The degradation of the seal involving the Kovar alloy viewport in a high-vacuum system with rubidium (Rb) vapor is likely not primarily due to chemical reactions between nickel (Ni), cobalt (Co), or rubidium under the specified conditions. Here's a breakdown:

1. Reactivity of Ni and Co with Rubidium

Nickel and cobalt are transition metals with relatively high chemical inertness. Rubidium, a...

Short answer

• Metallic Ni or Co do not appreciably “react” (form bulk compounds) with Rb at room temperature in UHV; Rb atoms simply chemisorb on clean Ni/Co surfaces and can desorb upon heating. Bulk alloying or intermetallic formation requires much higher temperatures.
• What Rb does react with very readily is the surface oxide that is essential for a glass-to-metal (Kovar–glass) seal. Rb reduc...

Reaction of Rubidium with Kovar in Vacuum Systems

The degradation you're observing at the Kovar-containing viewport is likely due to chemical reactions between rubidium vapor and the nickel/cobalt components of the Kovar alloy. This is a specialized area with limited published data, but I can provide some insights based on chemical principles.

Chemical Reactivity Considerations

Rubidium is...

Short answer
At room temperature the chemical interaction between rubidium vapour and the Ni-Co-Fe “Kovar” ring is essentially limited to a few mono-layers of physisorbed / chemisorbed Rb on the metal surface. No bulk alloying or corrosion of the Kovar takes place on any laboratory time-scale, so the seal you see degrading must be failing for some other reason (glass attack, thermal stress, res...

First, I need to recall what Kovar is. It's an iron-nickel-cobalt alloy used for sealing with glass because its thermal expansion matches ...

Short answer
• The bare metals Ni (Fe–36 %, Co ~17 %) that make up Kovar do not react appreciably with rubidium at room temperature – the corrosion (dissolution/alloy-formation) rate is essentially zero.
• What does react very readily with Rb is the oxide film that is deliberately grown on the Kovar surface so that the glass can wet and bond to it.
• Rubidium vapour reduces this oxide as fas...

Below is a semi-quantitative “back-of-the-envelope” estimate of what actually happens when Rb vapor at ∼10⁻⁷ mbar impinges on a Kovar (Fe–Ni–Co) flange:

1. Flux of Rb atoms
   – At 300 K and pRb≈1×10⁻⁷ mbar the one-way flux onto a surface is
   φ ≃ p/√(2πmRb kT) ≃10¹³ atoms cm⁻² s⁻¹.
   – That means you build up a 1 nm‐thick Rb film (∼10¹⁵ atoms cm⁻²) in ≃100 s.

2. State of the Rb film...

This is an interesting problem involving potential chemical reactions between rubidium vapor and the Kovar alloy components in your vacuum system.

Reaction Potential

Rubidium is one of the most reactive alkali metals and can indeed react with transition metals like nickel and cobalt, though these reactions are typically much slower than rubidium's reactions with oxygen, water, or halogens.

#...

Excellent and very specific question. This is a classic problem in experimental atomic physics and ultra-high vacuum (UHV) systems dealing with alkali metals.

Let's break down the likely chemical interactions.

Direct Answer to the Question

Finding specific, quantitative reaction rates (e.g., in units of ) for Rubidium vapor with solid Nick...