Despite the fact that we should all know better, the amount of electricity we use in the US continues to grow* at a steady clip. I guess it’s tough to put down that Xbox. If we don’t want Albany, NY to become ocean front property, we need to figure out how to create the electricity we need much more cleanly and efficiently.
An important technology for generating electricity from natural gas is the advanced gas turbine. Using natural gas produces roughly 30% less carbon dioxide than oil and 45% less than coal. Natural gas is the cleanest hydrocarbon fuel we can use to create electricity and the US has vast supplies of it which, if used carefully, should last us for at least a hundred years or so, well beyond the time when I’ll go to that great lab in the sky.
So given the need to bridge the gap from where we are today to much lower carbon footprint solutions that will exist at some point but which aren’t ready yet, natural gas is a crucial part of the US energy roadmap for the foreseeable future.
Because of the laws of thermodynamics, gas turbines run more efficiently the hotter they get but the limitation is the melting point of the materials used to build them. Metals have run out of gas (sorry, couldn’t resist) and high melting point ceramics are beginning to be used for the turbine blades. Because of the nature of the chemical bonds in ceramic materials (ionic or covalent for those nerds among you), in general they have high melting points and are strong, if somewhat brittle.
In an application like turbine blades, the ceramics need to have high melting points, be strong and tough, be easy to fabricate and finally be resistant to high-temperature corrosion. It is hard to find materials that can do all of the above well and one solution is to create a composite structure where one material is used for the body of the blade that has good mechanical properties and a different material is used as an anti-corrosion coating. The trick is to find a coating material that has the correct chemical properties, will stick to the underlying ceramic, is crack and pinhole free and can be applied easily and cheaply. This is where some folks from BU have ridden to the rescue.
In an important piece of work, Soumendra Basu, Vinod Sarin and their colleagues** have shown how to use chemical vapor deposition to deposit mullite (3Al2O3-2SiO2, if you must know) in a pinhole and crack free way on silicon based ceramics such as SiC. This opens the way to letting one pick a material for the turbine blades with good mechanical properties but have a coating that gives good chemical protection avoiding things like pitting and ultimately crack formation and propagation which would destroy the blades.
It is sort of like using a copper core in a stainless steel frying pan. The copper core has good thermal properties and the stainless steel good corrosion and wear properties and by creating a composite where one coats the other, one can have the best of both worlds, kind of a free lunch although we all know there is no such thing.
In any event, this paper is an example of how BU researchers are making a difference and creating technologies that will both allow us to play with our Xboxes AND have a habitable planet on which to live.
** S.N. Basu∗, T. Kulkarni, H.Z. Wang and V.K. Sarin, Journal of the European Ceramic Society 28 (2008) 437-445