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Fri Sep 1, 2017, 11:58 PM

An interesting thesis on the utility of MAX phases in the manufacture of turbine blades.

I'm sorting through some papers I collected back in 2015 but never got around to filing correctly after being diverted by other topics.

I came across a nice graduate thesis in my files that involve my interest in refractory materials, materials which exhibit high strength and corrosion resistance at very high temperatures. It's rather old, 17 years old to be precise, but it touches on the vapor phase synthesis or a remarkable class of materials, the MAX phases.

The thesis is in the public domain. It is here: Simulation of Diffusion Processes in Turbine Blades and Large Area Deposition of MAX Phase Thin Films with PVD

(Don't be put off by the acknowledgements in German; the thesis itself is in English.)

The industrial importance of refractory materials cannot be underestimated, they are essential components of jet engines, and regrettably - given the decision of our generation to strip all future generations of a safe and sustainable planet by enthusiasm for the dangerous fossil fuel "natural" gas, albeit with an idiotic and fraudulent so called "renewable energy" fig leaf - combined cycle dangerous natural gas power plants.

From a materials science perspective, all modern turbines, jet engines as well as dangerous natural gas plants, rely on what are known as "superalloys." A useful and informative monograph on the topic and properties of superalloys is this one: Superalloys: Alloying and Performance

In many turbines, especially gas turbines, superalloys actually function at temperatures higher than their melting point; this is possible only because they are generally coated with ceramic thermal barrier coatings, typically zirconium dioxide bonded to the superalloy surface with an alumina bonding agent. A paper I like a lot on this subject was published some years back by the great materials science engineer Emily Carter, now the Dean of Engineering at Princeton University: Atomic-scale insight and design principles for turbine engine thermal barrier coatings from theory

Superalloys are generally nickel based, but their performance is very much a function of their alloying agents. I referred to the aformentioned monograph in a post elsewhere sometime back relating to the important superalloy alloying element rhenium , which may property considered to be the rarest occurring stable element on earth; we will run out of it and do so soon, but maybe not fast enough.

That post is here: Technetium: Dangerous Nuclear Energy Waste or Essential Strategic Resource?

(Hopefully the depletion of rhenium reserves will effect the economics of dangerous natural gas in a more obvious way than the current generation is loathe to recognize. Some people, venal people, badly educated people or people who are simply indifferent and too lazy to think say natural gas is "cheap." It isn't. The real costs of dangerous natural gas are obscured by the fact that this fuel is allowed to kill people at will with almost no note as well as the fact that its users are allowed to dump an intractable waste form from it that can never and will never be contained and will destroy most major ecosystems on this planet, carbon dioxide. All future generations will pay for our terrible decision to use natural gas. Humanity will be paying for the natural gas we burn today forever. Don't worry, be happy: Current models of climate economics assume that lives in the future are less important than lives today, a value judgement that is rarely scrutinized and difficult to defend. Screw future generations; we have our own problems.)

MAX phases are ternary alloys that have the properties of both metals and ceramics. They are extremely refractory like very high temperature ceramics such as borides, silicides, nitrides and carbides (and in fact, formally they are either nitrides or carbides) but they have properties that ceramics lack: They are machinable, often flexible rather than brittle, and they can conduct both heat and electricity. MAX phases are ternary, and consist of three elements, one of which is an early transition element, one is a early non metal or semi-metal and one which is, again, either carbon or nitrogen. The most famous and most widely studied MAX phase is Ti3SiC2.

Dr. Walter has a nice brief description of the MAX phases in her thesis, albeit that some of her remarks are now dated:

MAX phases are ternary carbides or nitrides and their name is derived from their constituents, which are early transition metals (M), A-group elements (A), and carbon or nitrogen (X), see Fig. 6.1. Nowotny and Jeitschko discovered more than 100 ternary carbides and nitrides in the 1960s, among them more than 30 phases that would later be classified as MAX phases. Back then the experimental means for the synthesis of sufficient amounts of phase pure MAX phase material were not available in order to examine its properties. 30 years later in the 1990s Barsoum and El-Raghy succeeded in producing phase pure Ti3SiC2 bulk material by reactive hot pressing [37]. Since then some of these materials have been produced in bulk form, but until today only a few bulk phases, such as Ti3SiC2, are well characterized materials.


Michel Barsoum at Drexel University - a world leader in MAX phase research - has characterized a large number of MAX phases since Dr. Walter's thesis was published. (My son met Dr. Barsoum during an open house during his college search process, ironically and entirely coincidentally at precisely the same time I was reading Dr. Barsoum's book; my son was admitted to Drexel, but chose another university.)

Anyway, the thesis is interesting, if only for the account of a novel approach to synthesizing the MAX phases, a vapor phase approach. If I were researching this topic, I'd choose a different approach, and perhaps someone already has done what I would do, but again, it's interesting. Titanium silicon and carbon are some of the most common elements on the planet, and the discovery of the FCC process for titanium reduction a few years back now makes this metal industrially more accessible. While I detest natural gas and its defenders, I'm not against high temperature turbines; I think we need them.

I note that turbines operating at very high temperatures can achieve very high thermodynamic efficiency and high temperatures do not require filthy fuels like natural gas; they are accessible with nuclear energy.

Enjoy the holiday weekend.


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Reply An interesting thesis on the utility of MAX phases in the manufacture of turbine blades. (Original post)
NNadir Sep 2017 OP
Turbineguy Sep 2017 #1
NNadir Sep 2017 #2
Turbineguy Sep 2017 #3

Response to NNadir (Original post)

Sat Sep 2, 2017, 12:15 AM

1. Great to see some advances

in this amazing type of engine.

These crazy reciprocating engines don't really make sense.

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Response to Turbineguy (Reply #1)

Sat Sep 2, 2017, 09:39 AM

2. The power plant with the highest thermodynamic efficiency ever recorded is a dual turbine plant.

It's very clear that a turbine can have the highest thermal efficiency of any mechanical type device, particularly because they have low friction losses.

The plant to which I'm referring is the EDF Bouchain plant in France, which operates at 66.2% thermal efficiency:

The World's Most Efficient Combined Cycle Plant: EDF Bouchain

Unfortunately the power plant is also the dirtiest power plant in France except for France's lone coal plant. The big lie put forth by people who know nothing at all about energy and care nothing about the environment or the future of humanity is that nuclear power is dangerous and that natural gas is safe and cheap.

This gas power plant, even though it is the world's most efficient, will raise the carbon dioxide footprint of French electricity, and thus is a crime against all future generations. As usual, the attack on nuclear energy in favor of gas is obscured by claims about the stupid, expensive and environmentally dubious so called "renewable energy" industry which is an international scam which has raised the rate at which the atmosphere is being destroyed since it didn't work, isn't working and never will work. And as usual, the chemotoxic mess that this temporary, unsustainable so called "renewable energy" crap leaves behind will be yet another crime against all future generations.

For several years, since having my interest piqued in thermal barrier coatings when I came across Dr. Carter's paper in PNAS (cited in the OP) - I first got interested in her work when she headed the Andlinger Center for Energy and the Environment where I used to attend a lot of lectures - I have been thinking about the materials chemistry of turbines, as I've been thinking about the materials science chemistry of turbines.

It does seem possible to me that a quarternary array of turbines with appropriate materials chemistry which may become available would be able to achieve even higher efficiency than the very dirty EDF Bouchain plant which is "cheap" only because it is allowed to indiscriminately dump its waste directly into the atmosphere without charge. The plant I have in mind would rely on a very high temperature nuclear driven steam reformer producing very wet wastewater generated supercritical synthesis gas (H2 + CO2) expanding into a pressurized chamber after driving a steam rankine type generator, which would "burn" the synthesis gas by venting it over a dimethyl ether formation catalyst, with possibly another fourth turbine. The resultant product of this quarternary system would be a wonder fuel, dimethyether, which would represent a liquified (under pressure) stored form of energy that could do anything and everything that natural gas and/or LPG can do while also serving as a climate neutral refrigerant and thermal storage tool.

It would appear that you're even more into turbines than I am, since it's your screen name.

Cool.

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Response to NNadir (Original post)

Sat Sep 2, 2017, 06:19 PM

3. The previous blade cooling method was to create a protective blanket around the blade



Compressor bleed air runs into the power turbine blade and then creates a thin, moving layer of "cool" air covering the blade surface against which the combustion gas pushes and in turn pushes against the blade.

This method seems to create a new material while in use. With the method of swapping out the whole turbine at overhaul anyway it makes sense. The new Siemens turbine runs for 7 years before maintenance is required.

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