In honor of Sir Alistair Pilkington: float foam glass

logo_small2018 was indeed a fruitful year for the development of cellular glass.  In a previous post, I already declared the Aalborg – Ljubljana team as the one who made the largest progress during the last year with consequences on the market the next years.

But yesterday, I found a new paper, published in 2018 with an extremely important experimental fact. This paper proves that it is possible to produce a glass foam with an homogeneous and CLOSED cell structure with only a melting step at 1100°C without grinding and sintering process. I give here under the abstract:

Glass foams are being widely used as constructional materials due to their unique properties in thermal insulation, fire retardation, and shockwave absorption. However, the cost of energy consumption and processes in a conventional glass foam production limited the use of glass foams as sustainable materials. In this study,
for the very first time, thermally tunable CaO−SnO2−P2O5−SiO2 glass foams with controllable pore size were presented as a novel category of melt-casting and float-manufacturable glasses. It was found that the pore size and thermal properties become tunable by manipulating the glass network, i.e., connecting linear chained Sn−P
network with [SiO4] units. In addition, the unique combination of thermal properties and porous structure of CaO−SnO2−P2O5−SiO2 glasses shows potential in float glass foam production, which can produce glass foams sheet-by-sheet with less complexity in
manufacturing processes.

float foam

1575-004-FB2133B6This means that this glass foam can be formed with the floating method on a tin bath, generally know as the float glass process, invented by Sir Alistair Pilkington.

This foam should have NOX gases in the cells but density, thermal conductivity and compressive strength are not given. The authors claims that this will be the route to low cost cellular glass. I see the following positive and negative points.

  • By working with top rollers like for float glass, it could be possible to flatten the cells and to tune the couple thermal conductivity / compressive strength. 
  • There are no belts or molds which have to be replaced, molten tin is doing this. 
  • There is one heating step to 1100°C to be compared with a heating to 800°C after energy intensive grinding. 
  • The glass composition with phosphates and tin oxide is probably costly.
  • It is not clear that replacing tin is less costly than replacing a steel belt or molds.
  • A lot of (expensive) heat has to be extracted at the bottom of the tin bath to avoid that molten tin hits the steel casing. 
  • It is not clear how we keep the same temperature under and above the foam because heating the molten tin is not needed for float glass. 
  • A typical float glass line costs typically 130 000 000€ while a low cost cellular glass production line, based on direct foaming of waste glass costs less than 20 000 000€.

alistairNevertheless, this invention is of major importance especially when the waste glass becomes less available and in that way more expensive. In fact, we could speak about the continuous foaming second generation and it will be a major challenge to develop this new process. Alistair is dead, long live Alistair.

In a very short time, I see that phosphates are introduced in the cellular glass world. The first time as a crystallization inhibitor, the second time now for a “grinding-sintering free” cellular glass process.


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