, dry, and carbon-free reducing environment. Its composition is 75% H2 and 25% N2 with a dew point below 50°C. Its high hydrogen concentration promotes high deoxidizing abilities, eliminating metal surface oxides and prohibiting scaling during the heat treatment. 

Some of the dissociated ammonia-based atmosphere’s applications include bright heat treatment of nickel alloys and carbon steels, annealing of electrical elements, and as a carrier mixed gas for nitriding processes. 

6. Hydrogen Atmosphere

Commercial hydrogen is about 98 to 99.9% pure with signs of water vapor and oxygen, among others. Nitrogen, carbon dioxide, methane, and other gases can be present in small amounts as impurities in this atmosphere. When H2 is used in a lab oven, an appropriate amount of inert gas is employed to remove it. 

Hydrogen is an excellent deoxidizer, which is limited by moisture content. However, in a dry state, it decarburizes high carbon substances at extremely high temperatures to form methane. When H2 gets adsorbed, it results in hydrogen-embrittlement, particularly high carbon substances. 

Dry hydrogen is observed as a controlled atmosphere in sintering tungsten carbide and metal powder components, annealing of low carbon steels, stainless steels, and direct reduction of metal ores. 

7. Steam Atmosphere

This type of furnace atmosphere is utilized for scale-free tempering and stress-relieving of metals composed of iron and has magnetic components, such as alloy, carbon, and cast and wrought iron, in a temperature range of 345° to 650°C (655° to 1200°F). 

Steam processing reduces the porosity of sintered iron and brings increased strength and resistance against wear and corrosion. Before undergoing this treatment, the surfaces should be clean and oxide-free. 

8. Inert Gas Atmosphere

Inert gas atmosphere is used for heat treatment applications that need protection from oxidation. This atmosphere is typically used for bonding, curing, and heat-treating work.

Nitrogen is the most common compound and is used mainly as unreactive gas. This atmosphere provides a protective gas; its contents of carbon, oxygen, and nitrogen do not react to steel. Argon gas fulfills the inert gas judgment.

Inert gas atmosphere furnaces have precision microprocessor-based temperature controls and energy-efficient insulation for optimal cost savings and quality performance. 

Upgrade Your Laboratory with Controlled Atmosphere Furnaces

The different furnace atmospheres above only produce your desired results when using a suitable chamber. So, apart from choosing the atmosphere process for your product, you must also consider the types of lab furnaces to perform them. You must also use a high-quality furnace to ensure you’ll achieve the output you expect. 

Looking at lab furnaces can be tricky, especially if you’re unsure which one suits your projects. Thankfully, furnace companies like Across International Furnaces can help you find what you need exactly. Head over to AI Furnaces’ catalog to explore our selection of high-quality and energy-saving controlled atmosphere lab furnaces to add to your research and development laboratory.