The stainless steel in your vacuum-insulated products is constantly releasing trapped hydrogen gas, a process called outgassing that degrades performance over time. Untreated STS304 steel, for example, has an outgassing rate that can be over 20 times higher than heat-treated steel, slowly ruining the vacuum from the inside out. This is where a getter becomes essential.

This article breaks down the role of getter technology in maintaining a high-quality, long-lasting vacuum. We’ll examine the three mechanisms getters use to trap gas, the specific industrial processes for installation, and the high-heat activation required—often at temperatures up to 450°C—to make them effective.

The Problem of Steel Outgassing

Steel outgassing is the slow release of trapped gases, primarily hydrogen, from the metal’s bulk material when under vacuum. This process, a byproduct of manufacturing, can contaminate sensitive systems and raise internal pressure. Stainless steels typically show higher outgassing rates than mild steels unless specifically heat-treated.

The Source of Gas: Hydrogen Diffusion

The primary cause of steel outgassing is hydrogen diffusion from deep within the material. This hydrogen becomes trapped during the steelmaking and fabrication processes. When the steel is exposed to a vacuum, the significant pressure difference drives these trapped gases to migrate slowly toward the surface and release into the environment.

This gradual release can compromise sensitive applications. The escaping gas may contaminate high-vacuum systems, create microscopic pinholes in protective coatings, or cause unexpected pressure increases in sealed chambers.

Outgassing Rates for Common Steel Types

The rate of outgassing varies considerably between different types of steel and their treatments. For instance, untreated STS304 stainless steel has a relatively high outgassing rate. In contrast, mild steel S20C generally performs better with a much lower rate. A vacuum heat treatment can dramatically improve performance; heating stainless steel to 450 °C for 36 hours can reduce its outgassing rate by over 20 times, bringing it closer to the level of mild steel.

How Getters “Eat” Gas Molecules

Getters “eat” gas by trapping molecules through three main actions. They can adsorb gas onto their surface like a sticky film, absorb it into their bulk material like a sponge, or chemically react with it to form new, stable solid compounds. These processes permanently remove gas from the vacuum.

The Three Trapping Mechanisms

Getters capture gas molecules through three primary methods. The first is adsorption, a surface-level process where gas molecules physically stick to the getter material, forming a single atomic layer, or monolayer. This mechanism is common in transition metals like Titanium and Zirconium at room temperature. Its capacity is limited because the process halts once the entire surface is saturated with gas molecules.

The second method is absorption, where gas molecules penetrate beyond the surface and dissolve into the bulk volume of the getter. This is similar to how salt dissolves in water. Absorption provides a much higher capacity than adsorption and is the main way materials like Zirconium and Niobium capture and store hydrogen gas.

Finally, some getters work through direct chemical reaction. In this process, the getter material permanently binds with gas molecules to form new, stable solid compounds. A classic example is a flashed Barium getter, which is evaporated onto a surface inside the vacuum. This fresh Barium film reacts instantly with any residual oxygen to form a solid, stable oxide, effectively locking the oxygen away.

Material Forms and Sorption Capacity

The physical form of a getter material directly impacts its performance. Getters are produced as thin films (like St. 122), evaporated metals, or powders with fine particles (like St. 707, which uses 40-128 μm particles). Porous, powdered materials provide a vastly larger surface area and volume for trapping gas, which results in a significantly higher sorption capacity.

The difference in capacity can be dramatic. For example, a Ba-20 at% In powder has a sorption capacity for nitrogen that is approximately 500 times greater than an St. 122 film of similar mass. To unlock this full potential, many getter materials require an activation step. This often involves heating the material in a vacuum to clean contaminants from its surface and initiate deeper absorption or chemical reactions. For instance, St. 707 getter material requires heating to 500°C for 10 minutes before it becomes fully effective.

Installation: Spot Welding the Getter

Spot welding a getter requires dedicated industrial equipment, including a high-current power supply (e.g., 230V / 100A) and a pneumatic system delivering around 90 PSI of pressure. The process is defined by precise control over current, weld time, and electrode force to create a strong bond on thin metal (0.5–2.3 mm) without causing damage, often following standards requiring at least two weld spots per connection.

Equipment and Power Infrastructure

Setting up for resistance spot welding demands significant utility support. A dedicated electrical circuit is essential, often needing to supply 15 kVA at 230V and handle a 100A draw during operation. The pneumatic welding guns require a steady 90 PSI of air pressure delivered to the tool, which is typically fed from a larger facility network running at 100–130 PSI. A qualified electrician must oversee the installation to correctly manage power connections, like a 32A per phase hookup for a three-phase system, and to guarantee proper equipment grounding for safety.

Weld Parameters and Quality Specifications

A successful weld depends on precise control over mechanical and electrical parameters. Operators set the electrode force between 100 and 1000 lbf, carefully adjusting it based on the thickness of the material. To maintain the structural integrity of the part, the surface indentation left by the electrode tip cannot exceed 25% of the sheet’s thickness. For applications requiring high reliability, engineering standards like NASA PRC-0009 specify a minimum of two spot welds for each connection. A key quality check is measuring the final joint’s electrical resistance, which should be less than 1.0 mΩ to confirm a solid, effective bond.

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Activation Process (High Heat Baking)

Getter activation is a high-heat baking process, typically performed between 350-450°C under a high vacuum. This thermal treatment removes a protective passivation layer from the getter material, exposing its porous structure so it can effectively trap unwanted gas molecules and maintain the vacuum.

The Purpose of High-Temperature Baking

Getters are manufactured with a protective oxide layer, or passivation, which allows them to be handled in air without premature reactions. High-heat baking supplies the thermal energy needed to break down this protective layer and desorb contaminants. Once the surface is clean, the active material is exposed and ready to absorb gas molecules like hydrogen.

Process Parameters and Equipment

Activation temperatures for Zr-based getters range from 350°C to 450°C. The process occurs under high vacuum, often around 10⁻⁶ mbar, to efficiently remove the desorbed gases. A common cycle involves baking at 400°C for one hour, sometimes integrated with other manufacturing steps like anodic bonding. Specialized equipment, such as SRO-Getter ovens using infrared (IR) lamps, provides precise and uniform heating for reliable activation.

Noise Check: Is that Rattle the Getter?

A ‘getter rattle’ can refer to two distinct issues. It could be a physical noise from a loose or failed component inside a vacuum-sealed device, verified by vibration tests (e.g., 9 g at 15-55 Hz). It might also describe acoustic feedback or interference in audio systems, diagnosed using performance metrics like microphone sensitivity (-32 dB).

Differentiating Mechanical vs. Acoustic Noise

A “getter rattle” describes two fundamentally different problems. A mechanical rattle is a physical noise that signals a loose or delaminated component within a system. This is a critical concern in vacuum-encapsulated electronics like MEMS, where a loose part means the device has failed. In contrast, acoustic noise is an audio-related issue. It can manifest as feedback in a sound system or interference picked up by sensitive microphones. This type of noise is not caused by a loose physical part but by how the audio system is operating.

Key Diagnostic Metrics and Test Parameters

Engineers use specific tests to diagnose the source of a rattle. To ensure mechanical stability, industrial getters are subjected to vibration testing with forces up to 9 g of acceleration at frequencies between 15–55 Hz. This process confirms that no components break loose under stress. For audio systems, noise is evaluated using different metrics. In devices with microphones, performance specifications like sensitivity (-32 dB ±1 dB) and frequency range (4.1 Hz to 4.8 MHz) help quantify interference. When dealing with sound systems, potential feedback is assessed based on the maximum sound pressure level, which can reach 109 dB at one meter.

Final Thoughts

A getter is more than just a component; it’s a dedicated guardian for the vacuum inside an insulated product. Its entire job is to combat the slow, inevitable creep of gas molecules leaking from the steel walls. While it seems simple, making a getter work involves a precise manufacturing sequence, from secure spot welding to a high-temperature activation bake. These steps prepare its reactive surface to trap stray gas and protect the vacuum’s integrity.

This technology is a key feature that separates a premium vacuum flask from a simple insulated bottle. It ensures the product delivers consistent performance for years, not just months. This small, unseen part is essential for the long-term reliability that makes a high-quality insulated product last. It’s the silent worker that keeps your drinks hot or cold, long after you’ve bought it.

Frequently Asked Questions