Glass Coating

Fusion Edge Seal for Vacuum Glazing

June 15, 2021

Vacuum can never be completely appreciated unless it is fully known, and I've always noticed that those who work in the vacuum industry have a genuine commitment to their passion in vacuum science and a willingness to apply it to a range of scenarios.

For example, the concept of zero energy buildings is better achieved by vacuum glazing, and most importantly, the motivating factor that results in achievement and satisfaction. 

The belief that buildings cannot exist without glass is due to the imperious function of glazed windows in enabling natural daylighting, albeit at the expense of space-heating energy loss in cold-arid areas and space-cooling energy loss in hot-arid areas. 

As such, avoidable energy losses by buildings' glazed windows contribute indirectly to greenhouse pollution, thus accelerating climate change. However, when discussing vacuum glazing, we must often equate U value to vacuum pressure, and in order to attain ultra-high vacuum pressure, hermetic (air-tight) materials are needed, which are typically more expensive, use hazardous substances (Pb) and are complex to construct. 

What is fusion edge-sealed vacuum glazing?

Fusion edge-sealed vacuum glazing has a 0.15 mm thick cavity between two sheets of glass, supported with an array of tiny stainless-steel pillars i.e. 0.15 mm high and 0.3 wide. This cavity entails reduced atmospheric-air pressure down to high-vacuum pressure of 8.2·10-4 Pa. Subsequently, it suppresses gaseous heat conduction and convection to infinitesimal level because of an increase of mean-free path between two air molecules beyond 3000 m. The high-vacuum pressure was maintained with fusion edge-seal around the periphery of two sheets of glass, whilst avoiding the problems of future gas leaks, outgassing and absorption of moisture in order to provide long-term durability. Thus, the U value is dependent on the vacuum-tight edge seal of the vacuum glazing. The center-of-pane thermal transmittance (U value) was predicted to be 1.039 Wm-2K-1.

How is a fusion-edge sealed vacuum glazing created?

The fusion edge-seal is created using a method developed following a series of tests. It entails forming a thin, glass-metallic surface texture composed of B2O3 and/or Sn particles. This is then  fused with the hard Sn or Sn-In alloy to create a hermetic (vacuum-tight) edge-seal (the process involves creating a textured coating on the surface of the glass with a suitableB2O3 and/or Sn mixture). 

This system was developed after extensive research and experiments to better understand the behaviour of glass components and metals under various temperature regimes. Additionally, this article refers to the prediction of the thermal efficiency of the fusion edge-sealed vacuum glazing by using a validated finite element model of the fabricated.

What are the advantages of fusion-edge sealed vacuum?

One of the primary advantages of this innovation is its cost effectiveness as opposed to composite or indium sealed vacuum glazing, which are covered in this article, and the fact that it does not include harmful Pb metal, as solder glass sealed vacuum glazing does. 

Additional characteristics and benefits of the fusion edge-seal would become evident when the following comprehensive experimental evaluations of the fusion edge-sealed vacuum glazing are performed.

  1. Real Time Testing for its Thermal Performance

  2. Long-term stability of the vacuum pressure 

  3. Integration to Smart Intelligent Windows For Net Zero Energy Buildings 

What does the future of vacuum glazing look like?

Because of the cost-effectiveness of this fusion edge-sealed vacuum glazing, we anticipate to integrate it with PDLC thin film, semi-transparent photovoltaics for a vision of Smart Intelligent Windows that generate electrical power, minimizes heat loss through windows and provide control of transparency using IoT to consumers.

Leybold employee

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